From the Cover: Adiponectin supplementation in pregnant mice prevents the adverse effects of maternal obesity on placental function and fetal growth

Mothers with obesity or gestational diabetes mellitus have low circulating levels of adiponectin (ADN) and frequently deliver large babies with increased fat mass, who are susceptible to perinatal complications and to development of metabolic syndrome later in life. It is currently unknown if the inverse correlation between maternal ADN and fetal growth reflects a cause-and-effect relationship. We tested the hypothesis that ADN supplementation in obese pregnant dams improves maternal insulin sensitivity, restores normal placental insulin/mechanistic target of rapamycin complex 1 (mTORC1) signaling and nutrient transport, and prevents fetal overgrowth. Compared with dams on a control diet, female C57BL/6J mice fed an obesogenic diet before mating and throughout gestation had increased fasting serum leptin, insulin, and C-peptide, and reduced high-molecular-weight ADN at embryonic day (E) 18.5. Placental insulin and mTORC1 signaling was activated, peroxisome proliferator-activated receptor-α (PPARα) phosphorylation was reduced, placental transport of glucose and amino acids in vivo was increased, and fetal weights were 29% higher in obese dams. Maternal ADN infusion in obese dams from E14.5 to E18.5 normalized maternal insulin sensitivity, placental insulin/mTORC1 and PPARα signaling, nutrient transport, and fetal growth without affecting maternal fat mass. Using a mouse model with striking similarities to obese pregnant women, we demonstrate that ADN functions as an endocrine link between maternal adipose tissue and fetal growth by regulating placental function. Importantly, maternal ADN supplementation reversed the adverse effects of maternal obesity on placental function and fetal growth. Improving maternal ADN levels may serve as an effective intervention strategy to prevent fetal overgrowth caused by maternal obesity.Obesity and the metabolic syndrome are major risk factors for a wide array of diseases, including type 2 diabetes mellitus, cardiovascular disease, and cancer (1, 2). Compelling evidence shows that metabolic syndrome is caused, in part, by a suboptimal intrauterine environment (3). The strong association between maternal obesity during pregnancy and metabolic syndrome in childhood is of particular concern because almost two-thirds of American women now enter pregnancy either overweight or obese (4). Obesity during pregnancy therefore creates a vicious, detrimental cycle of intrauterine transmission of metabolic disease from the mother to her children (5). Intervention strategies involving lifestyle changes or antiobesity drugs remain largely unsuccessful, and it is therefore urgent to explore the possibility of intervening in utero to prevent the development of obesity and metabolic syndrome.Obesity in pregnant women is associated with activation of placental insulin and mechanistic target of rapamycin complex 1 (mTORC1) signaling, up-regulation of specific placental amino acid transporters, and fetal overgrowth (6, 7). In addition, circulating levels of adiponectin (ADN) are decreased in obese pregnant women (8, 9). The ADN protein is synthesized in adipose tissue and undergoes tightly regulated multimerization involving chaperone proteins, including disulfide-bond A oxidoreductase-like protein (DsbA-L), resulting in the assembly of oligomeric ADN proteins of different molecular weight (10). Multimerization into the high-molecular-weight (HMW) form increases the t_1/2 of ADN (11), and the insulin-sensitizing effect of ADN can largely be attributed to the HMW form (12). Low circulating levels of HMW ADN strongly predict the development of gestational diabetes mellitus (GDM) independent of maternal adiposity (13, 14).We recently reported that ADN, in contrast to its well-known insulin-sensitizing effects in skeletal muscle and liver, inhibits insulin and mTORC1 signaling and amino acid transport in cultured primary human trophoblast (PHT) cells (15) and in pregnant mice in vivo (16). This effect is mediated by activation of trophoblast peroxisome proliferator-activated receptor-α (PPARα) signaling and increased ceramide synthesis, resulting in inhibition of IRS-1 (17). Thus, low circulating ADN in maternal obesity may be causally linked to changes in placental function and increased fetal growth. These findings, together with the recent discovery of an orally active ADN receptor agonist (AdipoRon) (18), provide the rationale for exploring the possibility that maternal ADN supplementation may prevent the adverse fetal outcomes in maternal obesity.We recently established a mouse model of obesity in pregnancy, which shows extensive similarities to the human condition, including low maternal ADN and glucose intolerance, increased placental nutrient transport, and fetal overgrowth (19). In this study, we used this model to test the hypothesis that ADN supplementation in obese pregnant dams improves maternal insulin sensitivity, restores normal placental insulin signaling and nutrient transport, and prevents fetal overgrowth.