Antisense oligonucleotides targeting Notch2 ameliorate the osteopenic phenotype in a mouse model of Hajdu-Cheney syndrome

Notch receptors play critical roles in cell-fate decisions and in the regulation of skeletal development and bone remodeling. Gain?of?function NOTCH2 mutations can cause Hajdu-Cheney syndrome, an untreatable disease characterized by osteoporosis and fractures, craniofacial developmental abnormalities, and acro-osteolysis. We have previously created a mouse model harboring a point 6955C?T mutation in the Notch2 locus upstream of the PEST domain, and we termed this model Notch2(tm1.1Ecan). Heterozygous Notch2(tm1.1Ecan) mutant mice exhibit severe cancellous and cortical bone osteopenia due to increased bone resorption. In this work, we demonstrate that the subcutaneous administration of Notch2 antisense oligonucleotides (ASO) down-regulates Notch2 and the Notch target genes Hes-related family basic helix?loop?helix transcription factor with YRPW motif 1 (Hey1), Hey2, and HeyL in skeletal tissue from Notch2(tm1.1Ecan) mice. Results of microcomputed tomography experiments indicated that the administration of Notch2 ASOs ameliorates the cancellous osteopenia of Notch2(tm1.1Ecan) mice, and bone histomorphometry analysis revealed decreased osteoclast numbers in Notch2 ASO-treated Notch2(tm1.1Ecan) mice. Notch2 ASOs decreased the induction of mRNA levels of TNF superfamily member 11 (Tnfsf11, encoding the osteoclastogenic protein RANKL) in cultured osteoblasts and osteocytes from Notch2(tm1.1Ecan) mice. Bone marrow-derived macrophage cultures from the Notch2(tm1.1Ecan) mice displayed enhanced osteoclastogenesis, which was suppressed by Notch2 ASOs. In conclusion, Notch2(tm1.1Ecan) mice exhibit cancellous bone osteopenia that can be ameliorated by systemic administration of Notch2 ASOs.