Endoplasmic reticulum stress induces the expression of COX-2 through activation of eIF2α, p38-MAPK and NF-κB in advanced glycation end products stimulated human chondrocytes

Abstract

Introduction During aging, advanced glycation end products (AGEs) accumulate in articular cartilage. In this study we determined whether AGEs induce endoplasmic reticulum (ER) stress and studied the ER stress-activated pathways that stimulate cyclooxygenase-2 (COX-2) expression in human chondrocytes. Methods Chondrocytes were stimulated with AGE-BSA. Gene expression was determined by quantitative PCR and protein expression was studied by immunoblotting. Studies to elucidate involved pathways were executed using siRNAs and specific inhibitors of eukaryotic initiation factor-2α (eIF2α), MAPKs and NF-κB. Results AGE-BSA induced expression of GRP78 with concomitant increase in COX-2 expression was observed in human chondrocytes. In addition, expression of Bag-1, an ER stress marker was also increased by AGE-BSA. RAGE knockdown inhibited AGE-BSA-induced expression of GRP78 and COX-2. Treatment with eIF2α inhibitor or eIF2α knockdown inhibited AGE-BSA-induced expression of GRP78 and COX-2 with decreased PGE2 production. Treatment with SB202190 inhibited AGE-BSA-induced expression of GRP78 and COX-2, while treatment with PD98051 inhibited AGE-BSA-induced GRP78 protein expression but had no effect on COX-2 protein expression. SP600125 had no effect on either GRP78 or COX-2 protein expression. Bay 11-7082 suppressed AGE-BSA-induced GRP78 and COX-2 expression. AGE-BSA-induced activation of NF-κB was inhibited by treatment with SB202190 and by eIF2α knockdown, but was not inhibited when chondrocytes were treated with SP600125 or PD98059. Conclusion This study demonstrates that AGEs induce ER stress and stimulate the expression of COX-2 through eIF2α, p38-MAPK and NF-κB pathways in human chondrocytes. Our results provide important insights into cartilage degradation in osteoarthritis associated with latent ER stress.

Endoplasmic Reticulum Stress and Unfolded Protein Response in Cartilage Pathophysiology; Contributing Factors to Apoptosis and Osteoarthritis

“…AGEs contribute to the degradation of type II collagen via the upregulation of matrix metalloproteinase-13 (MMP-13) [18], the induction of ER stress signaling [19,20,21], and initiation of inflammatory NF-κB and MAPK signaling [19,22]. Although AGE/RAGE activity in articular cartilage has been shown to increase with age, Larkin et al (2013) demonstrated that, following knee destabilization surgery, young RAGE-knockout mice were protected from developing OA [23].…”

iRAGE as a novel carboxymethylated peptide that prevents advanced glycation end product-induced apoptosis and endoplasmic reticulum stress in vascular smooth muscle cells

“…ER stress was extensively studied in the context of diabetes 58,59,74,75 , but was linked to RAGE activation in only few reports [27][28][29] . Despite its clinical importance, the origin of ER stress in diabetes is still unclear and we propose here that RAGE could be one of the significant contributors in VSMC.…”

“…We previously observed increased granularity in VSMC following RAGE stimulation, a sign of endoplasmic reticulum (ER) stress, which prompted us to investigate the contribution of RAGE activation to apoptosis. Arising as a new RAGE signaling mechanism [27][28][29] , ER stress regulates apoptosis via diverse pathways, including HuR-dependent up-regulation of caspase-9 [30][31][32][33] . Thus, we set out to determine the cellular consequences of RAGE activation on VSMC apoptosis using carboxymethyllysine (CML)-modified human serum albumin (HSA) stimulation of the A7r5 cell line.…”

Mapping out p38MAPK

“…Advanced glycation end products (AGEs), produced by the non-enzymatic glycation of macromolecules can accumulate in different tissues and mediate p38 activation through the generation of ER stress. 22 ER stress induced by infection can also elevate p38 activation. 23 …”