Diabetes mellitus currently affects 285 million individuals and this is projected to increase to 439 million by 2030. Evidence from both the laboratory and large scale clinical trials has revealed that diabetic complications progress unimpeded via the phenomenon of metabolic memory even when glycemic control is pharmaceutically achieved. The epigenome is comprised of all chromatin modifications including DNA methylation and histone modifications and epigenetic processes allow cells and organisms to quickly respond to changing environmental stimuli. These processes not only allow for quick adaptation but also confer the ability of the cell to "memorize" these encounters. Investigation into the role of the epigenome in metabolic memory is recent and has been limited to the examination of specific histone modifications;however, the role of DNA methylation in metabolic memory has not been reported. Our long term objective is to decipher the molecular mechanisms of metabolic memory with a rationale that these studies will lead to the identification and development of novel therapeutic targets to control the progression of diabetic complications. To this end, we have developed an adult zebrafish model of type I diabetes mellitus and have characterized this model to show that diabetic zebrafish not only display the known secondary complications including impaired epidermal wound healing, but in addition, exhibit impaired limb regeneration (caudal fin regeneration). In our current studies, we demonstrate that hyperglycemic zebrafish can revert back to normal glycemia within 2 weeks of drug removal due to regeneration of endogenous pancreatic beta cells resulting in a physiologically normal glycemic state. However, in contrast, body wall epidermal wound healing and limb regeneration in these fish remains impaired to the same extent as in the acute diabetic state indicating these complications are persistent and are susceptible to metabolic memory. Moreover, examination of daughter tissue that was regenerated in the post hyperglycemia state was similarly reduced revealing the heritable transmission of the metabolic memory phenomenon. This data has led us to hypothesize that: hyperglycemia induces aberrant DNA methylation that contributes to metabolic memory. This hypothesis will be tested using the following two Specific Aims : 1. Determination of DNA methylation differences in the normal, acute diabetic, and metabolic memory states. and 2: Identification of the time course for hyperglycemia induced DNA methyltransferase and subsequent DNA methylation alterations. The completion of the experiments in this proposal will establish the genomic methylation patterns induced by hyperglycemia and maintained in the metabolic memory state. In the long term, these experiments will provide a foundation for the identification of appropriate targets for new treatments to prevent or reverse diabetic complications.
Metabolic memory is the phenomenon by which diabetic complications persist and progress unimpeded following return to normal glycemia. This proposal focuses on the role that epigenetic DNA methylation plays in the initiation and maintenance of metabolic memory. The proposed studies have a broad range of potential impact for delineation of key hyperglycemia-induced epigenetic events that will assist in the identification of appropriate targets for potential new treatments to prevent or reverse diabetic complications.
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