Antisense oligonucleotides targeting a NOTCH3 mutation in male mice ameliorate the cortical osteopenia of lateral meningocele syndrome.

Lateral Meningocele Syndrome (LMS) is a monogenic disorder associated with NOTCH3 pathogenic variants that result in the stabilization of NOTCH3 and a gain-of-function. A mouse model (Notch3) harboring a 6691-TAATGA mutation in the Notch3 locus that results in a functional outcome analogous to LMS exhibits cancellous and cortical bone osteopenia. We tested Notch3 antisense oligonucleotides (ASOs) specific to the Notch3 mutation for their effects on Notch3 downregulation and on the osteopenia of Notch3 mice. Twenty-four mouse Notch3 mutant ASOs were designed and tested for toxic effects in vivo, and 12 safe ASOs were tested for their impact on the downregulation of Notch3 and Notch3 mRNA in osteoblast cultures from Notch3 mice. Three ASOs downregulated Notch3 mutant transcripts specifically and were tested in vivo for their effects on the bone microarchitecture of Notch3 mice. All three ASOs were well tolerated. One of these ASOs had more consistent effects in vivo and was studied in detail. The Notch3 mutant ASO downregulated Notch3 mutant transcripts in osteoblasts and bone marrow stromal cells and had no effect on other Notch receptors. The subcutaneous administration of Notch3 mutant ASO at 50 mg/Kg decreased Notch3 mRNA in bone without apparent toxicity; microcomputed tomography demonstrated that the ASO ameliorated the cortical osteopenia of Notch3 mice but not the cancellous bone osteopenia. In conclusion, a Notch3 ASO that downregulates Notch3 mutant expression specifically ameliorates the cortical osteopenia in Notch3 mice. ASOs may become useful strategies in the management of monogenic disorders affecting the skeleton.