Involvement of cyclin-dependent kinase-5 in the kainic acid-mediated degeneration of glutamatergic synapses in the rat hippocampus

Abstract

Increased levels of glutamate causing excitotoxic damage accompany neurological disorders such as ischemia/stroke, epilepsy and some neurodegenerative diseases. Cyclin-dependent kinase-5 (Cdk5) is important for synaptic plasticity and is deregulated in neurodegenerative diseases. However, the mechanisms by which kainic acid (KA)-induced excitotoxic damage involves Cdk5 in neuronal injury are not fully understood. In this work, we have thus studied involvement of Cdk5 in the KA-mediated degeneration of glutamatergic synapses in the rat hippocampus. KA induced degeneration of mossy fiber synapses and decreased glutamate receptor (GluR)6/7 and post-synaptic density protein 95 (PSD95) levels in rat hippocampus in vivo after intraventricular injection of KA. KA also increased the cleavage of Cdk5 regulatory protein p35, and Cdk5 phosphorylation in the hippocampus at 12 h after treatment. Studies with hippocampal neurons in vitro showed a rapid decline in GluR6/7 and PSD95 levels after KA treatment with the breakdown of p35 protein and phosphorylation of Cdk5. These changes depended on an increase in calcium as shown by the chelators 1,2-bis(o-aminophenoxy)ethane-N,N,N ',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM) and glycol-bis (2-aminoethylether)-N,N,N ',N '-tetra-acetic acid. Inhibition of Cdk5 using roscovitine or employing dominant-negative Cdk5 and Cdk5 silencing RNA constructs counteracted the decreases in GluR6/7 and PSD95 levels induced by KA in hippocampal neurons. The dominant-negative Cdk5 was also able to decrease neuronal degeneration induced by KA in cultured neurons. The results show that Cdk5 is essentially involved in the KA-mediated alterations in synaptic proteins and in cell degeneration in hippocampal neurons after an excitotoxic injury. Inhibition of pathways activated by Cdk5 may be beneficial for treatment of synaptic degeneration and excitotoxicity observed in various brain diseases.

CDK5 knockdown in astrocytes provide neuroprotection as a trophic source via Rac1

“…CDK5 shRNAmiR induced Rac1 activation, and the subsequent lamellipodia formation was associated with BDNF release in astrocytes and induced the astrocytic neuroprotection. Various studies, most of which have utilized neurodegenerative models, have demonstrated that CDK5 suppression or inhibition favors cell viability in the presence of an insult, as ischemia, excitotoxicity and protein aggregation (Liu et al, 2003;Menn et al, 2010;Posada-Duque et al, 2015;Putkonen et al, 2011;Slevin and Krupinski, 2009;Zheng et al, 2005) Astrocytes provide trophic and metabolic support for neuronal development, maintenance of synaptic function, and neuronal survival (Allen, 2013;Parpura and Verkhratsky, 2012;Sofroniew, 2005). These results show that glutamate exerts a negative effect on cell viability and the morphology of C6 astrocyte-type cells.…”

Recent Insights into the Role of Unfolded Protein Response in ER Stress in Health and Disease

“…Glutamate acts via different types of glutamate receptors and thereby influences cell signaling cascades and elevates intracellular calcium in neurons. Increased ER stress is linked to brain ischemia (Su and Li, 2016) and to excitotoxic injury as studied by the use of the glutamate receptor agonist, kainic acid (Sokka et al, 2007; Putkonen et al, 2011). Salubrinal that is a specific inhibitor of the eIF2α phosphatase, PP1/GADD34 (Boyce et al, 2005) and was found to protect neurons against excitotoxicity in rat hippocampus and after cerebral ischemia induced by 15 min of brain vessel occlusion in gerbils (Sokka et al, 2007; Anuncibay-Soto et al, 2016).…”

Reciprocal Regulation of Very Low Density Lipoprotein Receptors (VLDLRs) in Neurons by Brain-derived Neurotrophic Factor (BDNF) and Reelin

“…The synthetic liver X receptor (LXR) ligand GW3965 was used to induce Mylip/Idol (27,29), actinomycin D (Sigma) was used to inhibit gene transcription, and bafilomycin A 1 (Sigma) was used to block lysosomes. To down-regulate Mylip/Idol, freshly prepared neurons were transfected with Mylip shRNA constructs using the Nucleofector rat neuron system (Amaxa GmbH) as described previously (32,33). To modulate Mylip/Idol activity, cultured neurons were infected with adenoviruses encoding wild-type Mylip/Idol (24) for 3 days following stimulation with Reelin for 24 h.…”

“…Immunoblotting and Immunoprecipitation-Neurons were lysed, and immunoblots were made essentially as described previously (31)(32)(33). Protein concentrations were determined using the Bradford assay, and an equal amount of protein per sample was subjected to SDS-PAGE and blotted onto nitrocellulose filters (Amersham Biosciences).…”