Genome-wide DNA methylation profiling of human diabetic peripheral neuropathy in subjects with type 2 diabetes mellitus

DNA methylation is an epigenetic mechanism important for the regulation of gene expression, which plays a vital role in the interaction between genetic and environmental factors. Aberrant epigenetic changes are implicated in the pathogenesis of diabetes and diabetic complications, but the role of DNA methylation in diabetic peripheral neuropathy (DPN) is not well understood. Therefore, our aim in this study was to explore the role of DNA methylation in the progression of DPN in type 2 diabetes. We compared genome-wide DNA methylation profiles of human sural nerve biopsies from subjects with stable or improving nerve fibre counts to biopsies from subjects with progressive loss of nerve fibres. Nerve fibre counts were determined by comparing myelinated nerve fibre densities between an initial and repeat biopsy separated by 52 weeks. Subjects with significant nerve regeneration (regenerators) and subjects with significant nerve degeneration (degenerators) represent the two extreme DPN phenotypes. Using reduced representation bisulfite sequencing, we identified 3,460 differentially methylated CpG dinucleotides between the two groups. The genes associated with differentially methylated CpGs were highly enriched in biological processes that have previously been implicated in DPN such as nervous system development, neuron development, and axon guidance, as well as glycerophospholipid metabolism and mitogen-activated protein kinase (MAPK) signalling. These findings are the first to provide a comprehensive analysis of DNA methylation profiling in human sural nerves of subjects with DPN and suggest that epigenetic regulation has an important role in the progression of this prevalent diabetic complication.

DNA甲基化（DNA methylation）是一类对基因表达调控至关重要的表观遗传机制，在遗传与环境因素的相互作用中扮演关键角色。异常表观遗传改变与糖尿病及其并发症的发病机制密切相关，但DNA甲基化在糖尿病周围神经病变（diabetic peripheral neuropathy, DPN）中的作用尚未得到充分阐明。为此，本研究旨在探究DNA甲基化在2型糖尿病患者DPN进展中的作用。本研究对两组人类腓肠神经活检标本的全基因组DNA甲基化谱进行了对比：一组受试者的神经纤维计数维持稳定或有所改善，另一组则存在进行性神经纤维丢失。神经纤维计数通过对比间隔52周获取的首次与复查活检标本中的有髓神经纤维密度得以确定。存在显著神经再生的受试者（再生组）与存在显著神经退行性变的受试者（退变组），构成了DPN的两种极端表型。本研究采用简化代表性亚硫酸氢盐测序（reduced representation bisulfite sequencing）技术，在两组间鉴定出3,460个差异甲基化CpG二核苷酸。差异甲基化CpG位点关联基因显著富集于此前已被证实与DPN相关的生物学过程，包括神经系统发育、神经元发育、轴突导向，以及甘油磷脂代谢和丝裂原活化蛋白激酶（mitogen-activated protein kinase, MAPK）信号通路。本研究首次对DPN患者的人类腓肠神经DNA甲基化谱开展全面分析，研究结果提示表观遗传调控在这一高发糖尿病并发症的进展中发挥重要作用。