A Diet Rich in Carbohydrates Induces Changes in Serum microRNA Levels Associated with Type 2 Diabetes Development.
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- Institutt for biologi 
It is known that the level of serum microRNAs, small RNA molecules involved in regulation of gene expression, is altered in diabetic patients compared to healthy individuals and that microRNAs may be involved in the regulation of inflammatory and insulin signaling pathways. Analysis of blood samples from the diet intervention in the main study revealed that variation in macronutrient composition is known to affect gene expression. The aim of this thesis was to establish a method for reliable miRNA detection and quantification and to find out if the level of serum miRNAs was affected by the macronutrient composition in the diet.This was done by analyzing the change in microRNA levels in serum samples from 10 subjects after completion of the intervention study mentioned above, consisting of two different diets; diet A, high in carbohydrates (AHC) and diet B, moderate in carbohydrates (BMC). Each diet period lasted for six days separated by an eight-day pause in which the subjects returned to regular eating habits. Fasting blood samples were collected before and after each diet period, denoted as A0, A6, B0 and B6. Total RNA was isolated from and cDNA-synthesis was done in all samples. The expression of selected microRNAs was analyzed by qPCR. The microRNA levels were normalized to a reference gene and were expressed as the change in the A6 and B6 samples relative to the A0 and B0 samples. cDNA-synthesis and qPCR were optimized, a standard for evaluation of RNA-isolation yield was suggested and several different control were applied to minimize technical variation. It was found that the AHC diet resulted in larger changes in miRNA expression than the BMC diet. The expression of miR-21, miR-29b, miR-93, miR-126 and miR-223 was found to be significantly down regulated after the AHC diet. Low plasma levels of some of these miRNA have previously been proposed to predict type 2 diabetes development. It was concluded that the dietary macronutrient composition is involved regulation of the level of serum miRNAs known to regulate insulin signaling, glucose uptake and development of type 2 diabetes after only 6 days. miR-93, a microRNA with no known role in diabetes development was also found to be significantly down regulated. However, it was concluded that it was necessary to apply more controls, do further optimization and perform the test on more individuals to be able to verify the findings in this thesis.