Human brown adipose tissue: Classical brown rather than brite/beige?

NEW FINDINGS: What is the topic of this symposium lecture? It has been suggested that human brown adipose tissue is more similar to the brite/beige adipose tissue of mice than to classical brown adipose tissue of mice. The basis of this is discussed in relation to the physiological conditions of standard experimental mice. What advances does it highlight? That - provided mouse adipose tissues are examined under physiological conditions closer to those prevalent for most humans - the gene expression profile of mouse classical brown adipose tissue is more similar to that of human brown adipose tissue than is the profile of mouse brite/beige adipose tissue. Human brown adipose tissue is therefore not of another nature than classical mouse brown adipose tissue. ABSTRACT: Since the general presence of brown adipose tissue was established in adult humans some 13 years ago, its physiological significance and its molecular characteristics have been discussed. Particularly, it has been proposed that the mouse adipose tissue depot most closely resembling and molecularly parallel to human brown adipose tissue is not classical mouse brown adipose tissue. Rather so-called brite or beige adipose tissue - characteristically observed in the inguinal "white" adipose tissue depot of mice - has been proposed to be the closest mouse equivalent of human brown adipose tissue. We summarize here published evidence examining this question. We emphasize the differences in tissue appearance and tissue transcriptomes from "standard" mice (young, chow-fed and in effect semi-cold-exposed (20°C)) versus "physiologically humanized" mice (middle-aged, high-fat diet fed mice living at thermoneutrality (30°C)). We find that in the physiologically humanized mice, classical brown adipose tissue displays molecular and cellular characteristics that are more akin to human brown adipose tissue than are those from brite/beige adipose tissues from either standard or physiologically humanized mice. We suggest, therefore, that mouse brown adipose tissue is the more relevant tissue for translational studies. - This is an invited summary of a presentation given at Physiology 2019 (Aberdeen). This article is protected by copyright. All rights reserved.