Mechanical strain and TLR4 synergistically induce cell-specific inflammatory gene expression in intestinal smooth muscle cells and peritoneal macrophages.

Mechanical trauma of the gut is an unavoidable event in abdominal surgery. Former studies demonstrated that intestinal manipulation induces a strong inflammation within the tunica muscularis. We hypothesized that mechanical strain initiates or aggravates proinflammatory responses in intestinal smooth muscle cells (iSMC) or macrophages. First, an appropriate isolation and culture method for neonatal rat iSMC was established. Purified iSMC and primary peritoneal macrophages (pMacs) were subjected to static or cyclic strain, and gene expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), IL-6, and IL-1β was analyzed by quantitative PCR. Supernatants from stretched iSMC were transferred to untreated pMacs or contrariwise, and medium transfer-triggered inflammatory gene expression was measured in unstretched cells. Finally, we investigated the synergistic effect of static strain on LPS-induced proinflammatory gene expression. Although cyclic strain failed, static strain significantly induced iNOS, COX-2, and IL-1β mRNA in iSMC. pMacs showed an increase in all inflammatory genes investigated as well as macrophage inflammatory protein (MIP)-1α and MIP-2 mRNA after static strain. Both cell entities liberated unknown mediators in response to stretch that mutually stimulated iNOS gene expression. Finally, mechanostimulation amplified LPS-induced iNOS and IL-1β gene expression in iSMC as well as COX-2 and IL-6 mRNA in pMacs. In conclusion, static strain initiates proinflammatory gene expression in iSMC and pMacs and triggers a bidirectional paracrine communication between both cultured cell entities via the liberation of unknown mediators. Furthermore, static strain synergistically operates with Toll-like receptor 4 ligation in a cell-specific manner. Hence, this study demonstrates that mechanical strain functions as an immunomodulatory stimulus in abdominal cells.