Chronic Nicotine Inhalation‐Induced Vascular Dysfunction is Mediated by the Alpha 7 Nicotinic Acetylcholine Receptor

Abstract

Cigarette smoking remains a leading risk factor for cardiopulmonary pathologies. However, the effects of nicotine, the addictive component of cigarettes, on cardiopulmonary function is not fully understood. Our laboratory has shown previously that chronic nicotine inhalation in mice leads to the development of pulmonary hypertension with right ventricular (RV) remodeling. This study aims to further examine the molecular mechanisms of nicotine-induced vascular dysfunction. We hypothesize that chronic nicotine inhalation-induced cardiopulmonary dysfunction is mediated by the α7-nicotinic acetylcholine receptor (nAChR). To investigate our hypothesis, male C57BL6/J wildtype (WT) and α7-nAChR global knockout (KO) mice were exposed to air (WT, n=10; α7-nAChR KO, n=7) or nicotine vapor (WT, n=10; α7-nAChR KO, n=10) daily, 12 hour on/12 hour off, for 3 months. After the 3-month exposure, mice were subjected to right heart catheterization to measure right ventricular systolic pressure (RVSP) as an index of pulmonary artery pressure. In contrast to WT mice, which developed increased RVSP (31.4 ± 1.5 mmHg in nicotine-exposed compared to 24.0 ± 1.3 mmHg in air controls, p = 0.002), α7-nAChR KO mice were protected from these nicotine effects (25.7 ± 0.8 mmHg in nicotine-exposed compared to 21.6 ± 2.0 mmHg in air controls, p = 0.218). In addition, thoracic aortas were isolated from WT and α7-nAChR KO mice following air or nicotine exposure and subjected to RNA-sequencing analysis. Aortas isolated from WT mice showed 123 differentially expressed genes (112 up and 11 down) in nicotine-exposed compared to controls, with 18 upregulated and 3 downregulated pathways as identified by the Ingenuity Pathway Analysis (IPA). Many of the top upregulated pathways are involved in inflammatory response, including acute phase response signaling (p = 4.91E-06), complement system (p = 5.71E-06), and interleukin (IL)-6 signaling (p = 1.88E-03). Furthermore, the Angiotensin II receptor type 1, an important effector controlling blood pressure and volume, was upregulated 4.48-fold (Adjusted p = 0.038). In contrast, only 7 none-overlapping genes were differentially regulated in α7-nAChR KO mice by nicotine compared with the air controls. Finally, vasoreactivity assays were performed on aortas isolated from air and nicotine-exposed WT mice, and aortas isolated from nicotine-exposed mice exhibited impaired endothelium-dependent vasodilation. In conclusion, we found that chronic nicotine inhalation-induced cardiopulmonary dysfunction is mediated by the α7-nAChR.