High glucose‐induced complement component 3 up‐regulation via RAGE‐p38MAPK‐NF‐κB signalling in astrocytes: In vivo and in vitro studies

Diabetes is considered as a risk for cognitive decline, which is characterized by neurodegenerative alteration and innate immunity activation. Recently, complement 3 (C3), the critical central component of complement system, has been reported to play a key role in neurodegenerative alterations under pathological condition. Receptor for advanced glycation end products (RAGE) activation is confirmed to mediate several inflammatory cytokines production. However, whether C3 activation participates in the diabetic neuropathology and whether this process is regulated by RAGE activation remains unknown. The present study aimed to investigate the role of C3 in streptozotocin-induced diabetic mice and high glucose-induced primary astrocytes and the underlying modulatory mechanisms. The decreased synaptophysin density and increased C3 deposition at synapses were observed in the diabetic brain compared to the control brain. Furthermore, the elevated C3 was co-localized with GFAP-positive astrocytes in the diabetic brain slice in vivo and high glucose-induced astrocytes culture in vitro. Diabetes/high glucose-induced up-regulation of C3 expression at gene, protein and secretion levels, which were attenuated by pre-treatment with RAGE, p38MAPK and NF-κB inhibitors separately. These results demonstrate that high glucose induces C3 up-regulation via RAGE- p38MAPK-NF-κB signalling in vivo and in vitro, which might be associated with synaptic protein loss.