CaSR activation triggers mandibular overgrowth in fMP patients and mice

Mandibular prognathism (MP) is the most common type of dento-maxillofacial deformity in East Asian populations. Genetic studies have revealed several MP-associated loci, suggesting that MP could be inherited as familial MP (fMP). However, functional verifications and in-depth mechanistic investigations of these loci are limited. For this study, we recruited 5 fMP families with 17 fMP members and 7 normal members. We first compared the clinical features of the 17 fMP members with 31 non-familial MP patients, finding a stronger mandibular overgrowth phenotype in the fMP subjects. Next, we performed whole-exome sequencing (WES) analysis with members of the 5 fMP families and singled out a potential fMP-associated pathogenic variant in the CASR gene—namely, rs117375173—the mutation introduces an amino acid substitution (A601G) in exon 7 and confers gain-of-function in Calcium-Sensing Receptor (CaSR). The rs11735173 variant changes the CaSR protein structure toward a semi-active state, similar to CaSR activated by L-tryptophan (L-Trp). To verify the regulating roles of CASR in mandibular bone growth, we further generated different mouse models with abnormal CaSR function. L-Trp administration effectively activate CaSR/GNAQ expression in vivo and in vitro. The MC3T3-E1 cell line transfected with CaSR with rs117375173 showed increased osteogenic differentiation and collagen synthesis at transcriptional level. Local injection of L-Trp in the mandible of growing mice significantly increased the mandibular length and BMD, due to activated osteogenic activity and suppressed bone resorption. At the same time, loss-of-function of CaSR in osteogenic progenitors caused mandibular growth retardation in Gli1-CreER; Casrfl/fl; tdTomatofl/+ mice. In conclusion, our study reveals that abnormal functioning of CaSR affects mandibular bone development and may contribute to the pathogenesis of fMP, providing a theoretical and experimental basis for the early diagnosis of and therapeutic strategies for fMP in clinical practice. The MC3T3-E1 cells were plated at a cell density between 500,000 and 800,000 cells/well in a 6-well plate and cultured with Dulbecco’s modified Eagle’s medium + GlutaMAX (Thermo Fisher Scientific) supplemented with 10% fetal bovine serum and 1% penicillin-streptomycin. After 24 h, the CaSRmut plasmid and CaSRwt plasmid were transfected into the cells with Lipofectamine 3000 (Thermo Fisher Scientific). After 48 h, cells were harvested, and RNA was extracted using TRIzol™ (Thermo Fisher Scientific). RNA integrity was assessed using the Bioanalyzer 2100 system (Agilent Technologies, CA, USA). And then bulk RNA sequencing.