The Journal of Neuroscience, October 15, 2000, 20(20):7505-7509
Deficiency of Complement Defense Protein CD59 May Contribute to
Neurodegeneration in Alzheimer's Disease
Li-Bang
Yang1,
Rena
Li1,
Seppo
Meri2,
Joseph
Rogers1, and
Yong
Shen1
1 L. J. Roberts Center for Alzheimer's Research,
Sun Health Research Institute, Sun City, Arizona 85351, and
2 Department of Immunology, Haartman Institute, University
of Helsinki, Finland
Complement defense 59 (CD59) is a cell surface
glycophosphoinositol (GPI)-anchored protein that prevents
complement membrane attack complex (MAC) assembly. Here, we present
evidence from ELISA assays that CD59 protein levels are significantly
decreased in the frontal cortex and hippocampus of Alzheimer's disease
(AD) compared with nondemented elderly (ND) patients, whereas
complement component 9, a final component to form MAC, is significantly
increased. To further confirm the CD59 deficit, PI-specific
phospholipase C (PIPLC) was used to cleave the CD59 GPI anchor at the
cell surface in intact slices from AD and ND cortex. CD59 released by
PIPLC cleavage was significantly reduced in AD compared with ND
samples. By the use of a ribonuclease protection technique, amyloid
-peptide was found to downregulate CD59 expression at the mRNA
level, suggesting a partial explanation of CD59 deficits in the AD
brain. To evaluate the pathophysiological significance of CD59
alterations in neurons, we exposed cultured NT2 cells,
which normally underexpress CD59, and NT2 cells transfected to
overexpress CD59 to homologous human serum. Lactic acid dehydrogenase
assays revealed significant complement-induced cell lysis in
CD59-underexpressing NT2 cells and significant protection from such
lysis in CD59-overexpressing NT2 cells. Moreover, cells expressing
normal levels of CD59 showed no evidence of MAC assembly or damage
after exposure to homologous serum, whereas pretreatment of these cells
with a CD59-neutralizing antibody resulted in MAC assembly at the cell
surface and morphological damage. Taken together, these data suggest
that CD59 deficits may play a role in the neuritic losses
characteristic of AD.
Key words:
neurodegeneration; Alzheimer; neuron death; amyloid
protein; complement; inflammation
Copyright © 2000 Society for Neuroscience 0270-6474/00/20207505-05$05.00/0