Study of Piezo channels and their role in gastro-intestinal function – Piezo

The identification of Piezo ion conducting pathway represents a crucial step for understanding these proteins at the molecular level, and this project will address this aim by combining molecular biology and electrophysiology.
Piezo genes are expressed in the gastro-intestinal tract and more specifically in the enteric nervous system (ENS). The ENS is involved in peristaltic reflex triggered by intestinal mechanical distension, which contributes to motility and digestion. This suggests that Piezos play a role in gastro-intestinal functions. This role will be explored in healthy state and in mouse model of digestive disease. Inflammatory bowel diseases, including Crohn’s disease and ulcerative colitis, are painful pathologies leading to altered motility and abnormal visceral perception and secretion that affect approximately 3.6 million people in the USA and Europe. This aim will be addressed by combining expression studies, in situ electrophysiological recordings and in vivo assays in conditional knock-out mice.
Visceral pain is a common and major complaint of patients with organic and functional bowel disorders. Notably, locally released inflammatory mediators sensitize primary afferent nociceptive nerve fibers in the intestine leading to visceral mechanical hypersensitivity. Using mouse model of inflammatory bowel disease and knock-out mice, the role of Piezo proteins in visceral pain will be characterized by combining expression studies and electrophysiological characterization of retrograde-labeled sensory neurons innervating the colon and behavior experiments.

Differences of biophysical properties such as unitary conductance (related to ion conducting pathway) and inactivation kinetics exist between mouse Piezo1 and 2 and Drosophila Piezo channels. These differences are used in the structure-function study of this project to test the functional consequences of swapping portions of protein between Piezo channels (generation of chimera constructs). Our results led us to focus on a portion of the protein of about sixty residues that could be involved in the passage of the ion flux and on the C-terminal part of the protein that could play a crucial role in channel inactivation/adaptation. These results allow us to design and generate new chimeric constructs to refine the area of interest and also to introduce point mutations to test involvement of specific residues to these processes.

Regarding the characterization of the physiological role of Piezo proteins in the gastrointestinal system, our results confirmed the preliminary results by showing that Piezo1 is expressed in enteric neurons. In addition, we crossed different strains of mice that will enable us to quickly have colonies of animals with the required genotypes for our study.

Inflammatory bowel diseases (IBD), including Crohn’s disease and ulcerative colitis, are painful pathologies that compromised quality of life in many patients. IBD affects approximately 3.6 million people in the USA and Europe. IBD is characterized by chronic inflammation within the gastrointestinal tract, giving rise to diarrhea, cramping and pain, all benchmark IBD symptoms. Each of these disorders seems to involve dysfunction of the enteric nervous system (ENS), leading to altered motility and abnormal visceral perception and secretion.
Despite advances in the understanding of the pathophysiology of IBD, there is a large unmet need for effective drugs for the treatment of gastrointestinal disorders. However, it is a real challenge to treat IBD because treatments are still based on empirical rather than mechanistic evidence. New therapeutic approaches are therefore clearly needed and are closely related to a better understanding of the mechanisms involved in IBD.
In this perspective, characterizing the molecular players involved in the initiation of fundamental intestinal reflexes involved in digestive function such as peristaltic reflex triggered by mechanical distension of the intestinal wall may provide perfect targets for new therapeutics. Similarly, identifying the primary sensors of mechanical forces in nociceptive sensory neurons projecting in the gut is of crucial interest to treat visceral pain and abdominal mechanical hypersensitivity that occurs in IBD patients. The recently identified mechanically-activated channels Piezo1 and 2 represent the best candidates to date to mediate these functions. This project should significantly advance the available knowledge of their structure and physiological function. These important advances are indispensable for the identification of future treatments.

Mechano-Gated Ion Channels in Sensory Systems. Patrick Delmas and Bertrand Coste. Cell, in press (review)

Mechanotransduction, the conversion of mechanical forces into biological signals, is perhaps the least understood mechanism of sensory transduction. In mammals, embryonic development, touch, pain, proprioception, hearing, adjustment of vascular tone and blood flow, flow sensing in kidney, gut motility and digestive function, lung growth and injury, bone and muscle homeostasis are all regulated by mechanotransduction. It has been postulated that ion channels directly activated by mechanical force are required for many of these biological processes. The recent identification of the Piezo family of mechanically activated ion channels provides promising candidates to explore the physiology of these fundamental mechanosensitive functions.
This project focuses on Piezo channels and will provide important and valuable progress in our understanding of these proteins and their physiological functions. Indeed, these channels are still largely unknown structurally, as well as physiologically. Piezo channels are large proteins with 30 to 40 transmembrane domains and homo-multimerize likely as tetramers to form mechanically activated channels. They are detected in many tissues in mice, including peripheral sensory neurons and gastro-intestinal tract, and have been shown to contribute to mechanical nociception in drosophila.
The identification of Piezo ion conducting pathway represents a crucial step for understanding these proteins at the molecular level, and this project will address this aim by combining molecular biology and electrophysiology.
Piezo genes are expressed in the gastro-intestinal tract and more specifically in the enteric nervous system (ENS). The ENS is involved in peristaltic reflex triggered by intestinal mechanical distension, which contributes to motility and digestion. This suggests that Piezos play a role in gastro-intestinal functions. This role will be explored in healthy state and in mouse model of digestive disease. Inflammatory bowel diseases, including Crohn’s disease and ulcerative colitis, are painful pathologies leading to altered motility and abnormal visceral perception and secretion that affect approximately 3.6 million people in the USA and Europe. This aim will be addressed by combining expression studies, in situ electrophysiological recordings and in vivo assays in conditional knock-out mice. As an effort to extend the study to humans, piezos implication in human bowel disease will be characterized by expression studies and electrophysiological recordings in portion of colon from patients with Crohn’s disease or ulcerative colitis.
Visceral pain is a common and major complaint of patients with organic and functional bowel disorders. Notably, locally released inflammatory mediators sensitize primary afferent nociceptive nerve fibers in the intestine leading to visceral mechanical hypersensitivity. Using mouse model of inflammatory bowel disease and knock-out mice, the role of Piezo proteins in visceral pain will be characterized by combining expression studies and electrophysiological characterization of retrograde-labeled sensory neurons innervating the colon and behavior experiments.
This study will lead to significant insight into the structure of piezo channels, and will define their role in gastro-intestinal physiology and pathology as well as their contribution to gut-related visceral pain.