Role of NADPH oxidase (Nox) 1/4 in adipocyte-derived aldosterone production and in inflammation and fibrosis in obesity

Even, Sarah Elisabeth Louise (2015) Role of NADPH oxidase (Nox) 1/4 in adipocyte-derived aldosterone production and in inflammation and fibrosis in obesity. MSc(R) thesis, University of Glasgow.

Abstract

Obesity plays a key role in the development of metabolic syndrome, but the underlying mechanisms still remain elusive. Factors that have been implicated include activation of the renin angiotensin aldosterone system (RAAS) and increased bioavailability of reactive oxygen species (ROS) (termed oxidative stress), which impact on inflammation in adipose and other tissues. Inflammatory processes in fat appear to be an important initiator of metabolic syndrome and associated cardiovascular disease. Oxidative stress and aldosterone levels are positively associated with adiposity. Exact mechanisms contributing to high aldosterone levels in obesity are unclear, but adipocytes can produce aldosterone, as well as ROS, phenomena that are amplified in obesity.

In the present studies, we examined the relationship between ROS, aldosterone and adipocytes in the context of obesity. In particular we questioned whether ROS influence aldosterone production by adipocytes and whether these processes influence adipocyte function related to cell maturation, inflammation and fibrosis. We also explored the enzymatic source of ROS in adipocytes, focusing specifically on Nox isoforms, Nox1 and Nox4.

To address these questions we performed in vivo and in vitro studies. Adipose tissue and mature adipocytes from obese db/db mice were studied. To translate our findings to humans, we also studied human mature adipocytes. To interrogate Nox1 and Nox4, we used a dual Nox1/4 inhibitor, GKT137831 (Genkyotex S.A, Geneva, Switzerland) in vivo and in vitro studies.

Aldosterone and corticosterone levels were measured by ELISA while plasma electrolyte, lipid and metabolic profile were assessed with an automated analyser. Gene expression was assessed by qPCR. Fibrosis was determined by picro Sirius red staining and polarized light microscopy. ROS production was determined by chemiluminescence, amplex Red and TBARS.

Our results demonstrate that aldosterone levels were increased by 4 fold in plasma and 4 fold in epididymal fat culture media from db/db mice compared to lean mice. These effects were decreased by high dose Nox1/4 inhibitor (GKT). Visceral fat from db/db mice had increased levels of oxidative stress and mRNA levels of inflammatory marker such as, CD206 (150%), F4/80 (600%), TNFα (230%), iNOS (50%), as well as collagen 6a (160%). Treatment of obese db/db mice with GKT did not significantly decrease fibrosis in epididymal fat but it did show a tendency to decrease with low dose treatment. In the perivascular fat from db/db mice GKT decreased the mRNA levels of pro-inflammatory markers, followed by an increase in mRNA levels of anti-inflammatory markers. Ang II stimulation of human adipocytes increased aldosterone (5 fold) and cortisol (3 fold) production, as well as superoxide (2 fold) and hydrogen peroxide (0.5 fold) levels. Aldosterone production was Nox1/4-dependent and cortisol was Nox4-dependent. These effects are amplified in obesity and may participate in adipocyte dysfunction as evidenced in adipose tissue from obese db/db mice. Our data also suggest that oxidative stress is increased in fat from obese animals and may play a role in obesity-associated adipose tissue inflammation and potentially fibrosis.

Based on these findings we conclude that in obesity Nox isoforms play an important role in visceral adipocyte tissue inflammation/fibrosis and aldosterone biosynthesis and that adipocyte Nox1/4 may be a putative therapeutic target in obesity-associated hyperaldosteronism and cardiovascular damage.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: obesity, adipocyte, Nox1/4, aldosterone
• Subjects: R Medicine > R Medicine (General); R Medicine > RC Internal medicine
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health > Cardiovascular & Metabolic Health
• Supervisor's Name: Touyz, Prof. Rhian M.
• Date of Award: 2015
• Depositing User: Miss Sarah Elisabeth Louise Even
• Unique ID: glathesis:2015-6387
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 25 May 2015 08:35
• Last Modified: 12 Aug 2015 07:48
• URI: https://theses.gla.ac.uk/id/eprint/6387