Almost all degenerative diseases of the CNS are associated with chronic inflammation. A central step in this process is the activation of brain mononuclear phagocyte cells, called microglia. While it is recognized that healthy neurons and astrocytes regulate the magnitude of microglia-mediated innate immune responses and limit excessive CNS inflammation, the endogenous signals governing this process are not fully understood. In the peripheral nervous system, recent studies suggest that an endogenous 'cholinergic anti-inflammatory pathway' regulates systemic inflammatory responses via a7 nicotinic acetylcholinergic receptors (nAChR) found on blood-borne macrophages. These data led us to investigate whether a similar cholinergic pathway exists in the brain that could regulate microglial activation. Here we report for the first time that cultured microglial cells express a7 nAChR subunit as determined by RT-PCR, western blot, immunofluorescent, and immunochistochemistry analyses. Acetylcholine and nicotine pre-treatment inhibit lipopolysaccharide (LPS)-induced TNF-a release in murine-derived microglial cells, an effect attenuated by a7 selective nicotinic antagonist, a-bungarotoxin. Furthermore, this inhibition appears to be mediated by a reduction in phosphorylation of p44/42 and p38 mitogen-activated protein kinase (MAPK). Though preliminary, our findings suggest the existence of a brain cholinergic pathway that regulates microglial activation through a7 nicotinic receptors. Negative regulation of microglia activation may also represent additional mechanism underlying nicotine's reported neuroprotective properties.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder pathologically characterized by deposition of ␤-amyloid (A␤) peptides as senile plaques in the brain. Recent studies suggest that green tea flavonoids may be used for the prevention and treatment of a variety of neurodegenerative diseases. Here, we report that (-)-epigallocatechin-3-gallate (EGCG), the main polyphenolic constituent of green tea, reduces A␤ generation in both murine neuron-like cells (N2a) transfected with the human "Swedish" mutant amyloid precursor protein (APP) and in primary neurons derived from Swedish mutant APP-overexpressing mice (Tg APP sw line 2576). In concert with these observations, we find that EGCG markedly promotes cleavage of the ␣-C-terminal fragment of APP and elevates the N-terminal APP cleavage product, soluble APP-␣. These cleavage events are associated with elevated ␣-secretase activity and enhanced hydrolysis of tumor necrosis factor ␣-converting enzyme, a primary candidate ␣-secretase. As a validation of these findings in vivo, we treated Tg APP sw transgenic mice overproducing A␤ with EGCG and found decreased A␤ levels and plaques associated with promotion of the nonamyloidogenic ␣-secretase proteolytic pathway. These data raise the possibility that EGCG dietary supplementation may provide effective prophylaxis for AD.

Background: Activated microglial cells have been implicated in a number of neurodegenerative disorders, including Alzheimer's disease (AD), multiple sclerosis (MS), and HIV dementia. It is well known that inflammatory mediators such as nitric oxide (NO), cytokines, and chemokines play an important role in microglial cell-associated neuron cell damage. Our previous studies have shown that CD40 signaling is involved in pathological activation of microglial cells. Many data reveal that cannabinoids mediate suppression of inflammation in vitro and in vivo through stimulation of cannabinoid receptor 2 (CB 2 ).

Recently, we have shown that green tea polyphenol (؊)-epigallocatechin-3-gallate (EGCG) exerts a beneficial role on reducing brain A␤ levels, resulting in mitigation of cerebral amyloidosis in a mouse model of Alzheimer disease. EGCG seems to accomplish this by modulating amyloid precursor protein (APP) processing, resulting in enhanced cleavage of the ␣-COOH-terminal fragment (␣-CTF) of APP and corresponding elevation of the NH 2 -terminal APP product, soluble APP-␣ (sAPP-␣). These beneficial effects were associated with increased ␣-secretase cleavage activity, but no significant alteration in ␤-or ␥-secretase activities. To gain insight into the molecular mechanism whereby EGCG modulates APP processing, we evaluated the involvement of three candidate ␣-secretase enzymes, a-disintegrin and metalloprotease ( Proteolytic processing of amyloid precursor protein (APP)4 to form amyloid-␤ (A␤) peptides are implicated in the pathogenesis and progression of Alzheimer disease (AD) (1-4). A␤ peptides from 40 -42 amino acids in length are constituents of senile plaques in AD brain and exhibit direct or indirect neurotoxic effects (5). Processing of APP is accomplished by enzymes known as secretases. Whereas non-amyloidogenic ␣-secretase cleavage produces the amino-terminal product named soluble APP␣ (sAPP-␣) and the carboxyl-terminal fragment (CTF) ␣-CTF (also known as C83), the action of amyloidogenic ␤-secretase on APP results in the amino-terminal product sAPP-␤ and the carboxyl-terminal product ␤-CTF (also known as C99). Subsequent ␥-secretase complex cleavage of ␤-CTF yields ␥-CTF (also known as C57), and releases A␤ (6 -10). Promotion of ␣-secretase processing leads to both a reduction in A␤ and an increase in sAPP-␣, a protein that exhibits neuroprotective properties (11)(12)(13)(14). A number of studies have sought to discern the molecular identity of ␣-secretase, with the hope of targeting such enzyme(s) to modulate A␤ production (15,16).A number of reports have implicated members of the a-disintegrin and metalloprotease (ADAM) family, a family of zinc metalloproteases including ADAM9, -10, and -17, as putative ␣-secretase candidates (15-17). Lammich and colleagues (18) first described the ability of ADAM10 to act as an ␣-secretase, whereas Buxbaum and co-workers (19) reported that ADAM17 contributes to ␣-secretase processing of APP. Others have demonstrated the ability of ADAM9 to promote ␣-secretase cleavage (20). However, Asai and colleagues (17) reported that ADAM9, -10, and -17 all have roles in the processing of APP to sAPP-␣ in vitro. In cerebrospinal fluid from AD patients, ADAM10 and corresponding sAPP/␣-CTFs are decreased (21,22). Moreover, ADAM10 is also decreased in AD and Down syndrome brains (23). A report by Lopez-Perez and colleagues (24) implicates ADAM10 as a contributor to constitutive sAPP-␣ production, whereas ADAM17 (also known as tumor necrosis factor-␣ converting enzyme, TACE) is implicated in a regulated mechanism of sAPP-␣ production (24). Recently, Postina and colleagues (25) showed th...