The Implication of STEP in Synaptic Plasticity and Cognitive Impairments in Alzheimer's Disease and Other Neurological Disorders

Neuronal plasticity and its role in Alzheimer's disease and Parkinson's disease

Neuronal plasticity, the brain's ability to adapt structurally and functionally, is essential for learning, memory, and recovery from injuries. In neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease, this plasticity is disrupted, leading to cognitive and motor deficits. This review explores the mechanisms of neuronal plasticity and its effect on Alzheimer's disease and Parkinson's disease. Alzheimer's disease features amyloid-beta plaques and tau tangles that impair synaptic function, while Parkinson's disease involves the loss of dopaminergic neurons affecting motor control. Enhancing neuronal plasticity offers therapeutic potential for these diseases. A systematic literature review was conducted using databases such as PubMed, Scopus, and Google Scholar, focusing on studies of neuronal plasticity in Alzheimer's disease and Parkinson's disease. Data synthesis identified key themes such as synaptic mechanisms, neurogenesis, and therapeutic strategies, linking molecular insights to clinical applications. Results highlight that targeting synaptic plasticity mechanisms, such as long-term potentiation and long-term depression, shows promise. Neurotrophic factors, advanced imaging techniques, and molecular tools (e.g., clustered regularly interspaced short palindromic repeats and optogenetics) are crucial in understanding and enhancing plasticity. Current therapies, including dopamine replacement, deep brain stimulation, and lifestyle interventions, demonstrate the potential to alleviate symptoms and improve outcomes. In conclusion, enhancing neuronal plasticity through targeted therapies holds significant promise for treating neurodegenerative diseases. Future research should integrate multidisciplinary approaches to fully harness the therapeutic potential of neuronal plasticity in Alzheimer's disease and Parkinson's disease.

Three STEPs forward: A trio of unexpected structures of PTPN5

Protein tyrosine phosphatases (PTPs) play pivotal roles in myriad cellular processes by counteracting protein tyrosine kinases. Striatal-enriched protein tyrosine phosphatase (STEP, PTPN5) regulates synaptic function and neuronal plasticity in the brain and is a therapeutic target for several neurological disorders. Here, we present three new crystal structures of STEP, each with unexpected features. These include high-resolution conformational heterogeneity at multiple sites, and a highly coordinated citrate molecule in the active site, a previously unseen conformational change at an allosteric site, an intramolecular disulfide bond that was characterized biochemically but had never been visualized structurally, and two serendipitous covalent ligand binding events at surface-exposed cysteines that are nearly or entirely unique to STEP among human PTPs. Together, our results offer new views of the conformational landscape of STEP that may inform structure-based design of allosteric small molecules to specifically inhibit this biomedically important enzyme.

VEGFD signaling balances stability and activity-dependent structural plasticity of dendrites

Mature neurons have stable dendritic architecture, which is essential for the nervous system to operate correctly. The ability to undergo structural plasticity, required to support adaptive processes like memory formation, is still present in mature neurons. It is unclear what molecular and cellular processes control this delicate balance between dendritic structural plasticity and stabilization. Failures in the preservation of optimal dendrite structure due to atrophy or maladaptive plasticity result in abnormal connectivity and are associated with various neurological diseases. Vascular endothelial growth factor D (VEGFD) is critical for the maintenance of mature dendritic trees. Here, we describe how VEGFD affects the neuronal cytoskeleton and demonstrate that VEGFD exerts its effects on dendrite stabilization by influencing the actin cortex and reducing microtubule dynamics. Further, we found that during synaptic activity-induced structural plasticity VEGFD is downregulated. Our findings revealed that VEGFD, acting on its cognate receptor VEGFR3, opposes structural changes by negatively regulating dendrite growth in cultured hippocampal neurons and in vivo in the adult mouse hippocampus with consequences on memory formation. A phosphoproteomic screening identified several regulatory proteins of the cytoskeleton modulated by VEGFD. Among the actin cortex-associated proteins, we found that VEGFD induces dephosphorylation of ezrin at tyrosine 478 via activation of the striatal-enriched protein tyrosine phosphatase (STEP). Activity-triggered structural plasticity of dendrites was impaired by expression of a phospho-deficient mutant ezrin in vitro and in vivo. Thus, VEGFD governs the equilibrium between stabilization and plasticity of dendrites by acting as a molecular brake of structural remodeling.

Reelin links Apolipoprotein E4, Tau, and Amyloid-β in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder that affects the cerebral cortex and hippocampus, and is characterised by progressive cognitive decline and memory loss. A recent report of a patient carrying a novel gain-of-function variant of RELN (H3447R, termed RELN-COLBOS) who developed resilience against presenilin-linked autosomal-dominant AD (ADAD) has generated enormous interest. The RELN-COLBOS variant enhances interactions with the apolipoprotein E receptor 2 (ApoER2) and very-low-density lipoprotein receptor (VLDLR), which are associated with delayed AD onset and progression. These findings were validated in a transgenic mouse model. Reelin is involved in neurodevelopment, neurogenesis, and neuronal plasticity. The evidence accumulated thus far has demonstrated that the Reelin pathway links apolipoprotein E4 (ApoE4), amyloid-β (Aβ), and tubulin-associated unit (Tau), which are key proteins that have been implicated in AD pathogenesis. Reelin and key components of the Reelin pathway have been highlighted as potential therapeutic targets and biomarkers for AD.

Uncovering the Significance of STEP61 in Alzheimer's Disease: Structure, Substrates, and Interactome

STEP (STriatal-Enriched Protein Tyrosine Phosphatase) is a brain-specific phosphatase that plays an important role in controlling signaling molecules involved in neuronal activity and synaptic development. The striatum is the main location of the STEP enzyme. An imbalance in STEP61 activity is a risk factor for Alzheimer's disease (AD). It can contribute to the development of numerous neuropsychiatric diseases, including Parkinson's disease (PD), schizophrenia, fragile X syndrome (FXS), Huntington's disease (HD), alcoholism, cerebral ischemia, and stress-related diseases. The molecular structure, chemistry, and molecular mechanisms associated with STEP61's two major substrates, Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPAr) and N-methyl-D-aspartate receptors (NMDARs), are crucial in understanding the relationship between STEP61 and associated illnesses. STEP's interactions with its substrate proteins can alter the pathways of long-term potentiation and long-term depression. Therefore, understanding the role of STEP61 in neurological illnesses, particularly Alzheimer's disease-associated dementia, can provide valuable insights for possible therapeutic interventions. This review provides valuable insights into the molecular structure, chemistry, and molecular mechanisms associated with STEP61. This brain-specific phosphatase controls signaling molecules involved in neuronal activity and synaptic development. This review can aid researchers in gaining deep insights into the complex functions of STEP61.

Abnormal phosphorylation of protein tyrosine in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and multiple sclerosis, are chronic disorders of the CNS that are characterized by progressive neuronal dysfunction. These diseases have diverse clinical and pathological features and their pathogenetic mechanisms are not yet fully understood. Currently, widely accepted hypotheses include the accumulation of misfolded proteins, oxidative stress from reactive oxygen species, mitochondrial dysfunction, DNA damage, neurotrophin dysfunction, and neuroinflammatory processes. In the CNS of patients with neurodegenerative diseases, a variety of abnormally phosphorylated proteins play important roles in pathological processes such as neuroinflammation and intracellular accumulation of β-amyloid plaques and tau. In recent years, the roles of abnormal tyrosine phosphorylation of intracellular signaling molecules regulated by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) in neurodegenerative diseases have attracted increasing attention. Here, we summarize the roles of signaling pathways related to protein tyrosine phosphorylation in the pathogenesis of neurodegenerative diseases and the progress of therapeutic studies targeting PTKs and PTPs that provide theoretical support for future studies on therapeutic strategies for these devastating and important neurodegenerative diseases.

Ferulic Acid Improves Synaptic Plasticity and Cognitive Impairments by Alleviating the PP2B/DARPP-32/PP1 Axis-Mediated STEP Increase and Aβ Burden in Alzheimer's Disease

The burden of Alzheimer's disease, the most prevalent neurodegenerative disease, is increasing exponentially due to the increase in the elderly population worldwide. Synaptic plasticity is the basis of learning and memory, but it is impaired in AD. Uncovering the disease's underlying molecular pathogenic mechanisms involving synaptic plasticity could lead to the identification of targets for better disease management. Using primary neurons treated with Aβ and APP/PS1 animal models, we evaluated the effect of the phenolic compound ferulic acid (FA) on synaptic dysregulations. Aβ led to synaptic plasticity and cognitive impairments by increasing STEP activity and decreasing the phosphorylation of the GluN2B subunit of NMDA receptors, as well as decreasing other synaptic proteins, including PSD-95 and synapsin1. Interestingly, FA attenuated the Aβ-upregulated intracellular calcium and thus resulted in a decrease in PP2B-induced activation of DARPP-32, inhibiting PP1. This cascade event maintained STEP in its inactive state, thereby preventing the loss of GluN2B phosphorylation. This was accompanied by an increase in PSD-95 and synapsin1, improved LTP, and a decreased Aβ load, together leading to improved behavioral and cognitive functions in APP/PS1 mice treated with FA. This study provides insight into the potential use of FA as a therapeutic strategy in AD.

Hereditable variants of classical protein tyrosine phosphatase genes: Will they prove innocent or guilty?

Protein tyrosine phosphatases, together with protein tyrosine kinases, control many molecular signaling steps that control life at cellular and organismal levels. Impairing alterations in the genes encoding the involved proteins is expected to profoundly affect the quality of life-if compatible with life at all. Here, we review the current knowledge on the effects of germline variants that have been reported for genes encoding a subset of the protein tyrosine phosphatase superfamily; that of the thirty seven classical members. The conclusion must be that the newest genome research tools produced an avalanche of data that suggest 'guilt by association' for individual genes to specific disorders. Future research should face the challenge to investigate these accusations thoroughly and convincingly, to reach a mature genotype-phenotype map for this intriguing protein family.

Tyrosine phosphatase STEP61 in human dementia and in animal models with amyloid and tau pathology

Synaptic degeneration is a precursor of synaptic and neuronal loss in neurodegenerative diseases such as Alzheimer's disease (AD) and frontotemporal dementia with tau pathology (FTD-tau), a group of primary tauopathies. A critical role in this degenerative process is assumed by enzymes such as the kinase Fyn and its counterpart, the phosphatase striatal-enriched tyrosine phosphatase 61 (STEP₆₁). Whereas the role of Fyn has been widely explored, less is known about STEP₆₁ that localises to the postsynaptic density (PSD) of glutamatergic neurons. In dementias, synaptic loss is associated with an increased burden of pathological aggregates. Tau pathology is a hallmark of both AD (together with amyloid-β deposition) and FTD-tau. Here, we examined STEP₆₁ and its activity in human and animal brain tissue and observed a correlation between STEP₆₁ and disease progression. In early-stage human AD, an initial increase in the level and activity of STEP₆₁ was observed, which decreased with the loss of the synaptic marker PSD-95; in FTD-tau, there was a reduction in STEP₆₁ and PSD-95 which correlated with clinical diagnosis. In APP23 mice with an amyloid-β pathology, the level and activity of STEP₆₁ were increased in the synaptic fraction compared to wild-type littermates. Similarly, in the K3 mouse model of FTD-tau, which we assessed at two ages compared to wild-type, expression and activity of STEP₆₁ were increased with ageing. Together, these findings suggest that STEP contributes differently to the pathogenic process in AD and FTD-tau, and that its activation may be an early response to a degenerative process.

Moringa Oleifera Alleviates Aβ Burden and Improves Synaptic Plasticity and Cognitive Impairments in APP/PS1 Mice

Alzheimer's disease is a global public health problem and the most common form of dementia. Due to the failure of many single therapies targeting the two hallmarks, Aβ and Tau, and the multifactorial etiology of AD, there is now more and more interest in nutraceutical agents with multiple effects such as Moringa oleifera (MO) that have strong anti-oxidative, anti-inflammatory, anticholinesterase, and neuroprotective virtues. In this study, we treated APP/PS1 mice with a methanolic extract of MO for four months and evaluated its effect on AD-related pathology in these mice using a multitude of behavioral, biochemical, and histochemical tests. Our data revealed that MO improved behavioral deficits such as anxiety-like behavior and hyperactivity and cognitive, learning, and memory impairments. MO treatment abrogated the Aβ burden to wild-type control mice levels via decreasing BACE1 and AEP and upregulating IDE, NEP, and LRP1 protein levels. Moreover, MO improved synaptic plasticity by improving the decreased GluN2B phosphorylation, the synapse-related proteins PSD95 and synapsin1 levels, the quantity and quality of dendritic spines, and neurodegeneration in the treated mice. MO is a nutraceutical agent with promising therapeutic potential that can be used in the management of AD and other neurodegenerative diseases.

Differential mRNA Expression Profiling Reveals the Role of MiR-375 in Inflammation of Bovine Mammary Epithelial Cells

Simple Summary

Bovine mammary epithelial cells (bMECs) are often used as cell models for mammary gland research. They are the most important cells for mammary gland function and the first line of defense for pathogen identification. MicroRNAs (miRNAs) are important regulatory factors involved in many physiological and pathological processes. Here, we examined a transcriptome profile of bovine mammary epithelial cell lines transfected with miR-375 inhibitor or negative control (NC) inhibitor, and further reveal the potential role of miR-375 in bMECs by differentially expressed mRNA analysis. We found that miR-375 potentially promotes inflammation in the mammary gland through the MAPK signaling pathway.

Abstract

MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate post-transcriptional gene expression and several biological processes. Bovine mammary epithelial cells (bMECs) mediate critical immune responses in the mammary gland and the occurrence of mastitis. Current research focuses on miRNA regulation of bMECs, but the miR-375 regulatory mechanism in bMECs is unclear. This study explored the role of miR-375 by profiling the transcriptome of miR-375-silenced bMECs using RNA-seq and identifying differentially expressed mRNAs (DIE-mRNAs). There were 63 DIE-mRNAs, including 48 down-regulated and 15 up-regulated mRNAs between miR-375-silenced bMECs and the controls. The Kyoto encyclopedia of genes and genomes (KEGG) and Gene Ontology (GO) functional analysis showed that the DIE-mRNAs enriched nuclear receptor subfamily 4 group A member 1 (NR4A1) and protein tyrosine phosphatase non-receptor type 5 (PTPN5) anti-inflammatory genes of the mitogen-activated protein kinase (MAPK) signaling pathway. However, they showed an opposite trend to the expression of miR-375 silencing, suggesting that miR-375 promotes bMEC inflammation through the MAPK signaling pathway. The findings of this study provide a new reference for understanding the regulation of bMEC inflammation and cow mastitis.