Complement activation sustains neuroinflammation and deteriorates adult neurogenesis and spatial memory impairment in rat hippocampus following sleep deprivation.

BACKGROUND

An association between neuroinflammation, reduced adult neurogenesis, and cognitive impairment has been established in sleep deprivation (SD). Complement receptors are expressed on neuronal and glial cells, thus, regulate the neuroinflammation, neurogenesis and learning/memory. However, understanding of the effect of SD on the brain-immune system interaction associated with cognitive dysfunction and its mechanisms is obscure. We hypothesized that complement activation induced changes in inflammatory and neurogenesis related proteins might be involved in the cognitive impairment during SD.

METHODOLOGY

Adult male Sprague Dawley rats were used. Rats were sleep deprived for 48 h using a novel automated SD apparatus. Dosage of BrdU (50 mg/kg/day, i.p. in 0.07 N NaOH), complement C3a receptor antagonist (C3aRA; SB290157; 1 mg/kg/day, i.p.) in 1.16% v/v PBS and complement C5a receptor antagonist (C5aRA; W-54011; 1 mg/kg/day, i.p.) in normal saline were used. Rats were subjected to spatial memory evaluation following SD. Hippocampal tissue was collected for biochemical, molecular, and immunohistochemical studies. T-test and ANOVA were used for the statistical analysis.

RESULTS

An up-regulation in the levels of complement components (C3, C5, C3a, C5a) and receptors (C3aR and C5aR) in hippocampus, displayed the complement activation during SD. Selective antagonism of C3aR/C5aR improved the spatial memory performance of sleep-deprived rats. C3aR antagonist (C3aRA) or C5aR antagonist (C5aRA) treatment inhibited the gliosis, maintained inflammatory cytokines balance in hippocampus during SD. Complement C3aR/C5aR antagonism improved hippocampal adult neurogenesis via up-regulating the BDNF level following SD. Administration of C3aRA and C5aRA significantly maintained synaptic homeostasis in hippocampus after SD. Gene expression analysis showed down-regulation in the mRNA levels of signal transduction pathways (Notch and Wnt), differentiation and axogenous proteins, which were found to be improved after C3aRA/C5aRA treatment. These findings were validated at protein and cellular level. Changes in the corticosterone level and ATP-adenosine-NO pathway were established as the key mechanisms underlying complement activation mediated consequences of SD.

CONCLUSION

Our study suggests complement (C3a-C3aR and C5a-C5aR) activation as the novel mechanism underlying spatial memory impairment via promoting neuroinflammation and adult neurogenesis decline in hippocampus during SD, thereby, complement (C3aR/C5aR) antagonist may serve as the novel therapeutics to improve the SD mediated consequences.