The body reprograms itself according to the outside temperature

The body of some warm-blooded mammals, including humans, is capable of global and profound metabolic adaptation to exposure to cold or extremely hot temperatures. This is shown by a study published on May 17, 2022 eLife Sciences, where a team of Swiss and German researchers studied the effect of temperature changes on the response of mouse genes. And the result is rather striking: the whole body will be affected by the process of reprogramming genes, which are expressed more or less intensively according to the needs of the organism.

cold sensitive adipose tissue

In humans, the receptivity of adipose tissue to low temperatures is a known phenomenon. When it is cold, our body consumes more calories to maintain an average temperature of 36.6°C. It is the hypothalamus, a structure of the central nervous system in the brain, that ensures this thermogenesis (the production of heat by the body) due to the burning of brown fat in the body. This “good” fat is especially present in newborn babies, who are still unable to properly tremble and control their temperature. This metabolic adaptation also works when the body is exposed to warm temperatures, which strengthens bone tissue and reduces the risk of osteoporosis. However, the consequences of temperature changes on other body tissues or organs are not clearly known.

In rats, thermoneutrality – the time the body no longer needs to regulate its own temperature – is between 29 °C and 33 °C. However, rats naturally live in environments with an average temperature of 22 °C. They devote a great deal of their energy to their thermoregulation, leading the researchers to suggest that “Thermal variations implement a functional reprogramming of the whole body“The researchers therefore used the effects of temperature on mice exposed to cold (10 °C), room temperature (22 °C) and moderate heat (34 °C).

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Responses proportional to temperature difference

To study this reprogramming, the use of RNA (ribonucleic acid) sequencing of mice was necessary to visualize the subtle molecular changes of the tissues or organs studied. Researchers analyzed samples of bone marrow, brain and hypothalamus, spinal cord, quadriceps, ileum (part of the small intestine), liver and even spleen. These samples were exposed to 10 °C, others to 34 °C, then compared with control tissues left at room temperature of 22 °C. the purpose was to observeTemperature Dependent Gene Expression Profiles“But this also”Adaptive role of each tissue from the point of view of the whole organism,

The researchers observed that the anatomically closest tissues (such as adipose tissue and quadriceps, or ileum and spleen) presented similar numbers of genes sensitive to the effects of temperature. There is therefore no general regulation of tissues, each one adapted to a particular situation by more or less strongly regulating the expression of its own genes. For example, between 10 °C and 22 °C, the researchers observed that 988 genes were down-regulated throughout the mouse organism. And from 22°C to 34°C, that was 2,126 down-regulated genes.

Thus, 76% of the 600 most up-regulated genes were downregulated between 10 °C and 34 °C. A result that leads researchers to believe that “The regulation of gene expression is proportional to the temperature gradient“: The hotter it is, the less the genes of some organs are expressed, in order to release the energy available for thermal regulation.

Better understand the effects of temperature on metabolism

The study shows how organs adapt to more or less increased activity of thermoregulation. Below 10 °C, adipose tissue is up-regulated but other genes are expressed downstream, so energy expenditure is balanced. In contrast, below 34 °C, other genes show upward regulation, for example in sensory perception of pain.

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Finally, this gene regulation was only observed downward in the spleen when the external temperature increases. This would be explained primarily by the immunological function of this organ, which, being affected by cold, reduces its activity. Maintaining immune functions is indeed very expensive in terms of energy and would be at risk of competing with thermogenesis.

Through this type of analysis, the team wants to move toward a better understanding of how mammals sense changes in temperature by demonstrating that all organs are involved in the re-programming of an organism. They have shown that, within the same family of genes, genes evolve and regulate themselves independently. This may suggest the existence of specific “specific regulators” for each organ, which will shed new light on how to interpret the mechanisms of adaptation to cold or heat.

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