BDNF Alleviates Neuroinflammation in the Hippocampus of Type 1 Diabetic Mice via Blocking the Aberrant HMGB1/RAGE/NF-κB Pathway

Diabetes is a systemic disease that can cause brain damage such as synaptic impairments in the hippocampus, which is partly because of neuroinflammation induced by hyperglycemia. Brain-derived neurotrophic factor (BDNF) is essential in modulating neuroplasticity. Its role in anti-inflammation in diabetes is largely unknown. In the present study, we investigated the effects of BDNF overexpression on reducing neuroinflammation and the underlying mechanism in mice with type 1 diabetes induced by streptozotocin (STZ). Animals were stereotactically microinjected in the hippocampus with recombinant adeno-associated virus (AAV) expressing BDNF or EGFP. After virus infection, four groups of mice, the EGFP+STZ, BDNF+STZ, EGFP Control and BDNF Control groups, received STZ or vehicle treatment as indicated. Three weeks later brain tissues were collected. We found that BDNF overexpression in the hippocampus significantly rescued STZ-induced decreases in mRNA and protein expression of two synaptic plasticity markers, spinophilin and synaptophysin. More interestingly, BDNF inhibited hyperglycemia-induced microglial activation and reduced elevated levels of inflammatory factors (TNF-α, IL-6). BDNF blocked the increase in HMGB1 levels and specifically, in levels of one of the HMGB1 receptors, RAGE. Downstream of HMGB1/RAGE, the increase in the protein level of phosphorylated NF-κB was also reversed by BDNF in STZ-treated mice. These results show that BDNF overexpression reduces neuroinflammation in the hippocampus of type 1 diabetic mice and suggest that the HMGB1/RAGE/NF-κB signaling pathway may contribute to alleviation of neuroinflammation by BDNF in diabetic mice.