Toll-like Receptor 2 Facilitates Oxidative Damage-Induced Retinal Degeneration

Abstract

Graphical Abstract Highlights d TLR2 activates the alternative complement pathway d TLR2 signaling triggers sub-lytic MAC formation on retinal pigment epithelial cells d TLR2 deficiency reduces oxidative stress-induced C3 and MAC in the outer retina d TLR2 blockade protects photoreceptors and RPE from oxidative stress-induced cell death SUMMARY Retinal degeneration is a form of neurodegenerative disease and is the leading cause of vision loss globally. The Toll-like receptors (TLRs) are primary components of the innate immune system involved in signal transduction. Here we show that TLR2 induces complement factors C3 and CFB, the common and rate-limiting factors of the alternative pathway in both retinal pigment epithelial (RPE) cells and mononuclear phagocytes. Neutralization of TLR2 reduces opsonizing fragments of C3 in the outer retina and protects photoreceptor neurons from oxidative stress-induced degeneration. TLR2 deficiency also preserves tight junction expression and promotes RPE resistance to fragmentation. Finally, oxidative stress-induced formation of the terminal complement membrane attack complex and Iba1+ cell infiltration are strikingly inhibited in the TLR2-deficient retina. Our data directly implicate TLR2 as a mediator of retinal degeneration in response to oxidative stress and present TLR2 as a bridge between oxidative damage and complement-mediated retinal pathology.

The Relevance of Oxidative Stress in the Pathogenesis and Therapy of Retinal Dystrophies

“…Genotype and smoking have been independently related to AMD with synergic effects [85]. Recently, TLR2 has been also reported as a mediator between oxidative stress damage in the RPE and the development of complement-mediated retinal pathology in AMD and other retinal neurodegeneration pathologies, so that TLR2 blockade protects photoreceptors and RPE from oxidative stress-induced cell death [86].…”

“…Neutralization of TLR2 reduces complement deposition, microglial activation, and protects photoreceptor neurons from oxidative stress-induced degeneration. TLR2 deficiency also promotes RPE resilience [86].…”

MicroRNA-223 Regulates Retinal Function and Inflammation in the Healthy and Degenerating Retina

“…In this model, the “wash out” period allows for RFP expression to be lost in circulating monocytes due to turnover, but RFP expression to be retained by long-lived resident microglia ( O’Koren et al, 2016 ). Following photo-oxidative damage, CX3CR1 YFP–CreER/wt :R26 RFP retinas were collected via corneal incision and digested using mechanical dissociation and papain digestion (LS003126; Worthington Biochemicals, Lakewood, NJ, United States), as described previously ( Mulfaul et al, 2020 ; Wooff et al, 2020b ). YFP + microglia/macrophages were FACS-isolated based on relative expression of RFP (BD FACS Aria III; JCSMR Imaging and Cytometry Facility).…”

“…Primary retinal CD11b + microglia were isolated from dim-reared mouse retinas and sorted by FACS (BD FACS Aria III; JCSMR Imaging and Cytometry Facility) into a 48-well plate at ∼1500 cells per well, as previously described ( Mulfaul et al, 2020 ; Wooff et al, 2020b ). Cells were stained with a PE anti-mouse/human CD11b antibody (clone M1/70, #101207; BioLegend) for 40 min prior to FACS.…”

“…Cells were stained with a PE anti-mouse/human CD11b antibody (clone M1/70, #101207; BioLegend) for 40 min prior to FACS. Isolated primary microglia were cultured for 4 weeks in Dulbecco's Modified Eagle Medium (DMEM)-F12 (Thermo Fisher Scientific) supplemented with 10% fetal bovine serum (FBS; Sigma Aldrich), 1% antibiotic-antimycotic (Thermo Fisher Scientific), 3% L-glutamine (Thermo Fisher Scientific), 0.25 ng/ml GM-CSF (Stem Cell Technologies, Vancouver, BC, Canada), and 2.5 ng/ml M-CSF (Miltenyi Biotec, Bergisch Gladbach, Germany), as previously described (Mulfaul et al, 2020;Wooff et al, 2020b).…”