Searching for signatures of cold adaptation in the Neanderthal and Denisovan genomes: hints from the brown adipose tissue genes

Neandertal and Denisovan clades of archaic hominins experienced temperatures significantly lower than the present ones, occupying geographical regions involved in the Pleni-Wurm for a time interval long enough to adapt to this cold environment. Paleoanthropological evidences prove that Neandertals body proportions are in accordance with a minimization of the ratio between body surface area and volume to avoid heat loss. Their supposed massive muscular apparatus and hunter-gatherer subsistence strategies also suggest that their life-style was similar to H. sapiens populations living in circumpolar regions, being characterized by a diet rich in fat and proteins to satisfy high calorie needs. This may have favored the isolation from cold and the thermogenic functions in these archaic hominins. Moreover, since the advent of new subsistence strategies and the increase of environmental temperature during recent human evolution may have been too fast for completely retuning the basic processes of thermogenesis and thermoregulation in our species, even slight differences in their regulation between H. sapiens and Neandertals/Denisovans could be the key between our way to store and spend energy and that of our ancestors. Thermogenesis and thermoregulation consist in complex functional patterns centered on the dissipation of heat in the mitochondria by uncoupling oxidation and ATP synthesis and are mainly provided by adipocytes belonging to the Brown Adipose Tissue (BAT). In this preliminary work, we investigated the genetic similarities between 27 Neandertal, Denisovan and modern human genes involved in BAT metabolism, storage and neogenesis, or being found to be associated with fat accumulation and body mass index by GWAS studies. Archaic sequence data were retrieved from public databases, together with those from modern humans belonging to the “1000Genomes” project populations, and exploited to identify Neandertal/Denisovan specific variants and to explore whether they exhibit genetic similarities with respect to modern populations exposed to cold environments.