Mazzone, Amelia

Objective This study was designed to evaluate the roles of microRNAs (miRNAs) in slow transit constipation (STC). Design All human tissue samples were from the muscularis externa of the colon. Expression of 372 miRNAs was examined in a discovery cohort of four patients with STC versus three age/sex-matched controls by a quantitative PCR array. Upregulated miRNAs were examined by quantitative reverse transcription qPCR (RT-qPCR) in a validation cohort of seven patients with STC and age/sex-matched controls. The effect of a highly differentially expressed miRNA on a custom human smooth muscle cell line was examined in vitro by RT-qPCR, electrophysiology, traction force microscopy, and ex vivo by lentiviral transduction in rat muscularis externa organotypic cultures. Results The expression of 13 miRNAs was increased in STC samples. Of those miRNAs, four were predicted to target SCN5A , the gene that encodes the Na + channel Na V 1.5. The expression of SCN5A mRNA was decreased in STC samples. Let-7f significantly decreased Na + current density in vitro in human smooth muscle cells. In rat muscularis externa organotypic cultures, overexpression of let-7f resulted in reduced frequency and amplitude of contraction. Conclusions A small group of miRNAs is upregulated in STC, and many of these miRNAs target the SCN5A-encoded Na + channel Na V 1.5. Within this set, a novel Na V 1.5 regulator, let-7f, resulted in decreased Na V 1.5 expression, current density and reduced motility of GI smooth muscle. These results suggest Na V 1.5 and miRNAs as novel diagnostic and potential therapeutic targets in STC.

ABSTRACT The Ca 2+ ‐activated Cl − channel, anoctamin 1 (Ano1, also known as transmembrane protein 16A) contributes to intestinal pacemaking, fluid secretion, cellular excitability, and tissue development. The human ANO1 promoter contains binding sites for the glioma‐associated oncogene (Gli) proteins. We investigated regulation of ANO1 transcription by Gli. ANO1 promoter activity was determined using a luciferase reporter system. Binding and functional effects of Glis on ANO1 transcription and expression were demonstrated by chromatin immunoprecipitation, small interfering RNA knockdown, PCR, immunolabeling, and recordings of Ca 2+ ‐activated Cl − currents in human embryonic kidney 293 (HEK293) cells. Results from previous genome‐wide association studies were used to test ANO1 promoter polymorphisms for association with disease. Gli1 and Gli2 bound to the promoter and repressed ANO1 transcription. Repression depended on Gli binding to a site close to the ANO1 transcriptional start site. Mutation of this site prevented Gli binding and transcriptional repression. Knockdown of Gli expression and inhibition of Gli activity increased expression of ANO1 RNA and Ca 2+ ‐activated Cl − currents in HEK293 cells. A single‐nucleotide polymorphism prevented Gli binding and showed association with irritable bowel syndrome. We conclude that Gli1 and Gli2 repress ANO1 by a novel mechanism that is independent of Gli cleavage and that has a role in gastrointestinal function.—Mazzone, A., Gibbons, S. J., Eisenman, S. T., Strege, P. R., Zheng, T., D'Amato, M., Ordog, T., Fernandez‐Zapico, M. E., Farrugia, G. Direct repression of anoctamin 1 (ANO1) gene transcription by Gli proteins. FASEB J. 33, 6632–6642 (2019). www.fasebj.org

The SCN5A-encoded voltage-gated mechanosensitive Na+channel NaV1.5 is expressed in human gastrointestinal smooth muscle cells and interstitial cells of Cajal. NaV1.5 contributes to smooth muscle electrical slow waves and mechanical sensitivity. In predominantly Caucasian irritable bowel syndrome (IBS) patient cohorts, 2–3% of patients have SCN5A missense mutations that alter NaV1.5 function and may contribute to IBS pathophysiology. In this study we examined a racially and ethnically diverse cohort of IBS patients for SCN5A missense mutations, compared them with IBS-negative controls, and determined the resulting NaV1.5 voltage-dependent and mechanosensitive properties. All SCN5A exons were sequenced from somatic DNA of 252 Rome III IBS patients with diverse ethnic and racial backgrounds. Missense mutations were introduced into wild-type SCN5A by site-directed mutagenesis and cotransfected with green fluorescent protein into HEK-293 cells. NaV1.5 voltage-dependent and mechanosensitive functions were studied by whole cell electrophysiology with and without shear force. Five of 252 (2.0%) IBS patients had six rare SCN5A mutations that were absent in 377 IBS-negative controls. Six of six (100%) IBS-associated NaV1.5 mutations had voltage-dependent gating abnormalities [current density reduction (R225W, R433C, R986Q, and F1293S) and altered voltage dependence (R225W, R433C, R986Q, G1037V, and F1293S)], and at least one kinetic parameter was altered in all mutations. Four of six (67%) IBS-associated SCN5A mutations (R225W, R433C, R986Q, and F1293S) resulted in altered NaV1.5 mechanosensitivity. In this racially and ethnically diverse cohort of IBS patients, we show that 2% of IBS patients harbor SCN5A mutations that are absent in IBS-negative controls and result in NaV1.5 channels with abnormal voltage-dependent and mechanosensitive function.NEW & NOTEWORTHY The voltage-gated Na+channel NaV1.5 contributes to smooth muscle physiology and electrical slow waves. In a racially and ethnically mixed irritable bowel syndrome cohort, 2% had mutations in the NaV1.5 gene SCN5A. These mutations were absent in irritable bowel syndrome-negative controls. Most mutant NaV1.5 channels were loss of function in voltage dependence or mechanosensitivity.

Anoctamin1 (Ano1 and TMEM16A) is a calcium-activated chloride channel specifically expressed in the interstitial cells of Cajal (ICC) of the gastrointestinal tract muscularis propria. Ano1 is necessary for normal electrical slow waves and ICC proliferation. The full-length human Ano1 sequence includes an additional exon, exon “0,” at the NH2 terminus. Ano1 with exon 0 [Ano1(0)] had a lower EC50 for intracellular calcium ([Ca2+]i) and faster chloride current ( ICl) kinetics. The Ano1 alternative splice variant with segment “c” encoding exon 13 expresses on the first intracellular loop four additional amino acid residues, EAVK, which alter ICl at low [Ca2+]i. Exon 13 is expressed in 75–100% of Ano1 transcripts in most human tissues but only 25% in the human stomach. Our aim was to determine the effect of EAVK deletion on Ano1(0) ICl parameters. By voltage-clamp electrophysiology, we examined ICl in HEK293 cells transiently expressing Ano1(0) with or without the EAVK sequence [Ano1(0)ΔEAVK]. The EC50 values of activating and deactivating ICl for [Ca2+]i were 438 ± 7 and 493 ± 9 nM for Ano1(0) but higher for Ano1(0)ΔEAVK at 746 ± 47 and 761 ± 26 nM, respectively. Meanwhile, the EC50 values for the ratio of instantaneous to steady-state ICl were not different between variants. Congruently, the time constant of activation was slower for Ano1(0)ΔEAVK than Ano1(0) currents at intermediate [Ca2+]i. These results suggest that EAVK decreases the calcium sensitivity of Ano1(0) current activation and deactivation by slowing activation kinetics. Differential expression of EAVK in the human stomach may function as a switch to increase sensitivity to [Ca2+]i via faster gating of Ano1. NEW & NOTEWORTHY Calcium-activated chloride channel anoctamin1 (Ano1) is necessary for normal slow waves in the gastrointestinal interstitial cells of Cajal. Exon 0 encodes the NH2 terminus of full-length human Ano1 [Ano1(0)], while exon 13 encodes residues EAVK on its first intracellular loop. Splice variants lack EAVK more often in the stomach than other tissues. Ano1(0) without EAVK [Ano1(0)ΔEAVK] has reduced sensitivity for intracellular calcium, attributable to slower kinetics. Differential expression of EAVK may function as a calcium-sensitive switch in the human stomach.

AbstractBackgroundThe SCN5A‐encoded voltage‐gated sodium channel NaV1.5 is expressed in human jejunum and colon. Mutations in NaV1.5 are associated with gastrointestinal motility disorders. The rat gastrointestinal tract expresses voltage‐gated sodium channels, but their molecular identity and role in rat gastrointestinal electrophysiology are unknown.MethodsThe presence and distribution of Scn5a‐encoded NaV1.5 was examined by PCR, Western blotting and immunohistochemistry in rat jejunum. Freshly dissociated smooth muscle cells were examined by whole cell electrophysiology. Zinc finger nuclease was used to target Scn5a in rats. Lentiviral‐mediated transduction with shRNA was used to target Scn5a in rat jejunum smooth muscle organotypic cultures. Organotypic cultures were examined by sharp electrode electrophysiology and RT‐PCR.Key ResultsWe found NaV1.5 in rat jejunum and colon smooth muscle by Western blot. Immunohistochemistry using two other antibodies of different portions of NaV1.5 revealed the presence of the ion channel in rat jejunum. Whole cell voltage‐clamp in dissociated smooth muscle cells from rat jejunum showed fast activating and inactivating voltage‐dependent inward current that was eliminated by Na+ replacement by NMDG+. Constitutive rat Scn5a knockout resulted in death in utero. NaV1.5 shRNA delivered by lentivirus into rat jejunum smooth muscle organotypic culture resulted in 57% loss of Scn5a mRNA and several significant changes in slow waves, namely 40% decrease in peak amplitude, 30% decrease in half‐width, and 7 mV hyperpolarization of the membrane potential at peak amplitude.Conclusions & InferencesScn5a‐encoded NaV1.5 is expressed in rat gastrointestinal smooth muscle and it contributes to smooth muscle electrophysiology.

Anoctamin 1 (Ano1; TMEM16A) is a Ca2+-activated Cl− channel (CACC) expressed in interstitial cells of Cajal. The mechanisms by which Ca2+ regulates Ano1 are incompletely understood. In the gastrointestinal tract, Ano1 is required for normal slow wave activity and is involved in regulating cell proliferation. Splice variants of Ano1 have varying electrophysiological properties and altered expression in disease states. Recently, we identified a transcript for human Ano1 containing a novel exon-“exon 0” upstream of and in frame with exon 1. The electrophysiological properties of this longer Ano1 isoform are unknown. Our aim was to determine the functional contribution of the newly identified exon to the Ca2+ sensitivity and electrophysiological properties of Ano1. Constructs with [Ano1(+0)] or without [Ano1(−0)] the newly identified exon were transfected into human embryonic kidney-293 cells. Voltage-clamp electrophysiology was used to determine voltage- and time-dependent parameters of whole cell Cl− currents between isoforms with varying concentrations of intracellular Ca2+, extracellular anions, or Cl− channel inhibitors. We found that exon 0 did not change voltage sensitivity and had no impact on the relative permeability of Ano1 to most anions. Ano1(+0) exhibited greater changes in current density but lesser changes in kinetics than Ano1(−0) in response to varying intracellular Ca2+. The CACC inhibitor niflumic acid inhibited current with greater efficacy and higher potency against Ano1(+0) compared with Ano1(−0). Likewise, the Ano1 inhibitor T16Ainh-A01 reduced Ano1(+0) more than Ano1(−0). In conclusion, human Ano1 containing exon 0 imparts its Cl− current with greater sensitivity to intracellular Ca2+ and CACC inhibitors.

Human jejunum smooth muscle cells (SMCs) and interstitial cells of Cajal (ICCs) express the SCN5A-encoded voltage-gated, mechanosensitive sodium channel NaV1.5. NaV1.5 contributes to small bowel excitability, and NaV1.5 inhibitor ranolazine produces constipation by an unknown mechanism. We aimed to determine the presence and molecular identity of Na+ current in the human colon smooth muscle and to examine the effects of ranolazine on Na+ current, mechanosensitivity, and smooth muscle contractility. Inward currents were recorded by whole cell voltage clamp from freshly dissociated human colon SMCs at rest and with shear stress. SCN5A mRNA and NaV1.5 protein were examined by RT-PCR and Western blots, respectively. Ascending human colon strip contractility was examined in a muscle bath preparation. SCN5A mRNA and NaV1.5 protein were identified in human colon circular muscle. Freshly dissociated human colon SMCs had Na+ currents (−1.36 ± 0.36 pA/pF), shear stress increased Na+ peaks by 17.8 ± 1.8% and accelerated the time to peak activation by 0.7 ± 0.3 ms. Ranolazine (50 μM) blocked peak Na+ current by 43.2 ± 9.3% and inhibited shear sensitivity by 25.2 ± 3.2%. In human ascending colon strips, ranolazine decreased resting tension (31%), reduced the frequency of spontaneous events (68%), and decreased the response to smooth muscle electrical field stimulation (61%). In conclusion, SCN5A-encoded NaV1.5 is found in human colonic circular smooth muscle. Ranolazine blocks both peak amplitude and mechanosensitivity of Na+ current in human colon SMCs and decreases contractility of human colon muscle strips. Our data provide a likely mechanistic explanation for constipation induced by ranolazine.

Anoctamin‐1 (Ano1) is a widely expressed protein responsible for endogenous Ca 2+ ‐activated Cl 2 currents. Ano1 is overexpressed in cancer. Differential expression of transcriptional variants is also found in other diseases. However, the mechanisms underlying regulation of Ano1 are unknown. This study identifies the Ano1 promoter and defines a mechanism for regulating its expression. Next‐generation RNA sequencing (RNA‐seq) analysis in human gastric muscle found a new exon upstream of the reported exon 1 and identified a promoter proximal to this new exon. Reporter assays in human embryonic kidney 293 cells showed a 6.7 ± 2.1fold increase in activity over empty vector. Treatment with a known regulator of Ano1 expression, IL‐4, increased promoter activity by 1.6 ± 0.02‐fold over untreated cells. The promoter region contained putative binding sites for multiple transcription factors including signal transducer and activator of transcription 6 (STAT6), a downstream effector of IL‐4. Chromatin immunoprecipitation (ChIP) experiments on T84 cells, which endogenously express Ano1, showed a 2.1 ± 0.12‐fold increase in binding of STAT6 to P0 after IL‐4 treatment. These results were confirmed by mutagenesis, expression, and RNA interference techniques. This work allows deeper understanding of the regulation of Ano1 in physiology and as a potential therapeutic target in a variety of diseases—Mazzone, A., Gibbons, S. J., Bernard, C. E., Nowsheen, S., Middha, S., Almada, L. L., Ordog, T., Kendrick, M. L., Reid Lombardo, KM., Shen, K. R., Galietta, L. J. V., Fernandez‐Zapico, M. E., and Farrugia, G., Identification and characterization of a novel promoter for the human ANO1 gene regulated by the transcription factor signal transducer and activator of transcription 6 (STAT6). FASEB J. 29, 152–163 (2015). www.fasebj.org

Key points Ano1, a Ca2+‐activated Cl− channel, is expressed in interstitial cells of Cajal (ICC) throughout the gut. We report here that it is required to maintain coordinated Ca2+ transients within myenteric ICC of mouse small intestine. Ca2+ transients in Ano1 WT mice were rhythmic and coordinated whereas uncoordinated Ca2+ transients were seen in knockout mice. Ca2+ transients were un‐coordinated following pharmacological block of Ano1 in WT mice using niflumic acid, 5‐nitro‐2‐(3‐phenylpropylamino) benzoic acid and 4,4′‐diisothiocyanato‐2,2′‐stilbenedisulfonic acid disodium salt. Transient knockdown of Ano1 in organotypic cultures with short hairpin RNA to Ano1 in WT tissues also caused loss of coordinated Ca2+ transients. Contractility of Ano1 knockout mouse intestinal segments in organ bath experiments was significantly decreased, less coordinated and non‐rhythmic. Spatiotemporal maps from knockout mouse small intestine also showed loss of phasic contractile activity. This study provides important information on the basic mechanisms driving coordinated contractile activity in the gastrointestinal tract. AbstractInterstitial cells of Cajal (ICC) are pacemaker cells that generate electrical activity to drive contractility in the gastrointestinal tract via ion channels. Ano1 (Tmem16a), a Ca2+‐activated Cl− channel, is an ion channel expressed in ICC. Genetic deletion of Ano1 in mice resulted in loss of slow waves in smooth muscle of small intestine. In this study, we show that Ano1 is required to maintain coordinated Ca2+ transients between myenteric ICC (ICC‐MY) of small intestine. First, we found spontaneous Ca2+ transients in ICC‐MY in both Ano1 WT and knockout (KO) mice. However, Ca2+ transients within the ICC‐MY network in Ano1 KO mice were uncoordinated, while ICC‐MY Ca2+ transients in Ano1 WT mice were rhythmic and coordinated. To confirm the role of Ano1 in the loss of Ca2+ transient coordination, we used pharmacological inhibitors of Ano1 activity and shRNA‐mediated knock down of Ano1 expression in organotypic cultures of Ano1 WT small intestine. Coordinated Ca2+ transients became uncoordinated using both these approaches, supporting the conclusion that Ano1 is required to maintain coordination/rhythmicity of Ca2+ transients. We next determined the effect on smooth muscle contractility using spatiotemporal maps of contractile activity in Ano1 KO and WT tissues. Significantly decreased contractility that appeared to be non‐rhythmic and uncoordinated was observed in Ano1 KO jejunum. In conclusion, Ano1 has a previously unidentified role in the regulation of coordinated gastrointestinal smooth muscle function through coordination of Ca2+ transients in ICC‐MY.