Role of E4orf1 in attenuation of renal fat accumulation and injury in mice exposed to high fat diet

Abstract

BackgroundPrevalence of chronic kidney disease (CKD) is increasing along with obesity. Hyperinsulinemia is often associated with obesity and in turn linked with CKD. Rodent studies show that a high fat diet induces hyperinsulinemia, accelerates renal lipogenesis (as determined by the expressions of fatty acid synthase (FAS) and Acetyl CoA Carboxylase (ACC), increases renal lipid accumulation and causes renal injury. We previously showed that transgenic expression of E4orf1 (E4), a virus‐derived protein, directly improves glycemic control and reduces endogenous insulin response to a glucose challenge in mice. Using this model, we tested the hypothesis that “Improvement in glycemic control and hyperinsulinemia in E4 mice will be accompanied by reduction in renal lipogenesis and lipid accumulation along with renal injury”.MethodsExperiment 1Twenty‐nine week old control (C57BL6/J, n=8) and E4orf1 transgenic (E4, n=6) mice were fed a chow‐doxycycline diet for 6 weeks, followed by 10 weeks of a high fat‐doxycycline diet (60% kcal).Experiment 2Fifty week old E4orf1 positive mice (E4; n=3) or E4orf1 negative littermates (control; n=4) were fed same high fat doxycycline diet for 20 weeks. In both experiments, E4 protein was inducibly expressed in the adipose tissue upon doxycycline ingestion in the E4 transgenic mice. As expected, E4 expression significantly improved glycemic control and reduced hyperinsulinemia as presented elsewhere. For this study, the protein expression of FAS and ACC and triglycerides (TG) accumulation was determined in the kidneys from these mice. Moreover, mRNA levels of kidney injury markers like fibronectin, type IV collagen, PA‐1, MCP‐1, TGF‐β, IL‐18, HAVCR/KIM‐1 and VEGF were also determined by RT‐PCR.ResultsKidney weights normalized to total body weight did not differ between groups. Renal expression of FAS and ACC as determined by Western blot was significantly reduced (p<0.005 and p<0.05 for FAS and ACC respectively) in E4 group compared to control. The amount of TG normalized to kidney weight was significantly lower for the E4 group compared to control (p<0.05). Moreover, no statistically significant changes were found in mRNA levels for markers of kidney injury between E4 and control mice.ConclusionE4 reduces lipogenesis and lipid accumulation in the kidneys, which may be linked to the improvement in hyperinsulinemia induced by E4. This is the first report for the role of E4 in influencing renal metabolism. More investigation is required to determine if the lowering of renal lipid accumulation by E4 protects from HFD‐induced renal injury in future studies.US and International patents received for the use of E4.Western blot analysis for FAS and ACC protein in high fat fed mice kidney. (A) and (C) represent data for experiment 1. (B) and (C) represent data for experiment 2. Data is presented as mean±SEM. *p <0.05 and **p <0.005 calculated by Student’s t test for unpaired data.Figure 1TG concentration in high fat fed mice kidney. (A) represents data for experiment 1 and (B) represents data for experiment 2. Data is presented as mean±SEM. *p <0.05 by calculated Student’s t test for unpaired data.Figure 2