Adipocyte aquaporin 7 (AQP7) expression in lean children and children with obesity. Possible involvement in molecular mechanisms of childhood obesity.

Abstract

Background Aquaporin 7 (AQP7), a water/glycerol transporting protein, regulates adipocyte glycerol efflux and influences lipid and glucose homeostasis. Altered AQP7 expression in adults leads to impaired glycerol dynamics, adipocyte hypertrophy and it predisposes them to obesity and diabetes. To assess its possible involvement in childhood obesity, this study investigated the expression of adipocyte AQP7 in cultured adipocytes of children. Methods Primary in vitro differentiated adipocyte cultures were developed from surgical biopsies of subcutaneous abdominal adipose tissue from 61 (46 prepubertal, 15 pubertal) lean children (body mass index [BMI] <85%) and 41 (22 prepubertal, 19 pubertal) children with obesity (BMI >95%). AQP7 expression was studied by reverse transcription polymerase chain reaction and Western immunoblotting and insulin by enzyme-linked immunosorbent assay. Results AQP7 messenger RNA (mRNA) was increased in the younger obese prepubertal (YOP) children but decreased in the obese adolescents (OA) (p=0.014) who also had increased insulin and homeostatic model assessment - insulin resistance (HOMA-IR). Lean pubertal (LP) children and YOP had increased 41 kDa AQP7 protein expression (p=0.001 and p=0.005, respectively). The OA who expressed 34 kDa AQP7 had lower triglyceride (TG) levels than those who did not express it (p=0.013). In the lean children, TG were negatively correlated with 34 kDa AQP7 (p=0.033). Conclusions The lower AQP7 mRNA expression in the OA may reflect a predisposition to adipocyte hypertrophy and metabolic dysfunction, as in the adults, whereas the YOP may be protected from this. The increased 41 kDa AQP7 protein expression in the LP may reflect the increased energy requirements of puberty for glycerol while in the YOP it may also be protective against the development of adipocyte hypertrophy.