Plasticity of seven-transmembrane-helix receptor heteromers in human vascular smooth muscle cells

Chemokine receptor hetero-oligomers regulate monocyte chemotaxis

It is known that stress influences immune cell function. The underlying molecular mechanisms are unclear. We recently reported that many chemokine receptors (CRs) heteromerize with α1-adrenoceptors (α1-ARs) through which CRs are regulated. Here, we show that arginine vasopressin receptor 1A (AVPR1A) heteromerizes with all human CRs, except chemokine (C-X-C motif) receptor (CXCR)1, in recombinant systems and that such heteromers are detectable in THP-1 cells and human monocytes. We demonstrate that ligand-free AVPR1A differentially regulates the efficacy of CR partners to mediate chemotaxis and that AVPR1A ligands disrupt AVPR1A:CR heteromers, which enhances chemokine (C-C motif) receptor (CCR)1-mediated chemotaxis and inhibits CCR2-, CCR8-, and CXCR4-mediated chemotaxis. Using bioluminescence resonance energy transfer to monitor G protein activation and CRISPR/Cas9 gene-edited THP-1 cells lacking AVPR1A or α1B-AR, we show that CRs that share the propensity to heteromerize with α1B/D-ARs and AVPR1A exist and function within interdependent hetero-oligomeric complexes through which the efficacy of CRs to mediate chemotaxis is controlled. Our findings suggest that hetero-oligomers composed of CRs, α1B/D-ARs, and AVPR1A may enable stress hormones to regulate immune cell trafficking.

Collagen XIII Is the Key Molecule of Neurovascular Junctions in the Neuroendocrine System

INTRODUCTION

Axons of magnocellular neurosecretory cells project from the hypothalamus to the posterior lobe (PL) of the pituitary. In the PL, a wide perivascular space exists between the outer basement membrane (BM), where nerve axons terminate, and the inner BM lining the fenestrated capillaries. Hypothalamic axon terminals and outer BMs in the PL form neurovascular junctions. We previously had found that collagen XIII is strongly localized in the outer BMs. In this study, we investigated the role of collagen XIII in the PL of rat pituitaries.

METHODS

We first studied the expression of Col13a1, the gene encoding the α1 chains of collagen XIII, in rat pituitaries via quantitative real-time polymerase chain reaction and in situ hybridization. We observed the distribution of COL13A1 in the rat pituitary using immunohistochemistry and immunoelectron microscopy. We examined the expression of Col13a1 and the distribution of COL13A1 during the development of the pituitary. In addition, we examined the effects of water deprivation and arginine vasopressin (AVP) signaling on the expression of Col13a1 in the PL.

RESULTS

Col13a1 was expressed in NG2-positive pericytes, and COL13A1 signals were localized in the outer BM of the PL. The expression of Col13a1 was increased by water deprivation and was regulated via the AVP/AVPR1A/Gαq/11 cascade in pericytes of the PL.

CONCLUSION

These results suggest that pericytes surrounding fenestrated capillaries in the PL secrete COL13A1 and are involved in the construction of neurovascular junctions. COL13A1 is localized in the outer BM surrounding capillaries in the PL and may be involved in the connection between capillaries and axon terminals.

α1-adrenoceptor ligands inhibit chemokine receptor heteromerization partners of α1B/D-adrenoceptors via interference with heteromer formation

We reported previously that α1-adrenoceptor (α1-AR) ligands inhibit chemokine receptor (CR) heteromerization partners of α1B/D-AR. The underlying mechanisms are unknown and in vivo evidence for such effects is missing. Utilizing CCR2 and α1B-AR as prototypical partners, we observed in recombinant systems and THP-1 cells that α1B-AR enhanced whereas its absence inhibited Gαi signaling of CCR2. Phenylephrine and phentolamine reduced the CCR2:α1B-AR heteromerization propensity and inhibited Gαi signaling of CCR2. Phenylephrine cross-recruited β-arrestin-2 to CCR2, and reduced expression of α1B/D-AR, CR partners (CCR1/2, CXCR4) and corresponding heteromers. Phentolamine reduced CR:α1B/D-AR heteromers without affecting β-arrestin-2 recruitment or receptor expression. Phenylephrine/phentolamine prevented leukocyte infiltration mediated via CR heteromerization partners in a murine air pouch model. Our findings document that α1-AR ligands inhibit leukocyte migration mediated by CR heteromerization partners in vivo and suggest interference with α1B-AR:CR heteromerization as a mechanism by which CR partners are inhibited. These findings provide new insights into the pharmacology of GPCR heteromers and indicate that an agonist and antagonist at one GPCR can act as antagonists at heteromerization partners of their target receptors.

Heteromerization between α1B -adrenoceptor and chemokine (C-C motif) receptor 2 biases α1B -adrenoceptor signaling: Implications for vascular function

Previously, we reported that chemokine (C-C motif) receptor 2 (CCR2) heteromerizes with α1B -adrenoceptor (α1B -AR) in leukocytes, through which α1B -AR controls CCR2. Whether such heteromers are expressed in human vascular smooth muscle cells (hVSMCs) is unknown. Bioluminescence resonance energy transfer confirmed formation of recombinant CCR2:α1b -AR heteromers. Proximity ligation assays detected CCR2:α1B -AR heteromers in hVSMCs and human mesenteric arteries. CCR2:α1B -AR heteromerization per se enhanced α1B -AR-mediated Gαq -coupling. Chemokine (C-C motif) ligand 2 (CCL2) binding to CCR2 inhibited Gαq activation via α1B -AR, cross-recruited β-arrestin to and induced internalization of α1B -AR in recombinant systems and in hVSMCs. Our findings suggest that CCR2 within CCR2:α1B -AR heteromers biases α1B -AR signaling and provide a mechanism for previous observations suggesting a role for CCL2/CCR2 in the regulation of cardiovascular function.

α1B/D-adrenoceptors regulate chemokine receptor-mediated leukocyte migration via formation of heteromeric receptor complexes

SignificanceHere we show that most chemokine receptors (CRs) form heteromeric complexes with α₁-adrenergic receptors (ARs) in recombinant systems and that such heteromers are detectable in human monocytes and in the human monocytic leukemia cell line THP-1. Furthermore, we provide evidence that α_1B/D-ARs control the function of their CR heteromerization partners. Our findings suggest that heteromeric complexes between α_1B/D-ARs and CRs are necessary for normal function of CR heteromerization partners, indicate receptor heteromerization as a molecular mechanism by which stress hormones regulate leukocyte trafficking in health and disease, and offer opportunities to modulate leukocyte and/or cancer cell trafficking in disease processes.