Chronic excessive alcohol consumption can cause cardiac dilation and dysfunction, clinically termed alcoholic cardiomyopathy (AC). While chronic alcohol abuse alone causes AC, clinical evidence indicates that alcohol can also exacerbate cardiac dysfunction due to other cardiac injury or stress. As many as one third of all dilated cardiomyopathies are attributed to alcohol abuse. The development of cardiac fibrosis appears to be a key mechanism of AC dysfunction, as fibrosis impairs ventricular filling and impedes cardiomyocyte contraction. Our long term goal is to identify the mechanisms responsible for alcohol-induced cardiac injury, which can then be targeted for clinical benefit. Although the cause of alcohol-induced fibrosis is not known, oxidative stress is believed to play a role. NADPH oxidases (NOX)-2 and -4 are the predominant subtypes found in the heart, and are the primary sources of cardiac oxidant stress. In non-cardiac cells, ethanol (EtOH) produces oxidative stress by increasing the expression of NOXs. Increased expression of NOXs is also associated with fibroblast activation. When fibroblasts are activated, they transform into myofibroblasts, and produce excess collagen. This transformation and activation of cardiac fibroblasts is mediated by NOXs. Our central hypothesis is that chronic exposure to ethanol exacerbates cardiac fibrosis and dysfunction in the volume overloaded heart by increasing oxidative stress via NOX-2 and -4. Using both in vivo EtOH exposure and volume overload models coupled with cardiac fibroblast cell culture, we investigate the following aims:
Aim 1. Assess the mechanisms by which ethanol causes fibroblast activation and fibrosis. The cellular mechanisms underlying EtOH upregulation of collagen and cardiac fibroblast activation are dissected in a systematic approach using cardiac fibroblasts from our EtOH exposure model. NOX-2 and 4 are targeting using lentiviral delivery of shRNA and pharmacological inhibitors. Flow cytometry is used to assess the relative number of myofibroblasts to fibroblasts in hearts of rats chronically exposed to EtOH. NOXs are also targeted in vivo to assess their role in EtOH-induced cardiac damage.
Aim 2. Test the prediction that chronic exposure to ethanol accelerates cardiac dysfunction in the volume overloaded heart by promoting oxidative stress and fibrosis. A clinically relevant rodent model of volume overload is used to examine the effects of ethanol on ventricular structural and functional remodeling. Outcome measures include cardiac diastolic and systolic function, ventricular chamber dimensions, collagen typing and cross-linking, oxidative stress, and interstitial fibrosis. Cardiac function is measured using both ultrasound echocardiography and pressure-volume conductance catheter. Fibrotic endpoints include histology (collagen volume fraction), and collagen mRNA and protein expression by qPCR and western blot. Multiple measures of tissue oxidant stress are made, including 8-isoprostane, oxidized/total glutathione and malondialdehyde. Studies will provide the groundwork for translation studies and targeted therapies for alcohol-induced fibrosis and cardiomyopathy.
The chronic abuse of alcohol causes alcoholic cardiomyopathy, which is characterized by cardiac fibrosis, ventricular chamber enlargement, and heart failure. Treatment and prevention strategies are limited, as the damaging cardiac effects of chronic alcohol abuse are poorly understood. Our studies will identify key mechanisms of alcohol-induced fibrosis and cardiac dysfunction, which can then be targeted for therapeutic benefit.