HSP-4 endoplasmic reticulum (ER) stress pathway is not activated in a C. elegans model of ethanol intoxication and withdrawal

Abstract

Acute and chronic exposure of Caenorhabditis elegans to concentrations of ethanol in the range 250-350 mM elicits distinct behaviours. Previous genetic analysis highlights specific neurobiological substrates for these effects. However, ethanol may also elicit cellular stress responses which may contribute to the repertoire of ethanol-induced behaviours. Here, we have studied the effect of ethanol on an important arm of the cellular stress pathways, which emanates from the endoplasmic reticulum (ER) in response to several conditions including heat shock and chemical or genetic perturbations that lead to protein misfolding. HSP-4 is a heat shock protein and homologue of mammalian BiP. It is a pivotal upstream component of the ER stress response. Therefore, we used a C. elegans heat shock protein mutant, hsp-4, and a strain carrying a transcriptional reporter, Phsp-4::gfp, to test the role of the ER following chronic ethanol conditioning. We found no evidence for an overt ER response during acute or prolonged exposure to concentrations of ethanol that lead to defined ethanol-induced behaviours. Furthermore, whilst hsp-4 was strongly induced by tunicamycin, pre-exposure of C. elegans to low doses of tunicamycin followed by ethanol was not sufficient to induce an additive ER stress response. Behavioural analysis of an hsp-4 mutant indicated no difference compared to wild type in susceptibility to ethanol intoxication and withdrawal. There is a clear precedent for a significance of ER stress pathways particularly in clinical conditions associated with toxic or pathological effects of high doses of alcohol consumption. The concentrations of ethanol used in this C. elegans study equate to the highest blood alcohol levels measured in patients with chronic alcohol dependency. Taken together, these observations imply that the classic ER stress pathway in C. elegans is relatively refractory to induction by ethanol.

Chronic Ethanol Exposure Increases Cytochrome P‐450 and Decreases Activated in Blocked Unfolded Protein Response Gene Family Transcripts in Caenorhabditis elegans

“…Our result that is abu genes were downregulated is unexpected as a previous study has shown upregulation of abu during ER stress triggered by oxidative stress in cultured neurons exposed to ethanol . However, another study showed lack of HSP‐4 ER stress pathway activation in a C. elegans model of ethanol intoxication supporting our present results . We also did not observe upregulation of hsp‐4 in this study.…”

New Insights into the Pathogenesis of Alcohol-Induced ER Stress and Liver Diseases

“…Thus, integrity of the ER or alcohol metabolism might be necessary for AERR [34]. In supporting this, in the species Caenorhabditis elegans without a liver for alcohol digestion/metabolism, little AERR has been detected [35]. The most important and clinically relevant studies regarding AERR are from human cells and patients.…”

The putative multidrug resistance proteinMRP‐7 inhibits methylmercury‐associated animal toxicity and dopaminergic neurodegeneration inCaenorhabditis elegans

“…HSP‐4 is a member of the hsp70 family of molecular chaperones that has been shown to be up‐regulated in response to endoplasmic reticulum (ER) stress (Ient et al . ). A 4‐h exposure to MeHg results in over 30‐fold increase in gst‐38 and hsp‐16.1 gene expression, suggesting as in vertebrate studies that the toxicant perturbs redox homeostasis, protein folding, and Ca 2+ regulation (Fig.…”

“…In contrast, following a chronic 96-h exposure to MeHg, there is a significant increase in hsp-4, hsp-6, and hsp-16.1 gene expression in mrp-7 RNAi animals relative to WT animals, suggesting that an increase in cellular Hg levels disrupts protein homeostasis or function within the endoplasmic reticulum, mitochondria, and Golgi complex, respectively ( Fig. 4d) (Ient et al 2012;Kourtis et al 2012;Lee and Lee 2013). We have also recently shown that the PD-associated GST-p homolog GST-1 in C. elegans is expressed in DA neuron and modulates toxicant-induced DA neurodegeneration .…”

“…HSP-6 and HSP-16.1 are expressed exclusively in the mitochondria and Golgi apparatus, respectively, with the latter involved in maintaining Ca 2+ homeostasis in the Gogi by functionally interacting with the Ca 2+ and Mn 2+ transporter PMR-1 (Kourtis et al 2012). HSP-4 is a member of the hsp70 family of molecular chaperones that has been shown to be up-regulated in response to endoplasmic reticulum (ER) stress (Ient et al 2012). A 4-h exposure to MeHg results in over 30-fold increase in gst-38 and hsp-16.1 gene expression, suggesting as in vertebrate studies that the toxicant perturbs redox homeostasis, protein folding, and Ca 2+ regulation ( Fig.…”