The interaction between PAK1, CXCL1, and mechanotransduction during the development of ileus

Background Ileus is a well-recognized clinical problem, significantly impacting patient outcomes and increasing patient care costs. The objective of this study was to understand the interactions between PAK1, CXCL1, and mechanotransduction that contribute to the development of ileus. Methods Contractile activity was investigated after ileus was induced by gut manipulation in wild-type and PAK1 knockout mice. Cellular changes were investigated using a cyclical stretching human intestinal smooth muscle cell model (hISMC). Increased stress (as in edematous tissue) was simulated in human intestinal smooth muscle cells (hISMCs) by increased cyclic stretch (ECS). The non-edematous condition was simulated using control cyclical stretch (CCS). Results Decreased spontaneous contractile activity was detected after gut manipulation in wild-type but not PAK1 knockout mice. Although intestinal wall inflammation developed after gut manipulation in the wild-type and PAK1 knockout mice, as indicated by increased mast cell protease activity and intestinal edema, several cytokines were selectively reduced in the PAK1 knockout mice compared with wild-type mice, including CXCL1. In hISMCs, CXCL1 decreased MLC and MYPT1 phosphorylation, indicating that CXCL1 reduces intestinal contractile activity via effects on intestinal smooth muscle. Subjecting hISMCs to ECS increased CXCL1 secretion compared with CCS, indicating that CXCL1 is induced via mechanotransductive signals, and the increased CXCL1 secretion was blocked by PAK1 inhibition. NF-κB nuclear translocation increased in hISMCs subjected to ECS compared with CCS, and PAK1 inhibition prevented the increased NF-κB nuclear translocation, indicating that stretch-induced increases in NF-kB activation are PAK1-dependent. Inhibiting NF-κB activity prevented stretch-induced increases in CXCL1 secretion. Conclusions These results demonstrate that interactions between mechanotransduction, CXCL1, and PAK1 contribute to ileus. Mechanical signals induce increased PAK1 activity, which activates NF-kB, and increased NF-kB activity induces increased CXCL1 secretion. CXCL1 inhibits intestinal contractile activity. Understanding the mechanism for ileus development will facilitate the identification of new drug targets to treat ileus.