The caveolin proteins

Insights into membrane interactions and their therapeutic potential

Recent research into membrane interactions has uncovered a diverse range of therapeutic opportunities through the bioengineering of human and non-human macromolecules. Although the majority of this research is focussed on fundamental developments, emerging studies are showcasing promising new technologies to combat conditions such as cancer, Alzheimer's and inflammatory and immune-based disease, utilising the alteration of bacteriophage, adenovirus, bacterial toxins, type 6 secretion systems, annexins, mitochondrial antiviral signalling proteins and bacterial nano-syringes. To advance the field further, each of these opportunities need to be better understood, and the therapeutic models need to be further optimised. Here, we summarise the knowledge and insights into several membrane interactions and detail their current and potential uses therapeutically.

Ago2/CAV1 interaction potentiates metastasis via controlling Ago2 localization and miRNA action

Ago2 differentially regulates oncogenic and tumor-suppressive miRNAs in cancer cells. This discrepancy suggests a secondary event regulating Ago2/miRNA action in a context-dependent manner. We show here that a positive charge of Ago2 K212, that is preserved by SIR2-mediated Ago2 deacetylation in cancer cells, is responsible for the direct interaction between Ago2 and Caveolin-1 (CAV1). Through this interaction, CAV1 sequesters Ago2 on the plasma membranes and regulates miRNA-mediated translational repression in a compartment-dependent manner. Ago2/CAV1 interaction plays a role in miRNA-mediated mRNA suppression and in miRNA release via extracellular vesicles (EVs) from tumors into the circulation, which can be used as a biomarker of tumor progression. Increased Ago2/CAV1 interaction with tumor progression promotes aggressive cancer behaviors, including metastasis. Ago2/CAV1 interaction acts as a secondary event in miRNA-mediated suppression and increases the complexity of miRNA actions in cancer.

Mechanical stretch leads to increased caveolin-1 content and mineralization potential in extracellular vesicles from vascular smooth muscle cells

BACKGROUND

Hypertension-induced mechanical stress on vascular smooth muscle cells (VSMCs) is a known risk factor for vascular remodeling, including vascular calcification. Caveolin-1 (Cav-1), an integral structural component of plasma membrane invaginations, is a mechanosensitive protein that is required for the formation of calcifying extracellular vesicles (EVs). However, the role of mechanics in Cav-1-induced EV formation from VSMCs has not been reported.

RESULTS

Exposure of VSMCs to 10% mechanical stretch (0.5 Hz) for 72 h resulted in Cav-1 translocation into non-caveolar regions of the plasma membrane and subsequent redistribution of Cav-1 from the VSMCs into EVs. Inhibition of Rho-A kinase (ROCK) in mechanically-stimulated VSMCs exacerbated the liberation of Cav-1 positive EVs from the cells, suggesting a potential involvement of actin stress fibers in this process. The mineralization potential of EVs was measured by incubating the EVs in a high phosphate solution and measuring light scattered by the minerals at 340 nm. EVs released from stretched VSMCs showed higher mineralization potential than the EVs released from non-stretched VSMCs. Culturing VSMCs in pro-calcific media and exposure to mechanical stretch increased tissue non-specific alkaline phosphatase (ALP), an important enzyme in vascular calcification, activity in EVs released from the cells, with cyclic stretch further elevating EV ALP activity compared to non-stretched cells.

CONCLUSION

Our data demonstrate that mechanical stretch alters Cav-1 trafficking and EV release, and the released EVs have elevated mineralization potential.

The T-type calcium channelosome

T-type calcium channels perform crucial physiological roles across a wide spectrum of tissues, spanning both neuronal and non-neuronal system. For instance, they serve as pivotal regulators of neuronal excitability, contribute to cardiac pacemaking, and mediate the secretion of hormones. These functions significantly hinge upon the intricate interplay of T-type channels with interacting proteins that modulate their expression and function at the plasma membrane. In this review, we offer a panoramic exploration of the current knowledge surrounding these T-type channel interactors, and spotlight certain aspects of their potential for drug-based therapeutic intervention.

Docetaxel radiosensitizes castration-resistant prostate cancer by downregulating CAV-1

PURPOSE

Docetaxel (DXL), a noted radiosensitizer, is one of the few chemotherapy drugs approved for castration-resistant prostate cancer (CRPC), though only a fraction of CRPCs respond to it. CAV-1, a critical regulator of radioresistance, has been known to modulate DXL and radiation effects. Combining DXL with radiotherapy may create a synergistic anticancer effect through CAV-1 and improve CRPC patients' response to therapy. Here, we investigate the effectiveness and molecular characteristics of DXL and radiation combination therapy in vitro.

MATERIALS AND METHODS

We used live/dead assays to determine the IC50 of DXL for PC3, DU-145, and TRAMP-C1 cells. Colony formation assay was used to determine the radioresponse of the same cells treated with radiation with/without IC50 DXL (4, 8, and 12 Gy). We performed gene expression analysis on public transcriptomic data collected from human-derived prostate cancer cell lines (C4-2, PC3, DU-145, and LNCaP) treated with DXL for 8, 16, and 72 hours. Cell cycle arrest and protein expression were assessed using flow cytometry and western blot, respectively.

RESULTS

Compared to radiation alone, combination therapy with DXL significantly increased CRPC death in PC3 (1.48-fold, p < .0001), DU-145 (1.64-fold, p < .05), and TRAMP-C1 (1.13-fold, p < .05) at 4 Gy of radiation. Gene expression of CRPC treated with DXL revealed downregulated genes related to cell cycle regulation and upregulated genes related to immune activation and oxidative stress. Confirming the results, G2/M cell cycle arrest was significantly increased after treatment with DXL and radiation. CAV-1 protein expression was decreased after DXL treatment in a dose-dependent manner; furthermore, CAV-1 copy number was strongly associated with poor response to therapy in CRPC patients.

CONCLUSIONS

Our results suggest that DXL sensitizes CRPC cells to radiation by downregulating CAV-1. DXL + radiation combination therapy may be effective at treating CRPC, especially subtypes associated with high CAV-1 expression, and should be studied further.

Is there any diagnostic value of serum caveolin-1 levels on the determination of pancreatic adenocarcinoma?

BACKGROUND

Caveolin-1 (CAV-1) is a vital component in cancer pathogenesis, as its expression determines the survival of patients with cancer. This study investigates CAV-1 serum levels in pancreatic adenocarcinoma (PA) patients and their role in tumor progression and prognostic factors.

METHOD

The trial included 33 patients with pathologically confirmed pancreatic cancer (PC). The enzyme-linked immunosorbent assay (ELISA) method was used to measure the concentrations of CAV-1 in the blood. The study also included 20 healthy subjects. The statistical analysis was two-sided, and a P value of ≤ 0.05 was determined as statistically significant.

RESULTS

The median age of the subjects was 59 years (32-84 years) at the time of diagnosis. There were 13 (39%) female participants. In 21 (63%) patients, the primary focus was the pancreatic head. In 23 stage IV patients, hepatic metastasis (n = 19, 83%) was observed. Only one patient (3%) was still alive at the end of the study period. Palliative chemotherapy (CTx) was provided, with 39% of the 23 patients responding to it. The overall survival (OS) rate in this cohort was 41.3 ± 8.3 weeks at a 95% confidence interval (CI), after 25-58 weeks. Serum baseline CAV-1 values among patients with PA were significantly higher compared with controls (p = 0.009). Patients with poor performance status, a pancreatic head tumor, lower albumin levels, higher serum carcinoembryonic antigen (CEA) levels, and higher CA 19.9 levels had significantly higher serum CAV-1 levels (p = 0.01, P = 0.05, P = 0.03, P = 0.02, and P = 0.04, respectively). However, CAV-1 did not show any prognostic value (p = 0.75).

CONCLUSION

Although serum CAV-1 is a useful diagnostic marker in PC patients, it is not a prognostic or predictive marker.

Unraveling the Cave: A Seventy-Year Journey into the Caveolar Network, Cellular Signaling, and Human Disease

In the mid-1950s, a groundbreaking discovery revealed the fascinating presence of caveolae, referred to as flask-shaped invaginations of the plasma membrane, sparking renewed excitement in the field of cell biology. Caveolae are small, flask-shaped invaginations in the cell membrane that play crucial roles in diverse cellular processes, including endocytosis, lipid homeostasis, and signal transduction. The structural stability and functionality of these specialized membrane microdomains are attributed to the coordinated activity of scaffolding proteins, including caveolins and cavins. While caveolae and caveolins have been long appreciated for their integral roles in cellular physiology, the accumulating scientific evidence throughout the years reaffirms their association with a broad spectrum of human disorders. This review article aims to offer a thorough account of the historical advancements in caveolae research, spanning from their initial discovery to the recognition of caveolin family proteins and their intricate contributions to cellular functions. Furthermore, it will examine the consequences of a dysfunctional caveolar network in the development of human diseases.

Molecular Mechanisms of Glaucoma Pathogenesis with Implications to Caveolin Adaptor Protein and Caveolin-Shp2 Axis

Glaucoma is a common retinal disorder characterized by progressive optic nerve damage, resulting in visual impairment and potential blindness. Elevated intraocular pressure (IOP) is a major risk factor, but some patients still experience disease progression despite IOP-lowering treatments. Genome-wide association studies have linked variations in the Caveolin1/2 (CAV-1/2) gene loci to glaucoma risk. Cav-1, a key protein in caveolae membrane invaginations, is involved in signaling pathways and its absence impairs retinal function. Recent research suggests that Cav-1 is implicated in modulating the BDNF/TrkB signaling pathway in retinal ganglion cells, which plays a critical role in retinal ganglion cell (RGC) health and protection against apoptosis. Understanding the interplay between these proteins could shed light on glaucoma pathogenesis and provide potential therapeutic targets.

Caveolin-1: A Review of Intracellular Functions, Tissue-Specific Roles, and Epithelial Tight Junction Regulation

Caveolin-1 (Cav1) is a vital protein for many cellular processes and is involved in both the positive and negative regulation of these processes. Cav1 exists in multiple cellular compartments depending on its role. Of particular interest is its contribution to the formation of plasma membrane invaginations called caveolae and its involvement in cytoskeletal interactions, endocytosis, and cholesterol trafficking. Cav1 participates in stem cell differentiation as well as proliferation and cell death pathways, which is implicated in tumor growth and metastasis. Additionally, Cav1 has tissue-specific functions that are adapted to the requirements of the cells within those tissues. Its role has been described in adipose, lung, pancreatic, and vascular tissue and in epithelial barrier maintenance. In both the intestinal and the blood brain barriers, Cav1 has significant interactions with junctional complexes that manage barrier integrity. Tight junctions have a close relationship with Cav1 and this relationship affects both their level of expression and their location within the cell. The ubiquitous nature of Cav1 both within the cell and within specific tissues is what makes the protein important for ongoing research as it can assist in further understanding pathophysiologic processes and can potentially be a target for therapies.

PKCα Isoform Inhibits Insulin Signaling and Aggravates Neuronal Insulin Resistance

Overexpression of PKCα has been linked to inhibit insulin signaling disrupting IRS-1 and Akt phosphorylations in skeletal muscle. PKCα inhibits IRS-1 and Akt phosphorylations, but not required for insulin-stimulated glucose transport in skeletal muscles. Inhibition of PKCα increased whereas in some studies decreased GLUT-4 levels at the plasma membrane in skeletal muscles and adipocytes. Controversial studies have reported opposite expression pattern of PKCα expression in insulin-resistant skeletal muscles. These findings indicate that the role of PKCα on insulin signaling is controversial and could be tissue specific. Evidently, studies are required to decipher the role of PKCα in regulating insulin signaling and preferably in other cellular systems. Utilizing neuronal cells, like Neuro-2a, SHSY-5Y and insulin-resistant diabetic mice brain tissues; we have demonstrated that PKCα inhibits insulin signaling, through IRS-Akt pathway in PP2A-dependent mechanism by an AS160-independent route involving 14-3-3ζ. Inhibition and silencing of PKCα improves insulin sensitivity by increasing GLUT-4 translocation to the plasma membrane and glucose uptake. PKCα regulates GSK3 isoforms in an opposite manner in insulin-sensitive and in insulin-resistant condition. Higher activity of PKCα aggravates insulin-resistant neuronal diabetic condition through GSK3β but not GSK3α. Our results mechanistically explored the contribution of PKCα in regulating neuronal insulin resistance and diabetes, which opens up new avenues in dealing with metabolic disorders and neurodegenerative disorders.

Molecular pathogenesis, mechanism and therapy of Cav1 in prostate cancer

Prostate cancer is the second incidence of malignant tumors in men worldwide. Its incidence and mortality are increasing year by year. Enhanced expression of Cav1 in prostate cancer has been linked to both proliferation and metastasis of cancer cells, influencing disease progression. Dysregulation of the Cav1 gene shows a notable association with prostate cancer. Nevertheless, there is no systematic review to report about molecular signal mechanism of Cav1 and drug treatment in prostate cancer. This article reviews the structure, physiological and pathological functions of Cav1, the pathogenic signaling pathways involved in prostate cancer, and the current drug treatment of prostate cancer. Cav1 mainly affects the occurrence of prostate cancer through AKT/mTOR, H-RAS/PLCε, CD147/MMPs and other pathways, as well as substance metabolism including lipid metabolism and aerobic glycolysis. Baicalein, simvastatin, triptolide and other drugs can effectively inhibit the growth of prostate cancer. As a biomarker of prostate cancer, Cav1 may provide a potential therapeutic target for the treatment of prostate cancer.

Simulations suggest a scaffolding mechanism of membrane deformation by the caveolin 8S complex

Caveolins form complexes of various sizes that deform membranes into polyhedral shapes. However, the recent structure of the 8S complex was disk-like with a flat membrane-binding surface. How can a flat complex deform membranes into nonplanar structures? Molecular dynamics simulations revealed that the 8S complex rapidly takes the form of a suction cup. Simulations on implicit membrane vesicles determined that binding is stronger when E140 gets protonated. In that case, the complex binds much more strongly to 5- and 10-nm-radius vesicles. A concave membrane-binding surface readily explains the membrane-deforming ability of caveolins by direct scaffolding. We propose that the 8S complex sits at the vertices of the caveolar polyhedra, rather than at the center of the polyhedral faces.

Caveolin-3 negatively regulates endocytic recycling of cardiac KATP channels

Sarcolemmal ATP-sensitive potassium (KATP) channels play a vital role in cardioprotection. Cardiac KATP channels are enriched in caveolae and physically interact with the caveolae structural protein caveolin-3 (Cav3). Disrupting caveolae impairs the regulation of KATP channels through several signaling pathways. However, the direct functional effect of Cav3 on KATP channels is still poorly understood. Here, we used the cardiac KATP channel subtype, Kir6.2/SUR2A, and showed that Cav3 greatly reduced KATP channel surface density and current amplitude in a caveolae-independent manner. A screen of Cav3 functional domains revealed that a 25 amino acid region in the membrane attachment domain of Cav3 is the minimal effective segment (MAD1). The peptide corresponding to the MAD1 segment decreased KATP channel current in a concentration-dependent manner with an IC50 of ∼5 μM. The MAD1 segment prevented KATP channel recycling, thus decreasing KATP channel surface density and abolishing the cardioprotective effect of ischemic preconditioning. Our research identified the Cav3 MAD1 segment as a novel negative regulator of KATP channel recycling, providing pharmacological potential in the treatment of diseases with KATP channel trafficking defects.NEW & NOTEWORTHY Cardiac KATP channels physically interact with caveolin-3 in caveolae. In this study, we investigated the functional effect of caveolin-3 on KATP channel activity and identified a novel segment (MAD1) in the C-terminus domain of Caveolin-3 that negatively regulates KATP channel surface density and current amplitude by impairing KATP channel recycling. The peptide corresponding to the MAD1 segment abolished the cardioprotective effect of ischemic preconditioning.

Caveolin-1 Autonomously Regulates Hippocampal Neurogenesis Via Mitochondrial Dynamics

The mechanisms underlying adult hippocampal neurogenesis (AHN) are not fully understood. AHN plays instrumental roles in learning and memory. Understanding the signals that regulate AHN has implications for brain function and therapy. Here we show that Caveolin-1 (Cav-1), a protein that is highly enriched in endothelial cells and the principal component of caveolae, autonomously regulates AHN. Conditional deletion of Cav-1 in adult neural progenitor cells (nestin +) led to increased neurogenesis and enhanced performance of mice in contextual discrimination. Proteomic analysis revealed that Cav-1 plays a role in mitochondrial pathways in neural progenitor cells. Importantly, Cav-1 was localized to the mitochondria in neural progenitor cells and modulated mitochondrial fission-fusion, a critical process in neurogenesis. These results suggest that Cav-1 is a novel regulator of AHN and underscore the impact of AHN on cognition.

JNTX-101, a novel albumin-encapsulated gemcitabine prodrug, is efficacious and operates via caveolin-1-mediated endocytosis

Albumin is an attractive candidate carrier for the development of novel therapeutic drugs. Gemcitabine has been FDA approved for the treatment of solid tumors; however, new drugs that optimize gemcitabine delivery are not available for clinical use. The aim of this study was to test the efficacy of a novel albumin-encapsulated gemcitabine prodrug, JNTX-101, and investigate whether Cav-1 expression predicts the therapeutic efficacy of JNTX-101. We first determined the treatment efficacy of JNTX-101 in a panel of pancreatic/lung cancer cell lines and found that increases in Cav-1 expression resulted in higher uptake of albumin, while Cav-1 depletion attenuated the sensitivity of cells to JNTX-101. In addition, decreased Cav-1 expression markedly reduced JNTX-101-induced apoptotic cell death in a panel of cells, particularly in low-serum conditions. Furthermore, we tested the therapeutic efficacy of JNTX-101 in xenograft models and the role of Cav-1 in JNTX-101 sensitivity using a Tet-on-inducible tumor model in vivo. Our data suggest that JNTX-101 effectively inhibits cell viability and tumor growth, and that Cav-1 expression dictates optimal sensitivity to JNTX-101. These data indicate that Cav-1 correlates with JNTX-101 sensitivity, especially under nutrient-deprived conditions, and supports a role for Cav-1 as a predictive biomarker for albumin-encapsulated therapeutics such as JNTX-101.

Caveolin Gene Expression Predicts Clinical Outcomes for Early-Stage HER2-Negative Breast Cancer Treated with Paclitaxel-Based Chemotherapy in the GeparSepto Trial

PURPOSE

Caveolin-1 and -2 (CAV1/2) dysregulation are implicated in driving cancer progression and may predict response to nab-paclitaxel. We explored the prognostic and predictive potential of CAV1/2 expression for patients with early-stage HER2-negative breast cancer receiving neoadjuvant paclitaxel-based chemotherapy regimens, followed by epirubicin and cyclophosphamide.

EXPERIMENTAL DESIGN

We correlated tumor CAV1/2 RNA expression with pathologic complete response (pCR), disease-free survival (DFS), and overall survival (OS) in the GeparSepto trial, which randomized patients to neoadjuvant paclitaxel- versus nab-paclitaxel-based chemotherapy.

RESULTS

RNA sequencing data were available for 279 patients, of which 74 (26.5%) were hormone receptor (HR)-negative, thus triple-negative breast cancer (TNBC). Patients treated with nab-paclitaxel with high CAV1/2 had higher probability of obtaining a pCR [CAV1 OR, 4.92; 95% confidence interval (CI), 1.70-14.22; P = 0.003; CAV2 OR, 5.39; 95% CI, 1.76-16.47; P = 0.003] as compared with patients with high CAV1/2 treated with solvent-based paclitaxel (CAV1 OR, 0.33; 95% CI, 0.11-0.95; P = 0.040; CAV2 OR, 0.37; 95% CI, 0.12-1.13; P = 0.082). High CAV1 expression was significantly associated with worse DFS and OS in paclitaxel-treated patients (DFS HR, 2.29; 95% CI, 1.08-4.87; P = 0.030; OS HR, 4.97; 95% CI, 1.73-14.31; P = 0.003). High CAV2 was associated with worse DFS and OS in all patients (DFS HR, 2.12; 95% CI, 1.23-3.63; P = 0.006; OS HR, 2.51; 95% CI, 1.22-5.17; P = 0.013), in paclitaxel-treated patients (DFS HR, 2.47; 95% CI, 1.12-5.43; P = 0.025; OS HR, 4.24; 95% CI, 1.48-12.09; P = 0.007) and in patients with TNBC (DFS HR, 4.68; 95% CI, 1.48-14.85; P = 0.009; OS HR, 10.43; 95% CI, 1.22-89.28; P = 0.032).

CONCLUSIONS

Our findings indicate high CAV1/2 expression is associated with worse DFS and OS in paclitaxel-treated patients. Conversely, in nab-paclitaxel-treated patients, high CAV1/2 expression is associated with increased pCR and no significant detriment to DFS or OS compared with low CAV1/2 expression.

An Extracellular/Membrane-Bound S100P Pool Regulates Motility and Invasion of Human Extravillous Trophoblast Lines and Primary Cells

Whilst S100P has been shown to be a marker for carcinogenesis, we have shown, in non-physio-pathological states, that its expression promotes trophoblast motility and invasion but the mechanisms explaining these cellular processes are unknown. Here we identify the presence of S100P in the plasma membrane/cell surface of all trophoblast cells tested, whether lines, primary extravillous (EVT) cells, or section tissue samples using either biochemical purification of plasma membrane material, cell surface protein isolation through biotinylation, or microscopy analysis. Using extracellular loss of function studies, through addition of a specific S100P antibody, our work shows that inhibiting the cell surface/membrane-bound or extracellular S100P pools significantly reduces, but importantly only in part, both cell motility and cellular invasion in different trophoblastic cell lines, as well as primary EVTs. Interestingly, this loss in cellular motility/invasion did not result in changes to the overall actin organisation and focal adhesion complexes. These findings shed new light on at least two newly characterized pathways by which S100P promotes trophoblast cellular motility and invasion. One where cellular S100P levels involve the remodelling of focal adhesions whilst another, an extracellular pathway, appears to be focal adhesion independent. Both pathways could lead to the identification of novel targets that may explain why significant numbers of confirmed human pregnancies suffer complications through poor placental implantation.

CAVIN2/SDPR Functioned as a Tumor Suppressor in Lung Adenocarcinoma from Systematic Analysis of Caveolae-Related Genes and Experimental Validation

Background: Caveolae-Related Genes include caveolins and cavins, which are the main component of the fossa and, play important roles in a variety of physiological and pathological processes. Although increasing evidence indicated that caveolins (CAVs) and cavins (CAVINs) are involved in carcinogenesis and progression, their clinical significance and biological function in lung cancer are still limited. Methods: We investigated the expression of CAVs and CAVINs at transcriptional levels using Oncomine and Gene Expression Profiling Interactive Analysis. The protein and mRNA expression levels of CAVs and CAVINs were determined by the human protein atlas website and our surgically resected samples, respectively. The clinical value of prognostic prediction based on the expression of CAVs and CAVINs was also assessed. cBioPortal, GeneMANIA and STRING were used to analyze the molecular characteristics of CAVs and CAVINs in lung adenocarcinoma (LUAD) comprehensively. Finally, we investigated the effect of CAVIN2/SDPR (serum deprivation protein response) on LUAD cells with biological experiments in vitro. Results: The expression of CAV1/2 and CAVIN1/2/3 were significantly downregulated in LUAD and lung squamous cell carcinoma (LUSC). The patients with high expression of CAV1, CAV2, CAV3, CAVIN1 and CAVIN2/SDPR were tightly correlated with a better prognosis in LUAD, while no statistical significances in LUSC. Further, our results found that CAVIN2/SDPR can be identified as a prognostic biomarker independent of other CAVINs in patients with LUAD. Mechanically, the overexpression of CAVIN2/SDPR inhibited cell proliferation and migration owing to the cell apoptosis induction and cell cycle arrest at S phase in LUAD cells. Conclusions: CAVIN2/SDPR functioned as a tumor suppressor, and was able to serve as prognostic biomarkers in precision medicine of LUAD. Mechanically, overexpression of CAVIN2/SDPR inhibited cell proliferation by inducing cell apoptosis and S phase arrest in LUAD cells.

Caveolin-1 and Atherosclerosis: Regulation of LDLs Fate in Endothelial Cells

Caveolae are 50-100 nm cell surface plasma membrane invaginations observed in terminally differentiated cells. They are characterized by the presence of the protein marker caveolin-1. Caveolae and caveolin-1 are involved in regulating several signal transduction pathways and processes. It is well recognized that they have a central role as regulators of atherosclerosis. Caveolin-1 and caveolae are present in most of the cells involved in the development of atherosclerosis, including endothelial cells, macrophages, and smooth muscle cells, with evidence of either pro- or anti-atherogenic functions depending on the cell type examined. Here, we focused on the role of caveolin-1 in the regulation of the LDLs' fate in endothelial cells.

Astragalus polysaccharide alleviates alcoholic-induced hepatic fibrosis by inhibiting polymerase I and transcript release factor and the TLR4/JNK/NF-κB/MyD88 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Astragali Radix (AR), the root of Astragalus membranaceus (Fisch.) Bge. or Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao, known as Huangqi in traditional Chinese medicine, has been widely used in traditional Chinese medicine prescriptions for acute and chronic liver injury. AR was the most important medicine in a Chinese traditional prescription called Huangqi Decoction (HQD), has been used to treat chronic liver diseases since the 11th century. In particular, its major active ingredient, Astragalus polysaccharide (APS), has demonstrated promising effects on inhibiting hepatic fibrosis. However, to date, the effect of APS against alcohol-induced hepatic fibrosis and its underlying molecular mechanisms remains unknown.

AIMS OF THE STUDY

This study aimed to explore the effect and potential molecular mechanisms of APS against alcohol-induced hepatic fibrosis by using network pharmacology and experimental validation.

MATERIALS AND METHODS

The potential targets and underling mechanism of AR in alcoholic liver fibrosis was first predicted using network pharmacology, followed by experimental validation using SD rat model with alcohol-induced hepatic fibrosis. Further, the predicted candidate signaling pathways and potential target polymerase I and transcript release factor (PTRF) were combined to explore the multifaceted mechanism of APS against alcohol-induced hepatic fibrosis. Finally, overexpression of PTRF was explored to reveal the role of PTRF in the mechanism of APS against alcohol-induced hepatic fibrosis.

RESULT

APS exerted potent anti-hepatic fibrosis effects by downregulating genes involved in the Toll-like receptor 4 (TLR4)/JNK/NF-κB/MyD88 pathway. Notably, APS treatment ameliorated the hepatic damage by inhibiting the overexpression of PTRF and decreasing the co-localisation of TLR4/PTRF. Overexpression of PTRF induced reversal of the protective effects of APS on alcohol-induced hepatic fibrosis.

CONCLUSION

This study indicated that APS may alleviate alcohol-induced hepatic fibrosis by inhibiting the activation of PTRF/TLR4/JNK/NF-κB/MyD88 pathway, which provides a scientific elucidation for the mechanisms of APS on the anti-hepatic fibrosis activity and presents a promising therapeutic approach for treating hepatic fibrosis.

The building blocks of caveolae revealed: caveolins finally take center stage

The ability of cells to divide, migrate, relay signals, sense mechanical stimuli, and respond to stress all rely on nanoscale invaginations of the plasma membrane known as caveolae. The caveolins, a family of monotopic membrane proteins, form the inner layer of the caveolar coat. Caveolins have long been implicated in the generation of membrane curvature, in addition to serving as scaffolds for signaling proteins. Until recently, however, the molecular architecture of caveolins was unknown, making it impossible to understand how they operate at a mechanistic level. Over the past year, two independent lines of evidence - experimental and computational - have now converged to provide the first-ever glimpse into the structure of the oligomeric caveolin complexes that function as the building blocks of caveolae. Here, we summarize how these discoveries are transforming our understanding of this long-enigmatic protein family and their role in caveolae assembly and function. We present new models inspired by the structure for how caveolins oligomerize, remodel membranes, interact with their binding partners, and reorganize when mutated. Finally, we discuss emerging insights into structural differences among caveolin family members that enable them to support the proper functions of diverse tissues and organisms.

Caveolin-1 genotypes as predictor for locoregional recurrence and contralateral disease in breast cancer

PURPOSE

Caveolin-1 (CAV1) has been implicated in breast cancer oncogenesis and metastasis and may be a potential prognosticator, especially for non-distant events. CAV1 functions as a master regulator of membrane transport and cell signaling. Several CAV1 SNPs have been linked to multiple cancers, but the prognostic impact of CAV1 SNPs in breast cancer remains unclear. Here, we investigated CAV1 polymorphisms in relation to clinical outcomes in breast cancer.

METHODS

A cohort of 1017 breast cancer patients (inclusion 2002-2012, Sweden) were genotyped using Oncoarray by Ilumina. Patients were followed for up to 15 years. Five out of six CAV1 SNPs (rs10256914, rs959173, rs3807989, rs3815412, and rs8713) passed quality control and were used for haplotype construction. CAV1 genotypes and haplotypes in relation to clinical outcomes were assessed with Cox regression and adjusted for potential confounders (age, tumor characteristics, and adjuvant treatments).

RESULTS

Only one SNP was associated with lymph node status, no other SNPs or haplotypes were associated with tumor characteristics. The CAV1 rs3815412 CC genotype (5.8% of patients) was associated with increased risk of contralateral breast cancer, adjusted hazard ratio (HR_adj) 4.26 (95% CI 1.86-9.73). Moreover, the TTACA haplotype (13% of patients) conferred an increased risk for locoregional recurrence HR_adj 2.24 (95% CI 1.24-4.04). No other genotypes or haplotypes were associated with clinical outcome.

CONCLUSION

CAV1 polymorphisms were associated with increased risk for locoregional recurrence and contralateral breast cancer. These findings may identify patients that could derive benefit from more tailored treatment to prevent non-distant events, if confirmed.

Exposure to acute waterborne cadmium caused severe damage on lipid metabolism of freshwater fish, revealed by nuclear lipid droplet deposition in hepatocytes of rare minnow

Cadmium (Cd) is a widely distributed aquatic toxic heavy metal with the potential to disrupt fish metabolism; however, more research is needed to clarify the underlying mechanisms. In the present study, rare minnows (Gobiocypris rarus) were used to detect the effects of cadmium on freshwater fish lipid metabolism and its underlying mechanism by histopathological observation, measurement of serum and liver biochemical indexes, and analysis of gene expression in terms of lipid oxidation, synthesis and transport. Here, severe damage, such as cytoplasmic lipid droplet (LD) accumulation, ectopic deposition of LDs, and the appearance of nuclear LDs (nLDs), was detected after exposure to 2.0 mg/L or higher concentrations (2.5 and 2.8 mg/L CdCl₂) for 96 h. Other damage included abnormal increases in rough endoplasmic reticulum (RER) lamellae in a fingerprint or concentric circle pattern and necrosis of hepatocytes, and which was observed in the livers of fish exposed to 2.0 mg/L CdCl_2.. Both hepatic and serum lipids, such as triglycerides and total cholesterol, were significantly increased after exposure to 2.0 mg/L CdCl₂, as was serum lipase (LPS). Hepatic lipase and lipoprotein lipase remained unchanged, in accordance with the unchanged hepatic mRNA transcripts of PPARɑ. Furthermore, the mRNA transcripts of both SCD and SQLE were significantly decreased. Moreover, hepatic and serum low-density and high-density lipoprotein cholesterol showed significant changes, which were accompanied by a significant increase and decrease in hepatic APOAI and APOB100 mRNA levels, respectively. All the results indicate the presence of severe damage to hepatic lipid metabolism and that disrupted lipid transport may play a key role in the accumulation of hepatic LDs. In addition, the hepatic nLDs of nonmammalian vertebrates and their location across the nuclear envelope are intriguing, suggesting that large-size nLDs are a common marker for severe liver damage.

Biomarkers in diabetic neuropathy

CONTEXT

The prevalence of diabetic neuropathy is drastically increasing in the world. To halt the progression of diabetic neuropathy, there is an unmet need to have potential biomarkers for the diagnosis and new drug discovery.

OBJECTIVE

To study various biomarkers involved in the pathogenesis of diabetic neuropathy.

METHODS

The literature was searched with the help of various scientific databases and resources like PubMed, ProQuest, Scopus, and Google scholar from the year 1976 to 2020.

RESULTS

Biomarkers of diabetic neuropathy are categorised as inflammatory biomarkers such as MCP-1, VEGF, TRPV1, NF-κB; oxidative biomarkers such as adiponectin, NFE2L2; enzyme biomarkers like NADPH, ceruloplasmin, HO-1, DPP-4, PARP α; miscellaneous biomarkers such as SIRT1, caveolin 1, MALAT1, and microRNA. All biomarkers have a significant role in the pathogenesis of diabetic neuropathy.

CONCLUSION

These biomarkers have a potential role in the progression of diabetic neuropathy and can be considered as potential targets for new drug discovery.

Decreased Expression of Urethral Caveolin-1, -2, and -3 in the Rat Model of Overactive Bladder: Potential Mediator of Functional Interaction of Urethra and Urinary Bladder

Purpose: To investigate the effect of detrusor overactivity (DO) on the urethral expression of caveolin (CAV)-1, -2, and -3 of urethra in an animal model of cyclophosphamide (CYP)-induced cystitis rat.Methods: Female Sprague-Dawley rats were divided into the control group (n=20) and the cystitis group (n=20). Cystitis was induced by intraperitoneal injection of CYP (200 mg/kg). An urodynamic study was done 3 days after the CYP injection to measure functional change of the urinary bladder and urethra. Cellular localization and expression of CAV-1, -2, and -3 in the rat urethra were determined by immunohistochemistry (IHC) and Western blot.Results: Urodynamic experiments demonstrated a decreased contraction interval in the cystitis group compared to the control (3.9±1.0 minutes vs. 6.6±1.2 minutes, P<0.05). Conversely, contraction pressure increased significantly in the cystitis group compared to the control (22.4±0.7 mmHg vs. 11.5±0.4 mmHg, P<0.05). The urethral pressure was decreased in the cystitis group compared to the control (4.05 ±2.5 mmHg vs. 5.8 ±2.8 mmHg, P <0.05). The IHC and Western blot data showed that CAV-1, -2, and -3 expression decreased significantly in the cystitis group compared control group (P<0.05).Conclusions: The decreased urethral CAV-1, -2, and -3 in the DO rats suggests that CAVs might be related with the functional change of urethra in association with DO of urinay bladder.

Unrevealing the Mystery of Latent Leishmaniasis: What Cells Can Host Leishmania?

Leishmania spp. (Kinetoplastida) are unicellular parasites causing leishmaniases, neglected tropical diseases of medical and veterinary importance. In the vertebrate host, Leishmania parasites multiply intracellularly in professional phagocytes, such as monocytes and macrophages. However, their close relative with intracellular development-Trypanosoma cruzi-can unlock even non-professional phagocytes. Since Leishmania and T. cruzi have similar organelle equipment, is it possible that Leishmania can invade and even proliferate in cells other than the professional phagocytes? Additionally, could these cells play a role in the long-term persistence of Leishmania in the host, even in cured individuals? In this review, we provide (i) an overview of non-canonical Leishmania host cells and (ii) an insight into the strategies that Leishmania may use to enter them. Many studies point to fibroblasts as already established host cells that are important in latent leishmaniasis and disease epidemiology, as they support Leishmania transformation into amastigotes and even their multiplication. To invade them, Leishmania causes damage to their plasma membrane and exploits the subsequent repair mechanism via lysosome-triggered endocytosis. Unrevealing the interactions between Leishmania and its non-canonical host cells may shed light on the persistence of these parasites in vertebrate hosts, a way to control latent leishmaniasis.

Muscle regeneration in gilthead sea bream: Implications of endocrine and local regulatory factors and the crosstalk with bone

Fish muscle regeneration is still a poorly known process. In the present study, an injury was done into the left anterior epaxial skeletal muscle of seventy 15 g gilthead sea bream (Sparus aurata) juveniles to evaluate at days 0, 1, 2, 4, 8, 16 and 30 post-wound, the expression of several muscle genes. Moreover, transcripts' expression in the bone (uninjured tissue) was also analyzed. Histology of the muscle showed the presence of dead tissue the first day after injury and how the damaged fibers were removed and replaced by new muscle fibers by day 16 that kept growing up to day 30. Gene expression results showed in muscle an early upregulation of igf-2 and a downregulation of ghr-1 and igf-1. Proteolytic systems expression increased with capn2 and ctsl peaking at 1 and 2 days post-injury, respectively and mafbx at day 8. A pattern of expression that fitted well with active myogenesis progression 16 days after the injury was then observed, with the recovery of igf-1, pax7, cmet, and cav1 expression; and later on, that of cav3 as well. Furthermore, the first days post-injury, the cytokines il-6 and il-15 were also upregulated confirming the tissue inflammation, while tnfα was only upregulated at days 16 and 30 to induce satellite cells recruitment; overall suggesting a possible role for these molecules as myokines. The results of the bone transcripts showed an upregulation first, of bmp2 and ctsk at days 1 and 2, respectively; then, ogn1 and ocn peaked at day 4 in parallel to mstn2 downregulation, and runx2 and ogn2 increased after 8 days of muscle injury, suggesting a possible tissue crosstalk during the regenerative process. Overall, the present model allows studying the sequential involvement of different regulatory molecules during muscle regeneration, as well as the potential relationship between muscle and other tissues such as bone to control musculoskeletal development and growth, pointing out an interesting new line of research in this group of vertebrates.

Early Subcellular Hepatocellular Alterations in Mice Post Hydrodynamic Transfection: An Explorative Study

Hydrodynamic transfection (HT) or hydrodynamic tail vein injection (HTVi) is among the leading technique that is used to deliver plasmid genes mainly into the liver of live mice or rats. The DNA constructs are composed of coupled plasmids, while one contains the gene of interest that stably integrate into the hepatocyte genome with help of the other consisting sleeping beauty transposase system. The rapid injection of a large volume of DNA-solution through the tail vein induces an acute cardiac congestion that refluxed into the liver, mainly in acinus zone 3, also found through our EM study. Although, HT mediated hydrodynamic force can permeabilizes the fenestrated sinusoidal endothelium of liver, but the mechanism of plasmid incorporation into the hepatocytes remains unclear. Therefore, in the present study, we have hydrodynamically injected 2 mL volume of empty plasmid (transposon vector) or saline solution (control) into the tail vein of anesthetized C57BL/6J/129Sv mice. Liver tissue was resected at different time points from two animal group conditions, i.e., one time point per animal (1, 5, 10-20, 60 min or 24 and 48 hrs after HT) or multiple time points per animal (0, 1, 2, 5, 10, 20 min) and quickly fixed with buffered 4% osmium tetroxide. The tissues fed with only saline solution was also resected and fixed in the similar way. EM evaluation from the liver ultrathin sections reveals that swiftly after 1 min, the hepatocytes near to the central venule in the acinus zone 3 shows cytoplasmic membrane-bound vesicles. Such vesicles increased in both numbers and size to vacuoles and precisely often found in the proximity to the nucleus. Further, EM affirm these vacuoles are also optically empty and do not contain any electron dense material. Although, some of the other hepatocytes reveals sign of cell damage including swollen mitochondria, dilated endoplasmic reticulum, Golgi apparatus and disrupted plasma membrane, but most of the hepatocytes appeared normal. The ultrastructural findings in the mice injected with empty vector or saline injected control mice were similar. Therefore, we have interpreted the vacuole formation as nonspecific endocytosis without specific interactions at the plasma membrane.

Effects of periodic mechanical stress on cytoskeleton dependent lipid raft-induced integrin ɑ1 activation in rat nucleus pulposus cells

Extracellular matrix (ECM) production and nucleus pulposus (NP) cell migration increase under periodic mechanical stress (PMS), but the underpinning regulatory mechanism remains unclear. This work aimed to examine the regulatory effects of cytoskeleton-lipid raft-integrin α1 signaling in NP cells exposed to PMS. Briefly, In NP cells, cytoskeleton rearrangement, lipid raft aggregation and integrin α1 expression in the stress and control groups were assessed by immunofluorescent staining and immunoblot. In addition, cell migration and ECM gene expression were detected by a scratch test and quantitative reverse transcription polymerase chain reaction (qRT‑PCR), respectively. As a result, PMS up-regulated ECM gene expression and enhanced NP cell migration (both P < 0.05), accompanied by increased integrin α1, lipid raft, caveolin-3, F-actin and β-tubulin amounts. Pretreatment with the lipid raft inhibitor methyl-β-cyclodextrin (MβCD) or small interfering RNA (siRNA) targeting caveolin-3 resulted in decreased ECM mRNA synthesis and cell migration induced by PMS (both P < 0.05); meanwhile, integrin α1 expression was also reduced. F-actin and β-tubulin inhibition by cytochalasin D and colchicine, respectively, not only reduced ECM mRNA synthesis and cell migration (both P < 0.05), but also disrupted lipid raft and caveolin-3 amount increases induced by PMS in NP cells. In conclusion, PMS promotes ECM mRNA up-regulation and cell migration through the cytoskeleton-lipid raft-integrin α1 signaling pathway, inhibiting cytoskeleton and lipid rafts could block the cellular effects.

The interaction of membrane estradiol receptors and metabotropic glutamate receptors in adaptive and maladaptive estradiol-mediated motivated behaviors in females

Estrogen receptors were initially identified as intracellular, ligand-regulated transcription factors that result in genomic change upon ligand binding. However, rapid estrogen receptor signaling initiated outside of the nucleus was also known to occur via mechanisms that were less clear. Recent studies indicate that these traditional receptors, estrogen receptor α and estrogen receptor β, can also be trafficked to act at the surface membrane. Signaling cascades from these membrane-bound estrogen receptors (mERs) can rapidly alter cellular excitability and gene expression, particularly through the phosphorylation of CREB. A principal mechanism of neuronal mER action has been shown to occur through glutamate-independent transactivation of metabotropic glutamate receptors (mGlu), which elicits multiple signaling outcomes. The interaction of mERs with mGlu has been shown to be important in many diverse functions in females, including driving motivated behaviors. Experimental evidence suggests that a large part of estradiol-induced neuroplasticity and motivated behaviors, both adaptive and maladaptive, occurs through estradiol-dependent mER activation of mGlu. Herein we will review signaling through estrogen receptors, both "classical" nuclear receptors and membrane-bound receptors, as well as estradiol signaling through mGlu. We will focus on how the interactions of these receptors and their downstream signaling cascades are involved in driving motivated behaviors in females, discussing a representative adaptive motivated behavior (reproduction) and maladaptive motivated behavior (addiction).

Increased Caveolin-2 Expression in Brain Endothelial Cells Promotes Age-Related Neuroinflammation

Aging is a major risk factor for common neurodegenerative diseases. Although multiple molecular, cellular, structural, and functional changes occur in the brain during aging, the involvement of caveolin-2 (Cav-2) in brain ageing remains unknown. We investigated Cav-2 expression in brains of aged mice and its effects on endothelial cells. The human umbilical vein endothelial cells (HUVECs) showed decreased THP-1 adhesion and infiltration when treated with Cav-2 siRNA compared to control siRNA. In contrast, Cav-2 overexpression increased THP-1 adhesion and infiltration in HUVECs. Increased expression of Cav-2 and iba-1 was observed in brains of old mice. Moreover, there were fewer iba-1-positive cells in the brains of aged Cav-2 knockout (KO) mice than of wild-type aged mice. The levels of several chemokines were higher in brains of aged wild-type mice than in young wild-type mice; moreover, chemokine levels were significantly lower in brains of young mice as well as aged Cav-2 KO mice than in their wild-type counterparts. Expression of PECAM1 and VE-cadherin proteins increased in brains of old wild-type mice but was barely detected in brains of young wild-type and Cav-2 KO mice. Collectively, our results suggest that Cav-2 expression increases in the endothelial cells of aged brain, and promotes leukocyte infiltration and age-associated neuroinflammation.

Biochemical and Biophysical Characterization of the Caveolin-2 Interaction with Membranes and Analysis of the Protein Structural Alteration by the Presence of Cholesterol

Caveolin-2 is a protein suitable for the study of interactions of caveolins with other proteins and lipids present in caveolar lipid rafts. Caveolin-2 has a lower tendency to associate with high molecular weight oligomers than caveolin-1, facilitating the study of its structural modulation upon association with other proteins or lipids. In this paper, we have successfully expressed and purified recombinant human caveolin-2 using E. coli. The structural changes of caveolin-2 upon interaction with a lipid bilayer of liposomes were characterized using bioinformatic prediction models, circular dichroism, differential scanning calorimetry, and fluorescence techniques. Our data support that caveolin-2 binds and alters cholesterol-rich domains in the membranes through a CARC domain, a type of cholesterol-interacting domain in its sequence. The far UV-CD spectra support that the purified protein keeps its folding properties but undergoes a change in its secondary structure in the presence of lipids that correlates with the acquisition of a more stable conformation, as shown by differential scanning calorimetry experiments. Fluorescence experiments using egg yolk lecithin large unilamellar vesicles loaded with 1,6-diphenylhexatriene confirmed that caveolin-2 adsorbs to the membrane but only penetrates the core of the phospholipid bilayer if vesicles are supplemented with 30% of cholesterol. Our study sheds light on the caveolin-2 interaction with lipids. In addition, we propose that purified recombinant caveolin-2 can provide a new tool to study protein-lipid interactions within caveolae.

PHLPP isoforms differentially regulate Akt isoforms and AS160 affecting neuronal insulin signaling and insulin resistance via Scribble

BACKGROUND

The aim of the present study was to determine the role of individual PHLPP isoforms in insulin signaling and insulin resistance in neuronal cells.

METHODS

PHLPP isoforms were either silenced or overexpressed individually, and the effects were observed on individual Akt isoforms, AS160 and on neuronal glucose uptake, under insulin sensitive and resistant conditions. To determine PHLPP regulation itself, we tested effect of scaffold protein, Scribble, on PHLPP isoforms and neuronal glucose uptake.

RESULTS

We observed elevated expression of both PHLPP1 and PHLPP2 in insulin resistant neuronal cells (Neuro-2A, mouse neuroblastoma; SHSY-5Y, human neuroblastoma) as well as in the whole brain lysates of high-fat-diet mediated diabetic mice. In insulin sensitive condition, PHLPP isoforms differentially affected activation of all Akt isoforms, wherein PHLPP1 regulated serine phosphorylation of Akt2 and Akt3, while PHLPP2 regulated Akt1 and Akt3. This PHLPP mediated Akt isoform specific regulation activated AS160 affecting glucose uptake. Under insulin resistant condition, a similar trend of results were observed in Akt isoforms, AS160 and glucose uptake. Over-expressed PHLPP isoforms combined with elevated endogenous expression under insulin resistant condition drastically affected downstream signaling, reducing neuronal glucose uptake. No compensation was observed amongst PHLPP isoforms under all conditions tested, indicating independent roles and pointing towards possible scaffolding interactions behind isoform specificity. Silencing of Scribble, a scaffolding protein known to interact with PHLPP, affected cellular localization of both PHLPP1 and PHLPP2, and caused increase in glucose uptake.

CONCLUSIONS

PHLPP isoforms play independent roles via Scribble in regulating Akt isoforms differentially, affecting AS160 and neuronal glucose uptake. Video abstract.

Stabilizing and upregulating Axin with tankyrase inhibitor reverses 5-fluorouracil chemoresistance and proliferation by targeting the WNT/caveolin-1 axis in colorectal cancer cells

Chemoresistance is a main obstacle for colorectal cancer treatment. In this study, we evaluated the effects and mechanisms of the WNT/β-catenin signaling pathway on the chemoresistance of SW480 and SW620 colorectal cancer cells. The activity of β-catenin was activated/inhibited by the small molecule compound GSK-3 inhibitor 6-bromo-indirubin-3'-oxime and the tankyrase inhibitor XAV939. The downstream target genes of the WNT/β-catenin signaling pathway were screened using a cDNA microarray and bioinformatics analysis. Apoptosis induced by 5-Fu, cell cycle distribution and expression levels of WNT/β-catenin/TCF12/caveolin-1 and multidrug resistance proteins were examed by flow cytometry and western blot after β-catenin activation/inhibition and caveolin-1 overexpression/interference. The effect and mechanism of XAV939 on proliferation and apoptosis induced by 5-Fu in xenograft tumors of nude mice were evaluated by immunohistochemistry and TUNEL staining. 6-Bromo-indirubin-3'-oxime treatment increased β-catenin expression by regulating GSK-3β phosphorylation, accompanied by upregulation of TCF12, caveolin-1, P-gp, and MRP2 and downregulation of apoptosis induced by 5-Fu. Conversely, XAV939 treatment decreased β-catenin expression by upregulating Axin, accompanied by downregulation of TCF12, Caveolin-1, P-gp, and MRP2 and upregulation of apoptosis induced by 5-Fu. The caveolin-1 gene was identified as an important downstream gene of the WNT/β-catenin signaling pathway. Caveolin-1 overexpression upregulated β-catenin expression, increased P-gp and MRP2 expression and decreased apoptosis induced by 5-Fu; conversely, caveolin-1 interference caused the opposite effects. In addition, in vivo experiments showed that XAV939 treatment reduced β-catenin expression, increased apoptosis induced by 5-Fu and repressed xenograft tumor growth. Our findings suggested that inhibition of WNT/β-catenin/TCF12/caveolin-1 provides a new promising therapeutic strategy for colorectal cancer treatment.

Caveolar and non-Caveolar Caveolin-1 in ocular homeostasis and disease

Caveolae, specialized plasma membrane invaginations present in most cell types, play important roles in multiple cellular processes including cell signaling, lipid uptake and metabolism, endocytosis and mechanotransduction. They are found in almost all cell types but most abundant in endothelial cells, adipocytes and fibroblasts. Caveolin-1 (Cav1), the signature structural protein of caveolae was the first protein associated with caveolae, and in association with Cavin1/PTRF is required for caveolae formation. Genetic ablation of either Cav1 or Cavin1/PTRF downregulates expression of the other resulting in loss of caveolae. Studies using Cav1-deficient mouse models have implicated caveolae with human diseases such as cardiomyopathies, lipodystrophies, diabetes and muscular dystrophies. While caveolins and caveolae are extensively studied in extra-ocular settings, their contributions to ocular function and disease pathogenesis are just beginning to be appreciated. Several putative caveolin/caveolae functions are relevant to the eye and Cav1 is highly expressed in retinal vascular and choroidal endothelium, Müller glia, the retinal pigment epithelium (RPE), and the Schlemm's canal endothelium and trabecular meshwork cells. Variants at the CAV1/2 gene locus are associated with risk of primary open angle glaucoma and the high risk HTRA1 variant for age-related macular degeneration is thought to exert its effect through regulation of Cav1 expression. Caveolins also play important roles in modulating retinal neuroinflammation and blood retinal barrier permeability. In this article, we describe the current state of caveolin/caveolae research in the context of ocular function and pathophysiology. Finally, we discuss new evidence showing that retinal Cav1 exists and functions outside caveolae.

Caveolin-1, GATA-3, and Ki67 expressions and their correlation with pathological findings in canine bladder urothelial carcinoma

The bladder urothelial carcinoma (UC) represents ~2% of malignant neoplasms in dogs and is a therapeutic challenge in veterinary medicine. Although it is considered the most common bladder cancer in dogs, few previous studies have investigated different markers that correlate with clinical and pathological parameters. Therefore, this study aimed to evaluate Caveolin-1, GATA-3, and Ki67 immunostaining in canine UC samples to evaluate their correlations with histopathological variables. Thirty tumor samples were obtained, and Caveolin-1, GATA-3, and Ki67 expression was assessed by immunohistochemistry and associated with pathological factors by univariate and multivariate analyses. Among the histopathological findings, lymphatic invasion was identified in 53.33% of the tumors, and the mean mitotic count (MC) was 31.82 ± 26.26. Caveolin-1 showed mild-to-high cytoplasmic expression in neoplastic cells, whereas GATA-3 showed mild-to-high nuclear expression. The Ki67 expression revealed a mean of 24.14 ± 16.88% positive cells. In the univariate analysis, no association was found between each marker and the pathological findings. On the other hand, in multivariate analysis, we identified a positive correlation between GATA-3 and MC and a negative correlation between Caveolin-1 and MC. Moreover, lymphatic invasion was positively correlated with histological type and grade, and negatively correlated with MC. In addition, the histological type was positively correlated with the histological grade. Overall, our results indicate that Caveolin-1 and GATA-3 expression could be promising markers for bladder UC aggressiveness.

Emerging Insights into the Molecular Architecture of Caveolin-1

Caveolins are an unusual family of membrane proteins whose primary biological function is to build small invaginated membrane structures at the surface of cells known as caveolae. Caveolins and caveolae regulate numerous signaling pathways, lipid homeostasis, intracellular transport, cell adhesion, and cell migration. They also serve as sensors and protect the plasma membrane from mechanical stress. Despite their many important functions, the molecular basis for how these 50-100 nm "little caves" are assembled and regulate cell physiology has perplexed researchers for 70 years. One major impediment to progress has been the lack of information about the structure of caveolin complexes that serve as building blocks for the assembly of caveolae. Excitingly, recent advances have finally begun to shed light on this long-standing question. In this review, we highlight new developments in our understanding of the structure of caveolin oligomers, including the landmark discovery of the molecular architecture of caveolin-1 complexes using cryo-electron microscopy.

Internalization of Leptospira interrogans via diverse endocytosis mechanisms in human macrophages and vascular endothelial cells

Leptospirosis, one of the leading global causes of morbidity and mortality, is an emerging public health problem, particularly in large urban centers of developing countries. Leptospirosis results from infection with an organism belonging to the Leptospira genus L. interrogans. The extensive invasive ability has previously been documented, however a mechanism that describes how the organism is internalized by human macrophages and transmigrates through human blood vessel remains poorly understood. In the present study, we utilized a human macrophage and vascular endothelial cell line to study the diverse invasive mechanisms by which L. interrogans infections occur. We found that THP-1 and HUVEC had a diverse expression of cell receptors and L. interrogans entered THP-1 and HUVEC by different pathways. In the macrophage model cell line, ITGB1/FAK-signaling mediated microfilament dependent endocytosis with lysosome fusion, whereas ITGB1/CAV-1/PI3K-signaling mediated microfilament dependent endocytosis and transcytosis without lysosome fusion in the endothelial cell model. Shedding of pathogenic leptospires from HUVEC displayed higher viability than those from THP-1. The monolayer of HUVEC maintained integrity during the infection, while 3D imaging showed that leptospires were transmigrated both intra- and intercellularly. These results indicate that endocytosis of leptospires in human macrophages and human vascular endothelial cells are quite different, macrophages are responsible for eliminating leptospires in the human body during the infection while vascular endothelial cells facilitate dissemination of leptospires from blood vessels into target organs where they cause injury.

Leptospirosis is a zoonotic bacterial disease which causes 1.03 million cases and 58,900 deaths each year. Human infections occur when the primary reservoir hosts, such as rodents, contaminate food and water with leptospires. Unlike other bacterial pathogens, leptospires invade the human body through mucosal barriers and enter the bloodstream, which can result in septicemia. Left untreated, leptospirosis can spread into multiple organs and tissues such as lungs, liver and kidneys. Pathological features of this disease include high fever, myalgia, lymphadenectasis, hemorrhaging and jaundice. Human macrophages and vascular endothelial cells play important roles in eliminating and preventing the transmission of this pathogen. We speculated that leptospires could be neutralized in macrophages and subsequently transported by vascular endothelial cells throughout the human body. In this research, the diverse mechanisms of human macrophages and vascular endothelial cells infected by leptospires were explored. Our findings can be used to improve the treatment, prevention, and supervision regarding leptospire transmission and infection.

Identification and validation of a prognostic risk model based on caveolin family genes for breast cancer

Background: Breast cancer (BC) is the most vicious killer of women’s health and is accompanied by increased incidence and mortality rates worldwide. Many studies have demonstrated that caveolins (CAVs) were abnormally expressed in a variety of tumors and implicated in tumorigenesis and cancer progression. However, the role of CAVs in BC remains somewhat contentious.

Methods: We comprehensively explored the expression and prognostic value of CAVs (CAV1-3) in BC utilizing public databases (ONCOMINE, TIMER, UALCAN, and TCGA databases). Then we constructed a prognostic model based on the expression profiles. Also, a prognostic nomogram was built to predict the overall survival (OS). We further investigated the relationship between this signature and immune cell infiltration and the mutational landscape in BC. The R package “pRRophetic” was used to predict chemotherapeutic response in BC patients. Finally, we employed loss-of-function approaches to validate the role of CAVs in BC.

Results: We found that CAVs were significantly downregulated in various cancer types, especially in BC. Low CAV expression was closely related to the malignant clinicopathological characteristics and worse OS and relapse-free survival (RFS) in BC. Then we constructed a prognostic model based on the expression profiles of CAVs, which divided BC patients into two risk groups. The Kaplan–Meier analysis showed that patients in the high-risk group tend to have a poorer prognosis than those in the low-risk group. Multivariate analysis indicated that the risk score and stage were both independent prognostic factors for BC patients, suggesting a complementary value. The clinical profiles and risk module were used to construct a nomogram that could accurately predict the OS in BC. In addition, we found that patients in the low-risk group tend to have a relatively high immune status and a lower mutation event frequency compared to the high-risk group. Furthermore, this signature could predict the response to chemotherapy and immunotherapy. Finally, CAV depletion promoted the colony formation, migration, and invasion of BC cells.

Conclusion: CAVs may serve as novel biomarkers and independent prognostic factors for BC patients. Also, the constructed signature based on CAVs may predict immunotherapeutic responses and provide a novel nomogram for precise outcome prediction of BC.

Selective sphingosine-1-phosphate receptor 1 modulator attenuates blood-brain barrier disruption following traumatic brain injury by inhibiting vesicular transcytosis

BACKGROUND

Traumatic brain injury (TBI) provokes secondary pathological damage, such as damage to the blood-brain barrier (BBB), ischaemia and inflammation. Major facilitator superfamily domain-containing 2a (Mfsd2a) has been demonstrated to be critical in limiting the increase in BBB vesicle transcytosis following brain injury. Recent studies suggest that a novel and selective modulator of the sphingosine-1-phosphate receptor 1 (S1P1), CYM-5442, maintains the integrity of the BBB by restricting vesicle transcytosis during acute ischaemic stroke. In the current study, we investigated whether CYM-5442, evaluated in a short-term study, could protect the brains of mice with acute-stage TBI by reversing the increase in vesicle transport due to reduced Mfsd2a expression after TBI.

METHODS

We used the well-characterized model of TBI caused by controlled cortical impact. CYM-5442 (0.3, 1, 3 mg/kg) was intraperitoneally injected 30 min after surgery for 7 consecutive days. To investigate the effect of CYM-5442 on vesicle transcytosis, we downregulated and upregulated Mfsd2a expression using a specific AAV prior to evaluation of the TBI model. MRI scanning, cerebral blood flow, circulating blood counts, ELISA, TEM, WB, and immunostaining evaluations were performed after brain injury.

RESULTS

CYM-5442 significantly attenuated neurological deficits and reduced brain oedema in TBI mice. CYM-5442 transiently suppressed lymphocyte trafficking but did not induce persistent lymphocytopenia. After TBI, the levels of Mfsd2a were decreased significantly, while the levels of CAV-1 and albumin were increased. In addition, Mfsd2a deficiency caused inadequate sphingosine-1-phosphate (S1P) transport in the brain parenchyma, and the regulation of BBB permeability by Mfsd2a after TBI was shown to be related to changes in vesicle transcytosis. Downregulation of Mfsd2a in mice markedly increased the BBB permeability, neurological deficit scores, and brain water contents after TBI. Intervention with CYM-5442 after TBI protected the BBB by significantly reducing the vesicle transcytosis of cerebrovascular endothelial cells.

CONCLUSION

In addition to transiently suppressing lymphocytes, CYM-5442 alleviated the neurological deficits, cerebral edema and protective BBB permeability in TBI mice by reducing the vesicle transcytosis of cerebrovascular endothelial cells.

Endocytosis-mediated vitellogenin absorption and lipid metabolism in the hindgut-derived placenta of the viviparous teleost Xenotoca eiseni

Certain viviparous animals possess mechanisms for mother-to-embryo nutrient transport during gestation. Xenotoca eiseni is one such viviparous teleost species in which the mother supplies proteins and other components to the offspring developing in the ovary. The embryo possesses trophotaenia, hindgut-derived placental structure, to receive the maternal supplement. However, research on the molecular mechanisms underlying viviparous species is scarce in non-mammalian vertebrates, including teleosts. Thus, we conducted this study to investigate the mechanism for nutrient absorption and degradation in trophotaeniae of X. eiseni. A tracer assay indicated that a lipid transfer protein, vitellogenin (Vtg), was absorbed into the epithelial layer cells of the trophotaeniae. Vtg uptake was significantly suppressed by Pitstop-2, an inhibitor of clathrin-mediated endocytosis. Gene expression analysis indicated that the genes involved in endocytosis-mediated lipolysis and lysosomal cholesterol transport were expressed in the trophotaeniae. In contrast, plasma membrane transporters expressed in the intestinal tract were not functional in the trophotaeniae. Our results suggested that endocytosis-mediated lysosomal lipolysis is one of the mechanisms underlying maternal component metabolism. Thus, our study demonstrated how viviparous teleost species have acquired a unique developmental system that is based on the hindgut-derived placenta.

iTRAQ proteomics of sentinel lymph nodes for identification of extracellular matrix proteins to flag metastasis in early breast cancer

Patients with early breast cancer are affected by metastasis to axillary lymph nodes. Metastasis to these nodes is crucial for staging and quality of surgery. Sentinel Lymph Node Biopsy that is currently used to assess lymph node metastasis is not effective. This necessitates identification of biomarkers that can flag metastasis. Early stage breast cancer patients were recruited. Surgical resection of breast was followed by identification of sentinel lymph nodes. Fresh frozen section biopsy was used to assign metastatic and non-metastatic sentinel lymph nodes. Discovery phase included iTRAQ proteomics coupled with mass spectrometric analysis to identify differentially expressed proteins. Data is available via ProteomeXchange with identifier PXD027668. Validation was done by bioinformatic analysis and ELISA. There were 2398 unique protein groups and 109 differentially expressed proteins comparing metastatic and non-metastatic lymph nodes. Forty nine proteins were up-regulated, and sixty proteins that were down regulated in metastatic group. Bioinformatic analysis showed ECM-receptor interaction pathways to be implicated in lymph node metastasis. ELISA confirmed up-regulation of ECM proteins in metastatic lymph nodes. ECM proteins have requisite parameters to be developed as a diagnostic tool to assess status of sentinel lymph nodes to guide surgical intervention in early breast cancer.

Endothelial β-Catenin Deficiency Causes Blood-Brain Barrier Breakdown via Enhancing the Paracellular and Transcellular Permeability

Disruption of the blood-brain barrier (BBB) causes or contributes to neuronal dysfunction and several central nervous system (CNS) disorders. Wnt/β-catenin signaling is essential for maintaining the integrity of the adult BBB in physiological and pathological conditions, including stroke. However, how the impairment of the endothelial Wnt/β-catenin signaling results in BBB breakdown remains unclear. Furthermore, the individual contributions of different BBB permeability-inducing mechanisms, including intercellular junction damage, endothelial transcytosis, and fenestration, remains unexplored. Here, we induced β-catenin endothelial-specific conditional knockout (ECKO) in adult mice and determined its impact on BBB permeability and the underlying mechanism. β-catenin ECKO reduced the levels of active β-catenin and the mRNA levels of Wnt target genes in mice, indicating downregulation of endothelial Wnt/β-catenin signaling. β-catenin ECKO mice displayed severe and widespread leakage of plasma IgG and albumin into the cerebral cortex, which was absent in wild-type controls. Mechanistically, both the paracellular and transcellular transport routes were disrupted in β-catenin ECKO mice. First, β-catenin ECKO reduced the tight junction protein levels and disrupted the intercellular junction ultrastructure in the brain endothelium. Second, β-catenin ECKO substantially increased the number of endothelial vesicles and caveolae-mediated transcytosis through downregulating Mfsd2a and upregulating caveolin-1 expression. Interestingly, fenestration and upregulated expression of the fenestration marker Plvap were not observed in β-catenin ECKO mice. Overall, our study reveals that endothelial Wnt/β-catenin signaling maintains adult BBB integrity via regulating the paracellular as well as transcellular permeability. These findings may have broad applications in understanding and treatment of CNS disorders involving BBB disruption.

Molecular Mechanisms Underlying Caveolin-1 Mediated Membrane Curvature

Caveolin-1 is one of the main protein components of caveolae that acts as a mechanosensor at the cell membrane. The interactions of caveolin-1 with membranes have been shown to lead to complex effects such as curvature and the clustering of specific lipids. Here, we review the emerging concepts on the molecular interactions of caveolin-1, with a focus on insights from coarse-grain molecular dynamics simulations. Consensus structural models of caveolin-1 report a helix-turn-helix core motif with flanking domains of higher disorder that could be membrane composition dependent. Caveolin-1 appears to be mainly surface-bound and does not embed very deep in the membrane to which it is bound. The most interesting aspect of caveolin-1 membrane binding is the interplay of cholesterol clustering and membrane curvature. Although cholesterol has been reported to cluster in the vicinity of caveolin-1 by several approaches, simulations show that the clustering is maximal in membrane leaflet opposing the surface-bound caveolin-1. The intrinsic negative curvature of cholesterol appears to stabilize the negative curvature in the opposing leaflet. In fact, the simulations show that blocking cholesterol clustering (through artificial position restraints) blocks membrane curvature, and vice versa. Concomitant with cholesterol clustering is sphingomyelin clustering, again in the opposing leaflet, but in a concentration-dependent manner. The differential stress due to caveolin-1 binding and the inherent asymmetry of the membrane leaflets could be the determinant for membrane curvature and needs to be further probed. The review is an important step to reconcile the molecular level details emerging from simulations with the mesoscopic details provided by state of the art experimental approaches.

Functional Diversity of Macropinocytosis

Eukaryotic cells are capable of internalizing different types of cargo by plasma membrane ruffling and forming vesicles in a process known as endocytosis. The most extensively characterized endocytic pathways are clathrin-coated pits, lipid raft/caveolae-mediated endocytosis, phagocytosis, and macropinocytosis. Macropinocytosis is unique among all the endocytic processes due to its nonselective internalization of extracellular fluid, solutes, and membrane in large endocytic vesicles known as macropinosomes with unique susceptibility toward Na+/H+ exchanger inhibitors. Range of cell types capable of macropinocytosis and known to play important role in different physiological processes, which include antigen presentation, nutrient sensing, migration, and signaling. Understanding the physiological function of macropinocytosis will be helpful in filling the gaps in our knowledge and which can be exploited to develop novel therapeutic targets. In this chapter, we discuss the different molecular mechanisms that initiate the process of macropinocytosis with special emphasis on proteins involved and their diversified role in different cell types.

Neuronal KCNQ2/3 channels are recruited to lipid raft microdomains by palmitoylation of BACE1

β-Secretase 1 (β-site amyloid precursor protein [APP]-cleaving enzyme 1, BACE1) plays a crucial role in the amyloidogenesis of Alzheimer’s disease (AD). BACE1 was also discovered to act like an auxiliary subunit to modulate neuronal KCNQ2/3 channels independently of its proteolytic function. BACE1 is palmitoylated at its carboxyl-terminal region, which brings BACE1 to ordered, cholesterol-rich membrane microdomains (lipid rafts). However, the physiological consequences of this specific localization of BACE1 remain elusive. Using spectral Förster resonance energy transfer (FRET), BACE1 and KCNQ2/3 channels were confirmed to form a signaling complex, a phenomenon that was relatively independent of the palmitoylation of BACE1. Nevertheless, palmitoylation of BACE1 was required for recruitment of KCNQ2/3 channels to lipid-raft domains. Two fluorescent probes, designated L10 and S15, were used to label lipid-raft and non-raft domains of the plasma membrane, respectively. Coexpressing BACE1 substantially elevated FRET between L10 and KCNQ2/3, whereas the BACE1-4C/A quadruple mutation failed to produce this effect. In contrast, BACE1 had no significant effect on FRET between S15 probes and KCNQ2/3 channels. A reduction of BACE1-dependent FRET between raft-targeting L10 probes and KCNQ2/3 channels by applying the cholesterol-extracting reagent methyl-β-cyclodextrin (MβCD), raft-disrupting general anesthetics, or pharmacological inhibitors of palmitoylation, all supported the hypothesis of the palmitoylation-dependent and raft-specific localization of KCNQ2/3 channels. Furthermore, mutating the four carboxyl-terminal cysteines (4C/A) of BACE1 abolished the BACE1-dependent increase of FRET between KCNQ2/3 and the lipid raft–specific protein caveolin 1. Taking these data collectively, we propose that the AD-related protein BACE1 underlies the localization of a neuronal potassium channel.

Inward Rectifier Potassium Channels: Membrane Lipid-Dependent Mechanosensitive Gates in Brain Vascular Cells

Cerebral arteries contain two primary and interacting cell types, smooth muscle (SMCs) and endothelial cells (ECs), which are each capable of sensing particular hemodynamic forces to set basal tone and brain perfusion. These biomechanical stimuli help confer tone within arterial networks upon which local neurovascular stimuli function. Tone development is intimately tied to arterial membrane potential (VM) and changes in intracellular [Ca2+] driven by voltage-gated Ca2+ channels (VGCCs). Arterial VM is in turn set by the dynamic interplay among ion channel species, the strongly inward rectifying K+ (Kir) channel being of special interest. Kir2 channels possess a unique biophysical signature in that they strongly rectify, display negative slope conductance, respond to elevated extracellular K+ and are blocked by micromolar Ba2+. While functional Kir2 channels are expressed in both smooth muscle and endothelium, they lack classic regulatory control, thus are often viewed as a simple background conductance. Recent literature has provided new insight, with two membrane lipids, phosphatidylinositol 4,5-bisphosphate (PIP2) and cholesterol, noted to (1) stabilize Kir2 channels in a preferred open or closed state, respectively, and (2) confer, in association with the cytoskeleton, caveolin-1 (Cav1) and syntrophin, hemodynamic sensitivity. It is these aspects of vascular Kir2 channels that will be the primary focus of this review.

Ring Finger Protein 213 in Moyamoya Disease With Pulmonary Arterial Hypertension: A Mini-Review

Moyamoya disease (MMD), most often diagnosed in children and adolescents, is a chronic cerebrovascular disease characterized by progressive stenosis at the terminal portion of the internal carotid artery and an abnormal vascular network at the base of the brain. Recently, many investigators show a great interest in MMD with pulmonary arterial hypertension (PAH). Ring finger protein 213 (RNF213) is a major susceptibility gene for MMD and also has strong correlations with PAH. Therefore, this review encapsulates current cases of MMD with PAH and discusses MMD with PAH in the aspects of epidemiology, pathology, possible pathogenesis, clinical manifestations, diagnosis, and treatment.