Hyperlipidemia Impacts Osteogenesis Via Lipophagy Mediated By Optn-Rab18 Interaction

The high-fat environment impairs osteoblast function and activates lipophagy; however, promoting lipophagy may improve osteogenesis under certain conditions. The underlying mechanisms are unclear. Our study investigated whether Rab18 interacting with OPTN is involved in regulating lipophagy of osteoblasts in high-fat environments, thereby affecting the osteogenic function. Primary mouse osteoblasts were cultured with/without high-fat medium. The lipid in osteoblasts was observed by Oil Red O staining and Bodipy493/503. The level of autophagy was examined by western blot (WB) and observed by immunofluorescence staining and transmission electron microscopy (TEM). Alkaline phosphatase (ALP) staining and WB were used to measure the osteogenesis level. OPTN and Rab18 protein expression in cells treated with/without Baf-A1 were examined by WB. OPTN-Rab18 protein interactions were verified by immunoprecipitation (Co-IP), and were visualized by immunofluorescence co-localization staining. All data were expressed as mean ± standard deviations (SD) in at least three independent measurements. A one-way ANOVA collapsed to a t-test when there were only two groups. Statistical significance was considered to be at a p-value of <0.05. High-fat medium decreased osteogenic indicators and reduced OPTN-Rab18 protein interactions. The absence of OPTN and Rab18 further impaired osteoblast biologic function. Rab18 activation improved OPTN-Rab18 protein interactions and ameliorated high-fat-induced osteogenesis impairment. High-fat environment may regulate lipophagy in osteoblasts by impairing protein interactions between OPTN and Rab18, thereby affecting osteogenesis. Facilitation of OPTN-Rab18 interactions may modulate osteoblast lipophagy and improve osteogenesis.