Phosphate position is key in mediating transmembrane ion channel TMEM16A-phosphatidylinositol 4,5-bisphosphate interaction

TransMEMbrane 16A (TMEM16A) is a Ca2+-activated Cl- channel that plays critical roles in regulating diverse physiologic processes, including vascular tone, sensory signal transduction, and mucosal secretion. In addition to Ca2+, TMEM16A activation requires the membrane lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). However, the structural determinants mediating this interaction are not clear. Here, we interrogated the parts of the PI(4,5)P2 head group that mediate its interaction with TMEM16A by using patch- and two-electrode voltage-clamp recordings on oocytes from the African clawed frog Xenopus laevis, which endogenously express TMEM16A channels. During continuous application of Ca2+ to excised inside-out patches, we found that TMEM16A-conducted currents decayed shortly after patch excision. Following this rundown, we show that the application of a synthetic PI(4,5)P2 analog produced current recovery. Furthermore, inducible dephosphorylation of PI(4,5)P2 reduces TMEM16A-conducted currents. Application of PIP2 analogs with different phosphate orientations yielded distinct amounts of current recovery, and only lipids that include a phosphate at the 4' position effectively recovered TMEM16A currents. Taken together, these findings improve our understanding of how PI(4,5)P2 binds to and potentiates TMEM16A channels.

TMEM16A regulates the cell cycle of pulmonary artery smooth muscle cells in high-flow-induced pulmonary arterial hypertension rat model

High-flow-induced pulmonary arterial hypertension (PAH) has attained global notoriety, the mechanism of which remains elusive. The present study investigated the regulation of Anoctamin-1, also known as transmembrane member 16A (TMEM16A), in the cell cycle progression of pulmonary artery smooth muscle cells (PASMCs) from a PAH rat model induced by high pulmonary blood flow. A total of 30 Sprague-Dawley rats were randomly assigned into control, sham and shunt groups. A rat model of high pulmonary blood flow-induced PAH was established by surgery using abdominal aorta-inferior vena cava fistula. Right ventricular pressure, right ventricular hypertrophy index and pulmonary arteriole structural remodeling were assessed 11 weeks following operation. The cell cycle statuses of PASMCs was assessed via flow cytometry, whereas western blot analysis was performed to measure the expression of cyclin D1, CDK2, p27KIP and cyclin E in primary PASMCs isolated from rats. The expression of cyclin E and cyclin D1 was revealed to be increased in the shunt group compared with the control group, which was accompanied with an increased expression of TMEM16A in the shunt group. Changes in the ratio of PASMCs in the G0/G1, S and G2/M phases of cycle induced by PAH were reversed by TMEM16A knockdown. The expression of cyclin E and cyclin D1 in the shunt group was significantly higher compared with the control group in vitro, which was reversed by TMEM16A-siRNA transfection. In conclusion, TMEM16A may be involved in high pulmonary blood flow-induced PAH by regulating PASMC cell cycle progression.

TMEM16A ameliorates vascular remodeling by suppressing autophagy via inhibiting Bcl-2-p62 complex formation

Rationale: Transmembrane member 16A (TMEM16A) is a component of calcium-activated chloride channels that regulate vascular smooth muscle cell (SMC) proliferation and remodeling. Autophagy, a highly conserved cellular catabolic process in eukaryotes, exerts important physiological functions in vascular SMCs. In the current study, we investigated the relationship between TMEM16A and autophagy during vascular remodeling. Methods: We generated a transgenic mouse that overexpresses TMEM16A specifically in vascular SMCs to verify the role of TMEM16A in vascular remodeling. Techniques employed included immunofluorescence, electron microscopy, co-immunoprecipitation, and Western blotting. Results: Autophagy was activated in aortas from angiotensin II (AngII)-induced hypertensive mice with decreased TMEM16A expression. The numbers of light chain 3B (LC3B)-positive puncta in aortas correlated with the medial cross-sectional aorta areas and TMEM16A expression during hypertension. SMC-specific TMEM16A overexpression markedly inhibited AngII-induced autophagy in mouse aortas. Moreover, in mouse aortic SMCs (MASMCs), AngII-induced autophagosome formation and autophagic flux were blocked by TMEM16A upregulation and were promoted by TMEM16A knockdown. The effect of TMEM16A on autophagy was independent of the mTOR pathway, but was associated with reduced kinase activity of the vacuolar protein sorting 34 (VPS34) enzyme. Overexpression of VPS34 attenuated the effect of TMEM16A overexpression on MASMC proliferation, while the effect of TMEM16A downregulation was abrogated by a VPS34 inhibitor. Further, co-immunoprecipitation assays revealed that TMEM16A interacts with p62. TMEM16A overexpression inhibited AngII-induced p62-Bcl-2 binding and enhanced Bcl-2-Beclin-1 interactions, leading to suppression of Beclin-1/VPS34 complex formation. However, TMEM16A downregulation showed the opposite effects. Conclusion: TMEM16A regulates the four-way interaction between p62, Bcl-2, Beclin-1, and VPS34, and coordinately prevents vascular autophagy and remodeling.

Slowed gastric emptying and improved oral glucose tolerance produced by a nanomolar-potency inhibitor of calcium-activated chloride channel TMEM16A

Interstitial cells of Cajal, which express the calcium-activated chloride channel transmembrane member 16A (TMEM16A), are an important determinant of gastrointestinal (GI) motility. We previously identified the acylaminocycloalkylthiophene class of TMEM16A inhibitors, which, following medicinal chemistry, gave analog 2-bromodifluoroacetylamino-5,6,7,8-tetrahydro-4H-cyclohepta[b]thiophene-3-carboxylic acid o-tolylamide (TMinh-23) with 30 nM half-maximal inhibitory concentration. Here, we tested the efficacy of TMinh-23 for inhibition of GI motility in mice. In isolated murine gastric antrum, TMinh-23 strongly inhibited spontaneous and carbachol-stimulated rhythmic contractions. Pharmacokinetic analysis showed predicted therapeutic concentrations of TMinh-23 for at least 4 h following a single oral or intraperitoneal dose at 10 mg/kg. Gastric emptying, as assessed following an oral bolus of phenol red or independently by [99mTc]-diethylenetriamine pentaacetic acid scintigraphy, was reduced by TMinh-23 by ∼60% at 20 min. Interestingly, there was little effect of TMinh-23 on baseline whole-gut transit time or time to diarrhea induced by castor oil. Consequent to the delay in gastric emptying, TMinh-23 administration significantly reduced the elevation in blood sugar in mice following an oral but not intraperitoneal glucose load. These results provide pharmacological evidence for involvement of TMEM16A in gastric emptying and suggest the utility of TMEM16A inhibition in disorders of accelerated gastric emptying, such as dumping syndrome, and potentially for improving glucose tolerance in diabetes mellitus/metabolic syndrome and enhancing satiety in obesity.-Cil, O., Anderson, M. O., Yen, R., Kelleher, B., Huynh, T. L., Seo, Y., Nilsen, S. P., Turner, J. R., Verkman, A. S. Slowed gastric emptying and improved oral glucose tolerance produced by a nanomolar-potency inhibitor of calcium-activated chloride channel TMEM16A.

Epithelial disruptions, but not immune cell invasion, induced secretory dysfunction following innate immune activation in a novel model of acute salivary gland injury

BACKGROUND

Salivary gland (SG) injurious agents are all translated into loss of salivation (xerostomia). An association has been established between activation of innate immunity and SG injury and dysfunction. However, it remains unclear how the secretory epithelia respond by halting saliva production.

METHODS

C57BL/6 submandibular glands (SMGs) were acutely challenged using a single dose of the innate immune stimulant: polyinosinic-polycytidylic acid (poly (I:C)). Secretory capacity of the infected SMGs was substantiated by assessing the flow rate in response to pilocarpine stimulation. Depletion of the acute inflammatory cells was achieved by pre-treating mice with RB6-8C5 depletion antibody. Flow cytometry, histology and immunohistochemistry were conducted to verify the immune cell depletion. Epithelial expression of saliva-driving molecules: muscarinic 3 receptor (M3R), aquaporin 5 water channel (AQP5), Na-K-CL-Cotransporter 1 (NKCC1) and transmembrane member 16A (TMEM16A), was characterized using RT-qPCR and immunohistochemistry. Tight junction (TJ) protein; zonula occludens (ZO-1) and basement membrane (BM) protein; and laminin were assessed by immunohistochemistry.

RESULTS

Innate immune challenge prompted dysfunction in the exocrine SGs. Dysregulated gene and protein expression of molecules that drive saliva secretion was substantiated. Aberrant expression of TJ and BM proteins followed innate immune activation. Hyposalivation in the current model was independent of myeloperoxidase (MPO)-positive, acute inflammatory cells.

CONCLUSIONS

In this study, we developed a novel injury model of the SGs, featuring acute secretory dysfunction and immediate structural disruptions. Our results ruled out the injurious role of aggressively infiltrating inflammatory cells.