Hyperglycemia potentiates brain susceptibility to lipopolysaccharide-induced neuroinflammation by astrocytes reprogramming
Hyperglycemia has been shown to modulate the immune response of peripheral immune cells and organs, but the impact of hyperglycemia on neuroinflammation within the brain remains elusive. In the present study, we provide evidences that streptozotocin (STZ)-induced hyperglycemic condition in mice drives a phenotypic switch of brain astrocytes to a proinflammatory and neurotoxic state, and increases brain vulnerability to mild peripheral inflammation. In particular, we found that hyperglycemia led to a significant increase in the astrocyte proliferation as determined by flow cytometric and immunohistochemical analyses of mouse brain. Transcriptomic analysis of isolated astrocytes from Aldh1l1CreER;tdTomato mice revealed that peripheral STZ injection induced astrocyte reprogramming into proliferative, proinflammatory and neurotoxic phenotype. Additionally, STZ-induced hyperglycemic condition significantly enhanced the infiltration of circulating myeloid cells into the brain and the disruption of blood-brain barrier in response to mild lipopolysaccharide (LPS) administration. Systemic hyperglycemia did not alter the intensity and sensitivity of peripheral inflammation in mice to LPS challenge, but increased the inflammatory potential of brain microglia. Furthermore, hyperglycemic mice exhibited a significant impairment in cognitive function after mild LPS administration compared to normoglycemic mice as determined by novel object recognition and Y-maze tasks. Taken together, these results demonstrate that hyperglycemia directly induces astrocyte reprogramming towards a proliferative and proinflammatory phenotype, which potentiates mild LPS-triggered inflammation within brain parenchymal regions. Overall design: To investigate the phenotypic changes in immune regulatory functions of astrocytes in hyperglycemic conditions. We sorted astrocytes from mice treated either with streptozotocin (STZ) or vehicle (Veh). Vehicle group being the control group, and  three samples (replicates) are assigned to each group for comparison. We then performed gene expression profiling analysis using data obtained from RNA-seq of astrocytes from two different groups (Veh and STZ group). Comparative gene expression profiling is done for the two group.