Molecular Bases of Disease
Hairy and enhancer of split 1 is a primary effector of NOTCH2 signaling and induces osteoclast differentiation and function
Notch2tm1.1Ecan mice, which harbor a mutation replicating that found in Hajdu–Cheney syndrome, exhibit marked osteopenia because of increased osteoclast number and bone resorption. Hairy and enhancer of split 1 (HES1) is a Notch target gene and a transcriptional modulator that determines osteoclast cell fate decisions. Transcript levels of Hes1 increase in Notch2tm1.1Ecan bone marrow–derived macrophages (BMMs) as they mature into osteoclasts, suggesting a role in osteoclastogenesis. To determine whether HES1 is responsible for the phenotype of Notch2tm1.1Ecan mice and the skeletal manifestations of Hajdu–Cheney syndrome, Hes1 was inactivated in Ctsk-expressing cells from Notch2tm1.1Ecan mice.Sustained Notch2 signaling in osteoblasts, but not in osteoclasts, is linked to osteopenia in a mouse model of Hajdu-Cheney syndrome
Individuals with Hajdu-Cheney syndrome (HCS) present with osteoporosis, and HCS is associated with NOTCH2 mutations causing deletions of the proline-, glutamic acid-, serine-, and threonine-rich (PEST) domain that are predicted to enhance NOTCH2 stability and cause gain-of-function. Previously, we demonstrated that mice harboring Notch2 mutations analogous to those in HCS (Notch2HCS) are severely osteopenic because of enhanced bone resorption. We attributed this phenotype to osteoclastic sensitization to the receptor activator of nuclear factor-κB ligand and increased osteoblastic tumor necrosis factor superfamily member 11 (Tnfsf11) expression.
