Deficiency of sphingomyelin synthase 1 but not sphingomyelin synthase 2 reduces bone formation due to impaired osteoblast differentiation

Abstract

Background: There are two isoforms of sphingomyelin synthase (SMS): SMS1 and SMS2. SMS1 is located in the Golgi apparatus only while SMS2 is located in both the plasma membrane and the Golgi apparatus. SMS1 and SMS2 act similarly to generate sphingomyelin (SM). We have undertaken the experiments reported here on SMS and osteoblast differentiation in order to better understand the role SMS plays in skeletal development. Methods: We analyzed the phenotype of a conditional knockout mouse, which was generated by mating a Sp7 promoter-driven Cre-expressing mouse with an SMS1-floxed SMS2-deficient mouse (Sp7-Cre;SMS1 f/f ;SMS2 −/− mouse). Results: When we compared Sp7-Cre;SMS1 f/f ;SMS2 −/− mice with C57BL/6, SMS2-deficient mice (SMS1 f/f ;SMS2 −/−) and SP7-Cre positive control mice (Sp7-Cre, Sp7-Cre;SMS1 +/+ ;SMS2 +/− and Sp7-Cre;SMS1 +/+ ;SMS2 −/−), we found that although cartilage formation is normal, Sp7-Cre;SMS1 f/f ;SMS2 −/− mice showed reduced trabecular and cortical bone mass, had lower bone mineral density, and had a slower mineral apposition rate than control mice. Next, we have used a tamoxifen-inducible knockout system in vitro to show that SMS1 plays an important role in osteoblast differentiation. We cultured osteoblasts derived from ERT2-Cre;SMS1 f/f SMS2 −/− mice. We observed impaired differentiation of these cells in response to Smad1/5/8 and p38 that were induced by bone morphogenic protein 2 (BMP2). However, Erk1/2 phosphorylation was unaffected by inactivation of SMS1. Conclusions: These findings provide the first genetic evidence that SMS1 plays a role in bone development by regulating osteoblast development in cooperation with BMP2 signaling. Thus, SMS1 acts as an endogenous signaling component necessary for bone formation.

Ceramide/Sphingomyelin Rheostat Regulated by Sphingomyelin Synthases and Chronic Diseases in Murine Models

“…In our recent study, complete depletion of SMS in osteoblasts by Sp7 promoter-driven Cre-expressing mice (Sp7-Cre;SMS1-CKO;SMS2-KO) induced osteopenia through reduction in bone formation. 141 Sp7-Cre;SMS1-CKO;SMS2-KO mice showed a decrease in trabecular and cortical mass, bone mineral density and mineral apposition as compared to SMS2-KO mice. In cultured osteoblasts purified from SMS double KO mice, the differentiation ability to osteocytes through the induction of Smad1/5/8 and p38 MAPK in response to bone morphogenic protein 2 (BMP2) was impaired.…”

Integrative Analyses of Genes Associated With Otologic Disorders in Turner Syndrome

“…SM synthase (SMS) family can be classified into two members: SMS1 and SMS2. A study established that SMS1 is necessary for the usual function of the inner ear ( Matsumoto et al, 2019 ). The 5 most prevalent target TSE in the TF-gene network were AGER, MYLPF, TM7SF2, KLF16, and HYAL3.…”

A Novel IFITM5 Variant Associated with Phenotype of Osteoporosis with Calvarial Doughnut Lesions: A Case Report

“…One such hypothetic link may be SP7 (osterix), a transcription factor of osteoblast differentiation, whose expression is under the control of several signaling pathways, endoplasmic reticulum stress and epigenetic factors [21]. SP7 has an activator that acts cooperatively with specificity protein 1 (SP1) and zinc finger protein GLI2 to synergistically induce the BRIL promoter [22], and reports show that complete depletion of SMS2 in osteoblasts by Sp7 promoter-driven Cre-expressing mice (Sp7-Cre; SMS1-CKO; SMS2-KO) induces osteopenia through reduced bone formation [23]. Although our findings would support such interaction, and functional in vitro studies suggest BRIL to similarly partake in matrix mineralization, results from animal studies are unclear and partly conflicting [24][25][26][27].…”