Type I Diabetes Leads to Tissue-Specific DNA Hypomethylation in Male Rats

Abstract

Numerous perturbations of methyl group and homocysteine metabolism have been documented as an outcome of diabetes. It has also been observed that there is a transition from hypo- to hyperhomocysteinemia in diabetes, often concurrent with the development of nephropathy. The objective of this study was to characterize the temporal changes in methyl group and homocysteine metabolism in the liver and kidney and to determine the impact these alterations have on DNA methylation in type 1 diabetic rats. Male Sprague-Dawley rats were injected with streptozotocin (60 mg/kg body weight) to induce diabetes and samples were collected at 2, 4, and 8 wk. At 8 wk, hepatic and renal betaine-homocysteine S-methyltransferase activities were greater in diabetic rats, whereas methionine synthase activity was lower in diabetic rat liver and kidney did not differ. Cystathionine beta-synthase abundance was greater in the liver but less in the kidney of diabetic rats. Both hepatic and renal glycine N-methyltransferase (GNMT) activity and abundance were greater in diabetic rats; however, changes in renal activity and/or abundance were present only at 2 and 4 wk, whereas hepatic GNMT was induced at all time points. Most importantly, we have shown that genomic DNA was hypomethylated in the liver, but not the kidney, in diabetic rats. These results suggest that diabetes-induced perturbations of methyl group and homocysteine metabolism lead to functional methyl deficiency, resulting in the hypomethylation of DNA in a tissue-specific fashion.

Germ cell abnormalities in streptozotocin induced diabetic mice do not correlate with blood glucose level

“…The hyperglycemic state did not show any significant difference in methylation pattern of germ cells after one or two spermatogenesis cycle except in preleptotene/zygotene cell population where labeling index was higher than control at 72 days suggesting hypermethyation. Diabetes induced perturbations of methylation has been observed in tissue-specific fashion [6] although the germ cell methylation changes are not reported till date. The changes in methylation pattern is a particularly a novel observation and supports our hypothesis that hyperglycemic condition affects germ cell methylation and may have implications on reproductive outcome.…”

“…DNA methylation is catalyzed by DNA methyl transferases (DNMTs) which regulate gene expression during development. It has been shown that diabetes-induced perturbation of methyl group lead to functional hypomethylation of DNA in a tissue specific fashion [6].…”

Exercise prevents hyperhomocysteinemia in a dietary folate-restricted mouse model

“…This shift is also reflected in other 270 gluconeogenic states, such as diabetes. We and others have demonstrated that a diabetic state or 271 administration of synthetic glucocorticoid compounds has a major impact on methyl group and 272 homocysteine metabolism [23][24][25][26][49][50][51][52]. A consistent finding from these reports is a reduction 273 in circulating homocysteine concentrations owing to an increase in folate-independent 274 remethylation (i.e., BHMT) and catabolism of homocysteine through the transsulfuration 275 pathway.…”

“…This was based on our previous 95 research demonstrating that a gluconeogenic state and related hormonal alterations, similar to 96 what is exhibited as a function of exercise, results in reduced homocysteine concentrations via 97 enhanced folate-independent remethylation of homocysteine, as well as increased catabolism 98 [23][24][25][26] initially housed in groups of 2 or 3 in a 12-h light: dark cycle and provided an AIN-93G semi-120 purified diet (Table 1) and water ad libitum [28]. No antibiotics were added to the diets or 121 drinking water, resulting in a moderate degree of folate deficiency as we have previously 122…”

“…Euthanasia consisted of exsanguination and removal of major organs for their subsequent 131 processing as described previously [23][24][25][26]. Heparinized whole blood was collected via cardiac 132 puncture, centrifuged at 4,000 g for 6 min, and plasma was stored at -20°C for subsequent 133 homocysteine analysis.…”