Formyl Peptide Receptor Exerts a Sentinel Role and is Important for the Dynamic Plasticity of the Vasculature

Abstract

The canonical view accepts that the vascular smooth muscle cells (VSMCs) cytoskeleton is not plastic and remains stationary during a contractile event. However, it is now recognized that VSMCs display a highly dynamic process that undergoes polymerization and depolymerization based upon cellular demand.One of the most powerful signaling pathways that induces actin polymerization, Ca2+ influx and movement in neutrophils is due to formyl peptide receptor‐1 (FPR) activation. These receptors were originally identified by their ability to bind bacterial N‐formyl peptides. Interestingly, mitochondria carry hallmarks of their bacterial ancestry and one of these hallmarks is that this organelle uses an N‐formyl‐methionyl‐tRNA as an initiator of protein synthesis. Consequently, both mitochondrial and bacterial N‐formyl peptides are recognized by FPR‐1 as ligands and are known to play a role in the activation of the innate immune system.We have observed that FPR‐1 is not only expressed in sentinel cells such as leukocytes, but also in endothelial cells and VSMCs. To better understand the role of FPR‐1 in the regulation of the vascular plasticity, we studied the hypothesis that F‐MITs (formylated peptide corresponding to the NH2‐terminus of mitochondria ND6) binds FPR‐1 and leads to actin polymerization in VSMCs similar to the observed in neutrophils when activated with bacterial fragments. On the other hand, FPR‐1 absence would disrupt VSMCs actin polymerization and decrease contraction. For this, VSMCs isolated from aorta [14 weeks male C57BL6 (WT) mice] were treated with F‐MIT (20 min, 10 μM) or nonformylated peptide (control) in the presence or absence of a cocktail of FPR antagonists (FPR‐1 antagonist, cyclosporine H: CsH, 1 μmol/L and FPR‐2 antagonist, WRW4, 10 μmol/L). We observed that F‐MIT induced VSMCs actin polymerization via a shift in the filamentous:globular actin equilibrium in favor of F‐actin (1.8 fold vs. control, p<0.05). Using confocal microscopy, it was observed that VSMCs from aorta or intrarenal arteries (resistance arteries) that do not express the FPR‐1 present disrupted F‐actin and cell migration as measured by scratch assay. Also, measurements of isometric tension in aorta, demonstrated that the absence of the FPR‐1 decreased both the first ‐(fast, Ca2+ influx) and second‐phase (slow, actin polymerization) (Figure 1) of KCl (120 mmol/L)‐induced contraction and the concentration response curve to phenylephrine (Emax: WT: 8.4±1.2 vs. FPR‐1 KO: 0.6±0.2 mN, p<0.05). Jasplakinolide, an actin polymerization inducer (0.1 μmol/L), but not RhoA activator (2 μg/mL, 3 hours) restored contraction. L‐type calcium channels (Cav1.2) and AHNAK (anchors Cav 1.2 to the actin) protein expression are decreased in VSMCs from FPR‐1 KO, and Cav 1.2 activator (BayK8644, 0.1 nmol/L −1 μmol/L) was able to restore contraction. This suggests a link between actin polymerization via FPR‐1 activation and Cav 1.2 integrity and function.We established a remarkable role for an innate immune receptor FPR‐1 in VSMCs contractility and motility. This discovery is fundamental for vascular immuno‐pathophysiology, given that FPR‐1 in VSMCs not only functions as an immune regulator and danger signal sensor, but also has an important role for the dynamic plasticity of the vasculature.Support or Funding InformationNational Institutes of Health (NIH:1K99GM118885‐01)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.