Down-regulation of cholesterol biosynthesis in forebrains of ERCC1-deficient mice

Background: Several genetic defects of the nucleotide excision repair (NER) pathway, including deficiency of the Excision Repair Cross-Complementing rodent repair deficiency, complementation group 1 (ERCC1), result in pre-mature aging, impaired growth, microcephaly and delayed development of the cerebellum. Such a phenotype also occurs in ERCC1-knockout mice which survive for up to 4 weeks after birth. Therefore, we analyzed cerebellar and hippocamapal transcriptomes of these animals at 3 weeks of age to identify the candidate mechanisms underlying brain consequences of reduced ERCC1 activity. Results: In the cerebellum, the most prominent change was upregulation of genes that are associated with gliosis. Although Purkinje cell degeneration has been reported in some mouse strains with NER impairment, Purkinje cell transcriptome was mostly unaffected by the ERCC1 knockout. In the hippocampus, the gliosis response was minimal. Instead, there was an extensive downregulation of genes related to lipid metabolism including several enzymes of the cholesterol biosynthesis pathway as well as lipoproteins and plasma membrane proteins. Reduced expression of the cholesterol biosynthesis pathway genes was also present in the neocortex of adult mice whose ERCC1 gene was replaced by a mutant allele with a partial activity. Conclusions: Downregulation of forebrain cholesterol biosynthesis genes is a newly identified consequence of ERCC1 deficiency. Its presence in adult mice suggests that it is not a secondary consequence of brain growth impairment. Instead, reduced cholesterol biosynthesis may contribute to such an impairment as well as affect function of mature synapses. We analyzed the hippocampus and cerebellum from three Ercc1-/- and three WT littermates using the Affymetrix Mouse Genome 430_2.0. Data was analyzed using the dChip DNA-Chip analyzer software .背景：核苷酸切除修复（nucleotide excision repair, NER）通路存在多种遗传缺陷，其中包括切除修复交叉互补大鼠修复缺陷互补组1（ERCC1）功能缺失，此类缺陷可导致早衰、生长发育障碍、小头畸形及小脑发育迟缓。ERCC1基因敲除小鼠亦会出现此类表型，且出生后存活时长仅可达4周。为此，本研究对3周龄该类小鼠的小脑与海马转录组进行分析，以期阐明ERCC1活性降低导致脑功能异常的潜在候选机制。 结果：在小脑中，最显著的变化为与胶质增生（gliosis）相关的基因上调。尽管已有研究报道部分NER缺陷小鼠品系存在浦肯野细胞变性，但ERCC1基因敲除并未对浦肯野细胞转录组造成显著影响。在海马体中，胶质增生反应极弱，取而代之的是脂质代谢相关基因的广泛下调，其中涵盖胆固醇生物合成通路的多种酶、脂蛋白及质膜蛋白。在ERCC1基因被部分活性突变等位基因替代的成年小鼠新皮层中，同样观察到胆固醇生物合成通路基因的表达降低。 结论：前脑胆固醇生物合成基因的下调是ERCC1缺陷新发现的表型。该现象在成年小鼠中存在，提示其并非脑生长受损的继发效应。相反，胆固醇生物合成降低可能加剧该类脑损伤，并影响成熟突触的功能。本研究使用Affymetrix小鼠基因组430_2.0芯片，对3只Ercc1基因敲除（Ercc1-/-）小鼠及3只野生型（wild type, WT）同窝对照小鼠的海马体与小脑组织进行转录组检测，数据采用dChip DNA芯片分析软件进行分析处理。