Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA.
Department of Molecular Medicine, Cleveland Clinic Lerner College of Medicine, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
Aging Cell. 2024 Nov;23(11):e14282. doi: 10.1111/acel.14282. Epub 2024 Aug 29.
Somatic mitochondrial DNA (mtDNA) mutation accumulation has been observed in individuals with retinal degenerative disorders. To study the effects of aging and mtDNA mutation accumulation in the retina, a polymerase gamma (POLG) exonuclease-deficient model, the Polg mutator mice (D257A), was used. POLG is an enzyme responsible for regulating mtDNA replication and repair. Retinas of young and older mice with this mutation were analyzed in vivo and ex vivo to provide new insights into the contribution of age-related mitochondrial (mt) dysfunction due to mtDNA damage. Optical coherence tomography (OCT) image analysis revealed a decrease in retinal and photoreceptor thickness starting at 6 months of age in mice with the D257A mutation compared to wild-type (WT) mice. Electroretinography (ERG) testing showed a significant decrease in all recorded responses at 6 months of age. Sections labeled with markers of different types of retinal cells, including cones, rods, and bipolar cells, exhibited decreased labeling starting at 6 months. However, electron microscopy analysis revealed differences in retinal pigment epithelium (RPE) mt morphology beginning at 3 months. Interestingly, there was no increase in oxidative stress and parkin-mediated mitophagy in the ages analyzed in the retina or RPE of D257A mice. Additionally, D257A RPE exhibited an accelerated rate of autofluorescence cytoplasmic granule formation and accumulation. Mt markers displayed different abundance in protein lysates obtained from retina and RPE samples. These findings suggest that the accumulation of mtDNA mutations leads to impaired mt function and accelerated aging, resulting in retinal degeneration.
体细胞线粒体 DNA（mtDNA）突变积累已在视网膜退行性疾病患者中观察到。为了研究衰老和视网膜 mtDNA 突变积累的影响，使用了聚合酶γ（POLG）外切酶缺陷型模型，即 Polg 突变体小鼠（D257A）。POLG 是一种负责调节 mtDNA 复制和修复的酶。分析了具有这种突变的年轻和老年小鼠的体内和体外视网膜，为年龄相关性线粒体（mt）功能障碍（由于 mtDNA 损伤引起）的贡献提供了新的见解。光学相干断层扫描（OCT）图像分析显示，与野生型（WT）小鼠相比，D257A 突变小鼠的视网膜和光感受器厚度从 6 个月大开始下降。视网膜电图（ERG）测试显示，在 6 个月大时，所有记录的反应均显著下降。用标记不同类型视网膜细胞（包括视锥细胞、视杆细胞和双极细胞）的标志物进行的切片显示，从 6 个月大开始标记减少。然而，电子显微镜分析显示，从 3 个月大开始，视网膜色素上皮（RPE）mt 形态就存在差异。有趣的是，在分析的年龄中，D257A 小鼠的视网膜或 RPE 中没有增加氧化应激和 parkin 介导的自噬。此外，D257A RPE 表现出加速的细胞质颗粒形成和积累的自发荧光。在从视网膜和 RPE 样本获得的蛋白质裂解物中，mt 标志物显示出不同的丰度。这些发现表明，mtDNA 突变的积累导致 mt 功能受损和衰老加速，从而导致视网膜变性。
