Purpose

Activation of bone morphogenetic protein (BMP) 4 signaling promotes the survival of retinal ganglion cell (RGC) after acute injury. Chordin-like 1 (CHRDL1) is an endogenous BMP antagonist. In this study, we researched whether CHRDL1 was involved in BMP4 signaling and regulation of RGC degeneration in a mouse model of glaucoma.

Methods

Magnetic microbeads were intracameral injected to induce experimental glaucoma in a mouse model. A recombinant adeno-associated virus (rAAV) system was designed for overexpression of BMP4 or CHRDL1 in mouse retina. Immunohistochemistry and hematoxylin-eosin (HE) stains were performed to identify changes in retinal morphology. Electroretinogram (ERG) recordings were used to assess changes in visual function.

Results

The mRNA expression levels of Bmp4 and its downstream BMPRIa, small mothers against decapentaplegic 1 (Smad1), were significantly upregulated in retinas with glaucoma. RGC survival was significantly enhanced in the beads + AAV-BMP4 group and significantly reduced in the beads + AAV-CHRDL1 group, compared with the beads + AAV-EGFP group. Similar results were observed in retinal explant culture in vitro. Consistent with these findings, the photopic negative response (PhNR)responses in ERG, which indicate RGC function, were restored in mice overexpressing BMP4, whereas a-wave and b-wave responses were not. Activation of CHRLD1 inhibited Smad1/5/8 phosphorylation and exacerbated RGC damage. The expression of Glial fibrillary acidic protein (GFAP) was decreased significantly in beads + AAV-BMP4 group.

Conclusions

BMP4 promoted RGC survival and visual function in an experimental glaucoma model. Activation of CHRDL1 exaggerated RGC degeneration by inhibiting the BMP4/Smad1/5/8 pathway. The mechanism of BMP4/Smad1/5/8 pathway may be related to the inhibition of glial cell activation. Our studies suggested that BMP4 and CHRLD1 might serve as therapeutic targets in glaucoma.

中文翻译：

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BMP4过表达保护实验性青光眼小鼠模型视网膜神经节细胞

目的

骨形态发生蛋白 (BMP) 4 信号的激活促进急性损伤后视网膜神经节细胞 (RGC) 的存活。Chordin-like 1 (CHRDL1) 是一种内源性 BMP 拮抗剂。在这项研究中，我们研究了 CHRDL1 是否参与了青光眼小鼠模型中 BMP4 信号传导和 RGC 变性的调节。

方法

前房内注射磁性微珠以诱导小鼠模型中的实验性青光眼。重组腺相关病毒 (rAAV) 系统设计用于在小鼠视网膜中过表达 BMP4 或 CHRDL1。进行免疫组织化学和苏木精-伊红 (HE) 染色以确定视网膜形态的变化。视网膜电图 (ERG) 记录用于评估视觉功能的变化。

结果

Bmp4 及其下游 BMPRIa（针对 decapentaplegic 1 (Smad1) 的小母体）的 mRNA 表达水平在患有青光眼的视网膜中显着上调。与珠子 + AAV-EGFP 组相比，珠子 + AAV-BMP4 组的 RGC 存活率显着提高，而珠子 + AAV-CHRDL1 组的 RGC 存活率显着降低。在体外视网膜外植体培养中观察到类似的结果。与这些发现一致，ERG 中的明视负反应 (PhNR) 反应表明 RGC 功能，在过度表达 BMP4 的小鼠中得到了恢复，而 a 波和 b 波反应则没有。CHRLD1 的激活抑制 Smad1/5/8 磷酸化并加剧 RGC 损伤。微珠+AAV-BMP4组胶质纤维酸性蛋白（GFAP）的表达显着降低。

结论

BMP4 在实验性青光眼模型中促进 RGC 存活和视觉功能。CHRDL1 的激活通过抑制 BMP4/Smad1/5/8 通路加剧了 RGC 的退化。BMP4/Smad1/5/8通路的机制可能与抑制胶质细胞活化有关。我们的研究表明 BMP4 和 CHRLD1 可能作为青光眼的治疗靶点。