The Jackson Laboratory, Bar Harbor, ME, USA.
Division of Eye and Vision, Department of Clinical Neuroscience, St. Erik Eye Hospital, Karolinska Institutet, Stockholm, Sweden.
J Neuroinflammation. 2020 Nov 11;17(1):336. doi: 10.1186/s12974-020-02011-z.
The risk of glaucoma increases significantly with age and exposure to elevated intraocular pressure, two factors linked with neuroinflammation. The complement cascade is a complex immune process with many bioactive end-products, including mediators of inflammation. Complement cascade activation has been shown in glaucoma patients and models of glaucoma. However, the function of complement-mediated inflammation in glaucoma is largely untested. Here, the complement peptide C3a receptor 1 was genetically disrupted in DBA/2J mice, an ocular hypertensive model of glaucoma, to test its contribution to neurodegeneration.
A null allele of C3ar1 was backcrossed into DBA/2J mice. Development of iris disease, ocular hypertension, optic nerve degeneration, retinal ganglion cell activity, loss of RGCs, and myeloid cell infiltration in C3ar1-deficient and sufficient DBA/2J mice were compared across multiple ages. RNA sequencing was performed on microglia from primary culture to determine global effects of C3ar1 on microglia gene expression.
Deficiency in C3ar1 lowered the risk of degeneration in ocular hypertensive mice without affecting intraocular pressure elevation at 10.5 months of age. Differences were found in the percentage of mice affected, but not in individual characteristics of disease progression. The protective effect of C3ar1 deficiency was then overcome by additional aging and ocular hypertensive injury. Microglia and other myeloid-derived cells were the primary cells identified that express C3ar1. In the absence of C3ar1, microglial expression of genes associated with neuroinflammation and other immune functions were differentially expressed compared to WT. A network analysis of these data suggested that the IL10 signaling pathway is a major interaction partner of C3AR1 signaling in microglia.
C3AR1 was identified as a damaging neuroinflammatory factor. These data help suggest complement activation causes glaucomatous neurodegeneration through multiple mechanisms, including inflammation. Microglia and infiltrating myeloid cells expressed high levels of C3ar1 and are the primary candidates to mediate its effects. C3AR1 appeared to be a major regulator of microglia reactivity and neuroinflammatory function due to its interaction with IL10 signaling and other immune related pathways. Targeting myeloid-derived cells and C3AR1 signaling with therapies is expected to add to or improve neuroprotective therapeutic strategies.
青光眼的风险随着年龄的增长和眼内压升高而显著增加，这两个因素都与神经炎症有关。补体级联反应是一个复杂的免疫过程，具有许多生物活性终产物，包括炎症介质。补体级联反应的激活已在青光眼患者和青光眼模型中得到证实。然而，补体介导的炎症在青光眼发病机制中的作用在很大程度上尚未得到验证。在这里，用基因敲除的方法使 DBA/2J 小鼠（一种青光眼的眼高压模型）中的补体肽 C3a 受体 1 失活，以测试其对神经退行性变的贡献。
将 C3ar1 的缺失等位基因回交至 DBA/2J 小鼠中。在多个年龄段比较 C3ar1 缺失和足够的 DBA/2J 小鼠中的虹膜疾病、眼高压、视神经变性、视网膜神经节细胞活性、RGC 丢失和髓样细胞浸润的发展。对原代培养的小胶质细胞进行 RNA 测序，以确定 C3ar1 对小胶质细胞基因表达的整体影响。
C3ar1 缺乏降低了眼高压小鼠发生退行性变的风险，但在 10.5 个月时不影响眼压升高。受影响的小鼠比例存在差异，但疾病进展的个体特征没有差异。然而，C3ar1 缺乏的保护作用被进一步的衰老和眼高压损伤所克服。小胶质细胞和其他髓样细胞是表达 C3ar1 的主要细胞。在缺乏 C3ar1 的情况下，小胶质细胞中与神经炎症和其他免疫功能相关的基因表达发生差异。与 WT 相比，这些数据的网络分析表明，IL10 信号通路是 C3AR1 信号在小胶质细胞中的主要相互作用伙伴。
C3AR1 被鉴定为一种具有破坏性的神经炎症因子。这些数据有助于表明补体激活通过多种机制导致青光眼神经退行性变，包括炎症。小胶质细胞和浸润的髓样细胞表达高水平的 C3ar1，是介导其作用的主要候选细胞。由于 C3AR1 与 IL10 信号和其他免疫相关途径的相互作用，C3AR1 似乎是小胶质细胞反应性和神经炎症功能的主要调节剂。用治疗方法靶向髓样细胞和 C3AR1 信号有望增加或改善神经保护治疗策略。
