Type 2 diabetes (T2D) is rapidly becoming a global pandemic and is projected to afflict more than 300 million individuals worldwide by the year 2025. This disease constitutes a major independent risk factor for heart attack and myocardial cell death. The current lines of drug therapy are insufficient to control this devastating disease and its serious cardiovascular complications. Based on our ample preliminary data, the current project is designed to test the following central HYPOTHESIS: Chronic inhibition of phosphodiesterase-5 (PDE-5) protects T2D hearts through suppression of myocardial oxidative stress and inflammasome formation via the AMPK/Sirt1/PGC-1 signal transduction network that leads to induction of mitochondrial antioxidant enzyme - glutathione S-transferase kappa 1 (GSTK1) and improvement of mitochondrial function. We propose the following 3 specific aims.
Aim 1 : PDE-5 inhibition with tadalafil activates AMPK/Sirt1/PGC-1 signaling pathway and attenuates cell death (necrosis/apoptosis) and mitochondrial respiratory chain dysfunction following myocardial ischemia/reperfusion (I/R) in T2D. Using db/db and high fat diet (HFD)-fed T2D mice, we will demonstrate the effect of tadalafil treatment on a) AMPK phosphorylation, eNOS and nitric oxide generation; b) the possible loss of cardioprotection in the AMPK2 dominant negative transgenic mice following I/R; c) the role of AMPK in activating Sirt1 and PGC-1; and d) the potential interplay of cGMP-dependent protein kinase (PKG) and AMPK/Sirt1/PGC-1 signal transduction network in attenuation of cardiomyocyte apoptosis/necrosis and mitochondrial respiratory chain dysfunction following I/R.
Aim 2 : PDE-5 inhibition restores depressed level of mitochondrial GSTK1 in the T2D hearts and attenuates I/R injury via its antioxidant as well as lipid-regulating properties. Using GSTK1 knockout mice with HFD-induced T2D, we will demonstrate the causative role of GSTK1 in PDE-5 inhibitor-induced cardioprotection and lipid regulating properties in T2D. We will also induce targeted overexpression of GSTK1 by direct intramyocardial injection of adenoviral GSTK1 to demonstrate the direct cause and effect relationship of GSTK1 in reducing I/R injury in T2D hearts.
Aim 3 : PDE-5 inhibitors attenuate inflammation through suppression of inflammasome and inhibition of caspase-1 in diabetic heart. We will examine: a) the role of PDE-5 inhibitors in attenuating inflammosome formation with consequent inhibition of caspase-1 activity following I/R in the heart and cardiomyocytes; b) the role of AMPK and Sirt-1 in attenuation of inflammasome formation; c) the involvement of AMPK, GSTK1, and PKG1 in prevention of inflammasome formation following I/R. Overall, the proposed studies will pave the way to a potentially novel pharmacotherapy against inflammation and cardiac injuries resulting from T2D conditions.
Oxidative stress, endothelial dysfunction and inflammation are critical early cellular events that lead to the development of Type 2 diabetes which has serious consequences in the development of cardiovascular diseases with devastating outcomes such as coronary artery disease, myocardial infarction, hypertrophy, and heart failure. The project goal is to test a novel and innovative hypothesis that phosphodiesterase-5 inhibitors including sildenafil (Viagra) and tadalafil (Cialis) may have a positive role in halting inflammatin and damage to the diabetic heart following heart attack. We believe that our study will have an immediate impact in the development of novel cardioprotective strategies leading to long-term beneficial outcome in heart disease, especially in patients with Type 2 diabetes.
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