Imprecise lineage definition associates with functional dissimilarity observed between IPSC-derived MSCS and primary MSCs

Abstract

Background & Aim Induced pluripotent stem cells (iPSCs) have been considered as a protential alternative source for generating mesenchymal stem cells (MSCs) to meet the increased cell demands for both research and therapeutic applications. Based on the minimal criteria for defining MSCs published by the International Society for Cellular Therapy (ISCT standard), several different protocols have claimed success in differentiating MSCs from iPSCs (iMSCs). However, questions have arisen relating to the phenotypic fidelity of iMSCs because, irrespective of the derivation methods used, the cells generally have less capacity for adipo- and chondro-genesis when compared with primary MSCs. The objective of this study was to understand the cellular mechanism behind these discrepancies. Methods, Results & Conclusion iMSCs were derived using the embryoid body-based outgrowth method. We compared the differentiation ability, immunophenotype and gene expression profiles (GEPs) between multiple iMSC and BM-MSC lines. In addition, the impact of culture expansion on cell state was evaluated. The results showed that iMSCs met the ISCT standard but displayed significantly negligible adipogenic and chondrogenic capacity compared to BM-MSCs. GEPs analysis revealed that iMSCs expressed very high levels of vascular progenitor cell (VPC) genes (KDR and MSX2), whereas BM-MSCs had significantly greater levels of paraxial mesodermal genes (PDGFRα and MESP2). These distinct GEPs were maintained during culture expansion, indicating that, unlike BM-MSCs, iMSCs were more closely related to VPCs. Interestingly, the revealed characteristics of iMSCs corresponded to the known cell property of VPCs, where the later one displays partially overlapped immunophenotype as primary MSCs. However, although VPCs have osteo-, adipo- and chondro-genic potential, which cannot be fully activated in primary MSCs preferred differentiation condition. In summary, our results suggest a lineage misidentification of iMSCs, indicate the inadequacy of using the ISCT standard to distinguish different mesodermal progenitors and emphasize a necessity to validate the iMSCs identity with various lineage markers.