Triglyceride metabolism in bone tissue is associated with osteoblast and osteoclast differentiation: a gene expression study

The role of bone marrow adipocytes in bone tissue is not yet understood. Adipocytes express enzymes for metabolism of free fatty acids and adipokines such as adiponectin, which have been shown to exert different effects on bone cells. Our aim was to find out whether triglyceride (TG) metabolism in bone tissue is associated with osteoblast and osteoclast differentiation by gene expression analysis of lipoprotein lipase (LPL), hormone sensitive lipase (HSL), fatty acid synthase (FASN), adiponectin, RUNX2, RANK, RANKL and OPG. Bone tissue was obtained from patients undergoing hip arthroplasty due to osteoporosis (OP) (50) or osteoarthritis (OA) (48) or from healthy autopsy controls (14). Lower bone mineral density and microstructural parameters were observed in OP compared to OA. The FASN expression did not differ between groups suggesting similar de novo lipogenesis. Lower LPL and HSL in OP suggest lower FFA release and uptake in OP bone tissue. Adiponectin expression was lower in OP than in OA and a trend was seen for controls. These results suggest OP bone has lower TG metabolism than OA and normal bone. In OP bone, lower osteoblastogenesis and higher osteoclast formation were observed and correlation analysis suggests adiponectin, LPL and HSL are associated with higher osteoblastogenesis and lower osteoclastogenesis. This study gives insights into TG metabolism in the human bone microenvironment. We conclude that OP bone tissue exhibits lower osteoblastogenesis, higher osteoclastogenesis and lower TG metabolism compared to OA or healthy controls.