Prion-like protein aggregates exploit the RHO GTPase to cofilin-1 signaling pathway to enter cells

Decoding the Cellular Trafficking of Prion-like Proteins in Neurodegenerative Diseases

The accumulation and spread of prion-like proteins is a key feature of neurodegenerative diseases (NDs) such as Alzheimer's disease, Parkinson's disease, or Amyotrophic Lateral Sclerosis. In a process known as 'seeding', prion-like proteins such as amyloid beta, microtubule-associated protein tau, α-synuclein, silence superoxide dismutase 1, or transactive response DNA-binding protein 43 kDa, propagate their misfolded conformations by transforming their respective soluble monomers into fibrils. Cellular and molecular evidence of prion-like propagation in NDs, the clinical relevance of their 'seeding' capacities, and their levels of contribution towards disease progression have been intensively studied over recent years. This review unpacks the cyclic prion-like propagation in cells including factors of aggregate internalization, endo-lysosomal leaking, aggregate degradation, and secretion. Debates on the importance of the role of prion-like protein aggregates in NDs, whether causal or consequent, are also discussed. Applications lead to a greater understanding of ND pathogenesis and increased potential for therapeutic strategies.

The Multifaceted Role of Cofilin in Neurodegeneration and Stroke: Insights into Pathogenesis and Targeting as a Therapy

This comprehensive review explores the complex role of cofilin, an actin-binding protein, across various neurodegenerative diseases (Alzheimer's, Parkinson's, schizophrenia, amyotrophic lateral sclerosis (ALS), Huntington's) and stroke. Cofilin is an essential protein in cytoskeletal dynamics, and any dysregulation could lead to potentially serious complications. Cofilin's involvement is underscored by its impact on pathological hallmarks like Aβ plaques and α-synuclein aggregates, triggering synaptic dysfunction, dendritic spine loss, and impaired neuronal plasticity, leading to cognitive decline. In Parkinson's disease, cofilin collaborates with α-synuclein, exacerbating neurotoxicity and impairing mitochondrial and axonal function. ALS and frontotemporal dementia showcase cofilin's association with genetic factors like C9ORF72, affecting actin dynamics and contributing to neurotoxicity. Huntington's disease brings cofilin into focus by impairing microglial migration and influencing synaptic plasticity through AMPA receptor regulation. Alzheimer's, Parkinson's, and schizophrenia exhibit 14-3-3 proteins in cofilin dysregulation as a shared pathological mechanism. In the case of stroke, cofilin takes center stage, mediating neurotoxicity and neuronal cell death. Notably, there is a potential overlap in the pathologies and involvement of cofilin in various diseases. In this context, referencing cofilin dysfunction could provide valuable insights into the common pathologies associated with the aforementioned conditions. Moreover, this review explores promising therapeutic interventions, including cofilin inhibitors and gene therapy, demonstrating efficacy in preclinical models. Challenges in inhibitor development, brain delivery, tissue/cell specificity, and long-term safety are acknowledged, emphasizing the need for precision drug therapy. The call to action involves collaborative research, biomarker identification, and advancing translational efforts. Cofilin emerges as a pivotal player, offering potential as a therapeutic target. However, unraveling its complexities requires concerted multidisciplinary efforts for nuanced and effective interventions across the intricate landscape of neurodegenerative diseases and stroke, presenting a hopeful avenue for improved patient care.

Impaired erythropoietin-producing hepatocellular B receptors signaling in the prefrontal cortex and hippocampus following maternal immune activation in male rats

An environmental risk factor for schizophrenia (SZ) is maternal infection, which exerts longstanding effects on the neurodevelopment of offspring. Accumulating evidence suggests that synaptic disturbances may contribute to the pathology of the disease, but the underlying molecular mechanisms remain poorly understood. Erythropoietin-producing hepatocellular B (EphB) receptor signaling plays an important role in synaptic plasticity by regulating the formation and maturation of dendritic spines and regulating excitatory neurotransmission. We examined whether EphB receptors and downstream associated proteins are susceptible to environmental risk factors implicated in the etiology of synaptic disturbances in SZ. Using an established rodent model, which closely imitates the characteristics of SZ, we observed the behavioral performance and synaptic structure of male offspring in adolescence and early adulthood. We then analyzed the expression of EphB receptors and associated proteins in the prefrontal cortex and hippocampus. Maternal immune activation offspring showed significantly progressive cognitive impairment and pre-pulse inhibition deficits together with an increase in the expression of EphB2 receptors and NMDA receptor subunits. We also found changes in EphB receptor downstream signaling, in particular, a decrease in phospho-cofilin levels which may explain the reduced dendritic spine density. Besides, we found that the AMPA glutamate, another glutamate ionic receptor associated with cofilin, decreased significantly in maternal immune activation offspring. Thus, alterations in EphB signaling induced by immune activation during pregnancy may underlie disruptions in synaptic plasticity and function in the prefrontal cortex and hippocampus associated with behavioral and cognitive impairment. These findings may provide insight into the mechanisms underlying SZ.

RGMa collapses the neuronal actin barrier against disease-implicated protein and exacerbates ALS

Repulsive guidance molecule A (RGMa) was originally identified as a neuronal growth cone-collapsing factor. Previous reports have demonstrated the multifunctional roles of RGMa mediated by neogenin1. However, the pathogenic involvement of RGMa in amyotrophic lateral sclerosis (ALS) remains unclear. Here, we demonstrated that RGMa concentration was elevated in the cerebrospinal fluid of both patients with ALS and transgenic mice overexpressing the mutant human superoxide dismutase1 (mSOD1 mice). Treatment with humanized anti-RGMa monoclonal antibody ameliorated the clinical symptoms in mSOD1 mice. Histochemical analysis revealed that the anti-RGMa antibody significantly decreased mutant SOD1 protein accumulation in the motor neurons of mSOD1 mice via inhibition of actin depolymerization. In vitro analysis revealed that the anti-RGMa antibody inhibited the cellular uptake of the mutant SOD1 protein, presumably by reinforcing the neuronal actin barrier. Collectively, these data suggest that RGMa leads to the collapse of the neuronal actin barrier and promotes aberrant protein deposition, resulting in exacerbation of the ALS pathology.

Macropinocytosis: mechanisms and regulation

Macropinocytosis is defined as an actin-dependent but coat- and dynamin-independent endocytic uptake process, which generates large intracellular vesicles (macropinosomes) containing a non-selective sampling of extracellular fluid. Macropinocytosis provides an important mechanism of immune surveillance by dendritic cells and macrophages, but also serves as an essential nutrient uptake pathway for unicellular organisms and tumor cells. This review examines the cell biological mechanisms that drive macropinocytosis, as well as the complex signaling pathways - GTPases, lipid and protein kinases and phosphatases, and actin regulatory proteins - that regulate macropinosome formation, internalization, and disposition.

Cofilin promotes tau pathology in Alzheimer's disease

The molecular mechanisms mediating the aggregation and transmission of tau in AD remain unclear. Here, we show that the actin-binding protein cofilin is cleaved by a cysteine protease asparagine endopeptidase (AEP) at N138 in the brains of patients with AD. The AEP-generated cofilin 1-138 fragment interacts with tau and promotes its aggregation. The mixed fibrils consisting of cofilin 1-138 and tau are more pathogenic to cells than pure tau fibrils. Furthermore, overexpression of cofilin 1-138 in the brain facilitates the propagation of pathological tau aggregates and promotes AD-like cognitive impairments in tau P301S mice. However, mice infected with adeno-associated viruses (AAVs) encoding an AEP-uncleavable cofilin mutant show attenuated tau pathology and cognitive impairments compared with mice injected with AAVs encoding wild-type cofilin. Together, these observations support the role of the cofilin 1-138 fragment in the aggregation and transmission of tau pathology during the onset and progression of AD.

Relationship between the expression of ARHGAP25 and RhoA in non-small cell lung cancer and vasculogenic mimicry

Background

Vasculogenic mimicry (VM) is a recently identified pattern of blood supply to tumor tissue. It has long been considered a functional element in the metastasis and prognosis of malignant tumors. Both Rho GTPase-activating protein 25 (ARHGAP25) and Ras homolog family member A (RhoA) are effective predictors of tumor metastasis. In this study, we examined the expression levels of ARHGAP25 and RhoA and the structure of VM in non-small cell lung cancer (NSCLC). At the same time, we used cytology-related experiments to explore the effect of ARHGAP25 on the migration ability of tumor cells. Furthermore, we analyzed the interaction between the three factors and their association with clinicopathological characteristics and the five-year survival time in patients using statistical tools.

Methods

A total of 130 well-preserved NSCLC and associated paracancerous tumor-free tissues were obtained. Cell colony formation, wound healing, and cytoskeleton staining assays were used to analyze the effect of ARHGAP25 on the proliferation and migration ability of NSCLC cells. Immunohistochemical staining was used to determine the positivity rates of ARHGAP25, RhoA, and VM. Statistical software was used to examine the relationships between the three factors and clinical case characteristics, overall survival, and disease-free survival.

Results

Cell colony formation, wound healing, and cytoskeleton staining assays confirmed that ARHGAP25 expression affects the proliferation and migratory abilities of NSCLC cells. ARHGAP25 positivity rates in NSCLC and paracancerous tumor-free tissues were 48.5% and 63.1%, respectively, whereas RhoA positivity rates were 62.3% and 18.5%, respectively. ARHGAP25 had a negative relationship with RhoA and VM, whereas RhoA and VM had a positive relationship (P < 0.05). ARHGAP25, RhoA, and VM affected the prognosis of patients with NSCLC (P < 0.05) according to Kaplan–Meier of survival time and Cox regression analyses. Furthermore, lowering ARHGAP25 expression increased NSCLC cell proliferation and migration.

Conclusions

ARHGAP25 and RhoA expression is associated with VM and may be of potential value in predicting tumor metastasis, prognosis, and targeted therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-02179-5.

Prionoids in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the third most frequent neurodegenerative disease after Alzheimer’s and Parkinson’s disease. ALS is characterized by the selective and progressive loss of motoneurons in the spinal cord, brainstem and cerebral cortex. Clinical manifestations typically occur in midlife and start with focal muscle weakness, followed by the rapid and progressive wasting of muscles and subsequent paralysis. As with other neurodegenerative diseases, the condition typically begins at an initial point and then spreads along neuroanatomical tracts. This feature of disease progression suggests the spreading of prion-like proteins called prionoids in the affected tissues, which is similar to the spread of prion observed in Creutzfeldt-Jakob disease. Intensive research over the last decade has proposed the ALS-causing gene products Cu/Zn superoxide dismutase 1, TAR DNA-binding protein of 43 kDa, and fused in sarcoma as very plausible prionoids contributing to the spread of the pathology. In this review, we will discuss the molecular and cellular mechanisms leading to the propagation of these prionoids in ALS.

Research progress on vesicular trafficking in amyotrophic lateral sclerosis

Vesicular trafficking is a basic physiological process by which vesicles transport materials between cells and environment (intercellular transport) and between different cellular compartments (intracellular trafficking). In recent years, more and more evidences have suggested that vesicular trafficking dysfunction plays a key role in pathogenesis of neurodegenerative diseases. Abnormal vesicular trafficking promotes the propagation of misfolded proteins by mechanisms involving endocytosis, endosomal-lysosomal pathway, endosomal escape and exosome release, leading to further acceleration of disease progression. Amyotrophic lateral sclerosis (ALS), as a neurodegenerative disease, is characterized by the selective death of upper and lower motor neurons. A variety of causative genes for ALS have been implicated in vesicle trafficking dysfunction, such as C9ORF72, TARDBP and SOD1. Therefore, the aggregation and propagation of misfolded proteins may be prevented through regulation of vesicle trafficking-related proteins, thus delay the progression of ALS. A more in-depth understanding of vesicular trafficking in ALS will be helpful in revealing the mechanism and clinical treatment of ALS. This review focuses on molecular mechanisms of vesicular trafficking in ALS, to provide reference for exploring new therapeutic strategies.

α-Synuclein at the Presynaptic Axon Terminal as a Double-Edged Sword

α-synuclein (α-syn) is a presynaptic, lipid-binding protein strongly associated with the neuropathology observed in Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and Alzheimer’s Disease (AD). In normal physiology, α-syn plays a pivotal role in facilitating endocytosis and exocytosis. Interestingly, mutations and modifications of precise α-syn domains interfere with α-syn oligomerization and nucleation that negatively affect presynaptic vesicular dynamics, protein expressions, and mitochondrial profiles. Furthermore, the integration of the α-syn oligomers into the presynaptic membrane results in pore formations, ion influx, and excitotoxicity. Targeted therapies against specific domains of α-syn, including the use of small organic molecules, monoclonal antibodies, and synthetic peptides, are being screened and developed. However, the prospect of an effective α-syn targeted therapy is still plagued by low permeability across the blood–brain barrier (BBB), and poor entry into the presynaptic axon terminals. The present review proposes a modification of current strategies, which includes the use of novel encapsulation technology, such as lipid nanoparticles, to bypass the BBB and deliver such agents into the brain.

Cofilin 1 promotes the pathogenicity and transmission of pathological α-synuclein in mouse models of Parkinson's disease

The pathological hallmark of Parkinson's disease (PD) is the presence of Lewy bodies (LBs) with aggregated α-synuclein being the major component. The abnormal α-synuclein aggregates transfer between cells, recruit endogenous α-synuclein into toxic LBs, and finally trigger neuronal injury. However, the molecular mechanisms mediating the aggregation and transmission of pathological α-synuclein remain unknown. Previously we found that cofilin 1, a member of the actin-binding protein, promotes the aggregation and pathogenicity of α-synuclein in vitro. Here we further investigated the effect of cofilin 1 in mouse models of PD. We found that the mixed fibrils composed of cofilin 1 and α-synuclein are more pathogenic to mice and more prone to propagation than pure α-synuclein fibrils. Overexpression of cofilin 1 enhances the seeding and spreading of α-synuclein aggregates, and induces PD-like behavioral impairments in mice. Together, these results illustrate the important role of cofilin 1 in the pathogenicity and transmission of α-synuclein during the onset and progression of PD.

Cofilin Signaling in the CNS Physiology and Neurodegeneration

All eukaryotic cells are composed of the cytoskeleton, which plays crucial roles in coordinating diverse cellular functions such as cell division, morphology, migration, macromolecular stabilization, and protein trafficking. The cytoskeleton consists of microtubules, intermediate filaments, and actin filaments. Cofilin, an actin-depolymerizing protein, is indispensable for regulating actin dynamics in the central nervous system (CNS) development and function. Cofilin activities are spatiotemporally orchestrated by numerous extra- and intra-cellular factors. Phosphorylation at Ser-3 by kinases attenuate cofilin’s actin-binding activity. In contrast, dephosphorylation at Ser-3 enhances cofilin-induced actin depolymerization. Cofilin functions are also modulated by various binding partners or reactive oxygen species. Although the mechanism of cofilin-mediated actin dynamics has been known for decades, recent research works are unveiling the profound impacts of cofilin dysregulation in neurodegenerative pathophysiology. For instance, oxidative stress-induced increase in cofilin dephosphorylation is linked to the accumulation of tau tangles and amyloid-beta plaques in Alzheimer’s disease. In Parkinson’s disease, cofilin activation by silencing its upstream kinases increases α-synuclein-fibril entry into the cell. This review describes the molecular mechanism of cofilin-mediated actin dynamics and provides an overview of cofilin’s importance in CNS physiology and pathophysiology.

Macropinocytosis: Biology and mechanisms

Macropinocytosis is a form of endocytosis performed by ruffles and cups of the plasma membrane. These close to entrap droplets of medium into micron-sized vesicles, which are trafficked through the endocytic system, their contents digested and useful products absorbed. Macropinocytosis is constitutive in certain immune cells and stimulated in many other cells by growth factors. It occurs across the animal kingdom and in amoebae, implying a deep evolutionary history. Its scientific history goes back 100 years, but increasingly work is focused on its medical importance in the immune system, cancer cell feeding, and as a backdoor into cells for viruses and drugs. Macropinocytosis is driven by the actin cytoskeleton whose dynamics can be appreciated with lattice light sheet microscopy: this reveals a surprising variety of routes for forming macropinosomes. In Dictyostelium amoebae, macropinocytic cups are organized around domains of PIP3 and active Ras and Rac in the plasma membrane. These attract activators of the Arp2/3 complex to their periphery, creating rings of actin polymerization that shape the cups. The size of PIP3 domains is controlled by RasGAPs, such as NF1, and the lipid phosphatase, PTEN. It is likely that domain dynamics determine the shape, evolution and closing of macropinocytic structures.

Prions and prion diseases: Insights from the eye

Prion diseases are invariably fatal neurodegenerative disorders that have gained much publicity due to their transmissible nature. Sporadic Creutzfeldt-Jakob disease (sCJD) is the most common human prion disorder, with an incidence of 1 in a million. Inherited prion disorders are relatively rare, and associated with mutations in the prion protein gene. More than 50 different point mutations, deletions, and insertions have been identified so far. Most are autosomal dominant and fully penetrant. Prion disorders also occur in animals, and are of major concern because of the potential for spreading to humans. The principal pathogenic event underlying all prion disorders is a change in the conformation of prion protein (PrP^C) from a mainly α-helical to a β-sheet rich isoform, PrP-scrapie (PrP^Sc). Accumulation of PrP^Sc in the brain parenchyma is the major cause of neuronal degeneration. The mechanism by which PrP^Sc is transmitted, propagates, and causes neurodegenerative changes has been investigated over the years, and several clues have emerged. Efforts are also ongoing for identifying specific and sensitive diagnostic tests for sCJD and animal prion disorders, but success has been limited. The eye is suitable for these evaluations because it shares several anatomical and physiological features with the brain, and can be observed in vivo during disease progression. The retina, considered an extension of the central nervous system, is involved extensively in prion disorders. Accordingly, Optical Coherence Tomography and electroretinogram have shown some promise as pre-mortem diagnostic tests for human and animal prion disorders. However, a complete understanding of the physiology of PrP^C and pathobiology of PrP^Sc in the eye is essential for developing specific and sensitive tests. Below, we summarize recent progress in ocular physiology and pathology in prion disorders, and the eye as an anatomically accessible site to diagnose, monitor disease progression, and test therapeutic options.

Linking Alpha-Synuclein to the Actin Cytoskeleton: Consequences to Neuronal Function

Alpha-Synuclein (αSyn), a protein highly enriched in neurons where it preferentially localizes at the pre-synapse, has been in the spotlight because its intraneuronal aggregation is a central phenomenon in Parkinson's disease. However, the consequences of αSyn accumulation to neuronal function are not fully understood. Considering the crucial role of actin on synaptic function and the fact that dysregulation of this cytoskeleton component is emerging in neurodegenerative disorders, the impact of αSyn on actin is a critical point to be addressed. In this review we explore the link between αSyn and actin and its significance for physiology and pathology. We discuss the relevance of αSyn-actin interaction for synaptic function and highlight the actin-depolymerizing protein cofilin-1 as a key player on αSyn-induced actin dysfunction in Parkinson's disease.

Cofilin 1 promotes the aggregation and cell-to-cell transmission of α-synuclein in Parkinson's disease

The histopathological hallmark of Parkinson's disease (PD) is the presence of fibrillar aggregates referred to as Lewy bodies (LBs), in which α-synuclein is the major component. Converging evidence supports the prion-like transmission of α-synuclein aggregates in the onset and progression of PD. Intracellular α-synuclein aggregates into pathological fibrils, which can be transferred from aggregate-producing cells to aggregate-free cells, triggering neuronal injury and the progression of pathology. However, the specific mechanisms mediating the aggregation and transmission of pathological α-synuclein remain unknown. Here we show that cofilin 1 binds to α-synuclein and promotes its aggregation. The mixed fibrils consist of cofilin 1 and α-synuclein are more compact and more potent than pure α-synuclein fibrils in seeding α-synuclein aggregation. Cofilin 1 also facilitates the uptake of α-synuclein fibrils and finally induces neuronal dysfunction. Together, these observations indicate that cofilin 1 acts as a crucial mediator in the aggregation and propagation of pathological α-synuclein, contributing to the pathogenesis of PD.

Biochemical pathways mediated by KLK6 protease in breast cancer

Kallikrein-related peptidase 6 (KLK6) is a serine protease normally expressed in mammary tissue and aberrantly regulated in breast cancer. At physiological levels, KLK6 functions as a suppressor of breast cancer, while its aberrant overexpression (> 50-fold higher than normal) is characteristic of a subset of breast cancers and has been linked to accelerated growth of primary breast tumors in severe combined immunodeficiency mice (Pampalakis et al. Cancer Res 2009, 69, 3779). Here, we investigated the molecular mechanisms underlying the concentration-dependent functions of KLK6 by comparing MDA-MB-231 stable transfectants expressing increasing levels of KLK6 in in vitro and in vivo tumorigenicity assays (soft agar, xenograft growth, tail vein metastasis). Quantitative proteomics was applied to identify proteins that are altered upon re-expression of KLK6 in MDA-MB-231 at normal or constitutive levels. Overexpression of KLK6 is associated with increased metastatic ability of breast cancer cells into lungs, increased expression of certain S100 proteins (S100A4, S100A11) and keratins (KRT), and downregulation of the apoptosis-related proteases CASP7 and CASP8, and RABs. On the other hand, KLK6 re-expression at physiological levels leads to inhibition of lung metastases associated with suppression of S100 proteins (S100A4, S100A10, S100A13, S100A16) and induced CASP7 and CASP8 expression. As this is the first report that KLK6 expression is associated with S100 proteins, caspases, RABs, and KRTs, we validated this finding in clinical datasets. By integrating proteomics and microarray data from breast cancer patients, we generated two composite scores, KLK6 + S100B-S100A7 and KLK6 + S100B-S100A14-S100A16, to predict long-term survival of breast cancer patients. We present previously unknown pathways implicating KLK6 in breast cancer. The findings promise to aid our understanding of the functional roles of KLK6 in breast cancer and may yield new biomarkers for the cancer types in which KLK6 is known to be aberrantly upregulated.

Prion protein modulates endothelial to mesenchyme-like transition in trabecular meshwork cells: Implications for primary open angle glaucoma

Endothelial-to-mesenchyme-like transition (Endo-MT) of trabecular meshwork (TM) cells is known to be associated with primary open angle glaucoma (POAG). Here, we investigated whether the prion protein (PrP^C), a neuronal protein known to modulate epithelial-to-mesenchymal transition in a variety of cell types, is expressed in the TM, and plays a similar role at this site. Using a combination of primary human TM cells and human, bovine, and PrP-knock-out (PrP^−/−) mouse models, we demonstrate that PrP^C is expressed in the TM of all three species, including endothelial cells lining the Schlemm’s canal. Silencing of PrP^C in primary human TM cells induces aggregation of β1-integrin and upregulation of α-smooth muscle actin, fibronectin, collagen 1A, vimentin, and laminin, suggestive of transition to a mesenchyme-like phenotype. Remarkably, intraocular pressure is significantly elevated in PrP^−/− mice relative to wild-type controls, suggesting reduced pliability of the extracellular matrix and increased resistance to aqueous outflow in the absence of PrP^C. Since PrP^C is cleaved by members of the disintegrin and matrix-metalloprotease family that are increased in the aqueous humor of POAG arising from a variety of conditions, it is likely that concomitant cleavage of PrP^C exaggerates and confounds the pathology by inducing Endo-MT-like changes in the TM.

Intersection of pathological tau and microglia at the synapse

Tauopathies are a heterogenous class of diseases characterized by cellular accumulation of aggregated tau and include diseases such as Alzheimer’s disease (AD), progressive supranuclear palsy and chronic traumatic encephalopathy. Tau pathology is strongly linked to neurodegeneration and clinical symptoms in tauopathy patients. Furthermore, synapse loss is an early pathological event in tauopathies and is the strongest correlate of cognitive decline. Tau pathology is additionally associated with chronic neuroinflammatory processes, such as reactive microglia, astrocytes, and increased levels of pro-inflammatory molecules (e.g. complement proteins, cytokines). Recent studies show that as the principal immune cells of the brain, microglia play a particularly important role in the initiation and progression of tau pathology and associated neurodegeneration. Furthermore, AD risk genes such as Triggering receptor expressed on myeloid cells 2 (TREM2) and Apolipoprotein E (APOE) are enriched in the innate immune system and modulate the neuroinflammatory response of microglia to tau pathology. Microglia can play an active role in synaptic dysfunction by abnormally phagocytosing synaptic compartments of neurons with tau pathology. Furthermore, microglia are involved in synaptic spreading of tau – a process which is thought to underlie the progressive nature of tau pathology propagation through the brain. Spreading of pathological tau is also the predominant target for tau-based immunotherapy. Active tau vaccines, therapeutic tau antibodies and other approaches targeting the immune system are actively explored as treatment options for AD and other tauopathies. This review describes the role of microglia in the pathobiology of tauopathies and the mechanism of action of potential therapeutics targeting the immune system in tauopathies.

Mechanistic insights into Nav1.7-dependent regulation of rat prostate cancer cell invasiveness revealed by toxin probes and proteomic analysis

Voltage-gated sodium channels are involved in tumor metastasis, as potentiating or attenuating their activities affects the migration and invasion process of tumor cells. In the present study, we tested the effect of two peptide toxins, JZTX-I and HNTX-III which function as Nav1.7 activator and inhibitor, respectively, on the migration and invasion ability of prostate cancer (PCa) cell line Mat-LyLu. These two peptides showed opposite effects, and subsequently a comparative proteomic analysis characterized 64 differentially expressed membrane proteins from the JZTX-I- and HNTX-III-treated groups. Among these, 15 proteins were down-regulated and 49 proteins were up-regulated in the HNTX-III group. Bioinformatic analysis showed eight proteins are cytoskeleton proteins or related regulators, which might play important roles in the metastasis of Mat-LyLu cells. The altered expressions of four of these proteins, fascin, muskelin, annexin A2, and cofilin-1, were validated by western blot analysis. Further function network analysis of these proteins revealed that the Rho family GTPases RhoA and Rac1 might be of particular importance for the rat PCa cell invasion. Pharmacological data revealed that JZTX-I and HNTX-III could modulate the Rho signaling pathway in a Nav1.7-dependent manner. In summary, this study suggests that the Nav1.7-dependent regulation of Rho GTPase activity plays a vital role in Mat-LyLu cell migration and invasion and provides new insights into the treatment of PCa.

PKCδ stimulates macropinocytosis via activation of SSH1-cofilin pathway

Macropinocytosis is an actin-dependent endocytic mechanism mediating internalization of extracellular fluid and associated solutes into cells. The present study was designed to identify the specific protein kinase C (PKC) isoform(s) and downstream effectors regulating actin dynamics during macropinocytosis. We utilized various cellular and molecular biology techniques, pharmacological inhibitors and genetically modified mice to study the signaling mechanisms mediating macropinocytosis in macrophages. The qRT-PCR experiments identified PKCδ as the predominant PKC isoform in macrophages. Scanning electron microscopy and flow cytometry analysis of FITC-dextran internalization demonstrated the functional role of PKCδ in phorbol ester- and hepatocyte growth factor (HGF)-induced macropinocytosis. Western blot analysis demonstrated that phorbol ester and HGF stimulate activation of slingshot phosphatase homolog 1 (SSH1) and induce cofilin Ser-3 dephosphorylation via PKCδ in macrophages. Silencing of SSH1 inhibited cofilin dephosphorylation and macropinocytosis stimulation. Interestingly, we also found that incubation of macrophages with BMS-5, a potent inhibitor of LIM kinase, does not stimulate macropinocytosis. In conclusion, the findings of the present study demonstrate a previously unidentified mechanism by which PKCδ via activation of SSH1 and cofilin dephosphorylation stimulates membrane ruffle formation and macropinocytosis. The results of the present study may contribute to a better understanding of the regulatory mechanisms during macrophage macropinocytosis.