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Complement-mediated neurotoxicity is regulated by homologous restriction
Y Shen1, J A Halperin, C M Lee
1Neuroscience Department, Abbott Laboratories, Abbott Park, IL 60064-3500, USA.
Insights
The complement system can cause neuronal cell death, particularly in Alzheimer's disease. However, the protein CD59 protects human neurons from complement-mediated damage by restricting the membrane attack complex.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Beta-amyloid peptides activate the complement cascade, and complement proteins like the membrane attack complex (C5b-9) are found in Alzheimer's disease brains.
- This suggests a potential role for the complement system in neurodegenerative disorders.
Purpose of the Study:
- To investigate the effect of complement activation on neuronal cell death.
- To determine the role of homologous restriction in protecting neurons from complement-mediated lysis.
Main Methods:
- Studied complement activation and cell death in nerve growth factor (NGF)-differentiated PC12 cells and retinoic acid (RA)-differentiated SH-SY5Y cells treated with human serum.
- Assessed the presence of CD59 on SH-SY5Y cells using PCR and immunocytochemistry.
- Investigated the effect of phosphatidylinositol-specific phospholipase C (PI-PLC) on SH-SY5Y cell vulnerability to complement.
Main Results:
- Human serum activated complement (iC3b formation) in both PC12 and SH-SY5Y cells, but only PC12 cells underwent lysis.
- SH-SY5Y cells expressed CD59, a glycosylphosphatidylinositol (GPI)-anchored protein that inhibits membrane attack complex formation, conferring resistance to complement.
- Treatment with PI-PLC removed GPI-anchored proteins, rendering SH-SY5Y cells susceptible to complement-mediated cell death; reconstituted C5b-9 was toxic to both cell types.
Conclusions:
- Complement activation can induce neuronal cell death.
- The protein CD59 plays a crucial role in protecting human neuronal cell lines from complement-mediated lysis through homologous restriction.
- These findings highlight the complex interplay between the complement system and neuronal survival in neurodegenerative contexts.
Abstract:
The ability of beta-amyloid peptides to activate the classical complement cascade and the presence of various complement proteins including the membrane attack complex (C5b-9) on dystrophic neurites in Alzheimer's disease brains, raises the possibility that the complement system may contribute to this neurodegenerative disorder. To address this issue, we have studied the effect of complement activation on nerve growth factor (NGF)-differentiated rat pheochromocytoma PC12 cells, and on retinoic acid (RA)-differentiated human neuroblastoma SH-SY5Y cells. Although incubation of both cell types with human serum resulted in activation of complement, as indicated by iC3b formation, only PC12 but not SH-SY5Y cells were killed by human serum treatment. In contrast, heat-inactivated serum (56 degrees C, 45 min) was not neurotoxic. On SH-SY5Y cells, both PCR amplification and immunocytochemistry demonstrated the presence of CD59, a glycosylphosphatidylinositol-anchored protein that restricts homologous complement activation by inhibiting the formation of the membrane attack complex. The presence of CD59 probably accounts for the inability of human complement to lyse the human cell lines. Indeed, removal of glycosylphosphatidylinositol (GPI)-anchored proteins with phosphatidylinositol-specific phospholipase C (PI-PLC) rendered SH-SY5Y cells vulnerable to complement attack and eventually led to serum-medicated cell death. Reconstituted C5b-9 was also toxic to both PC12 and PI-PLC-pretreated SH-SY5Y cells. These observations suggest that complement activation can cause neuronal cell death and that this process is regulated by homologous restriction.