Apolipoprotein E-containing lipoproteins and LRP1 protect from NMDA-induced excitotoxicity associated with reducing α2-macroglobulin in Müller Glia

Abstract

PURPOSE. Optic nerve damage leads to impairment of visual functions. We previously demonstrated that apolipoprotein E-containing lipoproteins (E-LPs) protect retinal ganglion cells (RGCs) from degeneration in a glaucoma model of glutamate/aspartate transporter-deficient mice. This study aimed to determine whether E-LPs protect RGCs from N-methyl-D-aspartate (NMDA)-induced excitotoxicity, and to investigate the details of an indirect neuroprotective mechanism of E-LPs by reducing α2-macroglobulin, which interferes with the neuroprotective effect of E-LPs, in Müller glia. METHODS. Excitotoxicity was caused by intravitreal injection of NMDA, and then retinae were subjected to immunoblotting or quantitative reverse transcription-PCR. Primary cultures of mouse mixed retinal cells and mouse Müller glia were used for evaluating the effects of E-LPs on the expression of α2-macroglobulin. RESULTS. Intravitreal injection of E-LPs protected the optic nerve from degeneration and attenuated the increase in α2-macroglobulin in aqueous humor and retina of rats. E-LPs directly decreased the expression and secretion of α2-macroglobulin in primary cultures of Müller glia; this decrease in production of α2-macroglobulin was blocked by knockdown of the low-density lipoprotein receptor-related protein 1 (LRP1) with small interfering RNA. E-LPs promoted the phosphorylation of STAT3, whereas Stattic, an inhibitor of STAT3, restored the expression of α2-macroglobulin decreased by E-LPs. CONCLUSIONS. In addition to our previous findings of the protection of RGCs by E-LPs, the new observations in Müller glia indicate that a reduction of the intraocular α2-macroglobulin, regulated by the E-LP-LRP1-STAT3 pathway, might be an additional protective mechanism against excitotoxicity in the retina.