Abstract
BackgroundLower levels of cytosine methylation have been found in the liver cell DNA from non-obese diabetic (NOD) mice under hyperglycemic conditions. Because the Fourier transform-infrared (FT-IR) profiles of dry DNA samples are differently affected by DNA base composition, single-stranded form and histone binding, it is expected that the methylation status in the DNA could also affect its FT-IR profile.Methodology/Principal FindingsThe DNA FT-IR signatures obtained from the liver cell nuclei of hyperglycemic and normoglycemic NOD mice of the same age were compared. Dried DNA samples were examined in an IR microspectroscope equipped with an all-reflecting objective (ARO) and adequate software.Conclusions/SignificanceChanges in DNA cytosine methylation levels induced by hyperglycemia in mouse liver cells produced changes in the respective DNA FT-IR profiles, revealing modifications to the vibrational intensities and frequencies of several chemical markers, including νas –CH3 stretching vibrations in the 5-methylcytosine methyl group. A smaller band area reflecting lower energy absorbed in the DNA was found in the hyperglycemic mice and assumed to be related to the lower levels of –CH3 groups. Other spectral differences were found at 1700–1500 cm−1 and in the fingerprint region, and a slight change in the DNA conformation at the lower DNA methylation levels was suggested for the hyperglycemic mice. The changes that affect cytosine methylation levels certainly affect the DNA-protein interactions and, consequently, gene expression in liver cells from the hyperglycemic NOD mice.
Highlights
Non-obese diabetic (NOD) mice are a useful experimental model in which an expressive amount of females spontaneously develop a form of autoimmune diabetes that closely resembles human diabetes [1]
The findings reveal that the hyperglycemia-induce changes in the methylation status of DNA from mouse liver cells produced differences in the corresponding DNA Fourier transform-infrared (FT-IR) profiles obtained using microspectroscopic procedures
Based on reports that the area under an absorption band peak in IR spectroscopy is related to the absorbed energy [16,18,23], this study showing a smaller band area for the hyperglycemic non-obese diabetic (NOD) mouse DNA –CH3 groups suggests a lower abundance of cytosine methylation in the liver cell nuclei of these mice, which is consistent with a report by Damasceno et al [7]
Summary
Non-obese diabetic (NOD) mice are a useful experimental model in which an expressive amount of females spontaneously develop a form of autoimmune diabetes that closely resembles human diabetes [1]. Lower cytosine methylation levels have been found in DNA from liver cells in NOD mice under hyperglycemic conditions when the bulk genome is considered [7]. Because Fourier transform-infrared (FT-IR) profiles of dry DNA samples are affected differently by certain DNA characteristics, such as base composition, single-strandedness and histone binding [9], the methylation status of DNA from NOD mice is expected to affect the DNA FT-IR profile. Lower levels of cytosine methylation have been found in the liver cell DNA from non-obese diabetic (NOD) mice under hyperglycemic conditions. Because the Fourier transform-infrared (FT-IR) profiles of dry DNA samples are differently affected by DNA base composition, single-stranded form and histone binding, it is expected that the methylation status in the DNA could affect its FT-IR profile
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