Angiotensin II type I and prostaglandin F2α receptors cooperatively modulate signaling in vascular smooth muscle cells.

The angiotensin II type I (AT1R) and the prostaglandin F2α (PGF2α) F prostanoid (FP) receptors are both potent regulators of blood pressure. Physiological interplay between AT1R and FP has been described. Abdominal aortic ring contraction experiments revealed that PGF2α-dependent activation of FP potentiated angiotensin II-induced contraction, whereas FP antagonists had the opposite effect. Similarly, PGF2α-mediated vasoconstriction was symmetrically regulated by co-treatment with AT1R agonist and antagonist. The underlying canonical Gαq signaling via production of inositol phosphates mediated by each receptor was also regulated by antagonists for the other receptor. However, binding to their respective agonists, regulation of receptor-mediated MAPK activation and vascular smooth muscle cell growth were differentially or asymmetrically regulated depending on how each of the two receptors were occupied by either agonist or antagonist. Physical interactions between these receptors have never been reported, and here we show that AT1R and FP form heterodimeric complexes in both HEK 293 and vascular smooth muscle cells. These findings imply that formation of the AT1R/FP dimer creates a novel allosteric signaling unit that shows symmetrical and asymmetrical signaling behavior, depending on the outcome measured. AT1R/FP dimers may thus be important in the regulation of blood pressure.

Allosteric and biased g protein-coupled receptor signaling regulation: potentials for new therapeutics.

G protein-coupled receptors (GPCRs) are seven-transmembrane proteins that participate in many aspects of the endocrine function and are important targets for drug development. They transduce signals mainly, but not exclusively, via hetero-trimeric G proteins, leading to a diversity of intracellular signaling cascades. Ligands binding at the hormone orthosteric sites of receptors have been classified as agonists, antagonists, and/or inverse agonists based on their ability to mainly modulate G protein signaling. Accumulating evidence also indicates that such ligands, alone or in combination with other ones such as those acting outside the orthosteric hormone binding sites (e.g., allosteric modulators), have the ability to selectively engage subsets of signaling responses as compared to the natural endogenous ligands. Such modes of functioning have been variously referred to as "functional selectivity" or "ligand-biased signaling." In this review, we provide an overview of the current knowledge regarding GPCR-biased signaling and their functional regulation with a focus on the evolving concept that receptor domains can also be targeted to allosterically bias signaling, and discuss the usefulness of such modes of regulation for the design of more efficient therapeutics.

Effect of progenitor cell mobilization with granulocyte-macrophage colony-stimulating factor in patients with peripheral artery disease: a randomized clinical trial.

IMPORTANCE: Many patients with peripheral artery disease (PAD) have walking impairment despite therapy. Experimental studies in animals demonstrate improved perfusion in ischemic hind limb after mobilization of bone marrow progenitor cells (PCs), but whether this is effective in patients with PAD is unknown. OBJECTIVE: To investigate whether therapy with granulocyte-macrophage colony-stimulating factor (GM-CSF) improves exercise capacity in patients with intermittent claudication. DESIGN, SETTING, AND PARTICIPANTS: In a phase 2 double-blind, placebo-controlled study, 159 patients (median [SD] age, 64 [8] years; 87% male, 37% with diabetes) with intermittent claudication were enrolled at medical centers affiliated with Emory University in Atlanta, Georgia, between January 2010 and July 2012. INTERVENTIONS: Participants were randomized (1:1) to received 4 weeks of subcutaneous injections of GM-CSF (leukine), 500 µg/day 3 times a week, or placebo. Both groups were encouraged to walk to claudication daily. MAIN OUTCOMES AND MEASURES: The primary outcome was peak treadmill walking time (PWT) at 3 months. Secondary outcomes were PWT at 6 months and changes in circulating PC levels, ankle brachial index (ABI), and walking impairment questionnaire (WIQ) and 36-item Short-Form Health Survey (SF-36) scores. RESULTS: Of the 159 patients randomized, 80 were assigned to the GM-CSF group. The mean (SD) PWT at 3 months increased in the GM-CSF group from 296 (151) seconds to 405 (248) seconds (mean change, 109 seconds [95% CI, 67 to 151]) and in the placebo group from 308 (161) seconds to 376 (182) seconds (change of 56 seconds [95% CI, 14 to 98]), but this difference was not significant (mean difference in change in PWT, 53 seconds [95% CI, -6 to 112], P = .08). At 3 months, compared with placebo, GM-CSF improved the physical functioning subscore of the SF-36 questionnaire by 11.4 (95% CI, 6.7 to 16.1) vs 4.8 (95% CI, -0.1 to 9.6), with a mean difference in change for GM-CSF vs placebo of 7.5 (95% CI, 1.0 to 14.0; P = .03). Similarly, the distance score of the WIQ improved by 12.5 (95% CI, 6.4 to 18.7) vs 4.8 (95% CI, -0.2 to 9.8) with GM-CSF compared with placebo (mean difference in change, 7.9 [95% CI, 0.2 to 15.7], P = .047). There were no significant differences in the ABI, WIQ distance and speed scores, claudication onset time, or mental or physical component scores of the SF-36 between the groups. CONCLUSIONS AND RELEVANCE: Therapy with GM-CSF 3 times a week did not improve treadmill walking performance at the 3-month follow-up. The improvements in some secondary outcomes with GM-CSF suggest that it may warrant further study in patients with claudication. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01041417.