BURN-INDUCED IMPAIRMENT OF ILEUM MUSCLE CONTRACTILITY IS ASSOCIATED WITH INCREASED EXTRACELLULAR MATRIX COMPONENTS
Claire Cummins*1, Yanping Gu3, Xiaofu Wang1, You-Min Lin2, Xuan-Zheng P. Shi2, Ravi Radhakrishnan1
1Surgery, University of Texas Medical Branch, Galveston, TX; 2Gastroenterology, University of Texas Medical Branch, Galveston, TX; 3Neuroscience, University of Texas Medical Branch, Galveston, TX
Introduction: Severe burns lead to marked impairment of gastrointestinal motility, such as delayed gastric emptying and small and large intestinal ileus. However, the cellular mechanism of these pathologic changes remains largely unknown. Recently, it has been reported that smooth muscle cells are highly sensitive to the state of the extracellular matrix (ECM), and ECM proteins are involved in the regulation of smooth muscle functions. The present study examines rat small intestine contractility and the expression of muscular layer ECM proteins after burn injury.
Methods: Male Sprague Dawley rats approximately 3 months old and weighing 300-350g were randomized to either a 60% total body surface area full-thickness scald burn or sham procedure and were sacrificed 24 hours after the procedure. A segment of small intestine 15 to 20 cm proximal to the ileocolonic junction was isolated, and placed in carbogenated Krebs solution. Ileal smooth muscle contractility was recorded in a 10-mm long segment mounted along the longitudinal orientation in individual muscle baths, using Grass isometric force transducers and amplifiers connected to a Biopac data-acquisition system. Muscularis externae was isolated from the ileal segment to prepare smooth muscle protein extracts for Western Blot analysis of ECM protein expression.
Results: Compared to sham controls, the baseline rhythmic contractile activities of the ileal smooth muscle strips were impaired in the burned rats. The smooth muscle contractile response to acetylcholine (10-7 M to 10-3 M) was significantly impaired in burned rats comparing to sham rats. Simultaneously, our data showed that ileal muscularis ECM proteins collagen type I, fibronectin, and laminin were significantly up-regulated in burned rats compared to sham rats. Of note, ileal mucosal ECM proteins were unchanged after burn. TGF-β signaling is an important stimulating factor for ECM protein expression. Our results revealed that TGF-β signaling was activated in the ileal muscle of burned rats evidenced by the activation of Smad2/3 expression and phosphorylation. In addition, the total and phosphorylated AKT, which is an important downstream factor of ECM/FAK signaling in smooth muscle cells, was also up-regulated in burned rats' ileal muscle.
Conclusion: Our results suggest that TGF-β/ECM/AKT signaling may be involved in burn-induced impairment of small intestinal contractility.
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