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The biological clock helps regulate the timing of various processes that occur in the body. Diurnal variability is demonstrated, among others, by genes that regulate insulin sensitivity. Polish scientists have shown that the expression of biological clock genes in subcutaneous adipose tissue is linked to the action of insulin: it is lower in obese people than in those with normal body weight.
'Two genes in particular are involved in insulin action: NR1D2 and DBP. The higher the expression of these genes in adipose tissue, the higher the body’s sensitivity to insulin. And the higher the body’s sensitivity to insulin, the better the regulation of blood glucose levels,’ says Professor Marek Strączkowski from the Department of Prophylaxis of Metabolic Diseases at the Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences in Olsztyn.
Insulin is a hormone that increases the transport of glucose into cells, which in turn lowers blood glucose levels. Insulin resistance is a pathological situation of reduced sensitivity of tissues to the action of insulin.
'Insulin resistance itself is not a disease, but it is a condition that can lead to the development of many diseases: first and foremost type 2 diabetes, but also cardiovascular disease, certain cancers or neurodegenerative diseases,' says Professor Strączkowski whose research concerns the pathogenesis of insulin resistance in people at risk of type 2 diabetes.
The biological clock is a circadian complex of biochemical processes occurring in the body. It is controlled centrally and by peripheral clocks in tissues such as subcutaneous adipose tissue. It stimulates or silences the expression of genes encoding proteins responsible for specific biological processes, depending on the time of day.
These genes concern various biological processes, including those regulating insulin sensitivity. Some of them exhibit diurnal variation, which is why the insulin sensitivity of adipose tissue is highest around midday and lowest around midnight.
Researchers from the Institute of Animal Reproduction and Food Research PAS decided to combine these issues. To that end, they analysed the expression of subcutaneous adipose tissue clock genes in relation to obesity and insulin sensitivity.
The study group consisted of 38 overweight or obese people. The researchers examined them twice: before and after a 12-week programme of weight reduction through diet. The control group consisted of 16 normal-weight subjects. Tissue insulin sensitivity was tested using the so-called metabolic clamp method.
It turned out that obese subjects initially had lower expression of biological clock genes in subcutaneous adipose tissue than controls. After weight reduction in the subjects, this expression increased. This concerned particularly two genes related to the action of the tested hormone: NR1D2 and DBP.
In other words: adipose tissue circadian gene expression is lower in obesity, but this decrease can be partially reversed by dietary intervention.
'We have shown that the aforementioned subcutaneous adipose tissue clock genes can be a starting point for further studies to better understand the pathogenesis of insulin resistance,’ says Professor Strączkowski.
He adds that he and his team intend to explore the problem in further studies on cell cultures. 'This is a developmental topic,’ he says.
The research results of scientists from the Institute of Animal Reproduction and Food Research PAS were published in the journal Nutrition. (PAP)
Katarzyna Czechowicz
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