Investigations on the biochemical and molecular actions of polyunsaturated fatty acids and dexamethasone in fetal rat calvaria cells

Experiments were conducted to examine the effects of polyunsaturated fatty acids (PUFA) and dexamethasone on osteoblast differentiation and function in fetal rat calvaria cells (FRCC) since these cells are commonly used as a model for studying the differentiation and function of osteoblasts. The results showed that PUFA type and level influenced in vitro nodule formation. PUFA effects on the expression of core binding factor alpha 1 (Cbfa1), a key transcription factor in osteoblast differentiation, revealed that both linoleic acid (LA) and arachidonic acid (AA) increased its protein level. Fatty acid analysis revealed that LA and AA were significantly enriched in the FRCC after 7 days of treatment and modified the fatty acid composition of these cells. Both LA and AA treatments significantly increased the levels of AA. It is believed that a higher level of AA would lead to greater PGE 2 production, which has been shown to stimulate Cbfa1 expression. Glucocorticoid-induced osteoporosis is a major health problem in the United States. In another series of experiments with FRCC, dexamethasone (DEX, a strong glucocorticoid) at a concentration of 10-7 M was found to stimulate nodule formation and the expression of pyruvate carboxylase (PC). The PC stimulatory effects of DEX were significant after 7, 14 and 21 days of treatment and could be readily observed after 24 hours. A dose response study indicated that the stimulatory effect was significant at a concentration of 10-9 M, but reaching a plateau at 10 -8 M. With a biotin-free medium, it was demonstrated that biotin deficiency did not fully limit PC expression; however, the expression of propionyl CoA carboxylase was compromised. Glucose did not stimulate the expression of this enzyme as it was demonstrated in pancreatic islets. In the experiments, some PUFA were found to modulate the expression of PC in FRCC. The high PC expression found with DEX treatment might be associated with glucocorticoid-induced osteoporosis. Therefore, PC could be a molecular target for studying glucocorticoid-induced osteoporosis. The investigations in FRCC revealed that PUFA influenced biochemical and physiological functions and modulated transcription factors relevant to bone biology and health. This research advances the knowledge of dietary PUFA actions in bone metabolism and skeletal health