Source: Mount Sinai Health System.
Researchers reveal that the sympathetic nervous system, not white blood cells, are critically important in the regulation of energy expenditure and thermogenesis.
A new study from the Icahn School of Medicine at Mount Sinai provides important insights into how the body regulates its production of heat, a process known as thermogenesis that is currently intensely studied as a target of diabetes and obesity treatment in humans.
While researchers had previously hypothesized that macrophages, a class of white blood cells, played a major role in thermogenesis, the new study suggests that the main driver of thermogenesis is the sympathetic nervous system, which is chiefly controlled by the brain. The results were published online today in Nature Medicine.
The Mount Sinai research team led by Christoph Buettner, MD, PhD, senior author of the study and Professor of Medicine (Endocrinology, Diabetes, and Bone Disease) at the Icahn School of Medicine at Mount Sinai, focused on catecholamines, hormones released by the sympathetic nervous system to activate brown fat tissue. Brown adipose tissue is a type of fat tissue that burns energy to produce heat and keep us warm. Catecholamines can also convert white fat tissue, the more familiar kind of fat tissue that stores lipids, into a tissue that resembles brown fat. The researchers tested whether macrophages could provide an alternative source of catecholamines, as had been proposed in recent years.
“Thermogenesis is a metabolic process that receives a lot of interest as a target of drugs that allow you to burn energy and hence reduce obesity and improve diabetes. It turns out that macrophages are not that important, as they are unable to make catecholamines, but clearly the brain through the sympathetic nervous system is,” says Dr. Buettner. “Therefore, it is very important to study the role of the brain and the sympathetic nervous system when it comes to understanding metabolism.”
The ability to generate heat is critical for the survival of warm-blooded animals, including humans, as it prevents death by hypothermia. “This evolutionary pressure shaped the biology of humans and that of other warm-blooded animals, and may in part explain why humans are susceptible to developing diabetes in the environment in which we live,” says Dr. Buettner.
According to Dr. Buettner, while a lot of effort has been invested in targeting the immune system to cure diabetes and insulin resistance, as of yet there are no anti-inflammatory drugs that have been shown to work well in humans with metabolic disease. “Our study suggests that perhaps the key to combating the devastating effects of diabetes and obesity in humans is to restore the control of thermogenesis and metabolism by the brain and the autonomic nervous system,” says Dr. Buettner.
This study was performed collaboratively between Mount Sinai and eight other institutions from around the world, most prominently with the group of Timo D. Müller, PhD, Institute for Diabetes and Obesity at the Helmholtz Center Munich in Germany.
Funding: This work was further supported by grant from the German Research Foundation DFG-TS226/1-1, DFG-TS226/3-1,SFB1123, Nutripathos Project ANR-15-CE14-0030, European Research Council ERC AdG HypoFlam no. 695054 (to M.H.T.); DFG He3260/8-1, the EU FP7 Network “DIABAT,” the EU ITN Network “TRAIN” 721531 (to S.H.); NIH R01AA023416, DK082724 and a career-development award from the American Diabetes Association (to C.B.); NIH R01DK099222 (to S.D.); NIH DK17844 (to S.C.W.); the Israeli Science Foundation and European Research Council (AdvERC grant 340345) (to S.J.) and the Swedish Research Council and the Knut and Alice Wallenberg Foundation (to J.N. and B.C.).
Source: Renatt Brodsky – Mount Sinai Health System
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Alternatively activated macrophages do not synthesize catecholamines or contribute to adipose tissue adaptive thermogenesis” by Katrin Fischer, Henry H Ruiz, Kevin Jhun, Brian Finan, Douglas J Oberlin, Verena van der Heide, Anastasia V Kalinovich, Natasa Petrovic, Yochai Wolf, Christoffer Clemmensen, Andrew C Shin, Senad Divanovic, Frank Brombacher, Elke Glasmacher, Susanne Keipert, Martin Jastroch, Joachim Nagler, Karl-Werner Schramm, Dasa Medrikova, Gustav Collden, Stephen C Woods, Stephan Herzig, Dirk Homann, Steffen Jung, Jan Nedergaard, Barbara Cannon, Matthias H Tschöp, Timo D Müller & Christoph Buettner in Nature Medicine. Published online April 17 2017 doi:10.1038/nm.4316
Alternatively activated macrophages do not synthesize catecholamines or contribute to adipose tissue adaptive thermogenesis
Adaptive thermogenesis is the process of heat generation in response to cold stimulation. It is under the control of the sympathetic nervous system, whose chief effector is the catecholamine norepinephrine (NE). NE enhances thermogenesis through β3-adrenergic receptors to activate brown adipose tissue and by ‘browning’ white adipose tissue. Recent studies have reported that alternative activation of macrophages in response to interleukin (IL)-4 stimulation induces the expression of tyrosine hydroxylase (TH), a key enzyme in the catecholamine synthesis pathway, and that this activation provides an alternative source of locally produced catecholamines during the thermogenic process. Here we report that the deletion of Th in hematopoietic cells of adult mice neither alters energy expenditure upon cold exposure nor reduces browning in inguinal adipose tissue. Bone marrow–derived macrophages did not release NE in response to stimulation with IL-4, and conditioned media from IL-4-stimulated macrophages failed to induce expression of thermogenic genes, such as uncoupling protein 1 (Ucp1), in adipocytes cultured with the conditioned media. Furthermore, chronic treatment with IL-4 failed to increase energy expenditure in wild-type, Ucp1−/− and interleukin-4 receptor-α double-negative (Il4ra−/−) mice. In agreement with these findings, adipose-tissue-resident macrophages did not express TH. Thus, we conclude that alternatively activated macrophages do not synthesize relevant amounts of catecholamines, and hence, are not likely to have a direct role in adipocyte metabolism or adaptive thermogenesis.
“Alternatively activated macrophages do not synthesize catecholamines or contribute to adipose tissue adaptive thermogenesis” by Katrin Fischer, Henry H Ruiz, Kevin Jhun, Brian Finan, Douglas J Oberlin, Verena van der Heide, Anastasia V Kalinovich, Natasa Petrovic, Yochai Wolf, Christoffer Clemmensen, Andrew C Shin, Senad Divanovic, Frank Brombacher, Elke Glasmacher, Susanne Keipert, Martin Jastroch, Joachim Nagler, Karl-Werner Schramm, Dasa Medrikova, Gustav Collden, Stephen C Woods, Stephan Herzig, Dirk Homann, Steffen Jung, Jan Nedergaard, Barbara Cannon, Matthias H Tschöp, Timo D Müller & Christoph Buettner in Nature Medicine. Published online April 17 2017 doi:10.1038/nm.4316