α2-Macroglobulin Induces Glial Fibrillary Acidic Protein Expression Mediated by Low-Density Lipoprotein Receptor-Related Protein 1 in Müller Cells

Although it is known that Müller cells express the glial fibrillary acidic protein (GFAP) in response to acute retinal damage, the regulatory mechanism is not completely understood. α(2)-Macroglobulin (α(2)M) and its receptor, low-density lipoprotein receptor-related protein 1 (LRP1), have also been found in injured retinas. Herein, the authors examined the involvement of the α(2)M/LRP1 system in GFAP expression in Müller cells using in vitro and in vivo experimental models.Using Western blot analysis and immunocytochemistry, the authors evaluated the effect of α(2)M* on GFAP expression in the Müller cell line MIO-M1, which constitutively expresses LRP1. Intracellular signaling pathways activated by α(2)M* were examined by Western blot analysis. The effect of α(2)M* on GFAP expression in the mouse retina was examined by intravitreal microinjection of α(2)M* in mouse eyes.These data demonstrate that α(2)M* induced GFAP expression in the MIO-M1 cell line, which was selectively blocked by RAP, an antagonist of LRP1 binding ligands. In addition, α(2)M* induced JAK/STAT pathway activation, determined by STAT3 phosphorylation (p-STAT3), which was also blocked by RAP. Finally, the authors showed that GFAP was expressed in the retinas of mice, preferentially in Müller cells at 3 and 6 days after a single intravitreal α(2)M* injection, whereas p-STAT3 staining increased at day 1 in both the ganglion cell layer and the inner nuclear layer.These results demonstrate that α(2)M* induces GFAP expression in retinal Müller cells through LRP1, which could be mediated by JAK/STAT pathway activation.