PTH1 Receptor Is Involved in Mediating Cellular Response to Long-Chain Polyunsaturated Fatty Acids

Abstract

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.

Activity of Bradykinin B2 Receptor Is Regulated by Long-Chain Polyunsaturated Fatty Acids

“…Note, EPA appears more potent in the FRET assay than in the ERK assay due to differences in treatment concentrations. Overall, our results are similar to those we earlier observed for the PTH1 receptor [1] and consistent with other studies in which specific GPCRs have been shown to become activated by fatty acids in a length-dependent manner [48]–[51].…”

“…The lipid bilayer effectively increases the concentration of LCPUFA in GPCR environment thereby increasing the probability of their interaction. In contrast to our earlier report on PTH1 receptor [1] we did not observe synergism from simultaneous stimulation by BK and LCPUFA (Fig. 2 A, 5 B, 5 C) supporting the hypothesis that EPA acts through the orthosteric site of B 2 R. However due to the high concentrations of LCPUFA in the membrane, contributions from allosteric and nonspecific interactions cannot be excluded.…”

“…The time scale of LCPUFA incorporation into membrane (Fig. 6) is within the same range as that one of EPA-induced conformational changes in both B 2 R and PTH1R [1]. This finding suggest that fatty acids first partition into the cell membrane and then may either specifically bind to the transmembrane/intracellular domain of the GPCR or affect membrane properties in a non-specific way, stabilizing GPCR in a tertiary conformation required for efficient signaling.…”

“…We have recently reported that LCPUFAs stimulate conformational changes and activate parathyroid hormone receptor (PTH1R) in a dose dependent manner [1]. PTH1R is a G protein coupled receptor (GPCR) involved in bone homeostasis [2].…”

Fish and omega-3 fatty acid intake in relation to circulating fibroblast growth factor 23 levels in renal transplant recipients

“…Of interest, interventions that reduced oxidative stress partially restored renal klotho expression in animal models [28]. As an alternative explanation, n-3 fatty acids could act directly on the PTH receptor, a potent inducer of FGF23 [29]; yet adjustment for phosphate, calcium and PTH did not change the observed association between n-3 fatty acid or fish intake and FGF23. Serum FGF23 levels have been shown to be influenced by phosphate-rich foods, particularly by protein from animal sources.…”