Hamilton Glaucoma Center and Shiley Eye Institute, Viterbi Family Department of Ophthalmology, University of California San Diego, La Jolla, California, USA.
Department of Ophthalmology, Duke University, Durham, North Carolina, USA.
Oxid Med Cell Longev. 2019 Nov 6;2019:8060962. doi: 10.1155/2019/8060962. eCollection 2019.
Glaucoma is characterized by a progressive optic nerve degeneration and retinal ganglion cell loss, but the underlying biological basis for the accompanying neurodegeneration is not known. Accumulating evidence indicates that structural and functional abnormalities of astrocytes within the optic nerve head (ONH) have a role in glaucomatous neurodegeneration. Here, we investigate the impact of activation of cyclic adenosine 3',5'-monophosphate (cAMP)/protein kinase A (PKA) pathway on mitochondrial dynamics of ONH astrocytes exposed to oxidative stress. ONH astrocytes showed a significant loss of astrocytic processes in the glial lamina of glaucomatous DBA/2J mice, accompanied by basement membrane thickening and collagen deposition in blood vessels and axonal degeneration. Serial block-face scanning electron microscopy data analysis demonstrated that numbers of total and branched mitochondria were significantly increased in ONH astrocytes, while mitochondrial length and volume density were significantly decreased. We found that hydrogen peroxide- (HO-) induced oxidative stress compromised not only mitochondrial bioenergetics by reducing the basal and maximal respiration but also balance of mitochondrial dynamics by decreasing dynamin-related protein 1 (Drp1) protein expression in rat ONH astrocytes. In contrast, elevated cAMP by dibutyryl-cAMP (dbcAMP) or isobutylmethylxanthine treatment significantly increased Drp1 protein expression in ONH astrocytes. Elevated cAMP exacerbated the impairment of mitochondrial dynamics and reduction of cell viability to oxidative stress in ONH astrocytes by decreasing optic atrophy type 1 (OPA1), and mitofusin (Mfn)1/2 protein expression. Following combined treatment with HO and dbcAMP, PKA inhibition restored mitochondrial dynamics by increasing mitochondrial length and decreasing mitochondrial number, and this promoted cell viability in ONH astrocytes. Also, PKA inhibition significantly promoted Akt/Bax phosphorylation and Mfn1/2 oligomerization in ONH astrocytes. These results suggest that modulation of the cAMP/PKA signaling pathway may have therapeutic potential by activating Akt/Bax phosphorylation and promoting Mfn1/2 oligomerization in glaucomatous ONH astrocytes.
青光眼的特征是视神经退行性变和视网膜神经节细胞丢失，但伴随的神经退行性变的潜在生物学基础尚不清楚。越来越多的证据表明，视神经头（ONH）内星形胶质细胞的结构和功能异常在青光眼神经退行性变中起作用。在这里，我们研究了 cAMP/蛋白激酶 A（PKA）通路激活对暴露于氧化应激的 ONH 星形胶质细胞中线粒体动力学的影响。DBA/2J 青光眼小鼠的神经胶层中，ONH 星形胶质细胞的星形胶质细胞突起明显丢失，同时伴有基底膜增厚和血管内胶原沉积以及轴突变性。连续块面扫描电子显微镜数据分析表明，ONH 星形胶质细胞中线粒体的总数和分支数明显增加，而线粒体长度和体积密度明显降低。我们发现，过氧化氢（HO-）诱导的氧化应激不仅通过降低基础呼吸和最大呼吸来损害线粒体生物能学，而且还通过降低与动力相关蛋白 1（Drp1）蛋白表达来破坏线粒体动力学平衡在大鼠 ONH 星形胶质细胞中。相反，用二丁酰环磷酸腺苷（dbcAMP）或异丁基甲基黄嘌呤处理可显著增加 ONH 星形胶质细胞中 Drp1 蛋白的表达。升高的 cAMP 通过降低视神经萎缩 1 型（OPA1）和融合蛋白（Mfn）1/2 蛋白表达，加剧了氧化应激对 ONH 星形胶质细胞中线粒体动力学和细胞活力的损害。在与 HO 和 dbcAMP 联合处理后，PKA 抑制通过增加线粒体长度和减少线粒体数量来恢复线粒体动力学，并促进 ONH 星形胶质细胞的细胞活力。此外，PKA 抑制还显著促进了 ONH 星形胶质细胞中 Akt/Bax 的磷酸化和 Mfn1/2 的寡聚化。这些结果表明，通过激活 Akt/Bax 磷酸化和促进 Mfn1/2 寡聚化，调节 cAMP/PKA 信号通路可能具有治疗青光眼 ONH 星形胶质细胞的潜力。
Zotero 插件
