Strong bones thanks to heat and microbiota

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Bone disease, a bone disease associated with aging, is characterized by an increased risk of bone density, micro-architectural defects of bones and fractures. It is a major public health problem, with one-third of postmenopausal women affected. Through epidemiological analyzes, laboratory experiments, and state-of-the-art metagenomic and metabolic equipment, a research team at the University of Geneva (UNIGE) in Switzerland has observed that exposure to warm ambient temperatures (34 ° C) increases bone strength is. , While preventing the loss of bone density typical of osteoporosis. Furthermore, this phenomenon is associated with changes in the composition of the heat-borne gut microbiota, which can be replicated by transplantation of the microbiota of mice living in a warm environment to mice suffering from osteoporosis. Indeed, after the transplant, his bones were strong and dense. These results, to be searched in Cell metabolism, Make it possible to imagine effective and innovative interventions for the prevention and treatment of osteoporosis.

Many biologists are familiar with Allen’s law from 19th-century naturalist Joel Esaf Allen, according to which animals living in warm areas have a larger surface area in relation to their volume than animals living in cold environments. In fact, a larger surface of the skin allows better drainage of body heat. “In one experiment, we housed newborn mice at a temperature of 34 ° C to reduce the heat shock associated with their birth. We found that they had longer and stronger bones, confirming that the bone growth environment Is influenced by temperature, ”explains. Mirko Trajkovski, professor in the Department of Cell Physiology and Metabolism and at the Diabetes Center of the UNIGE Faculty of Medicine, who led the study. But what about adulthood?

Persistent epidemiological data

By placing several groups of adult mice in a warm environment, scientists found that while bone size remained unchanged, the strength and density of bones improved significantly. He then repeated his experiment with mice following an ovariectomy modeling post-menopausal osteoporosis. “This effect was very interesting,” says Claire Chevalier, a researcher in Professor Trejkowski’s laboratory and the first author of this work. “The simple fact of warming the living environment of our mice saved them from osteoporosis bone loss!”

What about humans? The research team analyzed global epidemiological data on the incidence of osteoporosis in relation to average temperature, latitude, calcium consumption, and vitamin D levels. Interestingly, they found that high temperatures, low hip fractures – one of the main consequences of osteoporosis – regardless of other factors. “We found a clear correlation between geographic latitude and hip fracture, meaning that the incidence is higher in northern countries than in the warm south,” says Mirko Trajkowski. “Normalizing the analysis of known players such as vitamin D or calcium did not modify this correlation. However, the correlation was lost when we excluded temperature as a determinant. This is to say that calcium or vitamin D do not play. Are. Role, either alone or in combination. However, the determining factor is heat or lack thereof. ”

How does the microbiota adapt

Scientists in Geneva, an expert on microbiota, wanted to understand its role in these metabolic modifications. To this end, they transplanted the microbiota of mice living in a 34 ° environment into osteoporotic mice, whose bone quality was rapidly improved. “These findings may be an extension to Ellen’s rule, suggesting elongation-independent effects of heat, which favor bone density and strength during adulthood, primarily through microbiota changes,” Mirko Trajkowski it is said.

Thanks to the state-of-the-art metagonomic devices developed in their laboratory, scientists again succeeded in understanding the role played by the microtiota. When conducive to heat, it leads to disruption of the synthesis and degradation of polyamines, molecules that are involved in aging, and especially in bone health. “With heat, the synthesis of polyamines increases, while their degradation decreases. They thus affect the activity of osteoblasts (the cells that make up bones) and decrease the number of osteoclasts (cells that form bones). ) And with age and menopause. The excellent balance between osteoclast and osteoblast activity is disrupted, “explains Claire Chevalier. “However, by acting on heat, polyamines, which we observed were partially regulated by the microbiota, can maintain a balance between these two cell groups.” These data indicate that heat exposure may be a prevention strategy against osteoporosis.

Develop new treatments

The effect of the microbiota on metabolism is being better understood. However, to be able to use this knowledge to develop therapeutic strategies, scientists must specifically identify the role of bacteria in particular diseases. In the context of his work on osteoporosis, Professor Trejkowski’s team has been able to identify some important bacteria. “We still need to refine our analyzes, but our relatively short-term goal will be to identify candidate bacteria, and to develop several ‘bacterial cocktails’ for the treatment of metabolic and bone disorders, such as osteoporosis, but insulin.” Also improving sensitivity., “The author concludes.

Modifying bone cell recruitment to prevent osteoporosis

more information:
Clare Chevalier et al., Prevents heat damage through the warm microbiota, Cell metabolism (2020). DOI: 10.1016 / j.cmet.2020.08.012

Provided by the University of Geneva

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