Metabolic and Phenotypic Differences between Mice Producing a Werner Syndrome Helicase Mutant Protein and Wrn Null Mice

Abstract

Werner syndrome (WS) is a premature aging disorder caused by mutations in a RecQ-family DNA helicase, WRN. Mice lacking part of the helicase domain of the WRN orthologue exhibit many phenotypic features of WS, including metabolic abnormalities and a shorter mean life span. In contrast, mice lacking the entire Wrn protein (i.e. Wrn null mice) do not exhibit a premature aging phenotype. In this study, we used a targeted mass spectrometry-based metabolomic approach to identify serum metabolites that are differentially altered in young Wrn helicase mutant and Wrn null mice. An antibody-based quantification of 43 serum cytokines and markers of cardiovascular disease risk complemented this study. We found that Wrn helicase mutants exhibited elevated and decreased levels, respectively, of the anti-inflammatory cytokine IL-10 and the pro-inflammatory cytokine IL-18. Wrn helicase mutants also exhibited an increase in serum hydroxyproline and plasminogen activator inhibitor-1, markers of extracellular matrix remodeling of the vascular system and inflammation in aging. We also observed an abnormal increase in the ratio of very long chain to short chain lysophosphatidylcholines in the Wrn helicase mutants underlying a peroxisome perturbation in these mice. Remarkably, the Wrn mutant helicase protein was mislocalized to the endoplasmic reticulum and the peroxisomal fractions in liver tissues. Additional analyses with mouse embryonic fibroblasts indicated a severe defect of the autophagy flux in cells derived from Wrn helicase mutants compared to wild type and Wrn null animals. These results indicate that the deleterious effects of the helicase-deficient Wrn protein are mediated by the dysfunction of several cellular organelles.

Aging and Autophagy in the Heart

“…Increases in DNA damage and defective DNA repair have been shown to inhibit autophagy 66, 67 . Somatic mtDNA mutation inhibits autophagy, thereby allowing mutated mtDNA to escape degradation and promote mitochondrial dysfunction.…”

Serum vitamin C levels modulate the lifespan and endoplasmic reticulum stress response pathways in mice synthesizing a nonfunctional mutant WRN protein

“…We have reported that the mutant Wrn protein (Wrn Dhel ) is mislocalized in the cytoplasm of Wrn Δhel/Δhel mice (11). Further microscopy analyses indicated a colocalization of Wrn Dhel proteins with the PDI.…”

“…Oxidative stress in the liver tissue of Wrn Dhel/Dhel /Gulo 2/2 mice We had found that the liver of Wrn Δhel/Δhel and Gulo 2/2 mice treated with low amounts of ascorbate (,0.01% in drinking water) exhibit an oxidative stress in the ER (11,21,29). The liver plays a pivotal role in nutrient, hormone, lipid, and metabolic waste product processing, thereby maintaining body homeostasis (30).…”

“…S3). We also analyzed ATF4, CHOP, HSC70, and full-length and cleaved ATF6 protein levels in age-matched WT, Wrn Δhel/Δhel , and 0.01% ascorbate-treated Gulo 2/2 mice, because it had not been examined in our other studies (11,21,29). There was no significant difference in CHOP, HSC70, or full-length and cleaved ATF6 protein levels between these groups of mice, according to ANOVA results (Supplemental Fig.…”

“…Several years ago, we generated a mouse model with a deletion in the helicase domain of the murine WS RecQ-like helicase gene (Wrn) ortholog (10) (referred to as Wrn Δhel/Δhel , hereafter). This deletion abolishes both the helicase and exonuclease activities of the mouse Wrn protein (11). Wrn Δhel/Δhel mice develop abnormally high visceral fat content, hepatic steatosis (12), and aortic stenosis followed by cardiac fibrosis (13).…”