CUL4A-mediated ZEB1/microRNA-340-5p/HMGB1 axis promotes the development of osteoporosis

The critical role of toll-like receptor 4 in bone remodeling of osteoporosis: from inflammation recognition to immunity

Osteoporosis is a common chronic metabolic bone disorder. Recently, increasing numbers of studies have demonstrated that Toll-like receptor 4 (TLR4, a receptor located on the surface of osteoclasts and osteoblasts) plays a pivotal role in the development of osteoporosis. Herein, we performed a comprehensive review to summarize the findings from the relevant studies within this topic. Clinical data showed that TLR4 polymorphisms and aberrant TLR4 expression have been associated with the clinical significance of osteoporosis. Mechanistically, dysregulation of osteoblasts and osteoclasts induced by abnormal expression of TLR4 is the main molecular mechanism underlying the pathological processes of osteoporosis, which may be associated with the interactions between TLR4 and NF-κB pathway, proinflammatory effects, ncRNAs, and RUNX2. In vivo and in vitro studies demonstrate that many promising substances or agents (i.e., methionine, dioscin, miR-1906 mimic, artesunate, AEG-1 deletion, patchouli alcohol, and Bacteroides vulgatus) have been able to improve bone metabolism (i.e., inhibits bone resorption and promotes bone formation), which may partially attribute to the inhibition of TLR4 expression. The present review highlights the important role of TLR4 in the clinical significance and the pathogenesis of osteoporosis from the aspects of inflammation and immunity. Future therapeutic strategies targeting TLR4 may provide a new insight for osteoporosis treatment.

Long Non-coding RNA SNHG1 Suppresses the Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells by Binding with HMGB1

Osteoporosis (OP) has a significant detrimental impact on the health of the elder. Long-term clinical effectiveness of current drugs used for OP treatment is limited. Therefore, it is very important to explore novel treatment targets for OP. The expression of SNHG1, HMGB1, OCN and OPN in gene level was measured using RT-qPCR, and the protein expression was determined by Western blotting assay. The concentration of IL-1β and IL-18 in supernatant of the bone marrow mesenchymal stem cells (BMSCs) was measured by ELISA. The interaction between SNHG1 and HMGB1 was confirmed by RNA pull down. Besides, alizarin red staining was performed to evaluate the differentiation of BMSCs into osteoblast. SNHG1 and HMGB1 were found to be upregulated in the serum of OP patients. During the osteogenic differentiation of BMSCs, the expression of osteoblastogenesis markers (OCN and OPN) and the activity of ALP were upregulated, while the expression levels of SNHG1 and HMGB1 were decreased in a time-dependent manner. In addition, the interaction between SNHG1 and HMGB1, expression of pyroptosis-associated factors (caspase-1 p20 and GSDMD-N), and secretion of IL-1β and IL-18 were also decreased during osteogenic differentiation. Interestingly, increasing SNHG1 promoted HMGB1 expression, activated pyroptosis, but inhibited osteogenic differentiation. Silencing HMGB1 or inhibiting caspase-1 partially rescued the inhibitory effect of SNHG1 on osteogenic differentiation. Our findings indicate that SNHG1 suppresses the osteogenic differentiation of BMSCs by activating pyroptosis through interaction with HMGB1 and promotion of HMGB1 expression. Our work provides further evidence supporting SNHG1 acts as a potential target for OP treatment, and reveals for the first time that SNHG1 regulates osteogenic differentiation by affecting pyroptosis.