Adaptive strategies of the vertebrate heart to environmental stress; regulation of function and morphology

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The vertebrate heart is incredibly adaptable. An example of this is the rapid increase in the rate and strength of cardiac contraction that occurs when an animal gets startled. Another example is the increase in heart size that occurs in response to prolonged periods of exercise training. These changes in heart function and heart morphology increase the rate at which blood can be delivered to the tissues and enable a higher rate of physical activity. The heart can also undergo maladaptive changes following cardiac injury or disease. Here scar tissue forms in the heart and the amount of muscle decreases resulting in a weakened heart with impaired function. While the above adaptive and maladaptive changes have been well described at the organ level there is less known of the cellular pathways responsible for initiating and regulating them. The proposed research project is focused on the mechanisms that regulate cardiac contraction and those that drive the changes in cardiac morphology and composition in response to increased levels of stress on the heart. In the first set of studies we will determine how differences in the sequence of specific contractile proteins relate to the functional properties of trout, frog and rat hearts. We will specifically focus on the mechanisms responsible for the increase in cardiac function that occurs when an animal is scared and how this differs between species. To study the pathways that regulate the morphology and composition of the heart we will examine cardiac remodeling in trout. The trout heart undergoes significant changes in heart size and morphology with cold acclimation and we have recently found that warm acclimation causes a decrease in cardiac connective tissue. This is the first time that such a change has been reported in any animal. Characterizing the cellular pathways underlying this phenomenon will increase our understanding of what enables the vertebrate heart to adapt to stressors and may help develop treatments to control connective tissue (scar tissue) formation in patients who have suffered cardiac injury. Together these studies will provide novel insight into the processes that regulate cardiac function and adaptation.