Treatment of fetal growth restriction: Effects on signalling pathways in the endocrine pancreas and skeletal muscle

Abstract

Background: Fetal growth restriction (FGR), commonly caused by placental insufficiency, is the failure of the fetus to reach its growth potential. FGR individuals are at higher risk of perinatal morbidity and mortality. Additionally, the structure and function of metabolically active tissues are altered in FGR individuals, predisposing them to develop metabolic diseases such as T2DM. There are currently no proven interventions to improve fetal growth, or ameliorate the long-term metabolic effects of FGR. Aim: To investigate the effect of increasing growth of the growth-restricted lamb via intraamniotic insulin-like growth factor I (IGF-I), maternal sildenafil citrate treatment, or twin reduction surgery, on islet cell composition, signalling pathways involved with insulin secretion in the endocrine pancreas, and insulin signalling in skeletal muscle. Methods: Tissues were generated in three ovine studies of FGR, with interventions aimed to increase fetal growth. In studies one and two, FGR was induced following uterine artery embolisation at 0.7 of gestation. In study one, five once-weekly intraamniotic doses of 360 μg IGF-I were delivered. In study two, ewes received daily subcutaneous infusions of 150 mg sildenafil citrate from 107-131 days gestational age (dGA). In study three, twin pregnancies were reduced to a single pregnancy at 0.3 of gestation. Post mortem examination was performed at 18- months, 132 dGA, and 36-months for studies one through three, respectively. Pancreata from studies one and two underwent immunohistochemical analysis to measure islet cell composition, and RT-qPCR and Western blotting to explore the expression of genes and proteins involved with glucose-simulated insulin secretion (GSIS). Skeletal muscle from all three studies underwent RTqPCR and Western blotting to explore the insulin signalling pathway. Results: All three interventions modestly increased fetal growth. In a sexually dimorphic manner, intraamniotic IGF-I or maternal sildenafil citrate treatment of FGR modified the expression of components of the GSIS pathway. FGR affected more than just β-cell populations; increased α-cell mass was observed in treated growth-restricted males only in both studies. There was a sexually dimorphic effect of interventions on the insulin signalling pathway in skeletal muscle in all three studies. Independent of treatment group, increased relative lean mass at seven-days of age was associated with increased relative lean mass in adulthood (study one). Increased relative lean mass at adulthood was associated with increased insulin sensitivity in adulthood, independent of treatment group (studies one and three). Conclusions: These studies demonstrated that interventions to improve fetal growth had a sexually dimorphic effect on islet cell populations and signalling pathways in endocrine pancreas and skeletal muscle, in sheep. These novel findings contribute to the growing field of evidence that links the early life environment to the long-term metabolic health of the FGR individual. Results from this thesis demonstrate that preclinical research of antenatal interventions to improve outcomes after FGR must be conducted on experimental animals of both sexes; it is no longer adequate to assume that antenatal interventions will have similar short-term and long-term outcomes in males and females.