The Unfolded Protein Response (UPR) To Heightened Endoplasmic Reticulum (ER) Stress Is Impaired In The COPD Lung

Abstract

Endoplasmic reticulum (ER) stress, a condition caused by accumulation of unfolded or misfolded proteins in the ER lumen, is Rationale: heightened in the COPD lung as a result of impaired protein degradation. Normally, a highly sophisticated, compensatory response termed the unfolded protein response (UPR) relieves ER stress by up-regulating expression of a multi-gene program which codes for molecules that regulate protein folding, transport, degradation and translation. The present study examined UPR gene expression in cultured human type I and II pneumocytes in which ER stress was induced by thapsigargin, a SERCA pump inhibitor which depletes ER calcium. We also examined UPR gene expression in the lungs of subjects with advanced COPD (GOLD 4, n=24), moderate COPD (GOLD 2, n=12), and subjects at risk but without COPD (GOLD 0, n=11).Pneumocytes were treated with 1μM thapsigargin for 24 hr. Lung tissues were obtained from the Temple University Tissue Bank Methods: and the NIH Lung Tissue Research Consortium. Total RNA from cells and tissues was isolated with TRI reagent (Sigma-Aldrich) and purified by RNeasy column (Qiagen). Within each GOLD group, individual RNA samples were assayed for integrity (Bioanalyzer 2100, Agilent) and pooled in equal amounts. UPR gene expression was assessed using a commercially available RT kit and 84 gene PCR array (RT² Profiler PCR Array system, SABiosciences).Thapsigargin treatment increased (> 2-fold up-regulation) expression of 15 UPR genes in cultured type I cells and 22 genes in Results: type II pneumocytes, including the canonical UPR effectors i.e., the chaperones, GRP78, calreticulin and calnexin; the foldase phosphodiesterase isomerase (PDI); and the apoptosis-inducing transcription factor, CHOP. In contrast to thapsigargin-treated pneumocytes, GRP78, calnexin, calreticulin, and PDI mRNA levels were similar in lung tissue obtained from all 3 GOLD groups. However, CHOP mRNA was increased 1.8 fold in the GOLD 2 group compared to GOLD 0 and GOLD 4. This increase was validated (p<0.02 by ANOVA) by RT-PCR of all individual samples.These data indicate that a canonical UPR can be induced in vitro in human pneumocytes. In contrast, a UPR does not seem to Conclusion: occur in the lungs of subjects with advanced COPD. Failure to express a classic UPR chaperone response may contribute to heightened ER stress, CHOP up-regulation and pneumocyte apoptosis in COPD.

Cigarette smoking affects oxidative protein folding in endoplasmic reticulum by modifying protein disulfide isomerase

“…We did not detect a robust induction of classical ERSR genes at the level of mRNA following acute CSE; however, 25 of 84 genes on UPR array were mildly up-regulated (not shown). Up-regulation of several ER-resident proteins, such as BiP, PDI, and calreticulin, was demonstrated in the lungs of chronic smokers, but not in patients with COPD (24,48). Up-regulation of Chop protein in multiple human lung cell types, especially in alveolar macrophages, was reported after acute exposure, but the response weakened during chronic exposure (53).…”

“…This exclusion of the XBP1 branch in response to CS, especially at early times postexposure, correlates with a previously reported CS vapor inhibitory effect on XBP1 splicing in vitro (8, 21). Nevertheless, an increase in the total and spliced forms of XBP1 mRNA was seen in patients with COPD (48). Exposure to Tm that resulted in robust XBP1 splicing in livers caused a marginal 2‐fold increase in XBP1 splicing in lungs.…”

Curcumin effects on chronic obstructive pulmonary disease: A systematic review

“…It is associated with upregulation in the expression of the CHOP and GRP78 which are ERS‐associated markers. 49 Tang et al 31 have demonstrated that these two markers are elevated in COPD models and may be inhibited by SIRT1 which is a response to ERS. They have revealed that treatment with Curcumin significantly reduced CHOP and GRP78 via SIRT1 activation.…”

“…Evidence has considered elevated ERS as potential pathophysiology of COPD. It is associated with upregulation in the expression of the CHOP and GRP78 which are ERS‐associated markers 49 . Tang et al 31 have demonstrated that these two markers are elevated in COPD models and may be inhibited by SIRT1 which is a response to ERS.…”

Curcumin ameliorates chronic obstructive pulmonary disease by modulating autophagy and endoplasmic reticulum stress through regulation of SIRT1 in a rat model

“…25 A heightened ERS has been suggested as a potential pathophysiology of COPD, associated with increased expression of the ERS-related markers GRP78 and CHOP. 26 GRP78 encodes a member of the heat shock protein 70 family and is a major ER chaperone localized in the lumen of the ER and associated with activation of transmembrane ERS sensors. 27 Under normal conditions, CHOP shows low expression levels, but it is overexpressed in response to ERS-induced apoptosis.…”