Omega‐Hydroxylase Gene Family Contribution to Acetate Levels in Fasting and Starvation

Abstract

IntroductionSerum acetate levels have been shown to increase with fasting and are implicated in metabolic syndrome as well as tumorigenesis. While the gut microbiota is one source of acetate, studies have shown that short‐chain fatty acid supplementation rescues histone acylation in germ‐free mice. However, the mechanism of conversion of short‐chain fatty acids to serum acetate is unclear. In this study, we demonstrate that serum acetate levels rise with prolonged fasting in correlation with hepatic expression of members of the omega‐hydroxylase gene family.MethodsMale and female C57BL/6 mice, 10–16 weeks of age, previously on a standard chow diet, were removed to wire bottom cages with water ad libitum and fasted for 24, 48, 72 or 96 hours. After a period of fasting, body composition was measured using EchoMRI and mice were sacrificed. Metabolite levels in serum and liver homogenate were quantified using colorimetric assays while mRNA expression levels of a variety of metabolic genes were quantified using absolute qPCR with a dPCR‐confirmed external standard. mRNA expression level findings were confirmed with Western blot. In a supplemental experiment, C57BL/6 mice were injected with CYP4a14 in a viral vector and sacrificed one week later and subjected to similar analysis.ResultsMale and female both showed increased expression of CYP4a with fasting. Hepatic expression of CYP4a10 in males increases from 492 copies/ng cDNA (SD 163) in the fed state to 31,240 copies/ng (SD 3,465) after 24 hours of fasting, while females express 4,680 copies/ng (SD 2,790) at baseline with an increase to 49,072 copies/ng (SD 16,960) after 24 hours of fasting. Similarly, hepatic levels of CYP4a14 in fed females are 20,670 copies/ng (SD 10,280) and increase to 425,950 copies/ng (SD 288,370) at 48 hours of fasting, while males express only 1,300 copies/ng (SD 338) in the fed state but increase to 219,900 copies/ng (SD 213,060) after 48 hours of fasting. In males, serum acetate levels increase from 1.53 mg/dL (SD 2.65) in the fed state to 21.03 mg/dL (SD 10.89) at 24 hours of fasting. In females, serum acetate levels increase from 6.85 mg/dL (SD 2.20) in the fed state to 10.1 mg/dL (SD 2.43) after 24 hours of fasting. CYP4a14 adenovirus infected mice had enlarged livers with increased liver triacylglycerol, free fatty acids, cholesterol and increased serum acetate levels, suggesting that omega‐hydroxylated fatty acids may contribute to production of acetate.DiscussionElucidating the mechanism linking the epigenome to metabolism is critical for the development of strategies for the prevention and treatment of metabolic syndrome and its pathological complications. The CYP4a gene family—already implicated in renal hypertension and colonic tumorigenesis—likely plays a role in the pathogenesis of obesity and perhaps tumorigenesis through increased acetate, which can serve as an alternative energy source and epigenetic modifier of the genome. Further characterization of the omega‐hydroxylation gene family for the purposes of drug development may help ameliorate the metabolic health crises created by high‐fat diets.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.