Targeting HSP: Immune Tolerance to HSP60 Attenuates Neurodegeneration in Glaucoma

Abstract

Purpose : Our previous study suggests that a bacteria-primed T cell-mediated autoimmune mechanism underlies the pathogenesis of glaucoma, and heat shock proteins (HSPs) are thought to act as pathogenic autoantigens. We hypothesized that induction of immune tolerance to bacterial HSP60 might block such a pathogenic immune response and attenuate neuron loss in glaucoma.

Methods : Adult C57BL/6J mice were given a low dose of recombinant bacterial HSP60, Ovalbumin (OVA) or saline (both as controls) in the nostril each day for 7 days. Elevation of IOP was induced unilaterally by an anterior chamber injection of polystyrene microbeads (MB). Visual and retinal functions were assessed by optomotor response (OMR) and electroretinogram positive scotopic threshold response (pSTR). Mice were sacrificed 2, 4 and 8 weeks after MB injection. T cell responses to bacterial HSP60 were analyzed by ear DTH (delayed-type hypersensitivity responses) testing and flow cytometry. Glaucomatous neural damage was quantified by retinal ganglion cell (RGC) and axon counts.

Results : Nostril administration of a low dose HSP60 induced immune tolerance as shown by reduced DTH responses and increased levels of T regulatory cells as seen by analysis of flow cytometry. MB-injected eyes maintained an IOP level of 25±3 mmHg as compared to 12±2mmHg in the contralateral non-injected eyes. We observed no significant differences in IOP levels between HSP60-, OVA- and saline-treated mice. Treatment with HSP60 or OVA did not alter the basal levels of visual acuity (VA), contrast sensitivity (CS) or pSTR prior to MB-injection, as compared to naïve or saline-treated mice. However, after MB-injection, at all time points, VA and CS as assessed by OMR were significantly better in HSP60-treated micecompared to saline or OVA-treated mice. Consistently, both RGC function assessed by pSTR amplitudes and RGC counts were significantly higher in HSP60-treated mice compared to saline or OVA-treated mice after MB-injection.

Conclusions : Intranasal administration of multiple low doses of bacterial HSP60 induced immune tolerance and attenuated RGC loss and functional deterioration in an MB-induced mouse model of glaucoma. These results suggest an attractive antigen-specific therapeutic strategy for the prevention of vision loss in glaucoma.

This is a 2020 ARVO Annual Meeting abstract.