Chronic Alcohol Reduces Bone Formation Through Inhibiting Proliferation and Promoting Aging of Endothelial Cells in Type-H Vessels

Abstract

Background: Chronic alcohol is one of the leading risk factors for male osteoporosis . Angiogenesis and osteogenesis coupled by type-H vessels coordinate the biological process of bone homeostasis to prevent osteopenia. It is unknown whether alcohol inhibits type-H-vessel-dependent bone formation. Aims: This study aimed to determine whether alcohol hampers proliferation and promotes aging of endothelial cells of type-H vessels, and whether alcohol inhibits the differentiation of bone marrow-mesenchymal stem cells (BM-MSCs) into osteoblasts through reducing the number and secretion of endothelial cells in type-H vessels. Materials and Methods: Two-month-old mice fed with alcohol liquid diet (28% of calories) or normal liquid diet for two months. The tibias were isolated and detected with X-ray and micro-CT. Paraffin-embedded or frozen tibial sections were prepared and used for immunohistochemical or immunofluorescence staining respectively in vivo . Human Umbilical Vein Endothelial Cells (HUVECs) were treated with different-concentrated alcohol for 12 hours. The conditioned medium of the above HUVECs cells was collected to culture human BM-MSCs, which were induced to differentiate into osteoblasts in vitro . Results: The alcoholic diet retarded the bone growth and lead to osteoporosis, impaired bone formation of osteoblasts, and decreased CD31 hi EMCN hi type-H-vessel formation through inhibiting proliferation and promoting aging of endothelial cells in mice. Alcohol treatment obviously increased the expression of p16, while significantly decreased the expression of Bmi-1, CDK6, Cyclin D, E2F1 and BMP2 compared to vehicle. Alcohol inhibited the differentiation of BM-MSCs into osteoblasts through reducing the BMP2 secretion of endothelial cells in type-H vessels. Conclusions: Alcoholic diet impaired CD31 hi EMCN hi type-H-vessel formation through inhibiting proliferation and promoting aging of endothelial cells via Bmi-1/p16 signaling, and inhibited the differentiation of BM-MSCs into osteoblasts through reducing the BMP2 secretion of endothelial cells in type-H vessels. It provides a basis for developing a new treatment strategy targeting aging endothelial cells of type-H-vessel to prevent alcoholic osteopenia.