Fetal programming of adult disease: causes and consequences of metabolic dysregulation in an ovine model of PCOS

Abstract

Polycystic ovary syndrome (PCOS) is a common and complex endocrine condition with reproductive and metabolic complications, affecting up to 10% of reproductive-age women. Hyperandrogenemia, ovulatory dysfunction, and luteinising hormone hypersecretion are characteristic traits of PCOS however, it seems that the most concerning long-term key issues are metabolic problems associated with the syndrome, such as hyperinsulinemia, insulin resistance, obesity, dyslipidaemia and non-alcoholic liver disease. Despite the numerous studies on PCOS, its origin and pathophysiology are still not fully understood. However, there is increasing evidence that the adult PCOS phenotype is programmed in fetal life by androgen excess. Exposure to increased levels of testosterone in utero in rodents, sheep and monkeys result in adult reproductive and metabolic pathologies that parallel those seen in PCOS women. Since hyperandrogenemia is a hallmark of PCOS and daughters of PCOS mothers have elevated levels of androgens at birth, it is likely that prenatal androgenisation during early life predispose to the future development of PCOS. Animal models of PCOS provide an opportunity to examine the developmental aetiology and molecular mechanisms underlying the pathogenesis of this condition. Over last 10 years our lab has successfully utilised a well-established ovine model of PCOS, where pregnant ewes were treated with testosterone propionate (TP) through mid-gestation. From this model, we had a large sample bank of fixed and frozen tissues from the fetal, lamb and adolescent prenatally androgenised animals that allowed to carry a broad range of experiments. In addition, a new cohort of prenatally androgenised adult sheep enabled additional in vivo analysis. Past research documented that prenatal androgenisation result in hyperinsulinemia with altered pancreas structure and function, and early fatty liver without difference in body weight in adolescent sheep. This thesis examines the effects and consequences of increased in utero androgen exposure on metabolic dysregulation in adolescent and adult female sheep. During puberty, but not fetal or early life, there was decreased adipogenesis in subcutaneous adipose tissue (SAT), but not visceral adipose tissue (VAT), accompanied by decreased circulating concentrations of fibroblast growth factor 21 (FGF21), leptin and adiponectin, and increased concentrations of fasting free fatty acids (FFA) in prenatally androgenised sheep. This was countered by upregulated expression of FFA transporters in liver. As adults, TP-exposed animals had increased body weight, elevated fasting insulin and FFA concentrations but normal FGF21, leptin and adiponectin levels. Histological analysis revealed that adult TP-exposed animals had SAT hypertrophy, which was associated with increased expression of inflammatory markers and correlated with increased fasting FFA. Therefore, it is likely that impaired preadipocyte differentiation in SAT during adolescence resulted in hypertrophy and inflammation of adult SAT. This consequently lowered capacity of SAT to safely store fat and potentially explains metabolic perturbations observed in PCOS-like female sheep. To further investigate potential causes of obesity in adult PCOS-like sheep postprandial thermogenesis (PPT), an important constituent of energy expenditure, was measured through implantation of datalogger thermometers into interscapular adipose tissue. Adult prenatally androgenised sheep had decreased amplitude of PPT, without difference in basal body temperature, despite receiving the same caloric intake, and independent of obesity. These findings indicate that adult PCOS-like sheep have reduced capacity for energy expenditure, which is mirrored in women with PCOS. This reduced capacity for postprandial thermogenesis was correlated with hyperinsulinemia decreased noradrenaline levels and reduced thermogenic potential of brown and/or beige adipose tissue. This suggests that women with PCOS might be prenatally programmed to become obese. In summary, findings documented in this thesis provide better understanding into the pathophysiology of PCOS from puberty to adulthood and give opportunities for early clinical intervention to ameliorate the metabolic phenotype of PCOS.