Our results show that pretreatment with EP 80317 protected the heart against damage and dysfunction elicited by MI/R, along with a transient reduction in peripheral lipolysis. Our findings support CD36 as a novel target for the treatment of ischaemic cardiopathy.

The activation of G protein-coupled receptor 103 (GPR103) by its endogenous peptidic ligands, QRFPs, is involved in the central regulation of feeding by increasing food intake, body weight, and fat mass after intracerebroventricular injection in mice. However, the role of GPR103 in regulating peripheral metabolic pathways has not yet been explored. The present study aimed to investigate the role of GPR103 in adipogenesis and lipid metabolism using 3T3-L1 adipocyte cells. Our results show that differentiated 3T3-L1 cells expressed the GPR103b subtype mRNA and protein, as well as QRFP mRNA. QRFP-43 and -26 induced an increase in triglyceride accumulation of 50 and 41%, respectively, and elicited a dose-dependent increase in fatty acid uptake, by up to approximately 60% at the highest concentration, in 3T3-L1-differentiated cells. QRFP-43 and -26 inhibited isoproterenol (ISO)-induced lipolysis in a dose-dependent manner, with IC(50)s of 2.3 +/- 1.2 and 1.1 +/- 1.0 nm, respectively. The expression of genes involved in lipid uptake (FATP1, CD36, LPL, ACSL1, PPAR-gamma, and C/EBP-alpha), was increased by 2- to 3-fold after treatment with QRFP. The effects of QRFP on ISO-induced lipolysis and fatty acid uptake were abolished when GPR103b was silenced. In a mouse model of diet-induced obesity, the expression of GPR103b in epididymal fat pads was elevated by 16-fold whereas that of QRFP was reduced by 46% compared to lean mice. Furthermore, QRFP was bioactive in omental adipocytes from obese individuals, inhibiting ISO-induced lipolysis in these cells. Our results suggest that GPR103b and QRFP work in an autocrine/paracrine manner to regulate adipogenesis.

These findings suggest a central role for the prostanoid 15d-PGJ2 in PPARgamma activation and the upregulation of the ABC transporter pathway in response to CD36 activation by synthetic GHRPs analogues. The resulting enhanced cholesterol efflux might explain, at least in part, the atheroprotective effect of selective CD36 ligands.

The natriuretic peptide receptor‐A (NPR‐A) is composed of an extracellular ligand‐binding domain, a transmembrane‐spanning domain, a kinase homology domain (KHD) and a guanylyl cyclase domain. Because the presence of ATP or adenylylimidodiphosphate reduces atrial natriuretic peptide (ANP) binding and is required for maximal guanylyl cyclase activity, a direct interaction of ATP with the receptor KHD domain is plausible. Therefore, we investigated whether ATP interacts directly with a binding site on the receptor by analyzing the binding of a photoaffinity analog of ATP to membranes from human embryonic kidney 293 cells expressing the NPR‐A receptor lacking the guanylyl cyclase moiety (ΔGC). We demonstrate that this receptor (NPR‐A‐ΔGC) can be directly labeled by 8‐azido‐3′‐biotinyl‐ATP and that labeling is highly increased following ANP treatment. The mutant receptor ΔKC, which does not contain the KHD, is not labeled. Photoaffinity labeling of the NPR‐A‐ΔGC is reduced by 50% in the presence of 550 µm ATP, and competition curve fitting studies indicate a Hill slope of 2.2, suggestive of cooperative binding. This approach demonstrates directly that the interaction of ANP with its receptor modulates the binding of ATP to the KHD, probably through a conformational change in the KHD. In turn, this conformational change is essential for maximal activity. In addition, the ATP analog, 8‐azido‐adenylylimidodiphosphate, inhibits guanylyl cyclase activity but increases ANP binding to the extracellular domain. These results suggest that the KHD regulates ANP binding and guanylyl cyclase activity independently.

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are loop-shaped peptidic hormones that have multiple actions on body fluid homeostasis. Their physiological effects are mediated through the activation of their receptor, natriuretic peptide receptor A (NPRA). This receptor is a member of the membrane guanylyl cyclase family and catalyzes cyclic guanosine monophosphate (cGMP) production following its activation. To map the binding site of human NPRA, we applied the methionine proximity assay method to this receptor. We photolabeled NPRA mutants, presenting a single methionine in the binding domain of the receptor, and used benzoylphenylalanine- (Bpa-) substituted peptides at positions 0, 3, 18, 26, and 28 of the ligand. We identified that the N-terminus of the peptide is interacting with the region between Asp(177) and Val(183) of the receptor. Arg(3) is interacting in the vicinity of Phe(172). Leu(18) binds close to Val(116). Phe(26) binds in the vicinity of His(195), and the C-terminal Tyr(28) is located close to Met(173). We next proceeded with photolabeling of a dual Bpa-substituted peptide and showed that the N-terminus and Leu(18) interact with opposite receptor subunits. On the basis of our results, a molecular model of peptide-bound NPRA was developed by homology modeling with the C-type natriuretic peptide- (CNP-) bound natriuretic peptide receptor C (NPRC) crystal structure. The model has been validated by molecular dynamics simulations. Our work provides a rational basis for interpreting and predicting natriuretic peptide binding to the human NPRA.