A novel TMEM16A splice variant lacking the dimerization domain contributes to calcium‐activated chloride secretion in human sweat gland epithelial cells

Abstract

Sweating is an important physiological process to regulate body temperature in humans, and various disorders are associated with dysregulated sweat formation. Primary sweat secretion in human eccrine sweat glands involves Ca(2+) -activated Cl(-) channels (CaCC). Recently, members of the TMEM16 family were identified as CaCCs in various secretory epithelia; however, their molecular identity in sweat glands remained elusive. Here, we investigated the function of TMEM16A in sweat glands. Gene expression analysis revealed that TMEM16A is expressed in human NCL-SG3 sweat gland cells as well as in isolated human eccrine sweat gland biopsy samples. Sweat gland cells express several previously described TMEM16A splice variants, as well as one novel splice variant, TMEM16A(acΔe3) lacking the TMEM16A-dimerization domain. Chloride flux assays using halide-sensitive YFP revealed that TMEM16A is functionally involved in Ca(2+) -dependent Cl(-) secretion in NCL-SG3 cells. Recombinant expression in NCL-SG3 cells showed that TMEM16A(acΔe3) is forming a functional CaCC, with basal and Ca(2+) -activated Cl(-) permeability distinct from canonical TMEM16A(ac). Our results suggest that various TMEM16A isoforms contribute to sweat gland-specific Cl(-) secretion providing opportunities to develop sweat gland-specific therapeutics for treatment of sweating disorders.

Role of CFTR in epithelial physiology

“…These cells are responsible for producing the primary ‘sweat’ secretion, together with various glycoproteins and AMPs, respectively [185, 203]. Clear cells express CFTR [203, 204] as well as a CaCC, most probably TMEM16A (ANO1) [205]. The myoepithelial cells are the third type of cells (Fig.…”

“…However, in the secretory coil, the major physiological stimulus is acetylcholine (ACh), which is released from post-ganglionic sympathetic cholinergic fibres, and which stimulates copious fluid transport through a non-CFTR dependent pathway. Although not fully resolved, the most likely Cl − exit pathway is via the TMEM16A Cl − channel, which has been localised to secretory cells [205], and which is activated by increases in cytosolic calcium via cholinergic stimulation. However, recent studies suggest that dark cells may also contribute to sweat secretion, but employ a distinct anion channel known as best2 (see [186] for further discussion), which may have an additional role in sweat pH and fluid regulation.…”

Regulation of epithelial ion transport in exocrine glands by store-operated Ca2+ entry

“…These include the Na + /K + ATPase pump [62, 63] and Ca 2+ -activated K + channels [29, 55, 64, 65] that establish the membrane potential and maintain the driving force for Cl − secretion. The main channels mediating Cl − secretion at the luminal membrane of sweat gland acinar cells are CaCCs [53, 66, 67]. Recent studies have shed light on the molecular nature of the CaCCs in murine and human sweat glands [53, 61, 66, 68, 69].…”

“…The main channels mediating Cl − secretion at the luminal membrane of sweat gland acinar cells are CaCCs [53, 66, 67]. Recent studies have shed light on the molecular nature of the CaCCs in murine and human sweat glands [53, 61, 66, 68, 69]. Bestrophin 2 (BEST2) is a CaCC that is necessary for sweat secretion as Best2 −/− mice showed a complete defect in spontaneous sweat production [61].…”

“…Whether BEST2 plays a role in mediating sweat secretion in response to cholinergic stimulation in mice or in humans remains to be investigated. In the human eccrine sweat gland cell line NCL-SG3, another CaCC, TMEM16A (also known as anoctamin 1, ANO1) was shown to be expressed at the transcriptional level [66]. Overexpression of the canonical TMEM16A isoform or one of its splice variants in NCL-SG3 cells mediated Cl − secretion, suggesting that TMEM16A may also contribute to Cl − secretion in primary human sweat glands [66].…”