TET1 regulates skeletal stem cell (SSC) mediated cartilage regeneration in osteoarthritis
Objective: Skeletal stem cells are known to be regulated by their local self-regulating niche, that is comprised mainly of their progeny and secreted paracrine factors. What cell intrinsic factors govern the maintenance and function of the SSC remains elusive. Methods: Using the previously characterized Tet1-/- mice we investigated the differences in skeletal stem cell lineage tree. Further we examined the ability of these cells to differentiate into osteogenic and chondrogenic lineages, both with and without injury. Transcriptomic differences and inflammatory cytokines were investigated for differences in cartilage development pathways.  Results: Loss of Tet1 skews the SSC lineage tree by expanding the SSC pool at the expense of its progeny as well as by enhancing the chondrogenic differentiation of SSC and the multilineage bone cartilage stromal progenitors (BCSP). Tet1 inhibition leads to enhanced chondrogenesis in mouse BCSP upon injury, in human SSC and chondroprogenitors (CP) isolated from osteoarthritic (OA) human cartilage and in late stages of OA in a mouse model. Transcriptomic analyses of SSC and BCSP lacking Tet1 revealed dysregulated pathways including alterations in Tgfb signaling, melatonin degradation and cartilage development associated genes.  Conclusion: Tet1 was identified as critical regulator of SSC fate. Loss of Tet1 selectively enhances chondrogenic ability of skeletal stem cells. Supplementation of melatonin can dampen inflammation and lead to better cartilage health. Overall design: SSC and BCSP Wildtype v/s Tet1 KO