High Fatty Acid Content in Rabbit Serum Is Responsible for the Differentiation of Osteoblasts Into Adipocyte-like Cells

Abstract

Osteoblasts and adipocytes originate from common mesenchymal precursors. With aging, there is a decrease in osteoprogenitor cells that parallels an increase of adipocytes in bone marrow. We observed that rabbit serum (RS) induces adipocyte-like differentiation in human osteosarcoma SaOS-2/B10 and MG-63 cell lines, in rat ROS17/2.8 cells, and in mouse calvaria-derived osteoblastic MB1.8 cells, as evidenced by the accumulation of Oil Red O positive lipid vesicles and the decrease in alkaline phosphatase expression. Both SaOS-2/B10 and MG-63 cells, but not ROS17/2.8 nor MB1.8 cells, express significant levels of PPARgamma mRNA, a member of the peroxisome proliferator activated receptor (PPAR) family that has been implicated in the control of adipocyte differentiation. However, both ROS17/2.8 and MG-63 cells express significant levels of the adipocyte selective marker, aP2 fatty acid binding mRNA, which can be further increased by RS. These cell types express PPARdelta/NUC-1 but not PPARalpha, indicating that cells that do not express either PPARgamma or PPARalpha are capable of differentiating into adipocyte-like cells. Transfection experiments in COS cells showed that compared with fetal bovine serum (FBS), RS is rich in agents that stimulate PPAR-dependent transcription. The stimulatory activity was ethyl acetate extractable and was 35-fold more abundant in RS than in FBS. Purification and analysis revealed that the major components of this extract are free fatty acids. Furthermore, the same fatty acids, a mixture of palmitic, oleic, and linoleic acids, activate the PPARs and induce adipocyte-like differentiation of both ROS17/2.8 and SaOS-2/B10 cells. These findings suggest that fatty acids or their metabolites can initiate the switch from osteoblasts to adipocyte-like cells.

Effects of arachidonic acid and docosahexaenoic acid on differentiation and mineralization of MC3T3‐E1 osteoblast‐like cells

“…After 3 days, medium was changed and the cells cultured 3 more days in the presence of vehicle and test agents for a total of 6 days. 23 As positive control for adipogenesis, oleic acid (30 mg ml À1 ) was used. 23 At the end of culture, cells were rinsed with PBS, fixed in 10% paraformaldehyde in PBS for 15 minutes, and washed with PBS.…”

“…23 As positive control for adipogenesis, oleic acid (30 mg ml À1 ) was used. 23 At the end of culture, cells were rinsed with PBS, fixed in 10% paraformaldehyde in PBS for 15 minutes, and washed with PBS. The cover slips were then stained with Oil Red O for 30 min, and rinsed with 60% isopropanol.…”

“…23 These receptors are activated by free fatty acids and their oxidation products as well as by some prostaglandins derived from fatty acids that induce the differentiation of preadipocytes into adipocytic cells. [24][25][26][27] AA, which is a precursor for prostaglandins of the -2-family, has specifically been implicated in adipocyte differentiation.…”

“…[24][25][26][27] AA, which is a precursor for prostaglandins of the -2-family, has specifically been implicated in adipocyte differentiation. 23 With ageing there is a decrease in osteoprogenitor cells with an accompanying increase in adipocytes in bone marrow. This is due to altered differentiation of the common precursor cell, the mesenchymal stem cell (MSC).…”

“…This is due to altered differentiation of the common precursor cell, the mesenchymal stem cell (MSC). 23,25,28 Results from our laboratory have shown that AA (n-6 PUFA) and DHA (n-3 PUFA), at physiological concentrations (2.5-20 mg ml À1 ), inhibit osteoblast cell proliferation in a dose-dependent manner. 29 Since there is a reciprocal relationship between reduced proliferation and subsequent induction of cell differentiation in vitro, 20,21,30 the effects of AA and DHA on osteogenesis was investigated.…”