Hyperglycemia-independent neonatal streptozotocin-induced retinopathy (NSIR) in rats

Chemicals, such as MNU (N-methyl-N-nitrosourea) and NaIO3 (sodium iodate), are widely used to induce retinal degeneration in rodents. Streptozotocin (STZ) is an analog of N-acetyl glucosamine in which an MNU moiety is linked to a hexose and has a special toxic effect on insulin-producing pancreatic β-cells. It is commonly used to induce hyperglycemia to model diabetes. While intracerebroventricular injection of STZ can produce Alzheimer's disease independent of hyperglycemia, most retinal studies using STZ focus on the effects of hyperglycemia on the retina, but whether STZ has any impact on retinal cells independent of hyperglycemia is unknown. We aimed to investigate the role of cytotoxicity of STZ in rat retina. Intravitreal (5ug or 10ug) or subcutaneous (30mg/kg) injection of STZ at the early stage of newborn rats couldn’t induce hyperglycemia but caused NSIR (neonatal STZ-induced retinopathy), including reduced ERG amplitudes, retinal rosettes and apoptosis, cell cycle arrest, microglial activation, and delayed retinal angiogenesis. STZ did not affect the early-born retinal cell types but significantly reduced the late-born ones. Short-term and long-term hyperglycemia had no significant effects on the NSIR phenotypes. RNA sequencing revealed that STZ induces oxidative stress and activates the p53 pathway of retinal cells. Locally or systemically, STZ injection after P8 couldn’t induce NSIR when all retinal progenitors exit the cell cycle. Thus, NSIR in rats is independent of hyperglycemia but due to STZ’s direct cytotoxic effects on retinal progenitor cells. NSIR is a typical reaction to STZ-induced retinal oxidative stress and DNA damage. This significant finding suggests that NSIR may be a valuable model for studying retinal progenitor DNA damage-related diseases, potentially leading to new insights and treatments.诸如N-甲基-N-亚硝基脲(N-methyl-N-nitrosourea, MNU)、碘酸钠(sodium iodate, NaIO3)等化学物质，被广泛用于诱导啮齿类动物发生视网膜退化。链脲佐菌素(Streptozotocin, STZ)是N-乙酰葡糖胺的类似物，其结构中带有一个与己糖连接的MNU基团，对产胰岛素的胰腺β细胞具有特异性毒性作用。它常被用于诱导高血糖症以构建糖尿病模型。尽管脑室内注射STZ可在不依赖高血糖症的情况下诱发阿尔茨海默病，但多数使用STZ的视网膜相关研究均聚焦于高血糖症对视网膜的影响，而STZ是否可在不依赖高血糖症的情况下对视网膜细胞产生作用仍尚不明确。本研究旨在探究STZ的细胞毒性在大鼠视网膜中的作用。在新生大鼠早期阶段，以5μg或10μg剂量行玻璃体内注射，或30mg/kg剂量行皮下注射STZ，均不会诱导高血糖症，但可引发新生儿链脲佐菌素诱导性视网膜病(neonatal STZ-induced retinopathy, NSIR)，具体表现为视网膜电图振幅降低、视网膜玫瑰花结形成、细胞凋亡、细胞周期阻滞、小胶质细胞激活以及视网膜血管生成延迟。STZ不会影响早期生成的视网膜细胞类型，但可显著减少晚期生成的视网膜细胞类型。短期与长期高血糖症均未对NSIR表型产生显著影响。RNA测序结果显示，STZ可诱导视网膜细胞产生氧化应激并激活p53通路。当所有视网膜祖细胞退出细胞周期后，于出生后第8天（P8）进行局部或全身STZ注射，均无法诱导NSIR。因此，大鼠体内的NSIR并不依赖高血糖症，而是源于STZ对视网膜祖细胞的直接细胞毒性作用。NSIR是STZ诱导视网膜氧化应激与DNA损伤的典型表现。这一重要发现表明，NSIR或许可作为研究视网膜祖细胞DNA损伤相关疾病的理想模型，有望为相关疾病的治疗提供新的思路与方案。