S-Nitrosylation activates Cdk5 and contributes to synaptic spine loss induced by β-amyloid peptide

Abstract

The activity of Cdk5 and its regulatory subunit p35 is thought to be important in both normal brain function and neurodegenerative disease pathogenesis. Increased Cdk5 activity, via proteolytic cleavage of p35 to a p25 fragment by the calcium-activated protease calpain or by phosphorylation at Cdk5(Tyr15), can contribute to neurotoxicity. Nonetheless, our knowledge of regulation of Cdk5 activity in disease states is still emerging. Here we demonstrate that Cdk5 is activated by S-nitrosylation or reaction of nitric oxide (NO)-related species with the thiol groups of cysteine residues 83 and 157, to form SNO-Cdk5. We then show that S-nitrosylation of Cdk5 contributes to amyloid-β (Aβ) peptide-induced dendritic spine loss. Furthermore, we observed significant levels of SNO-Cdk5 in postmortem Alzheimer's disease (AD) but not in normal human brains. These findings suggest that S-nitrosylation of Cdk5 is an aberrant regulatory mechanism of enzyme activity that may contribute to the pathogenesis of AD.C dk5 is a cyclin-dependent kinase that is activated by proteins p35, p25, and p39 (1-3). As a predominantly neuronalspecific kinase, Cdk5 lacks a role in cell-cycle control but has been implicated in an array of neuronal functions, including cell survival, axon guidance, neuronal migration, and regulation of synaptic spine density (4-6). Dysregulation of Cdk5 activity may play a role in the pathogenesis of stroke and several neurodegenerative disorders, including Alzheimer's disease (AD), amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease (7-11). Cdk5 is also hyperactivated in response to oxidative stress, mitochondrial dysfunction, excitotoxicity, amyloid-β (Aβ) exposure, calcium overload, and neuroinflammation, thus contributing to neuronal damage. These neurotoxic stimuli activate calpain, which cleaves the Cdk5 activator p35 (or p39) into p25 (or p29); p25 accumulation thus contributes to Cdk5 activation (12-16). These changes trigger various events associated with neurodegeneration. Although increased Cdk5 activity has been observed in AD brains compared with nondemented control brains, the mechanism remains contentious (17).Similarly, nitric oxide (NO) and related species contribute to a number of neurodegenerative diseases. The major source of NO in neurons is neuronal nitric oxide synthase (NOS1). Excitotoxic stress increases intracellular Ca 2+ , which in turn activates NOS1, thus generating NO. In general, NO can stimulate soluble guanylate cyclase to form cGMP or can S-nitrosylate critical cysteine residues to regulate the activity of multiple target proteins, in some sense akin to phosphorylation. Indeed, S-nitrosylation may explain many cGMP-independent mechanisms of NO action in neurodegenerative diseases (18). Our group has demonstrated that NO contributes to neurodegenerative disorders by redox reaction consisting of S-nitrosylation; in some cases this reaction is followed by further oxidation. Proteins affected in this manner include the gelatinase enzyme matrix metalloprotineas...

Aβ induces astrocytic glutamate release, extrasynaptic NMDA receptor activation, and synaptic loss

“…Concerning the mechanism of Aβ-induced eNMDAR activity on synaptic damage, the pharmacological data presented here and elsewhere (37,38) indicate that tau phosphorylation, caspase-3 activation, and NO-mediated events [formation of S-nitrosylated (SNO)-Drp1 and SNO-Cdk5] all appear to be largely mediated by eNMDARs. Because these events occur rapidly, within minutes of eNMDAR activation, the early changes that we observed in synaptic function could serve as the harbinger of subsequent synaptic damage and loss.…”

“…NO has been shown to contribute to synaptic spine loss after Aβ exposure, at least in part via mitochondrial actions of S-nitrosylated dynamin-related protein 1 (Drp1) after transnitrosylation from cyclin-dependent kinase 5 (Cdk5) enzyme (37,38). Accordingly, in our cultures, in addition to a rise in neuronal Ca 2+ levels, Aβ induced an increase in NO, as monitored with diaminofluorescein (DAF) fluorescence imaging (38,39). Both memantine and NitroMemantine prevented this Aβ-induced increase in NO (Fig.…”

S -nitrosation of proteins relevant to Alzheimer’s disease during early stages of neurodegeneration

“…S2A). Cdk5 itself has been reported to be S-nitrosated, which enhances its serine/threonine kinase activity (37). Although SNO-Cdk5 was not detected by MS, it was elevated in CK-p25 mice (shown by SNOTRAP-Western blot; Fig.…”

Cdk5 activity in the brain – multiple paths of regulation

“…Cdk5 is S-nitrosylated at Cys83 and Cys157 when treated with Snitrosocysteine or S-nitrosoglutathione in vitro (Qu et al, 2011). Interestingly, nitrosylating agents at low concentration (200 mM) augment the activity of Cdk5 (Qu et al, 2011), whereas they inhibit it at high concentration (1 mM) (Zhang et al, 2010).…”