Characterization of the Mitochondrial Genome Landscape in MSCs, iPSCs and iMSCs from Osteoarthritis Patients and Healthy Donors.

Background/Objectives: Osteoarthritis (OA) is strongly associated with mitochondrial dysfunction, oxidative stress, and the accumulation of mitochondrial DNA (mtDNA) alterations in several joint-associated cell types, including chondrocytes, synoviocytes, and mesenchymal stromal cells (MSCs). These alterations contribute to impaired cellular homeostasis and reduced regenerative potential. In this study, we systematically characterized mtDNA heteroplasmy and variant distribution across bone marrow MSCs, induced pluripotent stem cells (iPSCs) and induced MSCs (iMSCs) derived from OA patients and healthy donors. Methods: Ultra-deep mitochondrial genome sequencing was integrated with transcriptomic and miRNome analyses to investigate mitochondrial remodeling during cellular reprogramming, encompassing changes in mtDNA heteroplasmy, variant distribution, mtDNA copy number and associated transcriptomic adaptations of nuclear-encoded mitochondrial pathways. Results: OA-derived MSCs exhibited a markedly increased heteroplasmic burden, followed by decrease in mtDNA copy number and accumulation of non-synonymous variants, particularly within OXPHOS-related genes, including MT-ND1-5, MT-ATP8, MT-CO1, and MT-RNR1/2. Reprogramming into iPSCs and subsequent differentiation into iMSCs were associated with an increase in mtDNA copy number and a progressive reduction in heteroplasmic variants predicted to have pathogenic potential, including m.7913C>T and m.7821G>A, as well as substantial reduction in heteroplasmic variant burden within several mitochondrial genes, suggesting mitochondrial genome remodeling during cellular reprogramming. Multiomic analysis further revealed coordinated deregulation of mitochondrial-associated nuclear genes and ceRNA regulatory networks involving lncRNAs MEG3 and SNHG14, along with multiple mitochondria-related miRNAs. These findings suggest post-transcriptional regulations associated with mitochondrial adaptation in iMSCs Conclusion: Collectively, our findings suggest that cellular reprogramming is associated with mitochondrial genomic reorganization in the donor-matched cell populations examined. These exploratory observations support the utility of iMSCs as a relevant model for studying OA-associated mitochondrial alterations and as a potential tool for regenerative approaches in OA.