| Smad7 has been well documented as a negative regulator of TGF-beta signaling, and its altered expression often leads to human diseases such as cancer and fibrosis. However, the role of Smad7 in regulating bone remodeling and related diseases remains unclear. We performed both in vivo and in vitro experiments as well as disease model and drug therapy studies using both wild-type (WT) and Smad7DeltaE1 (KO) mice to investigate the functional role of Smad7 in bone remodeling, osteoporosis, and MSCs differentiation.;The Smad7DeltaE1 mice were generated by replacing part of the exon1 of Smad7 gene as reported, which resulted in truncated protein and partial loss of Smad7 function. Mice were genotyped by PCR. The mu-CT, histological assays and bone histomorphometric assays in metaphysic region of the femurs showed lower trabecular number (TbN), trabecular thickness (TbTh), mineral apposition rate (MAR), higher trabecular separation (TbSp) and Osteoclast Surface (Oc.S/BS & Oc.N/BS) in the KO mice at 6, 12, to 24 weeks old; as well as lower bone mineral density (BMD) and bone volume fraction (BV/TV) at 24 weeks old in the KO mice. The in vitro BM-MSCs multi-lineage differentiation studies showed the suppressed osteogenic potential in the KO group with fewer mineralized nodules, lower ALP activity and expression of Col1A1, Runx2 and OCN; while the adipogenic potential was elevated with more lipid droplets formation and higher expression of Adipsin and C/EBPalpha. The osteoclastogenic potential of KO mice BMMs was also elevated, showing higher osteoclasts activity and larger resorptive areas, as well as elevated expression of TRAP and CTR. Both in vivo and in vitro studies of the osteoporotic models showed that the KO mice had lower BMD, TbTh, and higher TbSp compared to the WT mice at 4, 8, 16 weeks after OVX, similar results of lower BV/TV and TbN were observed at 4 weeks after OVX in the KO mice. The RANKL-induced osteoclastogenesis potential was elevated compared to WT mice, with more and bigger osteoclasts, larger resorptive areas, as well as elevated expression of TRAP and CTR. The osteoclastic cell fusion was also enhanced. Treatment of Asiatic acid (one traditional Chinese medicine that has been proved to induce the expression of Smad7 as reported) in the OVX mice reversed the osteoporotic process with increase BMD, BV/TV, TbN, TbTh, and decreased TbSp compared to the untreated group. The osteoclastic cell fusion was suppressed after AA treatment.;Partial loss of Smad7 function leads to impaired bone remodeling in vivo, reduced osteogenesis and enhanced osteoclastogenesis in vitro, and also accelerates the osteoporotic development and osteoclastic cell fusion. Asiatic acid may be a novel potential drug for prevention of osteoporosis. Our findings provide new evidences for a better understanding of the biological functions of Smad7 in bone remodeling and its therapeutic potential for metabolic bone diseases. |
