A new study was released this week suggesting that human muscle may be just as unique as the human brain.
Scientists from Shanghai's CAS-MPG Partner Institute for Computational Biology, along with teams from German Max Planck Institutes, studied the evolution of metabolites, which is small molecules like sugars, vitamins, amino acids and neurotransmitters that play key roles in our physiological functions, according to a press release issued by the institute.
They found that metabolite concentrations evolved over the course of human evolution in two tissues: in the brain and in muscle.
Their research was published on May 27 in the open-access journal PLOS Biology.
Genomes steadily go through changes over time, according to the release. Only a few of the genetic changes that have happened over the course of human evolution might be responsible for the rise of distinct human features.
In order to figure out what other molecules played a role in human evolution, scientists decided to look "beyond the genome," according to the study.
Dr. Philipp Khaitovich from Shanghai, and his colleagues examined the evolution of the human metabolome, which is the compendium of metabolites present in human tissues, for the first time ever for the study.
"Metabolites are more dynamic than the genome and they can give us more information about what makes us human," said Khaitovich, according to the release. "It is also commonly known that the human brain consumes way more energy than the brains of other species; we were curious to see which metabolic processes this involves."
They were able to determine that the metabolome of the human brain has evolved four times faster than that of the chimpanzee. The human muscle accumulated an even higher amount of metabolic change however, ten times that of the chimpanzee, according to the release.
Scientists performed additional measurements in specially treated macaque monkeys to rule out the possibility that this change reflects "our couch potato lifestyle," according to the release.
In order to imitate the environment of many contemporary humans, these macaques were moved from a countryside facility to small indoor enclosures and served fatty and sugary foods for several weeks.
These lifestyle changes had only a small effect on the macaque muscle metabolome.
"For a long time we were confused by metabolic changes in human muscle, until we realized that what other primates have in common, in contrast to humans, is their enormous muscle strength," said Dr Kasia Bozek, the lead author of the study, according to the release.
Hypothesis suggested by the researchers is that the metabolic roles of human brain and muscle are "intertwined."
"The world of human metabolomics is just starting to open up its secrets to us," adds Dr Patrick Giavalisco, who led the metabolome measurement effort at the Max Planck Institute for Molecular Plant Physiology in Golm. "Such human-specific metabolic features we find could be related not only to physical or cognitive performance but also to common human metabolic diseases."
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