Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, FL, USA.
Dev Neurobiol. 2020 Mar;80(3-4):98-110. doi: 10.1002/dneu.22741. Epub 2020 Apr 17.
Muller glia are the predominant glial cell type in the retina, and they structurally and metabolically support retinal neurons. Wnt/β-catenin signaling pathways play essential roles in the central nervous system, including glial and neuronal differentiation, axonal growth, and neuronal regeneration. We previously demonstrated that Wnt signaling activation in retinal ganglion cells (RGC) induces axonal regeneration after injury. However, whether Wnt signaling within the adjacent Muller glia plays an axongenic role is not known. In this study, we characterized the effect of Wnt signaling in Muller glia on RGC neurite growth. Primary Muller glia and RGC cells were grown in transwell co-cultures and adenoviral constructs driving Wnt regulatory genes were used to activate and inhibit Wnt signaling specifically in primary Muller glia. Our results demonstrated that activation of Wnt signaling in Muller glia significantly increased RGC average neurite length and branch site number. In addition, the secretome of Muller glia after induction or inhibition of Wnt signaling was characterized using protein profiling of conditioned media by Q Exactive mass spectrometry. The Muller glia secretome after activation of Wnt signaling had distinct and more numerous proteins involved in regulation of axon extension, axon projection and cell adhesion. Furthermore, we showed highly redundant expression of Wnt signaling ligands in Muller glia and Frizzled receptors in RGCs and Muller glia. Therefore, this study provides new information about potential neurite growth promoting molecules in the Muller glia secretome, and identified Wnt-dependent target proteins that may mediate the axonal growth.
Muller 胶质细胞是视网膜中主要的神经胶质细胞类型，它们在结构和代谢上支持视网膜神经元。Wnt/β-连环蛋白信号通路在中枢神经系统中发挥着重要作用，包括神经胶质和神经元分化、轴突生长和神经元再生。我们之前的研究表明，视网膜神经节细胞（RGC）中 Wnt 信号的激活可诱导损伤后的轴突再生。然而，相邻 Muller 胶质细胞内的 Wnt 信号是否具有轴生成作用尚不清楚。在这项研究中，我们研究了 Wnt 信号在 Muller 胶质细胞中对 RGC 神经突生长的影响。原代 Muller 胶质细胞和 RGC 细胞在 Transwell 共培养物中生长，并使用驱动 Wnt 调节基因的腺病毒构建体来特异性地激活和抑制原代 Muller 胶质细胞中的 Wnt 信号。我们的结果表明，Muller 胶质细胞中 Wnt 信号的激活显著增加了 RGC 平均神经突长度和分支点数量。此外，通过 Q Exactive 质谱对条件培养基进行蛋白质谱分析，对诱导或抑制 Wnt 信号后 Muller 胶质细胞的分泌组进行了表征。Wnt 信号激活后，Muller 胶质细胞的分泌组具有独特且更多数量的参与调节轴突延伸、轴突投射和细胞黏附的蛋白质。此外，我们还显示 Muller 胶质细胞中 Wnt 信号配体和 RGC 与 Muller 胶质细胞中的 Frizzled 受体具有高度冗余的表达。因此，这项研究为 Muller 胶质细胞分泌组中潜在的促进神经突生长的分子提供了新的信息，并确定了可能介导轴突生长的 Wnt 依赖性靶蛋白。
