Year: 2013
Type: article
Abstract: Brown adipose tissue (BAT) is the main site of non-shivering thermogenesis in mammals.In humans, BAT was first described in infants [1], and for several decades it was thought to be absent in adults.Recently, the presence of functional BAT was found in healthy adults [2][3][4].These findings opened new avenues for the investigation of BAT function in the regulation of energy metabolism.More strikingly, it was found that the white adipose tissue (WAT) can convert to BAT [5] in physiological conditions.Tools to investigate the regulation of BAT activity and conversion of WAT to BAT in vivo were lacking.In this issue of Molecular Metabolism, Quarta and colleagues [6] demonstrate the use of hybrid CT/PET imaging to identify the conversion of WAT to BAT in vivo in adult mice.These findings will lead to new opportunities for the prospective study of BAT function in mammals.BAT is a form of adipose tissue that contains a high density of specialized mitochondria, which dissipate the production of energy in the form of ATP to generate heat.The critical molecular player in brown adipocytes to allow thermogenesis is UCP1, a mitochondrial uncoupling protein that deviates the proton flux from ATPase to produce heat.UCP1 expression is highly specific to brown and beige adipocytes and absent in white adipocytes.Therefore, the expression of UCP1 has been used as a molecular marker of conversion of WAT in BAT, a process known as "browning".The role of BAT and UCP1 in energy metabolism and on physiology in general has been emphasized by a recent study showing that mutations in UCP1 might account for the exceptional longevity in the naked mole rat [7].Activation of BAT occurs during cold exposure, in a process that relies on sympathetic nervous system (SNS).In the study by Quarta et al. [6], the authors demonstrate the use of a PET tracer, 11C-meta-hydroxyephedrine, a NE analog, as an indirect tool to label BAT and the conversion of WAT to BAT.Because BAT is highly innervated by the SNS, and because the SNS is a critical determinant of BAT function, this tracer showed robust characteristics to label SNSdepended BAT activity in vivo.The authors showed functional applications of the tracer, for example, the utilization of PET/CT imaging to identify diet-induced changes in SNS-mediated BAT thermogenesis.In a rodent model of obesity, it has presented further in vivo evidences for impaired thermogenesis by BAT, a factor in the development of obesity and its associated disorders, in obese animals compared to lean controls.Utilizing similar approaches, it is possible to visualize the use of this tool to investigate the effects of distinct manipulations in the physiology of SNS-induced BAT activity.For example, such PET tracers could be used to identify mediators of diet/temperature/exercise-induced thermogenesis.Because physiological interventions can change BAT
Source: Molecular Metabolism
Author: Marcelo O. Dietrich
Institutions: Universidade Federal do Rio Grande do Sul, Yale University
Language: English
Subfield: Physiology (medical)
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $4,270
OpenAlex ID: W2061242617