This study was partially supported by the NIH/NIAMS K01AR071512 and CIRM DISC0-14350 to Dmitriy Sheyn. The two lentivirus packaging plasmids were a gift from the Simon Knott laboratory (Department of Biomedical Sciences, Cedars-Sinai Medical Center).

Harnessing iPSC-Derived iTenocytes for Effective Cell-Based Therapy

<ol>
	<li>Lim, W. L., Liau, L. L., Ng, M. H., Chowdhury, S. R., Law, J. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+progress+in+tendon+and+ligament+tissue+engineering.">Current progress in tendon and ligament tissue engineering.</a> Tissue Engineering and Regenerative. 16 (6), 549-571 (2019).</li><li>Sheyn, D., 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=Human+induced+pluripotent+stem+cells+differentiate+into+functional+mesenchymal+stem+cells+and+repair+bone+defects.">Human induced pluripotent stem cells differentiate into functional mesenchymal stem cells and repair bone defects.</a> Stem Cells Translational Medicine. 5 (11), 1447-1460 (2016).</li><li>Czaplewski, S. K., Tsai, T. L., Duenwald-Kuehl, S. E., Vanderby, R., Li, W. 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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+tendon-specific+markers+in+various+human+tissues,+tenocytes+and+mesenchymal+stem+cells.">Characterization of tendon-specific markers in various human tissues, tenocytes and mesenchymal stem cells.</a> Tissue Engineering and Regenerative. 16 (2), 151-159 (2019).</li><li>Shukunami, C., 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=Scleraxis+is+a+transcriptional+activator+that+regulates+the+expression+of+Tenomodulin,+a+marker+of+mature+tenocytes+and+ligamentocytes.">Scleraxis is a transcriptional activator that regulates the expression of Tenomodulin, a marker of mature tenocytes and ligamentocytes.</a> Scientific Reports. 8 (1), 3155 (2018).</li><li>Huang, A. H., Lu, H. H., Schweitzer, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+regulation+of+tendon+cell+fate+during+development.">Molecular regulation of tendon cell fate during development.</a> Journal of Orthopaedic Research. 33 (6), 800-812 (2015).</li><li>Harvey, T., Flamenco, S., Fan, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Tppp3(+)Pdgfra(+)+tendon+stem+cell+population+contributes+to+regeneration+and+reveals+a+shared+role+for+PDGF+signalling+in+regeneration+and+fibrosis.">A Tppp3(+)Pdgfra(+) tendon stem cell population contributes to regeneration and reveals a shared role for PDGF signalling in regeneration and fibrosis.</a> Nature Cell Biology. 21 (12), 1490-1503 (2019).</li><li>Yang, G., Rothrauff, B. B., Tuan, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tendon+and+ligament+regeneration+and+repair:+clinical+relevance+and+developmental+paradigm.">Tendon and ligament regeneration and repair: clinical relevance and developmental paradigm.</a> Birth Defects Research Part C: Embryo Today. 99 (3), 203-222 (2013).</li><li>Wang, T., 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=In+vitro+loading+models+for+tendon+mechanobiology.">In vitro loading models for tendon mechanobiology.</a> Journal of Orthopaedic Research. 36 (2), 566-575 (2018).</li><li>Wu, S. Y., Kim, W., Kremen, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+cellular+strain+models+of+tendon+biology+and+tenogenic+differentiation.">In vitro cellular strain models of tendon biology and tenogenic differentiation.</a> Frontiers in Bioengineering and Biotechnology. 10, 826748 (2022).</li><li>Screen, H. R., Lee, D. A., Bader, D. L., Shelton, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+investigation+into+the+effects+of+the+hierarchical+structure+of+tendon+fascicles+on+micromechanical+properties.">An investigation into the effects of the hierarchical structure of tendon fascicles on micromechanical properties.</a> Proceedings of the Institution of Mechanical Engineers, Part H. 218 (2), 109-119 (2004).</li><li>Tatullo, 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=Mechanical+influence+of+tissue+culture+plates+and+extracellular+matrix+on+mesenchymal+stem+cell+behavior:+A+topical+review.">Mechanical influence of tissue culture plates and extracellular matrix on mesenchymal stem cell behavior: A topical review.</a> International Journal of Immunopathology and Pharmacology. 29 (1), 3-8 (2016).</li><li>Ding, S., Kingshott, P., Thissen, H., Pera, M., Wang, P. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modulation+of+human+mesenchymal+and+pluripotent+stem+cell+behavior+using+biophysical+and+biochemical+cues:+A+review.">Modulation of human mesenchymal and pluripotent stem cell behavior using biophysical and biochemical cues: A review.</a> Biotechnology and Bioengineering. 114 (2), 260-280 (2017).</li><li>Papalamprou, A., 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=Directing+iPSC+differentiation+into+iTenocytes+using+combined+scleraxis+overexpression+and+cyclic+loading.">Directing iPSC differentiation into iTenocytes using combined scleraxis overexpression and cyclic loading.</a> Journal of Orthopaedic Research. 41 (6), 1148-1161 (2023).</li><li>Pryce, B. A., Brent, A. E., Murchison, N. D., Tabin, C. J., Schweitzer, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+transgenic+tendon+reporters,+ScxGFP+and+ScxAP,+using+regulatory+elements+of+the+scleraxis+gene.">Generation of transgenic tendon reporters, ScxGFP and ScxAP, using regulatory elements of the scleraxis gene.</a> Developmental Dynamics. 236 (6), 1677-1682 (2007).</li><li>Stewart, S. A., 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=Lentivirus-delivered+stable+gene+silencing+by+RNAi+in+primary+cells.">Lentivirus-delivered stable gene silencing by RNAi in primary cells.</a> RNA. 9 (4), 493-501 (2003).</li><li>Mendicino, M., Bailey, A. M., Wonnacott, K., Puri, R. K., Bauer, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MSC-based+product+characterization+for+clinical+trials:+an+FDA+perspective.">MSC-based product characterization for clinical trials: an FDA perspective.</a> Cell Stem Cell. 14 (2), 141-145 (2014).</li><li>Bourin, P., 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=Stromal+cells+from+the+adipose+tissue-derived+stromal+vascular+fraction+and+culture+expanded+adipose+tissue-derived+stromal/stem+cells:+a+joint+statement+of+the+International+Federation+for+Adipose+Therapeutics+and+Science+(IFATS)+and+the+International+Society+for+Cellular+Therapy+(ISCT).">Stromal cells from the adipose tissue-derived stromal vascular fraction and culture expanded adipose tissue-derived stromal/stem cells: a joint statement of the International Federation for Adipose Therapeutics and Science (IFATS) and the International Society for Cellular Therapy (ISCT).</a> Cytotherapy. 15 (6), 641-648 (2013).</li><li>Dunkman, A. A., 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=The+tendon+injury+response+is+influenced+by+decorin+and+biglycan.">The tendon injury response is influenced by decorin and biglycan.</a> Annals of Biomedical Engineering. 42 (3), 619-630 (2014).</li><li>Liu, 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=Crucial+transcription+factors+in+tendon+development+and+differentiation:+their+potential+for+tendon+regeneration.">Crucial transcription factors in tendon development and differentiation: their potential for tendon regeneration.</a> Cell and Tissue Research. 356 (2), 287-298 (2014).</li><li>Bloor, A. J. C., 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=Production,+safety+and+efficacy+of+iPSC-derived+mesenchymal+stromal+cells+in+acute+steroid-resistant+graft+versus+host+disease:+a+phase+I,+multicenter,+open-label,+dose-escalation+study.">Production, safety and efficacy of iPSC-derived mesenchymal stromal cells in acute steroid-resistant graft versus host disease: a phase I, multicenter, open-label, dose-escalation study.</a> Nature Medicine. 26 (11), 1720-1725 (2020).</li><li>McGrath, M., Tam, E., Sladkova, M., AlManaie, A., Zimmer, M., de Peppo, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GMP-compatible+and+xeno-free+cultivation+of+mesenchymal+progenitors+derived+from+human-induced+pluripotent+stem+cells.">GMP-compatible and xeno-free cultivation of mesenchymal progenitors derived from human-induced pluripotent stem cells.</a> Stem Cell Research and Therapy. 10 (1), 11 (2019).</li><li>Lian, Q., Zhang, Y., Liang, X., Gao, F., Tse, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directed+differentiation+of+human-induced+pluripotent+stem+cells+to+mesenchymal+stem+cells.">Directed differentiation of human-induced pluripotent stem cells to mesenchymal stem cells.</a> Methods in Molecular Biology. 1416, 289-298 (2016).</li><li>Gaspar, D., Ryan, C. N. M., Zeugolis, D. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+scleraxis+overexpression+combined+with+cyclic+strain+enhances+ligament+cell+differentiation.">Transient scleraxis overexpression combined with cyclic strain enhances ligament cell differentiation.</a> Tissue Engineering Part A. 24 (19-20), 1444-1455 (2018).</li><li>Chen, X., 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=Force+and+scleraxis+synergistically+promote+the+commitment+of+human+ES+cells+derived+MSCs+to+tenocytes.">Force and scleraxis synergistically promote the commitment of human ES cells derived MSCs to tenocytes.</a> Scientific Reports. 2, 977 (2012).</li><li>Kataoka, 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=In+vitro+neo-genesis+of+tendon/ligament-like+tissue+by+combination+of+mohawk+and+a+three-dimensional+cyclic+mechanical+stretch+culture+system.">In vitro neo-genesis of tendon/ligament-like tissue by combination of mohawk and a three-dimensional cyclic mechanical stretch culture system.</a> Frontiers in Cell and Developmental Biology. 8, 307 (2020).</li></ol>

All authors have no conflicts of interest to disclose.

In this protocol, iTenocytes are generated through three main steps: (1) induction of iPSCs to iMSCs, (2) overexpression of SCX using a lentiviral vector, and (3) maturation of cells through 2D uniaxial tension.
The protocol presented for differentiating iPSCs into iMSCs has been previously described by our group2. Since that publication, numerous protocols have been developed, including an established protocol for using iMSCs in clinical trials21</sup...

To tackle the contemporary issues in tendon and ligament repair, there&#39;s a requirement for a pertinent cell candidate suitable for cell-based therapies. One avenue of investigation in tissue engineering for tendon repair involves the exploration of bone marrow-derived mesenchymal stromal cells (BM-MSCs) and adipose tissue-derived stromal cells (ASCs) as potential strategies. These cells have multipotent capability, great abundance, and regenerative potential in vivo. Additionally, they have shown enhanced healing capacity and improved functional outcomes in animal models1. Nonetheless, these cells exhibit restricted self-renewal capabilities, phenotypic diversity, and notably, limited capacity for tendon formation. Induced pluripotent stem cell (iPSC) technology offers a solution to these constraints due to its remarkable self-renewal capacity and unmatched developmental adaptability. Our research team and others have achieved successful differentiation of iPSCs into mesenchymal stromal cell-like entities (iMSCs)2,3. As such, iMSCs have the potential to be an allogenic source for tendon cell therapy applications.
Scleraxis (SCX) is a transcription factor essential for tendon development and is considered the earliest detectable marker for differentiated tenocytes. Additionally, SCX activates downstream tendon differentiation markers, including type 1a1 chain collagen 1 (COL1a1), mohawk (MKX), and tenomodulin (TNMD), among others4,5,6. Other genes expressed during tendon maturation include tubulin polymerization-promoting protein family member 3 (TPPP3) and platelet-derived growth factor receptor alpha (PDGFRa)7. While these genes are essential for tendon development and maturation, they are unfortunately not unique to tendon tissue and are expressed in other musculoskeletal tissues like bone or cartilage5,7.
In addition to the expression of markers during tendon development, mechanostimulation is an essential element for embryonic tendon development and healing4,5,6. Tendons are mechanoresponsive, and their growth patterns change in response to their environment. At the molecular level, biomechanical cues affect the development, maturation, maintenance, and healing responses of tenocytes8. Various bioreactor systems have been utilized to model physiological loads and biomechanical cues. Some of these model systems include ex vivo tissue loading, 2D cell loading systems applying bi-axial or uniaxial tension, and 3D systems using scaffolds and hydrogels9,10. 2D systems are advantageous when studying the mechanical stimulation&#39;s effects on either tendon-specific genes or the morphology of the cells in the context of cell fate, while 3D systems can more accurately replicate cell-ECM interactions9,10.
In 2D loading systems, the strain between the cells and the culture substrate is homogeneous, meaning that the applied load on the cytoskeleton of the cells can be fully controlled. In comparison to bi-axial loading, uniaxial loading is more physiologically relevant, as tenocytes are predominantly subjected to uniaxial loading from collagen bundles in vivo9. It is found that during daily activities, tendons are subjected to uniaxial tensile loading up to 6% strain11. Specifically, previous studies have found that loading within the physiological ranges of 4%-5% has been shown to promote tenogenic differentiation by preserving tendon-related marker expression like SCX and TNMD, as well as increased collagen production9,10. Strains of more than 10% may be traumatically relevant but not physiologically relevant12,13.
Here, a protocol is presented that takes into account the synergistic effect of mechanical and biological stimulation that may be essential for the generation of tenocytes. We first describe a reproducible method to induce iPSCs into iMSCs via short-term exposure of embryoid bodies to growth factors, confirmed by MSC surface markers using flow cytometry. We then detail a lentiviral transduction method to engineer iMSCs to have stable overexpression of SCX (iMSCSCX+). For further cell maturation, the iMSCSCX+ are seeded into fibronectin-coated silicone plates and undergo an optimized uniaxial tension protocol using CellScale MCFX bioreactor. The tenogenic potential was confirmed by observing the upregulation of early and late tendon markers, as well as collagen deposition14. This method of generating iTenocytes is a proof-of-concept that may offer an unlimited off-the-shelf, allogeneic source for tendon cell therapy applications.

<table><tbody><tr><td>2-mercaptoethanol&amp;nbsp;</td><td>Sigma Aldrich</td><td>M3148</td><td></td></tr><tr><td>Accutase</td><td>StemCell Technologies</td><td>7920</td><td>cell dissociation reagent</td></tr><tr><td>Antibiotic-antimycotic solution</td><td>Thermofisher</td><td>15240096</td><td></td></tr><tr><td>Anti-CD105</td><td>Ancell</td><td>326-050</td><td></td></tr><tr><td>APC mouse anti-human CD44</td><td>BD Biosciences</td><td>559942</td><td></td></tr><tr><td>APC mouse IgG2 K isotype control</td><td>BD Biosciences</td><td>555745</td><td></td></tr><tr><td>BenchMark fetal bovine serum</td><td>GeminiBio</td><td>100-106</td><td></td></tr><tr><td>Biglycan</td><td>Thermofisher</td><td>Hs00959143_m1</td><td></td></tr><tr><td>Bovine serum albumin</td><td>Millipore Sigma</td><td>A3733</td><td></td></tr><tr><td>Collagen type I alpha 1 chain human Taqman primer</td><td>Thermofisher</td><td>Hs00164004_m1</td><td></td></tr><tr><td>Collagen type III alpha 1 chain human Taqman primer</td><td>Thermofisher</td><td>Hs00943809_m1</td><td></td></tr><tr><td>Dimethyl sulfoxide</td><td>Millipore Sigma</td><td>D8418</td><td></td></tr><tr><td>DMEM, low glucose, pyruvate, no glutamine, no phenol red</td><td>Thermofisher</td><td>11054020</td><td></td></tr><tr><td>Eagle&#039;s minimum essential medium (EMEM)</td><td>ATCC</td><td>30-2003</td><td></td></tr><tr><td>Fibronectin bovine plasma</td><td>Sigma Aldrich</td><td>F1141</td><td></td></tr><tr><td>FITC mouse anti-human CD90</td><td>BD Biosciences</td><td>555595</td><td></td></tr><tr><td>Gelatin from porcine skin</td><td>Sigma Aldrich</td><td>G1890</td><td></td></tr><tr><td>Goat anti Mouse IgG1-PE</td><td>Bio-Rad</td><td>STAR117</td><td></td></tr><tr><td>HEK 293T/17</td><td>ATCC</td><td>CRL-11268</td><td></td></tr><tr><td>IMDM, no phenol red</td><td>Thermofisher</td><td>21056023</td><td></td></tr><tr><td>iPSCs: 83i-cntr-33n1</td><td>Cedars-Sinai iPSC Core Facility</td><td>N/A</td><td>https://biomanufacturing.cedars-sinai.org/product/cs83ictr-33nxx/</td></tr><tr><td>Isotype Control Antibody, mouse IgG2a-FITC</td><td>Miltenyi Biotec</td><td>130-113-271</td><td></td></tr><tr><td>KnockOut serum replacement</td><td>Thermofisher</td><td>10828010</td><td></td></tr><tr><td>L-ascorbic acid</td><td>Sigma Aldrich</td><td>A4544</td><td></td></tr><tr><td>L-Glutamine</td><td>Thermofisher</td><td>2503081</td><td></td></tr><tr><td>Matrigel</td><td>Corning</td><td>354230</td><td>basement membrane matrix</td></tr><tr><td>MechanoCulture FX</td><td>CellScale</td><td>N/A</td><td>stretching apparatus</td></tr><tr><td>MEM non-essential amino acids solution</td><td>Thermofisher</td><td>11140050</td><td></td></tr><tr><td>Mohawk human Taqman primer</td><td>Thermofisher</td><td>Hs00543190_m1</td><td></td></tr><tr><td>mTeSR Plus</td><td>StemCell Technologies</td><td>100-0276</td><td></td></tr><tr><td>PBS</td><td>Thermofisher</td><td>10010023</td><td></td></tr><tr><td>Platelet-derived growth factor receptor A human Taqman primer</td><td>Thermofisher</td><td>Hs00998018_m1</td><td></td></tr><tr><td>Poly(2-hydroxyethyl methacrylate)</td><td>Sigma Aldrich</td><td>192066</td><td></td></tr><tr><td>Polybrene infection/transfection reagents</td><td>Millipore Sigma</td><td>TR-1003</td><td></td></tr><tr><td>Recombinant human&amp;nbsp; TGF-beta 1 protein human Taqman primer</td><td>RnD Systems</td><td>240-B</td><td></td></tr><tr><td>Scleraxis human Taqman primer</td><td>Thermofisher</td><td>Hs03054634_g1</td><td></td></tr><tr><td>SCXA (SCX) (NM_00108050514) human tagged ORF clone</td><td>OriGene</td><td>RC224305L4</td><td></td></tr><tr><td>Silicone plates</td><td>CellScale</td><td>N/A</td><td></td></tr><tr><td>Sodium azide</td><td>Millipore Sigma</td><td>S2002</td><td></td></tr><tr><td>Tenascin C human Taqman primer</td><td>Thermofisher</td><td>Hs00370384_m1</td><td></td></tr><tr><td>Tenomodulin human Taqman primer</td><td>Thermofisher</td><td>Hs00223332_m1</td><td></td></tr><tr><td>Thrombospondin 4 human Taqman primer</td><td>Thermofisher</td><td>Hs00170261_m1</td><td></td></tr><tr><td>Transfection reagent, BioT</td><td>Bioland Scientific LLC</td><td>B01-01</td><td></td></tr><tr><td>Trypsin-EDTA (0.25%)</td><td>Thermofisher</td><td>25200072</td><td></td></tr><tr><td>Tubulin polymerization promoting protein family member 3</td><td>Thermofisher</td><td>Hs03043892_m1</td><td></td></tr><tr><td>Y-27632 dihydrochloride</td><td>Biogems</td><td>1293823</td><td></td></tr></tbody></table>

generation of induced pluripotent stem cell-derived itenocytes via combined scleraxis overexpression and 2d uniaxial tension

Today&#39;s challenges in tendon and ligament repair necessitate the identification of a suitable and effective candidate for cell-based therapy to promote tendon regeneration. Mesenchymal stromal cells (MSCs) have been explored as a potential tissue engineering strategy for tendon repair. While they are multipotent and have regenerative potential in vivo, they are limited in their self-renewal capacity and exhibit phenotypic heterogeneity. Induced pluripotent stem cells (iPSCs) can circumvent these limitations due to their high self-renewal capacity and unparalleled developmental plasticity. In tenocyte development, Scleraxis (Scx) is a crucial direct molecular regulator of tendon differentiation. Additionally, mechanoregulation has been shown to be a central element guiding embryonic tendon development and healing. As such, we have developed a protocol to encapsulate the synergistic effect of biological and mechanical stimulation that may be essential for generating tenocytes. iPSCs were induced to become mesenchymal stromal cells (iMSCs) and were characterized with classic mesenchymal stromal cell markers via flow cytometry. Next, using a lentiviral vector, the iMSCs were transduced to stably overexpress SCX (iMSCSCX+). These iMSCSCX+ cells can be further matured into iTenocytes via uniaxial tensile loading using a 2D bioreactor. The resulting cells were characterized by observing the upregulation of early and late tendon markers, as well as collagen deposition. This method of generating iTenocytes can be used to assist researchers in developing a potentially unlimited off-the-shelf allogeneic cell source for tendon cell therapy applications.

Human iPSCs differentiation to iMSCs 
As previously described, the current protocol for differentiating iPSCs into iMSCs involves the formation of embryoid bodies2. This process takes approximately ten days to induce iMSCs from iPSCs (Figure 1A). However, it is highly recommended to passage the newly generated iMSCs at least twice. This not only helps eliminate the need for gelatin-coated plates but also establishes stable MSC expression. Flow cy...

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Author Spotlight: Advancements in Cell and Tissue Engineering for Tendon Repair 

This article describes a procedure to produce iTenocytes by generating iPSC-derived mesenchymal stromal cells with combined overexpression of Scleraxis using a lentiviral vector and uniaxial stretching via a 2D bioreactor.

Generation of Induced Pluripotent Stem Cell-Derived iTenocytes via Combined Scleraxis Overexpression and 2D Uniaxial Tension

Today&#39;s challenges in tendon and ligament repair necessitate the identification of a suitable and effective candidate for cell-based therapy to ...

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JoVE Journal

Bioengineering

1.5K Views.  Cedars-Sinai Medical Center. This article describes a procedure to produce iTenocytes by generating iPSC-derived mesenchymal stromal cells with combined overexpression of Scleraxis using a lentiviral vector and uniaxial stretching via a 2D bioreactor.

Video: Author Spotlight: Advancements in Cell and Tissue Engineering for Tendon Repair 

Generation of Aligned Functional Myocardial Tissue Through Microcontact Printing

Advanced heart failure represents a major unmet clinical challenge, arising from the loss of viable and/or fully functional cardiac muscle cells. Despite optimum drug therapy, heart failure represents a leading cause of mortality and morbidity in the developed world. A major challenge in drug development is the identification of cellular assays that accurately recapitulate normal and diseased human myocardial physiology in vitro. Likewise, the major challenges in regenerative cardiac biology revolve around the identification and isolation of patient-specific cardiac progenitors in clinically relevant quantities. These cells have to then be assembled into functional tissue that resembles the native heart tissue architecture. Microcontact printing allows for the creation of precise micropatterned protein shapes that resemble structural organization of the heart, thus providing geometric cues to control cell adhesion spatially. Herein we describe our approach for the isolation of highly purified myocardial cells from pluripotent stem cells differentiating in vitro, the generation of cell growth surfaces micropatterned with extracellular matrix proteins, and the assembly of the stem cell-derived cardiac muscle cells into anisotropic myocardial tissue.

The generation of aligned myocardial tissue is a key requirement for adapting the recent advances in stem cell biology to clinically useful purposes. Herein we describe a microcontact printing approach for the precise control of cell shape and function. Using highly purified populations of embryonic stem cell derived cardiac progenitors, we then generate anisotropic functional myocardial tissue.

Advanced heart failure represents a major unmet clinical challenge,  arising from the loss of viable and/or fully functional cardiac muscle  cells. ...

Development, Expansion, and In vivo Monitoring of Human NK Cells from Human Embryonic Stem Cells (hESCs) and Induced Pluripotent Stem Cells (iPSCs)

We present a method for deriving natural killer (NK) cells from undifferentiated hESCs and iPSCs using a feeder-free approach. This method gives rise to high levels of NK cells after 4 weeks culture and can undergo further 2-log expansion with artificial antigen presenting cells. hESC- and iPSC-derived NK cells developed in this system have a mature phenotype and function. The production of large numbers of genetically modifiable NK cells is applicable for both basic mechanistic as well as anti-tumor studies. Expression of firefly luciferase in hESC-derived NK cells allows a non-invasive approach to follow NK cell engraftment, distribution, and function. We also describe a dual-imaging scheme that allows separate monitoring of two different cell populations to more distinctly characterize their interactions in vivo. This method of derivation, expansion, and dual in vivo imaging provides a reliable approach for producing NK cells and their evaluation which is necessary to improve current NK cell adoptive therapies.

Development, Expansion, and In vivo Monitoring of Human NK Cells from Human Embryonic Stem Cells hESCs and Induced Pluripotent Stem Cells iPSCs

This protocol describes the development, expansion, and in vivo imaging of NK cells derived from hESCs and iPSCs.

We present a method for deriving natural killer (NK) cells from undifferentiated hESCs and iPSCs using a feeder-free approach. This method gives rise to ...

Transplantation of Induced Pluripotent Stem Cell-derived Mesoangioblast-like Myogenic Progenitors in Mouse Models of Muscle Regeneration

Patient-derived iPSCs could be an invaluable source of cells for future autologous cell therapy protocols. iPSC-derived myogenic stem/progenitor cells similar to pericyte-derived mesoangioblasts (iPSC-derived mesoangioblast-like stem/progenitor cells: IDEMs) can be established from iPSCs generated from patients affected by different forms of muscular dystrophy. Patient-specific IDEMs can be genetically corrected with different strategies (e.g. lentiviral vectors, human artificial chromosomes) and enhanced in their myogenic differentiation potential upon overexpression of the myogenesis regulator MyoD. This myogenic potential is then assessed in vitro with specific differentiation assays and analyzed by immunofluorescence. The regenerative potential of IDEMs is further evaluated in vivo, upon intramuscular and intra-arterial transplantation in two representative mouse models displaying acute and chronic muscle regeneration. The contribution of IDEMs to the host skeletal muscle is then confirmed by different functional tests in transplanted mice. In particular, the amelioration of the motor capacity of the animals is studied with treadmill tests. Cell engraftment and differentiation are then assessed by a number of histological and immunofluorescence assays on transplanted muscles. Overall, this paper describes the assays and tools currently utilized to evaluate the differentiation capacity of IDEMs, focusing on the transplantation methods and subsequent outcome measures to analyze the efficacy of cell transplantation.

Induced pluripotent stem cell (iPSC)-derived myogenic progenitors are promising candidates for cell therapy strategies to treat muscular dystrophies. This protocol describes transplantation and functional measurements required to evaluate the engraftment and differentiation of iPSC-derived mesoangioblasts (a type of muscle progenitors) in mouse models of acute and chronic muscle regeneration.

Patient-derived iPSCs could be an invaluable source of cells for future autologous cell therapy protocols. iPSC-derived myogenic stem/progenitor cells ...

In Vitro Generation of Somite Derivatives from Human Induced Pluripotent Stem Cells

In response to signals such as WNTs, bone morphogenetic proteins (BMPs), and sonic hedgehog (SHH) secreted from surrounding tissues, somites (SMs) give rise to multiple cell types, including the myotome (MYO), sclerotome (SCL), dermatome (D), and syndetome (SYN), which in turn develop into skeletal muscle, axial skeleton, dorsal dermis, and axial tendon/ligament, respectively. Therefore, the generation of SMs and their derivatives from human induced pluripotent stem cells (iPSCs) is critical to obtain pluripotent stem cells (PSCs) for application in regenerative medicine and for disease research in the field of orthopedic surgery. Although the induction protocols for MYO and SCL from PSCs have been previously reported by several researchers, no study has yet demonstrated the induction of SYN and D from iPSCs. Therefore, efficient induction of fully competent SMs remains a major challenge. Here, we recapitulate human SM patterning with human iPSCs in vitro by mimicking the signaling environment during chick/mouse SM development, and report on methods of systematic induction of SM derivatives (MYO, SCL, D, and SYN) from human iPSCs under chemically defined conditions through the presomitic mesoderm (PSM) and SM states. Knowledge regarding chick/mouse&#160;SM development was successfully applied to the induction of SMs with human iPSCs. This method could be a novel tool for studying human somitogenesis and patterning without the use of embryos and for cell-based therapy and disease modeling.

We present here a protocol for the differentiation of human induced pluripotent stem cells into each somite derivative (myotome, sclerotome, dermatome, and syndetome) in chemically defined conditions, which has applications in future disease modeling and cell-based therapies in orthopedic surgery.

In response to signals such as WNTs, bone morphogenetic proteins (BMPs), and sonic hedgehog (SHH) secreted from surrounding tissues, somites (SMs) give ...

Developmental Biology

Isolation of Adult Human Dermal Fibroblasts from Abdominal Skin and Generation of Induced Pluripotent Stem Cells Using a Non-Integrating Method

Induced pluripotent stem cells (iPSCs) could be considered, to date, a promising source of pluripotent cells for the management of currently untreatable diseases, for the reconstitution and regeneration of injured tissues and for the development of new drugs. Despite all the advantages related to the use of iPSCs, such as the low risk of rejection, the lessened ethical issues, and the possibility to obtain them from both young and old patients without any difference in their reprogramming potential, problems to overcome are still numerous. In fact, cell reprogramming conducted with viral and integrating viruses can cause infections and the introduction of required genes can induce a genomic instability of the recipient cell, impairing their use in clinic. In particular, there are many concerns about the use of c-Myc gene, well-known from several studies for its mutation-inducing activity. Fibroblasts have emerged as the suitable cell population for cellular reprogramming as they are easy to isolate and culture and are harvested by a minimally invasive skin punch biopsy. The protocol described here provides a detailed step-by-step description of the whole procedure, from sample processing to obtain cell cultures, choice of reagents and supplies, cleaning and preparation, to cell reprogramming by the means of a commercial non-modified RNAs (NM-RNAs)-based reprogramming kit. The chosen reprogramming kit allows an effective reprogramming of human dermal fibroblast to iPSCs and small colonies can be seen as early as 24 h after the first transfection, even with modifications with the respect to the standard datasheet. The reprogramming procedure used in this protocol offers the advantage of a safe reprogramming, without the risk of infections caused by viral vector-based methods, reduces the cellular defense mechanisms, and allows the generation of xeno-free iPSCs, all critical features that are mandatory for further clinical applications.

Cell reprogramming requires the introduction of key genes, which regulate and maintain the pluripotent cell state. The protocol described enables the formation of induced pluripotent stem cells (iPSCs) colonies from human dermal fibroblasts without viral/integrating methods but using non-modified RNAs (NM-RNAs) combined with immune evasion factors reducing cellular defense mechanisms.

Induced pluripotent stem cells (iPSCs) could be considered, to date, a promising source of pluripotent cells for the management of currently untreatable ...

Scalable Generation of Mature Cerebellar Organoids from Human Pluripotent Stem Cells and Characterization by Immunostaining

The cerebellum plays a critical role in the maintenance of balance and motor coordination, and a functional defect in different cerebellar neurons can trigger cerebellar dysfunction. Most of the current knowledge about disease-related neuronal phenotypes is based on postmortem tissues, which makes understanding of disease progression and development difficult. Animal models and immortalized cell lines have also been used as models for neurodegenerative disorders. However, they do not fully recapitulate human disease. Human induced pluripotent stem cells (iPSCs) have great potential for disease modeling and provide a valuable source for regenerative approaches. In recent years, the generation of cerebral organoids from patient-derived iPSCs improved the prospects for neurodegenerative disease modeling. However, protocols that produce large numbers of organoids and a high yield of mature neurons in 3D culture systems are lacking. The protocol presented is a new approach for reproducible and scalable generation of human iPSC-derived organoids under chemically-defined conditions using scalable single-use bioreactors, in which organoids acquire cerebellar identity. The generated organoids are characterized by the expression of specific markers at both mRNA and protein level. The analysis of specific groups of proteins allows the detection of different cerebellar cell populations, whose localization is important for the evaluation of organoid structure. Organoid cryosectioning and further immunostaining of organoid slices are used to evaluate the presence of specific cerebellar cell populations and their spatial organization.

This protocol describes a dynamic culture system to produce controlled size aggregates of human pluripotent stem cells and further stimulate differentiation in cerebellar organoids under chemically-defined and feeder-free conditions using a single-use bioreactor.

The cerebellum plays a critical role in the maintenance of balance and motor coordination, and a functional defect in different cerebellar neurons can ...

Guided Differentiation of Mature Kidney Podocytes from Human Induced Pluripotent Stem Cells Under Chemically Defined Conditions

Kidney disease affects more than 10% of the global population and costs billions of dollars in federal expenditures. The most severe forms of kidney disease and eventual end-stage renal failure are often caused by the damage to the glomerular podocytes, which are the highly specialized epithelial cells that function together with endothelial cells and the glomerular basement membrane to form the kidney&#8217;s filtration barrier. Advances in renal medicine have been hindered by the limited availability of primary tissues and the lack of robust methods for the derivation of functional human kidney cells, such as podocytes. The ability to derive podocytes from renewable sources, such as stem cells, could help advance current understanding of the mechanisms of human kidney development and disease, as well as provide new tools for therapeutic discovery. The goal of this protocol was to develop a method to derive mature, post-mitotic podocytes from human induced pluripotent stem (hiPS) cells with high efficiency and specificity, and under chemically defined conditions. The hiPS cell-derived podocytes produced by this method express lineage-specific markers (including nephrin, podocin, and Wilm&#8217;s Tumor 1) and exhibit the specialized morphological characteristics (including primary and secondary foot processes) associated with mature and functional podocytes. Intriguingly, these specialized features are notably absent in the immortalized podocyte cell line widely used in the field, which suggests that the protocol described herein produces human kidney podocytes that have a developmentally more mature phenotype than the existing podocyte cell lines typically used to study human kidney biology.

Presented here is a chemically defined protocol for the derivation of human kidney podocytes from induced pluripotent stem cells with high efficiency (&#62;90%) and independent of genetic manipulations or subpopulation selection. This protocol produces the desired cell type within 26 days and could be useful for nephrotoxicity testing and disease modeling.

Kidney disease affects more than 10% of the global population and costs billions of dollars in federal expenditures. The most severe forms of kidney ...

Generation of Myospheres From hESCs by Epigenetic Reprogramming

Generation of a homogeneous and abundant population of skeletal muscle cells from human embryonic stem cells (hESCs) is a requirement for cell-based therapies and for a "disease in a dish" model of human neuromuscular diseases. Major hurdles, such as low abundance and heterogeneity of the population of interest, as well as a lack of protocols for the formation of three-dimensional contractile structures, have limited the applications of stem cells for neuromuscular disorders. We have designed a protocol that overcomes these limits by ectopic introduction of defined factors in hESCs - the muscle determination factor MyoD and SWI/SNF chromatin remodeling complex component BAF60C - that are able to reprogram hESCs into skeletal muscle cells. Here we describe the protocol established to generate hESC-derived myoblasts and promote their clustering into tridimensional miniaturized structures (myospheres) that functionally mimic miniaturized skeletal muscles7.

Here, we describe a protocol based on epigenetic reprogramming of human embryonic stem cells (hESCs) toward generating a homogeneous population of skeletal muscle progenitors that under permissive culture conditions form three-dimensional clusters of contractile myofibers (myospheres), which recapitulate biological features of human skeletal muscles.

Generation of a homogeneous and abundant population of skeletal muscle cells from human embryonic stem cells (hESCs) is a requirement for cell-based ...

Biology

Three-Step Organoid Model for Tendon Research and Engineering

Demonstration of Self-Assembled Cell Sheet Culture and Manual Generation of a 3D Tendon/Ligament-Like Organoid by using Human Dermal Fibroblasts

Tendons and ligaments (T/L) are strong hierarchically organized structures uniting&#160;the&#160;musculoskeletal system. These tissues have a strictly arranged collagen type&#160;I-rich extracellular matrix (ECM) and T/L-lineage cells mainly positioned in parallel rows. After injury, T/L require a long time for rehabilitation with high failure risk and often unsatisfactory repair outcomes. Despite recent advancements in T/L biology research, one of the remaining challenges is that the T/L field still lacks a standardized differentiation protocol that is able to recapitulate T/L formation process in vitro. For example, bone and fat differentiation of mesenchymal precursor cells require just standard two-dimensional (2D) cell culture and the addition of specific stimulation media. For differentiation to cartilage, three-dimensional (3D) pellet culture and supplementation of TGF&#223; is necessary. However, cell differentiation to tendon needs a very orderly 3D culture model, which ideally should also be subjectable to dynamic mechanical stimulation. We have established a 3-step (expansion, stimulation, and maturation) organoid model to form a 3D rod-like structure out of a self-assembled cell sheet, which delivers a natural microenvironment with its own ECM, autocrine, and paracrine factors. These rod-like organoids have a multi-layered cellular architecture within rich ECM and can be handled quite easily for exposure to static mechanical strain. Here, we demonstrated the 3-step protocol by using commercially available dermal fibroblasts. We could show that this cell type forms robust and ECM-abundant organoids. The described procedure can be further optimized in terms of culture media and optimized toward dynamic axial mechanical stimulation. In the same way, alternative cell sources can be tested for their potential to form T/L organoids and thus undergo T/L differentiation. In sum, the established 3D T/L organoid approach can be used as a model for tendon basic research and even for scaffold-free T/L engineering.

Author Spotlight: Advancing Tendon Tissue Engineering with 3D Organoid Models

Herein, we demonstrate a three-step organoid model (two-dimensional [2D] expansion, 2D stimulation, three-dimensional [3D] maturation) offering a promising tool for tendon fundamental research and a potential scaffold-free method for tendon tissue engineering.

Tendons and ligaments (T/L) are strong hierarchically organized structures uniting&#160;the&#160;musculoskeletal system. These tissues have a strictly ...

Applying a Three-dimensional Uniaxial Mechanical Stimulation Bioreactor System to Induce Tenogenic Differentiation of Tendon-Derived Stem Cells

Tendinopathy is a common chronic tendon disease relating to inflammation and degeneration in an orthopaedic area. With high morbidity, limited self-repairing capacity and, most importantly, no definitive treatments, tendinopathy still influences patients&#8217; life quality negatively. Tendon-derived stem cells (TDSCs), as primary precursor cells of tendon cells, play an essential role in both the development of tendinopathy, and functional and structural restoration after tendinopathy. Thus, a method that can in vitro mimic the in vivo differentiation of TDSCs into tendon cells would be useful. Here, the present protocol describes a method based on a three-dimensional (3D) uniaxial stretching system to stimulate the TDSCs to differentiate into tendon-like tissues. There are seven stages of the present protocol: isolation of mice TDSCs, culture and expansion of mice TDSCs, preparation of stimulation culture medium for cell sheet formation, cell sheet formation by culturing in stimulation medium, preparation of 3D tendon stem cell construct, assembly of the uniaxial-stretching mechanical stimulation complex, and evaluation of the mechanical stimulated in vitro tendon-like tissue. The effectiveness was demonstrated by histology. The entire procedure takes less than 3 weeks. To promote extracellular matrix deposition, 4.4 mg/mL ascorbic acid was used in the stimulation culture medium. A separated chamber with a linear motor provides accurate mechanical loading and is portable and easily adjusted, which is applied for the bioreactor. The loading regime in the present protocol was 6% strain, 0.25 Hz, 8 h, followed by 16 h rest for 6 days. This protocol could mimic cell differentiation in the tendon, which is helpful for the investigation of the pathological process of tendinopathy. Moreover, the tendon-like tissue is potentially used to promote tendon healing in tendon injury as an engineered autologous graft. To sum up, the present protocol is simple, economic, reproducible and valid.

A three-dimensional uniaxial mechanical stimulation bioreactor system is an ideal bioreactor for tenogenic-specific differentiation of tendon-derived stem cells and neo-tendon formation.