Complement and microglia mediate early synapse loss in Alzheimer mouse models

Area of Science:

• Neuroscience
• Immunology
• Pathology

Background:

• Synapse loss is a key feature of Alzheimer's disease (AD), correlating with cognitive decline.
• Microglia and complement system involvement in AD is typically linked to late-stage neuroinflammation.
• The precise mechanisms and timing of microglial and complement involvement in early AD pathogenesis remain unclear.

Purpose of the Study:

• To investigate the role of complement and microglia in mediating early synapse loss in Alzheimer's disease models.
• To determine if inhibiting complement or microglial pathways can prevent early synaptic damage in AD.

Main Methods:

• Utilized mouse models of Alzheimer's disease.
• Assessed levels of C1q and its association with synapses.
• Measured microglial phagocytic activity and synapse loss.
• Inhibited components of the complement cascade (C1q, C3) and microglial complement receptor CR3.
• Evaluated the impact of soluble beta-amyloid (Aβ) oligomers on synapses and long-term potentiation.

Main Results:

• Increased C1q levels were observed at synapses prior to plaque deposition in AD mouse models.
• Inhibition of C1q, C3, or CR3 significantly reduced phagocytic microglia and early synapse loss.
• C1q was essential for the detrimental effects of soluble Aβ oligomers on synapses and hippocampal function.
• Microglia were found to engulf synaptic material in a CR3-dependent manner when exposed to soluble Aβ oligomers.

Conclusions:

• The complement cascade, initiated by C1q, and microglia play a critical role in mediating early synapse loss in Alzheimer's disease.
• These pathways, normally involved in synaptic pruning during development, are inappropriately activated in AD.
• Targeting the complement-dependent pathway and microglial CR3 presents a potential therapeutic strategy for preventing early synaptic damage in AD.