Pro-inflammatory mediators, such as IL-1 beta and TNF-alpha, are known to inhibit smooth muscle contractility in part by acting directly on smooth muscle. Our hypothesis is that these mediators inhibit contractility by inducing or suppressing the expression of critical targets in the signaling pathways mediating contraction and relaxation. In preliminary studies on control and TNBS colitis muscle strips, and on freshly dispersed and cultured muscle cells, we have identified six novel cytokine (IL-1 beta)-mediated effects reflecting changes in the expression and/or activity of specific signaling targets. These include: (i) up-regulation of RGS4 and RGS12 expression, which leads to inhibition of initial Ca2+-dependent contraction by Gq and Gi-coupled receptor agonists, respectively; (ii) down-regulation of the endogenous MLC phosphatase inhibitor, CPI-17, which leads to inhibition of sustained RhoA-dependent contraction; (iii) up-regulation of SERCA2 and IP3R-I, which regulate Ca2+ uptake and Ca2+ release, respectively; (iv) up-regulation of PDE4D5 and PDE5A expression, which leads to greater degradation of cAMP and cGMP, respectively; (v) down-regulation of soluble guanylyl cyclase (sGC) expression via a PKG/JNK-dependent post-transcriptional mechanism, which leads to inhibition of cGMP synthesis; and (vi) inactivation of adenylyl cyclase (AC) via iNOS-dependent nitrosylation, which leads to inhibition of cAMP synthesis. Where examined so far, the effects elicited in IL-1 beta-treated colonic muscle were observed also in colonic muscle from TNBS colitis.
The specific aims are to: (1) characterize the changes in the expression and activity of signaling targets (RGS4/RGS12, CPI-17, SERCA2 and IP3R-I) mediating initial Ca2+-dependent and sustained Ca2+-independent contraction; (2) characterize the changes in expression and activity of signaling targets (PDE3A, PDE4D5, PDE5A; sGC and AC) that regulate relaxation; and (3) characterize the transcriptional regulation of RGS4/RGS12 and CPI-17 by NF-kappa B and modulatory kinases (p38 MAP kinase, ERK1/2 and the PI 3-kinase/Akt/GSK3beta pathway), and the post-transcriptional regulation of sGC expression via a PKG/JNK/AP-1/HuR pathway. These studies will provide a comprehensive analysis of the mechanisms by which inflammatory cytokines inhibit contractility at cellular level, both in vitro and in an established model of colonic inflammation. ? ? ?
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