Accumulating evidence links human obesity and diabetes with cognitive dysfunction and dementia 1-51. While the causality is unknown in humans, and likely bi-directional, it is clear from work in rodents that diet induced obesity and associated metabolic dysfunction cause impaired cognition52-56. The mechanisms supporting this effect and the relative contribution of adiposity, diet and metabolic dysfunction remain unknown. Of particular interest to the funding opportunity announcement to which we respond is elucidating the link between glucose regulation and cognition. Although glucose intolerance is diagnostic of type 2 diabetes (T2D), a recent systematic review of 86 papers examining T2D and cognition only found a weak association between glycaemia and cognition 68 and there is even less evidence for an association with other measures of peripheral glucose regulation (e.g., insulin concentration, insulin action, insulin resistance)68. This represents a major gap in knowledge because it impedes the development of strategies to mitigate the risk of neurocognitive complications. The proposed research directly addresses this gap in knowledge. More specifically, we aim to provide a definitive test of the role of peripheral glucose intolerance on neurocognition, by longitudinal evaluation of cognitive and brain function in youth enrolled in the Pathogenesis of Youth Onset Diabetes (PYOD) study (R01DK111038) who are either glucose tolerant or intolerant but matched for age, gender, BMI and central adiposity. The PYOD cohort provides an exceptional opportunity to study cognitive impairment in T2D because the participants are pre-diabetic and thus do not suffer from chronic conditions associated with T2D. We also propose to use a new neuroimaging paradigm developed to assess central insulin resistance (IR) so that we may disentangle the effects of central and peripheral IR on neurocognition 46 and an indirect marker of striatal dopamine signaling to investigate the relation between IR, dopamine and neurocognition. More specifically, our aims are to (1) To test whether impaired peripheral glucose tolerance (IGT) and/or central IR influence neurocognitive function independently from adiposity; (2) To test whether change in glucose metabolism and/or adiposity predicts and precedes change in neurocognition; and (3) To test whether cognitive dysfunction and decline is associated with dopamine signaling. We anticipate that these results will inform the development of strategies to mitigate the risk of developing neurocognitive impairment, aid in the identification of individuals who are at-risk and who might benefit from additional therapy, provide a novel therapeutic target for pharmacological intervention and provide critical information about the rate of cognitive decline.
The proposed work will provide a definitive test of the role of peripheral glycemia in cognition by performing a longitudinal study of neurocognition and brain function in youth aged 8-16 currently enrolled in the Pathogenesis of Youth Onset Diabetes who are glucose tolerant or intolerant but who are matched for measures of adiposity, gender, IQ and age. In addition, towards identifying a pathogenic mechanism of neurocognitive impairment in type 2 diabetes, we will determine whether glucose intolerance and central insulin resistance preferentially influence dopamine-dependent functions, suggesting that dopamine- adaptations provide a mechanistic link between diabetes and neurocognitive impairment.
