Deciphering Ion Channel Mechanisms Underlying Mechanosensitivity in the Gut

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Gastrointestinal (GI) motility is controlled by intestinal pacemaker cells, smooth muscle cells and the enteric nervous system (ENS) acting independently as the “second brain” in the gut. ENS abnormalities cause many GI motility disorders. In 1899, Bayliss and Starling proposed the classic “The law of the intestine” stating that “excitation at any point of the gut excites contraction above, inhibition below”, suggesting that distinct intrinsic excitatory and inhibitory intestinal motor behaviors can be elicited by mechanical forces. Recent studies have also demonstrated that mechanosensitivity is required to drive intestinal motor behaviors such as the colonic migrating motor complex (CMMC) resulting from either direct activation of ENS or by serotonin release from enterochromaffin cells (ECs) in the gut epithelium by mechanical forces. However, the molecules, cells, and neural circuits governing the process of mechanosensitivity in the gut still remain poorly understood. Membrane-bound ion channels play an essential role in mechanotransduction. Recent exciting studies have identified the mechanosensitive Piezo channels as molecular sensors for mechanical forces in the skin and have significantly advanced our knowledge about the role of the Piezo channels in our senses of light touch and mechanical pain. However, The role of Piezo channels involved in the mechanosensitivity in the gut and other visceral organs is poorly understood. Preliminary studies showed that chemical activation of Piezo1 promotes colon contraction and increases CMMC frequency, suggesting that Piezo1 is functionally expressed by both cholinergic excitatory and nitrergic enteric neural circuits. More importantly, Piezo1 is required for normal colonic motility in vivo. We thus hypothesize that Piezo1 is a molecular sensor for mechanical forces in the GI tract and potentially could serve as a therapeutic drug target for treating GI motility disorders such as slow transit constipation. To test this hypothesis, we will take a multidisciplinary approach using live-cell Ca2+ imaging, patch-clamp recordings and pharmacological approaches in combination to mouse genetics and intestinal motor behavioral methods to elucidate the cellular and molecular mechanisms underlying the Piezo1-mediated mechanosensitivity in both ENS and intestinal epithelium. Successful completion of these studies will advance our understanding of the previously unrecognized roles of Piezo1 and Piezo1-expressing enteric neurons and ECs in controlling GI motility. More importantly, these studies will offer new opportunities for developing effective and safer medicines for GI motility disorders.