Obesity Energy, Thermogenesis and Appetite
Dr. Richard Rogers
Obesity and its evil twin, diabetes, are rapidly becoming our #1 health epidemic. Today 10% of all medical costs in the U.S. are dueto an overweight population, and this percentage is growing rapidly. Today, the breakdown is about $1500 per year in medical costs for obese versus normal weight individuals. This translates into more than $145 billion spent annually.
Given the size of the epidemic, a growing focus for my company is providing reagents to researchers who study bioprocesses involved in energy metabolism. This includes researchers studying what happens to energy expenditure when the “fuel tank” is full and also empty. Both states could give clues as to why we overeat.
In my routine follow up with researchers using our reagents, I started to get an appreciation on how these complex energy pathways are being unraveled and better understood. That appreciation forms the roots of this “News Behind the Neuroscience News” story. It is a story that has the hormones Leptin and TRH playing a starring role supported by hindbrain neuro/glial-circuitry and brown adipose tissue (BAT).
The Rogers Lab
I became aware of the Richard Rogers Lab in my follow up with Montina Van Meter checking on our LepRb/OBRb antibody. She shared that it was giving them results better than most others they has used. She then gave me an overview of her research involved with the control of feeding behavior and energy utilization including thermogenesis (“heat generation”) catalyzed in BAT. Cool…this was a lab we wanted to make sure we served and served well.
Tina not only kept me informed on how our reagents were working, but also generously alerted to me publications referencing use of our reagents:
· Maria J. Barnes, Richard C. Rogers, Montina J. Van Meter and Gerlinda E. Hermann. Co-localization of TRHR1 and LepRb
receptors on neurons in the hindbrain of the rat. doi:10.1016/j.brainres.2010.07.094…Included are excellent images of stained LepRb (OB-Rb)-(Dilution 1:500) and GAD1-Dilution (2ug/ml) expressing neurons localized in loose clusters of cells in the DMN, NST, and the VLM…
· Hung Hsuchou, Yi He, Abba J. Kastin, Hong Tu, Emily N. Markadakis, Richard C. Rogers, Paul B. Fossier, and Weihong Pan. Obesity induces functional astrocytic leptin receptors in hypothalamus. Brain, Mar 2009; doi:10.1093/brain/awp029…unique sequence of ObRb at its cytoplasmic tail (CH14104, Neuromics, Edina, MN, USA). This antibody was raised
against rat ObRb…
I found this research to be unique and intriguing. This led me to an interview with Dr. Rogers. Here is his backstory.
Dr. Rogers credits serendipity as a driving force in his interest in Neuroscience. It started with a bike ride and chance introduction with a ham radio operator when he was a youngster. This catalyzed his interest in electronics and circuitry.
This interest morphed to a passion for Neuroscience (circuits and signaling). He entered the first college program devoted to Neuroscience studies at UCLA. He received his Ph. D. in 1979. His post-doc focused on digestive regulation. Here, he investigated the neural circuitry involved in the normal control of gastric function.
In collaboration with his wife Dr. Gerlinda Hermann, his work evolved to solving the mystery of why we don’t eat (abnormal gastric function). What causes gastro-intestinal shutdown? The breakthrough was their ability to show cross-talk between the immune system and nervous system. This research is a foundation for the discovery of therapies for sufferers of appetite shut down cause by cancer therapies and certain immune related pathologies.
The main culprit is TNF-α. The blood level of this peptide is elevated as a consequence of immune activation caused by infection, cancer, radiation exposure and chronic autoimmune disease. The breakthrough was showing that TNF-α receptors are on neurons in the brainstem that control gastric functions, including emesis. Neurons in the nucleus of the solitary tract (NST) respond to TNF-α greatly increasing the sensitivity of gastric vagal control circuitry. This causes emptying of the gut to dramatically slow,l leading to nausea, vomiting and cessation of appetite.
Currently, they are delving into the complexities of TNF-α signaling processes. This includes the role of astrocytes and glia.
See: Gerlinda E Hermann and Richard C Rogers. TNF activates astrocytes and catecholaminergic neurons in the solitary nucleus: implications for autonomic control. doi: 10.1016/j.brainres.2009.03.059.
Energy,Obesity and Thermogenesis-Active Astrocytes
Recently, the lab took another road less traveled. Dr. Gerlinda Hermann discovered interesting aspects of leptin and thyrotropin releasing hormone (TRH) signaling. This research looks at signaling in thermogenesis and feeding behavior. A most interesting aspect includes conclusions concerning the role of astrocytes. Their colleague Dr. Weihong Pan showed that adult obese mice, (2 months after being placed on a high-fat diet) showed a striking increase of leptin receptor (+) astrocytes, most prominent in the dorsomedial hypothalamus and arcuate nucleus. Agouti viable yellow mice with their adult-onset obesity showed similar changes, but the increase of leptin receptor (+) astrocytes was barely seen in ob/ob or db/db mice with their early-onset obesity and defective leptin systems. The results indicate that metabolic changes in obese mice can rapidly alter leptin receptor expression and astrocytic activity, and that leptin receptor is responsible for leptin-induced calcium signalling in astrocytes. This novel and clinically relevant finding opens new avenues in astrocyte biology (doi: 10.1093/brain/awp029).
Non-shivering thermogenesis usually occurs in BAT. It uncouples the ATP energy producing process by generating heat rather than driving the conversion of ADP to ATP. This creates an ingenious way to untangle complex processes related to Leptin signaling. What happens when there is sufficient energy for the thermogenic process? Conversely, what happens when there is insufficient energy?
Leptin and TRH act synergistically in the hindbrain to drive thermogenesis. However, in a starving condition there is a subsequent drop in Leptin and thermogenesis. Behind these simple facts are complex processes that occur in the hindbrain. The team is providing important insights including location of events and relevant signaling molecules. (doi:10.1016/j.brainres.2010.07.094).
The Future-Caged Compounds and Live Cell Signaling
Caged compounds are bioactive molecules attached to photolabile groups, that release the active component on contact with photons of the right energy level – the process of photolysis. Photolysis is now widely applied in biology to induce neurotransmitter and otherm ligand-receptor interactions in conditions that are otherwise subject to poor diffusional access and receptor desensitization, as well as for labile ligands.
This novel technology affords Dr. Rogers and his team the capability do live cell imaging of calcium signaling. From these they will help us gain a deeper understanding of what is happing and where. Specifically, we will more exactly learn the role that astrocytes and glia play in controlling the role of Leptin and related signaling molecules in controlling energy, metabolism and feeding behavior. This could lead to important target for future therapies.