Dihydrosterculic acid induces hepatic PPARα target gene expression in mice

Cottonseed oil (CSO) is a seed oil with a unique fatty acid composition and the ability to reduce lipid levels in humans and mice. The present study aimed to characterize the effects of dihydrosterculic acid (DHSA), a cyclopropyl fatty acid found in CSO, on lipid metabolism. First, male wild-type mice were fed CSO- or isocaloric oil-enriched diets (lacking DHSA) for 6 weeks. Tissues were analyzed via RNA-sequencing which identified 45 differentially expressed genes within the CSO group, the majority of which are associated with lipid metabolic processes. Despite being a moderate-fat diet, no changes in hepatic or plasma triglyceride were observed in the CSO group. Confirmational tissue analysis showed an increase in hepatic peroxisome proliferator-activated receptor alpha (PPARα) and PPARα target gene expression in the CSO group compared to control groups, suggesting that DHSA effects may be mediated through increased PPARα transcriptional activity and fatty acid oxidation (FAO). To test this hypothesis, female PPARα knockout mice were fed a CSO-enriched diet. In the absence of PPARα, the lipid-lowering effect of the CSO diet was lost. Next, FAO was assessed in DHSA-treated HepG2 cells by measuring mitochondrial respiration with long-chain fatty acids and adenosine diphosphate substrates. Compared to the control, DHSA-treated cells demonstrated a higher capacity to utilize FAO for energy production. Lastly, CSO-fed mice exhibited significantly lower respiratory exchange ratio with an elevated energy expenditure (EE) compared to SFO-fed mice. In total, these data suggest that the effects of CSO are the result of a DHSA-dependent increase in EE via PPARα induction of FAO pathways. KEY POINTS: Previous studies with cottonseed oil- (CSO) enriched diets showed reductions in hepatic and plasma lipids; however, it is unclear whether linoleic acid or dihydrosterculic acid (DHSA), a cyclopropyl fatty acid found in CSO, is responsible for these phenotypic changes. This study utilized a unique diet design in which mice were fed either a CSO-enriched diet (DHSA + linoleic acid) or an isocaloric oil-enriched diet (containing linoleic acid but lacking DHSA). RNA-sequencing analysis indicated CSO-fed mice demonstrated increased expression of genes associated with fatty acid oxidation (FAO) in addition to increases in the transcription factor and FAO regulator peroxisome proliferator-activated receptor alpha (PPARα) and its oxidative target genes. Knockout of PPARα confirmed this transcription factor is required for the lipid-lowering phenotype seen following CSO-enriched diets. CSO-fed mice demonstrated significantly lower respiratory exchange ratio and higher energy expenditure compared to chow- and SFO-fed mice, indicative of elevated FAO exclusive to the CSO group.