Citations

This study presents gastric ablation as a novel tool for modulating gastric bioelectrical activation, including eliminating the normal gastric pacemaker site as well as abnormal ectopic pacemaker sites underlying gastric dysrhythmias. Targeted application of radiofrequency ablation was able to eliminate these pacemaker sites without disrupting surrounding conduction capability or tissue structure. Gastric ablation presents a powerful new research tool for modulating gastric electrical activation and may likely hold therapeutic potential for disorders of gastric function.

BACKGROUND Enteroendocrine cells (EECs) in the gastrointestinal (GI) epithelium are specialized sensors of luminal chemicals and forces. Upon stimulation, EECs release a variety of neurotransmitters and hormones, but cellular mechanisms of excitation‐secretion coupling are poorly understood. We recently discovered that a population of EECs expresses the mechanosensitive ion channel Piezo2, which is necessary for force‐dependent intracellular Ca2+ increase and serotonin release. However, the molecular mechanism that links Piezo2 and serotonin release is unknown. In other sensory systems, the Cacna1h ‐encoded t‐type voltage‐gated calcium channel Cav3.2 is important in mechanotransduction for linking mechanical activation with neurotransmitter release. AIM to determine if Cav3.2 is expressed and functionally relevant in EECs. METHODS Quantitative RT‐PCR for Cacna1h mRNA expression was evaluated in colon epithelium of control and NeuroD1 Cre x RiboTag mice, in which actively transcribed mRNA specifically from EECs is tagged with hemagglutinin (HA). NeuroD1 Cre x tdTomato colon cross‐sections were fixed and immunolabeled with anti‐Cav3.2 antibody. Single primary NeuroD1 cre x GCaMP5 EECs were mechanically stimulated and Cav3.2 role in mechanotransduction was tested by pharmacology (Ca2+ free, nickel, mibefradil, ω‐agatoxin IVA) and Cacna1h siRNA knockdown. RESULTS Murine colon epithelium expressed Cav3.2 mRNA. In NeuroD1 Cre x RiboTag mouse, HA co‐localized with EEC marker Chromogranin A (Chga). NeuroD1+ EEC ribosomal trapped mRNA was enriched for markers of epithelium (Vil1), EEC (Chga), and enriched 7.0‐fold for Cav3.2 (n=3, p<0.05 compared to whole epithelium). Immunohistochemistry in NeuroD1 Cre x tdTomato showed that Cav3.2 co‐localized specifically with tdTomato (NeuroD1+) EECs. In primary NeuroD1+ EECs, Cav3.2 inhibition by all pharmacologic agents and siRNA knockdown inhibited mechanically induced Ca2+ response (96±1% for Ca2+ free, 71±9% nickel, 61±6% mibefradil, 80±4% ω‐agatoxin IVA and 96±1% Cav3.2 siRNA, n=3–18, p<0.05 compared to control untreated cells or cells treated with non‐targeted siRNA). CONCLUSIONS Cav3.2 is densely and specifically expressed in mouse colon EECs and it is important for regulating Ca2+ in EEC mechanotransduction. Future studies will determine how Cav3.2 channels contribute to EEC electrical excitability, excitation‐secretion coupling, and ultimately EEC Cav3.2 roles in GI physiology. Support or Funding Information Supported by NIH DK106456, NIH DK084567, and AGA RSA This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Disruption of intracellular calcium likely underlies the upregulation of cyclic AMP (cAMP) signaling and the proliferative and secretory phenotype of the cystic epithelium in ADPKD. However, the mechanisms by which polycystins reduce cytoplasmic calcium remain elusive. Impaired flow‐induced calcium entry through ciliary polycystin complex has been previously proposed as a pathogenic mechanism, but newer evidence suggests the involvement of polycystins in modulation of other mechanosensitive ion channels such as Piezo1, the newly‐identified stretch‐activated non‐selective cation channel. We hypothesized that polycystins, through their physical and functional interaction with Piezo1, modulate various cellular responses to mechanical stimulation. Piezo1 was expressed in both wild type mouse inner medullary collecting duct cells (mIMCD3) cells and PKD2 null cells (~3 fold higher than wild type). Wild type mIMCD3 cells were stably transfected with genetically encoded biosensors, jRGeco1a and Flamindo2, to study spatiotemporal dynamics of calcium and cAMP during live cell imaging, respectively. Piezo1 activation by Yoda1 increased cytoplasmic calcium and simultaneously lowered forskolin‐induced cAMP (Figure 1A). Additionally, exerting physiological fluid shear stress (FSS) (ibidi pump system) led to reduction in cAMP (Figure 1B). Both Yoda1 and FSS lead to an increase in ATP release in mIMCD3 cells (Figure 1C). Furthermore, Yoda1 significantly reduced forskolin‐induced in vitro cystogenesis by 68% in WT and by 48% in PKD2 null mIMCD3 cells (Figure 1D). These results suggest that Piezo1 is involved in renal cystogenesis by controlling FSS‐induced calcium entry. Further studies are required to determine in vivo effect of Piezo1 on renal cystogenesis. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

INTRODUCTION Intestinal enterochromaffin (EC) cells are the specialized epithelial mechanosensors of the gastrointestinal (GI) epithelium and are functionally and developmentally like Merkel cells in the skin. EC cells release serotonin (5‐HT) in response to mechanical stimuli. Recently, we discovered that like Merkel cells, human and mouse EC cells express the mechanosensitive (MS) ion channel Piezo2. However, little is known about the functional properties of this channel in primary EC cells. AIM To determine the role of Piezo2 in primary EC cells. METHODS The enteroendocrine cell transcription factor NeuroD1 was used to mark the late stage of EC cell development and generate NeuroD1‐cre::GCaMP5/tdTomato mouse to identify EC cells and examine their Ca 2+ dynamics. We examined colocalization of tdTomato with 5‐HT and Piezo2 by immunohistochemistry. We established and used primary colon epithelium cultures for whole‐cell patch clamp and Ca 2+ imaging experiments and mechanically stimulated by membrane displacement with a piezoelectrically driven glass probe or shear flow. RESULTS Immunostaining showed no tdTomato labeling outside of the GI epithelium, and epithelial tdTomato cells were 5‐HT+ and Piezo2+. Mechanical stimulation of primary EC cells by membrane displacement produced inward MS currents (20.8±4.9 pA/pF, C m =3.5 pF, n=6) with fast activation and inactivation kinetics (τ inact 11.1±2.8 ms), steep mechanosensitivity (Boltzmann function fit with a mid‐point of 3.46±0.80 μm and slope 0.79±0.27 μm) and a linear current‐voltage relationship (slope 0.61±0.17 pA/mV, x‐intercept −4.26±1.34 mV, n=5). Shear flow (20 s) transiently increased intracellular calcium ((Ca 2+ ) i ) (2.15±0.5 ΔF/F0, upstroke 3–5 s, return to baseline in 60 s, n=12). MS currents were inhibited by the MS ion channel blocker Gd 3+ (20.8±4.9 pA/pF versus 5.3±1.9 pA/pF), Piezo channel blocker GsMTx‐4 (20.8±4.9 pA/pF versus 2.5±0.9 pA/pF) and Piezo2 siRNA (20.8±4.9 pA/pF versus 1.1±0.3 pA/pF), but not non‐targeted (NT) siRNA (20.8±4.9 pA/pF versus 16.0±5.2 pA/pF and) (n=4–6 for each condition, p <0.05 for all except NT siRNA). Similarly, the (Ca 2+ ) i responses to force were inhibited by Gd 3+ (2.28±0.7 ΔF/F0 to 0.09±0.05 ΔF/F0), GsMTx‐4 (2.0±0.6 ΔF/F0 to 0.3±0.1 ΔF/F0), Piezo2 siRNA (2.15±0.5 ΔF/F0 to 0.08±0.05 ΔF/F0), but not NT siRNA (2.15±0.5 ΔF/F0 to 2.7±0.3 ΔF/F0) (n=4–6, p <0.05 for all except NT siRNA). CONCLUSIONS In the mouse epithelium, Piezo2+ EC cells were specifically marked by NeuroD1. Primary colonic NeuroD1+ cells had inward and non‐rectifying MS currents that could be blocked by Gd 3+ , GsMTx‐4 and Piezo2 siRNA. Similarly, shear flow evoked changes in (Ca 2+ ) i that were also blocked by Piezo2 inhibitors and dependent on extracellular Ca 2+ . These results suggest that the MS ion channel Piezo2 acts as the primary EC cell mechanosensor, whose activation by force leads to MS ionic current and (Ca 2+ ) i increase that may mediate mechanically‐induced 5‐HT release. Support or Funding Information This work was supported by NIH K08 DK106456, AGA Research Scholar Award, Mayo Clinic Center for Biomedical Discovery, Mayo Clinic Center for Cell Signaling in Gastroenterology (P30DK084567) and DK52766. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Objective Haemorrhoidal disease (HEM) affects a large and silently suffering fraction of the population but its aetiology, including suspected genetic predisposition, is poorly understood. We report the first genome-wide association study (GWAS) meta-analysis to identify genetic risk factors for HEM to date. Design We conducted a GWAS meta-analysis of 218 920 patients with HEM and 725 213 controls of European ancestry. Using GWAS summary statistics, we performed multiple genetic correlation analyses between HEM and other traits as well as calculated HEM polygenic risk scores (PRS) and evaluated their translational potential in independent datasets. Using functional annotation of GWAS results, we identified HEM candidate genes, which differential expression and coexpression in HEM tissues were evaluated employing RNA-seq analyses. The localisation of expressed proteins at selected loci was investigated by immunohistochemistry. Results We demonstrate modest heritability and genetic correlation of HEM with several other diseases from the GI, neuroaffective and cardiovascular domains. HEM PRS validated in 180 435 individuals from independent datasets allowed the identification of those at risk and correlated with younger age of onset and recurrent surgery. We identified 102 independent HEM risk loci harbouring genes whose expression is enriched in blood vessels and GI tissues, and in pathways associated with smooth muscles, epithelial and endothelial development and morphogenesis. Network transcriptomic analyses highlighted HEM gene coexpression modules that are relevant to the development and integrity of the musculoskeletal and epidermal systems, and the organisation of the extracellular matrix. Conclusion HEM has a genetic component that predisposes to smooth muscle, epithelial and connective tissue dysfunction.

Mechanosensation, the ability to properly sense mechanical stimuli and transduce them into physiologic responses, is an essential determinant of gastrointestinal (GI) function. Abnormalities in this process result in highly prevalent GI functional and motility disorders. In the GI tract, several cell types sense mechanical forces and transduce them into electrical signals, which elicit specific cellular responses. Some mechanosensitive cells like sensory neurons act as specialized mechanosensitive cells that detect forces and transduce signals into tissue-level physiological reactions. Nonspecialized mechanosensitive cells like smooth muscle cells (SMCs) adjust their function in response to forces. Mechanosensitive cells use various mechanoreceptors and mechanotransducers. Mechanoreceptors detect and convert force into electrical and biochemical signals, and mechanotransducers amplify and direct mechanoreceptor responses. Mechanoreceptors and mechanotransducers include ion channels, specialized cytoskeletal proteins, cell junction molecules, and G protein-coupled receptors. SMCs are particularly important due to their role as final effectors for motor function. Myogenic reflex—the ability of smooth muscle to contract in response to stretch rapidly—is a critical smooth muscle function. Such rapid mechanotransduction responses rely on mechano-gated and mechanosensitive ion channels, which alter their ion pores’ opening in response to force, allowing fast electrical and Ca 2+ responses. Although GI SMCs express a variety of such ion channels, their identities remain unknown. Recent advancements in electrophysiological, genetic, in vivo imaging, and multi-omic technologies broaden our understanding of how SMC mechano-gated and mechanosensitive ion channels regulate GI functions. This review discusses GI SMC mechanosensitivity's current developments with a particular emphasis on mechano-gated and mechanosensitive ion channels.

This study presents gastric ablation as a new method for modulating slow wave activation and propagation in vivo, by creating localized electrical conduction blocks in the stomach, validated by high-resolution electrical mapping and histological tissue analysis. The results define the effective energy dose range for creating conduction blocks, while maintaining the mucosal and submucosal integrity, and demonstrate the electrophysiological effects of ablation. In future, gastric ablation can now be translated toward disrupting dysrhythmic slow wave activation.

AbstractBackgroundGastrointestinal (GI) motility is a complex physiological process that is critical for normal GI function. Disruption of GI motility frequently occurs in GI diseases or as side effects of therapeutics. Whole gut transit measurements, like carmine red leading‐edge transit, in mice form the cornerstone of in vivo preclinical GI motility studies.MethodWe have developed an easily achievable, labor‐saving method to measure whole gut transit time in mice. This approach uses inexpensive, commercially available materials to monitor pellet production over time via high definition cameras capturing time‐lapse video for offline analysis.Key ResultWe describe the assembly of our automated gut transit setup and validate this approach by comparing the results with loperamide to delay transit and conventional transit measurements. We demonstrate that compared to the control group, the loperamide group had slowed transit, evidenced by a decrease in total pellet production and prolonged whole gut transit time. The control group had an extended transit time compared with the results reported in the literature. Whole gut transit rates accelerated to times comparable to the literature by disrupting cages every 10‐15 min to imitate the conventional approach, suggesting that disruption affects the assay and supports the use of an automated approach.Conclusion & InferencesA novel automated, inexpensive, and easily assembled whole gut transit setup is labor‐saving and allows minimal disruption to animal behavior compared with the conventional approach.

AbstractBackgroundThe gut is the only organ system with intrinsic neural reflexes. Intrinsic primary afferent neurons (IPANs) of the enteric nervous system initiate intrinsic reflexes, form gut‐brain connections, and undergo considerable neuroplasticity to cause digestive diseases. They remain inaccessible to study in mice in the absence of a selective marker. Advillin is used as a marker for primary afferent neurons in dorsal root ganglia. The aim of this study was to test the hypothesis that advillin is expressed in IPANs of the mouse jejunum.MethodsAdvillin expression was assessed with immunohistochemistry and using transgenic mice expressing an inducible Cre recombinase under the advillin promoter were used to drive tdTomato and the genetically encoded calcium indicator GCaMP5. These mice were used to characterize the morphology and physiology of advillin‐expressing enteric neurons using confocal microscopy, calcium imaging, and whole‐cell patch‐clamp electrophysiology.Key ResultsAdvillin is expressed in about 25% of myenteric neurons of the mouse jejunum, and these neurons demonstrate the requisite properties of IPANs. Functionally, they demonstrate calcium responses following mechanical stimuli of the mucosa and during antidromic action potentials. They have Dogiel type II morphology with neural processes that mostly remain within the myenteric plexus, but also project to the mucosa and express NeuN and calcitonin gene‐related peptide (CGRP), but not nNOS.Conclusions and InferencesAdvillin marks jejunal IPANs providing accessibility to this important neuronal population to study and model digestive disease.

BACKGROUND Mechanical stimulation of the gastrointestinal (GI) epithelium causes changes in epithelial ion transport by an unclear mechanism. We recently discovered the mechanosensitive ion channel Piezo2 is specifically expressed by the enteroendocrine cells (EECs) and is necessary for EEC mechanosensitivity. Further, in mouse small bowel, the pharmacologic inhibition or genetic knockout of the epithelial Piezo2 led to an inhibition of the pressure‐induced short‐circuit current (I sc ) in the Ussing chamber. These results suggested that EEC Piezo2 plays a role in pressure‐induced epithelial ion transport, but the mechanism and whether these responses are region‐specific remains uknown. AIM Determine whether epithelial Piezo2‐mediated pressure‐induced I sc is due to Clsecretion in the mouse colon. METHODS Full‐thickness mid‐colon preparations of Vil Cre/+ ::Piezo2 f/f ( Piezo2 CKO ) or Vil +/+ ::Piezo2 f/f ( Piezo2 WT ) mice at 0.3 cm 2 were mounted in 4mL Ussing chambers with normal Krebs solution. The epithelial side was intermittently pressure‐clamped at a range of pressures (5, 10, 20, 30, 40, 60 mmHg) for 10s each. Forskolin (FSK, 10μM) was applied at the end of the experiments, and FSK response was used to normalize the pressure‐induced responses (ΔI sc /ΔI sc,FSK ). RESULTS Pressure applied to the mucosa of Piezo2 CKO and Piezo2 WT colons caused a pressure‐dependent increase in I sc . Responses in Piezo2 CKO colons were smaller than Piezo2 WT at 40mmHg (0.41±0.1 vs. 0.76±0.1) and 60mmHg (0.51±0.1 vs. 0.87±0.1) (n=9–11, P <0.05, two‐way ANOVA). To determine the nature of the pressure‐induced I sc we removed Cl − from the Krebs solutions. Cl‐removal resulted in XX. We found a nearloss in the mechanically induced ΔI sc in both Piezo2 WT tissues and Piezo2 CKO : 5mmHg (− 88.85±0.1% and −87.44±0.1% Piezo2 WT ), 10mmHg (−86.46±0.1% Piezo2 CKO and − 90.30±0.1% Piezo2 WT ), 20mmHg (−88.50±0.01% Piezo2 CKO and −89.86±0.1% Piezo2 WT ), 40mmHg (−91.78±0.1% Piezo2 CKO and −91.35±0.04% Piezo2 WT ), and 60mmHg (−93.93±0.04% Piezo2 CKO and −92.08±0.04% Piezo2 WT (n= 5–10, P <0.05, unpaired t ‐test). Replacement of Cl − led to full recovery of the mechanically induced ΔI sc in both Piezo2 WT and Piezo2 CKO tissues when tested at 30 mmHg ( Piezo2 WT : 2.51±1.4 vs. 73.52±33.8, n=6 and 3, P <0.05, unpaired t ‐test), ( Piezo2 CKO : 1.80±1.0 vs. 45.14±12.4, n=5 and 4, P <0.05, unpaired t ‐test). CONCLUSIONS Hydrostatic pressure applied to the colon epithelium leads to an increase in epithelial secretion that depends chloride and Piezo2 contributes to this mechanosensitive chloride secretion. Support or Funding Information Supported by AGA RSA, NIH DK106456, NIH DK119683, NIH DK123549