The author wishes to thank Annette Blak Rasmussen and Kristine Moeller for their technical support

The collection of skin samples from healthy adult volunteers undergoing plastic surgery requires approval from the ethical committee in the host institutions. This protocol was approved by the Regional Ethical Committee of Region Midtjylland, Denmark (M-20110027). The method described here is derived from similar studies by Maciaq et al.10 and Liu and Karasek11.
1. Isolation of Keratinocytes from Human Skin
<ol>
	<li>Start by making the following solutions: 50 mL solution of 0.25% trypsin and 0.1% glucose in DPBS. Mix and filter sterilize (0.2 &#181;m) the solution. Prepare 10 mL of RPMI-1640 + 2% FBS solution, 50 mL of DPBS and keratinocyte serum-free medium (KSFM). Add KSFM supplements and 250 &#181;L of gentamycin to 500 mL of KSFM. Pre-warm the solutions to 37 &#176;C before use.</li>
	<li>Collect skin from healthy adult volunteers undergoing plastic surgery. The skin samples used are approximately 10 cm x 15 cm, but can vary in size. Keep the skin cool under transportation by transporting the skin samples in a Styrofoam box containing a cooling element. If necessary, the skin sample can be stored at 4 &#176;C overnight.</li>
	<li>Remove fat from underneath the skin section using sterilized scissors, scalpels, and forceps.</li>
	<li>Buckle out the skin section (approximately 10 cm x 15 cm) on a sterile cover on top of a plate using needles. First, clean the skin with a dry sterilized gauze pad. Then clean the skin using a sterilized gauze pad with 70% ethanol.</li>
	<li>Using a foot planer, cut of the upper layer (epidermis) of the skin section and put it in a 9 cm Petri dish. Then, immediately add 25 mL of the DPBS/trypsin/glucose solution (prepared in step 1.1) to the Petri dish. Incubate for 30 min at 37 &#176;C.</li>
	<li>Using a pipette remove the DPBS/trypsin/glucose solution from the Petri dish and add 10 mL of RPMI-1640 + 2% FBS to inactivate the trypsin.</li>
	<li>Using two forceps, now release the epidermal cells into the medium by gently scraping and agitating both the epidermal and the dermal compartment of the skin sections.</li>
	<li>Filter the epidermal cell suspension through a metal filter (1 mm hole size), and collect in a 50 mL tube. Add the remaining skin sections to a 50 mL tube containing 10 mL of RPMI-1640 without FBS and vortex for 10 s. Filter the suspension through the metal filter into a 50 mL tube containing the epidermal cell suspension. Add DPBS to a total volume of 50 mL.</li>
	<li>Centrifuge the cell suspension for 10 min at 450 x g at room temperature.</li>
	<li>Remove the supernatant and resuspend the epidermal cell pellet in approximately 10 mL of 37 &#176;C KSFM depending on the size of the cell pellet. Count the cells using the Trypan Blue staining method under microscope. The number of cells obtained from a 10 cm x 15 cm skin section is approximately 50 - 100 x 106 cells. To each 75 cm2 culture flask, transfer 8 x 106 cells together with 12 mL of 37 &#176;C KSFM. Gently shake the culture flasks to ensure uniform distribution of the cells.</li>
	<li>Incubate the keratinocytes in a 37 &#176;C incubator with 100% humidity and 5% CO2. Change the medium after 2 days and three times weekly. Passage cells when the culture is 70 - 80% confluent, which takes approximately 2 weeks depending on the proliferation rate of the keratinocytes.</li>
</ol>
2. Passaging of Keratinocytes
<ol>
	<li>Heat the appropriate amount of 0.05% Trypsin-EDTA solution to 37 &#176;C in an incubator. Use 4.5 mL of 0.05% Trypsin-EDTA solution for a 75 cm2 culture flask.</li>
	<li>Remove medium from the cells, and add 4.5 mL/75 cm2 culture flask pre-warmed 0.05% Trypsin-EDTA solution to the cells. Place the culture flask in the incubator (37 &#176;C) and after approximately 5 min, check under the microscope if the cells have started loosening.</li>
	<li>When approximately 50% of the cells have loosened, gently hit the culture flask against the hand to loosen the remaining cells. Then, to inactivate the trypsin, add 6 mL of RPMI-1640 + 2% FBS (37 &#176;C) to the 75 cm2 culture flask and transfer the cell suspension to 50 mL tubes.</li>
	<li>Rinse the culture flasks with 3 mL of RPMI 1640 + 2% FBS and add to the 50 mL tubes. Centrifuge cells for 10 min at 450 x g at room temperature.
	<ol>
		<li>Resuspend the pelleted cells in 10 mL of KSFM (37 &#176;C). Count the cells and transfer 3 x 106 cells to a 150 cm2 culture flask together with 20 mL of KSFM (37 &#176;C). Gently shake the culture flask to ensure uniform distribution of the cells. Freeze the cells when the culture is 80 - 90% confluent, which takes approximately 4-6 days depending on the proliferation rate of the keratinocytes (see Section 3, freezing protocol below). Expand the keratinocytes to generate appropriate frozen stocks.</li>
	</ol>
	</li>
</ol>
3. Freezing of Keratinocytes
<ol>
	<li>Heat the appropriate amount of 0.05% Trypsin-EDTA solution to 37 &#176;C in an incubator. Use 9 mL of 0.05% Trypsin-EDTA solution for a 150 cm2 culture flask.</li>
	<li>Remove medium from the cells, and add 9 mL/150 cm2 culture flask pre-warmed 0.05% Trypsin-EDTA solution to the cells. Place the culture flask in the incubator (37 &#176;C) and after approximately 5 min, check under the microscope if the cells have started loosening.</li>
	<li>When approximately 50% of the cells have loosened, gently hit the culture flask against the hand in order to loosen the remaining cells. Then, to inactivate the trypsin, add 12 mL of RPMI-1640 + 2% FBS (37 &#176;C) to the 150 cm2 culture flask and aspirate the cell suspension to 50 mL tubes.</li>
	<li>Rinse the culture flasks with 6 mL of RPMI 1640 + 2% FBS and add to the 50 mL tubes. Centrifuge the tubes for 10 min at 450 x g at 4 &#176;C. Prepare ice-cold cell freezing medium (KSFM + 10% DMSO).</li>
	<li>Resuspend the cell pellet in KSFM + 10% DMSO, count the cells, and freeze cells at a density of 6 x 106 cells/mL using standard slow-freezing cryopreservation methods12.</li>
	<li>Store the keratinocytes in liquid nitrogen (vapor phase) until ready to use.</li>
</ol>
4. Thawing and Culturing Frozen Keratinocytes
<ol>
	<li>Rapidly thaw the appropriate frozen vials in a 37 &#176;C water bath. Use 70% ethanol to clean the outside of the cryovial. Transfer the appropriate number of cells (approximately 15,000 cells/cm2) to a culture flask and immediately add pre-warmed growth medium (KSFM) to the culture flask. 
	Any size of culture flasks can be used depending on the setup of the experiment.</li>
	<li>Use 5 mL culture medium for a 25 cm2 culture flask. The number of cells added the culture flask might vary because the growth of the cells varies from donor to donor. Incubate cells in a 37 &#176;C incubator with 100% humidity and 5% CO2.</li>
	<li>Change the medium after 2 days and three times weekly using fresh pre-warmed KSFM. 
	Note: Our data have demonstrated that on average 95% of the cells isolated by the protocol described here are positive for the keratinocyte-marker cytokeratine-1413.</li>
</ol>

<ol>
	<li>Barker, J. N., Mitra, R. S., Griffiths, C. E., Dixit, V. M., Nickoloff, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keratinocytes+as+initiators+of+inflammation.">Keratinocytes as initiators of inflammation.</a> Lancet. 337 (8735), 211-214 (1991).</li><li>Nickoloff, B. J., Turka, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keratinocytes:+key+immunocytes+of+the+integument.">Keratinocytes: key immunocytes of the integument.</a> Am J Pathol. 143 (2), 325-331 (1993).</li><li>Fuchs, E., Raghavan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Getting+under+the+skin+of+epidermal+morphogenesis.">Getting under the skin of epidermal morphogenesis.</a> Nat Rev Genet. 3 (3), 199-209 (2002).</li><li>Bos, J. D., Kapsenberg, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+skin+immune+system+Its+cellular+constituents+and+their+interactions.">The skin immune system Its cellular constituents and their interactions.</a> Immunol Today. 7 (7-8), 235-240 (1986).</li><li>Nestle, F. O., Di Meglio, P., Qin, J. Z., Nickoloff, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+immune+sentinels+in+health+and+disease.">Skin immune sentinels in health and disease.</a> Nat Rev Immunol. 9 (10), 679-691 (2009).</li><li>Albanesi, C., Scarponi, C., Giustizieri, M. L., Girolomoni, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keratinocytes+in+inflammatory+skin+diseases.">Keratinocytes in inflammatory skin diseases.</a> Curr Drug Targets Inflamm Allergy. 4 (3), 329-334 (2005).</li><li>Gilliet, M., Lande, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antimicrobial+peptides+and+self-DNA+in+autoimmune+skin+inflammation.">Antimicrobial peptides and self-DNA in autoimmune skin inflammation.</a> Curr Opin Immunol. 20 (4), 401-407 (2008).</li><li>Rohani, M. G., Pilcher, B. K., Chen, P., Parks, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cdc42+inhibits+ERK-mediated+collagenase-1+(MMP-1)+expression+in+collagen-activated+human+keratinocytes.">Cdc42 inhibits ERK-mediated collagenase-1 (MMP-1) expression in collagen-activated human keratinocytes.</a> J Invest Dermatol. 134 (5), 1230-1237 (2014).</li><li>Meephansan, J., Tsuda, H., Komine, M., Tominaga, S., Ohtsuki, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+IL-33+expression+by+IFN-gamma+and+tumor+necrosis+factor-alpha+in+normal+human+epidermal+keratinocytes.">Regulation of IL-33 expression by IFN-gamma and tumor necrosis factor-alpha in normal human epidermal keratinocytes.</a> J Invest Dermatol. 132 (11), 2593-2600 (2012).</li><li>Maciag, T., Nemore, R. E., Weinstein, R., Gilchrest, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+endocrine+approach+to+the+control+of+epidermal+growth:+serum-free+cultivation+of+human+keratinocytes.">An endocrine approach to the control of epidermal growth: serum-free cultivation of human keratinocytes.</a> Science. 211 (4489), 1452-1454 (1981).</li><li>Liu, S. C., Karasek, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+growth+of+adult+human+epidermal+keratinocytes+in+cell+culture.">Isolation and growth of adult human epidermal keratinocytes in cell culture.</a> J Invest Dermatol. 71 (2), 157-162 (1978).</li><li>Naaldijk, Y., Friedrich-Stockigt, A., Sethe, S., Stolzing, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+different+cooling+rates+for+fibroblast+and+keratinocyte+cryopreservation.">Comparison of different cooling rates for fibroblast and keratinocyte cryopreservation.</a> J Tissue Eng Regen Med. 10 (10), E354-E364 (2016).</li><li>Otkjaer, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IL-20+gene+expression+is+induced+by+IL-1beta+through+mitogen-activated+protein+kinase+and+NF-kappaB-dependent+mechanisms.">IL-20 gene expression is induced by IL-1beta through mitogen-activated protein kinase and NF-kappaB-dependent mechanisms.</a> J Invest Dermatol. 127 (6), 1326-1336 (2007).</li><li>Watt, F. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Involucrin+and+other+markers+of+keratinocyte+terminal+differentiation.">Involucrin and other markers of keratinocyte terminal differentiation.</a> J Invest Dermatol. 81 (1 Suppl), 100s-103s (1983).</li><li>Boyce, S. T., Ham, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium-regulated+differentiation+of+normal+human+epidermal+keratinocytes+in+chemically+defined+clonal+culture+and+serum-free+serial+culture.">Calcium-regulated differentiation of normal human epidermal keratinocytes in chemically defined clonal culture and serum-free serial culture.</a> J Invest Dermatol. 81 (1 Suppl), 33s-40s (1983).</li><li>Hennings, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium+regulation+of+growth+and+differentiation+of+mouse+epidermal+cells+in+culture.">Calcium regulation of growth and differentiation of mouse epidermal cells in culture.</a> Cell. 19 (1), 245-254 (1980).</li><li>Carlson, M. W., Alt-Holland, A., Egles, C., Garlick, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+tissue+models+of+normal+and+diseased+skin.">Three-dimensional tissue models of normal and diseased skin.</a> Curr Protoc Cell Biol. , (2008).</li><li>Kamsteeg, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+2+helper+T-cell+cytokines+induce+morphologic+and+molecular+characteristics+of+atopic+dermatitis+in+human+skin+equivalent.">Type 2 helper T-cell cytokines induce morphologic and molecular characteristics of atopic dermatitis in human skin equivalent.</a> Am J Pathol. 178 (5), 2091-2099 (2011).</li><li>van den Bogaard, E. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crosstalk+between+keratinocytes+and+T+cells+in+a+3D+microenvironment:+a+model+to+study+inflammatory+skin+diseases.">Crosstalk between keratinocytes and T cells in a 3D microenvironment: a model to study inflammatory skin diseases.</a> J Invest Dermatol. 134 (3), 719-727 (2014).</li><li>Raaby, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Langerhans+cell+markers+CD1a+and+CD207+are+the+most+rapidly+responding+genes+in+lesional+psoriatic+skin+following+adalimumab+treatment.">Langerhans cell markers CD1a and CD207 are the most rapidly responding genes in lesional psoriatic skin following adalimumab treatment.</a> Exp Dermatol. , (2017).</li></ol>

.The author has no conflict of interest.

Here, we describe how to easily isolate primary human keratinocytes from adult skin, and how to culture them in vitro. This model can have a broad application for investigation of epidermal cell biology, and can be useful for researchers interested in studying cutaneous diseases.
Some of the advantages of the protocol described here is that in contrast to keratinocytes isolated from neonatal foreskin obtained from newborn males undergoing circumcision, primary human keratinocytes from adult patients are isolated from both men and women and can include any age &#8805;18 years. Thus, the biological diversity is much larger in these cells compared with keratinocytes from neonatal foreskin. Moreover, relatively large pieces of skin samples can be obtained from patients undergoing plastic surgery, such as breast reduction surgery or weight loss surgery.
As mentioned above the epidermis is organized in different layers corresponding to the specific differentiation stage of the keratinocytes. In order to study skin biology, the model described here is limited by the lack of a three-dimensional microenvironment. The different layers of the epidermis as well as the different cell types present in the skin are not mimicked in this model. To overcome this, human skin equivalent models can be used, which consist of a multilayered epithelium where keratinocytes differentiate upon exposure to an air-liquid interface, and thus, more closely mimicking the native epidermis17,18,19. Another model which can be obtained in order to study skin biology is the ex vivo skin model, in which skin biopsies are kept in cultures at an air-liquid interphase as previously described20.

The skin is the biggest organ of the human body and serves as a protective barrier against the external environment. The skin is composed of two main layers: the dermis and the epidermis, where the epidermis constitutes the outermost layer of the skin. The most abundant cell type in the epidermis is the keratinocytes comprising more than 95% of the cell mass1,2. The keratinocytes are maintained at various stages of differentiation in the epidermis and are organized into basal, spinous, granular, and cornified layers that correspond to specific stages of differentiation3. The primary function of keratinocytes is to provide the structural integrity of the epidermis, thereby producing an intact barrier to the outside world.
The keratinocytes also represent the first line of defense against pathogens in the skin, and therefore play an important role in the innate immune response4,5. Exposure of the keratinocytes to external stimuli leads to activation of intracellular signaling pathways and subsequently, production of a number of various inflammatory mediators including cytokines, chemokines, and antimicrobial peptides. These keratinocyte-derived proteins participate in the inflammatory response by recruiting and activating immune cells such as dendritic cells, neutrophils, and specific T cells6,7. Thus, because keratinocytes play a crucial part in numerous biological processes, the rationale behind the technique presented here was to generate an in vitro model to study skin biology. Primary keratinocyte cultures obtained from neonatal foreskin are often used to study skin biology8,9. However, with the technique described here, keratinocytes from both genders are obtained resulting in a higher biological diversity of the cells.
Here, we present a detailed protocol for the isolation and generation of primary human keratinocytes from adult skin, including maintenance and freezing of the keratinocytes. The overall goal of this method is to generate primary human keratinocytes that can be used as a model to study cutaneous biology in vitro.

<table border="0" cellpadding="0" cellspacing="0" width="621">
	<tbody>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">KSFM</td>
			<td style="width:119px;">ThermoFisher Scientific</td>
			<td style="width:119px;">17005-034</td>
			<td style="width:167px;">Cell culture medium</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">KSFM supplements</td>
			<td style="width:119px;">ThermoFisher Scientific</td>
			<td style="width:119px;">37000-015</td>
			<td style="width:167px;">Supplements for KSFM</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">DPBS</td>
			<td style="width:119px;">ThermoFisher Scientific</td>
			<td style="width:119px;">14190-144</td>
			<td style="width:167px;">DPBS without Calcium and Magnesium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DMSO</td>
			<td style="width:119px;">Sigma-Aldrich</td>
			<td style="width:119px;">D8418</td>
			<td style="width:167px;">Dimethyl sulfoxid</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Gentamycin</td>
			<td style="width:119px;">ThermoFisher Scientific</td>
			<td style="width:119px;">15710-049</td>
			<td style="width:167px;">Cell culture medium additive</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Sterilization filter</td>
			<td style="width:119px;">Sartorius</td>
			<td style="width:119px;">16534</td>
			<td style="width:167px;">Syringe filter with a pore size of 0.2 &#181;m</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypsin</td>
			<td style="width:119px;">Sigma-Aldrich</td>
			<td style="width:119px;">T7409</td>
			<td style="width:167px;">Used to trypsinize cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glucose</td>
			<td style="width:119px;">Sigma-Aldrich</td>
			<td style="width:119px;">G7528</td>
			<td style="width:167px;">-</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">RPMI-1640</td>
			<td style="width:119px;">ThermoFisher Scientific</td>
			<td style="width:119px;">61870-010</td>
			<td style="width:167px;">-</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">FBS</td>
			<td style="width:119px;">ThermoFisher Scientific</td>
			<td style="width:119px;">16000044</td>
			<td style="width:167px;">Used to inactivate trypsin</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Forceps</td>
			<td style="width:119px;">-</td>
			<td style="width:119px;">-</td>
			<td style="width:167px;">Forceps from any company can be used</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Scissors</td>
			<td style="width:119px;">-</td>
			<td style="width:119px;">-</td>
			<td style="width:167px;">Scissors from any company can be used</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Scalpel</td>
			<td style="width:119px;">Swann Morton</td>
			<td style="width:119px;">0501</td>
			<td style="width:167px;">Scalpels from any company can be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">70% ethanol</td>
			<td style="width:119px;">-</td>
			<td style="width:119px;">-</td>
			<td style="width:167px;">-</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Gauze pads</td>
			<td style="width:119px;">NOBAMED</td>
			<td style="width:119px;">875420</td>
			<td style="width:167px;">Gauze pads from any provider can be used</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Foot planer</td>
			<td style="width:119px;">Credo Solingen</td>
			<td style="width:119px;">1510</td>
			<td style="width:167px;">Foot planer from any provider can be used</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Petri dishes</td>
			<td style="width:119px;">TPP</td>
			<td style="width:119px;">93100</td>
			<td style="width:167px;">Petri dishes from any provider can be used</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Metal filter</td>
			<td style="width:119px;">-</td>
			<td style="width:119px;">-</td>
			<td style="width:167px;">In-house 1 mm hole size metal filter</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:216px;">75 cm2 culture flasks</td>
			<td style="width:119px;">NUNC</td>
			<td style="width:119px;">156499</td>
			<td style="width:167px;">-</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:216px;">150 cm2 culture flasks</td>
			<td style="width:119px;">TTP</td>
			<td style="width:119px;">90151</td>
			<td style="width:167px;">-</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">0.05% Trypsin-EDTA solution</td>
			<td style="width:119px;">ThermoFisher Scientific</td>
			<td style="width:119px;">25300-062</td>
			<td style="width:167px;">Used to trypsinize cells when passaging</td>
		</tr>
	</tbody>
</table>

generation and culturing of primary human keratinocytes from adult skin

The main function of keratinocytes is to provide the structural integrity of the epidermis, thereby maintaining a mechanical barrier to the outside world. In addition, keratinocytes play an essential role in the initiation, maintenance, and regulation of epidermal immune responses by being part of the innate immune system responding to antigenic stimuli in a fast, nonspecific manner. Here, we describe a protocol for isolation of primary human keratinocytes from adult skin, and demonstrate that these cells respond to calcium-induced terminal differentiation, as measured by an increased expression of the differentiation marker involucrin. In addition, we show that the isolated keratinocytes are responsive to IL-1&#946;-induced activation of intracellular signaling pathways as measured by the activation of the p38 MAPK pathway. Taken together, we describe a method for isolation and culturing of primary human keratinocytes from adult skin. Because the keratinocytes are the predominant cell type in the epidermis, this method is useful to study molecular mechanisms in cutaneous biology in vitro.

Calcium-induced Terminal Differentiation 
Human keratinocytes undergo terminal differentiation upon treatment with calcium14,15,16. Primary human keratinocytes were isolated and cultured as described in the above protocol. When approximately 50 - 60% confluent, the cells were stimulated with calcium (1.2 mM) or vehicle and pictures of the cells were taken on day 0, 1, and 2. Figure 1 shows the morphological changes of the keratinocytes observed upon calcium stimulation.
The Expression of Involucrin is Increased Upon Calcium Stimulation 
Cultured human keratinocytes were grown until approximately 50 - 60% confluent after which the cells were stimulated with calcium (1.2 mM) or a vehicle for 24 and 48 h. We demonstrated that in parallel with the increased differentiation of the cells as observed by the morphological changes of the keratinocytes, the mRNA expression of the differentiation marker involucrin increased significantly upon calcium stimulation. After 24 and 48 h of stimulation, the involucrin mRNA expression was increased approximately 5.5-fold and 3.5-fold, respectively, compared with vehicle (Figure 2).
IL-1&#946;-induced Phosphorylation of p38 MAPK 
To determine if the isolated human keratinocytes were responsive to cytokine-induced activation of intracellular signaling pathways, cultured keratinocytes were stimulated with IL-1&#946; (10 ng/mL) for various time points. Within 5 min, IL-1&#946; stimulation led to a rapid activation/phosphorylation of p38 MAPK, as determined by Western blotting. After 1 h, IL-1&#946;-induced p38 MAPK phosphorylation had returned to basal level (Figure 3). Only the phosphorylated form of p38 MAPK was increased, as IL-1&#946; stimulation had no effect on the total protein level of p38 MAPK (Figure 3).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56863/56863fig1.jpg" /> 
Figure 1: Representative images of calcium-induced differentiation of keratinocytes. Cultured primary human keratinocytes were stimulated with vehicle (dH2O) or calcium (1.2 mM) for the indicated time points. (A - E) Phase contrast images of keratinocytes on day 0 (A), day 1 (B and C), and day 2 (D and E) after calcium stimulation. Scale bar = 100 &#181;m. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56863/56863fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56863/56863fig2.jpg" /> 
Figure 2: Increased mRNA expression of involucrin upon calcium stimulation. Calcium (1.2 mM) or vehicle (dH2O) was added to cultured primary human keratinocytes for the indicated time points (n = 3). RNA was isolated and the expression of the differentiation marker involucrin analyzed by qPCR. RPLP0 (Ribosomal Protein Large P0) mRNA expression was used for normalization. Results represent mean &#177; S.D. from three different experiments. *p &#60;0.05 compared with vehicle. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56863/56863fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56863/56863fig3.jpg" /> 
Figure 3: IL-1&#946;-induced phosphorylation of p38 MAPK. Cultured primary human keratinocytes were stimulated with vehicle (PBS + 0.15% BSA) or IL-1&#946; (10 ng/mL) for the indicated time points. Protein extracts were isolated and Western blotting analysis used to measure the phosphorylated level of p38 MAPK and total p38 MAPK. Equal loading was verified by incubation with an anti-&#946;-actin antibody. Data from one representative experiment out of three are shown. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56863/56863fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Generation and Culturing of Primary Human Keratinocytes from Adult Skin at JoVE.com

Generation and Culturing of Primary Human Keratinocytes from Adult Skin

The human skin acts as a first line of defense against the external environment. We present a method for isolating primary human keratinocytes from adult skin. These isolated keratinocytes are useful in numerous experimental setups, and are a highly suitable model for studying molecular mechanisms in cutaneous biology in vitro.

The main function of keratinocytes is to provide the structural integrity of the epidermis, thereby maintaining a mechanical barrier to the outside world. ...

generation-culturing-primary-human-keratinocytes-from-adult

Nanyang Technological University

Research

JoVE Journal

Developmental Biology

16.2K Views.  Aarhus University Hospital. The human skin acts as a first line of defense against the external environment. We present a method for isolating primary human keratinocytes from adult skin. These isolated keratinocytes are useful in numerous experimental setups, and are a highly suitable model for studying molecular mechanisms in cutaneous biology in vitro.

Video: Generation and Culturing of Primary Human Keratinocytes from Adult Skin

Isolation and Quantitative Immunocytochemical Characterization of Primary Myogenic Cells and Fibroblasts from Human Skeletal Muscle

The repair and regeneration of skeletal muscle requires the action of satellite cells, which are the resident muscle stem cells. These can be isolated from human muscle biopsy samples using enzymatic digestion and their myogenic properties studied in culture. Quantitatively, the two main adherent cell types obtained from enzymatic digestion are: (i) the satellite cells (termed myogenic cells or muscle precursor cells), identified initially as CD56+ and later as CD56+/desmin+ cells and (ii) muscle-derived fibroblasts, identified as CD56&#8211; and TE-7+. Fibroblasts proliferate very efficiently in culture and in mixed cell populations these cells may overrun myogenic cells to dominate the culture. The isolation and purification of different cell types from human muscle is thus an important methodological consideration when trying to investigate the innate behavior of either cell type in culture. Here we describe a system of sorting based on the gentle enzymatic digestion of cells using collagenase and dispase followed by magnetic activated cell sorting (MACS) which gives both a high purity (&#62;95% myogenic cells) and good yield (~2.8 x 106 &#177; 8.87 x 105 cells/g tissue after 7 days in vitro) for experiments in culture. This approach is based on incubating the mixed muscle-derived cell population with magnetic microbeads beads conjugated to an antibody against CD56 and then passing cells though a magnetic field. CD56+ cells bound to microbeads are retained by the field whereas CD56&#8211; cells pass unimpeded through the column. Cell suspensions from any stage of the sorting process can be plated and cultured. Following a given intervention, cell morphology, and the expression and localization of proteins including nuclear transcription factors can be quantified using immunofluorescent labeling with specific antibodies and an image processing and analysis package.

The main adherent cell types derived from human muscle are myogenic cells and fibroblasts. Here, cell populations are enriched using magnetic-activated cell sorting based on the CD56 antigen. Subsequent immunolabelling with specific antibodies and use of image analysis techniques allows quantification of cytoplasmic and nuclear characteristics in individual cells.

The repair and regeneration of skeletal muscle requires the action of satellite cells, which are the resident muscle stem cells. These can be isolated ...

Transfection, Selection, and Colony-picking of Human Induced Pluripotent Stem Cells TALEN-targeted with a GFP Gene into the AAVS1 Safe Harbor

Targeted transgene addition can provide persistent gene expression while circumventing the gene silencing and insertional mutagenesis caused by viral vector mediated random integration. This protocol describes a universal and efficient transgene targeted addition platform in human iPSCs based on utilization of validated open-source TALENs and a gene-trap-like donor to deliver transgenes into a safe harbor locus. Importantly, effective gene editing is rate-limited by the delivery efficiency of gene editing vectors. Therefore, this protocol first focuses on preparation of iPSCs for transfection to achieve high nuclear delivery efficiency. When iPSCs are dissociated into single cells using a gentle-cell dissociation reagent and transfected using an optimized program, >50% cells can be induced to take up the large gene editing vectors. Because the AAVS1 locus is located in the intron of an active gene (PPP1R12C), a splicing acceptor (SA)-linked puromycin resistant gene (PAC) was used to select targeted iPSCs while excluding random integration-only and untransfected cells. This strategy greatly increases the chance of obtaining targeted clones, and can be used in other active gene targeting experiments as well. Two weeks after puromycin selection at the dose adjusted for the specific iPSC line, clones are ready to be picked by manual dissection of large, isolated colonies into smaller pieces that are transferred to fresh medium in a smaller well for further expansion and genetic and functional screening. One can follow this protocol to readily obtain multiple GFP reporter iPSC lines that are useful for in vivo and in vitro imaging and cell isolation.

TALEN-mediated gene editing at the safe harbor AAVS1 locus enables high-efficiency transgene addition in human iPSCs. This protocol describes the procedures for preparing iPSCs for TALEN and donor vector delivery, transfecting iPSCs, and selecting and isolating iPSC clones to achieve targeted integration of a GFP gene to generate reporter lines.

Targeted transgene addition can provide persistent gene expression while circumventing the gene silencing and insertional mutagenesis caused by viral ...

Generation of Integration-free Human Induced Pluripotent Stem Cells Using Hair-derived Keratinocytes

Recent advances in reprogramming allow us to turn somatic cells into human induced pluripotent stem cells (hiPSCs). Disease modeling using patient-specific hiPSCs allows the study of the underlying mechanism for pathogenesis, also providing a platform for the development of in vitro drug screening and gene therapy to improve treatment options. The promising potential of hiPSCs for regenerative medicine is also evident from the increasing number of publications (>7000) on iPSCs in recent years. Various cell types from distinct lineages have been successfully used for hiPSC generation, including skin fibroblasts, hematopoietic cells and epidermal keratinocytes. While skin biopsies and blood collection are routinely performed in many labs as a source of somatic cells for the generation of hiPSCs, the collection and subsequent derivation of hair keratinocytes are less commonly used. Hair-derived keratinocytes represent a non-invasive approach to obtain cell samples from patients. Here we outline a simple non-invasive method for the derivation of keratinocytes from plucked hair. We also provide instructions for maintenance of keratinocytes and subsequent reprogramming to generate integration-free hiPSC using episomal vectors.

This manuscript provides a step-by-step procedure for the derivation and maintenance of human keratinocytes from plucked hair and subsequent generation of integration-free human induced pluripotent stem cells (hiPSCs) by episomal vectors.

Recent advances in reprogramming allow us to turn somatic cells into human induced pluripotent stem cells (hiPSCs). Disease modeling using ...

Generation of Genetically Modified Organotypic Skin Cultures Using Devitalized Human Dermis

Organotypic cultures allow the reconstitution of a 3D environment critical for cell-cell contact and cell-matrix interactions which mimics the function and physiology of their in vivo tissue counterparts. This is exemplified by organotypic skin cultures which faithfully recapitulates the epidermal differentiation and stratification program. Primary human epidermal keratinocytes are genetically manipulable through retroviruses where genes can be easily overexpressed or knocked down. These genetically modified keratinocytes can then be used to regenerate human epidermis in organotypic skin cultures providing a powerful model to study genetic pathways impacting epidermal growth, differentiation, and disease progression. The protocols presented here describe methods to prepare devitalized human dermis as well as to genetically manipulate primary human keratinocytes in order to generate organotypic skin cultures. Regenerated human skin can be used in downstream applications such as gene expression profiling, immunostaining, and chromatin immunoprecipitations followed by high throughput sequencing. Thus, generation of these genetically modified organotypic skin cultures will allow the determination of genes that are critical for maintaining skin homeostasis.

The goal of this paper is to provide a comprehensive and detailed protocol on how to generate genetically modified human organotypic skin from epidermal keratinocytes and devitalized human dermis.

Organotypic cultures allow the reconstitution of a 3D environment critical for cell-cell contact and cell-matrix interactions which mimics the function ...

Isolating Hair Follicle Stem Cells and Epidermal Keratinocytes from Dorsal Mouse Skin

The hair follicle (HF) is an ideal system for studying the biology and regulation of adult stem cells (SCs). This dynamic mini organ is replenished by distinct pools of SCs, which are located in the permanent portion of the HF, a region known as the bulge. These multipotent bulge SCs were initially identified as slow cycling label retaining cells; however, their isolation has been made feasible after identification of specific cell markers, such as CD34 and keratin 15 (K15). Here, we describe a robust method for isolating bulge SCs and epidermal keratinocytes from mouse HFs utilizing fluorescence activated cell-sorting (FACS) technology. Isolated hair follicle SCs (HFSCs) can be utilized in various in vivo grafting models and are a valuable in vitro model for studying the mechanisms that govern multipotency, quiescence and activation.

An ideal model for studying adult stem cell biology is the mouse hair follicle. Here we present a protocol for isolating different populations of hair follicles stem cells and epidermal keratinocytes, employing enzymatic digestion of mouse dorsal skin followed by FACS analysis.

The hair follicle (HF) is an ideal system for studying the biology and regulation of adult stem cells (SCs). This dynamic mini organ is replenished by ...

Preparation and Culture of Myogenic Precursor Cells/Primary Myoblasts from Skeletal Muscle of Adult and Aged Humans

Skeletal muscle homeostasis depends on muscle growth (hypertrophy), atrophy and regeneration. During ageing and in several diseases, muscle wasting occurs. Loss of muscle mass and function is associated with muscle fiber type atrophy, fiber type switching, defective muscle regeneration associated with dysfunction of satellite cells, muscle stem cells, and other pathophysiological processes. These changes are associated with changes in intracellular as well as local and systemic niches. In addition to most commonly used rodent models of muscle ageing, there is a need to study muscle homeostasis and wasting using human models, which due to ethical implications, consist predominantly of in vitro cultures. Despite the wide use of human Myogenic Progenitor Cells (MPCs) and primary myoblasts in myogenesis, there is limited data on using human primary myoblast and myotube cultures to study molecular mechanisms regulating different aspects of age-associated muscle wasting, aiding in the validation of mechanisms of ageing proposed in rodent muscle. The use of human MPCs, primary myoblasts and myotubes isolated from adult and aged people, provides a physiologically relevant model of molecular mechanisms of processes associated with muscle growth, atrophy and regeneration. Here we describe in detail a robust, inexpensive, reproducible and efficient protocol for the isolation and maintenance of human MPCs&#160;and their progeny&#160;&#8212; myoblasts and myotubes from human muscle samples using enzymatic digestion. Furthermore, we have determined the passage number at which primary myoblasts from adult and aged people undergo senescence in an in vitro culture. Finally, we show the ability to transfect these myoblasts and the ability to characterize their proliferative and differentiation capacity and propose their suitability for performing functional studies of molecular mechanisms of myogenesis and muscle wasting in vitro.

This protocol describes a robust, reproducible and simple method of isolation and culture of myoblast progenitor cells from the skeletal muscle of adult and aged people. The muscles used here include foot and leg muscles. This approach enables the isolation of an enriched population of primary myoblasts for functional studies.

Skeletal muscle homeostasis depends on muscle growth (hypertrophy), atrophy and regeneration. During ageing and in several diseases, muscle wasting ...

Defined and Scalable Generation of Hepatocyte-like Cells from Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs) possess great value for biomedical research. hPSCs can be scaled and differentiated to all cell types found in the human body. The differentiation of hPSCs to human hepatocyte-like cells (HLCs) has been extensively studied, and efficient differentiation protocols have been established. The combination of extracellular matrix and biological stimuli, including growth factors, cytokines, and small molecules, have made it possible to generate HLCs that resemble primary human hepatocytes. However, the majority of procedures still employ undefined components, giving rise to batch-to-batch variation. This serves as a significant barrier to the application of the technology. To tackle this issue, we developed a defined system for hepatocyte differentiation using human recombinant laminins as extracellular matrices in combination with a serum-free differentiation process. Highly efficient hepatocyte specification was achieved, with demonstrated improvements in both HLC function and phenotype. Importantly, this system is easy to scale up using research and GMP-grade hPSC lines&#160;promising advances in cell-based modelling and therapies.

The method presented here describes a scalable and good manufacturing practice (GMP)-ready differentiation system to generate human hepatocyte-like cells from pluripotent stem cells. It serves as a cost-effective and standardized system to generate human hepatocyte-like cells for basic and applied human liver research.

Human pluripotent stem cells (hPSCs) possess great value for biomedical research. hPSCs can be scaled and differentiated to all cell types found in the ...

The Isolation and Culture of Primary Epicardial Cells Derived from Human Adult and Fetal Heart Specimens

The epicardium, an epithelial cell layer covering the myocardium, has an essential role during cardiac development, as well as in the repair response of the heart after ischemic injury. When activated, epicardial cells undergo a process known as epithelial to mesenchymal transition (EMT) to provide cells to the regenerating myocardium. Furthermore, the epicardium contributes via secretion of essential paracrine factors. To fully appreciate the regenerative potential of the epicardium, a human cell model is required. Here we outline a novel cell culture model to derive primary epicardial derived cells (EPDCs) from human adult and fetal cardiac tissue. To isolate EPDCs, the epicardium is dissected from the outside of the heart specimen and processed into a single cell suspension. Next, EPDCs are plated and cultured in EPDC medium containing the ALK 5-kinase inhibitor SB431542 to maintain their epithelial phenotype. EMT is induced by stimulation with TGF&#946;. This method enables, for the first time, the study of the process of human epicardial EMT in a controlled setting, and facilitates gaining more insight in the secretome of EPDCs that may aid heart regeneration. Furthermore, this uniform approach allows for direct comparison of human adult and fetal epicardial behavior.

The epicardium plays a crucial role in the development and repair of the heart by providing cells and growth factors to the myocardial wall. Here, we describe a method to culture human primary epicardial cells that enables the study and comparison of their developmental and adult characteristics.

The epicardium, an epithelial cell layer covering the myocardium, has an essential role during cardiac development, as well as in the repair response of ...

A Simplified and Efficient Method to Isolate Primary Human Keratinocytes from Adult Skin Tissue

Primary human keratinocytes isolated from fresh skin tissues and their expansion in vitro have been widely used for laboratory research and for clinical applications. The conventional isolation method of human keratinocytes involves a two-step sequential enzymatic digestion procedure, which has been proven to be inefficient in generating primary cells from adult tissues due to the low cell recovery rate and reduced cell viability. We recently reported an advanced method to isolate human primary epidermal progenitor cells from skin tissues that utilizes the Rho kinase inhibitor Y-27632 in the medium. Compared with the traditional protocol, this new method is simpler, easier, and less time-consuming, and increases epithelial stem cell yield and enhances their stem cell characteristics. Moreover, the new methodology does not require the separation of the epidermis from the dermis, and, therefore, is suitable for isolating cells from different types of adult tissues. This new isolation method overcomes the major shortcomings of conventional methods and is more suitable for producing large numbers of epidermal cells with high potency both for laboratory and for clinical applications. Here, we describe the new method in detail.

Here we present a protocol to efficiently isolate primary human keratinocytes from adult skin tissues. This method simplifies the conventional procedure by using the ROCK Inhibitor Y-27632 in the inoculation medium to spontaneously separate epidermal cells from dermal cells.

Primary human keratinocytes isolated from fresh skin tissues and their expansion in vitro have been widely used for laboratory research and for clinical ...

Generation of 3D Skin Organoid from Cord Blood-derived Induced Pluripotent Stem Cells

The skin is the body&#8217;s largest organ and has many functions. The skin acts as a physical barrier and protector of the body and regulates bodily functions. Biomimetics is the imitation of the models, systems, and elements of nature for the purpose of solving complex human problems1. Skin biomimetics is a useful tool for in vitro disease research and in vivo regenerative medicine. Human induced pluripotent stem cells (iPSCs) have the characteristic of unlimited proliferation and the ability of differentiation to three germ layers. Human iPSCs are generated from various primary cells, such as blood cells, keratinocytes, fibroblasts, and more. Among them, cord blood mononuclear cells (CBMCs) have emerged as an alternative cell source from the perspective of allogeneic regenerative medicine. CBMCs are useful in regenerative medicine because human leukocyte antigen (HLA) typing is essential to the cell banking system. We provide a method for the differentiation of CBMC-iPSCs into keratinocytes and fibroblasts and for generation of a 3D skin organoid. CBMC-iPSC-derived keratinocytes and fibroblasts have characteristics similar to a primary cell line. The 3D skin organoids are generated by overlaying an epidermal layer onto a dermal layer. By transplanting this 3D skin organoid, a humanized mice model is generated. This study shows that a 3D human iPSC-derived skin organoid may be a novel, alternative tool for dermatologic research in vitro and in vivo.

We propose a protocol that shows how to differentiate induced pluripotent stem cell-derived keratinocytes and fibroblasts and generate a 3D skin organoid, using these keratinocytes and fibroblasts. This protocol contains an additional step of generating a humanized mice model. The technique presented here will improve dermatologic research.

The skin is the body&#8217;s largest organ and has many functions. The skin acts as a physical barrier and protector of the body and regulates bodily ...