Influence of cholesterol/caveolin-1/caveolae homeostasis on membrane properties and substrate adhesion characteristics of adult human mesenchymal stem cells

Post-translational modifications in prion diseases

More than 650 reversible and irreversible post-translational modifications (PTMs) of proteins have been listed so far. Canonical PTMs of proteins consist of the covalent addition of functional or chemical groups on target backbone amino-acids or the cleavage of the protein itself, giving rise to modified proteins with specific properties in terms of stability, solubility, cell distribution, activity, or interactions with other biomolecules. PTMs of protein contribute to cell homeostatic processes, enabling basal cell functions, allowing the cell to respond and adapt to variations of its environment, and globally maintaining the constancy of the milieu interieur (the body's inner environment) to sustain human health. Abnormal protein PTMs are, however, associated with several disease states, such as cancers, metabolic disorders, or neurodegenerative diseases. Abnormal PTMs alter the functional properties of the protein or even cause a loss of protein function. One example of dramatic PTMs concerns the cellular prion protein (PrPC), a GPI-anchored signaling molecule at the plasma membrane, whose irreversible post-translational conformational conversion (PTCC) into pathogenic prions (PrPSc) provokes neurodegeneration. PrPC PTCC into PrPSc is an additional type of PTM that affects the tridimensional structure and physiological function of PrPC and generates a protein conformer with neurotoxic properties. PrPC PTCC into PrPSc in neurons is the first step of a deleterious sequence of events at the root of a group of neurodegenerative disorders affecting both humans (Creutzfeldt-Jakob diseases for the most representative diseases) and animals (scrapie in sheep, bovine spongiform encephalopathy in cow, and chronic wasting disease in elk and deer). There are currently no therapies to block PrPC PTCC into PrPSc and stop neurodegeneration in prion diseases. Here, we review known PrPC PTMs that influence PrPC conversion into PrPSc. We summarized how PrPC PTCC into PrPSc impacts the PrPC interactome at the plasma membrane and the downstream intracellular controlled protein effectors, whose abnormal activation or trafficking caused by altered PTMs promotes neurodegeneration. We discussed these effectors as candidate drug targets for prion diseases and possibly other neurodegenerative diseases.

Cav-1 regulates the bile salt export pump on the canalicular membrane of hepatocytes by PKCα-associated signalling under cholesterol stimulation

BACKGROUND AND AIMS

The secretion of bile salts transported by the bile salt export pump (BSEP) is the primary driving force for the generation of bile flow; thus, it is closely related to the formation of cholesterol stones. Caveolin-1 (Cav-1), an essential player in cell signalling and endocytosis, is known to co-localize with cholesterol-rich membrane domains. This study illustrates the role of Cav-1 and BSEP in cholesterol stone formation.

METHODS

Adult male C57BL/6 mice were used as an animal model. HepG2 cells were cultured under different cholesterol concentrations and BSEP, Cav-1, p-PKCα and Hax-1 expression levels were determined via Western blotting. Expression levels of BSEP and Cav-1 mRNA were detected using real-time PCR. Immunofluorescence and immunoprecipitation assays were performed to study BSEP and Hax-1 distribution. Finally, an ATPase activity assay was performed to detect BSEP transport activity under different cholesterol concentrations in cells.

RESULTS

Under low-concentration stimulation with cholesterol, Cav-1 and BSEP protein and mRNA expression levels significantly increased, PKCα phosphorylation significantly decreased, BSEP binding capacity to Hax-1 weakened, and BSEP function increased. Under high-concentration stimulation with cholesterol, Cav-1 and BSEP protein and mRNA expression levels decreased, PKCα phosphorylation increased, BSEP binding capacity to Hax-1 rose, and BSEP function decreased.

CONCLUSION

Cav-1 regulates the bile salt export pump on the canalicular membrane of hepatocytes via PKCα-associated signalling under cholesterol stimulation.

Can extracellular vesicles be considered as a potential frontier in the treatment of intervertebral disc disease?

As a global public health problem, low back pain (LBP) caused by intervertebral disc degeneration (IDD) seriously affects patients' quality of life. In addition, the prevalence of IDD tends to be younger, which brings a huge burden to individuals and society economically. Current treatments do not delay or reverse the progression of IDD. The emergence of biologic therapies has brought new hope for the treatment of IDD. Among them, extracellular vesicles (EVs), as nanoscale bioactive substances that mediate cellular communication, have now produced many surprising results in the research of the treatment of IDD. This article reviews the mechanisms and roles of EVs in delaying IDD and describes the prospects and challenges of EVs.

Lipid rafts mediate multilineage differentiation of human dental pulp-derived stem cells (DPSCs)

Cell outer membranes contain glycosphingolipids and protein receptors, which are integrated into glycoprotein domains, known as lipid rafts, which are involved in a variety of cellular processes, including receptor-mediated signal transduction and cellular differentiation process. In this study, we analyzed the lipidic composition of human Dental Pulp-Derived Stem Cells (DPSCs), and the role of lipid rafts during the multilineage differentiation process. The relative quantification of lipid metabolites in the organic fraction of DPSCs, performed by Nuclear Magnetic Resonance (NMR) spectroscopy, showed that mono-unsaturated fatty acids (MUFAs) were the most representative species in the total pool of acyl chains, compared to polyunsatured fatty acids (PUFAs). In addition, the stimulation of DPSCs with different culture media induces a multilineage differentiation process, determining changes in the gangliosides pattern. To understand the functional role of lipid rafts during multilineage differentiation, DPSCs were pretreated with a typical lipid raft affecting agent (MβCD). Subsequently, DPSCs were inducted to differentiate into osteoblast, chondroblast and adipoblast cells with specific media. We observed that raft-affecting agent MβCD prevented AKT activation and the expression of lineage-specific mRNA such as OSX, PPARγ2, and SOX9 during multilineage differentiation. Moreover, this compound significantly prevented the tri-lineage differentiation induced by specific stimuli, indicating that lipid raft integrity is essential for DPSCs differentiation. These results suggest that lipid rafts alteration may affect the signaling pathway activated, preventing multilineage differentiation.

Loss of Caveolin-1 Expression in Tumor Cells is Associated with Increased Aggressiveness and Cell Invasion in Oral Squamous Cell Carcinoma

BACKGROUND

Changes in Caveolin-1 (CAV-1) expression are related to tumorigenesis. The aim of this study was to evaluate the role of CAV-1 in tumor progression in oral squamous cell carcinoma (SCC) tissue samples and the effect of CAV-1 silencing on two oral tongue SCC (OTSCC) cell lines (SCC-25, from a primary tumor, and HSC-3 from lymph node metastases).

METHODS

Mycroarray hybridization, mRNA expression, and immunohistochemistry were performed on OSCC tissue samples and corresponding non-tumoral margin tissues. The effects of CAV-1 silencing (siCAV-1) on cell viability, membrane fluidity, on the expression of epithelial to mesenchymal transition (EMT) markers and on cell migration and invasion capacity of OTSCC cell lines were evaluated.

RESULTS

Microarray showed a greater CAV-1 expression (1.77-fold) in OSCC tumors than in non-tumoral tissues and 2.0-fold more in less aggressive OSCCs. However, significant differences in CAV-1 gene expression were not seen between tumors and non-tumoral margins nor CAV-1 with any clinicopathological parameters. CAV-1 protein was localized both in carcinoma and in spindle cells of the tumor microenvironment (TME), and CAV-1 positive TME cells were associated with smaller/more aggressive tumors, independent of the carcinoma cells' expression. Silencing of CAV-1 increased cell viability only in SCC-25 cells. It also stimulated the invasion of HSC-3 cells and increased ECAD and BCAT mRNA in these cells; however, the protein levels of the EMT markers were not affected.

CONCLUSION

Decreased expression of CAV-1 by tumor cells in OSCC and an increase in the TME were associated with increased cell invasiveness and tumor aggressiveness.

Cholesterol-Depletion-Induced Membrane Repair Carries a Raft Conformer of P-Glycoprotein to the Cell Surface, Indicating Enhanced Cholesterol Trafficking in MDR Cells, Which Makes Them Resistant to Cholesterol Modifications

The human P-glycoprotein (P-gp), a transporter responsible for multidrug resistance, is present in the plasma membrane's raft and non-raft domains. One specific conformation of P-gp that binds to the monoclonal antibody UIC2 is primarily associated with raft domains and displays heightened internalization in cells overexpressing P-gp, such as in NIH-3T3 MDR1 cells. Our primary objective was to investigate whether the trafficking of this particular P-gp conformer is dependent on cholesterol levels. Surprisingly, depleting cholesterol using cyclodextrin resulted in an unexpected increase in the proportion of raft-associated P-gp within the cell membrane, as determined by UIC2-reactive P-gp. This increase appears to be a compensatory response to cholesterol loss from the plasma membrane, whereby cholesterol-rich raft micro-domains are delivered to the cell surface through an augmented exocytosis process. Furthermore, this exocytotic event is found to be part of a complex trafficking mechanism involving lysosomal exocytosis, which contributes to membrane repair after cholesterol reduction induced by cyclodextrin treatment. Notably, cells overexpressing P-gp demonstrated higher total cellular cholesterol levels, an increased abundance of stable lysosomes, and more effective membrane repair following cholesterol modifications. These modifications encompassed exocytotic events that involved the transport of P-gp-carrying rafts. Importantly, the enhanced membrane repair capability resulted in a durable phenotype for MDR1 expressing cells, as evidenced by significantly improved viabilities of multidrug-resistant Pgp-overexpressing immortal NIH-3T3 MDR1 and MDCK-MDR1 cells compared to their parents when subjected to cholesterol alterations.

Cholesterol depletion affects caveolin-1 expression, migration and invasion of oral tongue squamous cell carcinoma cell lines

INTRODUCTION

Cholesterol is a key lipid molecule within cell membranes. This is especially true in cavelolas, invaginated membrane nanodomains, which present the protein caveolin-1 (CAV-1). It is important to note that this structure is involved in many cell signalling pathways. Additionally, high cholesterol is seen in different tumor types but little is known in regards to oral tongue squamous cell carcinoma (OTSCC). The aim of this study was to evaluate the influence of cholesterol depletion on primary (SCC-25) and metastatic (HSC-3) OTSCC cell lines.

MATERIALS AND METHODS

Cell membrane fluidity, cell viability, gene and protein expression of CAV-1 and of epithelial-mesenchymal transition (EMT) markers, cell migration in Myogel and invasion-myoma assay were evaluated after cholesterol depletion with methyl-β-cyclodextrin (MβCD - 7.5, 10 or 15 mM) RESULTS: Decreased cell viability and increased membrane fluidity of SCC-25 cells was seen with cholesterol depletion but cell viability was less affected and there was no effect on membrane fluidity in HSC-3. Cholesterol depletion also decreased CAV-1 at 6 h but increased it after 24 h.; both epithelial and mesenchymal EMT genes were upregulated after 6 h, followed by downregulation at 24 h in SCC-25. In HSC-3, CAV-1 was downregulated, and E-cadherin gene (ECAD) was upregulated at 6 h. Only the protein β-catenin in SCC-25 was affected, and cell migration of both cell lines was decreased, affecting SCC-25 more intensely. The invasive capacity within human myoma organotypic model was increased in SCC-25 and decreased in HSC-3.

CONCLUSION

Cholesterol depletion affects CAV-1 and ECAD inversely. This affect also depends on cell type since the invasive capacity was augmented in primary cells while decreased in metastatic cells.

Rafting on the Plasma Membrane: Lipid Rafts in Signaling and Disease

The plasma membrane is not a uniform phospholipid bilayer; it has specialized membrane nano- or microdomains called lipid rafts. Lipid rafts are small cholesterol and sphingolipid-rich plasma membrane islands. Although their existence was long debated, their presence in the plasma membrane of living cells is now well accepted with the advent of super-resolution imaging techniques. It is interesting to note that lipid rafts function to compartmentalize receptors and their regulators and substantially modulate cellular signaling. In this review, we will examine the role of lipid rafts and caveolae-lipid raft-like microdomains with a distinct 3D morphology-in cellular signaling. Moreover, we will investigate how raft compartmentalized signaling regulates diverse physiological processes such as proliferation, apoptosis, immune signaling, and development. Also, the deregulation of lipid raft-mediated signaling during tumorigenesis and metastasis will be explored.

Lipid Raft Facilitated Receptor Organization and Signaling: A Functional Rheostat in Embryonic Development, Stem Cell Biology and Cancer

Molecular views of plasma membrane organization and dynamics are gradually changing over the past fifty years. Dynamics of plasma membrane instigate several signaling nexuses in eukaryotic cells. The striking feature of plasma membrane dynamics is that, it is internally transfigured into various subdomains of clustered macromolecules. Lipid rafts are nanoscale subdomains, enriched with cholesterol and sphingolipids, reside as floating entity mostly on the exoplasmic leaflet of the lipid bilayer. In terms of functionality, lipid rafts are unique among other membrane subdomains. Herein, advances on the roles of lipid rafts in cellular physiology and homeostasis are discussed, precisely, on how rafts dynamically harbor signaling proteins, including GPCRs, catalytic receptors, and ionotropic receptors within it and orchestrate multiple signaling pathways. In the developmental proceedings signaling are designed for patterning of overall organism and they differ from the somatic cell physiology and signaling of fully developed organisms. Some of the developmental signals are characteristic in maintenance of stemness and activated during several types of tumor development and cancer progression. The harmony between extracellular signaling and lineage specific transcriptional programs are extremely important for embryonic development. The roles of plasma membrane lipid rafts mediated signaling in lineage specificity, early embryonic development, stem cell maintenance are emerging. In view of this, we have highlighted and analyzed the roles of lipid rafts in receptor organization, cell signaling, and gene expression during embryonic development; from pre-implantation through the post-implantation phase, in stem cell and cancer biology.

The prognosis of lipid reprogramming with the HMG-CoA reductase inhibitor, rosuvastatin, in castrated Egyptian prostate cancer patients: Randomized trial

AIM

The role of surgical castration and rosuvastatin treatment on lipid profile and lipid metabolism related markers was evaluated for their prognostic significance in metastatic prostate cancer (mPC) patients.

METHODS

A total of 84 newly diagnosed castrated mPC patients treated with castration were recruited and divided into two groups: Group I served as control (statin non-users) while group II treated with Rosuvastatin (20 mg/day) for 6 months and served as statin users. Prostate specific antigen (PSA), epidermal growth factor receptor (EGFR), Caveolin-1 (CAV1), lipid profile (LDL, HDL, triglycerides (TG) and total cholesterol (TC)) and lipid metabolism related markers (aldoketoreductase (AKR1C4), HMG-CoA reductase (HMGCR), ATP-binding cassette transporter A1 (ABCA1), and soluble low density lipoprotein receptor related protein 1 (SLDLRP1)) were measured at baseline, after 3 and 6 months. Overall survival (OS) was analyzed by Kaplan-Meier and COX regression for prognostic significance.

RESULTS

Before castration, HMG-CoA reductase was elevated in patients <65 years (P = 0.009). Bone metastasis was associated with high PSA level (P = 0.013), but low HMGCR (P = 0.004). Patients with positive family history for prostate cancer showed high levels of EGFR, TG, TC, LDL, alkaline phosphatase (ALP), but low AKR1C4, SLDLRP1, CAV1 and ABCA-1 levels. Smokers had high CAV1 level (P = 0.017). After 6 months of castration and rosuvastatin administration, PSA, TG, LDL and TC were significantly reduced, while AKR1C4, HMGCR, SLDLRP1, CAV1 and ABCA-1 were significantly increased. Overall survival was reduced in patients with high baseline of SLDLRP1 (>3385 pg/ml, P = 0.001), PSA (>40 ng/ml, P = 0.003) and CAV1 (>4955 pg/ml, P = 0.021).

CONCLUSION

Results of the current study suggest that the peripheral lipidogenic effects of rosuvastatin may have an impact on the treatment outcome and survival of castrated mPC patients.

TRAIL REGISTRATION

This trial was registered at the Pan African Clinical Trial Registry with identification number PACTR202102664354163 and at ClinicalTrials.gov with identification number NCT04776889.

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.

Adeno-associated virus-based caveolin-1 delivery via different routes for the prevention of cholesterol gallstone formation

BACKGROUND

Hepatic caveolin-1 (CAV1) is reduced in cholesterol gallstone disease (CGD). Mice with CAV1 deficiency were prone to develop CGD. However, it remains unknown whether restored hepatic CAV1 expression prevents the development of CGD.

METHODS

C57BL/6 mice were injected with adeno-associated virus 2/8 (AAV2/8) vectors carrying the CAV1 gene (^AAV2/8CAV1) via intravenous (i.v.) or intraperitoneal (i.p.) route and then subjected to a lithogenic diet (LD) for 8 weeks. Uninjected mice were used as controls. The functional consequences of rescuing CAV1 expression by either i.v. or i.p. ^AAV2/8CAV1 treatment for CGD prevention and its subsequent molecular mechanisms were examined.

RESULTS

CAV1 expression was reduced in the liver and gallbladder of LD-fed CGD mice. We discovered that ^AAV2/8CAV1 i.p. delivery results in higher transduction efficiency in the gallbladder than tail vein administration. Although either i.v. or i.p. injection of ^AAV2/8CAV1 improved liver lipid metabolic abnormalities in CGD mice but did not affect LD feeding-induced bile cholesterol supersaturation. In comparison with i.v. administration route, i.p. administration of ^AAV2/8CAV1 obviously increased CAV1 protein levels in the gallbladder of LD-fed mice, and i.p. delivery of ^AAV2/8CAV1 partially improved gallbladder cholecystokinin receptor (CCKAR) responsiveness and impeded bile cholesterol nucleation via the activation of adenosine monophosphate-activated protein kinase (AMPK) signaling, which induced a reduction in gallbladder mucin-1 (MUC1) and MUC5ac expression and gallbladder cholesterol accumulation.

CONCLUSION

CGD prevention by i.p. ^AAV2/8CAV1 injection in LD-fed mice was associated with the improvement of gallbladder stasis, which again supported the notion that supersaturated bile is required but not sufficient for the formation of cholesterol gallstones. Additionally, AAV treatment via the local i.p. injection offers particular advantages over the systemic i.v. route for much more effective gallbladder gene delivery, which will be an excellent tool for conducting preclinical functional studies on the maintenance of normal gallbladder function to prevent CGD.

The Importance of the Plasma Membrane in Atherogenesis

Atherosclerotic cardiovascular diseases are an important medical problem due to their high prevalence, impact on quality of life and prognosis. The pathogenesis of atherosclerosis is an urgent medical and social problem, the solution of which may improve the quality of diagnosis and treatment of patients. Atherosclerosis is a complex chain of events, which proceeds over many years and in which many cells in the bloodstream and the vascular wall are involved. A growing body of evidence suggests that there are complex, closely linked molecular mechanisms that occur in the plasma membranes of cells involved in atherogenesis. Lipid transport, innate immune system receptor function, and hemodynamic regulation are linked to plasma membranes and their biophysical properties. A better understanding of these interrelationships will improve diagnostic quality and treatment efficacy.

Changes of cell membrane fluidity for mesenchymal stem cell spheroids on biomaterial surfaces

BACKGROUND

The therapeutic potential of mesenchymal stem cells (MSCs) in the form of three-dimensional spheroids has been extensively demonstrated. The underlying mechanisms for the altered cellular behavior of spheroids have also been investigated. Cell membrane fluidity is a critically important physical property for the regulation of cell behavior, but it has not been studied for the spheroid-forming cells to date.

AIM

To explore the association between cell membrane fluidity and the morphological changes of MSC spheroids on the surface of biomaterials to elucidate the role of membrane fluidity during the spheroid-forming process of MSCs.

METHODS

We generated three-dimensional (3D) MSC spheroids on the surface of various culture substrates including chitosan (CS), CS-hyaluronan (CS-HA), and polyvinyl alcohol (PVA) substrates. The cell membrane fluidity and cell morphological change were examined by a time-lapse recording system as well as a high-resolution 3D cellular image explorer. MSCs and normal/cancer cells were pre-stained with fluorescent dyes and co-cultured on the biomaterials to investigate the exchange of cell membrane during the formation of heterogeneous cellular spheroids.

RESULTS

We discovered that vesicle-like bubbles randomly appeared on the outer layer of MSC spheroids cultured on different biomaterial surfaces. The average diameter of the vesicle-like bubbles of MSC spheroids on CS-HA at 37 °C was approximately 10 μm, smaller than that on PVA substrates (approximately 27 μm). Based on time-lapse images, these unique bubbles originated from the dynamic movement of the cell membrane during spheroid formation, which indicated an increment of membrane fluidity for MSCs cultured on these substrates. Moreover, the membrane interaction in two different types of cells with similar membrane fluidity may further induce a higher level of membrane translocation during the formation of heterogeneous spheroids.

CONCLUSION

Changes in cell membrane fluidity may be a novel path to elucidate the complicated physiological alterations in 3D spheroid-forming cells.

Interactions between the Nicotinic and Endocannabinoid Receptors at the Plasma Membrane

Compartmentalization, together with transbilayer and lateral asymmetries, provide the structural foundation for functional specializations at the cell surface, including the active role of the lipid microenvironment in the modulation of membrane-bound proteins. The chemical synapse, the site where neurotransmitter-coded signals are decoded by neurotransmitter receptors, adds another layer of complexity to the plasma membrane architectural intricacy, mainly due to the need to accommodate a sizeable number of molecules in a minute subcellular compartment with dimensions barely reaching the micrometer. In this review, we discuss how nature has developed suitable adjustments to accommodate different types of membrane-bound receptors and scaffolding proteins via membrane microdomains, and how this "effort-sharing" mechanism has evolved to optimize crosstalk, separation, or coupling, where/when appropriate. We focus on a fast ligand-gated neurotransmitter receptor, the nicotinic acetylcholine receptor, and a second-messenger G-protein coupled receptor, the cannabinoid receptor, as a paradigmatic example.

Mechanisms of Natural Extracts of Andrographis paniculata That Target Lipid-Dependent Cancer Pathways: A View from the Signaling Pathway

Andrographis paniculata is a local medicinal plant that is widely cultivated in Malaysia. It is comprised of numerous bioactive compounds that can be isolated using water, ethanol or methanol. Among these compounds, andrographolide has been found to be the major compound and it exhibits varieties of pharmacological activities, including anti-cancer properties, particularly in the lipid-dependent cancer pathway. Lipids act as crucial membrane-building elements, fuel for energy-demanding activities, signaling molecules, and regulators of several cellular functions. Studies have shown that alterations in lipid composition assist cancer cells in changing microenvironments. Thus, compounds that target the lipid pathway might serve as potential anti-cancer therapeutic agents. The purpose of this review is to provide an overview of the medicinal chemistry and pharmacology of A. paniculata and its active compounds in terms of anti-cancer activity, primary mechanism of action, and cellular targets, particularly in the lipid-dependent cancer pathway.

Sterolight as imaging tool to study sterol uptake, trafficking and efflux in living cells

Information about cholesterol subcellular localization and transport pathways inside cells is essential for understanding and treatment of cholesterol-related diseases. However, there is a lack of reliable tools to monitor it. This work follows the fate of Sterolight, a BODIPY-labelled sterol, within the cell and demonstrates it as a suitable probe for visualization of sterol/lipid trafficking. Sterolight enters cells through an energy-independent process and knockdown experiments suggest caveolin-1 as its potential cellular carrier. Intracellular transport of Sterolight is a rapid process, and transfer from ER and mitochondria to lysosomes and later to lipid droplets requires the participation of active microtubules, as it can be inhibited by the microtubule disruptor nocodazole. Excess of the probe is actively exported from cells, in addition to being stored in lipid droplets, to re-establish the sterol balance. Efflux occurs through a mechanism requiring energy and may be selectively poisoned with verapamil or blocked in cells with mutated cholesterol transporter NPC1. Sterolight is efficiently transferred within and between different cell populations, making it suitable for monitoring numerous aspects of sterol biology, including the live tracking and visualization of intracellular and intercellular transport.

Cellular stress signaling and the unfolded protein response in retinal degeneration: mechanisms and therapeutic implications

Background

The retina, as part of the central nervous system (CNS) with limited capacity for self-reparation and regeneration in mammals, is under cumulative environmental stress due to high-energy demands and rapid protein turnover. These stressors disrupt the cellular protein and metabolic homeostasis, which, if not alleviated, can lead to dysfunction and cell death of retinal neurons. One primary cellular stress response is the highly conserved unfolded protein response (UPR). The UPR acts through three main signaling pathways in an attempt to restore the protein homeostasis in the endoplasmic reticulum (ER) by various means, including but not limited to, reducing protein translation, increasing protein-folding capacity, and promoting misfolded protein degradation. Moreover, recent work has identified a novel function of the UPR in regulation of cellular metabolism and mitochondrial function, disturbance of which contributes to neuronal degeneration and dysfunction. The role of the UPR in retinal neurons during aging and under disease conditions in age-related macular degeneration (AMD), retinitis pigmentosa (RP), glaucoma, and diabetic retinopathy (DR) has been explored over the past two decades. Each of the disease conditions and their corresponding animal models provide distinct challenges and unique opportunities to gain a better understanding of the role of the UPR in the maintenance of retinal health and function.

Method

We performed an extensive literature search on PubMed and Google Scholar using the following keywords: unfolded protein response, metabolism, ER stress, retinal degeneration, aging, age-related macular degeneration, retinitis pigmentosa, glaucoma, diabetic retinopathy.

Results and conclusion

We summarize recent advances in understanding cellular stress response, in particular the UPR, in retinal diseases, highlighting the potential roles of UPR pathways in regulation of cellular metabolism and mitochondrial function in retinal neurons. Further, we provide perspective on the promise and challenges for targeting the UPR pathways as a new therapeutic approach in age- and disease-related retinal degeneration.

Nanoscale Sub-Compartmentalization of the Dendritic Spine Compartment

Compartmentalization of the membrane is essential for cells to perform highly specific tasks and spatially constrained biochemical functions in topographically defined areas. These membrane lateral heterogeneities range from nanoscopic dimensions, often involving only a few molecular constituents, to micron-sized mesoscopic domains resulting from the coalescence of nanodomains. Short-lived domains lasting for a few milliseconds coexist with more stable platforms lasting from minutes to days. This panoply of lateral domains subserves the great variety of demands of cell physiology, particularly high for those implicated in signaling. The dendritic spine, a subcellular structure of neurons at the receiving (postsynaptic) end of central nervous system excitatory synapses, exploits this compartmentalization principle. In its most frequent adult morphology, the mushroom-shaped spine harbors neurotransmitter receptors, enzymes, and scaffolding proteins tightly packed in a volume of a few femtoliters. In addition to constituting a mesoscopic lateral heterogeneity of the dendritic arborization, the dendritic spine postsynaptic membrane is further compartmentalized into spatially delimited nanodomains that execute separate functions in the synapse. This review discusses the functional relevance of compartmentalization and nanodomain organization in synaptic transmission and plasticity and exemplifies the importance of this parcelization in various neurotransmitter signaling systems operating at dendritic spines, using two fast ligand-gated ionotropic receptors, the nicotinic acetylcholine receptor and the glutamatergic receptor, and a second-messenger G-protein coupled receptor, the cannabinoid receptor, as paradigmatic examples.

Metabolomics and cytokine profiling of mesenchymal stromal cells identify markers predictive of T-cell suppression

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) have shown great promise in the field of regenerative medicine, as many studies have shown that MSCs possess immunomodulatory function. Despite this promise, no MSC therapies have been licensed by the Food and Drug Administration. This lack of successful clinical translation is due in part to MSC heterogeneity and a lack of critical quality attributes. Although MSC indoleamine 2,3-dioxygnease (IDO) activity has been shown to correlate with MSC function, multiple predictive markers may be needed to better predict MSC function.

METHODS

Three MSC lines (two bone marrow-derived, one induced pluripotent stem cell-derived) were expanded to three passages. At the time of harvest for each passage, cell pellets were collected for nuclear magnetic resonance (NMR) and ultra-performance liquid chromatography mass spectrometry (MS), and media were collected for cytokine profiling. Harvested cells were also cryopreserved for assessing function using T-cell proliferation and IDO activity assays. Linear regression was performed on functional data against NMR, MS and cytokines to reduce the number of important features, and partial least squares regression (PLSR) was used to obtain predictive markers of T-cell suppression based on variable importance in projection scores.

RESULTS

Significant functional heterogeneity (in terms of T-cell suppression and IDO activity) was observed between the three MSC lines, as were donor-dependent differences based on passage. Omics characterization revealed distinct differences between cell lines using principal component analysis. Cell lines separated along principal component one based on tissue source (bone marrow-derived versus induced pluripotent stem cell-derived) for NMR, MS and cytokine profiles. PLSR modeling of important features predicted MSC functional capacity with NMR (R² = 0.86), MS (R² = 0.83), cytokines (R² = 0.70) and a combination of all features (R² = 0.88).

CONCLUSIONS

The work described here provides a platform for identifying markers for predicting MSC functional capacity using PLSR modeling that could be used as release criteria and guide future manufacturing strategies for MSCs and other cell therapies.

Multiomics of synaptic junctions reveals altered lipid metabolism and signaling following environmental enrichment

Membrane lipids and their metabolism have key functions in neurotransmission. Here we provide a quantitative lipid inventory of mouse and rat synaptic junctions. To this end, we developed a multiomics extraction and analysis workflow to probe the interplay of proteins and lipids in synaptic signal transduction from the same sample. Based on this workflow, we generate hypotheses about novel mechanisms underlying complex changes in synaptic connectivity elicited by environmental stimuli. As a proof of principle, this approach reveals that in mice exposed to an enriched environment, reduced endocannabinoid synthesis and signaling is linked to increased surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) in a subset of Cannabinoid-receptor 1 positive synapses. This mechanism regulates synaptic strength in an input-specific manner. Thus, we establish a compartment-specific multiomics workflow that is suitable to extract information from complex lipid and protein networks involved in synaptic function and plasticity.

The role of caveolae in endothelial dysfunction

Caveolae, the specialized cell-surface plasma membrane invaginations which are abundant in endothelial cells, play critical roles in regulating various cellular processes, including cholesterol homeostasis, nitric oxide production, and signal transduction. Endothelial caveolae serve as a membrane platform for compartmentalization, modulation, and integration of signal events associated with endothelial nitric oxide synthase, ATP synthase β, and integrins, which are involved in the regulation of endothelial dysfunction and related cardiovascular diseases, such as atherosclerosis and hypertension. Furthermore, these dynamic microdomains on cell membrane are modulated by various extracellular stimuli, including cholesterol and flow shear stress. In this brief review, we summarize the critical roles of caveolae in the orchestration of endothelial function based on recent findings as well as our work over the past two decades.

Molecular Mechanisms of Lipid Metabolism Disorders in Infectious Exacerbations of Chronic Obstructive Pulmonary Disease

Exacerbations largely determine the character of the progression and prognosis of chronic obstructive pulmonary disease (COPD). Exacerbations are connected with changes in the microbiological landscape in the bronchi due to a violation of their immune homeostasis. Many metabolic and immune processes involved in COPD progression are associated with bacterial colonization of the bronchi. The objective of this review is the analysis of the molecular mechanisms of lipid metabolism and immune response disorders in the lungs in COPD exacerbations. The complex role of lipid metabolism disorders in the pathogenesis of some infections is only beginning to be understood, however, there are already fewer and fewer doubts even now about its significance both in the pathogenesis of infectious exacerbations of COPD and in general in the progression of the disease. It is shown that the lipid rafts of the plasma membranes of cells are involved in many processes related to the detection of pathogens, signal transduction, the penetration of pathogens into the cell. Smoking disrupts the normally proceeded processes of lipid metabolism in the lungs, which is a part of the COPD pathogenesis.

Caveolin-1 mediates soft scaffold-enhanced adipogenesis of human mesenchymal stem cells

BACKGROUND

Human bone marrow-derived mesenchymal stem cells (hBMSCs) can differentiate into adipocytes upon stimulation and are considered an appropriate cell source for adipose tissue engineering. In addition to biochemical cues, the stiffness of a substrate that cells attach to has also been shown to affect hBMSC differentiation potential. Of note, most current studies are conducted on monolayer cultures which do not directly inform adipose tissue engineering, where 3-dimensional (3D) scaffolds are often used to create proper tissue architecture. In this study, we aim to examine the adipogenic differentiation of hBMSCs within soft or stiff scaffolds and investigate the molecular mechanism mediating the response of hBMSCs to substrate stiffness in 3D culture, specifically the involvement of the integral membrane protein, caveolin-1 (CAV1), known to regulate signaling in MSCs via compartmentalizing and concentrating signaling molecules.

METHODS

By adjusting the photo-illumination time, photocrosslinkable gelatin scaffolds with the same polymer concentration but different stiffnesses were created. hBMSCs were seeded within soft and stiff scaffolds, and their response to adipogenic induction under different substrate mechanical conditions was characterized. The functional involvement of CAV1 was assessed by suppressing its expression level using CAV1-specific siRNA.

RESULTS

The soft and stiff scaffolds used in this study had a compressive modulus of ~0.5 kPa and ~23.5 kPa, respectively. hBMSCs showed high viability in both scaffold types, but only spread out in the soft scaffolds. hBMSCs cultured in soft scaffolds displayed significantly higher adipogenesis, as revealed by histology, qRT-PCR, and immunostaining. Interestingly, a lower CAV1 level was observed in hBMSCs in the soft scaffolds, concomitantly accompanied by increased levels of Yes-associated protein (YAP) and decreased YAP phosphorylation, when compared to cells seeded in the stiff scaffolds. Interestingly, reducing CAV1 expression with siRNA was shown to further enhance hBMSC adipogenesis, which may function through activation of the YAP signaling pathway.

CONCLUSIONS

Soft biomaterials support superior adipogenesis of encapsulated hBMSCs in 3D culture, which is partially mediated by the CAV1-YAP axis. Suppressing CAV1 expression levels represents a robust method in the promotion of hBMSC adipogenesis.

Celastrol Attenuates Lipid Accumulation and Stemness of Clear Cell Renal Cell Carcinoma via CAV-1/LOX-1 Pathway

Clear cell renal cell carcinoma (ccRCC) is characterized by abnormal lipid accumulation. Celastrol is a pentacyclic triterpene extracted from Tripterygium wilfordii Hook F with anti-cancer activity. In the present study, the anticancer effects of celastrol on ccRCC and the underlying mechanisms were studied. Patients with reduced high density lipoprotein (HDL) and elevated levels of triglyceride (TG), total cholesterol (TC), low density lipoprotein (LDL) was found to have higher risk of ccRCC. In ccRCC clinical samples and cell lines, caveolin-1 (CAV-1) was highly expressed. CAV-1 was identified as a potential prognostic biomarker for ccRCC. Celastrol inhibited tumor growth and decreased lipid deposition promoted by high-fat diet in vivo. Celastrol reduced lipid accumulation and caveolae abundance, inhibited the binding of CAV-1 and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) in ccRCC cells. Furthermore, celastrol attenuated stemness through blocking Wnt/β-catenin pathway after knockdown of CAV-1 and LOX-1. Therefore, the findings suggest that celastrol may be a promising active ingredient from traditional Chinese medicine for anti-cancer therapy.

Comparison of the Physical Characteristics and Behavior in ABC Transporter A1, A7 or Apolipoprotein E Knockout Mice with Lipid Transport Dysfunction

The physical characteristics and behavior of the ATP-binding cassette (ABC) A1, A7, and apolipoprotein (apo) E knockout (KO) mice with lipid transport dysfunction were investigated. These KO mice exhibited adequate growth, and their body masses increased steadily. No remarkable changes were observed in their blood pressure and heart rate. However, there was a slight increase in the heart rate of the ABCA7 KO mice compared with that of the wild-type (WT) mice. ABCA1 and apoE KO mice showed hypo- and hyper-cholesterol concentrations in the plasma, respectively. With regard to the cerebrum, however, the weight of the ABCA1 KO mice was lighter than those of the other genotypes. Furthermore, the cholesterol, triglyceride and phospholipid concentrations, and fatty acid composition were generally similar. Compared with the WT mice, ABCA1 KO mice stayed for a shorter time in the closed arm of the elevated plus maze, and performed worse in the initial stage of the Morris water maze. To thermal stimuli, the ABCA1 and apoE KO mice showed hyper- and hypo-sensitivities, respectively. Only the response of the ABCA1 KO mice was significantly inhibited by pretreatment with indomethacin. A low concentration of the prostaglandin E metabolites was detected in the plasma of the ABCA1 KO mice. Thus, ABCA1 is thought to play a specific role in the neural function.

Caveolin-1, tetraspanin CD81 and flotillins in lymphocyte cell membrane organization, signaling and immunopathology

The adaptive immune system relies on B and T lymphocytes to ensure a specific and long-lasting protection of an individual from a wide range of potential pathogenic hits. Lymphocytes are highly potent and efficient in eliminating pathogens. However, lymphocyte activation must be tightly regulated to prevent incorrect activity that could result in immunopathologies, such as autoimmune disorders or cancers. Comprehensive insight into the molecular events underlying lymphocyte activation is of enormous importance to better understand the function of the immune system. It provides the basis to design therapeutics to regulate lymphocyte activation in pathological scenarios. Most reported defects in immunopathologies affect the regulation of intracellular signaling pathways. This highlights the importance of these molecules, which control lymphocyte activation and homeostasis impacting lymphocyte tolerance to self, cytokine production and responses to infections. Most evidence for these defects comes from studies of disease models in genetically engineered mice. There is an increasing number of studies focusing on lymphocytes derived from patients which supports these findings. Many indirectly involved proteins are emerging as unexpected regulators of the immune system. In this mini-review, we focus in proteins that regulate plasma membrane (PM) compartmentalization and thereby impact the steady state and the activation of immunoreceptors, namely the T cell antigen receptor (TCR) and the B cell antigen receptor (BCR). Some of these membrane proteins are shown to be involved in immune abnormalities; others, however, are not thoroughly investigated in the context of immune pathogenesis. We aim to highlight them and stimulate future research avenues.

Therapeutic effect of integrin-linked kinase gene-modified bone marrow-derived mesenchymal stem cells for streptozotocin-induced diabetic cystopathy in a rat model

Background

Diabetic cystopathy (DCP) is a chronic complication of diabetes mainly within the submucosal and muscular layers of the bladder due to the hyperglycemia-induced ischemia. As no effective therapies are currently available, the administration of optimized mesenchymal stem cells (MSCs) provides a potential treatment of DCP. Thus far, new strategy, such as genetic modification of MSCs, has been developed and has shown promising outcomes of various disorders.

Methods

This study was conducted using integrin-linked kinase (ILK) gene-modified bone marrow-derived stem cells (BMSCs) for streptozotocin (STZ)-induced diabetic cystopathy in a rat model. In total, 68 male Sprague-Dawley rats were randomized into five groups: sham control (control group, n = 10); DCP model alone (DM group, n = 10); DCP rats intravenously treated with BMSCs (BMSC group, n = 16); DCP rats accepted adenoviral vector-infected BMSCs (Ad-null-BMSC group, n = 16) and DCP rats accepted ILK adenoviral vector-infected BMSCs (Ad-ILK-BMSC group, n = 16). Diabetic rats accepted cell transplantation in the experimental group (2 rats per group) were sacrificed for the bladder tissue on the third day, 7th day, and 14th day of treatment respectively ahead of schedule. At 4 weeks after treatment, all rats in five groups accepted urodynamic studies to evaluate bladder function and were sacrificed for bladder tissue.

Results

Our data showed that the underactive bladder function was significantly improved in DCP rats intravenously treated with ILK gene-modified BMSCs compared to those in the DM, BMSCs, and Ad-null-BMSC group. Meanwhile, we found that gene-modified BMSC treatment significantly promoted the activation of the AKT/GSK-3β pathway by increasing phosphorylation and led to the enhancement of survival. In addition, the expression levels of angiogenesis-related protein vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and stromal cell-derived factor-1 (SDF-1) were significantly higher in the Ad-ILK-BMSC group than that in the DM, BMSCs, and Ad-null-BMSC group as assessed by enzyme-linked immunosorbent assay and western blot. As two indicators of vascular endothelial cell markers, the expression of von Willebrand factor (vWF) and CD31 by western blot and immunofluorescent staining revealed that the percentage of the vascular area of the bladder tissue significantly increased in Ad-ILK-BMSC group compared with the BMSCs and Ad-null-BMSC group on the 14th day of treatment. Histological and immunohistochemical staining (hematoxylin and eosin (HE), vWF, Ki67, and TUNNEL) on the bladder tissue revealed statistically different results between groups.

Conclusion

ILK gene-modified BMSCs restored the bladder function and histological construction via promoting the process of angiogenesis and protecting cells from high glucose-associated apoptosis in STZ-induced DCP rat model, which provides a potential for the treatment of patients with DCP.

Selective LXR agonist DMHCA corrects retinal and bone marrow dysfunction in type 2 diabetes

In diabetic dyslipidemia, cholesterol accumulates in the plasma membrane, decreasing fluidity and thereby suppressing the ability of cells to transduce ligand-activated signaling pathways. Liver X receptors (LXRs) make up the main cellular mechanism by which intracellular cholesterol is regulated and play important roles in inflammation and disease pathogenesis. N, N-dimethyl-3β-hydroxy-cholenamide (DMHCA), a selective LXR agonist, specifically activates the cholesterol efflux arm of the LXR pathway without stimulating triglyceride synthesis. In this study, we use a multisystem approach to understand the effects and molecular mechanisms of DMHCA treatment in type 2 diabetic (db/db) mice and human circulating angiogenic cells (CACs), which are hematopoietic progenitor cells with vascular reparative capacity. We found that DMHCA is sufficient to correct retinal and BM dysfunction in diabetes, thereby restoring retinal structure, function, and cholesterol homeostasis; rejuvenating membrane fluidity in CACs; hampering systemic inflammation; and correcting BM pathology. Using single-cell RNA sequencing on lineage-sca1+c-Kit+ (LSK) hematopoietic stem cells (HSCs) from untreated and DMHCA-treated diabetic mice, we provide potentially novel insights into hematopoiesis and reveal DMHCA's mechanism of action in correcting diabetic HSCs by reducing myeloidosis and increasing CACs and erythrocyte progenitors. Taken together, these findings demonstrate the beneficial effects of DMHCA treatment on diabetes-induced retinal and BM pathology.

Effects of Lipids and Lipoproteins on Mesenchymal Stem Cells Used in Cardiac Tissue Regeneration

Mesenchymal stem cells (MSCs) have two characteristics of interest for this paper: the ability to self-renew, and the potential for multiple-lineage differentiation into various cells. MSCs have been used in cardiac tissue regeneration for over a decade. Adult cardiac tissue regeneration ability is quite low; it cannot repair itself after injury, as the heart cells are replaced by fibroblasts and lose function. It is therefore important to search for a feasible way to repair and restore heart function through stem cell therapy. Stem cells can differentiate and provide a source of progenitor cells for cardiomyocytes, endothelial cells, and supporting cells. Studies have shown that the concentrations of blood lipids and lipoproteins affect cardiovascular diseases, such as atherosclerosis, hypertension, and obesity. Furthermore, the MSC lipid profiles, such as the triglyceride and cholesterol content, have been revealed by lipidomics, as well as their correlation with MSC differentiation. Abnormal blood lipids can cause serious damage to internal organs, especially heart tissue. In the past decade, the accumulated literature has indicated that lipids/lipoproteins affect stem cell behavior and biological functions, including their multiple lineage capability, and in turn affect the outcome of regenerative medicine. This review will focus on the effect of lipids/lipoproteins on MSC cardiac regenerative medicine, as well as the effect of lipid-lowering drugs in promoting cardiomyogenesis-associated MSC differentiation.

The Genetic and Endoplasmic Reticulum-Mediated Molecular Mechanisms of Primary Open-Angle Glaucoma

Glaucoma is a heterogenous, chronic, progressive group of eye diseases, which results in irreversible loss of vision. There are several types of glaucoma, whereas the primary open-angle glaucoma (POAG) constitutes the most common type of glaucoma, accounting for three-quarters of all glaucoma cases. The pathological mechanisms leading to POAG pathogenesis are multifactorial and still poorly understood, but it is commonly known that significantly elevated intraocular pressure (IOP) plays a crucial role in POAG pathogenesis. Besides, genetic predisposition and aggregation of abrogated proteins within the endoplasmic reticulum (ER) lumen and subsequent activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent unfolded protein response (UPR) signaling pathway may also constitute important factors for POAG pathogenesis at the molecular level. Glaucoma is commonly known as a ‘silent thief of sight’, as it remains asymptomatic until later stages, and thus its diagnosis is frequently delayed. Thereby, detailed knowledge about the glaucoma pathophysiology is necessary to develop both biochemical and genetic tests to improve its early diagnosis as well as develop a novel, ground-breaking treatment strategy, as currently used medical therapies against glaucoma are limited and may evoke numerous adverse side-effects in patients.

Lipid Raft Destabilization Impairs Mouse TRPA1 Responses to Cold and Bacterial Lipopolysaccharides

The Transient Receptor Potential ankyrin 1 cation channel (TRPA1) is expressed in nociceptive sensory neurons and epithelial cells, where it plays key roles in the detection of noxious stimuli. Recent reports showed that mouse TRPA1 (mTRPA1) localizes in lipid rafts and that its sensitivity to electrophilic and non-electrophilic agonists is reduced by cholesterol depletion from the plasma membrane. Since effects of manipulating membrane cholesterol levels on other TRP channels are known to vary across different stimuli we here tested whether the disruption of lipid rafts also affects mTRPA1 activation by cold or bacterial lipopolysaccharides (LPS). Cooling to 12 °C, E. coli LPS and allyl isothiocyanate (AITC) induced robust Ca2+ responses in CHO-K1 cells stably transfected with mTRPA1. The amplitudes of the responses to these stimuli were significantly lower in cells treated with the cholesterol scavenger methyl β-cyclodextrin (MCD) or with the sphingolipids hydrolyzer sphingomyelinase (SMase). This effect was more prominent with higher concentrations of the raft destabilizers. Our data also indicate that reduction of cholesterol does not alter the expression of mTRPA1 in the plasma membrane in the CHO-K1 stable expression system, and that the most salient effect is that on the channel gating. Our findings further indicate that the function of mTRPA1 is regulated by the local lipid environment and suggest that targeting lipid-TRPA1 interactions may be a strategy for the treatment of pain and neurogenic inflammation.

Fungal allergen-induced IL-33 secretion involves cholesterol-dependent, VDAC-1-mediated ATP release from the airway epithelium

KEY POINTS

Alternaria aeroallergens induce the release of ATP from human bronchial epithelial (HBE) cells by activating a conductive pathway involving voltage-dependent anion channel-1 (VDAC-1) and by exocytosis of ATP localized within membrane vesicles. Inhibition of VDAC-1 blocked Alternaria-evoked Ca²⁺ uptake across the plasma membrane of HBE cells and interleukin (IL)-33 release into the extracellular media. Reducing cholesterol content with a cholesterol scavenger (β-methylcyclodextrin) or statin compound (simvastatin) blocked ATP and IL-33 release by lowering the expression of VDAC-1 in the plasma membrane. Pretreatment with simvastatin for 24 h also inhibited the increase in tight junction macromolecule permeability that occurs following Alternaria exposure. These results establish a novel role for VDAC-1 as a mechanism underlying ATP release induced by fungal allergens and suggests a possible therapeutic use for cholesterol lowering compounds in reducing Alternaria-stimulated allergic inflammation.

ABSTRACT

Human bronchial epithelial (HBE) cells exposed to allergens derived from the common saprophytic fungus, Alternaria alternata release ATP, which in turn stimulates P2X₇ receptor-mediated Ca²⁺ uptake across the plasma membrane. The subsequent increase in intracellular calcium concentration induces proteolytic processing and secretion of interleukin (IL)-33, a critical cytokine involved in the initiation of allergic airway inflammation. A major objective of the present study was to identify the mechanism responsible for conductive ATP release. The results show that pretreatment of HBE cells with inhibitors of the voltage-dependent anion channel-1 (VDAC-1) or treatment with a VDAC-1 selective blocking antibody or silencing mRNA expression of the channel by RNA interference, inhibit Alternaria-evoked ATP release. Moreover, inhibition of VDAC-1 channel activity or reducing protein expression blocked the secretion of IL-33. Similarly, reducing the cholesterol content of HBE cells with simvastatin or the cholesterol scavenger β-methylcyclodextrin also blocked ATP release and IL-33 secretion by decreasing the level of VDAC-1 expression in the plasma membrane. In addition, simvastatin inhibited the increase in tight junction macromolecule permeability that was previously observed after Alternaria exposure. These results demonstrate a novel function for VDAC-1 as the conductive mechanism responsible for Alternaria-induced ATP release, an essential early step in the processing, mobilization and secretion of IL-33 by the airway epithelium. Furthermore, the simvastatin-evoked reduction of VDAC-1 expression in the plasma membrane, suggests the possibility that cholesterol lowering compounds may be beneficial in alleviating allergic airway inflammation induced by fungal allergens.

The importance of caveolins and caveolae to dermatology: Lessons from the caves and beyond

Caveolae are flask-shaped invaginations of the cell membrane rich in cholesterol and sphingomyelin, with caveolin proteins acting as their primary structural components that allow compartmentalization and orchestration of various signalling molecules. In this review, we discuss how pleiotropic functions of caveolin-1 (Cav1) and its intricate roles in numerous cellular functions including lipid trafficking, signalling, cell migration and proliferation, as well as cellular senescence, infection and inflammation, are integral for normal development and functioning of skin and its appendages. We then examine how disruption of the homeostatic levels of Cav1 can lead to development of various cutaneous pathophysiologies including skin cancers, cutaneous fibroses, psoriasis, alopecia, age-related changes in skin and aberrant wound healing and propose how levels of Cav1 may have theragnostic value in skin physiology/pathophysiology.

Molecular regulation and clinical significance of caveolin-1 methylation in chronic lung diseases

Chronic lung diseases represent a largely global burden whose pathogenesis remains largely unknown. Research increasingly suggests that epigenetic modifications, especially DNA methylation, play a mechanistic role in chronic lung diseases. DNA methylation can affect gene expression and induce various diseases. Of the caveolae in plasma membrane of cell, caveolin-1 (Cav-1) is a crucial structural constituent involved in many important life activities. With the increasingly advanced progress of genome-wide methylation sequencing technologies, the important impact of Cav-1 DNA methylation has been discovered. The present review overviews the biological characters, functions, and structure of Cav-1; epigenetic modifications of Cav-1 in health and disease; expression and regulation of Cav-1 DNA methylation in the respiratory system and its significance; as well as clinical potential as disease-specific biomarker and targets for early diagnosis and therapy.

Caveolin as a Universal Target in Dermatology

Caveolin-1 is strongly expressed in different dermal and subdermal cells and physically interacts with signaling molecules and receptors, among them with transforming growth factor beta (TGF-β), matrix metalloproteinases, heat shock proteins, toll-like and glucocorticoid receptors. It should therefore be heavily involved in the regulation of cellular signaling in various hyperproliferative and inflammatory skin conditions. We provide an overview of the role of the caveolin-1 expression in different hyperproliferative and inflammatory skin diseases and discuss its possible active involvement in the therapeutic effects of different well-known drugs widely applied in dermatology. We also discuss the possible role of caveolin expression in development of the drug resistance in dermatology. Caveolin-1 is not only an important pathophysiological factor in different hyperproliferative and inflammatory dermatological conditions, but can also serve as a target for their treatment. Targeted regulation of caveolin is likely to serve as a new treatment strategy in dermatology.

Caveolin-1 in skin aging - From innocent bystander to major contributor

Caveolin-1 (Cav-1) appears to be both a pathophysiological contributor and a target in different inflammatory and hyperproliferative skin conditions as well as in skin aging. Skin fibroblasts demonstrate an up-regulation of Cav-1 expression both in chronological and UV-induced aging, and such an up-regulation was observed both in vitro and in vivo. Typical alterations in aging skin involve a reduction of the dermis thickness, a significant expansion of the dermal white adipose tissue as well as modifications of the content and distribution of hyaluronan, impairment of autophagic flux, a reduction of collagen expression and an increase in tissue inflammation. All of these phenomena can be connected with changes in Cav-1 expression in the aging skin. Modified expression of Cav-1 can also significantly influence the mechanical properties of individual skin layers, thus changing the total mechanical stability of the layered composite skin/WAT, leading to typical structural modifications of the skin surface in the aging skin. Selective reduction of Cav-1 expression has the potential to exert anti-aging effects on the skin.

Porcine sapelovirus enters PK-15 cells via caveolae-dependent endocytosis and requires Rab7 and Rab11

To comprehensively understand the endocytosis of Sapelovirus A (PSV) entry into PK-15 cells, we studied PSV infection in the context of cell perturbations through drug inhibition, siRNA silencing and overexpression of dominant negative (DN) mutants. We showed here that PSV infection of PK-15 cells was unaffected by pretreated with chlorpromazine, EIPA, knockdown of the clathrin heavy chain or overexpression of Eps15 DN mutant. Conversely, PSV infection was sensitive to NH₄Cl, chloroquine, dynasore, nystatin, MβCD and wortmannin with reduced PSV VP1 expression levels and virus titer. Additionally, PSV invasion leaded to rapid actin rearrangement and disruption of the cellular actin network enhanced PSV infection. After internalization the virus was transported to late endosomes and/or cycling endosomes that requires the participation of Rab7 and Rab11. Our findings demonstrate that PSV uses caveolae-dependent endocytosis as the predominant entry portal into PK-15 cells which requires low pH, dynamin, Rab7 and Rab11.