Total Flavonoids from Rhizoma Drynariae (Gusuibu) Alleviates Diabetic Osteoporosis by Activating BMP2/Smad Signaling Pathway

Introduction: Diabetic osteoporosis (DOP) is a widespread public health problem. The flavonoids of Rhizoma Drynariae (RDF) have a clear preventive and therapeutic effect on osteoporosis (OP), but it is not yet clear whether RDF has an anti-DOP and whether its mechanism is related to the activation of the BMP2/Smad signaling pathway. The current study aimed to study this effect of RDF in DOP rats and the possible involvement of the BMP2/Smad signaling pathway activation. Methods: Following intragastric administration of RDF for 12 weeks, the body weight, blood glucose, and the bone histopathological changes detected by hematoxylin-eosin (H&E) and calcein staining were monitored, while bone parameters were regularly assessed from observations made by micro-CT. At the end of the experiment, the expression of Bmp2, Bmpr1a, Runx2, and Smad4/5 genes was detected by real-time PCR (RT-PCR). Meanwhile, western blotting or immunohistochemical staining monitored the protein expressions of BMP2, RUNX2, and SMAD5 in the bone. Results: The results firstly indicated that RDF significantly alleviated the signs and symptoms of DOP, which manifested as improved body weight and blood glucose. As obtained from the results of histopathology and micro-CT, RDF could promote the formation of bone trabeculae and alter several the bone microstructure parameters, including an increase in the bone volume/total volume (BV/TV), connective density (Conn-Dens), and trabecular bone number (Tb.N), as well as a decrease in the trabecular spacing (Tb.Sp). The western blotting analysis and RT-PCR results also confirmed that RDF could markedly increase the mRNA expression levels of Bmp2, Bmpr1α, Smad4, Runx2, and Smad5 in the bone, as well as the corresponding protein expression levels of BMP2, RUNX2, and SMAD5. These results reveal that RDF can activate the BMP2/Smad signaling pathway, thus promoting bone remodeling in DOP rats. Conclusion: RDF can increase bone trabeculae and bone mineral density by promoting bone formation and inhibiting bone absorption, thereby playing a role in improving DOP. This effect is related to the regulation of the BMP2/Smad signaling pathway.