PTH1 receptor is involved in mediating cellular response to long-chain polyunsaturated fatty acids.
The molecular pathways by which long chain polyunsaturated fatty acids (LCPUFA) influence skeletal health remain elusive. Both LCPUFA and parathyroid hormone type 1 receptor (PTH1R) are known to be involved in bone metabolism while any direct link between the two is yet to be established. Here we report that LCPUFA are capable of direct, PTH1R dependent activation of extracellular ligand-regulated kinases (ERK). From a wide range of fatty acids studied, varying in chain length, saturation, and position of double bonds, eicosapentaenoic (EPA) and docosahexaenoic fatty acids (DHA) caused the highest ERK phosphorylation. Moreover, EPA potentiated the effect of parathyroid hormone (PTH(1-34)) in a superagonistic manner. EPA or DHA dependent ERK phosphorylation was inhibited by the PTH1R antagonist and by knockdown of PTH1R. Inhibition of PTH1R downstream signaling molecules, protein kinases A (PKA) and C (PKC), reduced EPA and DHA dependent ERK phosphorylation indicating that fatty acids predominantly activate G-protein pathway and not the β-arrestin pathway. Using picosecond time-resolved fluorescence microscopy and a genetically engineered PTH1R sensor (PTH-CC), we detected conformational responses to EPA similar to those caused by PTH(1-34). PTH1R antagonist blocked the EPA induced conformational response of the PTH-CC. Competitive binding studies using fluorescence anisotropy technique showed that EPA and DHA competitively bind to and alter the affinity of PTH1 receptor to PTH(1-34) leading to a superagonistic response. Finally, we showed that EPA stimulates protein kinase B (Akt) phosphorylation in a PTH1R-dependent manner and affects the osteoblast survival pathway, by inhibiting glucocorticoid-induced cell death. Our findings demonstrate for the first time that LCPUFAs, EPA and DHA, can activate PTH1R receptor at nanomolar concentrations and consequently provide a putative molecular mechanism for the action of fatty acids in bone.
In human studies, it has been shown that consuming EPA improved bone quality in elderly female subjects . Consumption of ω-3 fatty acids was also associated with reduced incidence and severity of inflammatory bone/joint diseases in humans . There is evidence of the potential of EPA to counteract bone loss associated with spaceflight; higher consumption of fish (ω-3) was associated with reduced loss of bone mineral density (BMD) after flight . BMD of the total body showed a significant negative correlation with serum concentrations of oleic acids and monounsaturated fatty acids and significant correlations with DHA and ω-3 fatty acids . A higher ratio of ω-6 to ω-3 fatty acids is associated with lower BMD at the hip in both sexes suggesting the relative amounts of dietary PUFA may play a vital role in preserving skeletal integrity in older age .