Cerebellar oxidative DNA damage and altered DNA methylation in the BTBR T+tf/J mouse model of autism and similarities with human post mortem cerebellum

The molecular pathogenesis of autism is complex and involves numerous genomic, epigenomic, proteomic, metabolic, and physiological alterations. Elucidating and understanding the molecular processes underlying the pathogenesis of autism is critical for effective clinical management and prevention of this disorder. The goal of this study is to investigate key molecular alterations postulated to play a role in autism and their role in the pathophysiology of autism. In this study we demonstrate that DNA isolated from the cerebellum of BTBR T+tf/J mice, a relevant mouse model of autism, and from human post-mortem cerebellum of individuals with autism, are both characterized by an increased levels of 8-oxo-7-hydrodeoxyguanosine (8-oxodG), 5-methylcytosine (5mC), and 5-hydroxymethylcytosine (5hmC). The increase in 8-oxodG and 5mC content was associated with a markedly reduced expression of the 8-oxoguanine DNA-glycosylase 1 (Ogg1) and increased expression of de novo DNA methyltransferases 3a and 3b (Dnmt3a and Dnmt3b). Interestingly, a rise in the level of 5hmC occurred without changes in the expression of ten-eleven translocation expression 1 (Tet1) and Tet2 genes, but significantly correlated with the presence of 8-oxodG in DNA. This finding and similar elevation in 8-oxodG in cerebellum of individuals with autism and in the BTBR T+tf/J mouse model warrant future large-scale studies to specifically address the role of genetic alterations in OGG1 in pathogenesis of autism. Gene expression profiles in the cerebellum of 8 weeks old BTBR T+tf/J mice that exhibit an autism-like behavioral phenotype and control C57BL/6J mice were examined using high-throughput Agilent whole genome 8x60K mouse microarrays.自闭症的分子发病机制极为复杂，涉及基因组、表观基因组、蛋白质组、代谢组及生理学层面的诸多异常改变。阐明并理解自闭症发病的核心分子过程，对该疾病的有效临床管理与预防至关重要。本研究旨在探究被认为参与自闭症发病的关键分子改变，及其在自闭症病理生理学中的作用。本研究证实，从自闭症相关小鼠模型BTBR T+tf/J的小脑组织中分离得到的DNA，以及自闭症患者死后小脑组织的DNA，均呈现出8-氧代-7-氢脱氧鸟苷（8-oxo-7-hydrodeoxyguanosine, 8-oxodG）、5-甲基胞嘧啶（5-methylcytosine, 5mC）与5-羟甲基胞嘧啶（5-hydroxymethylcytosine, 5hmC）水平升高的特征。8-oxodG与5mC的含量升高，与8-氧鸟嘌呤DNA糖苷酶1（8-oxoguanine DNA-glycosylase 1, Ogg1）的表达显著下调，以及新发DNA甲基转移酶3a和3b（de novo DNA methyltransferases 3a and 3b, Dnmt3a与Dnmt3b）的表达上调显著相关。值得注意的是，5hmC水平的升高并未伴随十-十一易位酶1（ten-eleven translocation expression 1, Tet1）与Tet2基因的表达变化，但与DNA中8-oxodG的存在显著相关。这一发现，以及自闭症患者与BTBR T+tf/J小鼠模型小脑组织中8-oxodG的类似升高，为后续开展大规模研究以专门探讨OGG1的遗传改变在自闭症发病机制中的作用提供了依据。本研究采用高通量安捷伦（Agilent）全基因组8x60K小鼠微阵列芯片，对表现出自闭症样行为表型的8周龄BTBR T+tf/J小鼠与对照C57BL/6J小鼠的小脑组织基因表达谱进行了检测分析。