RPS23RG1 modulates tau phosphorylation and axon outgrowth through regulating p35 proteasomal degradation

Chronic glial activation and behavioral alterations induced by acute/subacute pioglitazone treatment in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) is a disabling neurotraumatic condition and the leading cause of injury-related deaths and disability in the United States. Attenuation of neuroinflammation early after TBI is considered an important treatment target; however, while these inflammatory responses can induce secondary brain injury, they are also involved in the repair of the nervous system. Pioglitazone, which activates peroxisome proliferator-activated receptor gamma, has been shown to decrease inflammation acutely after TBI, but the long-term consequences of its use remain unknown. For this reason, the impacts of treatment with pioglitazone during the acute/subacute phase (30 min after injury and each subsequent 24 h for 5 days) after TBI were interrogated during the chronic phase (30- and 274-days post-injury (DPI)) in mice using the controlled cortical impact model of experimental TBI. Acute/subacute pioglitazone treatment after TBI results in long-term deleterious consequences, including disruption of tau homeostasis, chronic glial cell activation, neuronal pathology, and worsened injury severity particularly at 274 DPI, with male mice being more susceptible than female mice. Further, male pioglitazone-treated TBI mice exhibited increased dominant and offensive-like behavior while having a decreased non-social exploring behavior at 274 DPI. After TBI, both sexes exhibited glial activation at 30 DPI when treated with pioglitazone; however, while injury severity was increased in females it was not impacted in male mice. This work reveals that although pioglitazone has been shown to lead to attenuated TBI outcomes acutely, sex-based differences, timing and long-term consequences of treatment with glitazones must be considered and further studied prior to their clinical use for TBI therapy.

Dysregulated N6-methyladenosine modification in peripheral immune cells contributes to the pathogenesis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurogenerative disorder with uncertain origins. Emerging evidence implicates N6-methyladenosine (m6A) modification in ALS pathogenesis. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and liquid chromatography-mass spectrometry were utilized for m6A profiling in peripheral immune cells and serum proteome analysis, respectively, in patients with ALS (n = 16) and controls (n = 6). The single-cell transcriptomic dataset (GSE174332) of primary motor cortex was further analyzed to illuminate the biological implications of differentially methylated genes and cell communication changes. Analysis of peripheral immune cells revealed extensive RNA hypermethylation, highlighting candidate genes with differential m6A modification and expression, including C-X3-C motif chemokine receptor 1 (CX3CR1). In RAW264.7 macrophages, disrupted CX3CR1 signaling affected chemotaxis, potentially influencing immune cell migration in ALS. Serum proteome analysis demonstrated the role of dysregulated immune cell migration in ALS. Cell type-specific expression variations of these genes in the central nervous system (CNS), particularly microglia, were observed. Intercellular communication between neurons and glial cells was selectively altered in ALS CNS. This integrated approach underscores m6A dysregulation in immune cells as a potential ALS contributor.

Cdk5 phosphorylation-dependent C9orf72 degradation promotes neuronal death in Parkinson's disease models

AIMS

Chromosome 9 open reading frame 72 (C9orf72) is one of the most dazzling molecules in neurodegenerative diseases, albeit that its role in Parkinson's disease (PD) remains unknown. This article aimed to explore the potential mechanism of C9orf72 involved in the pathogenesis of PD.

METHODS

The expression and phosphorylation levels of C9orf72 were examined by Western blotting, RT-PCR, and immunoprecipitation using PD models. Multiple bioinformatics software was used to predict the potential phosphorylation sites of C9orf72 by Cdk5, followed by verification of whether Cdk5-inhibitor ROSCOVITINE could reverse the degradation of C9orf72 in PD. By constructing the sh-C9orf72-knockdown adenovirus and overexpressing the FLAG-C9orf72 plasmid, the effects of C9orf72 knockdown and overexpression, respectively, were determined. A short peptide termed Myr-C9orf72 was used to verify whether interfering with Cdk5 phosphorylation at the Ser9 site of the C9orf72 protein could alleviate autophagy disorder, neuronal death, and movement disorder in PD models.

RESULTS

The expression level of the C9orf72 protein was significantly reduced, albeit the mRNA expression was not changed in the PD models. Moreover, the phosphorylation level was enhanced, and its reduction was mainly degraded by the ubiquitin-proteasome pathway. The key nervous system kinase Cdk5 directly phosphorylated the S9 site of the C9orf72 protein, which promoted the degradation of the C9orf72 protein. The knockdown of C9orf72 aggravated autophagy dysfunction and increased neuronal loss and motor dysfunction in substantia nigra neurons of PD mice. The overexpression of C9orf72 alleviated autophagy dysfunction in PD neurons. Specifically, interference with Cdk5 phosphorylation at the S9 site of C9orf72 alleviated autophagy dysfunction, neuronal death, and motor dysfunction mediated by C9orf72 protein degradation during PD.

CONCLUSIONS

Cumulatively, our findings illustrate the importance of the role of C9orf72 in the regulation of neuronal death during PD progression via the Cdk5-dependent degradation.

Mutation of S461, in the GOLGA3 phosphorylation site, does not affect mouse spermatogenesis

Background

Golgin subfamily A member 3 (Golga3), a member of the golgin subfamily A, is highly expressed in mouse testis. The GOLGA3 protein, which contains eight phosphorylation sites, is involved in protein transport, cell apoptosis, Golgi localization, and spermatogenesis. Although it has been previously reported that nonsense mutations in Golga3 cause multiple defects in spermatogenesis, the role of Golga3 in the testis is yet to be clarified.

Methods

Immunofluorescence co-localization in cells and protein dephosphorylation experiments were performed. Golga3 ^S461L/S461Lmice were generated using cytosine base editors. Fertility tests as well as computer-assisted sperm analysis (CASA) were then performed to investigate sperm motility within caudal epididymis. Histological and immunofluorescence staining were used to analyze testis and epididymis phenotypes and TUNEL assays were used to measure germ cell apoptosis in spermatogenic tubules.

Results

Immunofluorescence co-localization showed reduced Golgi localization of GOLGA3^S465L with some protein scattered in the cytoplasm of HeLa cells .In addition, protein dephosphorylation experiments indicated a reduced band shift of the dephosphorylated GOLGA3^S465L, confirming S461 as the phosphorylation site. Golga3 is an evolutionarily conserved gene and Golga3 ^S461L/S461Lmice were successfully generated using cytosine base editors. These mice had normal fertility and spermatozoa, and did not differ significantly from wild-type mice in terms of spermatogenesis and apoptotic cells in tubules.

Conclusions

Golga3 was found to be highly conserved in the testis, and GOLGA3 was shown to be involved in spermatogenesis, especially in apoptosis and Golgi complex-mediated effects. Infertility was also observed in Golga3 KO male mice. Although GOLGA3^S465Lshowed reduced localization in the Golgi with some expression in the cytoplasm, this abnormal localization did not adversely affect fertility or spermatogenesis in male C57BL/6 mice. Therefore, mutation of the S461 GOLGA3 phosphorylation site did not affect mouse spermatogenesis.

Research Progress on the Etiology and Pathogenesis of Alzheimer's Disease from the Perspective of Chronic Stress

Due to its extremely complex pathogenesis, no effective drugs to prevent, delay progression, or cure Alzheimer's disease (AD) exist at present. The main pathological features of AD are senile plaques composed of β-amyloid, neurofibrillary tangles formed by hyperphosphorylation of the tau protein, and degeneration or loss of neurons in the brain. Many risk factors associated with the onset of AD, including gene mutations, aging, traumatic brain injury, endocrine and cardiovascular diseases, education level, and obesity. Growing evidence points to chronic stress as one of the major risk factors for AD, as it can promote the onset and development of AD-related pathologies via a mechanism that is not well known. The use of murine stress models, including restraint, social isolation, noise, and unpredictable stress, has contributed to improving our understanding of the relationship between chronic stress and AD. This review summarizes the evidence derived from murine models on the pathological features associated with AD and the related molecular mechanisms induced by chronic stress. These results not only provide a retrospective interpretation for understanding the pathogenesis of AD, but also provide a window of opportunity for more effective preventive and identifying therapeutic strategies for stress-induced AD.

Phenazopyridine promotes RPS23RG1/Rps23rg1 transcription and ameliorates Alzheimer-associated phenotypes in mice

Alzheimer's disease (AD) is the most common form of dementia with no effective treatment options. A complete elucidation of its underlying molecular mechanisms, including the transcription regulation of genes critically involved in AD, may shed light on new therapeutic development. RPS23RG1 is a newly identified AD-associated gene, whose expression is decreased in AD and restoration can attenuate AD-like phenotypes in animal models. However, the transcription regulation of RPS23RG1 remains unknown. In this study, we explored the promoter of RPS23RG1 and identified its transcription initiation site (TSS) at 1525 bp upstream of the ATG translation start codon. Progressive deletion analysis determined the presence of a negative regulatory region and a positive regulatory region within nucleotide positions +1127 to +1187 and +732 to +1127 relative to the TSS (+1), respectively. We conducted a reporter system to screen for compounds that increase RPS23RG1 expression through antagonizing its negative regulatory elements and identified phenazopyridine. Importantly, we demonstrated that phenazopyridine not only promoted RPS23RG1/Rps23rg1 expression, but also reduced AD-like pathologies and cognitive impairments in the APP/PS1 AD model mice. We also determined a critical negative regulatory domain of RPS23RG1 within nucleotide positions +1177 to +1187 and found that the transcription factor SMAD3 bound to this domain. Inhibition of SMAD3 promoted RPS23RG1 expression. Moreover, phenazopyridine reduced SMAD3 binding to the RPS23RG1 promoter without affecting SMAD3 phosphorylation and nuclear localization. Taken together, our results determine the transcription regulation mechanism of RPS23RG1 and show that phenazopyridine has potential for AD treatment through regulating RPS23RG1 transcription.

Rose Bengal inhibits β-amyloid oligomers-induced tau hyperphosphorylation via acting on Akt and CDK5 kinases

RATIONALE

Tau hyperphosphorylation and aggregation is considered as a main pathological mechanism underlying Alzheimer's disease (AD). Rose Bengal (RB) is a synthetic dye used for disease diagnosis, which was reported to inhibit tau toxicity via inhibiting tau aggregation in Drosophila. However, it was unknown if RB could produce anti-AD effects in rodents.

OBJECTIVES

The research aimed to investigate if and how RB could prevent β-amyloid (Aβ) oligomers-induced tau hyperphosphorylation in rodents.

METHODS AND RESULTS

RB was tested in vitro (0.3-1 μM) and prevented Aβ oligomers-induced tau hyperphosphorylation in PC12 cells. Moreover, RB (10-30 mg/kg, i.p.) effectively attenuated cognitive impairments induced by Aβ oligomers in mice. Western blotting analysis demonstrated that RB significantly increased the expression of pSer473-Akt, pSer9-glycogen synthase kinase-3β (GSK3β) and reduced the expression of cyclin-dependent kinase 5 (CDK5) both in vitro and in vivo. Molecular docking analysis suggested that RB might directly interact with GSK3β and CDK5 by acting on ATP binding sites. Gene Ontology enrichment analysis indicated that RB might act on protein phosphorylation pathways to inhibit tau hyperphosphorylation.

CONCLUSIONS

RB was shown to inhibit tau neurotoxicity at least partially via inhibiting the activity of GSK3β and CDK5, which is a novel neuroprotective mechanism besides the inhibition of tau aggregation. As tau hyperphosphorylation is an important target for AD therapy, this study also provided support for investigating the drug repurposing of RB as an anti-AD drug candidate.

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.

CDK5 Mediates Proinflammatory Effects of Microglia through Activated DRP1 Phosphorylation in Rat Model of Intracerebral Hemorrhage

Introduction

Cyclin-dependent kinase-5 (CDK5) is a key kinase involved in brain development and function and recently found to be involved in neuronal and astroglial apoptosis, neural stem/progenitor cell stemness, mitochondrial fission, and synaptic transmission. But the specific mechanism of CDK5-mediated anti-inflammatory remains unclear in ICH. The aim of the present study was to explore the role of CDK5 in mediating microglia activity through activated DRP1 phosphorylation in a rat ICH model.

Methods

We measured behavioral change after ICH; detected the expression of CDK5 in the rat brain using immunohistochemistry; and measured the protein levels of CDK5, p35, p25, p-histone H1, and p-DRP1 using Western blot analysis. Coimmunoprecipitation analysis indicated interaction of CDK5 and DRP1. Tumor necrosis factor-α, interleukin- (IL-) 1β, and IL-6 levels were measured using enzyme-linked immunosorbent assay (ELISA).

Results

After ICH, CDK5 protein level and kinase activity increased. Western blot data showed that CDK5 expression increased from 6 h and peaked at 2 d after ICH (p < 0.05), and the expression of p35 was lowest at 12 h, while the expression of p25 peaked at 2 d after ICH. Besides, p-DRP1 expression change follows with CDK5 kinase activity change. Coimmunoprecipitation showed that interaction between CDK5 and DRP1 certainly exists in microglia. Then, knockdown CDK5 or p35 expression by siRNA reduced the expression level of p-DRP1. ELISA data showed that the protein levels of proinflammatory mediators, such as TNF-α, IL-1β, and IL-6, were decreased by knockdown of CDK5.

Conclusion

CDK5 may regulate DRP1 by direct phosphorylation in microglia and further induce microglia secreting proinflammation factor.

Tau Toxicity in Neurodegeneration

Tau is a microtubule-associated protein widely distributed in the central nervous system (CNS). The main function of tau is to promote the assembly of microtubules and stabilize their structure. After a long period of research on neurodegenerative diseases, the function and dysfunction of the microtubule-associated protein tau in neurodegenerative diseases and tau neurotoxicity have attracted increasing attention. Tauopathies are a series of progressive neurodegenerative diseases caused by pathological changes in tau, such as abnormal phosphorylation. The pathological features of tauopathies are the deposition of abnormally phosphorylated tau proteins and the aggregation of tau proteins in neurons. This article first describes the normal physiological function and dysfunction of tau proteins and then discusses the enzymes and proteins involved in tau phosphorylation and dephosphorylation, the role of tau in cell dysfunction, and the relationships between tau and several neurodegenerative diseases. The study of tau neurotoxicity provides new directions for the treatment of tauopathies.

Potential role of Drug Repositioning Strategy (DRS) for management of tauopathy

Tauopathy is a term that has been used to represent a pathological condition in which hyperphosphorylated tau protein aggregates in neurons and glia which results in neurodegeneration, synapse loss and dysfunction and cognitive impairments. Recently, drug repositioning strategy (DRS) becomes a promising field and an alternative approach to advancing new treatments from actually developed and FDA approved drugs for an indication other than the indication it was originally intended for. This paradigm provides an advantage because the safety of the candidate compound has already been established, which abolishes the need for further preclinical safety testing and thus substantially reduces the time and cost involved in progressing of clinical trials. In the present review, we focused on correlation between tauopathy and common diseases as type 2 diabetes mellitus and the global virus COVID-19 and how tau pathology can aggravate development of these diseases in addition to how these diseases can be a risk factor for development of tauopathy. Moreover, correlation between COVID-19 and type 2 diabetes mellitus was also discussed. Therefore, repositioning of a drug in the daily clinical practice of patients to manage or prevent two or more diseases at the same time with lower side effects and drug-drug interactions is a promising idea. This review concluded the results of pre-clinical and clinical studies applied on antidiabetics, COVID-19 medications, antihypertensives, antidepressants and cholesterol lowering drugs for possible drug repositioning for management of tauopathy.

Roles and Mechanisms of Axon-Guidance Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by progressive memory decline and cognitive dysfunctions. Although the causes of AD have not yet been established, many mechanisms have been proposed. Axon-guidance molecules play the roles in the occurrence and development of AD by participating in different mechanisms. Therefore, what roles do axon-guidance molecules play in AD? This study aimed at elucidating how axon-guidance molecules Netrins, Slits, Semaphorins, and Ephrins regulate the levels of Aβ, hyperphosphorylation of tau protein, Reelin, and other ways through different signaling pathways, in order to show the roles of axon-guidance molecules in the occurrence and development of AD. And it is hoped that this study can provide a theoretical basis and new perspectives in the search for new therapeutic targets for AD.