uPA-uPAR molecular complex is involved in cell signaling during neuronal migration and neuritogenesis

IL4 stimulated macrophages promote axon regeneration after peripheral nerve injury by secreting uPA to stimulate uPAR upregulated in injured axons

Accumulating evidences suggest that M2 macrophages are involved with repair processes in the nervous system. However, whether M2 macrophages can promote axon regeneration by directly stimulating axons nor its precise molecular mechanism remains elusive. Here, the current study demonstrated that typical M2 macrophages, which were generated by IL4 simulation, had the capacity to stimulate axonal growth by their direct effect on axons and that the graft of IL4 stimulated macrophages into the region of Wallerian degeneration enhanced axon regeneration and improved functional recovery after PNI. Importantly, uPA (urokinase plasminogen activator)-uPA receptor (uPAR) was identified as the central axis underlying the axon regeneration effect of IL4 stimulated macrophages. IL4 stimulated macrophages secreted uPA, and its inhibition abolished their axon regeneration effect. Injured but not intact axons expressed uPAR to be sensitive to uPA. These results unveil a cellular and molecular mechanism underlying the macrophage related axon regeneration and provide a basis of a novel therapy for PNI.

Modulation of Cellular Function by the Urokinase Receptor Signalling: A Mechanistic View

Urokinase-type plasminogen activator receptor (uPAR or CD87) is a glycosyl-phosphatidyl-inositol anchored (GPI) membrane protein. The uPAR primary ligand is the serine protease urokinase (uPA), converting plasminogen into plasmin, a broad spectrum protease, active on most extracellular matrix components. Besides uPA, the uPAR binds specifically also to the matrix protein vitronectin and, therefore, is regarded also as an adhesion receptor. Complex formation of the uPAR with diverse transmembrane proteins, including integrins, formyl peptide receptors, G protein-coupled receptors and epidermal growth factor receptor results in intracellular signalling. Thus, the uPAR is a multifunctional receptor coordinating surface-associated pericellular proteolysis and signal transduction, thereby affecting physiological and pathological mechanisms. The uPAR-initiated signalling leads to remarkable cellular effects, that include increased cell migration, adhesion, survival, proliferation and invasion. Although this is beyond the scope of this review, the uPA/uPAR system is of great interest to cancer research, as it is associated to aggressive cancers and poor patient survival. Increasing evidence links the uPA/uPAR axis to epithelial to mesenchymal transition, a highly dynamic process, by which epithelial cells can convert into a mesenchymal phenotype. Furthermore, many reports indicate that the uPAR is involved in the maintenance of the stem-like phenotype and in the differentiation process of different cell types. Moreover, the levels of anchor-less, soluble form of uPAR, respond to a variety of inflammatory stimuli, including tumorigenesis and viral infections. Finally, the role of uPAR in virus infection has received increasing attention, in view of the Covid-19 pandemics and new information is becoming available. In this review, we provide a mechanistic perspective, via the detailed examination of consolidated and recent studies on the cellular responses to the multiple uPAR activities.

Mechanical Aspects of Angiogenesis

Simple Summary

The formation of new blood vessels from already existing ones is a process of high clinical relevance, since it is of great importance for both physiological and pathological processes. In regard to tumors, the process is crucial, since it ensures the supply with nutrients and the growth of the tumor. The influence of mechanical factors on this biological process is an emerging field. Until now, the shear force of the blood flow has been considered the main mechanical parameter during angiogenesis. This review article provides an overview of further mechanical cues, with particular focus on the surrounding extracellular matrix impacting the cell behavior and, thus, regulating angiogenesis. This underlines the enormous importance of the mechanical properties of the extracellular matrix on cell biological processes and shows how changing the mechanics of the extracellular matrix could be used as a possible therapeutic approach in cancer therapy.

Abstract

Angiogenesis is of high clinical relevance as it plays a crucial role in physiological (e.g., tissue regeneration) and pathological processes (e.g., tumor growth). Besides chemical signals, such as VEGF, the relationship between cells and the extracellular matrix (ECM) can influence endothelial cell behavior during angiogenesis. Previously, in terms of the connection between angiogenesis and mechanical factors, researchers have focused on shear forces due to blood flow. However, it is becoming increasingly important to include the direct influence of the ECM on biological processes, such as angiogenesis. In this context, we focus on the stiffness of the surrounding ECM and the adhesion of cells to the ECM. Furthermore, we highlight the mechanical cues during the main stages of angiogenesis: cell migration, tip and stalk cells, and vessel stabilization. It becomes clear that the different stages of angiogenesis require various chemical and mechanical cues to be modulated by/modulate the stiffness of the ECM. Thus, changes of the ECM during tumor growth represent additional potential dysregulations of angiogenesis in addition to erroneous biochemical signals. This awareness could be the basis of therapeutic approaches to counteract specific processes in tumor angiogenesis.

PLAUR as a Potential Biomarker Associated with Immune Infiltration in Bladder Urothelial Carcinoma

Background

Bladder urothelial carcinoma (BLCA) is one of the most lethal and aggressive malignancies of genitourinary system that affects human health. The urokinase plasminogen activator receptor (PLAUR) plays essential roles in tumorigenesis and immune modulation, and its aberrant expression is closely correlated with cancer progression. However, whether PLAUR has the potential to be one promising biomarker or immunotherapy target for BLCA is unknown.

Methodology

Various online databases were applied to assess the expression profile and prognostic value of PLAUR, as well as its correlation with immune infiltration in BLCA, including Oncomine, PrognoScan, TCGA, cBioPortal, TIMER, TISIDB, UALCAN, and MethSurv. The expression of PLAUR in BLCA was confirmed with ELISA assay for serum samples and immunohistochemistry for tissue samples.

Results

The results showed that the expression of PLAUR was elevated in BLCA, which was further confirmed by ELISA and immunohistochemistry. Patients with higher PLAUR level were predicted to have lower overall survival and disease specific survival rates, which were not impacted by the genetic alterations of PLAUR. In addition, the expression of PLAUR was positively associated with immune infiltration, and also the expression levels of gene markers of various immune cells. The negative correlation between PLAUR expression and PLAUR methylation level was observed, among which PLAUR expression was positively correlated with the abundance of 28 kinds of tumor-infiltrating lymphocytes, while PLAUR methylation level was negatively correlated with the abundance of 11 types of tumor-infiltrating lymphocytes. Moreover, the methylation level of PLAUR was closely correlated with patients’ clinicopathological features, and hypomethylation of PLAUR was associated with better outcomes of BLCA patients.

Conclusion

These findings suggested that PLAUR had the potential to serve as a valuable detection and prognostic biomarker or immunotherapeutic target for BLCA.

Bioinformatic analysis identifies potential key genes of epilepsy

Background

Epilepsy is one of the most common brain disorders worldwide. It is usually hard to be identified properly, and a third of patients are drug-resistant. Genes related to the progression and prognosis of epilepsy are particularly needed to be identified.

Methods

In our study, we downloaded the Gene Expression Omnibus (GEO) microarray expression profiling dataset GSE143272. Differentially expressed genes (DEGs) with a fold change (FC) >1.2 and a P-value <0.05 were identified by GEO2R and grouped in male, female and overlapping DEGs. Functional enrichment analysis and Protein-Protein Interaction (PPI) network analysis were performed.

Results

In total, 183 DEGs overlapped (77 ups and 106 downs), 302 DEGs (185 ups and 117 downs) in the male dataset, and 750 DEGs (464 ups and 286 downs) in the female dataset were obtained from the GSE143272 dataset. These DEGs were markedly enriched under various Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) terms. 16 following hub genes were identified based on PPI network analysis: ADCY7, C3AR1, DEGS1, CXCL1 in male-specific DEGs, TOLLIP, ORM1, ELANE, QPCT in female-specific DEGs and FCAR, CD3G, CLEC12A, MOSPD2, CD3D, ALDH3B1, GPR97, PLAUR in overlapping DEGs.

Conclusion

This discovery-driven study may be useful to provide a novel insight into the diagnosis and treatment of epilepsy. However, more experiments are needed in the future to study the functional roles of these genes in epilepsy.

Urokinase-type plasminogen activator promotes N-cadherin-mediated synaptic recovery in the ischemic brain

Urokinase-type plasminogen activator (uPA) is a serine proteinase that catalyzes the generation of plasmin on the cell surface and activates cell signaling pathways that promote remodeling and repair. Neuronal cadherin (NCAD) is a transmembrane protein that in the mature brain mediates the formation of synaptic contacts in the II/III and V cortical layers. Our studies show that uPA is preferentially found in the II/III and V cortical laminae of the gyrencephalic cortex of the non-human primate. Furthermore, we found that in murine cerebral cortical neurons and induced pluripotent stem cell (iPSC)-derived neurons prepared from healthy human donors, most of this uPA is associated with pre-synaptic vesicles. Our in vivo experiments revealed that in both, the gyrencephalic cortex of the non-human primate and the lissecephalic murine brain, cerebral ischemia decreases the number of intact synaptic contacts and the expression of uPA and NCAD in a band of tissue surrounding the necrotic core. Additionally, our in vitro data show that uPA induces the synthesis of NCAD in cerebral cortical neurons, and in line with these observations, intravenous treatment with recombinant uPA three hours after the onset of cerebral ischemia induces NCAD-mediated repair of synaptic contacts in the area surrounding the necrotic core.

Urokinase-type plasminogen activator-mediated crosstalk between N-cadherin and β-catenin promotes wound healing

Urokinase-type plasminogen activator (uPA; encoded by Plau) is a serine proteinase that, in the central nervous system, induces astrocytic activation. β-Catenin is a protein that links the cytoplasmic tail of cadherins to the actin cytoskeleton, thus securing the formation of cadherin-mediated cell adhesion complexes. Disruption of cell-cell contacts leads to the detachment of β-catenin from cadherins, and β-catenin is then degraded by the proteasome following its phosphorylation by GSK3β. Here, we show that astrocytes release uPA following a scratch injury, and that this uPA promotes wound healing via a plasminogen-independent mechanism. We found that uPA induces the detachment of β-catenin from the cytoplasmic tail of N-cadherin (NCAD; also known as CDH2) by triggering its phosphorylation at Tyr654. Surprisingly, this is not followed by degradation of β-catenin because uPA also induces the phosphorylation of the low density lipoprotein receptor-related protein 6 (LRP6) at Ser1490, which then blocks the kinase activity of GSK3β. Our work indicates that the ensuing cytoplasmic accumulation of β-catenin is followed by its nuclear translocation and β-catenin-triggered transcription of the receptor for uPA (Plaur), which in turn is required for uPA to induce astrocytic wound healing.

Plasminogen Activators in Neurovascular and Neurodegenerative Disorders

The neurovascular unit (NVU) is a dynamic structure assembled by endothelial cells surrounded by a basement membrane, pericytes, astrocytes, microglia and neurons. A carefully coordinated interplay between these cellular and non-cellular components is required to maintain normal neuronal function, and in line with these observations, a growing body of evidence has linked NVU dysfunction to neurodegeneration. Plasminogen activators catalyze the conversion of the zymogen plasminogen into the two-chain protease plasmin, which in turn triggers a plethora of physiological events including wound healing, angiogenesis, cell migration and inflammation. The last four decades of research have revealed that the two mammalian plasminogen activators, tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), are pivotal regulators of NVU function during physiological and pathological conditions. Here, we will review the most relevant data on their expression and function in the NVU and their role in neurovascular and neurodegenerative disorders.

The fibrinolytic system in the cornea: A key regulator of corneal wound healing and biological defense

The cornea is a relatively unique tissue in the body in that it possesses specific features such as a lack of blood vessels that contribute to its transparency. The cornea is supplied with soluble blood components such as albumin, globulin, and fibrinogen as well as with nutrients, oxygen, and bioactive substances by diffusion from aqueous humor and limbal vessels as well as a result of its exposure to tear fluid. The healthy cornea is largely devoid of cellular components of blood such as polymorphonuclear leukocytes, monocytes-macrophages, and platelets. The location of the cornea at the ocular surface renders it susceptible to external insults, and its avascular nature necessitates the operation of healing and defense mechanisms in a manner independent of a direct blood supply. The fibrinolytic system, which was first recognized for its role in the degradation of fibrin clots in the vasculature, has also been found to contribute to various biological processes outside of blood vessels. Fibrinolytic factors thus play an important role in biological defense of the cornea. In this review, we address the function of the fibrinolytic system in corneal defense including wound healing and the inflammatory response.

Urokinase receptor deficiency results in EGFR-mediated failure to transmit signals for cell survival and neurite formation in mouse neuroblastoma cells

Urokinase-type plasminogen activator uPA and its receptor (uPAR) are the central players in extracellular matrix proteolysis, which facilitates cancer invasion and metastasis. EGFR is one of the important components of uPAR interactome. uPAR/EGFR interaction controls signaling pathways that regulate cell survival, proliferation and migration. We have previously established that uPA binding to uPAR stimulates neurite elongation in neuroblastoma cells, while blocking uPA/uPAR interaction induces neurite branching and new neurite formation. Here we demonstrate that blocking the uPA binding to uPAR with anti-uPAR antibody decreases the level of pEGFR and its downstream pERK1/2, but does increase phosphorylation of Akt, p38 and c-Src Since long-term uPAR blocking results in a severe DNA damage, accompanied by PARP-1 proteolysis and Neuro2a cell death, we surmise that Akt, p38 and c-Src activation transmits a pro-apoptotic signal, rather than a survival. Serum deprivation resulting in enhanced neuritogenesis is accompanied by an upregulated uPAR mRNA expression, while EGFR mRNA remains unchanged. EGFR activation by EGF stimulates neurite growth only in uPAR-overexpressing cells but not in control or uPAR-deficient cells. In addition, AG1478-mediated inhibition of EGFR activity impedes neurite growth in control and uPAR-deficient cells, but not in uPAR-overexpressing cells. Altogether these data implicate uPAR as an important regulator of EGFR and ERK1/2 signaling, representing a novel mechanism which implicates urokinase system in neuroblastoma cell survival and differentiation.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

Urokinase receptor regulates nerve regeneration through its interaction with α5β1-integrin

PURPOSE

Urokinase receptor (uPAR) promotes extracellular matrix proteolysis, regulates adhesion and cell migration, transduces intracellular signals through interactions with the lateral partners. The expression of uPAR and urokinase (uPA) is significantly upregulated in peripheral nerves after injury, however, little is known about uPAR function in nerve regeneration or the molecular mechanisms involved. The purpose of this study is to investigate the role of uPAR in nerve regeneration after traumatic injury of n. Peroneus communis in uPA-/-, uPAR-/- or control mice (WT) and in neuritogenesis in an in vitro Neuro 2A cell model.

RESULTS

Electrophysiological analysis indicates that nerve recovery is significantly impaired in uPAR-/- mice, but not in uPA-/- mice. These data correlate with the reduced amount of NF200-positive axons in regenerating nerves from uPAR-/- mice compared to uPA-/- or control mice. There is an increase in uPAR expression and remarkable colocalization of uPAR with α5 and β1 integrin in uPA-/- mice in recovering nerves, pointing to a potential link between uPAR and its lateral partner α5β1-integrin. Using an in vitro model of neuritogenesis and α325 blocking peptide, which abrogates uPAR-α5β1 interaction in Neuro 2A cells but has no effect on their function, we have further confirmed the significance of uPAR-α5β1 interaction.

CONCLUSION

Taken together, we report evidence pointing to an important role of uPAR, rather than uPA, in peripheral nerve recovery and neuritogenesis.

Urokinase-type plasminogen activator (uPA) regulates the expression and function of growth-associated protein 43 (GAP-43) in the synapse

Growth-associated protein 43 (GAP-43) plays a central role in the formation of presynaptic terminals, synaptic plasticity, and axonal growth and regeneration. During development, GAP-43 is found in axonal extensions of most neurons. In contrast, in the mature brain, its expression is restricted to a few presynaptic terminals and scattered axonal growth cones. Urokinase-type plasminogen activator (uPA) is a serine proteinase that, upon binding to its receptor (uPAR), catalyzes the conversion of plasminogen into plasmin and activates signaling pathways that promote cell migration, proliferation, and survival. In the developing brain, uPA induces neuritogenesis and neuronal migration. In contrast, the expression and function of uPA in the mature brain are poorly understood. However, recent evidence reveals that different forms of injury induce release of uPA and expression of uPAR in neurons and that uPA/uPAR binding triggers axonal growth and synapse formation. Here we show that binding of uPA to uPAR induces not only the mobilization of GAP-43 from the axonal shaft to the presynaptic terminal but also its activation in the axonal bouton by PKC-induced calcium-dependent phosphorylation at Ser-41 (pGAP-43). We found that this effect requires open presynaptic N-methyl-d-aspartate receptors but not plasmin generation. Furthermore, our work reveals that, following its activation by uPA/uPAR binding, pGAP-43 colocalizes with presynaptic vesicles and triggers their mobilization to the synaptic release site. Together, these data reveal a novel role of uPA as an activator of the synaptic vesicle cycle in cerebral cortical neurons via its ability to induce presynaptic recruitment and activation of GAP-43.

Urokinase-Type Plasminogen Activator System in Norm and in Life-Threatening Processes (Review)

The multifunctional urokinase-type plasminogen activator system (uPA-system) includes serine proteinase — uPA or urokinase, its receptor (uPAR) and two inhibitors (PAI-1 and PAI-2). The review discusses the structural features and involvement of the system components in the development of life-threatening processes including carcinogenesis, inflammation, neurogenesis and fibrinolysis, in regulation of which the destruction of extracellular matrix (ECM), cell mobility and signaling inside and outside the cell play a decisive role. uPA triggers the processes by activating the plasminogen and its convertion into plasmin involved in the activation of matrix metalloproteinases (MMPs) in addition to the regulation of fibrinolysis. MMPs can hydrolyze all the major ECM components and therefore play a key role in invasion, metastasis, and cell mobility. MMPs activates a cassette of biologically active regulatory molecules and release them from ECM. uPAR, PAI-1 and PAI-2 are responsible for regulation of the uPA activity. In addition, being a signaling receptor, uPAR along with MMPs lead to the stimulation of a number of signaling pathways that are associated with the regulation of proliferation, apoptosis, adhesion, growth and migration of cells contributing to tumor progression, inflammation, chemotaxis, and angiogenesis. Effective participation of the uPA system components in ECM destruction and regulation of intracellular and extracellular signaling pathways demonstrates that the system significantly contributes to the regulation of various physiological and pathological processes.

The developing optic tectum: An asymmetrically organized system and the need for a redefinition of the notion of sensitive period

The present article summarizes the main events involved in the isthmic organizer and optic tectum determination and analyses how optic tectum patterning is translated, by the organized operation of several specific cell behaviors, into the terminally differentiated optic tectum. The paper proposes that this assembling of temporally/spatially organized cell behaviors could be incorporated into a wider notion of patterning and that, given the asymmetric organization of the developing optic tectum, the notion of "sensitive period" does not capture the whole complexity of midbrain development and the pathogenesis of congenital disorders. The cell behaviors involved in the optic tectum development are organized in time and space by the isthmic organizer. A comprehensive description of the normal optic tectum development, and also its alterations, should consider both domains. Significantly, the identity of each neuronal cohort depends critically on its "time and place of birth". Both parameters must be considered at once to explain how the structural and functional organization of the optic tectum is elaborated. The notion of "patterning" applies only to the early events of the optic tectum development. Besides, the notion of "sensitive period" considers only a temporal domain and disregards the asymmetric organization of the developing optic tectum. The present paper proposes that these notions might be re-defined: (a) a wider meaning of the term patterning and (b) a replacement of the term "sensitive period" by a more precise concept of "sensitive temporal/spatial window".

Urokinase-type plasminogen activator (uPA) promotes ezrin-mediated reorganization of the synaptic cytoskeleton in the ischemic brain

Synaptic repair in the ischemic brain is a complex process that requires reorganization of the actin cytoskeleton. Ezrin, radixin, and moesin (ERM) are a group of evolutionarily conserved proteins that link the plasma membrane to the actin cytoskeleton and act as scaffolds for signaling transduction. Urokinase-type plasminogen activator (uPA) is a serine proteinase that upon binding to the urokinase-type plasminogen activator receptor (uPAR) catalyzes the conversion of plasminogen into plasmin on the cell surface and activates intracellular signaling pathways. Early studies indicate that uPA and uPAR expression increase during the recovery phase from an ischemic stroke and that uPA binding to uPAR promotes neurorepair in the ischemic brain. The in vitro and in vivo studies presented here show that either the release of neuronal uPA or treatment with recombinant uPA induces the local synthesis of ezrin in the synapse and the recruitment of β3-integrin to the postsynaptic density (PSD) of cerebral cortical neurons by a plasminogen-independent mechanism. We found that β3-integrin has a double effect on ezrin, inducing its recruitment to the PSD via the intercellular adhesion molecule-5 (ICAM-5) and its subsequent activation by phosphorylation at Thr-567. Finally, our data indicate that by triggering the reorganization of the actin cytoskeleton in the postsynaptic terminal, active ezrin induces the recovery of dendritic spines and synapses that have been damaged by an acute ischemic stroke. In summary, our data show that uPA-uPAR binding promotes synaptic repair in the ischemic brain via ezrin-mediated reorganization of the actin cytoskeleton in the postsynaptic terminal.

hiPSC-derived neural stem cells from patients with schizophrenia induce an impaired angiogenesis

Schizophrenia is a neurodevelopmental disease characterized by cerebral connectivity impairment and loss of gray matter. It was described in adult schizophrenia patients (SZP) that concentration of VEGFA, a master angiogenic factor, is decreased. Recent evidence suggests cerebral hypoperfusion related to a dysfunctional Blood Brain Barrier (BBB) in SZP. Since neurogenesis and blood-vessel formation occur in a coincident and coordinated fashion, a defect in neurovascular development could result in increased vascular permeability and, therefore, in poor functionality of the SZP's neurons. Here, we characterized the conditioned media (CM) of human induced Pluripotent Stem Cells (hiPSC)-derived Neural Stem Cells of SZP (SZP NSC) versus healthy subjects (Ctrl NSC), and its impact on angiogenesis. Our results reveal that SZP NSC have an imbalance in the secretion and expression of several angiogenic factors, among them non-canonical neuro-angiogenic guidance factors. SZP NSC migrated less and their CM was less effective in inducing migration and angiogenesis both in vitro and in vivo. Since SZP originates during embryonic brain development, our findings suggest a defective crosstalk between NSC and endothelial cells (EC) during the formation of the neuro-angiogenic niche.

Quercetin Has Antimetastatic Effects on Gastric Cancer Cells via the Interruption of uPA/uPAR Function by Modulating NF-κb, PKC-δ, ERK1/2, and AMPKα

Gastric cancer (GC) is a malignancy with few effective treatment options after metastasis occurs. Quercetin (Qu) intake has been associated with reduced incidence and slow development of GC, probably due to its anti-proliferative and apoptotic effects, but it is unclear whether Qu can inhibit the metastatic activity. The urokinase plasminogen activator (uPA)/uPA receptor (uPAR) system plays an important role in cancer metastasis. In this study, we measured both uPA activity and uPAR expression in GC and pericarcinous tissues, and we investigated the correlation between uPAR expression and the migratory and invasive activities of various GC cell lines. GC BGC823 and AGS cells were subjected to treatment with 10 μM Qu for 72 hours and uPAR knockdown, alone or in combination, before evaluating cell metastasis. The results showed that uPA activity and uPAR expression were higher in GC tissues than in pericarcinous tissues. Migratory and invasive activities of GC cell lines positively correlated with uPAR expression. Qu treatment decreased BGC823 and AGS cell migration and invasion, accompanied by reduced uPA and uPAR protein expression. Both Qu treatment and uPAR knockdown decreased matrix metalloproteinase-2 and -9 activity and blocked Pak1-Limk1-cofilin signaling. Qu treatment was associated with inhibition of NF-κb, PKC-δ, and ERK1/2, and with AMPKα activation. Specific inhibitors of NF-κb, PKC, and ERK1/2, and an AMPKα activator suppressed uPA and uPAR expression in GC cells. Collectively, Qu showed an antimetastatic effect on GC cells via the interruption of uPA/uPAR function and modulation of NF-κb, PKC-δ, ERK1/2, and AMPKα. This suggests that Qu is a promising agent against GC metastasis.

Urokinase-type plasminogen activator modulates mammalian circadian clock phase regulation in tissue-type plasminogen activator knockout mice

Glutamate phase shifts the circadian clock in the mammalian suprachiasmatic nucleus (SCN) by activating NMDA receptors. Tissue-type plasminogen activator (tPA) gates phase shifts by activating plasmin to generate m(ature) BDNF, which binds TrkB receptors allowing clock phase shifts. Here, we investigate phase shifting in tPA knockout (tPA^-/- ; B6.129S2-Plat^tm1Mlg /J) mice, and identify urokinase-type plasminogen activator (uPA) as an additional circadian clock regulator. Behavioral activity rhythms in tPA^-/- mice entrain to a light-dark (LD) cycle and phase shift in response to nocturnal light pulses with no apparent loss in sensitivity. When the LD cycle is inverted, tPA^-/- mice take significantly longer to entrain than C57BL/6J wild-type (WT) mice. SCN brain slices from tPA^-/- mice exhibit entrained neuronal activity rhythms and phase shift in response to nocturnal glutamate with no change in dose-dependency. Pre-treating slices with the tPA/uPA inhibitor, plasminogen activator inhibitor-1 (PAI-1), inhibits glutamate-induced phase delays in tPA^-/- slices. Selective inhibition of uPA with UK122 prevents glutamate-induced phase resetting in tPA^-/- but not WT SCN slices. tPA expression is higher at night than the day in WT SCN, while uPA expression remains constant in WT and tPA^-/- slices. Casein-plasminogen zymography reveals that neither tPA nor uPA total proteolytic activity is under circadian control in WT or tPA^-/- SCN. Finally, tPA^-/- SCN tissue has lower mBDNF levels than WT tissue, while UK122 does not affect mBDNF levels in either strain. Together, these results suggest that either tPA or uPA can support photic/glutamatergic phase shifts of the SCN circadian clock, possibly acting through distinct mechanisms.

Effects of Fluoxetine on Human Embryo Development

The use of antidepressant treatment during pregnancy is increasing, and selective serotonin reuptake inhibitors (SSRIs) are the most widely prescribed antidepressants in pregnant women. Serotonin plays a role in embryogenesis, and serotonin transporters are expressed in two-cell mouse embryos. Thus, the aim of the present study was to evaluate whether fluoxetine, one of the most prescribed SSRI antidepressant world-wide, exposure influences the timing of different embryo developmental stages, and furthermore, to analyze what protein, and protein networks, are affected by fluoxetine in the early embryo development. Human embryos (n = 48) were randomly assigned to treatment with 0.25 or 0.5 μM fluoxetine in culture medium. Embryo development was evaluated by time-lapse monitoring. The fluoxetine-induced human embryo proteome was analyzed by shotgun mass spectrometry. Protein secretion from fluoxetine-exposed human embryos was analyzed by use of high-multiplex immunoassay. The lower dose of fluoxetine had no influence on embryo development. A trend toward reduced time between thawing and start of cavitation was noted in embryos treated with 0.5 μM fluoxetine (p = 0.065). Protein analysis by shotgun mass spectrometry detected 45 proteins that were uniquely expressed in fluoxetine-treated embryos. These proteins are involved in cell growth, survival, proliferation, and inflammatory response. Culturing with 0.5 μM, but not 0.25 μM fluoxetine, caused a significant increase in urokinase-type plasminogen activator (uPA) in the culture medium. In conclusion, fluoxetine has marginal effects on the timing of developmental stages in embryos, but induces expression and secretion of several proteins in a manner that depends on dose. For these reasons, and in line with current guidelines, the lowest possible dose of SSRI should be used in pregnant women who need to continue treatment.

Urokinase and urokinase receptor participate in regulation of neuronal migration, axon growth and branching

PURPOSE

Recent findings indicate the significant contribution of urokinase and urokinase receptor (uPA and uPAR) in the processes of nerve regeneration, however, their role in axonal growth and branching is unclear. Using a 3D model of mouse Dorsal Root Ganglia (DRG) explants, differentiated into neurons Neuro 2a cells and transgenic mice lacking the urokinase gene, we studied the involvement of the uPA/uPAR system in the neural cell migration, neurite outgrowth, elongation and branching.

RESULTS

uPA and uPAR are expressed in the growth cones of axons. Using an ex vivo model of DRG explants in Matrigel we have found that uPA inhibition attenuates neural cell migration and axonal growth, pointing to an important role of urokinase in these processes. Apparently, uPA mediates its effects through its specific receptor uPAR: anti-uPAR antibody, which blocks the uPA binding to uPAR, stimulates axon branching and attenuates neural cell migration from DRG explants. Simultaneous inhibition of uPA and uPAR almost completely prevents the axonal outgrowth from explants into the Matrigels. Experiments in vitro using Neuro 2a cells differentiated into neurons demonstrate that administration of exogenous uPA increases the neurite growth rate (elongation), most likely via the interaction of uPA with uPAR. Blocking of uPAR stimulates neurite formation and enhances branching of preexisting neurites. The results obtained on DRG explants from transgenic mice lacking uPA gene support the assumption that uPA stimulates neurite growth via uPA/uPAR interaction and uPAR role in axons branching and neural cell migration.

CONCLUSIONS

The uPA/uPAR system plays an essential role in neural cell migration, axonal growth and branching.

Rho-Associated Kinase Inhibitors Promote Microglial Uptake Via the ERK Signaling Pathway

Microglia are immunocompetent cells in the central nervous system that take up tissue debris and pathogens. Rho-associated kinase (ROCK) has been identified as an important regulator of uptake, proliferation, secretion, and differentiation in a number of cell types. Although ROCK plays critical roles in the microglial secretion of inflammatory factors, migration, and morphology, its effects on microglial uptake activity have not been well characterized. In the present study, we found that treatment of BV2 microglia and primary microglia with the ROCK inhibitors Y27632 and fasudil increased uptake activity and was associated with morphological changes. Furthermore, western blots showed that this increase in uptake activity was mediated through the extracellular-signal-regulated kinase (ERK) signaling cascade, indicating the importance of ROCK in regulating microglial uptake activity.