Silencing the Adipocytokine NOV: A Novel Approach to Reversing Oxidative Stress-Induced Cardiometabolic Dysfunction

NOV/CCN3 is an adipocytokine recently linked to obesity, insulin resistance, and cardiometabolic dysfunction. NOV is manufactured and secreted from adipose tissue, with blood levels highly correlated with BMI. NOV levels are increased in obesity and a myriad of inflammatory diseases. Elevated NOV levels cause oxidative stress by increasing free radicals, decreasing antioxidants, and decreasing heme oxygenase (HO-1) levels, resulting in decreased vascular function. Silencing NOV in NOV knockout mice improved insulin sensitivity. We wanted to study how suppressing NOV expression in an obese animal model affected pathways and processes related to obesity, inflammation, and cardiometabolic function. This is the first study to investigate the interaction of adipose tissue-specific NOV/CCN3 and cardiometabolic function.

We constructed a lentivirus containing the adiponectin-promoter-driven shNOV to examine the effect of NOV inhibition (shNOV) in adipose tissue on the heart of mice fed a high-fat diet. Mice were randomly divided into three groups (five per group): (1) lean (normal diet), (2) high-fat diet (HFD)+ sham virus, and (3) HFD + shNOV lentivirus. Blood pressure, tissue inflammation, and oxygen consumption were measured. Metabolic and mitochondrial markers were studied in fat and heart tissues.

Mice fed an HFD developed adipocyte hypertrophy, fibrosis, inflammation, and decreased mitochondrial respiration. Inhibiting NOV expression in the adipose tissue of obese mice by shNOV increased mitochondrial markers for biogenesis (PGC-1α, the nuclear co-activator of HO-1) and functional integrity (FIS1) and insulin signaling (AKT). The upregulation of metabolic and mitochondrial markers was also evident in the hearts of the shNOV mice with the activation of mitophagy. Using RNA arrays, we identified a subgroup of genes that highly correlated with increased adipocyte mitochondrial autophagy in shNOV-treated mice. A heat map analysis in obese mice confirmed that the suppression of NOV overrides the genetic susceptibility of adiposity and the associated detrimental metabolic changes and correlates with the restoration of anti-inflammatory, thermogenic, and mitochondrial genes.

Our novel findings demonstrate that inhibiting NOV expression improves adipose tissue function in a positive way in cardiometabolic function by inducing mitophagy and improving mitochondrial function by the upregulation of PGC-1α, the insulin sensitivity signaling protein. Inhibiting NOV expression increases PGC-1, a key component of cardiac bioenergetics, as well as key signaling components of metabolic change, resulting in improved glucose tolerance, improved mitochondrial function, and decreased inflammation. These metabolic changes resulted in increased oxygen consumption, decreased adipocyte size, and improved cardiac metabolism and vascular function at the structural level. The crosstalk of the adipose tissue-specific deletion of NOV/CCN3 improved cardiovascular function, representing a novel therapeutic strategy for obesity-related cardiometabolic dysfunction.