Targeting terminal pathway reduces brain complement activation, amyloid load and synapse loss, and improves cognition in a mouse model of dementia

Abstract Background Neuroinflammation is a critical factor of Alzheimer’s Disease (AD). Dysregulation of complement leads to excessive inflammation, direct damage to self‐cells and propagation of injury. This is likely of particular relevance in the brain where inflammation is poorly tolerated and brain cells are vulnerable to direct damage by complement. Membrane attack complex (MAC) is highly pro‐inflammatory product of the complement cascade killing cells by lysis and/or causing ‘bystander’ damage initiating NLRP3 inflammasome activation and provoking other immune damaging responses leading to death of the vulnerable nerve cells. Method The role of MAC in AD was investigated in MAC‐deficient animals and by using a newly developed anti‐C7 monoclonal antibody (mAb) that efficiently inhibits formation of the MAC in vitro and in vivo . Impact of C7 deficiency on brain complement dysregulation, synapse loss, amyloid load and cognitive decline was examined by comparing APP NL‐G‐F mice back‐crossed to C7 deficiency (APP NL‐G‐F xC7) with unmodified APP NL‐G‐F mice. To assess the effect of therapeutic C7 blockade, unmodified APP NL‐G‐F mice were treated systemically (for four weeks) with anti‐C7 mAb or control IgG and the same set of parameters of complement dysregulation, pathology and cognition measured. Result C7 deficiency in App NL−G−F mice reduced levels of complement activation markers, reduced amyloid load and increased synapse density with a commensurate improvement in cognitive test performance. Systemic treatment of App NL−G−F mice with a blocking anti‐C7 mAb reduced brain levels of complement activation markers, amyloid load and increased neuronal spine density in treated mice in peri‐plaque areas when compared to controls. in App NL−G−F mice. APP NL‐G‐F xC7 performed significanlty better in behavioural cognitive tests. Conclusion We demonstrate that complement dysregulation occurs in brain in mouse models of AD. C7 deficiency reduced brain complement dysregulation, improved pathological parameters and cognitive function; systemic anti‐C7 therapy reduced complement dysregulation and protected from synapse loss in the model. Modification for brain delivery of the anti‐C7 mAb will enhance efficacy in the model. The findings highlight the potential for complement inhibition at the level of MAC as a therapy in AD.