Submitted on June 30, 2004
Accepted on August 23, 2004
Synergistic amplification of 
-Amyloid and INF
-induced microglial neurotoxic response by the senile plaque component, Chromogranin A
Gilad Twig1, Solomon A Graf2, Mark A Messerli3, Peter J Smith3, Seung H Yoo4, and Orian S Shirihai2*
1 Pharmacology, Tufts University School of Medicine, Boston, MA, USA; BioCurrents Research Center, MBL, Woods Hole, MA, USA; Physiology, Technion, Haifa, Israel
2 Pharmacology, Tufts University School of Medicine, Boston, MA, USA; BioCurrents Research Center, MBL, Woods Hole, MA, USA
3 BioCurrents Research Center, MBL, Woods Hole, MA, USA
4 Physiology, Technion, Haifa, Israel
* To whom correspondence should be addressed. E-mail: orian.shirihai{at}tufts.edu.
Activation of microglial neurotoxic response by components of the senile plaque plays a critical role in the pathophysiology of Alzheimer's disease (AD). Microglia induce neurodegeneration primarily by secreting nitric oxide (NO), tumor necrosis factor alpha (TNF
) and hydrogen peroxide. Central to the activation of microglia is the membrane receptor CD40, which is the target of co-stimulators such as interferon-gamma (IFN
). Chromogranin A (CGA) is a recently identified endogenous component of the neurodegenerative plaques of AD and Parkinson's disease. CGA stimulates microglial secretion of NO and TNF, resulting in both neuronal and microglial apoptosis. Using electrochemical recording from primary rat microglial cells in culture, we show here that CGA alone induces a fast-initiating oxidative burst in microglia. We compared the potency of CGA to that of beta-Amyloid (
A) under identical conditions and found that CGA induces 5-7 times greater NO and TNF secretion. Co-application of CGA with A or with IFN resulted in a synergistic effect on NO and TNF secretion. CD40 expression was induced by CGA and was further increased when A or IFN were added in combination. Tyrphostin A1 (TyrA1), which inhibits the CD40 cascade, exerted a dose-dependent inhibition of the CGA effect alone and in combination with IFN and A. Furthermore, CGA-induced mitochondrial depolarization, which precedes microglial apoptosis, was fully blocked in the presence of TyrA1. Our results demonstrate the involvement of CGA with other components of the senile plaque and raise the possibility that a narrow-acting agent such as TyrA1 will attenuate plaque formation.
