Complement factor B as a strategic target for inhibiting neuroinflammation and protecting retinal ganglion cells in a microbead-induced mouse model of glaucoma

Abstract

Purpose : Glaucoma is a leading cause of irreversible blindness worldwide and the complement system plays an important role in its pathogenesis. Inhibition of complement factor B (Fb), a key regulator of the alternative complement pathway (AP), is a potential therapeutic target for neurodegeneration in the CNS, where specifically inhibiting Fb was neuroprotective and attenuated complement-mediated neuroinflammation in experimental models of spinal cord injury and traumatic brain injury. Herein we use Fb knockout mice (deficient in the AP) to determine the extent to which Fb and the AP contribute to neuroinflammation and optic nerve degeneration in a microbead-induced mouse model of glaucoma.

Methods :
Intracameral injection of magnetic microbeads (control: saline) was used to elevate the intraocular pressure in complement factor B knockout (Fb^-/-) and wild type (WT) mice. At 2 and 5 weeks post-microbead injection, retinas were processed for qPCR (n=4-8/group). At 5 weeks post-microbead injection, visual acuity was measured by optomotor reflex, optic nerves were assessed for axon density, and retinas were assessed for RGC density, microglia activation, and gene expression.

Results : IOP was increased equally in microbead-injected Fb^-/- and WT mice. Microbead-injected WT mice showed a significant increase in Fb expression as compared to saline controls; 5-fold increase at 2 weeks and 8-fold increase at 5 weeks post microbead injecton. Furthermore, the induction of C3, C5a receptors C5ar1 and C5l2, chemokine Cxcl10, and Gfap in the retina of microbead-injected WT mice was significantly reduced by 2-fold or greater in microbead-injected Fb^-/- mice. This inhibition of complement and inflammatory mediators in Fb^-/- mice coincided with reduced microglia activation and significant preservation of visual acuity, and RGC and axon density as compared to WT mice.

Conclusions : Our findings confirm Fb as a therapeutic target for the treatment of glaucoma, where knocking out Fb provides significant neuroprotection. Moreover, knocking out Fb downregulates the anaphylatoxin C5a receptors, C5ar1 and C5l2, and reduces glial activation, underscoring the neurodestructive potential of the alternative complement pathway and its crucial involvement in propagating glial activation and
neuroinflammation in glaucoma.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.