ANO1 (TMEM16A) Genetic Variants, Promoter Methylation, and Chloride Dysregulation in Pulmonary Hypertension

Background: Pulmonary arterial hypertension (PAH) is a rare and progressive disorder characterized by increased pulmonary vascular resistance and vascular remodeling. Genetic polymorphisms, epigenetic modifications, and ion channel dysregulation are increasingly recognized as key contributors to disease pathogenesis. Anoctamin-1 (ANO1/TMEM16A), a calcium-activated chloride channel, plays a critical role in vascular tone regulation. Objective: This study aimed to investigate the association between ANO1 gene polymorphisms (rs7127129 and rs2509153), promoter methylation status, and serum chloride levels in patients with idiopathic pulmonary arterial hypertension (IPAH), congenital heart disease (CHD), and chronic thromboembolic pulmonary hypertension (CTEPH). Methods: A total of 106 IPAH patients, 40 CHD patients, and 30 CTEPH patients, together with 125 healthy controls, were included. The control group had a comparable age distribution, with a balanced sex ratio, whereas females predominated in all three PH groups. Genotyping was performed using TaqMan-based real-time PCR. Promoter methylation was analyzed using bisulfite conversion followed by quantitative real-time PCR. Serum chloride levels were measured using an ion-selective electrode method. Results: No significant association was observed between rs7127129 and rs2509153 polymorphisms and IPAH or CTEPH (p > 0.05). However, rs7127129 showed a significant association with CHD (p < 0.05). After excluding hypertensive patients, both polymorphisms remained significantly associated with CHD. Serum chloride levels differed significantly among groups (p < 0.001), with higher levels observed particularly in the CTEPH and CHD groups compared to controls, while IPAH patients exhibited intermediate but still elevated levels relative to controls. In contrast, promoter methylation levels were significantly lower in all patient groups compared to controls. An inverse relationship between chloride levels and methylation status was observed. Conclusions: ANO1 polymorphisms are not major determinants of IPAH or CTEPH but may contribute to CHD susceptibility. Increased serum chloride levels, together with decreased promoter methylation, suggest a potential mechanistic link between ion channel dysregulation and epigenetic alterations in pulmonary hypertension. Further large-scale and functional studies are warranted.