Inserm UMRS 1256 NGERE - Nutrition, Genetics, and Environmental Risk Exposure, University of Lorraine, 54500, Vandoeuvre-lès-Nancy, France.
Department of Ophthalmology, University Regional Hospital Center of Nancy, 54000, Nancy, France.
Clin Epigenetics. 2023 Oct 5;15(1):158. doi: 10.1186/s13148-023-01567-w.
MTR gene encodes the cytoplasmic enzyme methionine synthase, which plays a pivotal role in the methionine cycle of one-carbon metabolism. This cycle holds a significant importance in generating S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), the respective universal methyl donor and end-product of epigenetic transmethylation reactions. cblG type of inherited disorders of vitamin B12 metabolism due to mutations in MTR gene exhibits a wide spectrum of symptoms, including a retinopathy unresponsive to conventional therapies.
To unveil the underlying epigenetic pathological mechanisms, we conducted a comprehensive study of epigenomic-wide alterations of DNA methylation by NGS of bisulfited retinal DNA in an original murine model with conditional Mtr deletion in retinal tissue. Our focus was on postnatal day 21, a critical developmental juncture for ocular structure refinement and functional maturation.
We observed delayed eye opening and impaired visual acuity and alterations in the one-carbon metabolomic profile, with a notable dramatic decline in SAM/SAH ratio predicted to impair DNA methylation. This metabolic disruption led to epigenome-wide changes in genes involved in eye development, synaptic plasticity, and retinoid metabolism, including promoter hypermethylation of Rarα, a regulator of Lrat expression. Consistently, we observed a decline in cone photoreceptor cells and reduced expression of Lrat, Rpe65, and Rdh5, three pivotal genes of eye retinoid metabolism.
We introduced an original in vivo model for studying cblG retinopathy, which highlighted the pivotal role of altered DNA methylation in eye development, cone differentiation, and retinoid metabolism. This model can be used for preclinical studies of novel therapeutic targets.
MTR 基因编码细胞质酶蛋氨酸合成酶，该酶在一碳代谢的蛋氨酸循环中起着关键作用。该循环在生成 S-腺苷甲硫氨酸（SAM）和 S-腺苷同型半胱氨酸（SAH）方面具有重要意义，SAM 和 SAH 分别是表观遗传转甲基反应的通用甲基供体和终产物。由于 MTR 基因突变导致 cblG 型维生素 B12 代谢遗传缺陷，表现出广泛的症状，包括对常规治疗无反应的视网膜病变。
为了揭示潜在的表观病理机制，我们通过对视网膜组织中条件性 Mtr 缺失的原始鼠模型进行 bisulfited 视网膜 DNA 的 NGS，对全基因组 DNA 甲基化的表观基因组改变进行了全面研究。我们的重点是在出生后第 21 天，这是眼部结构细化和功能成熟的关键发育阶段。
我们观察到眼睛张开延迟，视力受损，一碳代谢组学图谱改变，SAM/SAH 比值显著下降，预计会损害 DNA 甲基化。这种代谢紊乱导致参与眼部发育、突触可塑性和视黄醇代谢的基因的全基因组表观基因组改变，包括 Lrat 表达调节剂 Rarα的启动子超甲基化。一致地，我们观察到锥状光感受器细胞减少和 Lrat、Rpe65 和 Rdh5 的表达减少，这三个基因是眼部视黄醇代谢的关键基因。
我们引入了一种研究 cblG 视网膜病变的原创体内模型，该模型突出了改变的 DNA 甲基化在眼部发育、锥状细胞分化和视黄醇代谢中的关键作用。该模型可用于新的治疗靶点的临床前研究。
