Dextran sulfate sodium-induced chronic colitis attenuates Ca²⁺-activated Cl⁻ secretion in murine colon by downregulating TMEM16A

Abstract

Attenuated Ca-activated Cl secretion has previously been observed in the model of dextran sulfate sodium (DSS)-induced colitis. Prior studies have implicated dysfunctional muscarinic signaling from basolateral membranes as the potential perpetrator leading to decreased Ca-activated Cl secretion. However, in our chronic model of DSS-colitis, cholinergic receptor muscarinic 3 ( Chrm3) transcript (1.028 ± 0.12 vs. 1.029 ± 0.27, P > 0.05) and CHRM3 protein expression (1.021 ± 0.24 vs. 0.928 ± 0.09, P > 0.05) were unchanged. Therefore, we hypothesized that decreased carbachol (CCH)-stimulated Cl secretion in DSS-induced colitis could be attributed to a loss of Ca-activated Cl channels (CaCC) in apical membranes of colonic epithelium. To establish this chemically-induced colitis, Balb/C mice were exposed to 4% DSS for five alternating weeks to stimulate a more moderate, chronic colitis. Upon completion of the protocol, whole thickness sections of colon were mounted in an Ussing chamber under voltage-clamp conditions. DSS-induced colitis demonstrated a complete inhibition of basolateral administration of CCH-stimulated Cl secretion that actually displayed a reversal in polarity (15.40 ± 2.22 μA/cm vs. -2.47 ± 0.25 μA/cm). Western blotting of potential CaCCs, quantified by densitometric analysis, demonstrated no change in bestrophin-2 and cystic fibrosis transmembrane regulator, whereas anoctamin-1 [ANO1, transmembrane protein 16A (TMEM16A)] was significantly downregulated (1.001 ± 0.13 vs. 0.510 ± 0.12, P < 0.05). Our findings indicate that decreased expression of TMEM16A in DSS-induced colitis contributes to the decreased Ca-activated Cl secretion in murine colon.

Normal Calcium-Activated Anion Secretion in a Mouse Selectively Lacking TMEM16A in Intestinal Epithelium

“…Experiments in the Tmem16a -/- mouse pups have shown that there is a reduction in the intestinal Ca 2+ -dependent chloride secretion (Ousingsawat et al, 2009). Similar results were observed when Tmem16a was specifically silenced from the intestinal epithelium of adult mice (Schreiber et al, 2015) and, more recently, calcium-activated chloride secretion has been reported to be decreased concomitantly to TMEM16A expression in mouse colon (Rottgen et al, 2018). Nevertheless, we and others have determined that both cAMP and Ca +2 -activated chloride secretion are occurring via CFTR exclusively in both human and mouse intestine (Seidler et al, 1997; Mall et al, 2000a,b; Zdebik et al, 2004; Bijvelds et al, 2009; Flores et al, 2009; Philp et al, 2018).…”

Goblet cell LRRC26 regulates BK channel activation and protects against colitis in mice

“…We therefore measured short circuit current (I SC ) across pieces of distal colon stripped of smooth muscle after equilibrating the tissues for 30 min in symmetrical Krebs solution. Similar to previously reported values for basal I SC of mouse distal colonic mucosae (30, 47, 48), our WT tissues showed on average a basal I SC = 21.6 ± 10.0 μA/cm 2 (mean ± SD, n=10) (Fig. 4A-B, E).…”

Dual role of Ca2+-activated Cl− channel transmembrane member 16A in lipopolysaccharide-induced intestinal epithelial barrier dysfunction in vitro

“…Dysfunction of Cl − secretion has been observed in intestinal inflammation, and TMEM16A has been identified as the primary mediator of Ca 2+ -activated Cl − secretion in the colonic epithelium 43,44 . TMEM16A protein levels were decreased in a DSS-induced colitis model, and the authors predicted that the colitis was caused by downregulation of TMEM16A due to the stimulation of Th2 cytokines by DSS 45 . However, the mechanism responsible for mediating the downregulation of TMEM16A is unclear.…”