Imbalance of NKCC1/KCC2 contributes to the pathogenesis of primary focal hyperhidrosis.

Background: Primary focal hyperhidrosis (PFH) is characterized by excessive sweating in localized regions, significantly impacting patients' quality of life. The imbalance between sodium-potassium-chloride cotransporter 1 (NKCC1) and potassium-chloride cotransporter 2 (KCC2) disrupts chloride ion homeostasis, potentially contributing to the pathogenesis of PFH.

Methods: Sweat gland tissues from 76 healthy controls and 76 PFH patients were collected. Expression levels of NKCC1 and KCC2 were assessed using quantitative real-time PCR and Western blotting. Primary sweat gland cells isolated from PFH patients (PFH-SG) and controls (NPFH-SG) were subjected to NKCC1 knockdown via lentiviral shRNA transfection. A hyperhidrosis mouse model was induced by intraperitoneal injection of pilocarpine hydrochloride, and mice were pretreated with the NKCC1 inhibitor bumetanide for one week. Sweat secretion, serum acetylcholine, and chloride ion concentrations were measured. Expression levels of aquaporin 5 (AQP5), brain-derived neurotrophic factor (BDNF), and neuregulin-1 (NRG-1) proteins were analyzed.

Results: PFH tissues showed significantly elevated NKCC1 and decreased KCC2 expression compared to controls, correlating with lower sweat chloride levels. NKCC1 knockdown in PFH-SG cells reduced elevated AQP5 expression. In vivo, bumetanide treatment markedly reduced sweat secretion, lowered serum acetylcholine, and restored chloride ion concentrations in hyperhidrosis mice. Furthermore, bumetanide treatment significantly decreased expressions of BDNF and NRG-1 in sympathetic ganglia axons, indicating attenuation of sympathetic hyperactivity associated with hyperhidrosis. NKCC1/KCC2 imbalance contributes significantly to PFH pathology.

Conclusions: Bumetanide effectively improves this imbalance, reducing excessive sweating and modulating related neurotransmitter signaling, offering potential therapeutic avenues for PFH.