Investigating the molecular mechanisms of the metabolic syndrome

Abstract

This thesis aims to highlight molecular mechanisms that have been altered by prenatal undernutrition and may be involved in the metabolic syndrome. Two sepa- rate studies were conducted both using a rat model developed through manipulation of the maternal diet to provoke the key features of the metabolic syndrome in adult o spring. Microarray technology was used to detect changes in gene expression in tar- get tissues between o spring of control (normally fed, AD) and undernourished (UN) mothers to obtain a broader picture of the cellular functions and genetic pathways that may be implicated in the metabolic syndrome. The rst study compared gene expression di erences in liver, skeletal muscle, and white adipose tissue between 55 day old male o spring of AD and UN mothers. No signi cant changes were found in muscle or adipose tissue; however, the di erences in the liver suggested the UN animals had been metabolically programmed to favour fat as an energy source. To investigate whether DNA methylation might be responsible for the observed transcriptional changes, pooled liver samples from the rst study were used with the McrBC restriction enzyme assay to determine full, partial, incomplete, or no methylation between AD and UN. Two di erentially expressed genes (Zfand2a and Mapk4) showed methylation changes. The same liver samples were hybridised to a miRNA array. Two miRNAs showed a nearly 2-fold upregulation in the UN livers. Both were found to be either directly or indirectly associated with the metabolic syndrome. MiR-335 has been shown to be upregulated in the livers of obese/diabetic mice. By association with miR-27a, miR-451 might be involved in aspects of lipid metabolism in adipose tissue. A second study used microarray to analyse the liver tissues of day 170 female o - spring of the same rat model with additional insults (neonatal leptin treatment and post-weaning high-fat (HF) diet). Leptin has been shown to reverse the programming e ects of the restricted maternal diet and this study aimed to highlight mechanisms that could be involved in this reversal. The results revealed the importance of the in- teraction between treatments. Signi cant gene expression changes were only present when two or more treatments were combined. This study revealed signi cantly, dif- ferentially expressed genes involved in immune function, regulation of the circadian rhythm, and metabolism. These ndings provide a number of interesting genes and pathways for further studies and also highlight the need to conduct a thorough study in multiple tissues at di erent time-points to pinpoint the window of developmental plasticity.