A Drosophila CDK5alpha-like molecule and its possible role in response to O(2) deprivation

Characterization of the CDK5 gene in Apis cerana cerana (AccCDK5) and a preliminary identification of its activator gene, AccCDK5r1

Cyclin-dependent kinase 5 (CDK5) is an unusual CDK whose function has been implicated in protecting the central nervous system (CNS) from oxidative damage. However, there have been few studies of CDK5 in insects. In this study, we identified the AccCDK5 gene from Apis cerana cerana and investigated its role in oxidation resistance. We found that AccCDK5 is highly conserved across species and contains conserved features of the CDK5 family. The results of qPCR analysis indicated that AccCDK5 is highly expressed during the larval and pupal stages and in the adult head and muscle. We further observed that AccCDK5 is induced by several environmental oxidative stresses. Moreover, the overexpression of the AccCDK5 protein in E. coli enhances the resistance of the bacteria to oxidative stress. The activation of CDK5 requires binding to its activator. Therefore, we also identified and cloned cyclin-dependent kinase 5 regulatory subunit 1, which we named AccCDK5r1, from Apis cerana cerana. AccCDK5r1 contains a conserved cell localization targeting domain as well as binding and activation sites for CDK5. Yeast two-hybrid analysis demonstrated the interaction between AccCDK5 and AccCDK5r1. The expression patterns of the two genes were similar after stress treatment. Collectively, these results suggest that AccCDK5 plays a pivotal role in the response to oxidative stresses and that AccCDK5r1 is a potential activator of AccCDK5.

Genome-Wide Association Study of a Varroa-Specific Defense Behavior in Honeybees (Apis mellifera)

Honey bees are exposed to many damaging pathogens and parasites. The most devastating is Varroa destructor, which mainly affects the brood. A promising approach for preventing its spread is to breed Varroa-resistant honey bees. One trait that has been shown to provide significant resistance against the Varroa mite is hygienic behavior, which is a behavioral response of honeybee workers to brood diseases in general. Here, we report the use of an Affymetrix 44K SNP array to analyze SNPs associated with detection and uncapping of Varroa-parasitized brood by individual worker bees (Apis mellifera). For this study, 22 000 individually labeled bees were video-monitored and a sample of 122 cases and 122 controls was collected and analyzed to determine the dependence/independence of SNP genotypes from hygienic and nonhygienic behavior on a genome-wide scale. After false-discovery rate correction of the P values, 6 SNP markers had highly significant associations with the trait investigated (α < 0.01). Inspection of the genomic regions around these SNPs led to the discovery of putative candidate genes.

Genetic animal models of preconditioning

The preconditioning phenomena have been well established in heart as well as brain. In this review, we detail some of the original studies on preconditioning as well as studies from our lab using rodents and a genetic model system (fruit fly). We have used Drosophila in our lab to solve some of the questions related to tolerance or susceptibility to hypoxia. We believe that these pro-survival strategies and genetic pathways help us understand some of the preconditioning mechanisms that protect the brain from ischemia or ischemia.

Cdk5 interacts with Hif-1α in neurons: a new hypoxic signalling mechanism?

The cyclin dependent kinase 5 (Cdk5)/p35 complex is essential for regulation of cell survival during development and in models of neuronal excitotoxicity. Dysregulation of Cdk5, by cleavage of its neuronal specific activators p35 and p39, has been implicated in various neurodegenerative disorders such as Alzheimer's disease, however targets of the complex that regulate neuronal survival physiologically and/or during pathogenesis are largely unknown. Since hypoxia is a key feature in the pathogenesis of several neuronal disorders we investigated a role for Cdk5/p35 in the neuronal hypoxic response. Our data show that hypoxia modulates the p35/Cdk5 complex in primary cortical neurons at the transcriptional and protein level. Furthermore hypoxic induction of Cdk5 activity correlates with Hif-1α stabilisation, and direct interaction between these proteins can occur. Importantly, we demonstrate that Cdk5-mediated signaling is involved in Hif-1α stabilisation since inhibition of Cdk5 by roscovitine abrogates Hif-1α accumulation and induces cell death. Taken together our results show that the Cdk5/p35 complex may significantly contribute to modulation of Hif-1α stabilisation and impact neuronal survival during oxygen deprivation. Thus this study highlights a new hypoxia-mediated signaling pathway and implicates the cytoskeleton as a potential regulator of Hif-1α.

Survival in acute and severe low o environment: use of a genetic model system

Hypoxia whether present during physiologic states (e.g., embryogenesis) or during pathologic states (e.g., obstructive sleep apnea and sickle cell anemia), challenges the vertebrate or invertebrate organism. Clearly, hypoxia can lead to sublethal cell injury or death and consequently organ or systemic injury and failure, depending on severity. We discovered that the adult Drosophila melanogaster is tolerant to a low O(2) environment, withstanding approximately 3-4 hours of total O(2) deprivation or anoxia without showing any evidence of cell injury. This opened major avenues for us since the Drosophila has been used so effectively in so many relevant research areas. We investigated the changes in gene expression in D. melanogaster after severe (1% O(2)) intermittent or constant hypoxia treatment for 2.5 hours. Our microarray analysis has identified multiple gene families that are up- or downregulated in response to acute constant (CH) and intermittent hypoxia (IH). We observed that even for short-term the gene expression response to IH and CH varied not only in the number of genes but also type of gene families. Furthermore, by utilizing powerful Drosophila genetic tools we studied the role of single genes (up- or downregulated in arrays) in survival under either paradigm in adult flies. We observed significant increased adult survival (as compared to controls) of P-element lines for Hsp70 and Hsp23 genes during CH and Mdr49 and l (2)08717 genes during IH. This suggests that the increased transcript levels as observed in array data after either paradigm play an important role under severe hypoxia. Indeed, we found for example that over-expressing Hsp70 in vivo in specific fly organs (such as heart) significantly increased adult survival during CH as compared to controls. These data provide further clues about the mechanisms by which intermittent and constant hypoxia lead to cell injury and morbidity or adaptation and survival.

Contribution of hypoxia to Alzheimer's disease: is HIF-1alpha a mediator of neurodegeneration?

The mammalian brain is extremely sensitive to alterations in cellular homeostasis as a result of environmental or physiological insults. In particular, hypoxic/ischemic challenges (i.e. reduced oxygen and/or glucose delivery) cause severe and detrimental alterations in brain function and can trigger neuronal cell death within minutes. Unfortunately, as we age, oxygen delivery to cells and tissues is impaired, thereby increasing the susceptibility of neurons to damage. Thus, hypoxic (neuronal) adaptation is significantly compromised during aging. Many neurological diseases, such as stroke, Alzheimer's disease (AD), Parkinson's disease and diabetes, are characterized by hypoxia, a state that is believed to only exacerbate disease progression. However, the contribution of hypoxia and hypoxia-mediated pathways to neurodegeneration remains unclear. This review discusses current evidence on the contribution of oxygen deprivation to AD, with an emphasis on hypoxia inducible transcription factor-1 (HIF-1)-mediated pathways and the association of AD with the cytoskeleton regulator cyclin-dependent kinase 5.

S/P and T/P phosphorylation is critical for tau neurotoxicity inDrosophila

The microtubule-associated protein tau is hyperphosphorylated abnormally in AD and related neurodegenerative disorders. Many phospho epitopes created by proline directed kinases (SP/TP sites) show relative specificity for disease states. To test whether phosphorylation at the disease-associated SP/TP sites affects tau toxicity in vivo, we expressed a form of tau in Drosophila in which all SP/TP sites are mutated to alanine. We find that blocking phosphorylation at SP/TP motifs markedly reduces tau toxicity in vivo. Using phosphorylation-specific antibodies, we identify a positive correlation between increased phosphorylation at disease-associated sites and neurotoxicity. We use the phosphorylation-incompetent version of tau to show that kinase and phosphatase modifiers of tau neurotoxicity, including cdk5/p35, the JNK kinase hemipterous and PP2A act via SP/TP phosphorylation sites. We provide direct evidence in an animal model system to support the role of phosphorylation at SP/TP sites in playing a critical role in tau neurotoxicity.

Neuronal cyclin-dependent kinase 5: role in nervous system function and its specific inhibition by the Cdk5 inhibitory peptide

Cyclin-dependent kinase 5 (Cdk5) is a member of the cyclin-dependent kinase family that is involved in the regulation of the cell cycle. As their name suggests, the Cdks require association with activator proteins called cyclins for their activity. Cdk5, however, is unique to this family of proline-directed serine/threonine kinases on two accounts. Firstly, Cdk5 has not been found to function in the cell cycle and, although expressed in a number of tissues, its activity is restricted to the nervous system. Secondly, unlike the other members of the Cdk family, Cdk5 is not activated by association with a cyclin, although it can bind them. Instead, Cdk5 is activated by the activator proteins p35 and p39 that are structurally distinct from cyclins and have, for the most part, a neuronal-specific expression pattern. In the past decade of research on Cdk5, it is now established that Cdk5 activity is critical for the proper formation and function of the brain. Moreover, its role as a central kinase, phosphorylating its substrates in its 'cross-talk' control of other kinase and signal transduction pathways, has also been determined. In addition to the normal physiological role of Cdk5, the kinase has been implicated in certain neurodegenerative disorders. For example, Cdk5 associates with the proteolytic, more active p25 fragment that is derived through the cleavage of p35. In turn, the p25/Cdk5 complex aberrantly phosphorylates its substrates tau and neurofilaments, which has been implicated in the pathogenesis of these disorders. Here, we attempt to review the past decade of research on Cdk5 from our laboratory and others, on the roles of Cdk5 in nervous system function. Additionally, our research has recently uncovered a possible therapeutic avenue of research, focusing on inhibition of aberrant Cdk5 hyperactivity which may well be used to treat the symptoms of a number of neurodegenerative diseases. The elucidation of a specific inhibitor of p25/Cdk5, termed CIP, also inhibits p25/Cdk5-mediated tau phosphorylation. This may well provide us with avenues of research focusing on the inhibition of pathologically damaging p25/Cdk5 species.

Cyclin-dependent kinase-5 in neurodegeneration

Cyclin-dependent kinase-5 (CDK5) is predominantly active in the nervous system and it is well established that CDK5 is essential in neuronal development. In addition to its recognized role in development, there is increasing evidence that CDK5 may be involved in the pathogenesis of several neurodegenerative disorders. Although studies have shown that CDK5 can modulate cell death and survival, controversy still exists as to the exact role CDK5 may play in neurodegenerative processes. This review will highlight recent data on the possible roles of CDK5 in neurodegeneration.

Genetic Modifiers of Tauopathy in Drosophila

In Alzheimer's disease and related disorders, the microtubule-associated protein Tau is abnormally hyperphosphorylated and aggregated into neurofibrillary tangles. Mutations in the tau gene cause familial frontotemporal dementia. To investigate the molecular mechanisms responsible for Tau-induced neurodegeneration, we conducted a genetic modifier screen in a Drosophila model of tauopathy. Kinases and phosphatases comprised the major class of modifiers recovered, and several candidate Tau kinases were similarly shown to enhance Tau toxicity in vivo. Despite some clinical and pathological similarities among neurodegenerative disorders, a direct comparison of modifiers between different Drosophila disease models revealed that the genetic pathways controlling Tau and polyglutamine toxicity are largely distinct. Our results demonstrate that kinases and phosphatases control Tau-induced neurodegeneration and have important implications for the development of therapies in Alzheimer's disease and related disorders.

Cdk5 mediates changes in morphology and promotes apoptosis of astrocytoma cells in response to heat shock

The cyclin-dependent kinase member, Cdk5, is expressed in a variety of cell types, but neuron-specific expression of its activator, p35, is thought to limit its activity to neurons. Here we demonstrate that both Cdk5 and p35 are expressed in the human astrocytoma cell line, U373. Cdk5 and p35 are present in the detergent-insoluble cytoskeletal fraction of this cell line and Cdk5 localizes to filopodia and vinculin-rich regions of cell-matrix contact in lamellopodia. When exposed to a 46(o)C heat shock, U373 cells change shape, lose cell-matrix contacts and show increased levels of apoptosis. To test whether Cdk5 activation might play a role in these events, U373 cells were stably transfected with histidine-tagged or green fluorescent protein-tagged constructs of Cdk5 or a dominant negative mutation, Cdk5T33. Under normal growth conditions, growth characteristics of the stably transfected lines were indistinguishable from untransfected U373 cells and Cdk5 localization was not changed. However, when subjected to heat shock, cells stably transfected with Cdk5-T33 remained flattened, showed little loss of cell-matrix adhesion, and exhibited significantly lower levels of apoptosis. In contrast, cells that overexpressed wild-type Cdk5 showed morphological changes similar to those seen in untransfected U373 cells in response to heat shock and had significantly higher levels of apoptosis. Heat-shocked cells showed changes in p35 mobility and stability of the Cdk5/p35 complex consistent with endogenous Cdk5 activity. Together these findings suggest that endogenous Cdk5 activity may play a key role in regulating morphology, attachment, and apoptosis in U373 cells, and raise the possibility that Cdk5 may be a general regulator of cytoskeletal organization and cell adhesion in both neuronal and non-neuronal cells.