Role of PI3K/Akt and MEK/ERK Signalling in cAMP/Epac-Mediated Endothelial Barrier Stabilisation

Resveratrol and its metabolites elicit neuroprotection via high-affinity binding to the laminin receptor at low nanomolar concentrations

Resveratrol prevents various neurodegenerative diseases in animal models despite reaching only low nanomolar concentrations in the brain after oral administration. In this study, based on the quenching of intrinsic tryptophan fluorescence and molecular docking, we found that trans-resveratrol, its conjugates (glucuronide and sulfate), and dihydro-resveratrol (intestinal microbial metabolite) bind with high affinities (Kd, 0.2-2 nm) to the peptide G palindromic sequence (near glycosaminoglycan-binding motif) of the 67-kDa laminin receptor (67LR). Preconditioning with low concentrations (0.01-10 nm) of these polyphenols, especially resveratrol-glucuronide, protected neuronal cells from death induced by serum withdrawal via activation of cAMP-mediated signaling pathways. This protection was prevented by a 67LR-blocking antibody, suggesting a role for this cell-surface receptor in neuroprotection by resveratrol metabolites.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Modular Hub Genes in DNA Microarray Suggest Potential Signaling Pathway Interconnectivity in Various Glioma Grades

Gliomas have displayed significant challenges in oncology due to their high degree of invasiveness, recurrence, and resistance to treatment strategies. In this work, the key hub genes mainly associated with different grades of glioma, which were represented by pilocytic astrocytoma (PA), oligodendroglioma (OG), anaplastic astrocytoma (AA), and glioblastoma multiforme (GBM), were identified through weighted gene co-expression network analysis (WGCNA) of microarray datasets retrieved from the Gene Expression Omnibus (GEO) database. Through this, four highly correlated modules were observed to be present across the PA (GSE50161), OG (GSE4290), AA (GSE43378), and GBM (GSE36245) datasets. The functional annotation and pathway enrichment analysis done through the Database for Annotation, Visualization, and Integrated Discovery (DAVID) showed that the modules and hub genes identified were mainly involved in signal transduction, transcription regulation, and protein binding, which collectively deregulate several signaling pathways, mainly PI3K/Akt and metabolic pathways. The involvement of several hub genes primarily linked to other signaling pathways, including the cAMP, MAPK/ERK, Wnt/β-catenin, and calcium signaling pathways, indicates potential interconnectivity and influence on the PI3K/Akt pathway and, subsequently, glioma severity. The Drug Repurposing Encyclopedia (DRE) was used to screen for potential drugs based on the up- and downregulated hub genes, wherein the synthetic progestin hormones norgestimate and ethisterone were the top drug candidates. This shows the potential neuroprotective effect of progesterone against glioma due to its influence on EGFR expression and other signaling pathways. Aside from these, several experimental and approved drug candidates were also identified, which include an adrenergic receptor antagonist, a PPAR-γ receptor agonist, a CDK inhibitor, a sodium channel blocker, a bradykinin receptor antagonist, and a dopamine receptor agonist, which further highlights the gene network as a potential therapeutic avenue for glioma.

Methylglyoxal-Derived Nucleoside Adducts Drive Vascular Dysfunction in a RAGE-Dependent Manner

Diabetic kidney disease (DKD) is a leading cause of death in patients with diabetes. An early precursor to DKD is endothelial cell dysfunction (ECD), which often precedes and exacerbates vascular disease progression. We previously discovered that covalent adducts formed on DNA, RNA, and proteins by the reactive metabolic by-product methylglyoxal (MG) predict DKD risk in patients with type 1 diabetes up to 16 years pre-diagnosis. However, the mechanisms by which MG adducts contribute to vascular disease onset and progression remain unclear. Here, we report that the most predominant MG-induced nucleoside adducts, N2-(1-carboxyethyl)-deoxyguanosine (CEdG) and N2-(1-carboxyethyl)-guanosine (CEG), drive endothelial dysfunction. Following CEdG or CEG exposure, primary human umbilical vein endothelial cells (HUVECs) undergo endothelial dysfunction, resulting in enhanced monocyte adhesion, increased reactive oxygen species production, endothelial permeability, impaired endothelial homeostasis, and exhibit a dysfunctional transcriptomic signature. These effects were discovered to be mediated through the receptor for advanced glycation end products (RAGE), as an inhibitor for intracellular RAGE signaling diminished these dysfunctional phenotypes. Therefore, we found that not only are MG adducts biomarkers for DKD, but that they may also have a role as potential drivers of vascular disease onset and progression and a new therapeutic modality.

Effects of liraglutide on ANP secretion and cardiac dynamics

To observe the effects of liraglutide (analog of glucagon-like peptide 1 (GLP-1)) on atrial natriuretic peptide (ANP) secretion and atrial dynamics, an ex vivo isolated rat atrial perfusion model was used to determine atrial ANP secretion and pulse pressure. DPP-4-/- mice were also established in vivo. ANP levels were determined by radioimmunoassay; GLP-1 content was determined by Elisa. The expression levels of GLP-1 receptor (GLP-1R), PI3K/AKT/mTOR, piezo 1, and cathepsin K were analyzed by Western blot. In the clinical study, patients with acute coronary syndrome (ACS) had low levels of plasma GLP-1 but relatively high levels of plasma ANP. In ex vivo (3.2 nmol/L) and in vivo (30 μg/kg) models, liraglutide significantly decreased ANP levels and atrial pulse pressure. Exendin9-39 alone (GLP-1R antagonist) reversibly significantly increased ANP secretion, and the reduction effect of liraglutide on the secretion of ANP was significantly alleviated by Exendin9-39. Exendin9-39 demonstrated slightly decreased atrial pulse pressure; however, combined liraglutide and Exendin9-39 significantly decreased atrial pulse pressure. Ly294002 (PI3K/AKT inhibitor) inhibited the increase of ANP secretion by liraglutide for a short time, while Ly294002 didn't counteract the decrease in pulse pressure by liraglutide in atrial dynamics studies. Liraglutide increased the expression of GLP-1R and PI3K/AKT/mTOR in isolated rat atria and the hearts of mice in vivo, whereas Exendin9-39 reversibly reduced the expression of GLP-1R and PI3K/AKT/mTOR. Piezo 1 was significantly decreased in wild type and DPP-4-/- mouse heart or isolated rat atria after being treated with liraglutide. Cathepsin K expression was only decreased in in vivo model hearts. Liraglutide can inhibit ANP secretion while decreasing atrial pulse pressure mediated by GLP-1R. Liraglutide probably plays a role in the reduction of ANP secretion via the PI3K/AKT/mTOR signaling pathway. Piezo 1 and cathepsin K may be involved in the liraglutide mechanism of reduction.

cAMP: A master regulator of cadherin-mediated binding in endothelium, epithelium and myocardium

Regulation of cadherin-mediated cell adhesion is crucial not only for maintaining tissue integrity and barrier function in the endothelium and epithelium but also for electromechanical coupling within the myocardium. Therefore, loss of cadherin-mediated adhesion causes various disorders, including vascular inflammation and desmosome-related diseases such as the autoimmune blistering skin dermatosis pemphigus and arrhythmogenic cardiomyopathy. Mechanisms regulating cadherin-mediated binding contribute to the pathogenesis of diseases and may also be used as therapeutic targets. Over the last 30 years, cyclic adenosine 3',5'-monophosphate (cAMP) has emerged as one of the master regulators of cell adhesion in endothelium and, more recently, also in epithelial cells as well as in cardiomyocytes. A broad spectrum of experimental models from vascular physiology and cell biology applied by different generations of researchers provided evidence that not only cadherins of endothelial adherens junctions (AJ) but also desmosomal contacts in keratinocytes and the cardiomyocyte intercalated discs are central targets in this scenario. The molecular mechanisms involve protein kinase A- and exchange protein directly activated by cAMP-mediated regulation of Rho family GTPases and S665 phosphorylation of the AJ and desmosome adaptor protein plakoglobin. In line with this, phosphodiesterase 4 inhibitors such as apremilast have been proposed as a therapeutic strategy to stabilize cadherin-mediated adhesion in pemphigus and may also be effective to treat other disorders where cadherin-mediated binding is compromised.

The Expression of Epac2 and GluA3 in an Alzheimer's Disease Experimental Model and Postmortem Patient Samples

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases, characterized by amyloid beta (Aβ) and hyperphosphorylated tau accumulation in the brain. Recent studies indicated that memory retrieval, rather than memory formation, was impaired in the early stage of AD. Our previous study reported that pharmacological activation of hippocampal Epac2 promoted memory retrieval in C57BL/6J mice. A recent study suggested that pharmacological inhibition of Epac2 prevented synaptic potentiation mediated by GluA3-containing AMPARs. In this study, we aimed to investigate proteins associated with Epac2-mediated memory in hippocampal postmortem samples of AD patients and healthy controls compared with the experimental AD model J20 and wild-type mice. Epac2 and phospho-Akt were downregulated in AD patients and J20 mice, while Epac1 and phospho-ERK1/2 were not altered. GluA3 was reduced in J20 mice and tended to decrease in AD patients. PSD95 tended to decrease in AD patients and J20. Interestingly, AKAP5 was increased in AD patients but not in J20 mice, implicating its role in tau phosphorylation. Our study points to the downregulation of hippocampal expression of proteins associated with Epac2 in AD.

Host Cell Rap1b mediates cAMP-dependent invasion by Trypanosoma cruzi

Trypanosoma cruzi cAMP-mediated invasion has long been described, however, the detailed mechanism of action of the pathway activated by this cyclic nucleotide still remains unknown. We have recently demonstrated a crucial role for Epac in the cAMP-mediated invasion of the host cell. In this work, we gathered evidence indicating that the cAMP/Epac pathway is activated in different cells lines. In accordance, data collected from pull-down experiments designed to identify only the active form of Rap1b (Rap1b-GTP), and infection assays using cells transfected with a constitutively active mutant of Rap1b (Rap1b-G12V), strongly suggest the participation of Rap1b as mediator of the pathway. In addition to the activation of this small GTPase, fluorescence microscopy allowed us to demonstrate the relocalization of Rap1b to the entry site of the parasite. Moreover, phospho-mimetic and non-phosphorylable mutants of Rap1b were used to demonstrate a PKA-dependent antagonistic effect on the pathway, by phosphorylation of Rap1b, and potentially of Epac. Finally, Western Blot analysis was used to determine the involvement of the MEK/ERK signalling downstream of cAMP/Epac/Rap1b-mediated invasion.

Perspectives of PDE inhibitor on treating idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease (ILD) without an identifiable cause. If not treated after diagnosis, the average life expectancy is 3-5 years. Currently approved drugs for the treatment of IPF are Pirfenidone and Nintedanib, as antifibrotic drugs, which can reduce the decline rate of forced vital capacity (FVC) and reduce the risk of acute exacerbation of IPF. However these drugs can not relieve the symptoms associated with IPF, nor improve the overall survival rate of IPF patients. We need to develop new, safe and effective drugs to treat pulmonary fibrosis. Previous studies have shown that cyclic nucleotides participate in the pathway and play an essential role in the process of pulmonary fibrosis. Phosphodiesterase (PDEs) is involved in cyclic nucleotide metabolism, so PDE inhibitors are candidates for pulmonary fibrosis. This paper reviews the research progress of PDE inhibitors related to pulmonary fibrosis, so as to provide ideas for the development of anti-pulmonary fibrosis drugs.

Role of ceramides in diabetic foot ulcers (Review)

Diabetes mellitus (DM) is a metabolic disorder, which if not managed properly, can lead to serious health problems over time and impose significant financial burden on the patient, their family and society as a whole. The study of this disease and the underlying biological mechanism is gaining momentum. Multiple pieces of conclusive evidence show that ceramides are involved in the occurrence and development of diabetes. The present review focuses on the function of ceramides, a type of sphingolipid signaling molecule, to provide a brief description of ceramides and their metabolism, discuss the significant roles of ceramides in the healthy skin barrier, and speculate on the potential involvement of ceramides in the pathogenesis and development of diabetic foot ulcers (DFUs). Understanding these aspects of this disease more thoroughly is crucial to establish how ceramides contribute to the etiology of diabetic foot infections and identify possible therapeutic targets for the treatment of DFUs.

A Dietary Supplement Containing Fucoidan Preserves Endothelial Glycocalyx through ERK/MAPK Signaling and Protects against Damage Induced by CKD Serum

(1) Damage to the endothelial glycocalyx (eGC), a protective layer lining the endothelial luminal surface, is associated with chronic kidney disease (CKD), which leads to a worsening of cardiovascular outcomes in these patients. Currently, there are no targeted therapeutic approaches. Whether the dietary supplement Endocalyx^TM (ECX) protects against endothelial damage caused by uremic toxins is unknown. (2) We addressed this question by performing atomic force microscopy measurements on living endothelial cells. We examined the effect of ECX on eGC thickness at baseline and with pooled serum from hemodialysis patients. ECX was also successfully administered in vivo in mice, in which eGC was assessed using perfused boundary region measurements by intravital microscopy of cremasteric vessels. (3) Both ECX and fucoidan significantly improved baseline eGC thickness. Our data indicate that these effects are dependent on ERK/MAPK and PI3K signaling. After incubation with eGC damaging serum from dialysis patients, ECX increased eGC height. Intravital microscopy in mice revealed a relevant increase in baseline eGC dimensions after feeding with ECX. (4) We identified a dietary supplement containing glycocalyx substrates and fucoidan as potential mediators of eGC preservation in vitro and in vivo. Our findings suggest that fucoidan may be an essential component responsible for protecting the eGC in acute settings. Moreover, ECX might contribute to both protection and rebuilding of the eGC in the context of CKD.

Differential endothelial hydrogen peroxide signaling via Nox isoforms: Critical roles for Rac1 and modulation by statins

Statins have manifold protective effects on the cardiovascular system. In addition to lowering LDL cholesterol levels, statins also have antioxidant effects on cardiovascular tissues involving intracellular redox pathways that are incompletely understood. Inhibition of HMG-CoA reductase by statins not only modulates cholesterol synthesis, but also blocks the synthesis of lipids necessary for the post-translational modification of signaling proteins, including the GTPase Rac1. Here we studied the mechanisms whereby Rac1 and statins modulate the intracellular oxidant hydrogen peroxide (H2O2) via NADPH oxidase (Nox) isoforms. In live-cell imaging experiments using the H2O2 biosensor HyPer7, we observed robust H2O2 generation in human umbilical vein endothelial cells (HUVEC) following activation of cell surface receptors for histamine or vascular endothelial growth factor (VEGF). Both VEGF- and histamine-stimulated H2O2 responses were abrogated by siRNA-mediated knockdown of Rac1. VEGF responses required the Nox isoforms Nox2 and Nox4, while histamine-stimulated H2O2 signals are independent of Nox4 but still required Nox2. Endothelial H2O2 responses to both histamine and VEGF were completely inhibited by simvastatin. In resting endothelial cells, Rac1 is targeted to the cell membrane and cytoplasm, but simvastatin treatment promotes translocation of Rac1 to the cell nucleus. The effects of simvastatin both on receptor-dependent H2O2 production and Rac1 translocation are rescued by treatment of cells with mevalonic acid, which is the enzymatic product of the HMG-CoA reductase that is inhibited by statins. Taken together, these studies establish that receptor-modulated H2O2 responses to histamine and VEGF involve distinct Nox isoforms, both of which are completely dependent on Rac1 prenylation.

The peripheral Epac1/p-Cav-1 pathway underlies the disruption of the vascular endothelial barrier following skin/muscle incision and retraction-induced chronic postsurgical pain

Background

Vascular endothelial barrier disruption is pivotal in the development of acute and chronic pain. Here, we demonstrate a previously unidentified molecular mechanism in which activation of the peripheral Epac1/p-Cav-1 pathway accelerated the disruption of the vascular endothelial barrier, thereby promoting chronic postsurgical pain (CPSP).

Methods

We established a rat model of CPSP induced by skin/muscle incision and retraction (SMIR). Pain behaviors were assessed by the mechanical withdrawal threshold (MWT) at different times. Local muscle tissues around the incision were isolated to detect the vascular permeability and the expression of Epac1 and Cav-1. They were assessed by western blot and immunofluorescence staining.

Results

SMIR increased vascular endothelial permeability and the number of macrophages and endothelial cells in the muscle tissues around the incision. The peripheral upregulation of Epac1 was macrophage-derived, whereas that of p-Cav-1 was both macrophage and endothelial cell-derived in the SMIR model. Moreover, the Epac1 agonist 8-pCPT could induce mechanical sensitivity, increase the expression of p-Cav-1, and disrupt vascular endothelial barrier in normal rats. The Epac1 inhibitor CE3F4 attenuated established SMIR-induced mechanical hyperalgesia, the upregulation of p-Cav-1 and vascular endothelial barrier. Finally, we showed that intrathecal injection of Cav-1siRNA relieved SMIR-induced mechanical allodynia, but had no effects of the expression of Epac1.

Conclusions

Collectively, these results revealed a molecular mechanism for modulating CPSP through the peripheral Epac1/Cav-1 pathway. Importantly, targeting Epac1/Cav-1 signaling might be a potential treatment for CPSP.

The dipeptidyl peptidase-4 inhibitor linagliptin ameliorates LPS-induced acute lung injury by maintenance of pulmonary microvascular barrier via activating the Epac1/AKT pathway

Pulmonary microvascular endothelial cells (PMVECs) barrier dysfunction is a main pathophysiological feature of sepsis-related acute lung injury (ALI). This study aimed to investigate whether the dipeptidyl peptidase (DPP)-4 inhibitor linagliptin could protect against LPS-induced PMVECs barrier disruption and its underlying molecular mechanisms. A classical ALI animal model and LPS-treated PMVECs were applied and all were treated with or without linagliptin. Cellular experiments demonstrated that linagliptin could mitigate LPS-induced PMVECs hyperpermeability and intercellular junction (VE-cadherin, β-catenin, and ZO-1) disruption in a dose-dependent manner. Correspondingly, it was observed that linagliptin pretreatment distinctly relieved LPS-induced lung injury, oxidative stress, and pulmonary edema in vivo. Furthermore, we found that the inhibition of oxidative stress by linagliptin may be achieved by reversing impaired mitochondrial function. Mechanistically, linagliptin administration promoted the activation of the Epac1 pathway and its downstream AKT pathway, while inhibition of the Epac1/Akt signaling pathway significantly alleviated the above-mentioned protective effect of linagliptin on the PMVECs barrier. Taken together, these data suggest that linagliptin can effectively reserve PMVECs barrier dysfunction and inhibit oxidative stress to protect against ALI via activating the Epac1/AKT signaling pathway, and thus may become a potential clinical therapeutic strategy for ALI.

BRAF increases endothelial cell stiffness through reorganization of the actin cytoskeleton

The dynamics of the actin cytoskeleton and its connection to endothelial cell-cell junctions determine the barrier function of endothelial cells. The proper regulation of barrier opening/closing is necessary for the normal function of vessels, and its dysregulation can result in chronic and acute inflammation leading to edema formation. By using atomic force microscopy, we show here that thrombin-induced permeability of human umbilical vein endothelial cells, associated with actin stress fiber formation, stiffens the cell center. The depletion of the MEK/ERK kinase BRAF reduces thrombin-induced permeability prevents stress fiber formation and cell stiffening. The peripheral actin ring becomes stabilized by phosphorylated myosin light chain, while cofilin is excluded from the cell periphery. All these changes can be reverted by the inhibition of ROCK, but not of the MEK/ERK module. We propose that the balance between the binding of cofilin and myosin to F-actin in the cell periphery, which is regulated by the activity of ROCK, determines the local dynamics of actin reorganization, ultimately driving or preventing stress fiber formation.

Epac: A Promising Therapeutic Target for Vascular Diseases: A Review

Vascular diseases affect the circulatory system and comprise most human diseases. They cause severe symptoms and affect the quality of life of patients. Recently, since their identification, exchange proteins directly activated by cAMP (Epac) have attracted increasing scientific interest, because of their role in cyclic adenosine monophosphate (cAMP) signaling, a well-known signal transduction pathway. The role of Epac in cardiovascular disease and cancer is extensively studied, whereas their role in kidney disease has not been comprehensively explored yet. In this study, we aimed to review recent studies on the regulatory effects of Epac on various vascular diseases, such as cardiovascular disease, cerebrovascular disease, and cancer. Accumulating evidence has shown that both Epac1 and Epac2 play important roles in vascular diseases under both physiological and pathological conditions. Additionally, there has been an increasing focus on Epac pharmacological modulators. Therefore, we speculated that Epac could serve as a novel therapeutic target for the treatment of vascular diseases.

Lactate induces vascular permeability via disruption of VE-cadherin in endothelial cells during sepsis

Circulating lactate levels are a critical biomarker for sepsis and are positively correlated with sepsis-associated mortality. We investigated whether lactate plays a biological role in causing endothelial barrier dysfunction in sepsis. We showed that lactate causes vascular permeability and worsens organ dysfunction in CLP sepsis. Mechanistically, lactate induces ERK-dependent activation of calpain1/2 for VE-cadherin proteolytic cleavage, leading to the enhanced endocytosis of VE-cadherin in endothelial cells. In addition, we found that ERK2 interacts with VE-cadherin and stabilizes VE-cadherin complex in resting endothelial cells. Lactate-induced ERK2 phosphorylation promotes ERK2 disassociation from VE-cadherin. In vivo suppression of lactate production or genetic depletion of lactate receptor GPR81 mitigates vascular permeability and multiple organ injury and improves survival outcome in polymicrobial sepsis. Our study reveals that metabolic cross-talk between glycolysis-derived lactate and the endothelium plays a critical role in the pathophysiology of sepsis.

Echinacoside exhibits antidepressant-like effects through AMPAR-Akt/ERK-mTOR pathway stimulation and BDNF expression in mice

Background

Several natural products have been demonstrated to be effective in the treatment of depressive disorders. Echinacoside, a naturally occurring phenol extracted from Cistanche tubulosa, Echinacea angustifolia, and Cistanche spp, has a wide range of physiological effects, such as antioxidation, neuroprotection, anti-inflammatory, and immunoregulation, which are closely related to depression. In addition, echinacoside can activate protein kinase B (Akt), extracellular signal–regulated kinase (ERK), and brain-derived neurotrophic factor (BDNF) in the brain. A key downstream event of the Akt, ERK, and BDNF signaling pathways, namely mechanistic target of rapamycin (mTOR) signaling, plays a crucial role in generating an rapid antidepressant effect. Thus, echinacoside is a promising therapeutic agent for depression. However, research regarding the role of echinacoside in antidepressant effect and brain mTOR activation remains lacking.

Materials and methods

The forced swimming test and Western blot analysis in C57BL/6 mice was used to investigate the antidepressant-like activities of echinacoside and the underlying mechanism involved inα-amino3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)–Akt/ERK–mTOR pathway.

Results

We confirmed the suggestions by previous reports that echinacoside activates Akt/ERK signaling and further demonstrated that echinacoside could provide antidepressant-like effects in mice via the activation of AMPAR–Akt/ERK–mTOR pathway in the hippocampus.

Conclusions

To the best of our knowledge, our study is the first to reveal that echinacoside is a potential treatment for depressive disorders. Moreover, the present study suggests a mechanism for the neuroprotective effect of echinacoside.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00549-5.

The Tyrosine Phosphatase hPTPRβ Controls the Early Signals and Dopaminergic Cells Viability via the P2X7 Receptor

ATP, one of the signaling molecules most commonly secreted in the nervous system and capable of stimulating multiple pathways, binds to the ionotropic purinergic receptors, in particular, the P2X₇ receptor (P2X₇R) and stimulates neuronal cell death. Given this effect of purinergic receptors on the viability of dopaminergic neurons model cells and that Ras GTPases control Erk1/2-regulated mitogen-activated cell proliferation and survival, we have investigated the role of the small GTPases of the Ras superfamily, together with their regulatory and effector molecules as the potential molecular intermediates in the P2X₇R-regulated cell death of SN4741 dopaminergic neurons model cells. Here, we demonstrate that the neuronal response to purinergic stimulation involves the Calmodulin/RasGRF1 activation of the small GTPase Ras and Erk1/2. We also demonstrate that tyrosine phosphatase PTPRβ and other tyrosine phosphatases regulate the small GTPase activation pathway and neuronal viability. Our work expands the knowledge on the intracellular responses of dopaminergic cells by identifying new participating molecules and signaling pathways. In this sense, the study of the molecular circuitry of these neurons is key to understanding the functional effects of ATP, as well as considering the importance of these cells in Parkinson’s Disease.

Metformin alleviates bevacizumab-induced vascular endothelial injury by up-regulating GDF15 and activating the PI3K/AKT/FOXO/PPARγ signaling pathway

Background

Previous studies have reported that the combination of metformin and bevacizumab exhibit favorable efficacy in the treatment of cancer patients, and metformin possesses effects on relieving vascular injury in multiple diseases. Nonetheless, the effect of metformin in alleviating bevacizumab-induced vascular injury remains unknown. Therefore, the present study aimed to investigate the impact of metformin on apoptosis, vascular endothelial injury marker expressions, and inflammation in human umbilical vein endothelial cells (HUVECs), as well as its possible molecular mechanism.

Methods

HUVECs were treated with bevacizumab, metformin or both, and subsequently treated with growth differentiation factor 15 (GDF15) overexpression plasmid, negative control (NC) plasmid, GDF15 small interfering ribonucleic acid (siRNA), NC siRNA, and the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, respectively. After treatment, apoptosis, levels of endothelial injury biomarkers and the potential downstream proteins were detected.

Results

Bevacizumab increased the levels of apoptosis, vascular endothelial injury marker expressions and pro-inflammatory cytokine expressions in HUVECs, while metformin alleviated these effects in bevacizumab-treated HUVECs. Furthermore, GDF15 overexpression reduced the apoptosis, vascular endothelial injury marker expressions, pro-inflammatory cytokine expressions, and activated the PI3K/protein kinase B (AKT)/forkhead box O (FOXO)/peroxisome proliferator-activated receptor γ (PPARγ) signaling pathway in bevacizumab-treated HUVECs. Subsequently, GDF15 siRNA reduced the effects of metformin on the bevacizumab-induced vascular endothelial injury (as described above) in HUEVCs. Lastly, the PI3K inhibitor exhibited similar effects to those of GDF15 siRNA in bevacizumab-treated HUVECs.

Conclusions

Metformin protected against bevacizumab-induced vascular endothelial injury via activation of GDF15 and the PI3K/AKT/FOXO/PPARγ signaling pathway.

Sortilin regulates blood-brain barrier integrity

Brain homeostasis depends on the existence of the blood-brain barrier (BBB). Despite decades of research, the factors and signalling pathways for modulating and maintaining BBB integrity are not fully elucidated. Here, we characterise the expression and function of the multifunctional receptor, sortilin, in the cells of the BBB, in vivo and in vitro. We show that sortilin acts as an important regulatory protein of the BBB's tightness. In rats lacking sortilin, the BBB was leaky, which correlated well with relocated distribution of the localisation of zonula occludens-1, VE-cadherin and β-catenin junctional proteins. Furthermore, the absence of sortilin in brain endothelial cells resulted in decreased phosphorylation of Akt signalling protein and increased the level of phospho-ERK1/2. As a putative result of MAPK/ERK pathway activity, the junctions between the brain endothelial cells were disintegrated and the integrity of the BBB became compromised. The identified barrier differences between wild-type and Sort1-/- brain endothelial cells can pave the way for a better understanding of sortilin's role in the healthy and diseased BBB.

Saccharin and Sucralose Protect the Glomerular Microvasculature In Vitro against VEGF-Induced Permeability

Diabetic kidney disease (DKD) has become a global health concern, with about 40% of people living with type 1 and type 2 diabetes mellitus developing DKD. Upregulation of vascular endothelial growth factor (VEGF) in the kidney is a significant pathology of DKD associated with increased glomerular vascular permeability. To date, however, current anti-VEGF therapies have demonstrated limited success in treating DKD. Recent studies have shown that artificial sweeteners exhibit anti-VEGF potential. The aim of this study was therefore to assess the effects of aspartame, saccharin, and sucralose on VEGF-induced leak using an in vitro model of the glomerular endothelium. Saccharin and sucralose but not aspartame protected against VEGF-induced permeability. Whilst the sweeteners had no effect on traditional VEGF signalling, GC-MS analysis demonstrated that the sweetener sucralose was not able to enter the glomerular endothelial cell to exert the protective effect. Chemical and molecular inhibition studies demonstrated that sweetener-mediated protection of the glomerular endothelium against VEGF is dependent on the sweet taste receptor, T1R3. These studies demonstrate the potential for sweeteners to exert a protective effect against VEGF-induced increased permeability to maintain a healthy endothelium and protect against vascular leak in the glomerulus in settings of DKD.

Leptin receptor-expressing pericytes mediate access of hypothalamic feeding centers to circulating leptin

Knowledge of how leptin receptor (LepR) neurons of the mediobasal hypothalamus (MBH) access circulating leptin is still rudimentary. Employing intravital microscopy, we found that almost half of the blood-vessel-enwrapping pericytes in the MBH express LepR. Selective disruption of pericytic LepR led to increased food intake, increased fat mass, and loss of leptin-dependent signaling in nearby LepR neurons. When delivered intravenously, fluorescently tagged leptin accumulated at hypothalamic LepR pericytes, which was attenuated upon pericyte-specific LepR loss. Because a paracellular tracer was also preferentially retained at LepR pericytes, we pharmacologically targeted regulators of inter-endothelial junction tightness and found that they affect LepR neuronal signaling and food intake. Optical imaging in MBH slices revealed a long-lasting, tonic calcium increase in LepR pericytes in response to leptin, suggesting pericytic contraction and vessel constriction. Together, our data indicate that LepR pericytes facilitate localized, paracellular blood-brain barrier leaks, enabling MBH LepR neurons to access circulating leptin.

The Crossroads between RAS and RHO Signaling Pathways in Cellular Transformation, Motility and Contraction

Ras and Rho proteins are GTP-regulated molecular switches that control multiple signaling pathways in eukaryotic cells. Ras was among the first identified oncogenes, and it appears mutated in many forms of human cancer. It mainly promotes proliferation and survival through the MAPK pathway and the PI3K/AKT pathways, respectively. However, the myriad proteins close to the plasma membrane that activate or inhibit Ras make it a major regulator of many apparently unrelated pathways. On the other hand, Rho is weakly oncogenic by itself, but it critically regulates microfilament dynamics; that is, actin polymerization, disassembly and contraction. Polymerization is driven mainly by the Arp2/3 complex and formins, whereas contraction depends on myosin mini-filament assembly and activity. These two pathways intersect at numerous points: from Ras-dependent triggering of Rho activators, some of which act through PI3K, to mechanical feedback driven by actomyosin action. Here, we describe the main points of connection between the Ras and Rho pathways as they coordinately drive oncogenic transformation. We emphasize the biochemical crosstalk that drives actomyosin contraction driven by Ras in a Rho-dependent manner. We also describe possible routes of mechanical feedback through which myosin II activation may control Ras/Rho activation.

A network-based method for mechanistic investigation and neuroprotective effect on treatment of tanshinone Ⅰ against ischemic stroke in mouse

ETHNOPHARMACOLOGICAL RELEVANCE

Tanshinone-Ⅰ (TSNⅠ), a member of the mainly active components of Salvia miltiorrhiza Bunge (Dan Shen), which is widely used for the treatment for modern clinical diseases including cardiovascular and cerebrovascular diseases, has been reported to show the properties of anti-oxidation, anti-inflammation, neuroprotection and other pharmacological actions. However, whether TSNⅠ can improve neuron survival and neurological function against transient focal cerebral ischemia (tMCAO) in mice is still a blank field.

AIM OF THE STUDY

This study aims to investigate the neuroprotective effects of TSNⅠ on ischemic stroke (IS) induced by tMCAO in mice and explore the potential mechanism of TSNⅠ against IS by combining network pharmacology approach and experimental verification.

MATERIALS AND METHODS

In this study, the pivotal candidate targets of TSNⅠ against IS were screened by network pharmacology firstly. Enrichment analysis and molecular docking of those targets were performed to identify the possible mechanism of TSNⅠ against IS. Afterwards, experiments were carried out to further verify the mechanism of TSNⅠ against IS. The infarct volume and neurological deficit were evaluated by 2, 3, 5-triphenyl tetrazolium chloride (TTC) staining and Longa respectively. Immunohistochemistry was used to observe neuronal death in the hippocampus and cortical regions by detecting the change of NeuN. The predicting pathways of signaling-related proteins were assessed by Western blot in vitro and in vivo experiments.

RESULTS

In vivo, TSNⅠ was found to dose-dependently decrease mice's cerebral infarct volume induced by tMCAO. In vitro, pretreatment with TSNⅠ could increase cell viability of HT-22 cell following oxygen-glucose deprivation (OGD/R). Moreover, the results showed that 125 candidate targets were identified, Protein kinase B (AKT) signaling pathway was significantly enriched by Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and mitogen-activated protein kinases 1 (MAPK1) and AKT1 could be bound to TSNⅠ more firmly by molecular docking analysis, which implies that TSNⅠ may play a role in neuroprotection through activating AKT and MAPK signaling pathways. Meanwhile, TSNⅠ was confirmed to significantly protect neurons from injury induced by IS through activating AKT and MAPK signaling pathways.

CONCLUSION

In conclusion, our study clarifies that the mechanism of TSNⅠ against IS might be related to AKT and MAPK signaling pathways, which may provide the basic evidence for further development and utilization of TSNⅠ.

Blockade of platelet glycoprotein receptor Ib ameliorates blood-brain barrier disruption following ischemic stroke via Epac pathway

Glycoprotein (GP) Ib is a platelet membrane receptor complex exposed to vascular injury, proposed as an effective target for stroke therapy. Previously, we have observed that the GPIb antagonist anfibatide (ANF) could mitigate blood-brain barrier (BBB) disruption following cerebral ischemia/reperfusion (CI/R) injury. The current study was designed to investigate whether the amelioration of the BBB by ANF is mediated via the Epac signaling pathway. A murine model of CI/R injury was induced following 90 min of transient middle cerebral artery occlusion (MCAO). ANF (4 μg/kg) was intravenously injected 1 h after reperfusion. Herein, ANF ameliorated BBB disruption, increased the expression of tight junction proteins, suppressed F-actin cytoskeleton rearrangement, decreased the permeability of the ischemic brain tissue, and relieved brain edema. ANF-treated mice had smaller infarct volumes and less severe neurological deficits than the MCAO mice. Moreover, the effects of ANF and Epac1 agonists were very similar in the MCAO mice. Epac activation with a cAMP analog, 8-CPT-2'-O-Me-cAMP, mitigated the breakdown of BBB function and CI/R injury. The Epac specific antagonist, ESI-09, worsened barrier damage and cerebral impairment, antagonizing the protective effects afforded by ANF. In addition, ANF upregulated the expression of Epac1 protein in the ischemic cerebral cortex. Collectively, our results indicate that the protective effect of ANF on the BBB after CI/R could be attributed to the activation of the Epac pathway.

Epac-1/Rap-1 signaling pathway orchestrates the reno-therapeutic effect of ticagrelor against renal ischemia/reperfusion model

Despite the renal expression of P₂Y₁₂, the purinergic receptor for adenosine diphosphate, few data are available to discuss the renotherapeutic potential of ticagrelor, one of its reversible blockers. Indeed, the tonic inhibitory effect of this receptor has been linked to the activation of exchange protein activated by cyclic adenosine monophosphate-1 (Epac-1) protein through the cyclic adenosine monophosphate cascade. Epac-1 is considered a crossroad protein, where its activation has been documented to manage renal injury models. Hence, the current study aimed to investigate the possible therapeutic effectiveness of ticagrelor, against renal ischemia/reperfusion (I/R) model with emphasis on the involvement of Epac-1 signaling pathway using R-CE3F4, a selective Epac-1 blocker. Accordingly, rats were randomized into four groups; viz., sham-operated, renal I/R, I/R post-treated with ticagrelor for 3 days, and ticagrelor + R-CE3F4. Treatment with ticagrelor ameliorated the I/R-mediated structural alterations and improved renal function manifested by the reduction in serum BUN and creatinine. On the molecular level, ticagrelor enhanced renal Epac-1 mRNA expression, Rap-1 activation (Rap-1-GTP) and SOCS-3 level. On the contrary, it inhibited the protein expression of JAK-2/STAT-3 hub, TNF-α and MDA contents, as well as caspase-3 activity. Additionally, ticagrelor enhanced the protein expression/content of AKT/Nrf-2/HO-1 axis. All these beneficial effects were obviously antagonized upon using R-CE3F4. In conclusion, ticagrelor reno-therapeutic effect is partly mediated through modulating the Epac-1/Rap-1-GTP, AKT/Nrf-2/HO-1 and JAK-2/STAT-3/SOCS-3 trajectories, pathways that integrate to afford novel explanations to its anti-inflammatory, anti-oxidant, and anti-apoptotic potentials.

The Potentially Therapeutic Role of EPAC in Curbing the Process of Idiopathic Pulmonary Fibrosis via Differential Cellular Pathways

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive fibrosis disease caused by genetic susceptibility (causative) and other indirect risk factors such as smoking, micro-aspiration and air pollution. Repeated damage of lung epithelial cells can cause fibroblast activation and excessive collagen will lead the scar formation and severe fibrosis. It has been decades since drugs for the treatment of IPF were developed, but clinical choices were limited. Exchange Protein directly Activated by cAMP (EPAC), as a newly emerging cAMP (adenosine 3ʹ,5ʹ-cyclic monophosphate) downstream molecule, plays a vital role in the cellular pathways of IPF such as inhibiting fibroblast proliferation, stress fiber formation and epithelium cell adhesion, so it may be a novel target for drug development and treatment for curbing IPF. Here, we hypothesize that EPAC may participate in the signaling pathways related to IPF in different cell types (fibroblasts; airway smooth muscle cells; vascular endothelial cells; lung epithelial cells; macrophages; mesenchymal stem cells; T cells), thereby playing a potentially therapeutic role in resisting the process of fibrosis. We summarize the current correlation between EPAC and IPF in these different cell types, and further insights into EPAC will help to optimize the pharmacological treatment for IPF.

Purinergic Regulation of Endothelial Barrier Function

Increased vascular permeability is a hallmark of several cardiovascular anomalies, including ischaemia/reperfusion injury and inflammation. During both ischaemia/reperfusion and inflammation, massive amounts of various nucleotides, particularly adenosine 5'-triphosphate (ATP) and adenosine, are released that can induce a plethora of signalling pathways via activation of several purinergic receptors and may affect endothelial barrier properties. The nature of the effects on endothelial barrier function may depend on the prevalence and type of purinergic receptors activated in a particular tissue. In this review, we discuss the influence of the activation of various purinergic receptors and downstream signalling pathways on vascular permeability during pathological conditions.

Overexpression of Rab40b Promotes Hepatocellular Carcinoma Cell Proliferation and Metastasis via PI3K/AKT Signaling Pathway

Background

Rab40b is an evolutionarily conserved Rab GTPase that plays an important role in intracellular trafficking and is closely related to cancer progression. However, the role and potential molecular mechanism of Rab40b in hepatocellular carcinoma (HCC) have not yet been elucidated.

Materials and Methods

The expression of Rab40b in HCC tissues and peritumour tissues was tested by qRT-PCR, Western blotting and histological analysis. A Kaplan-Meier survival curve was generated based on the expression of Rab40b in the HCC samples. Cell proliferation assays, wound healing assays, and transwell assays are used to examine the effect of Rab40b on HCC cell growth in vitro. The effect of Rab40b on cell cycle was examined by flow cytometry. A xenograft implantation model was used to assess the effect of Rab40b on the development of HCC cells in vivo.

Results

Rab40b protein expression is upregulated in HCC tissues, and this upregulation is associated with high pathological stage and poor prognosis in HCC patients. Rab40b overexpression promotes the proliferation and metastasis of HCC cells by upregulating cyclin D1, cyclin E1 and matrix metalloproteinase 2 (MMP2) through the PI3K/AKT signalling pathway. Conversely, Rab40b inhibitors can significantly inhibit the proliferation and metastasis of HCC cell lines and induce G0/G1 cell cycle arrest and apoptosis. Studies of a nude mouse xenograft model demonstrated that Rab40b knockdown can significantly inhibit the proliferation and progression of HCC tumours in vivo.

Conclusion

Overall, this study demonstrates that Rab40b is an important oncoprotein that promotes HCC progression by regulating the expression of cyclin D1, cyclin E1, p21 and MMP2 through the PI3K/AKT signalling pathway.