Transforming Growth Factor-β-Induced KDM4B Promotes Chondrogenic Differentiation of Human Mesenchymal Stem Cells

Abstract

The high prevalence of cartilage diseases and limited treatment options create a significant biomedical burden. Due to the inability of cartilage to regenerate itself, introducing chondrocyte progenitor cells to the affected site is of significant interest in cartilage regenerative therapies. Tissue engineering approaches using human mesenchymal stem cells (MSCs) are promising due to their chondrogenic potential, but a comprehensive understanding of the mechanisms governing the fate of MSCs is required for precise therapeutic applications in cartilage regeneration. TGF-β is known to induce chondrogenesis by activating SMAD signaling pathway and upregulating chondrogenic genes such as SOX9; however, the epigenetic regulation of TGF-β-mediated chondrogenesis is not understood. In this report, we found that TGF-β dramatically induced the expression of KDM4B in MSCs. When KDM4B was overexpressed, chondrogenic differentiation was significantly enhanced while KDM4B depletion by shRNA led to a significant reduction in chondrogenic potential. Mechanistically, upon TGF-β stimulation, KDM4B was recruited to the SOX9 promoter, removed the silencing H3K9me3 marks, and activated the transcription of SOX9. Furthermore, KDM4B depletion reduced the occupancy of SMAD3 in the SOX9 promoter, suggesting that KDM4B is required for SMAD-dependent coactivation of SOX9. Our results demonstrate the critical role of KDM4B in the epigenetic regulation of TGF-β-mediated chondrogenic differentiation of MSCs. Since histone demethylases are chemically modifiable, KDM4B may be a novel therapeutic target in cartilage regenerative therapy.

SOX9 is dispensable for the initiation of epigenetic remodeling and the activation of marker genes at the onset of chondrogenesis

“…The removal of H3K27me3 repressor marks typically involves histone demethylases. The ARID5B transcriptional co-activator physically associates with SOX9 and recruits the histone demethylase PHF2 to SOX9 target genes in chondrocytes in vitro (Hata et al, 2013), and the histone demethylase KDM4B has been proposed to promote chondrogenesis downstream of TGFβ (Lee et al, 2016;Yapp et al, 2016). Many histone demethylases are broadly expressed, and we did not find evidence that SOX9 upregulates any of their genes in limb buds.…”

Kdm6b regulates cartilage development and homeostasis through anabolic metabolism

“…For example, histone deacetylase (HDAC)1 and HDAC2 can inhibit the expression of cartilage-specific genes in human chondrocytes 32. Recently, Lee et al 33 found that KDM4B could mediate SOX9 activation by removing a repressive epigenetic mark (H3K9me3) from the SOX9 promoter region, which in turn promoted TGF-β-mediated chondrogenesis. These findings illustrate that histone methylation and acetylation act as important epigenetic regulators during chondrogenic differentiation.…”

KDM5A controls bone morphogenic protein 2-induced osteogenic differentiation of bone mesenchymal stem cells during osteoporosis

“…28 Kdm4b was also required for recruitment of SMAD3 and Sox9 activation during TGF- β -mediated chondrogenic differentiation of MSCs. 29 Interestingly, G9a, H3K9 methyltransferase, was found to repress adipogenesis by inhibiting PPAR γ expression and facilitating Wnt10a expression independent of its enzymatic activity. 30 In a prostate cancer cell line, it was found that Runx2 target genes required recruitment of G9a for their expression, but did not depend on its histone methyltransferase activity.…”

“…Interestingly, in this study, we found that although Kdm5a was downregulated during osteogenic differentiation (Figures 3a and b), BMP2 did not change the expression of Kdm5a during 72 h. Previous study showed that TGF- β decreased KDM4B expression and therefore promoted chondrogenic differentiation. 29 So, it demands more meticulous researches to identify the original causes to explain the Kdm5a expression pattern in osteoporosis.…”