Caveolin-1 plays a critical role in the differentiation of monocytes into macrophages

Anti-CAMP1 IgG promotes macrophage phagocytosis of Cutibacterium acnes type II

Among 5 types of the Christie-Atkins-Munch-Petersen factor (CAMP) of Cutibacterium acnes, CAMP1 is highly expressed in phylotype II as well as IB, and thought to be a virulence factor of opportunistic but fatal blood, soft tissue, and implant-related infections. The target of a human single-chain variable antibody fragment (scFv), recently isolated from a phage display library, has been identified as CAMP1 of phylotype II, using immunoprecipitation followed by mass spectrometry, phage display peptide biopanning, 3D-modelling, and ELISA. The IgG1 format of the antibody could enhance phagocytosis of C. acnes DMST 14916 by THP-1 human monocytes. Our results suggest that the antibody-dependent phagocytosis process is mediated by the caveolae membrane system and involves the induction of IL-1β. This is the first report on the study of a human antibody against CAMP1 of C. acnes phylotype II, of which a potential use as therapeutic antibody against virulence C. acnes infection is postulated.

What could be the function of the spinal muscular atrophy-causing protein SMN in macrophages?

Spinal Muscular Atrophy (SMA), a neurodegenerative disorder, extends its impact beyond the nervous system. The central protein implicated in SMA, Survival Motor Neuron (SMN) protein, is ubiquitously expressed and functions in fundamental processes such as alternative splicing, translation, cytoskeletal dynamics and signaling. These processes are relevant for all cellular systems, including cells of the immune system such as macrophages. Macrophages are capable of modulating their splicing, cytoskeleton and expression profile in order to fulfil their role in tissue homeostasis and defense. However, less is known about impairment or dysfunction of macrophages lacking SMN and the subsequent impact on the immune system of SMA patients. We aimed to review the potential overlaps between SMN functions and macrophage mechanisms highlighting the need for future research, as well as the current state of research addressing the role of macrophages in SMA.

Caveolin-1 forms a complex with P2X7 receptor and tunes P2X7-mediated ATP signaling in mouse bone marrow-derived macrophages

The ionotropic purinergic P2X7 receptor responds to extracellular ATP and can trigger proinflammatory immune signaling in macrophages. Caveolin-1 (Cav-1) is known to modulate functions of macrophages and innate immunity. However, it is unknown how Cav-1 modulates P2X7 receptor activity in macrophages. We herein examined P2X7 receptor activity and macrophage functions using bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Cav-1 knockout (KO) mice. ATP (1 mM) application caused biphasic increase in cytosolic [Ca2+] and sustained decrease in cytosolic [K+]. A specific P2X7 receptor blocker, A-740003, inhibited the maintained cytosolic [Ca2+] increase and cytosolic [K+] decrease. Total internal reflection fluorescent imaging and proximity ligation assays revealed a novel molecular complex formation between P2X7 receptors and Cav-1 in WT BMDMs that were stimulated with lipopolysaccharides. This molecular coupling was increased by ATP application. Specifically, the ATP-induced Ca2+ influx and K+ efflux through P2X7 receptors were increased in Cav-1 KO BMDMs, even though the total and surface protein levels of P2X7 receptors in WT and Cav-1 KO BMDMs were unchanged. Cell-impermeable dye (TO-PRO3) uptake analysis revealed that macropore formation of P2X7 receptors was enhanced in Cav-1 KO BMDMs. Cav-1 KO BMDMs increased ATP-induced IL-1β secretion, reactive oxygen species production, Gasdermin D (GSDMD) cleavage, and lactate dehydrogenase release indicating pyroptosis. A-740003 completely prevented ATP-induced pyroptosis. In combination, these datasets show that Cav-1 has a negative effect on P2X7 receptor activity in BMDMs and that Cav-1 in macrophages may contribute to finely tuned immune responses by preventing excessive IL-1β secretion and pyroptosis.NEW & NOTEWORTHY In bone marrow-derived macrophages, Cav-1 suppresses the macropore formation of P2X7 receptors through their direct or indirect interactions, resulting in reduced membrane permeability of cations (Ca2+ and K+) and large cell-impermeable dye (TO-PRO3) induced by ATP. Cav-1 also inhibits ATP-induced IL-1β secretion, ROS production, GSDMD cleavage, and pyroptosis. Cav-1 contributes to the maintenance of proper immune responses by finely tuning IL-1β secretion and cell death in macrophages.

Quantifying stimulus-response specificity to probe the functional state of macrophages

Immune sentinel macrophages initiate responses to pathogens via hundreds of immune response genes. Each immune threat demands a tailored response, suggesting that the capacity for stimulus-specific gene expression is a key functional hallmark of healthy macrophages. To quantify this property, termed "stimulus-response specificity" (SRS), we developed a single-cell experimental workflow and analytical approaches based on information theory and machine learning. We found that the response specificity of macrophages is driven by combinations of specific immune genes that show low cell-to-cell heterogeneity and are targets of separate signaling pathways. The "response specificity profile," a systematic comparison of multiple stimulus-response distributions, was distinctly altered by polarizing cytokines, and it enabled an assessment of the functional state of macrophages. Indeed, the response specificity profile of peritoneal macrophages from old and obese mice showed characteristic differences, suggesting that SRS may be a basis for measuring the functional state of innate immune cells. A record of this paper's transparent peer review process is included in the supplemental information.

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 is a primary determinant of endothelial stiffening associated with dyslipidemia, disturbed flow, and ageing

Endothelial stiffness is emerging as a major determinant in endothelial function. Here, we analyzed the role of caveolin-1 (Cav-1) in determining the stiffness of endothelial cells (EC) exposed to oxidized low density lipoprotein (oxLDL) under static and hemodynamic conditions in vitro and of aortic endothelium in vivo in mouse models of dyslipidemia and ageing. Elastic moduli of cultured ECs and of the endothelial monolayer of freshly isolated mouse aortas were measured using atomic force microscopy (AFM). We found that a loss of Cav-1 abrogates the uptake of oxLDL and oxLDL-induced endothelial stiffening, as well as endothelial stiffening induced by disturbed flow (DF), which was also oxLDL dependent. Mechanistically, Cav-1 is required for the expression of CD36 (cluster of differentiation 36) scavenger receptor. Genetic deletion of Cav-1 abrogated endothelial stiffening observed in the DF region of the aortic arch, and induced by a high fat diet (4-6 weeks) and significantly blunted endothelial stiffening that develops with advanced age. This effect was independent of stiffening of the sub-endothelium layer. Additionally, Cav-1 expression significantly increased with age. No differences in elastic modulus were observed between the sexes in advanced aged wild type and Cav-1 knockout mice. Taken together, this study demonstrates that Cav-1 plays a critical role in endothelial stiffening induced by oxLDL in vitro and by dyslipidemia, disturbed flow and ageing in vivo.

The genomic response of human granulosa cells (KGN) to melatonin and specific agonists/antagonists to the melatonin receptors

Melatonin is a known modulator of follicle development; it acts through several molecular cascades via binding to its two specific receptors MT1 and MT2. Even though it is believed that melatonin can modulate granulosa cell (GC) functions, there is still limited knowledge of how it can act in human GC through MT1 and MT2 and which one is more implicated in the effects of melatonin on the metabolic processes in the dominant follicle. To better characterize the roles of these receptors on the effects of melatonin on follicular development, human granulosa-like tumor cells (KGN) were treated with specific melatonin receptor agonists and antagonists, and gene expression was analyzed with RNA-seq technology. Following appropriate normalization and the application of a fold change cut-off of 1.5 (FC 1.5, p ≤ 0.05) for each treatment, lists of the principal differentially expressed genes (DEGs) are generated. Analysis of major upstream regulators suggested that the MT1 receptor may be involved in the melatonin antiproliferative effect by reprogramming the metabolism of human GC by activating the PKB signaling pathway. Our data suggest that melatonin may act complementary through both MT1 and MT2 receptors to modulate human GC steroidogenesis, proliferation, and differentiation. However, MT2 receptors may be the ones implicated in transducing the effects of melatonin on the prevention of GC luteinization and follicle atresia at the antral follicular stage through stimulating the PKA pathway.

The Immunomodulatory Role of Hypoxic Tumor-Derived Extracellular Vesicles

Simple Summary

Hypoxia, a characteristic of many cancer types, can suppress the antitumor effector functions of the adaptive and innate immune system. Tumor-cell-derived extracellular vesicles, which function as a mechanism of communication between tumor cells and immune cells, are also affected by hypoxia, and may drive immunosuppression. The aim of this review is to summarize the current knowledge on hypoxic cancer-cell-derived extracellular vesicles in immunosuppression, and to provide an overview of enriched factors (i.e., miRNA and proteins) in hypoxic tumor-derived EVs and their role in immunomodulation. This complete overview may indicate relevant directions for future research into the role of hypoxia in immunosuppression during cancer.

Abstract

Tumor-associated immune cells frequently display tumor-supportive phenotypes. These phenotypes, induced by the tumor microenvironment (TME), are described for both the adaptive and the innate arms of the immune system. Furthermore, they occur at all stages of immune cell development, up to effector function. One major factor that contributes to the immunosuppressive nature of the TME is hypoxia. In addition to directly inhibiting immune cell function, hypoxia affects intercellular crosstalk between tumor cells and immune cells. Extracellular vesicles (EVs) play an important role in this intercellular crosstalk, and changes in both the number and content of hypoxic cancer-cell-derived EVs are linked to the transfer of hypoxia tolerance. Here, we review the current knowledge about the role of these hypoxic cancer-cell-derived EVs in immunosuppression. In addition, we provide an overview of hypoxia-induced factors (i.e., miRNA and proteins) in tumor-derived EVs, and their role in immunomodulation.

Role of Caveolin-1 in Sepsis – A Mini-Review

Sepsis is a generalized disease characterized by an extreme response to a severe infection. Moreover, challenges remain in the diagnosis, treatment and management of septic patients. In this mini-review we demonstrate developments on cellular pathogenesis and the role of Caveolin-1 (Cav-1) in sepsis. Studies have shown that Cav-1 has a significant role in sepsis through the regulation of membrane traffic and intracellular signaling pathways. In addition, activation of apoptosis/autophagy is considered relevant for the progression and development of sepsis. However, how Cav-1 is involved in sepsis remains unclear, and the precise mechanisms need to be further investigated. Finally, the role of Cav-1 in altering cell permeability during inflammation, in sepsis caused by microorganisms, apoptosis/autophagy activation and new therapies under study are discussed in this mini-review.

Targeting macrophage TFEB-14-3-3 epsilon Interface by naringenin inhibits abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a lethal cardiovascular disease, and there is no proven drug treatment for this condition. In this study, by using the Connectivity Map (CMap) approach, we explored naringenin, a naturally occurring citrus flavonoid, as a putative agent for inhibiting AAA. We then validated the prediction with two independent mouse models of AAA, calcium phosphate (CaPO₄)-induced C57BL/6J mice and angiotensin II-infused ApoE^−/− mice. Naringenin effectively blocked the formation of AAAs and the progression of established AAAs. Transcription factor EB (TFEB) is the master regulator of lysosome biogenesis. Intriguingly, the protective role of naringenin on AAA was abolished by macrophage-specific TFEB depletion in mice. Unbiased interactomics, combined with isothermal titration calorimetry (ITC) and cellular thermal shift assays (CETSAs), further revealed that naringenin is directly bound to 14-3-3 epsilon blocked the TFEB-14-3-3 epsilon interaction, and therefore promoted TFEB nuclear translocation and activation. On one hand, naringenin activated lysosome-dependent inhibition of the NLRP3 inflammasome and repressed aneurysmal inflammation. On the other hand, naringenin induced TFEB-dependent transcriptional activation of GATA3, IRF4, and STAT6 and therefore promoted reparative M2 macrophage polarization. In summary, naturally derived naringenin or macrophage TFEB activation shows promising efficacy for the treatment of AAA.

Neuroretinal-Derived Caveolin-1 Promotes Endotoxin-Induced Inflammation in the Murine Retina

Purpose

The immune-privileged environment and complex organization of retinal tissue support the retina's essential role in visual function, yet confound inquiries into cell-specific inflammatory effects that lead to dysfunction and degeneration. Caveolin-1 (Cav1) is an integral membrane protein expressed in several retinal cell types and is implicated in immune regulation. However, whether Cav1 promotes or inhibits inflammatory processes in the retina (as well as in other tissues) remains unclear. Previously, we showed that global-Cav1 depletion resulted in reduced retinal inflammatory cytokine production but paradoxically elevated retinal immune cell infiltration. We hypothesized that these disparate responses are the result of differential cell-specific Cav1 functions in the retina.

Methods

We used Cre/lox technology to deplete Cav1 specifically in the neural retinal (NR) compartment to clarify the role NR-specific Cav1 (NR-Cav1) in the retinal immune response to intravitreal inflammatory challenge induced by activation of Toll-like receptor-4 (TLR4). We used multiplex protein suspension array and flow cytometry to evaluate innate immune activation. Additionally, we used bioinformatics assessment of differentially expressed membrane-associated proteins to infer relationships between NR-Cav1 and immune response pathways.

Results

NR-Cav1 depletion, which primarily affects Müller glia Cav1 expression, significantly altered immune response pathway regulators, decreased retinal inflammatory cytokine production, and reduced retinal immune cell infiltration in response to LPS-stimulated inflammatory induction.

Conclusions

Cav1 expression in the NR compartment promotes the innate TLR4-mediated retinal tissue immune response. Additionally, we have identified novel potential immune modulators differentially expressed with NR-Cav1 depletion. This study further clarifies the role of NR-Cav1 in retinal inflammation.

High intraluminal pressure promotes vascular inflammation via caveolin-1

The aetiology and progression of hypertension involves various endogenous systems, such as the renin angiotensin system, the sympathetic nervous system, and endothelial dysfunction. Recent data suggest that vascular inflammation may also play a key role in the pathogenesis of hypertension. This study sought to determine whether high intraluminal pressure results in vascular inflammation. Leukocyte adhesion was assessed in rat carotid arteries exposed to 1 h of high intraluminal pressure. The effect of intraluminal pressure on signaling mechanisms including reactive oxygen species production (ROS), arginase expression, and NFĸB translocation was monitored. 1 h exposure to high intraluminal pressure (120 mmHg) resulted in increased leukocyte adhesion and inflammatory gene expression in rat carotid arteries. High intraluminal pressure also resulted in a downstream signaling cascade of ROS production, arginase expression, and NFĸB translocation. This process was found to be angiotensin II-independent and mediated by the mechanosensor caveolae, as caveolin-1 (Cav1)-deficient endothelial cells and mice were protected from pressure-induced vascular inflammatory signaling and leukocyte adhesion. Cav1 deficiency also resulted in a reduction in pressure-induced glomerular macrophage infiltration in vivo. These findings demonstrate Cav1 is an important mechanosensor in pressure-induced vascular and renal inflammation.

Statins Directly Influence the Polarization of Adipose Tissue Macrophages: A Role in Chronic Inflammation

Statins represent one of the most widely used classes of drugs in current medicine. In addition to a substantial decrease in atherogenic low density lipoprotein (LDL) particle concentrations, several large trials have documented their potent anti-inflammatory activity. Based on our preliminary data, we showed that statins are able to decrease the proportion of pro-inflammatory macrophages (CD14+16+CD36high) in visceral adipose tissue in humans. In the present study including 118 healthy individuals (living kidney donors), a very close relationship between the pro-inflammatory macrophage proportion and LDL cholesterol levels was found. This was confirmed after adjustment for the most important risk factors. The effect of statins on the proportion of pro-inflammatory macrophages was also confirmed in an experimental model of the Prague hereditary hypercholesterolemia rat. A direct anti-inflammatory effect of fluvastatin on human macrophage polarization in vitro was documented. Based on modifying the LDL cholesterol concentrations, statins are suggested to decrease the cholesterol inflow through the lipid raft of macrophages in adipose tissue and hypercholesterolemia to enhance the pro-inflammatory macrophage phenotype polarization. On the contrary, due to their opposite effect, statins respond with anti-inflammatory activity, affecting the whole organism.

A live attenuated Edwardsiella tarda vaccine induces immunological expression pattern in Japanese flounder (Paralichthys olivaceus) in the early phase of immunization

A previous study showed that an attenuated Edwardsiella tarda strain, TXhfq, as a live vaccine could elicit protective immune effects in fish against E. tarda infection. In the current study, in order to clarify the molecular mechanism of fish immune response at the early stage after TXhfq vaccination, RNA-Seq technology was used to compare the transcriptomes of skin, intestine, and spleen between bath-vaccinated and unvaccinated Japanese flounder (Paralichthys olivaceus). An average of 46.6 million clean reads per library was obtained, ~88.04% of which were successfully mapped to the reference genome, and approximately 24,600 genes were detected in each sample. A total of 565, 878, and 1258 differential expression genes (DEGs) were found in skin, intestine, and spleen, respectively, including 1263 up-regulated genes and 1438 down-regulated genes. The DEGs exhibited different characteristics in each tissue. One hundred and sixteen DEGs belonging to six immune related categories were scrutinized, i.e., inflammatory factors, cytokines, complement and coagulation system, mucins, phagocytosis, and antigen processing and presentation. A protein-protein interaction network was constructed to get the interaction network between immune genes during the early stage of immunization. The top six hub genes highly regulated by TXhfq formed complicated interaction relationship with each other, which were involved in immune processes, notably inflammation and phagocytosis. Our results provide valuable information for the understanding of the immune mechanism underlying the protection of live attenuated vaccines in fish.

Cellular and molecular events of inflammation induced transdifferentiation (EMT) and regeneration (MET) in mesenteric mesothelial cells

In this review we summarize the cellular and molecular events of inflammation induced epithelial-to-mesenchymal (EMT) and mesothelial-to-macrophage transition (MET) during regeneration. Since the receptor transmits the environmental stimulus, downregulating or upregulating the process on an epigenetic level, the intracellular localization of receptors (signaling organelles: early endosomes or lysosomal degradation: late endosomes) plays a crucial role in the signaling events regulating inflammation and regeneration. Therefore, we focused on the internalization of the receptors as well as the intracellular compartmentalization of signaling molecules during EMT and MET. The review draws the reader's attention to the plasticity of mesothelial cells and supports the idea that during inflammation an ambient macrophage population might derive from mesothelial cells.

Increased IL-10+CD206+CD14+M2-like macrophages in alveolar lavage fluid of patients with small cell lung cancer

There are significant differences in pathology, etiology, clinical features, and treatment options between small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). However, the differences of macrophage distribution and its associated function between SCLC and NSCLC are not fully investigated. Through methods of flow cytometry and cytometric bead array, we examined the levels of various subtypes of macrophages, monocytes, and regulatory T cells (Tregs) as well as interleukin (IL)-10 in bronchoalveolar lavage fluid (BALF) of patients with SCLC or NSCLC. Our study showed that the frequency of CD14+, CD206+CD14+ and IL-10+CD206+CD14+M2-like macrophages were significantly increased, with simultaneously elevated IL-10 in BALF of SCLC patients, as compared to those in BALF of NSCLC patients. Furthermore, the increased frequency of IL-10+CD206+CD14+M2-like macrophages and elevated level of IL-10 in BALF of SCLC patients were positively correlated with advanced tumor stage, but negatively correlated with their survival time. On the other hand, the level of supernatant IL-10 and frequency of IL-10+CD206+CD14+M2-like macrophages in SCLC patients were positively correlated. The frequency of above mentioned macrophages was also positively correlated with that of Foxp3+CD25+CD4+Tregs. Compared to NSCLC patients, the level of circulating IL-10+CD206+CD14+M2-like monocytes in SCLC patients were significantly increased after chemotherapy. Overall, increased IL-10+CD206+CD14+M2-like macrophages were an important feature of SCLC, rather than NSCLC, and it is associated with development of SCLC.

The N6-methyladenosine (m6A)-forming enzyme METTL3 facilitates M1 macrophage polarization through the methylation of STAT1 mRNA

Compelling evidence indicates that epigenetic regulations orchestrate dynamic macrophage polarization. N⁶-methyladenosine (m⁶A) methylation is the most abundant epigenetic modification of mammalian mRNA, but its role in macrophage polarization is still completely unknown. Here, we show that the m⁶A-catalytic enzyme methyltransferase like 3 (METTL3) is specifically upregulated following the M1 polarization of mouse macrophages. Furthermore, METTL3 knockdown through siRNA transfection markedly inhibited M1, but enhanced M2, macrophage polarization. Conversely, its overexpression via plasmid transfection greatly facilitated M1, but attenuated M2, macrophage polarization. Further methylated RNA immunoprecipitation and in vitro m⁶A methylation assays suggested that METTL3 directly methylates mRNA encoding signal transducer and activator of transcription 1 (STAT1), a master transcription factor controlling M1 macrophage polarization, at its coding sequence and 3'-untranslated regions. In addition, METTL3-mediated STAT1 mRNA methylation significantly increased mRNA stability and subsequently upregulated STAT1 expression. In conclusion, METTL3 drives M1 macrophage polarization by directly methylating STAT1 mRNA, potentially serving as an anti-inflammatory target.

Downregulated Caveolin-1 expression in circulating monocytes may contribute to the pathogenesis of psoriasis

Caveolin-1 (CAV-1) is the principal component of caveolae that regulates a variety of signaling molecules and receptors. Our previous study revealed CAV-1 reduction in the epidermis of patients with psoriasis, which leads to enhanced Janus kinase/signal transducer and activator of transcription activation and cytokine production, suggesting that aberrant CAV-1 expression may contribute to psoriatic inflammation. This study aimed to investigate whether abnormal modulation of CAV-1 on immune cells is involved in the pathogenesis of psoriasis. We observed that CAV-1 level in psoriasis patients was apparently reduced in peripheral blood mononuclear cells (PBMCs) and it was prominent in CD14⁺ monocytes. CAV-1 silencing in monocytes represented elevated levels of interleukin (IL)-1β and IL-6, and those had enhanced chemotaxis activity. In a murine model of psoriasis-like inflammation induced by imiquimod, we observed a significant CAV-1 reduction in PBMCs. Systemic administration of CAV-1 scaffolding domain peptide significantly improved the skin phenotype with less macrophage infiltration. Taken together, aberrant CAV-1 expression in monocytes may be involved in the pathogenesis of psoriasis.

Inflammation-Induced Epithelial-to-Mesenchymal Transition and GM-CSF Treatment Stimulate Mesenteric Mesothelial Cells to Transdifferentiate into Macrophages

In our previous work, we showed that during inflammation-induced epithelial-to-mesenchymal transition (EMT), mesenteric mesothelial cells express ED1 (pan-macrophage marker), indicating that they are transformed into macrophage-like cells. In this paper, we provide additional evidences about this transition by following the phagocytic activity and the TNFα production of mesenteric mesothelial cells during inflammation. Upon injection of India ink particles or fluorescent-labeled bioparticles (pHrodo) into the peritoneal cavity of rats pretreated with Freund's adjuvant, we found that mesothelial cells efficiently engulfed these particles. A similar increase of internalization could be observed by mesothelial cells in GM-CSF pretreated primary mesenteric culture. Since macrophages are the major producers of tumor necrosis factor, TNFα, we investigated expression level of TNFα during inflammation-induced EMT and found that TNFα was indeed expressed in these cells, reaching the highest level at the 5th day of inflammation. Since TNFα is one of the target genes of early growth response (EGR1) transcription factor, playing important role in monocyte-macrophage differentiation, expression of EGR1 in mesothelial cells was also investigated by Western blot and immunocytochemistry. While mesothelial cells did not express EGR1, a marked increase was observed in mesothelial cells by the time of inflammation. Parallel to this, nuclear translocation of EGR1 was shown by immunocytochemistry at the day 5 of inflammation. Caveolin-1 level was high and ERK1/2 became phosphorylated as the inflammation proceeded showing a slight decrease when the regeneration started. Our present data support the idea that under special stimuli, mesenteric mesothelial cells are able to transdifferentiate into macrophages, and this transition is regulated by the caveolin-1/ERK1/2/EGR1 signaling pathway.

Role of caveolin-1 in epidermal stem cells during burn wound healing in rats

Local transplantation of stem cells has therapeutic effects on skin damage but cannot provide satisfactory wound healing. Studies on the mechanisms underlying the therapeutic effects of stem cells on skin wound healing will be needed. Hence, in the present study, we explored the role of Caveolin-1 in epidermal stem cells (EpiSCs) in the modulation of wound healing. We first isolated EpiSCs from mouse skin tissues and established stable EpiSCs with overexpression of Caveolin-1 using a lentiviral construct. We then evaluated the epidermal growth factor (EGF)-induced cell proliferation ability using cell counting Kit-8 (CCK-8) assay and assessed EpiSC pluripotency by examining Nanog mRNA levels in EpiSCs. Furthermore, we treated mice with skin burn injury using EpiSCs with overexpression of Caveolin-1. Histological examinations were conducted to evaluate re-epithelialization, wound scores, cell proliferation and capillary density in wounds. We found that overexpression of Caveolin-1 in EpiSCs promoted EGF-induced cell proliferation ability and increased wound closure in a mouse model of skin burn injury. Histological evaluation demonstrated that overexpression of Caveolin-1 in EpiSCs promoted re-epithelialization in wounds, enhanced cellularity, and increased vasculature, as well as increased wound scores. Taken together, our results suggested that Caveolin-1 expression in the EpiSCs play a critical role in the regulation of EpiSC proliferation ability and alteration of EpiSC proliferation ability may be an effective approach in promoting EpiSC-based therapy in skin wound healing.

Deletion of caveolin-1 attenuates LPS/GalN-induced acute liver injury in mice

Acute hepatic injury caused by inflammatory liver disease is associated with high mortality. This study examined the role of caveolin-1 (Cav-1) in lipopolysaccharide (LPS) and D-galactosamine (GalN)-induced fulminant hepatic injury in wild type and Cav-1-null (Cav-1-/- ) mice. Hepatic Cav-1 expression was induced post-LPS/GalN treatment in wild-type mice. LPS/GalN-treated Cav-1-/- mice showed reduced lethality and markedly attenuated liver damage, neutrophil infiltration and hepatocyte apoptosis as compared to wild-type mice. Cav-1 deletion significantly reduced LPS/GalN-induced caspase-3, caspase-8 and caspase-9 activation and pro-inflammatory cytokine and chemokine expression. Additionally, Cav-1-/- mice showed suppressed expression of Toll-like receptor 4 (TLR4) and CD14 in Kupffer cells and reduced expression of vascular cell adhesion molecule 1 and intercellular adhesion molecule 1 in liver cells. Cav-1 deletion impeded LPS/GalN-induced inducible nitric oxide synthase expression and nitric oxide production and hindered nuclear factor-κB (NF-κB) activation. Taken together, Cav-1 regulated the expression of mediators that govern LPS-induced inflammatory signalling in mouse liver. Thus, deletion of Cav-1 suppressed the inflammatory response mediated by the LPS-CD14-TLR4-NF-κb pathway and alleviated acute liver injury in mice.

Loss of Caveolin-1 in Metastasis-Associated Macrophages Drives Lung Metastatic Growth through Increased Angiogenesis

Although it is well established that tumor-associated macrophages take part in each step of cancer progression, less is known about the distinct role of the so-called metastasis-associated macrophages (MAMs) at the metastatic site. Previous studies reported that Caveolin-1 (Cav1) has both tumor-promoting and tumor-suppressive functions. However, the role of Cav1 in bone-marrow-derived cells is unknown. Here, we describe Cav1 as an anti-metastatic regulator in mouse models of lung and breast cancer pulmonary metastasis. Among all the recruited inflammatory cell populations, we show that MAMs uniquely express abundant levels of Cav1. Using clodronate depletion of macrophages, we demonstrate that macrophage Cav1 signaling is critical for metastasis and not for primary tumor growth. In particular, Cav1 inhibition does not affect MAM recruitment to the metastatic site but, in turn, favors angiogenesis. We describe a mechanism by which Cav1 in MAMs specifically restrains vascular endothelial growth factor A/vascular endothelial growth factor receptor 1 (VEGF-A/VEGFR1) signaling and its downstream effectors, matrix metallopeptidase 9 (MMP9) and colony-stimulating factor 1 (CSF1).

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Macrophage Cav1 signaling is critical for restraining lung metastatic growth

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Cav1 deletion in macrophages favors angiogenesis at the lung metastatic site

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Cav1 suppresses VEGF-A/VEGFR1 activity and its downstream effectors, MMP9 and CSF1

Caveolin-1 promotes pituitary adenoma cells migration and invasion by regulating the interaction between EGR1 and KLF5

Caveolin-1 (Cav-1) is a principal structural protein of caveolae. Cav-1 has been implicated in cancer progression, but its precise functional roles in pituitary adenoma cells remain largely unclear. In this study, we evidenced that the level of cav-1 was elevated in the invasive pituitary adenoma. Cav-1 knockdown restrained the migration and invasion of pituitary adenoma cells. In cav-1-depleting cells, the expression of miR-145, miR-124 and miR-183 were up-regulated. Further investigation showed that cav-1 knockdown inhibited the nuclear translocation of EGR1, reducing the interaction between EGR1 and KLF5. The resulting free KLF5 promoted the expression of miR-145, miR-124 and miR-183 by binding to their promoters, which was blocked by EGR1. Luciferase reporter assay indicated that miR-145 targeted FSCN1, miR-124 targeted PTTG1IP, and miR-183 targeted EZR in pituitary adenoma cells, respectively. Knockdown of FSCN1, PTTG1IP or EZR suppressed the migration and invasion of pituitary adenoma cells. In conclusion, our data suggested that the elevated cav-1 promoted pituitary adenoma cells migration and invasion by regulating the interaction between EGR1 and KLF5.

Caveolin-1 and Caveolin-2 Can Be Antagonistic Partners in Inflammation and Beyond

Caveolins, encoded by the CAV gene family, are the main protein components of caveolae. In most tissues, caveolin-1 (Cav-1) and caveolin-2 (Cav-2) are co-expressed, and Cav-2 targeting to caveolae depends on the formation of heterooligomers with Cav-1. Notwithstanding, Cav-2 has unpredictable activities, opposing Cav-1 in the regulation of some cellular processes. While the major roles of Cav-1 as a modulator of cell signaling in inflammatory processes and in immune responses have been extensively discussed elsewhere, the aim of this review is to focus on data revealing the distinct activity of Cav-1 and Cav-2, which suggest that these proteins act antagonistically to fine-tune a variety of cellular processes relevant to inflammation.

Downregulation of Cavin-1 Expression via Increasing Caveolin-1 Degradation Prompts the Proliferation and Migration of Vascular Smooth Muscle Cells in Balloon Injury-Induced Neointimal Hyperplasia

BACKGROUND

Percutaneous coronary intervention has been widely used in the treatment of ischemic heart disease, but vascular restenosis is a main limitation of percutaneous coronary intervention. Our previous work reported that caveolin-1 had a key functional role in intimal hyperplasia, whereas whether Cavin-1 (another important caveolae-related protein) was involved is still unknown. Therefore, we will investigate the effect of Cavin-1 on neointimal formation.

METHODS AND RESULTS

Balloon injury markedly reduced Cavin-1 protein and enhanced ubiquitin protein expression accompanied with neointimal hyperplasia in injured carotid arteries, whereas Cavin-1 mRNA had no change. In cultured vascular smooth muscle cells (VSMCs), Cavin-1 was downregulated after inhibition of protein synthesis by cycloheximide, which was distinctly prevented by pretreatment with proteasome inhibitor MG132 but not by lysosomal inhibitor chloroquine, suggesting that proteasomal degradation resulted in Cavin-1 downregulation. Knockdown of Cavin-1 by local injection of Cavin-1 short hairpin RNA (shRNA) into balloon-injured carotid arteries in vivo promoted neointimal formation. In addition, inhibition or overexpression of Cavin-1 in cultured VSMCs in vitro prompted or suppressed VSMC proliferation and migration via increasing or decreasing extracellular signal-regulated kinase phosphorylation and matrix-degrading metalloproteinases-9 activity, respectively. However, under basic conditions, the effect of Cavin-1 on VSMC migration was stronger than on proliferation. Moreover, our results indicated that Cavin-1 regulated caveolin-1 expression via lysosomal degradation pathway.

CONCLUSIONS

Our study revealed the role and the mechanisms of Cavin-1 downregulation in neointimal formation by promoting VSMC proliferation, migration, and synchronously enhancing caveolin-1 lysosomal degradation. Cavin-1 may be a potential therapeutic target for the treatment of postinjury vascular remodeling.

Bone marrow transplantation prevents right ventricle disease in the caveolin-1-deficient mouse model of pulmonary hypertension

Accumulating evidence shows a causative role for the bone marrow (BM) in the genesis and progression of pulmonary hypertension (PH). Engraftment of BM hematopoietic stem cells from PH patients to mice reproduces the cardiopulmonary pathology of PH. However, it is unknown whether healthy BM can prevent the development of right heart disease. Caveolin-1-deficient (CAV-1 KO) mice develop cardiopulmonary disease with manifestations resembling PH, including elevated right ventricular (RV) systolic pressure (RVSP), RV hypertrophy, and pulmonary endothelial proliferative disease. Here, we hypothesize that engraftment of healthy BM to CAV-1 KO mice will prevent pulmonary vascular remodeling and development of the cardiopulmonary disease. CAV-1 KO mice and wild-type (WT) mice underwent transplantation with WT or CAV-1 KO BM. Hematopoietic differentiation was analyzed by flow cytometry. Pulmonary endothelial remodeling was quantified by CD31 image analysis. RVSP and RV cardiomyocyte area or Fulton's index were used to analyze RV hypertrophy. Maladaptive RV hypertrophy was determined by quantification of RV fibrosis. Transplantation of CAV-1 KO BM into healthy recipient WT mice led to elevation of RVSP, RV hypertrophy, and pulmonary endothelial remodeling. Reconstitution of CAV-1 KO with WT BM prevented spontaneous development of PH, including elevation of RVSP and maladaptive RV hypertrophy, but not pulmonary endothelial remodeling. Healthy BM has a protective role in the right ventricle independent of pulmonary vascular disease.

Dexmedetomidine may upregulate the expression of caveolin‑1 in lung tissues of rats with sepsis and improve the short‑term outcome

Dexmedetomidine (DXM) is a selective α2-adrenoceptor (α2‑AR) and imidazoline receptor (IR) agonist that has been reported to regulate inflammatory responses mediated by diverse signaling pathways through α2‑AR. The majority of the reported receptors or downstream molecules have been demonstrated to locate with caveolin‑1, a protein suggested to participate in regulating Toll‑like receptor 4 (TLR4)‑mediated inflammatory responses and the pathogen endocytosis capability of macrophages. The present study hypothesized that DXM may influence these pathways by regulating the expression of caveolin‑1 and mediating the subsequent effects. Using a cecal‑ligation and puncture‑induced rat sepsis model, it was initially observed that pre‑emptive DXM is able to upregulate and stabilize the amount of caveolin‑1 expression, which may be partly antagonized by both α2‑AR and the IR antagonist atepamezole (APZ). The pathophysiological parameters indicated that DXM is able to inhibit secondary lung injury, in addition to the rise of body temperature and arterial lactate accumulation, however it marginally increased arterial glucose and the murine sepsis score, which can be largely antagonized by APZ. The overall effect was beneficial and improved the 24‑h cumulative survival rate of rats with sepsis. In conclusion, preemptive clinical sedative doses of DXM may upregulate the expression of caveolin‑1 downregulated by sepsis, which may contribute to the inhibition of inflammatory pathways such as TLR4‑mediated pathways. Furthermore, DXM may favor the improvement of short‑term outcomes by the regulation of other metabolic pathways.

Inverse expression of caveolin-1 and EGFR in thyroid cancer patients

Cytological analysis of fine-needle aspiration (FNA) is the first step in evaluation of patients with nodular thyroid disease with the primary goal to exclude thyroid malignancy. Its improvement by combining cytology with molecular markers is still a matter of investigation. In this study, 2 molecular markers were used: caveolin-1 and epidermal growth factor receptor (EGFR), along with the well-established genetic marker BRAF V600E mutation. We set out to determine the expression signatures of EGFR and caveolin-1 in patients with thyroid malignancy as well as to determine their possible association with disease severity. In FNA biopsy samples (n=186), immunocytochemical expression of caveolin-1 and BRAF V600E mutation coincided with malignancy. The patients were sorted according to 3 parameters: final histopathological diagnosis, caveolin-1 expression, and BRAF V600E mutation status before measurement of EGFR mRNA expression. EGFR upregulation was detected in the group of patients with malignant diagnosis, no caveolin-1 expression, and wild-type BRAF. Spearman rank correlation yielded a statistically significant negative correlation of EGFR and caveolin-1. Double immunofluorescence confirmed colocalization and inverse expression of EGFR and caveolin-1. Our data demonstrated that EGFR overexpression is associated with malignancy but not with tumor aggressiveness. Furthermore, high-caveolin-1/low-EGFR cases were associated with an advanced pT status and had a greater degree of neoplastic infiltration than low-caveolin-1/high-EGFR cases. Combining caveolin-1 and BRAF V600E with EGFR might help in recognizing more aggressive thyroid lesions in a pool of relatively indolent tumors in FNA biopsies and thus be useful for early risk stratification of thyroid cancer patients.

Adipose tissue and atherosclerosis

High-energy intake which exceeds energy expenditure leads to the accumulation of triglycerides in adipose tissue, predominantly in large-size adipocytes. This metabolic shift, which drives the liver to produce atherogenic dyslipidemia, is well documented. In addition, an increasing amount of monocytes/macrophages, predominantly the proinflammatory M1-type, cumulates in ectopic adipose tissue. The mechanism of this process, the turnover of macrophages in adipose tissue and their direct atherogenic effects all remain to be analyzed.

Caveolins and caveolae in ocular physiology and pathophysiology

Caveolae are specialized, invaginated plasma membrane domains that are defined morphologically and by the expression of signature proteins called, caveolins. Caveolae and caveolins are abundant in a variety of cell types including vascular endothelium, glia, and fibroblasts where they play critical roles in transcellular transport, endocytosis, mechanotransduction, cell proliferation, membrane lipid homeostasis, and signal transduction. Given these critical cellular functions, it is surprising that ablation of the caveolae organelle does not result in lethality suggesting instead that caveolae and caveolins play modulatory roles in cellular homeostasis. Caveolar components are also expressed in ocular cell types including retinal vascular cells, Müller glia, retinal pigment epithelium (RPE), conventional aqueous humor outflow cells, the corneal epithelium and endothelium, and the lens epithelium. In the eye, studies of caveolae and other membrane microdomains (i.e., "lipid rafts") have lagged behind what is a substantial body of literature outside vision science. However, interest in caveolae and their molecular components has increased with accumulating evidence of important roles in vision-related functions such as blood-retinal barrier homeostasis, ocular inflammatory signaling, pathogen entry at the ocular surface, and aqueous humor drainage. The recent association of CAV1/2 gene loci with primary open angle glaucoma and intraocular pressure has further enhanced the need to better understand caveolar functions in the context of ocular physiology and disease. Herein, we provide the first comprehensive review of literature on caveolae, caveolins, and other membrane domains in the context of visual system function. This review highlights the importance of caveolae domains and their components in ocular physiology and pathophysiology and emphasizes the need to better understand these important modulators of cellular function.

Nitroxyl (HNO) reduces endothelial and monocyte activation and promotes M2 macrophage polarization

In the present study, the effect of nitroxyl anion (HNO) donors on factors that precede atherosclerosis was examined. They reduced endothelial cell inflammation and monocyte activation and as such may be an effective treatment for coronary artery disease.

E3 ubiquitin ligase CHIP interacts with C-type lectin-like receptor CLEC-2 and promotes its ubiquitin-proteasome degradation

C-type lectin-like receptor 2 (CLEC-2) was originally identified as a member of non-classical C-type lectin-like receptors in platelets and immune cells. Activation of CLEC-2 is involved in thrombus formation, lymphatic/blood vessel separation, platelet-mediated tumor metastasis and immune response. Nevertheless, the regulation of CLEC-2 expression is little understood. In this study, we identified that the C terminus of Hsc70-interacting protein (CHIP) interacted with CLEC-2 by mass spectrometry analysis, and CHIP decreased the protein expression of CLEC-2 through lysine-48-linked ubiquitination and proteasomal degradation. Deleted and point mutation also revealed that CHIP controlled CLEC-2 protein expression via both tetratricopeptide repeats (TPR) domain and Ubox domain in a HSP70/90-independent manner. Moreover, reduced CHIP expression was associated with decreased CLEC-2 polyubiquitination and increased CLEC-2 protein levels in PMA-induced differentiation of THP-1 monocytes into macrophages. These results indicate that CLEC-2 is the target substrate of E3 ubiquitin ligase CHIP, and suggest that the CHIP/CLEC-2 axis may play an important role in the modulation of immune response.

PICK1 confers anti-inflammatory effects in acute liver injury via suppressing M1 macrophage polarization

Protein interacting with C kinase 1 (PICK1) is a scaffolding protein mainly implicated in neurological diseases, however, the function of PICK1 in acute liver injury (ALI) remains unknown. Our study found a dramatical decrease in mRNA and protein levels of PICK1 in liver tissues and isolated Kupffer cells (KCs) from the liver in mice with ALI. Furthermore, pretreatment the mice with ALI with FSC-231, a pharmacological inhibitor of PICK1, could significantly augment inflammatory response. Furthermore, in vitro studies showed that both lipopolysaccharide (LPS) and interferon gamma (IFN-γ) significantly reduced the expression of PICK1, while IL-4 elevated its expression in RAW 264.7 cells. Additionally, over-expression of PICK1 inhibited the expression of M1 biomarkers by suppressing NF-κB activity, and enhanced the expression of M2 biomarkers by promoting STAT6 activity. In contrast, knockdown of PICK1 or FSC-231 pretreatment promoted M1 polarization and suppressed M2 polarization. Besides, caveolin-1 was identified as a potential target gene controlled by PICK1 in RAW 264.7 cells. Mechanistic investigation revealed a dual role of PICK1 in regulating macrophage polarization and implied PICK1 as a potential therapeutic target in ALI.

Caveolin-1 regulates osteoclast differentiation by suppressing cFms degradation

Caveolae are flask-shaped cell-surface membranes, which consist of cholesterol, sphingolipids and caveolin proteins. In a microarray analysis, we found that caveolin-1 (Cav-1) was upregulated by receptor activator of NFκB ligand (RANKL), the osteoclast differentiation factor. Silencing of Cav-1 inhibited osteoclastogenesis and also decreased the activation of mitogen-activated protein kinase and the induction of NFATc1 by RANKL. Cav-1 knockdown suppressed the expression of cFms and RANK, two major receptors for osteoclastogenesis. Interestingly, cFms expression was decreased only at the protein level, not at the messenger RNA (mRNA) level, whereas RANK expression was decreased at both the mRNA and protein levels. Furthermore, Cav-1 deficiency increased the lysosomal degradation of cFms. Taken together, these results demonstrate that Cav-1-dependent cFms stabilization contributes to efficient osteoclastogenesis.

High-density lipoprotein inhibits human M1 macrophage polarization through redistribution of caveolin-1

BACKGROUND AND PURPOSE

Monocyte-derived macrophages are critical in the development of atherosclerosis and can adopt a wide range of functional phenotypes depending on their surrounding milieu. High-density lipoproteins (HDLs) have many cardio-protective properties including potent anti-inflammatory effects. We investigated the effects of HDL on human macrophage phenotype and the mechanisms by which these occur.

EXPERIMENTAL APPROACH

Human blood monocytes were differentiated into macrophages in the presence or absence of HDL and were then induced to either an inflammatory macrophage (M1) or anti-inflammatory macrophage (M2) phenotype using LPS and IFN-γ or IL-4, respectively.

KEY RESULTS

HDL inhibited the induction of macrophages to an M1-phenotype, as evidenced by a decrease in the expression of M1-specific cell surface markers CD192 and CD64, as well as M1-associated inflammatory genes TNF-α, IL-6 and MCP-1 (CCL2). HDL also inhibited M1 function by reducing the production of ROS. In contrast, HDL had no effect on macrophage induction to the M2-phenotype. Similarly, methyl-β-cyclodextrin, a non-specific cholesterol acceptor also suppressed the induction of M1 suggesting that cholesterol efflux is important in this process. Furthermore, HDL decreased membrane caveolin-1 in M1 macrophages. We confirmed that caveolin-1 is required for HDL to inhibit M1 induction as bone marrow-derived macrophages from caveolin-1 knockout mice continued to polarize into M1-phenotype despite the presence of HDL. Moreover, HDL decreased ERK1/2 and STAT3 phosphorylation in M1 macrophages.

CONCLUSIONS AND IMPLICATIONS

We concluded that HDL reduces the induction of macrophages to the inflammatory M1-phenotype via redistribution of caveolin-1, preventing the activation of ERK1/2 and STAT3.

Caveolin-1 single-nucleotide polymorphism and arterial stiffness in non-dialysis chronic kidney disease

BACKGROUND

Arteriosclerosis is an independent predictor of increased cardiovascular mortality in chronic kidney disease (CKD). Histologically it is characterized by hypertrophy and fibrosis of the arterial media wall leading to increased arterial stiffness and end-organ damage. Caveolin-1 acts as an intracellular signalling pathway chaperone in human fibrotic and vascular diseases. The purpose of this study was to assess the association between caveolin-1 (CAV1) single-nucleotide polymorphism (SNP) rs4730751 and arterial stiffness as measured by arterial pulse wave velocity (PWV) in an early-stage CKD cohort and in a cohort with more severe CKD.

METHODS

Two prospectively maintained patient cohorts with non-dialysis CKD were studied: 144 patients in the Chronic Renal Impairment in Birmingham (CRIB) cohort and 147 patients in the Renal Impairment in Secondary Care (RIISC) cohort, with matched exclusion criteria and DNA sampling availability. At entry to each cohort database, each patient's initial arterial PWV was measured, as well as their anthropomorphic and biochemical data. CAV1 rs4730751 SNP genotyping was performed using Taqman technology.

RESULTS

The CAV1 rs4730751 SNP CC genotype was associated with lower arterial PWV in both CRIB early stage CKD patients [8.1 versus 8.6 m/s; coefficient -0.780 (-1.412, -0.149); P = 0.016] and RIISC more advanced stage CKD patients [8.7 versus 9.4 m/s; coefficient -0.695 (-1.288, -0.102); P = 0.022]; these relationships held following adjustment for other important confounders.

CONCLUSIONS

This replicated study suggests potential utility of the studied CAV1 SNP as a genetic biomarker in CKD and a role for CAV1 in the development of arteriosclerosis in this setting. Further studies are warranted to further explore the basic science driving these clinical observations.

Compound 21, a selective agonist of angiotensin AT2 receptors, prevents endothelial inflammation and leukocyte adhesion in vitro and in vivo

BACKGROUND AND PURPOSE

Angiotensin AT2 receptors are upregulated in disease states such as atherosclerosis and blockade of the AT2 receptors exacerbates plaque formation. Direct stimulation of these receptors is anti-atherogenic but the mechanisms and pathways involved remain unknown. We examined the effect of direct AT2 receptor stimulation with Compound 21 (C21) on the leukocyte adhesion cascade in vitro, right through to plaque formation in vivo.

EXPERIMENTAL APPROACH

Effects of C21 on TNFα-induced inflammation were assessed in human umbilical vein endothelial cells (HUVECs), activation of monocytes, polarisation of monocyte-derived macrophages and in intact mouse aortae.

KEY RESULTS

C21 attenuated TNFα-induced: monocyte adhesion to cultured HUVECs, adhesion molecule expression and abolished TNFα-induced ROS production. TNFα-induced NFκB translocation from the cytoplasm to the nucleus, essential for cytokine production, was prevented by C21. C21 did not influence monocyte activation or macrophage polarisation but did reduce TNFα and IL-6 mRNA expression in M1 macrophages. The anti-inflammatory effects of C21 were abolished by an AT2 receptor antagonist confirming that the effects of C21 were AT2 receptor-mediated. Also, leukocyte adhesion and cytokine gene expression, induced by high-fat diet (HFD), was attenuated in ApoE(-/-) mice treated with C21. Plaque size and stability were improved with C21 treatment with increased smooth muscle cell composition and decreased lipid size, compared with HFD-saline treated mice.

CONCLUSION AND IMPLICATIONS

C21 prevented TNFα-induced and HFD-induced vascular inflammation in vitro and in vivo. Our data provide strong evidence that the anti-atherosclerotic actions of C21 were due to vascular anti-inflammatory effects, mediated by AT2 receptors.

Role of caveolin-3 in lymphocyte activation

AIMS

Caveolins are structural proteins clustered in lipid-rich regions of plasma membrane involved in coordinating signal transduction in various organ systems. While caveolin-1 (Cav-1) has been shown to regulate lymphocyte activation, the role of caveolin-3 (Cav-3) in immune system signaling has not been investigated. We tested the hypothesis that Cav-3 modulates lymphocyte activation.

MAIN METHODS

Lymphocyte/leukocyte subpopulations from WT and Cav-3 mice were profiled with flow cytometry. Cytokine production in quiescent and activated splenocytes from WT and Cav-3 mice was assessed with ELISA.

KEY FINDINGS

Levels of T-cells, monocytes, and natural killer cells were not different between WT and KO mice, however KO mice had lower B-cell population-percentage. Functionally, activated lymphocytes from Cav-3 KO mice demonstrated significantly reduced expression of IL-2 compared to WT, while expression of TNFα, IL-6, and IL-10 was not different. Finally, expression of IL-17 was significantly reduced in T-helper cells from KO mice, while IFNγ was not, suggesting that Cav-3 is a determinant in the development of the Th-17 subpopulation.

SIGNIFICANCE

This study is the first to demonstrate that Cav-3 may be a novel participant in B-cell expression, T-cell cytokine production and activation of inflammation.

Role of aquaglyceroporins and caveolins in energy and metabolic homeostasis

Aquaglyceroporins and caveolins are submicroscopic integral membrane proteins that are particularly abundant in many mammalian cells. Aquaglyceroporins (AQP3, AQP7, AQP9 and AQP10) encompass a subfamily of aquaporins that allow the movement of water, but also of small solutes, such as glycerol, across cell membranes. Glycerol constitutes an important metabolite as a substrate for de novo synthesis of triacylglycerols and glucose as well as an energy substrate to produce ATP via the mitochondrial oxidative phosphorylation. In this sense, the control of glycerol influx/efflux in metabolic organs by aquaglyceroporins plays a crucial role with the dysregulation of these glycerol channels being associated with metabolic diseases, such as obesity, insulin resistance, non-alcoholic fatty liver disease and cardiac hypertrophy. On the other hand, caveolae have emerged as relevant plasma membrane sensors implicated in a wide range of cellular functions, including endocytosis, apoptosis, cholesterol homeostasis, proliferation and signal transduction. Caveolae-coating proteins, namely caveolins and cavins, can act as scaffolding proteins within caveolae by concentrating signaling molecules involved in free fatty acid and cholesterol uptake, proliferation, insulin signaling or vasorelaxation, among others. The importance of caveolae in whole-body homeostasis is highlighted by the link between homozygous mutations in genes encoding caveolins and cavins with metabolic diseases, such as lipodystrophy, dyslipidemia, muscular dystrophy and insulin resistance in rodents and humans. The present review focuses on the role of aquaglyceroporins and caveolins on lipid and glucose metabolism, insulin secretion and signaling, energy production and cardiovascular homeostasis, outlining their potential relevance in the development and treatment of metabolic diseases.

Caveolin-1 increases proinflammatory chemoattractants and blood-retinal barrier breakdown but decreases leukocyte recruitment in inflammation

PURPOSE

Caveolin-1 (Cav-1), the signature protein of caveolae, modulates inflammatory responses, and innate immunity. However, Cav-1's role in retinal inflammation has not been rigorously tested. In this study, we examined the effect of Cav-1 ablation on the sensitivity of the retina to inflammation.

METHODS

Cav-1 knockout (KO) mice were challenged by intravitreal injection of lipopolysaccharide (LPS) and inflammatory cell recruitment was assessed by flow cytometry and immunohistochemistry. Leukostasis was assessed in retinal flatmounts after perfusion with FITC-labeled Concanavalin A (FITC-ConA). Chemoattractants were measured by multiplex immunoassays. Blood-retinal barrier (BRB) breakdown was assessed quantitatively by a FITC-dextran permeability assay. The ratio of extravascular to total immune cells was determined by CD45 immunohistochemistry of retinal flatmounts.

RESULTS

Inflammatory challenge resulted in significant blunting of proinflammatory cytokine (monocyte chemoattractant protein-1 [MCP-1/CCL2], CXCL1/KC, IL-6, and IL-1β) responses as well as reduced inflammatory BRB breakdown in Cav-1 KO retinas. Paradoxically, Cav-1 deficiency resulted in significantly increased recruitment of immune cells compared with controls as well as increased leukostasis. A similar ratio of extravascular/total leukocytes were found in Cav-1 KO and wild-type (WT) retinas suggesting that Cav-1 deficient leukocytes were as competent to extravasate as those from WT mice. We found increased levels of circulating immune cells in naïve (not challenged with LPS) Cav-1 KO mice compared with controls.

CONCLUSIONS

Caveolin-1 paradoxically modulates inflammatory signaling and leukocyte infiltration through distinct mechanisms. We hypothesize that Cav-1 expression may enhance inflammatory signaling while at the same time supporting the physical properties of the BRB.

Caveolin-1 deletion exacerbates cardiac interstitial fibrosis by promoting M2 macrophage activation in mice after myocardial infarction

Adverse remodeling following myocardial infarction (MI) leading to heart failure is driven by an imbalanced resolution of inflammation. The macrophage cell is an important control of post-MI inflammation, as macrophage subtypes secrete mediators to either promote inflammation and extend injury (M1 phenotype) or suppress inflammation and promote scar formation (M2 phenotype). We have previously shown that the absence of caveolin-1 (Cav1), a membrane scaffolding protein, is associated with adverse cardiac remodeling in mice, but the mechanisms responsible remain to be elucidated. We explore here the role of Cav1 in the activation of macrophages using wild type C57BL6/J (WT) and Cav1(tm1Mls/J) (Cav1(-/-)) mice. By echocardiography, cardiac function was comparable between WT and Cav1(-/-) mice at 3days post-MI. In the absence of Cav1, there were a surprisingly higher percentage of M2 macrophages (arginase-1 positive) detected in the infarcted zone. Conversely, restoring Cav1 function after MI in WT mice by adding back the Cav1 scaffolding domain reduced the M2 activation profile. Further, adoptive transfer of Cav1 null macrophages into WT mice on d3 post-MI exacerbated adverse cardiac remodeling at d14 post-MI. In vitro studies revealed that Cav1 null macrophages had a more pronounced M2 profile activation in response to IL-4 stimulation. In conclusion, Cav1 deletion promotes an array of maladaptive repair processes after MI, including increased TGF-β signaling, increased M2 macrophage infiltration and dysregulation of the M1/M2 balance. Our data also suggest that cardiac remodeling can be improved by therapeutic intervention regulating Cav1 function during the inflammatory response phase.

The interaction of enolase-1 with caveolae-associated proteins regulates its subcellular localization

Cell-surface-associated proteolysis plays a crucial role in embryonic development, monocyte/macrophage recruitment and tumour cell invasion. The glycolytic enzyme ENO-1 (enolase-1) is translocated from the cytoplasm to the cell surface, where it binds PLG (plasminogen) to enhance pericellular plasmin production and cell motility. In the present study, ENO-1 was found to localize to a specialized subset of lipid rafts called caveolae as demonstrated by fluorescence confocal microscopy and sucrose gradient ultracentrifugation. Co-immunoprecipitation studies revealed that ENO-1 interacts with Cav-1 (caveolin-1), but not with Cav-2, via the CSD (Cav-scaffolding domain). Moreover, an evolutionarily conserved CBM (Cav-binding motif) F296DQDDWGAW304 was identified within ENO-1. The point mutation W301A within the ENO-1 CBM was, however, not sufficient to disrupt ENO-1-Cav-1 interaction, whereas the mutations F296A and W304A markedly affected ENO-1 protein expression. Furthermore, ENO-1 was found associated with Annx2 (annexin 2), representing another caveolar protein, and this interaction was dependent on Cav-1 expression. Knockdown of Cav-1 and Annx2 markedly decreased cell surface expression of ENO-1. ENO-1 overexpression increased cell migration and invasion in a Cav-1-dependent manner. Thus the differential association of ENO-1 with caveolar proteins regulates ENO-1 subcellular localization and, consequently, ENO-1-dependent cell migration and invasion.

Role of caveolin-1 in asthma and chronic inflammatory respiratory diseases

Caveolin-1 (Cav-1) is the major protein present in invaginations of the plasma membrane of cells known as caveolae. Cav-1 is expressed in numerous resident and inflammatory cells implicated in the pathogenesis of asthma and chronic inflammatory respiratory diseases including chronic obstructive pulmonary disease. A remarkable repertoire of functions has been identified for Cav-1 and these extend to, and have relevance to, asthma and chronic inflammatory respiratory diseases. Important processes influenced by Cav-1 include inflammation, fibrosis, smooth muscle contractility, regulation of apoptosis and cell senescence as well as epithelial barrier function and homeostasis. A better understanding of Cav-1 may be useful in developing new therapies for chronic inflammatory respiratory diseases.

Cav-1 deletion impaired hematopoietic stem cell function

A tightly controlled balance between hematopoietic stem and progenitor cell compartments is required to maintain normal blood cell homeostasis throughout life, and this balance is regulated by intrinsic and extrinsic cellular factors. Cav-1 is a 22-kDa protein that is located in plasma membrane invaginations and is implicated in regulating neural stem cell and embryonic stem cell proliferation. However, the role of Cav-1 in hematopoietic stem cell (HSC) function is largely unknown. In this study, we used Cav-1^−/− mice to investigate the role of Cav-1 in HSCs function during aging. The results showed that Cav-1^−/− mice displayed a decreased percentage of B cells and an increased percentage of M cells in the bone marrow and peripheral blood, and these changes were due to an increased number of HSCs. FACS analysis showed that the numbers of Lin⁻Sca1⁺c-kit⁺ cells (LSKs), long-term HSCs (LT-HSCs), short-term HSCs and multipotent progenitors were increased in Cav-1^−/− mice compared with Cav-1^+/+ mice, and this increase became more pronounced with aging. An in vitro clonogenic assay showed that LT-HSCs from Cav-1^−/− mice had reduced ability to self-renew. Consistently, an in vivo competitive transplantation assay showed that Cav-1^−/− mice failed to reconstitute hematopoiesis. Moreover, a Cav-1 deletion disrupted the quiescence of LSKs and promoted cell cycle progression through G2/M phase. In addition, we found that Cav-1 deletion impaired the ability of HSCs to differentiate into mature blood cells. Taken together, these data suggest that Cav-1-deficient cells impaired HSCs quiescence and induced environmental alterations, which limited HSCs self-renewal and function.

Microdomains in the membrane landscape shape antigen-presenting cell function

The plasma membrane of immune cells is a highly organized cell structure that is key to the initiation and regulation of innate and adaptive immune responses. It is well-established that immunoreceptors embedded in the plasma membrane have a nonrandom spatial distribution that is important for coupling to components of intracellular signaling cascades. In the last two decades, specialized membrane microdomains, including lipid rafts and TEMs, have been identified. These domains are preformed structures ("physical entities") that compartmentalize proteins, lipids, and signaling molecules into multimolecular assemblies. In APCs, different microdomains containing immunoreceptors (MHC proteins, PRRs, integrins, among others) have been reported that are imperative for efficient pathogen recognition, the formation of the immunological synapse, and subsequent T cell activation. In addition, recent work has demonstrated that tetraspanin microdomains and lipid rafts are involved in BCR signaling and B cell activation. Research into the molecular mechanisms underlying membrane domain formation is fundamental to a comprehensive understanding of membrane-proximal signaling and APC function. This review will also discuss the advances in the microscopy field for the visualization of the plasma membrane, as well as the recent progress in targeting microdomains as novel, therapeutic approach for infectious and malignant diseases.