Tissue-type plasminogen activator regulates p35-mediated Cdk5 activation in the postsynaptic terminal

tPA supplementation preserves neurovascular and cognitive function in Tg2576 mice

INTRODUCTION

Amyloid beta (Aβ) impairs the cerebral blood flow (CBF) increase induced by neural activity (functional hyperemia). Tissue plasminogen activator (tPA) is required for functional hyperemia, and in mouse models of Aβ accumulation tPA deficiency contributes to neurovascular and cognitive impairment. However, it remains unknown if tPA supplementation can rescue Aβ-induced neurovascular and cognitive dysfunction.

METHODS

Tg2576 mice and wild-type littermates received intranasal tPA (0.8 mg/kg/day) or vehicle 5 days a week starting at 11 to 12 months of age and were assessed 3 months later.

RESULTS

Treatment of Tg2576 mice with tPA restored resting CBF, prevented the attenuation in functional hyperemia, and improved nesting behavior. These effects were associated with reduced cerebral atrophy and cerebral amyloid angiopathy, but not parenchymal amyloid.

DISCUSSION

These findings highlight the key role of tPA deficiency in the neurovascular and cognitive dysfunction associated with amyloid pathology, and suggest potential therapeutic strategies involving tPA reconstitution.

HIGHLIGHTS

Amyloid beta (Aβ) induces neurovascular dysfunction and impairs the increase of cerebral blood flow induced by neural activity (functional hyperemia). Tissue plasminogen activator (tPA) deficiency contributes to the neurovascular and cognitive dysfunction caused by Aβ. In mice with florid amyloid pathology intranasal administration of tPA rescues the neurovascular and cognitive dysfunction and reduces brain atrophy and cerebral amyloid angiopathy. tPA deficiency plays a crucial role in neurovascular and cognitive dysfunction induced by Aβ and tPA reconstitution may be of therapeutic value.

Metformin inhibits nerve growth factor-induced sympathetic neuron differentiation through p35/CDK5 inhibition

The authors' previous research has shown the pivotal roles of cyclin-dependent kinase 5 (CDK5) and its regulatory protein p35 in nerve growth factor (NGF)-induced differentiation of sympathetic neurons in PC12 cells. During the process of differentiation, neurons are susceptible to environmental influences, including the effects of drugs. Metformin is commonly used in the treatment of diabetes and its associated symptoms, particularly in diabetic neuropathy, which is characterized by dysregulation of the sympathetic neurons. However, the impacts of metformin on sympathetic neuronal differentiation remain unknown. In this study, we investigated the impact of metformin on NGF-induced sympathetic neuronal differentiation using rat pheochromocytoma PC12 cells as a model. We examined the regulation of TrkA-p35/CDK5 signaling in NGF-induced PC12 differentiation. Our results demonstrate that metformin reduces NGF-induced PC12 differentiation by inactivating the TrkA receptor, subsequently inhibiting ERK and EGR1. Inhibition of this cascade ultimately leads to the downregulation of p35/CDK5 in PC12 cells. Furthermore, metformin inhibits the activation of the presynaptic protein Synapsin-I, a substrate of CDK5, in PC12 differentiation. In addition, metformin alters axonal and synaptic bouton formation by inhibiting p35 at both the axons and axon terminals in fully differentiated PC12 cells. In summary, our study elucidates that metformin inhibits sympathetic neuronal differentiation in PC12 cells by disrupting TrkA/ERK/EGR1 and p35/CDK5 signaling. This research contributes to uncovering a novel signaling mechanism in drug response during sympathetic neuronal differentiation, enhancing our understanding of the intricate molecular processes governing this critical aspect of neurodevelopment.NEW & NOTEWORTHY This study unveils a novel mechanism influenced by metformin during sympathetic neuronal differentiation. By elucidating its inhibitory effects from the nerve growth factor (NGF) receptor, TrkA, to the p35/CDK5 signaling pathways, we advance our understanding of metformin's mechanisms of action and emphasize its potential significance in the context of drug responses during sympathetic neuronal differentiation.

Tumor-suppressive microRNA-152 inhibits the proliferation of Ewing's sarcoma cells by targeting CDK5R1

We elucidated the mechanism through which the reduced expression of miR-152 leads to the overexpression of its target cyclin-dependent kinase-5 activator 1 (CDK5R1) in Ewing's sarcoma (ES) cells and the role of this mechanism in the proliferation of ES cells. To explore possible oncogenic factors in ES, we conducted microarray-based investigation and profiled the changes in miRNA expression and their effects on downstream mRNAs in five ES cell lines and human mesenchymal stem cells (hMSCs). miR-152 was significantly downregulated, while cyclin-dependent kinase-5 activator 1 (CDK5R1) expression was significantly upregulated in all tested ES cells as compared to hMSCs. The overexpression of CDK5R1 led to the activation of CDK5, enabling the phosphorylation of retinoblastoma protein and persistent overexpression of CCNE. Moreover, miR-152 suppressed cell proliferation via cell cycle retardation, and its upregulation reduced tumor size and CCNE expression in tumor tissues. The overexpression of cyclin E (CCNE) has been detected in ES cells, but the detailed mechanisms have not been previously elucidated. These findings identify the miR152-CDK5R1 signaling axis as a critical mechanism for tumorigenesis that may serve as a new therapeutic target in Ewing's sarcoma. We believe that our results will aid in the development of effective treatment strategies for patients with ES.

Tissue Plasminogen Activator in Central Nervous System Physiology and Pathology: From Synaptic Plasticity to Alzheimer's Disease

Tissue plasminogen activator's (tPA) fibrinolytic function in the vasculature is well-established. This specific role for tPA in the vasculature, however, contrasts with its pleiotropic activities in the central nervous system. Numerous physiological and pathological functions have been attributed to tPA in the central nervous system, including neurite outgrowth and regeneration; synaptic and spine plasticity; neurovascular coupling; neurodegeneration; microglial activation; and blood–brain barrier permeability. In addition, multiple substrates, both plasminogen-dependent and -independent, have been proposed to be responsible for tPA's action(s) in the central nervous system. This review aims to dissect a subset of these different functions and the different molecular mechanisms attributed to tPA in the context of learning and memory. We start from the original research that identified tPA as an immediate-early gene with a putative role in synaptic plasticity to what is currently known about tPA's role in a learning and memory disorder, Alzheimer's disease. We specifically focus on studies demonstrating tPA's involvement in the clearance of amyloid-β and neurovascular coupling. In addition, given that tPA has been shown to regulate blood–brain barrier permeability, which is perturbed in Alzheimer's disease, this review also discusses tPA-mediated vascular dysfunction and possible alternative mechanisms of action for tPA in Alzheimer's disease pathology.

Potential new therapeutic target for Alzheimer's disease: Glucagon-like peptide-1

Increasing evidence shows a close relationship between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). Recently, glucagon-like peptide-1 (GLP-1), a gut incretin hormone, has become a well-established treatment for T2DM and is likely to be involved in treating cognitive impairment. In this mini review, the similarities between AD and T2DM are summarised with the main focus on GLP-1-based therapeutics in AD.

tPA Deficiency Underlies Neurovascular Coupling Dysfunction by Amyloid-β

The amyloid-β (Aβ) peptide, a key pathogenic factor in Alzheimer's disease, attenuates the increase in cerebral blood flow (CBF) evoked by neural activity (functional hyperemia), a vital homeostatic response in which NMDA receptors (NMDARs) play a role through nitric oxide, and the CBF increase produced by endothelial factors. Tissue plasminogen activator (tPA), which is reduced in Alzheimer's disease and in mouse models of Aβ accumulation, is required for the full expression of the NMDAR-dependent component of functional hyperemia. Therefore, we investigated whether tPA is involved in the neurovascular dysfunction of Aβ. tPA activity was reduced, and the tPA inhibitor plasminogen inhibitor-1 (PAI-1) was increased in male mice expressing the Swedish mutation of the amyloid precursor protein (tg2576). Counteracting the tPA reduction with exogenous tPA or with pharmacological inhibition or genetic deletion of PAI-1 completely reversed the attenuation of the CBF increase evoked by whisker stimulation but did not ameliorate the response to the endothelium-dependent vasodilator acetylcholine. The tPA deficit attenuated functional hyperemia by suppressing NMDAR-dependent nitric oxide production during neural activity. Pharmacological inhibition of PAI-1 increased tPA activity, prevented neurovascular uncoupling, and ameliorated cognition in 11- to 12-month-old tg2576 mice, effects associated with a reduction of cerebral amyloid angiopathy but not amyloid plaques. The data unveil a selective role of the tPA in the suppression of functional hyperemia induced by Aβ and in the mechanisms of cerebral amyloid angiopathy, and support the possibility that modulation of the PAI-1-tPA pathway may be beneficial in diseases associated with amyloid accumulation.SIGNIFICANCE STATEMENT Amyloid-β (Aβ) peptides have profound neurovascular effects that may contribute to cognitive impairment in Alzheimer's disease. We found that Aβ attenuates the increases in blood flow evoked by neural activation through a reduction in tissue plasminogen activator (tPA) caused by upregulation of its endogenous inhibitor plasminogen inhibitor-1 (PAI-1). tPA deficiency prevents NMDA receptors from triggering nitric oxide production, thereby attenuating the flow increase evoked by neural activity. PAI-1 inhibition restores tPA activity, rescues neurovascular coupling, reduces amyloid deposition around blood vessels, and improves cognition in a mouse model of Aβ accumulation. The findings demonstrate a previously unappreciated role of tPA in Aβ-related neurovascular dysfunction and in vascular amyloid deposition. Restoration of tPA activity could be of therapeutic value in diseases associated with amyloid accumulation.

Long Noncoding RNA H19 Induces Neuropathic Pain by Upregulating Cyclin-Dependent Kinase 5-Mediated Phosphorylation of cAMP Response Element Binding Protein

Objective

Neuropathic pain (NP) is a debilitating condition caused by nervous system injury and chronic diseases. LncRNA H19 is upregulated in many human diseases, including NP. Cyclin-dependent kinase 5 (CDK5) aggressively worsens inflammatory action and nerve damage to cause severe NP. Phosphorylated cAMP response element binding protein (CREB) is detrimental to nerves and promotes NP progression. Herein, aim of our study was to assess the mechanism of lncRNA H19.

Methods

The NP rat model was established using chronic constriction injury (CCI). Paw withdrawal threshold (PWT) tests and paw withdrawal latency (PWL) tests were performed. Then, small interfering (si)RNA against H19 was intrathecally injected into rats to suppress H19 expression. Schwann cells were isolated from NP rats and transfected with siRNA-H19 or a lentivirus (LV)-based vector expressing H19. Inflammatory factors and glial fibrillary acidic protein (GFAP) were detected. Western blot analysis was conducted to detect CDK5/p35 and p-CREB expression. Finally, H19, CDK5 and CREB phosphorylation were tested with the combination of the CDK5 inhibitor roscovitine and transfection of LV-H19 and siRNA-H19. Finally, we investigated the binding relationships between H19 and miR-196a-5p and between miR-196a-5p and CDK5 and detected the mRNA expression of miR-196a-5p and CDK5 in rats with H19 knockdown and in Schwann cells with H19 knockdown.

Results

Highly expressed H19, CDK5/p-35 and p-CREB were observed in NP rats, accompanied by obviously decreased PWT and PWL, upregulated inflammatory factors and GFAP levels, and reduced 5-HT_2A and GABA_B2 expression. siRNA-H19 restored NP-related indexes and downregulated CDK5/p35 and p-CREB phosphorylation. siRNA-H19, together with the CDK5 inhibitor roscovitine, reduced CDK5 and p-CREB expression in Schwann cells isolated from NP rats. Binding sites between H19 and miR-196a-5p and between miR-196a-5p and CDK5 were identified. Silencing H19 upregulated miR-196a-5p expression and downregulated CDK5 levels.

Conclusion

Our study demonstrated that silencing H19 inhibited NP by suppressing CDK5/p35 and p-CREB phosphorylation via the miR-196a-5p/CDK5 axis, which may provide new insight into NP treatment.

Interference With Complex IV as a Model of Age-Related Decline in Synaptic Connectivity

Age-related impairment of mitochondrial function may negatively impact energy-demanding processes such as synaptic transmission thereby triggering cognitive decline and processes of neurodegeneration. Here, we present a novel model for age-related mitochondrial impairment based on partial inhibition of cytochrome c oxidase subunit 4 (Cox4) of complex IV of the respiratory chain. miRNA-mediated knockdown of Cox4 correlated with a marked reduction in excitatory and inhibitory synaptic marker densities in vitro and in vivo as well as an impairment of neuronal network activity in primary neuronal cultures. Transcriptome analysis identified the deregulation of gene clusters, which link induced mitochondrial perturbation to impaired synaptic function and plasticity as well as processes of aging. In conclusion, the model of Cox4 deficiency reflects aspects of age-related dementia and might, therefore, serve as a novel test system for drug development.

Future Aspects of CDK5 in Prostate Cancer: From Pathogenesis to Therapeutic Implications

Cyclin-dependent kinase 5 (CDK5) is a unique member of the cyclin-dependent kinase family. CDK5 is activated by binding with its regulatory proteins, mainly p35, and its activation is essential in the development of the central nervous system (CNS) and neurodegeneration. Recently, it has been reported that CDK5 plays important roles in regulating various biological and pathological processes, including cancer progression. Concerning prostate cancer, the androgen receptor (AR) is majorly involved in tumorigenesis, while CDK5 can phosphorylate AR and promotes the proliferation of prostate cancer cells. Clinical evidence has also shown that the level of CDK5 is associated with the progression of prostate cancer. Interestingly, inhibition of CDK5 prevents prostate cancer cell growth, while drug-triggered CDK5 hyperactivation leads to apoptosis. The blocking of CDK5 activity by its small interfering RNAs (siRNA) or Roscovitine, a pan-CDK inhibitor, reduces the cellular AR protein level and triggers the death of prostate cancer cells. Thus, CDK5 plays a crucial role in the growth of prostate cancer cells, and AR regulation is one of the important pathways. In this review paper, we summarize the significant studies on CDK5-mediated regulation of prostate cancer cells. We propose that the CDK5–p35 complex might be an outstanding candidate as a diagnostic marker and potential target for prostate cancer treatment in the near future.