PERK and XBP1 differentially regulate CXCL10 and CCL2 production

Abstract

Inflammation plays a key role in the pathogenesis of many retinal degenerative diseases related with photoreceptor dysfunction/degeneration. However the involvement of photoreceptor cells in inflammatory reactions is largely unknown as they are not considered as inflammatory cells. In this study, we assessed whether photoreceptor cells can produce CCL2 and CXCL10, two important players in inflammation during endoplasmic reticulum (ER) stress. After photoreceptor 661W cells were treated with ER stress inducer thapsigargin (TG), induction of ER stress increased CXCL10 and CCL2 expression at both mRNA and protein levels, which was significantly blocked by an ER stress blocker 4-phenylbutyrate. ER stress contains three pathways: PERK, ATF6 and IRE1α. Knockdown of PERK attenuated TG-induced CXCL10 and CCL2 mRNA expression, associated with significant decreases in phosphorylation of NF-κB RelA and STAT3. In contrast to PERK, knockdown of XBP1, which is activated by IRE1α-mediated splicing, robustly enhanced TG-induced CXCL10 and CCL2 expression and phosphorylation of NF-κB RelA and STAT3. Blockade of NF-κB or STAT3 markedly diminished TG-induced CXCL10 and CCL2 expression. The specific roles of PERK and XBP1 in CXCL10 and CCL2 expression were further investigated by treating photoreceptor cells with advanced glycation end products (AGE) and high glucose (HG), two of the major contributors to diabetic complications. Similarly, AGE and HG induced CXCL10 and CCL2 expression in which PERK was a positive regulator while XBP1 was a negative regulator. These studies suggest that photoreceptors may be involved in retinal inflammation by expressing chemokines CXCL10 and CCL2. PERK and IRE1α/XBP1 in the unfolded protein response differentially regulate the expression of CXCL10 and CCL2 likely through modulation of ER stress-induced NF-κB RelA and STAT3 activation.

Caffeic acid attenuates the inflammatory stress induced by glycated LDL in human endothelial cells by mechanisms involving inhibition of AGE‐receptor, oxidative, and endoplasmic reticulum stress

“…In addition, MCP‐1 secretion is reduced by SAL in gLDL‐exposed HEC. Reported data show that eIF2α/CHOP pathway activated by ERS is important for the stimulation of VCAM‐1 and MCP‐1 production in other experimental models . Interestingly, in agreement with these studies, we have previously revealed that in HEC after 24 h incubation with gLDL, only eIF2α/CHOP pathway of the unfolded protein response remains upregulated .…”

p38MAPK plays a critical role in induction of a pro-inflammatory phenotype of retinal Müller cells following Zika virus infection

“…These data indicate that ZIKV can effectively infect and replicate in Müller cells. As a comparison, we infected human retinal microvascular endothelial cells (HRMECs) and mouse retinal photoreceptor cells (661W cells (Zhu et al, 2017)) at a higher MOI of 0.2. Similar to Müller cells, ZIKV viral RNA in HRMECs was detected at day 1 and increased at day 4 after infection (Fig.…”

“…Therefore, we next treated cells at day 3 post infection with the inhibitors for ERK (PD98059), p38MAPK (SB202190), NF-κB (PDTC), STAT3 (Stattic) and JAK1/JAK2 (AG490), and determined their effects on ZIKV-induced inflammatory and growth factors. Since endoplasmic reticulum (ER) stress and NADPH oxidase have been shown to regulate the activation of these kinases and transcription factors in response to different stimuli (Valadao et al, 2016; Zhang et al, 2009; Zhu et al, 2017), the inhibitors for ER stress and NADPH oxidase were also included: TUDCA and PBA–chemical chaperones blocking ER stress, GSK2606414–inhibitor of ER stress branch PERK, 4μ8C–inhibitor of ER stress branch IRE1, and apocynin–inhibitor of NADPH oxidase. Most inhibitors were not toxic to cells, while PBA, 4μ8C and Apocynin slightly reduced Müller cell viability as determined by MTT assay (Supplementary Figure 1).…”

“…Human retinal microvascular endothelial cells (HRMECs) and mouse photoreceptor cell line 661W were cultured as described previously (Ameri et al, 2014; Zhu et al, 2017). Vero cells were cultured in Minimum Essential Medium Eagle medium (MEM, Cellgro) supplemented with 8% FBS.…”

“…The cytotoxicity and cell viability were determined by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay (Stockert et al, 2012; Zhu et al, 2017). Cells were seeded at a density of 1 × 10 4 cells/well in 96-well plates and treated with inhibitors at day 3.…”