Activation of cyclin‐dependent kinase 5 by calpains contributes to human immunodeficiency virus‐induced neurotoxicity

Abstract

Although the specific mechanism of neuronal damage in human immunodeficiency virus (HIV) -associated dementia is not known, a prominent role for NMDA receptor (NMDAR)-induced excitotoxicity has been demonstrated in neurons exposed to HIV-infected/activated macrophages. We hypothesized NMDAR-mediated activation of the calcium-dependent protease, calpain, would contribute to cell death by induction of cyclin-dependent kinase 5 (CDK5) activity. Using an in vitro model of HIV neurotoxicity, in which primary rat cortical cultures are exposed to supernatants from primary human HIV-infected macrophages, we have observed increased calpain-dependent cleavage of the CDK5 regulatory subunit, p35, to the constitutively active isoform, p25. Formation of p25 is dependent upon NMDAR activation and calpain activity and is coincident with increased CDK5 activity in this model. Further, inhibition of CDK5 by roscovitine provided neuroprotection in our in vitro model. Consistent with our observations in vitro, we have observed a significant increase in calpain activity and p25 levels in midfrontal cortex of patients infected with HIV, particularly those with HIV-associated cognitive impairment. Taken together, our data suggest calpain activation of CDK5, a pathway activated in HIVinfected individuals, can mediate neuronal damage and death in a model of HIV-induced neurotoxicity. Keywords: calpain, cyclin-dependent kinase 5, cell cycle, dementia, encephalitis, neurodegeneration, NMDA receptor. Before the widespread use of highly active antiretroviral therapy (HAART), approximately 20% of patients infected with human immunodeficiency virus (HIV) developed HIVassociated dementia (HAD) (Kaul et al. 2001;Garden 2002;Gonzalez-Scarano and Martin-Garcia 2005). In the post-HAART era, the incidence of HAD has declined to approximately 8%; however, the prevalence has increased. In addition, an increasing number (40%) of HIV-infected patients on HAART are developing a constellation of less severe neurologic symptoms referred to as minor cognitive motor disorder (MCMD) (Janssen et al. 1989;Sacktor et al. 2002;McArthur et al. 2003). Pathologic studies of the brains of patients with HAD suggest an inflammatory mechanism in the progression of this disease, as evidenced by astrogliosis, microgliosis, and perivascular macrophage infiltration (Kaul et al. 2001;Garden 2002;Ghorpade et al. 2003). Although neuronal, dendritic, and synaptic loss are features of HAD, there is little evidence of direct HIV infection of neurons (Shi et al. 1996;Corasaniti et al. 2001). Instead, neuronal dys- Abbreviations used: CDK5, cyclin-dependent kinase 5; DIV, days in vitro; DTT, dithiothreitol; ERK1/2, extracellular signal-regulated kinase 1 and 2; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HAART, highly active antiretroviral therapy; HAD, HIV-associated dementia; HIV MDM, HIV-infected, monocyte-derived macrophage; HIV, human immunodeficiency virus; HIVE, human immunodeficiency virus encephalitis; LR, linear range; MAP2, microtubule-associated protein 2...

Increased CDK5 Expression in HIV Encephalitis Contributes to Neurodegeneration via Tau Phosphorylation and Is Reversed with Roscovitine

“…87,88 This, in turn, could activate calpain cleavage of p35 into p25 and result in abnormal activation of CDK5. 36 This is consistent with the proposed neurotoxic mechanism of abnormal CDK5 activation in AD, 37,38 and with studies in the brains of HIV patients and in primary neurons treated with conditioned media from HIV-infected macrophages showing NMDAR-dependent activation of p25/CDK5. 36 In agreement with a role for aberrant CDK5 activation in neurodegeneration in HIV models, a previous in vitro study by Wang et al 36 showed that treatment with the CDK5 inhibitor roscovitine protected primary neurons from the neurotoxic effects of HIV-infected monocytederived macrophages.…”

“…This is consistent with recent studies showing that aberrant activation of the CDK5 7,36 and GSK3␤ 7,[33][34][35]58 signaling pathways contribute to the neurodegenerative pathology in patients with HIV-associated neurocognitive impairment. Although a previous study focused on the role of p35 and CDK5 activation via the N-methyl-D-aspartate receptor (NMDAR), 36 the present study investigated the contribution of abnormal activation of this pathway to tau hyperphosphorylation in patients with HIVE. In patients with AD, abnormal activation of CDK5 and GSK3␤ have been implicated in the aberrant phosphorylation of tau and associated substrates.…”

“…31 In addition, activation of calciumdependent signaling pathways might also contribute to neurodegeneration. Among these, activation of mitogenactivated protein kinase 10 (MAPK10; also known as c-Jun N-terminal kinase 3, or JNK3), double-stranded RNA-activated protein kinase (PKR), 32 glycogen syn-thase kinase-3␤ (GSK3␤), 7,[33][34][35] and cyclin-dependent kinase 5 (CDK5) 7,36 have been shown to play a role. Recent studies have shown that the abnormal activation of CDK5 might play a role in Alzheimer's disease (AD), 37,38 Parkinson's disease 39 and Huntington's disease.…”

“…42 Moreover, a recent study showed that in the brains of patients with HIV, calpain activity and the subsequent calpain-mediated generation of p25 from p35 were increased, leading to activation of the CDK5 pathway; however, the downstream targets involved in mediating the neurotoxic effects of HIV via abnormal CDK5 activation remain unclear. 36 Thus, given the role of tau in CDK5-mediated neurotoxicity in AD, this protein is an important candidate to consider in the pathogenesis of HIVE. 37,38 The primary objective of our study was to investigate in vivo the involvement of abnormal CDK5 activation and tau phosphorylation in the mechanisms of neurodegeneration in human cases of HIVE and in gp120 transgenic (Tg) mice.…”

Calpain-Mediated N-Cadherin Proteolytic Processing in Brain Injury

“…Under these pathological conditions, calpain cleaves a number of neuronal substrates essential for neuron survival. For example, the neuron-specific activator of cyclin-dependent kinase 5 (cdk5), p35, is a well known calpain substrate (Kusakawa et al, 2000; M. S. Patzke and Tsai, 2002;Wang et al, 2007). The calpain-mediated cleavage of p35 to p25 is involved in the pathogenesis of Alzheimer's disease, and the calpainmediated p35 cleavage pathway may serve as a target for pharmacological intervention (Patrick et al, 1999; M. S. .…”