Independent phenotypic plasticity axes define distinct obesity sub-types [RNA-seq, human]

Studies in genetically ‘identical’ individuals indicate that as much as 50% of complex trait variation cannot be traced to genetics or to the environment. The mechanisms that generate this ‘unexplained’ phenotypic variation (UPV) remain largely unknown. Here, we identify neuronatin (NNAT) as a conserved factor that buffers against UPV. We find that Nnat deficiency in isogenic mice triggers the emergence of a bi-stable polyphenism, where littermates emerge into adulthood either ‘normal’ or ‘overgrown’. Mechanistically, this is mediated by an insulin-dependent overgrowth that arises from histone deacetylase (HDAC)-dependent β-cell hyperproliferation. A multi-dimensional analysis of monozygotic twin discordance reveals the existence of two patterns of human UPV, one of which (Type B) phenocopies the NNAT-buffered polyphenism identified in mice. Specifically, Type-B monozygotic co-twins exhibit coordinated increases in fat and lean mass across the body; decreased NNAT expression; increased HDAC-responsive gene signatures; and clinical outcomes linked to insulinemia. Critically, the Type-B UPV signature stratifies both childhood and adult cohorts into four metabolic states, including two phenotypically and molecularly distinct types of obesity. The Leipzig Childhood adipose tissue cohort comprises Caucasian children aged 0-18 years who underwent elective orthopedic surgery, herniotomy/orchidopexie, or other surgeries. Exclusion criteria were severe diseases and medication that might affect adipose tissue biology, such as: diabetes, generalized inflammation, malignant diseases, genetic syndromes, or permanent immobilization. Written informed consent was obtained from all parents and study protocols were approved by the local Ethics Committee (265–08, 265– 08-ff) and registered in the National Clinical Trials database (NCT02208141). BMI data were standardized to age- and sex- specific centiles by applying German reference data, and are represented as BMI standard score (SDS). Overweight and obesity are defined by a cutoff of 1.28 and 1.88 SDS (90th or 97th centile), respectively. Subcutaneous adipose tissue samples were excised during surgery, washed three times in PBS, and immediately frozen in liquid nitrogen for RNA isolation.