Kabuki syndrome stem cell models reveal locus specificity of histone methyltransferase 2D (KMT2D/MLL4)

Knockdown of Kmt2d leads to growth impairment by activating the Akt/β-catenin signaling pathway

The KMT2D variant-caused Kabuki syndrome (KS) is characterized by short stature as a prominent clinical characteristic. The initiation and progression of body growth are fundamentally influenced by chondrocyte proliferation. Uncertainty persists regarding the possibility that KMT2D deficiency affects growth by impairing chondrocyte proliferation. In this study, we used the CRISPR/Cas13d technique to knockdown kmt2d in zebrafish embryos and lentivirus to create a stable Kmt2d gene knockdown cell line in chondrocytes (ATDC5 cells). We also used CCK8 and flow cytometric studies, respectively, to determine proliferation and cell cycle state. The relative concentrations of phosphorylated Akt (ser473), phosphorylated β-catenin (ser552), and cyclin D1 proteins in chondrocytes and zebrafish embryos were determined by using western blots. In addition, Akt inhibition was used to rescue the phenotypes caused by kmt2d deficiency in chondrocytes, as well as a zebrafish model that was generated. The results showed that a knockdown of kmt2d significantly decreased body length and resulted in aberrant cartilage development in zebrafish embryos. Furthermore, the knockdown of Kmt2d in ATDC5 cells markedly increased proliferation and accelerated the G1/S transition. In addition, the knockdown of Kmt2d resulted in the activation of the Akt/β-catenin signaling pathway in ATDC5 cells. Finally, Akt inhibition could partly rescue body length and chondrocyte development in the zebrafish model. Our study demonstrated that KMT2D modulates bone growth conceivably via regulation of the Akt/β-catenin pathway.