Abstract P1174: Nicotine Alters PHLPP Isoforms In The Heart To Increase Susceptibility To Injury

Abstract

Rationale: The impact of nicotine exposure through vaping on cardiovascular (CV) protective signaling basally or following injury remains largely unknown. Recent studies have shown that PHLPP1 deletion increased activity of AKT in the heart and reduced injury whereas PHLPP2 deletion exacerbated cardiac injury. Preliminary studies in vivo found that systemic exposure to nicotine increased PHLPP1 and decreased PHLPP2 expression in heart. Determining the mechanism of nicotine induced PHLPP alterations will demonstrate the impact of nicotine use on CV function and physiology and whether targeting PHLPP will reduce injury. Hypothesis: We hypothesize that nicotine compromises metabolic adaptation of the heart to injury by altering PHLPP isoforms and dysregulating mitochondrial biogenesis and oxidative stress signaling. Methods: Male and female wild-type (WT, n=4) and PHLPP1 knockout (KO, n=4) 4-6 weeks of age were implanted with osmotic minipumps containing nicotine (5mg/kg/day) or saline for 7 days. For in vitro study, NRVMs were isolated and PHLPP isoforms were targeted with siRNA or overexpressed using adenoviruses. Cardiomyocytes were stimulated with nicotine (100nM, 48hrs). Results: Nicotine increased PHLPP1 expression (1.7 ± 0.25-fold vs. WT saline) in the heart and decreased PHLPP2 (0.8 ± 0.04-fold vs. WT saline) whereas the KO exhibited increased PHLPP2 (1.5 ± 0.04-fold vs KO saline) levels. Nicotine administration significantly decreased genes involved in mitochondrial biogenesis and antioxidant signaling in WT mice while significantly increasing in KO hearts. Cardiomyocytes stimulated with nicotine (48h) significantly increased PHLPP1 (1.9 ± 0.39-fold vs PBS) and ROS. Nicotine significantly decreased mitochondrial respiration as did overexpression of PHLPP1. Finally, knockdown of PHLPP1 significantly increased mitochondrial respiration. Conclusions: Increases in PHLPP1 in the heart and cardiomyocytes from nicotine exposure has detrimental effects on oxidative stress and mitochondrial respiration. Future studies will investigate the molecular mechanisms by which nicotine alters PHLPP protein expression in heart and whether targeting PHLPP1 could reduce cardiovascular injury induced by nicotine exposure.