The effect of obesity and aging on NAD+/Sirtuin metabolism transcription and DNA methylation in subcutaneous adipose tissue of monozygotic twin pairs discordant for BMI

The expression and/or activity of sirtuins (SIRTs), nicotinamide adenine dinucleotide (NAD + )-dependent enzymes that regulate cellular energy metabolism, is decreased in obesity and in aging in animal models. However, the impact of obesity compared to aging on NAD + /SIRT expression in human white adipose tissue (AT) remains unexplored. Here, we unravel the effects of obesity and aging on the expression of NAD + /SIRT pathway and their associated genes in subcutaneous AT of identical twin pairs discordant for weight, in two age groups. We examined 49 monozygotic twin pairs discordant for BMI (within-pair difference in BMI ≥ 2.5 kg/m 2 , with mean BMIs 25.6 kg/m 2 (leaner) and 30.8 kg/m 2 (heavier), aged 22–38 and 56–69 years. Detailed phenotyping included body composition, insulin resistance (oral glucose tolerance test) and plasma lipids and inflammation markers. RNA sequencing and DNA methylation analyses in AT identified differentially expressed and methylated NAD + /SIRT pathway genes in obesity and aging, with linear mixed models linking gene expression to metabolic features. SIRT5 and NAD + biosynthetic genes were downregulated in AT in both obesity and aging. Obesity was characterized by downregulation of AT NAD + /SIRT genes, and NAD + /SIRT regulated mitochondrial oxidative metabolism genes, and upregulation of stress markers. Aging showed a downregulation of AT PARPs, except upregulation for PARP1, a main consumer of NAD + . Mitochondrial metabolism and glycolysis genes were linked to corresponding DNA methylation. Downregulation of NAD + /SIRT genes correlated with increased adiposity, insulin resistance, inflammation, and dyslipidemia. Impaired NAD + /SIRT metabolism in AT may play a key role in obesity- and aging-related diseases. Both conditions are characterized by downregulation of NAD + /SIRT pathway genes, correlating with increased adiposity, insulin resistance, inflammation, and dyslipidemia. Obesity uniquely disrupts expression of NAD + /SIRT regulated mitochondrial genes, while aging is characterized by altered PARP expression, particularly increased PARP1, likely exacerbating metabolic dysfunction in AT.