Microdomain Ca2+ influx in Heart Failure

Temple Univ Of The Commonwealth, Philadelphia PA

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Abstract

Myocardial infarction, Ml causes the death of the cardiac tissue reliant on a constant blood flow for oxygen and nutrients. The death of a portion of the heart causes the pump function to decrease. A host of responses ensure that elevate contractile performance in surviving myocytes and repair (primarily with scar tissue) the damaged region. The major responses involve activation of sympathetic and other neurohormonal signaling cascades and inflammatory processes. These processes help maintain basal cardiac function, but the persistent nature of the responses appear to elicit detrimental effects on the heart that ultimately lead to cardiac dilation and CHF. A major component of the surviving myocyte response to Ml is an increase in Ca2 influx through the L-type Ca^* channels (LTCCs), which enhances myocyte contractility to help maintain cardiac pump function. However, when this signal is persistent it leads to pathological hypertrophy, via activation of the calcineurin (Cn) - nuclear factor of activated T (NFAT) cell pathway, cardiacarrhythmias and cell death. Blocking those aspects of Ca^* entry that produces pathological phenotypes in cardiac myocytes would be beneficial. However, it is not currently possible to inhibit excess Ca^ influx through the LTCCs that promote pathological processes without also blocking the Ca^* influx that initiates and regulates contraction. This Ca2+ is essential for both the normal and diseased heart. To achieve block of hypertrophic Ca we have developed a novel approach to inhibit Ca influx through LTCCs that are housed in caveolin-3 enriched membrane signaling domains, by fusing a Rem protein (a member of the RGK GTPase protein family that is known to inhibit LTCCs) construct (termed Rem (1-265) (R)) with its native membrane targeting motif deleted to a consensus caveolin binding domain (termed Rem[1-265]-Cav). The objective of the research is to determine if reducing excess Ca2+ influx through L-type Ca2+ channels (LTCC) housed in hypertrophic signaling (but not EC coupling) microdomains in the post Ml heart reduces pathological hypertrophy and death signaling to improve ventricular structure and function. The SPECIFIC AIMS of this research are AIM 1:: To determine if a novel LTCC antagonist strategy (Rem[1-265]-Cav) can selectively inhibit excess Ca2+ influx in signaling microdomains to reduce pathological hypertrophy and cell death without depressing EC coupling. Adult feline (or porcine) ventricular myocytes in primary culture will be infected with Ad-Rem[1-265] -Cav (and other Rem constructs described later) to detennine its effect on whole cell L-type Ca2+ current (ICS-L). Ca handling, EC coupling, Cn-NFAT signaling, myocyte hypertrophy and death. Aim 2: To determine if expression of Rem [1-265]Cav in cardiac myocytes (inducible, cardiac specific expression system) can reduce pathological remodeling after myocardial infarction (Ml). Experiments will initially be performed in genetically modified mice (without Ml) to determine the effects of Rem[1-265]-Cav on Ca2+ influx and the basal myocyte phenotype. We will then determine if Rem[1-265]-Cav improves myocyte (and cardiac pump) function and reduces myocyte hypertrophy and death after Ml. Aim 3: We will determine if, and by what mechanism, Rem[1-265]-Cav (via AAV gene therapy) improves cardiac structure and function in adult pigs (with Ca2+ signaling similar to that found in humans) after Ml. These experiments have the potential to provide novel approaches for modifying local Ca2+ signaling involved in pathological remodeling.