Epigenetic deregulation has a role in the etiology of type 2 diabetes mellitus (T2DM), as well as in the development of its complications. Recent studies show that hyperglycemia can induce both global and site-specific demethylation but the underlying molecular mechanisms are under investigation. Our previous research suggests a role of
PARP-1 (poly-ADP-ribose polymerase) in controlling both the expression and the catalytic activity of Ten-eleven Translocation (TET) enzymes, which are responsible for catalyzing DNA demethylation by converting 5 methyl-cytosine (5mC) into cytosine, through different oxidized intermediates, namely 5hmC, 5fC and 5caC (5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine).
Our preliminary data reveal variation both in DNA methylation state and in cellular PARP activity in PBMCs (peripheral blood mononuclear cells) from a cohort of T2DM patients. In particular, PBMCs from patients with high glycated hemoglobin (HbA1c>7.5%) accumulated the oxidized forms of methylated cytosines (5hmC and 5fC) versus patients with low HbA1c and healthy subjects. In parallel, we observed a significant gain in PAR (polyADP-ribose) level, suggesting that PARP1 activation, most likely induced by the oxidative stress, may cause the block of the DNA demethylation cascade.
This evidence opens up to the hypothesis that PARylation may have implications on the TET enzyme machinery and DNA demethylation. In the present project, we aim to test the hypothesis that the altered DNA methylation pattern, observed in patients with poor glycemic control (HbA1c>7.5%), depends on PARP-1 activity. The understanding of the mechanism controlling 5hmC and 5fC accumulation in T2DM is important, since restoring the control of DNA demethylation cycle promises beneficial effects. In this context, the use of PARP inhibitors may be therapeutically relevant.
HIGHLIGHTS
Relevance: the project points out the molecular links between uncontrolled diabetes and epimutations underlying aetiology, progression and development of complications in T2DM. Epimutation is a heritable change in gene activity associated with gain or loss of DNA methylation (or other heritable modifications of chromatin). Our results may highlight that the ability of PARylation to alter the epigenetic profile via DNA methylation may hold the key to epigenetic control T2DM.
Innovativeness: PARylation may be considered a key process able to transduce the insults due to poor glycemic control into variations of the epigenetic code, paving the way to: 1) the exploitation of PAR detection as marker of chronic inflammation associated to DMT2, 2) to the use of PARP inhibitors in diabetes management.
Originality: PARylation could constitute a link between oxidative stress, typical of a condition of poor glycemic control, and epigenetic deregulation.
Feasibility: The project will combine expertise in PARylation and DNA methylation with expertise in clinical medicine of diabetes. The proponents have the required background and possess the basic equipment to address the experimental aims of the project.
Far-reaching relevant clinical implications of this research include the use of PARs as indicators of peripheral DNA damage and cellular stress and they would represent new biomarkers for the follow-up monitoring of the diabetic patient. In addition, PARP inhibitors can be exploited as new therapeutic drugs in the management of diabetes by delaying some complications thus improving the patient outcome.
Further, the hyperglycaemia-driven overproduction of reactive oxygen species and oxidative stress are the major biochemical abnormalities underlying diabetes pathogenesis and complications and have been proposed as the primary mediators of 'glucotoxicity'. In this process, the ROS-mediated activation of PARP1 has been proposed to trigger cell death and impairment of glucose disposal. More recently, it was found that glucotoxicity generates permanent changes of the expression of genes associated with the control of glucose homeostasis through epigenetic regulatory mechanisms. This finding offers an elegant explanation of the phenomenon of "metabolic memory", which accounts for the correlation between transient/chronic poor glycaemic control and the irreversible progression of diabetic complications. In this context, by investigating the link between PARP activation and HG-induced DNA methylation defects, this project aims to collect initial evidence that may form an understanding for the mechanistic basis of the emerging connection between defective glucose metabolism and epigenetic modifications of chromatin in diabetes.
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