Obesity-associated disease is the fifth leading cause of death worldwide. Obesity is a major risk factor for the development of diabetes, cardiovascular disease, cancer and osteoarthritis. A growing body of animal and human studies implicates deregulation of central dopamine circuits in excessive feeding behavior in obesity. Neuroimaging studies of obese individuals reveal a BMI-dependent decrease in striatal dopamine receptor levels. Interestingly, insulin enhances the surface expression of the dopamine transporter (DAT) while inhibiting that of the nor epinephrine transporter (NET). Together these transporters tune extracellular dopamine levels in the striatum and cortex respectively, areas critically involved in reward, habits, and cognitive control. This suggests tha impaired central insulin signaling, such as has been observed in animals placed on an obesogenic diet could, by blunting striatal, and enhancing cortical dopamine clearance, result in functional impairments in systems mediating food acquisition and overconsumption. In this study, obese individuals with mild impaired insulin signaling, randomized to receive insulin or placebo, will undergo longitudinal nuclear and functional imaging to examine insulin's ability to normalize deregulated striatal and cortical dopamine neurotransmission in obesity. Further, the interaction between dopamine neurotransmission and the effects of insulin specifically on prefrontal cortical function of inhibitory control will be examined. The overarching aim of this study is to assess whether the resetting of central insulin tone will normalize the opposing cortical and striatal dopamine deregulation sub serving the feeding behavior that progressively leads to obesity. This applicant-designed project exploits and expands upon a larger ongoing investigator-initiated patient-oriented clinical study, providing the applicant the opportunity to engage in directly translational research spanning the fields of neuroscience, endocrinology, and biomedical imaging. The proposed research program provides mentorship and training in all of these areas from leading physician scientists and researchers, neuroscience and neuroimaging coursework, and renowned institutional resources for both biomedical imaging and diabetes research. The training plan integrates the core principles of medical and scientific knowledge surrounding the path physiology of neuroendocrine dysfunction in the clinical research setting with the aim of directly translating animal and human research. The training plan emphasizes the acquisition and development of skills required for advanced neuroimaging research, including didactic and extracurricular training in functional and molecular neuroimaging. The finding of whether exogenous insulin modulates dopamine neurotransmission and behavior in a way that is beneficial will ultimately inform the current treatment and management of the global obesity epidemic.
The obesity epidemic places over 1.5 billion people worldwide at risk for multiple chronic illnesses, including diabetes, cardiovascular disease, osteoarthritis, and cancer. This patient-oriented, translational research project unites molecular and functional neuroimaging to examine the role of obesity-associated impairment in insulin signaling on brain function, and will provide evidence for how optimizing pharmacologic management of obesity can prevent continued weight gain and obesity associated disease.