High-carbohydrate, High-fat Diet-induced Hyperlipidemia Hampers the Differentiation Balance of Bone Marrow Mesenchymal Stem Cells by Suppressing Autophagy via the AMPK/ mTOR Pathway in Rat Models

Background: Disorders of bone metabolism caused by hyperlipidemia is not conducive to osseointegration of implants. Autophagy, an evolutionarily conserved, lysosomal-mediated degradation process, is indispensable for bone homeostasis, its effects on hyperlipidemia-induced osteoporosis remain to be elucidated. The objective of this study was to determine whether autophagy affects bone metabolism and implant osseointegration through regulating the function of bone marrow mesenchymal stem cells (BMMSCs) in rats with hyperlipidemia and to confirm signaling pathway involved in the regulation of autophagy. Methods: Hyperlipidemia models were established through a long-term high-carbohydrate, high-fat diet in 6-week-old male Sprague-Dawley rats. The impact of hyperlipidemia on bone metabolism and early osseointegration of implants was explored by the methods including serum biochemical detection, micro-computed tomography and bone morphology detection. Biological properties and autophagy levels of BMMSCs were also determined. Further, we determined if autophagy was involved in bone metabolism changes resulting from high-fat diet by focusing on the lineage differentiation of BMMSCs. The signaling pathway involved in the regulation of autophagy was also explored.Results: The high-carbohydrate, high-fat diet (HCHF) was given to the rats for seven months aggravated bone loss in the cancellous bone and reduced osseointegration of implants. BMMSCs from hyperlipidemia rats exhibited decreased osteogenesis, increased adipogenesis and decreased autophagic activity compared with regular diet (RD) BMMSCs. Rapamycin treatment restored the impaired osteogenic differentiation and inhibited the adipogenic differentiation of HCHF-BMMSCs through the activation of autophagy. Further, AMPK/mTOR signaling pathways was related to the impairment of autophagy of HCHF-BMMSCs. Conclusions: Our data indicate that long-term high-carbohydrate, high-fat diet-induced hyperlipidemia hampers the differentiation balance of bone marrow mesenchymal stem cells by suppressing autophagy via the AMPK/ mTOR pathway, which ultimately led to aggravated bone loss in the cancellous bone and reduced osseointegration of implants in rat models.