Abstract 3884: S1P/S1P2-mediated Rho-independent Increases in Vasoconstrictor- and Myogenic- Responses Accompany Increased Peripheral Resistance in Heart Failure
Background:Cardiac output (CO) in heart failure (HF) is diminished by increased peripheral vascular resistance (PVR). However, the molecular mechanisms underlying the latter are poorly understood.
Objective:To determine the molecular bases for vasoconstrictor- (VR) and myogenic-responses (MR) of mesenteric arteries (MA) in a mouse coronary ligation model of myocardial infarction (MI)-induced HF.
Methods:10 –12 weeks male C57Bl6 mice underwent LAD ligation or sham surgery. At defined time points (1–12 wks) post-op, isolated MA were analyzed for MR, VR, and activation of myosin light chain (MLC), myosin light chain phosphatase (MLCP), Rho, and the p38 and p42/44 (ERK1/2) mitogen activated protein kinases (MAPK). Expression of known MLCP-inhibitors (and p38 MAPK and ERK1/2 targets) zipper interacting protein kinase (ZIPK) and integrin-linked kinase (ILK) were also examined.
Results:Heart, lung, body weights as well as echocardiographic and hemodynamic measurements confirmed development of HF, with reduced CO and increased PVR post-MI. MR and VR of isolated MA to ET-1 and S1P were increased in HF vs. sham mice at all time points examined. VR to phenylephrine (PE) was decreased 1 wk post-MI, while those to PE at later time points were not. The S1P2 receptor antagonist JTE-013 progressively abolished the enhanced MR of HF mice, having modest effect on the MR of sham controls. Western blots of MA extracts revealed markedly reduced levels of the Ca2+-sensitizing agent GTP-Rho (1.00±0.11 vs 0.07±0.07, p=0.007, n=3–5) in HF. By contrast, increased levels of phosphorylated MLC (1.00±0.10 vs 1.28±0.05, p=0.04, n=8) and-MYPT1 (1.00±0.05 vs 2.33±0.15, p=0.0002, n=8), the targeting subunit of MLCP, were found in HF. Although the expression of ILK and ZIPK did not differ between HF and sham operated mice, phosphorylation of p38 MAPK (1.00±0.03 vs 2.21±0.23, p=0.007, n=8) and ERK1/2 (1.00±0.07 vs 1.37±0.13, p=0.01, n=6) was significantly increased in HF.
Conclusion: These data reveal a heretofore unrecognized mechanism of S1P/S1P2- mediated but Rho-independent inhibition of MLCP in HF. This novel mechanism may underlie the increased PVR of HF and may be driven by p38 MAPK- and ERK1/2-activated inhibitory phosphorylation of MLCP through ZIPK and or ILK.