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Ajay Kumar, Pawan Kumar Singh, Ashok Kumar; Involvement of endoplasmic reticulum (ER) stress in the pathogenesis of bacterial endophthalmitis . Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4057.
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© ARVO (1962-2015); The Authors (2016-present)
Endoplasmic Reticulum (ER), through the unfolded protein response (UPR), regulates various cellular functions, including inflammation. Here, we have investigated the role of UPR signaling, specifically IRE1α in regulating intraocular inflammation in an experimental model of Staphylococcus aureus (SA) endophthalmitis
Endophthalmitis was induced by intravitreal injection of S. aureus in WT (C57BL/6), TLR2-/-, and MyD88-/- mice. After 24 hours of infection, retinal tissue was collected; RNA was extracted, and RT-PCR was performed to assess ER stress marker genes (XBP-1s, IRE1α, PD1, CHOP, WSF, BiP, and ERDj4) using specific primers. To determine the role of IRE1α, inhibition studies were performed using IRE1α specific inhibitor, 4μ8C, given prior to S. aureus challenge. Secretion of inflammatory mediators and the activation of TLR-downstream signaling pathways (JNK1/2, MAPK, and NF-kB) were assessed using ELISAs and western blot analyses respectively. Mechanistic studies were performed using cultured BV2 microglial cells.
S. aureus did not induce the classical UPR response as evidenced by upregulation of ER stress markers (PD1, CHOP, WSF, BiP, and ERDj4) in the infected retina. However, S. aureus caused the splicing of XBP1 in both the mouse retina and the BV2 microglia. Concomitant with increased XBP-1s levels, the level of IRE1α was also increased in infected cells/tissue. The IRE1 inhibitor (4μ8C) reduced the levels of both XBP-1s and IRE1α in WT mice and microglia, but not in TLR2-/- and MyD88-/- mice. Similarly, the expression and secretion of inflammatory cytokines were attenuated in 4μ8C-treated WT mice and microglia cells, while no reduction was observed in TLR2-/- and MyD88-/- mice. Furthermore, S. aureus-induced the activation of ERK1/2, p38 MAPK, and NF-kB signaling was down regulated by the IRE1α inhibition.
Taken together, our study, for the first time, provides evidence of IRE1α-mediated UPR stress signaling in generating retinal innate responses in bacterial endophthalmitis. Furthermore, these findings suggest a potential cross-talk between TLR and UPR-signaling in orchestrating inflammatory responses in the retina.
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