Author Interviews, Baylor College of Medicine Houston, Biomarkers, Weight Research / 22.09.2016
Brain RAP is a Critical Mediator of Leptin Resistance and Obesity
MedicalResearch.com Interview with:
[caption id="attachment_28232" align="alignleft" width="144"]
Dr. Makoto Fukuda[/caption]
Makoto Fukuda Ph.D.
Assistant Professor
Children's Nutrition Research Center
Department of Pediatrics
Baylor College of Medicine
Houston, Texas 77030
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: A hallmark characteristic of obesity is diminished actions of metabolic hormones that are critically required to maintain whole body energy balance and glucose homeostasis. Leptin is a crucial and powerful hormone that keeps body weight normal. It was hoped that leptin might be a “magic bullet” that could cure obesity. Shortly after the discovery, however, obese individuals were found to have little or no response to exogenously administered leptin, a state of “leptin resistance”. These observations created a central question to be addressed in the field, which would help our understanding of the core of pathophysiology of obesity. While we and other groups previously demonstrated that Epac, a signaling molecule known as a GTP/GDP exchange factor directly activated by cAMP, is involved in cellular leptin resistance, the role of brain Epac signaling in the whole body metabolism has not yet established.
We approached this question by using brain-specific knockout mice of Rap1, a direct activator of Epac. As expected from previous results, mice with brain-specific deficiency of Rap1 failed to develop leptin resistance even when they were challenged with a hypercaloric diet. What impressed us most in this study was that Rap1 in the brain plays a key role in the whole body metabolic control, beyond its role in controlling leptin sensitivity. Loss of brain Rap1 protects mice from diet-induced obesity and disordered glucose balance, whereas these knockout mice maintained a similar body weight to that of control mice on a normal regular diet. Further, pharmacological inhibition of this pathway reversed leptin resistance and reduced the body weight of dietary obese mice. At the cellular level, we found an unexpected link between Rap1 and endoplasmic reticulum (ER) stress that has emerged as a causative contributor to the development of leptin resistance.
Dr. Makoto Fukuda[/caption]
Makoto Fukuda Ph.D.
Assistant Professor
Children's Nutrition Research Center
Department of Pediatrics
Baylor College of Medicine
Houston, Texas 77030
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: A hallmark characteristic of obesity is diminished actions of metabolic hormones that are critically required to maintain whole body energy balance and glucose homeostasis. Leptin is a crucial and powerful hormone that keeps body weight normal. It was hoped that leptin might be a “magic bullet” that could cure obesity. Shortly after the discovery, however, obese individuals were found to have little or no response to exogenously administered leptin, a state of “leptin resistance”. These observations created a central question to be addressed in the field, which would help our understanding of the core of pathophysiology of obesity. While we and other groups previously demonstrated that Epac, a signaling molecule known as a GTP/GDP exchange factor directly activated by cAMP, is involved in cellular leptin resistance, the role of brain Epac signaling in the whole body metabolism has not yet established.
We approached this question by using brain-specific knockout mice of Rap1, a direct activator of Epac. As expected from previous results, mice with brain-specific deficiency of Rap1 failed to develop leptin resistance even when they were challenged with a hypercaloric diet. What impressed us most in this study was that Rap1 in the brain plays a key role in the whole body metabolic control, beyond its role in controlling leptin sensitivity. Loss of brain Rap1 protects mice from diet-induced obesity and disordered glucose balance, whereas these knockout mice maintained a similar body weight to that of control mice on a normal regular diet. Further, pharmacological inhibition of this pathway reversed leptin resistance and reduced the body weight of dietary obese mice. At the cellular level, we found an unexpected link between Rap1 and endoplasmic reticulum (ER) stress that has emerged as a causative contributor to the development of leptin resistance.























