Caveolae and the Aged Myocardium

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DESCRIPTION (provided by applicant): With the aging of the United States population, it is estimated that the elderly (>65 years of age) will increase from 13-14% to 25% by 2035. If this trend continues, >50% of the United States population and >2 billion people worldwide will be "aged" in the next 50 years. Aged individuals face formidable challenges to their health, as aging is associated with a myriad of diseases. Cardiovascular disease is the leading cause of morbidity and mortality in the United States with >50% of mortality attributed to coronary artery disease and >80% of these deaths occurring in those age 65 and older. Aged hearts are more sensitive than young hearts to ischemic insults and less responsive to cardiac protective strategies. A number of theories have been proposed to account for this aging deficit. These theories either invoke a genetic (i.e., there is a programmed regulation of gene expression that declines or accelerates with age in post-mitotic cells), a biochemical (i.e., altered metabolism leading to a mismatch of energy utilization/generation, diminished mitochondrial function leading to generation of toxic species such as free radicals and protein modification to reduce function), a catabolic (i.e., an inability to recycle cellular material at the cellular and organelle level and altered mitochondrial turnover), or a physiologic (i.e., declining ischemic tolerance) component. Though the mechanisms that underlie an age-related deficit in ischemic tolerance are not clear, they likely involve abnormalities in cellular signaling and mitochondria that are a combined result of genetic, biochemical, catabolic, and physiologic deficiencies. Therapeutics that target these mechanisms have potential to rescue the aged myocardium. Our preliminary studies show that caveolin is localized to motochondria and can modulate mitochondrial function/dynamics. We propose the following hypotheses: 1) targeted cellular trafficking of caveolin to key regulatory junctions (i.e., sarcolemmal membrane and mitochondria) is a critical response to ischemic stress; 2) cellular trafficking of caveolin to mitochondria is disrupted in the aged myocardium due to loss of membrane-localized caveolin; 3) restoration of caveolin in distinct cellular compartments via membrane and mitochondrial targeting in aged animals may provide a means to restore tolerance to myocardial ischemia. The following specific objectives will be addressed: Specific Objective 1: Determine if loss of membrane-localized caveolin leads to loss of caveolin expression/caveolae formation thus limiting trafficking of caveolin to mitochondria and if membrane- targeted expression of caveolin in aged myocardium restores trafficking to mitochondria. Specific Objective 2: Determine if aging results in reduced mitochondria-localized caveolin to alter mitochondrial function (i.e., reactive oxygen species generation and regulation of mPTP) and mitochondrial dynamics (i.e., fusion-fission to regulate mitochondrial turnover and mitophagy) and if mitochondria-targeted caveolin expression is necessary and sufficient to restore mitochondrial function/dynamics. Specific Objective 3: Determine if targeted expression of caveolin in membrane or mitochondria is necessary and sufficient to restore ischemic tolerance in aged hearts. PUBLIC HEALTH RELEVANCE: Cardiovascular disease is reaching epidemic proportions in the aged population. The current proposal aims to unravel the molecular mechanism of cardiac injury and utilize re-expression strategies to restore ischemic tolerance in the aged heart. We will assess the role of caveolins in mitochondria dysfunction. If caveolin serves to keep the cell "young" by maintaining mitochondrial function then caveolin therapy may be a viable means to protect the aged myocardium. The proposed research would further allow for the dissection of molecular and sub-cellular events that are responsible for adaptation to stress. An understanding of how caveolins contribute to normal heart function and how this is perturbed with loss of expression due to aging can shed critical insights into the mechanisms that are at play in endogenous tolerance of the myocardium. The work described in this proposal focuses on elucidating mechanisms to support the use of caveolin proteins as novel therapeutic targets for patients at risk of ischemia and is of relevance to the VA patient care mission.)