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Non-human primates (NHP), and in particular Old World monkeys including macaques and baboons, are key animal models for the late preclinical testing of novel stem cell-based therapies and other advanced therapy medical products (ATMP) for the treatment of degenerative diseases. These pathologies are characterized by the loss of functional cells in an organ, as in Parkinson's disease, age-related macular degeneration, or after myocardial infarction. For preclinically relevant testing of induced pluripotent stem cell (iPSC)-based therapies, robust, and standardized protocols for the generation, characterization, and differentiation of NHP-iPSCs are required. Since the discovery of iPSCs by Takahashi and Yamanaka in 2006, human reprogramming protocols have been continuously refined. However, the generation of integration-free NHP-iPSC lines and a stable feeder- and serum-free long-term culture turned out to be difficult or even impossible with the current protocols established for human iPSCs. Here, we provide a robust protocol for the generation of transgene-free Old World monkey (and human) iPSCs and long-term cultivation under chemically defined conditions. This protocol was successfully applied to generate human, baboon (Papio anubis), rhesus (Macaca mulatta), and cynomolgus macaque (Macaca fascicularis) iPSCs from skin fibroblasts. The resulting NHP-iPSCs provide a valuable resource for the preclinical testing of regenerative therapies in NHP.

Clinical application of regenerative therapies using embryonic or induced pluripotent stem cells is within reach. Progress made during recent years has encouraged researchers to address remaining open questions in order to finally translate experimental cell replacement therapies into application in patients. To achieve this, studies in translationally relevant animal models are required to make the final step to the clinic. In this context, the baboon (Papio anubis) may represent a valuable nonhuman primate (NHP) model to test cell replacement therapies because of its close evolutionary relationship to humans and its large body size. In this study, we describe the reprogramming of adult baboon skin fibroblasts using the piggyBac transposon system. Via transposon-mediated overexpression of six reprogramming factors, we generated five baboon induced pluripotent stem cell (iPSC) lines. The iPSC lines were characterized with respect to alkaline phosphatase activity, pluripotency factor expression analysis, teratoma formation potential, and karyotype. Furthermore, after initial cocultivation with mouse embryonic fibroblasts, we were able to adapt iPSC lines to feeder-free conditions. In conclusion, we established a robust and efficient protocol for iPSC generation from adult baboon fibroblasts.

Generation of homogeneous populations of subtype-specific cardiomyocytes (CMs) derived from human induced pluripotent stem cells (iPSCs) and their comprehensive phenotyping is crucial for a better understanding of the subtype-related disease mechanisms and as tools for the development of chamber-specific drugs. The goals of this study were to apply a simple and efficient method for differentiation of iPSCs into defined functional CM subtypes in feeder-free conditions and to obtain a comprehensive understanding of the molecular, cell biological, and functional properties of atrial and ventricular iPSC-CMs on both the single-cell and engineered heart muscle (EHM) level. By a stage-specific activation of retinoic acid signaling in monolayer-based and well-defined culture, we showed that cardiac progenitors can be directed towards a highly homogeneous population of atrial CMs. By combining the transcriptome and proteome profiling of the iPSC-CM subtypes with functional characterizations via optical action potential and calcium imaging, and with contractile analyses in EHM, we demonstrated that atrial and ventricular iPSC-CMs and -EHM highly correspond to the atrial and ventricular heart muscle, respectively. This study provides a comprehensive understanding of the molecular and functional identities characteristic of atrial and ventricular iPSC-CMs and -EHM and supports their suitability in disease modeling and chamber-specific drug screening.

Brugada syndrome (BrS) is a rare cardiac rhythm disorder associated with sudden cardiac death. Mutations in the sodium channel gene SCN5A are found in ~20% of cases while mutations in other genes collectively account for INa) in hiPSC-CMs from the 3 BrS patients compared to 2 unrelated controls. Moreover, action potential upstroke velocity (Vmax), reflecting INa, was not different between hiPSC-CMs from the BrS patients and the controls. hiPSC-CMs harboring the BrS-associated SCN5A-1795insD mutation exhibited a reduction in both INa and Vmax, demonstrating our ability to detect reduced sodium channel function. hiPSC-CMs from one of the BrS lines demonstrated a mildly reduced action potential duration, however, the transient outward potassium current (Ito) and the L-type calcium current (ICa,L), both implicated in BrS, were not different compared to the controls. Our findings indicate that ion channel dysfunction, in particular in the cardiac sodium channel, may not be a prerequisite for BrS.

Spermatogonial stem cells (SSCs) constitute one of the most important stem cell systems in the adult body. SSCs are unipotent and respond for spermatogenesis in the male as they can only differentiate into sperms within the testicular niche. The long-term culture of SSCs without loss of their properties provides the opportunity to develop therapeutic strategies and re-initiate spermatogenesis for the patients who become infertile after cancer therapy. Moreover, SSCs can be spontaneously reprogrammed into pluripotent germline stem cells (GSCs) similar to embryonic stem cells (ESCs) when they are removed from their in vivo niche and cultured in vitro under specific conditions. The advantage of pluripotent GSCs over induced pluripotent stem cells is that conversion of SSCs into pluripotent GSCs does not require addition of genes using the virus system, which may avoid unpredictable genetic dysfunction. In addition, this may also circumvent ethical problems associated with human ESCs. The ability to generate patient-specific pluripotent GSCs for autologous transplantation provides the opportunity for cell replacement therapy without the need for immunosuppressant. In this review, we discuss the origin, properties and regenerative potential of SSCs. We summarize recent research findings regarding the mechanisms that regulate the self-renewal of SSCs. We believe that studying the biology of SSCs provides us important information to better understand male fertility. Furthermore, we address the contribution of SSCs and pluripotent GSCs to stem cell-based therapy for infertility treatment as well as for organ regeneration in the future.

Aims Induced pluripotent stem cells (iPSCs) provide a unique opportunity for the generation of patient-specific cells for use in disease modelling, drug screening, and regenerative medicine. The aim of this study was to compare human-induced pluripotent stem cells (hiPSCs) derived from different somatic cell sources regarding their generation efficiency and cardiac differentiation potential, and functionalities of cardiomyocytes. Methods and results We generated hiPSCs from hair keratinocytes, bone marrow mesenchymal stem cells (MSCs), and skin fibroblasts by using two different virus systems. We show that MSCs and fibroblasts are more easily reprogrammed than keratinocytes. This corresponds to higher methylation levels of minimal promoter regions of the OCT4 and NANOG genes in keratinocytes than in MSCs and fibroblasts. The success rate and reprogramming efficiency was significantly higher by using the STEMCCA system than the OSNL system. All analysed hiPSCs are pluripotent and show phenotypical characteristics similar to human embryonic stem cells. We studied the cardiac differentiation efficiency of generated hiPSC lines ( n = 24) and found that MSC-derived hiPSCs exhibited a significantly higher efficiency to spontaneously differentiate into beating cardiomyocytes when compared with keratinocyte-, and fibroblast-derived hiPSCs. There was no significant difference in the functionalities of the cardiomyocytes derived from hiPSCs with different origins, showing the presence of pacemaker-, atrial-, ventricular- and Purkinje-like cardiomyocytes, and exhibiting rhythmic Ca2+ transients and Ca2+ sparks in hiPSC-derived cardiomyocytes. Furthermore, spontaneously and synchronously beating and force-developing engineered heart tissues were generated. Conclusions Human-induced pluripotent stem cells can be reprogrammed from all three somatic cell types, but with different efficiency. All analysed iPSCs can differentiate into cardiomyocytes, and the functionalities of cardiomyocytes derived from different cell origins are similar. However, MSC-derived hiPSCs revealed a higher cardiac differentiation efficiency than keratinocyte- and fibroblast-derived hiPSCs.

Purpose: The ability to generate patient-specific human induced pluripotent stem cells (ps-iPSCs) provides a unique opportunity for modeling heart disease. Dilated cardiomyopathy (DCM) is due to a progressive enlargement of the heart leading finally to heart failure. Mutations in many genes have been implicated in the pathogenesis of DCM including the RNA-binding motif 20 (RBM20). We aimed to generate iPSCs from DCM patients with a RBM20 mutations, and to analyze the functionality and cell biology of cardiomyocytes derived from these ps-iPSCs (ps-iPSC-CM) with regard to the cardiac DCM phenotype. Methods and Results: Dermal fibroblasts from two patients (34y; 75y) with DCM harboring different RBM20 mutations were reprogrammed to ps-iPSCs via lentiviral infection using the STEMCCA system. The ps-iPSCs show pluripotent characteristics by expressing pluripotency markers on mRNA and protein level similar to human embryonic stem cells. Furthermore, bisulfite sequencing analysis showed that the OCT4 and NANOG promoters were significantly demethylated in ps-iPSCs compared to their parental cells. In addition, the generated RBM20-iPSCs are able to differentiate in vitro and in vivo into derivatives of all three germ layers. The cardiac in vitro differentiation efficiency into beating cardiomyocytes of the RBM20-iPSCs is similar to control iPSCs. Electrophysiological studies showed that under basal conditions ps-iPSC-CM exhibited spontaneous action potentials characteristic for pacemaker-, atrial-, ventricular- and Purkinje-like cells in a similar manner as control iPSC-CM. Using Fast Fourier Transformation the sarcomere-associated periodic signal amplitude was analyzed for α-actinin. A significant higher percentage of RBM20-iPSC-CM showed abnormal sarcomeric α-actinin distribution compared to control CM, suggesting disorganized myofilament structure. But no significant difference was observed in cell size between RBM20-iPSC-CMs and control cells. Further, we found a different isoform expression pattern of the cardiac titin in the mutant ps-iPSC-CM compared to the control cells. This demonstrates a RBM20-dependent regulation of organized myofilament structure and titin splicing in an in vitro ps-DCM-iPSC-model. Conclusion: We demonstrate that iPSC-derived cardiomyocytes from young and old DCM patients harboring a RBM20 mutation recapitulate the abnormalities that were found in individuals with DCM caused by the same mutation. The differentiated cardiomyocytes may be used for individual drug testing and development of novel treatments for this inherited disorder.