A NOTCH2 pathogenic variant and HES1 regulate osteoclastogenesis in induced pluripotent stem cells.

Hajdu Cheney Syndrome (HCS), a monogenic disorder associated with NOTCH2 pathogenic variants, presents with neurological, craniofacial and skeletal abnormalities. Mouse models of the disease exhibit osteopenia. To determine the consequences of a HCS pathogenic variant in human cells, induced pluripotent NCRM1 and NCRM5 stem (iPS) cells harboring a NOTCH26949C>T mutation or null for HES1 alleles were created. Parental iPSCs, NOTCH26949C>T, HES1 null and control cells, free of chromosomal aberrations were cultured under conditions of neural crest, mesenchymal and osteogenic cell differentiation, or of embryoid body, hematopoietic and osteoclast cell differentiation. The expected cell phenotype was confirmed by cell surface markers and gene signature. NOTCH26949C>T cells displayed enhanced expression of Notch target genes demonstrating the presence of a NOTCH2 gain-of-function. There was a modest enhancement of osteogenesis in NOTCH26949C>T cells manifested by increased mineralized nodule formation and SP7, ALPL and BGLAP mRNA expression. There was enhanced osteoclastogenesis in NOTCH26949C>T cells as evidenced by increased number of osteoclasts and a transient increase in ACP5, CALCR and CTSK transcripts. Osteoblastogenesis was minimally affected by the HES1 deletion, but osteoclast differentiation was significantly impaired. In conclusion, a NOTCH2 pathogenic variant causes modest increases in osteoblastogenesis and osteoclastogenesis and HES1 is required for osteoclast differentiation in human iPS cells in vitro.