Autophagy Regulates Müller Glial Cell Inflammatory Activation.

PURPOSE

We tested whether Müller cells utilize autophagy to support immune privilege in the eye.

METHODS

The essential autophagy gene Atg5 was deleted in retinal Müller cells. Inflammation was induced by intravitreal injection of lipopolysaccharide (LPS) that was monitored by hematoxylin and eosin (H&E) staining, immunofluorescent confocal microscopy, and flow cytometry. Single-cell RNA sequencing was performed on retinal Müller cells isolated from control and Atg5-deficient mice. Markers of Müller cell gliosis were assessed, and cytokine production in the eye was measured. Small interfering RNA knockdown techniques were used to examine LPS-induced inflammatory pathways in culture.

RESULTS

We observed increased and prolonged intraocular inflammation when Müller cells were autophagy (Atg5) deficient. Müller cell gliosis was significantly increased, and the retinae contained increased inflammatory mediators. Gene expression analysis revealed a heterogeneous response to LPS in Müller cells, revealing two states of activation. The normal retinae contained both basal and activated Müller cells, whereas the autophagy-deficient retinae contained only activated cells. Analysis of the gliosis markers glial fibrillary acidic protein (Gfap) and lipocalin-2 (Lcn2) confirmed this heterogeneity, as in control eyes basal and activated (gliotic) Müller glia were observed; however, with autophagy deficiency, all Müller cells were gliotic. Activated cells were largely indistinguishable between autophagy-sufficient and -deficient Müller cells. In cultured Müller cells, knockdown of Atg5 resulted in heightened mechanistic target of rapamycin (mTOR) activation, increased Gfap expression, and upregulated cytokine/chemokine production in response to LPS.

CONCLUSIONS

Autophagy regulates the activation state of Müller cells in response to LPS. Thus, autophagy restrains cellular activation and inflammation, supporting immune privilege by preventing excessive and potentially destructive immune responses.