TFP5 is comparable to mild hypothermia in improving neurological outcomes in early-stage ischemic stroke of adult rats

Cdk5-p25 as a key element linking amyloid and tau pathologies in Alzheimer's disease: Mechanisms and possible therapeutic interventions

Despite the fact that the small atypical serine/threonine cyclin-dependent kinase 5 (Cdk5) is expressed in a number of tissues, its activity is restricted to the central nervous system due to the neuron-only localization of its activators p35 and p39. Although its importance for the proper development and function of the brain and its role as a switch between neuronal survival and death are unmistakable and unquestionable, Cdk5 is nevertheless increasingly emerging, as supported by a large number of publications on the subject, as a therapeutic target of choice in the fight against Alzheimer's disease. Thus, its aberrant over activation via the calpain-dependent conversion of p35 into p25 is observed during the pathogenesis of the disease where it leads to the hyperphosphorylation of the β-amyloid precursor protein and tau. The present review highlights the pivotal roles of the hyperactive Cdk5-p25 complex activity in contributing to the development of Alzheimer's disease pathogenesis, with a particular emphasis on the linking function between Aβ and tau that this kinase fulfils and on the fact that Cdk5-p25 is part of a deleterious feed forward loop giving rise to a molecular machinery runaway leading to AD pathogenesis. Additionally, we discuss the advances and challenges related to the possible strategies aimed at specifically inhibiting Cdk5-p25 activity and which could lead to promising anti-AD therapeutics.

The role of Cdk5 in neurological disorders

Neurological disorders are a group of disorders with motor, sensory or cognitive damage, caused by dysfunction of the central or peripheral nervous system. Cyclin-dependent kinases 5 (Cdk5) is of vital significance for the development of the nervous system, including the migration and differentiation of neurons, the formation of synapses, and axon regeneration. However, when the nervous system is subject to pathological stimulation, aberrant activation of Cdk5 will induce abnormal phosphorylation of a variety of substrates, resulting in a cascade signaling pathway, and thus lead to pathological changes. Cdk5 is intimately related to the pathological mechanism of a variety of neurological disorders, such as A-β protein formation in Alzheimer’s disease, mitochondrial fragmentation in cerebral ischemia, and apoptosis of dopaminergic neurons in Parkinson’s disease. It is worth noting that Cdk5 inhibitors have been reported to have neuroprotective effects by inhibiting related pathological processes. Therefore, in this review, we will briefly introduce the physiological and pathological mechanisms of Cdk5 in the nervous system, focusing on the recent advances of Cdk5 in neurological disorders and the prospect of targeted Cdk5 for the treatment of neurological disorders.

CDK4 and CDK5 Inhibition Have Comparable Mild Hypothermia Effects in Preventing Drp1-Dependent Mitochondrial Fission and Neuron Death Induced by MPP. Mol Neurobiol 2020;57:4090-4105. [PMID: 32666227 DOI: 10.1007/s12035-020-02014-0]

Mild hypothermia has promising effects in the treatment of acute brain insults and also affects cell cycle progression. Mitochondrial dynamics, fusion and fission, are changed along with the cell cycle and disrupted in neurodegenerative diseases, including Parkinson's disease (PD). However, the effects of hypothermia on aberrant mitochondrial dynamics in PD remain unknown. We hypothesized that mild hypothermia protects neurons by regulating cell cycle-dependent protein expression and mitochondrial dynamics in a 1-methyl-4-phenylpyridinium (MPP⁺)-induced cell model of PD. We found that the hypothermia treatment at 32 °C prevented MPP⁺-induced neuron death; however, 32 °C treatment itself also reduced cell viability. This reduction was associated with cell cycle arrest and downregulation of cyclin-dependent kinase 4 (CDK4) in proliferating human SK-N-SH neuroblastoma cells but upregulation in well-differentiated primary rat cortical neurons. In both types of neurons, hypothermia upregulated p27 (an endogenous inhibitor of CDKs) and p35 (CDK5 activator) protein expression. Treatment with hypothermia, or a selective CDK4 inhibitor, or roscovitine (CDK5 inhibitor) prevented MPP⁺-induced mitochondrial fission, upregulation of mitochondrial fission protein dynamin-related protein 1 (Drp1), and neuron death. In addition, overexpression of dominant negative mutant Drp1^K38A improved MPP⁺-induced mitochondrial fission while overexpression of wild-type Drp1 blunted the prevention of mitochondrial fission by hypothermia as well as CDK4 inhibitor and roscovitine. These results elucidate that hypothermia may inhibit CDK4 and CDK5 activation by upregulating p27 and p35 expression to prevent Drp1-dependent mitochondrial fission and neuron loss after MPP⁺ treatment. CDK4 and CDK5 inhibition imitates the neuroprotective functions of hypothermia as a potential therapy for PD.

Hypothermia treatment ameliorated cyclin-dependent kinase 5-mediated inflammation in ischemic stroke and improved outcomes in ischemic stroke patients

OBJECTIVES

The inflammatory response is a key mechanism of neuronal damage and loss during acute ischemic stroke. Hypothermia has shown promise as a treatment for ischemic stroke. In this study, we investigated the molecular signaling pathways in ischemic stroke after hypothermia treatment.

METHODS

Cyclin-dependent kinase 5 (CDK5) was overexpressed or silenced in cultured cells. Nuclear transcription factor-κB (NF-κB) activity was assessed by measurement of the luciferase reporter gene. An ischemic stroke model was established in Sprague-Dawley (SD) rats using the suture-occluded method. Animals were assigned to three groups: sham operation control, ischemic stroke, and ischemic stroke + hypothermia treatment groups. Interleukin 1β (IL-1β) levels in the culture supernatant and blood samples were assessed by ELISA. Protein expression was measured by Western blotting.

RESULTS

In HEK293 cells and primary cortical neuronal cultures exposed to hypothermia, CDK5 overexpression was associated with increased IL-1β, caspase 1, and NF-κB levels. In both a murine model of stroke and in patients, increased IL-1β levels were observed after stroke, and hypothermia treatment was associated with lower IL-1β levels. Furthermore, hypothermia-treated patients showed significant improvement in neurophysiological functional outcome.

CONCLUSIONS

Overall, hypothermia offers clinical benefit, most likely through its effects on the inflammatory response.