Testosterone downregulates the Nrf2 system and promotes vascular dysfunction in HFD‐fed mice

Abstract

BackgroundObesity is an important cause of morbidity and mortality worldwide. Mechanisms triggered by the endocrine system justify the increase in body fat depots in obese individuals. Testosterone, the predominant and most active androgen, is linked to the metabolism of insulin, glucose and lipids. In the cardiovascular system, testosterone increases reactive oxygen species (ROS) generation. Considering that 1) obesity leads to vascular oxidative stress, 2) testosterone is a potent ROS inducer, and 3) the nuclear factor E2–related factor 2 (Nrf2) is a redox‐sensitive transcription factor that activates the expression of many key antioxidant genes, we hypothesized that testosterone downregulates the Nrf2 antioxidant system, favoring ROS accumulation and subsequent vascular dysfunction in high fat diet (HFD)‐fed obese mice.MethodsFour weeks‐old male C57Bl/6J mice were anesthetized and submitted to orchiectomy (the efferent duct of each testicle was ligated and the testicles were removed) or sham‐operation. Mice received control (CD) or high fat diet (HFD) for 18 weeks. Vascular function was assessed in endothelium‐intact thoracic aortic rings and molecular mechanisms by which testosterone contribute to vascular dysfunction were determined.ResultsHFD reduced acetylcholine‐induced vascular relaxation in sham mice [(Relaxation %) CD Sham: 95.3 ± 2.7 vs. HFD Sham: 63.7 ± 1.7, n=6]. However, castration prevented HFD‐induced vascular dysfunction [(Relaxation %) CD Castrated: 94.1 ± 2.5 vs. HFD Castrated: 85.2 ± 2.4, n=7]. CD‐fed castrated mice treated with testosterone propionate exhibited decreased sensitivity to acetylcholine [(pD2) CD Sham: 7.4 ± 0.06 vs. CD Castrated + Testo: 6.7 ± 0.05, n=6]. In addition, the effects of castration in acetylcholine vasodilation in HFD mice were lost after testosterone treatment [(Relaxation %) HFD Castrated 85.2 ± 2.4 vs. HFD Castrated + Testo: 67.1 ± 1.3, n=6]. HFD increased vascular ROS generation, determined by lucigenin and amplex red assays, and castration prevented this increase. HFD increased Nrf2 expression in cytosolic fraction and decreased Nrf2 nuclear accumulation, which was linked to a decrease in mRNA expression of Nrf2‐regulated enzymes, such as catalase, heme oxygenase‐1, peroxiredoxin as well as decreased thioredoxin activity. These events were prevented in HFD‐fed castrated mice. The activation of the Nrf2 system by bardoxolone improved acetylcholine‐induced vascular relaxation in HFD‐fed mice [(Relaxation %) HFD Sham: 63.7 ± 1.7 vs. HFD Sham + Bardoxolone: 77.2 ± 1.8, n=6]. Bardoxolone and castration effects on acetylcholine vasodilation were similar. Bardoxolone increased nuclear accumulation of Nrf2 and decreased ROS generation in HFD‐fed Sham mice.ConclusionThese results indicate that testosterone downregulates Nrf2, favoring oxidative stress and vascular dysfunction in HFD‐fed obese mice.Support or Funding InformationCNPq, CAPES and FAPESP