The role of maternal high fat feeding on the developmental programming of adulthood disease
thesisposted on 01.03.2017 by Henry, Sarah
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
It is now well understood that the maternal environment encountered as a fetus can profoundly influence an individual’s risk of developing a myriad of diseases in later life. In particular, maternal nutritional challenges can have significant developmental impacts to the fetus and this concept is generally referred to as the Developmental Programming of Adulthood Health and Disease. As many developed nations, including Australia, shift to states of nutritional excess, research focusing on adverse maternal conditions such as obesity, diabetes and high fat feeding is becoming critically relevant. Whilst numerous studies have begun to characterise the role of maternal obesity on offspring health, there is almost no understanding of how consumption of a maternal high fat diet, that does not cause frank obesity, might contribute to the programming of offspring health. Maternal obesity is not an isolated condition, and confounding factors such as altered hormonal profiles and gestational diabetes can make it difficult to delineate what factors are driving the varied developmental changes observed in offspring. While the longer term impacts of maternal high fat feeding on adult offspring is relatively well understood, there is limited information on the impact of high fat intake on the in utero environment, including the amniotic fluid and placenta. Furthermore, greater characterisation of the fetal phenotype is needed following maternal high fat feeding. In particular, limited information is available on the role of maternal fat intake and renal development. Finally, although several studies have assessed the role of maternal fat intake on aspects of postnatal vascular and cardiovascular function, adult renal function has not been fully assessed, despite strong evidence that disrupted renal development may increase the risk of developing disease in later life. AIMS & OBJECTIVES We aimed to investigate the impact of high maternal dietary saturated fat intake on fetal and postnatal development, including identifying the in utero adaptations to amniotic fluid lipid composition, fetal (including kidney) and placental growth and function. Long-term aims included investigation of the postnatal phenotype of offspring born to fat fed mothers, with particular focus on evaluating the long-term effects on renal, cardiovascular and sympathetic function. We hypothesised that maternal high fat feeding would modify placental transport of nutrients, resulting in a hyperlipidaemic fetal amniotic environment. As a result, fetal growth trajectory and organ development, specifically the kidneys, would be disrupted. Furthermore, we postulated that exposure to maternal high fat feeding would result in augmented blood pressure and renal dysfunction in offspring in later life and that increased sympathetic nerve activity may be responsible for these disruptions in physiological function. METHODS Investigations were carried out using Sprague-Dawley rats. For embryonic studies, female breeders were fed either a control (C; 7% canola oil) or a lard rich high fat (HF) (3% canola oil and 20% lard) diet for 3 weeks prior to mating and throughout pregnancy until embryonic day (E) 14.25, E17.25 or E20. At collection, embryos and placentas were weighed. Amniotic fluid and maternal plasma lipid profiles were determined using a lipidomics approach facilitated by liquid chromatography mass spectrometry (LCMS). Renal development was examined via culturing of embryonic kidneys and quantification of branching morphogenesis. In addition, gene expression of placental transporters and fetal liver substrates involved in lipid metabolism were determined using qPCR. For postnatal studies, female Sprague-Dawley rats were exposed to either C or HF diet for 3 weeks prior to mating, throughout pregnancy and lactation. From weaning, offspring were chow fed ad libitum. Physiological experiments were undertaken at 6 and 12 months of age. Renal glomerular filtration rate (GFR), effective renal plasma (eRPF) and blood flow (eRBF) were estimated in anaesthetized rats by 3H-inulin and 14C-para-aminohippurate clearance. Mean arterial pressure (MAP) and heart rate (HR) were determined in conscious animals using radiotelemetry. At 1 year of age, whole body noradrenaline spillover was estimated in anaesthetized rats. 3H-noradrenaline was infused and whole body noradrenaline spillover was calculated. Sodium nitroprusside (SNP) was then infused to determine changes in sympathetic arousal in response to acute hypotension. In addition, renal noradrenaline content was determined during development (E20) and in postnatal animals at 21 days and 1 year as a proxy measure of sympathetic nerve development and long-term sympathetic nerve activity respectively. RESULTS & DISCUSSION Maternal high fat feeding resulted in hyperlipidaemia, and this was reflected in amniotic fluid lipid content, with significant increases in amniotic fluid triglyceride concentrations in late gestation. In contrast to our hypothesis, fetal renal development did not differ between C and HF exposed embryos, however minor changes were observed in placental growth and transporter expression. These placental modifications do not fully explain the significant increases in amniotic fluid lipid content in late gestation. Further investigation indicated that increased fetal hepatic lipogenic gene expression was not a mechanism involved with increased triglyceride concentration in amniotic fluid. To further characterise our phenotype, development of offspring was followed into the postnatal period. We found that maternal high fat feeding was associated with significantly increased blood pressure in both male and female offspring at 12 months. In addition, sexually dimorphic renal dysfunction was evident in offspring of fat fed dams at 12 months of age. To our knowledge, this is one of the first studies to analyse renal function in a model of maternal high fat feeding, using gold standard techniques. Again, in contrast to our hypothesis, investigation into sympathetic nervous system revealed there was no difference in sympathetic activity between experimental groups, and that this was not a mechanism contributing to the renal and cardiovascular dysfunction in offspring exposed to in utero HF conditions. As such, it appears that other factors are driving the physiological dysfunction in this model. We hypothesise that vascular function may be impaired in HF exposed offspring and that this may be the major mechanisms driving the observed renal and cardiovascular dysfunction. CONCLUSION The findings from this thesis clearly demonstrate that even modest increases in saturated fat intake can alter the in utero environment, and the consequences of these early life modifications are seen in postnatal life, with significant renal and cardiovascular dysfunction. Importantly, this model of high fat feeding is not dissimilar to what many women are consuming during pregnancy – that is, the consumption of high saturated fats without apparent obesity. From an obstetrics perspective, it is clear that there is more to the picture than factors such as maternal obesity, and that dietary levels of saturated fatty acids should also be monitored. Whilst it appears that maternal obesity leads to a more severe phenotype in models of programming, high saturated fat intake during pregnancy cannot be ignored, and increased intake of this fatty acid has long term detrimental effects on the fetus. As we move to an increasing burden of chronic diseases, such as kidney and cardiovascular disease, it is vitally important to understand the impact of the early life environment on health and disease in later life. Furthermore, an understanding of the mechanism contributing to perturbed tissue and organ development may aid early intervention and as such disease prevention in later life. Controlling saturated fat intake during pregnancy may be a small but significant step in reducing the risk of developing adulthood diseases in later life. Finally, from a clinical perspective, the dietary model used in this project is not dissimilar to what many pregnant women in developed nations would be consuming. It highlights an important concept that women who consume a high fat diet during pregnancy, but do not develop obesity, are still placing the developing fetus at risk. Furthermore, it highlights that early intervention may be clinically important in potentially reducing the prevalence of adult chronic diseases.