Flotillin-1 facilitates toll-like receptor 3 signaling in human endothelial cells

Toll-like receptor 3 involvement in vascular function

Maintaining endothelial cell (EC) and vascular smooth muscle cell (VSMC) integrity is an important component of human health and disease because both EC and VSMC regulate various functions, including vascular tone control, cellular adhesion, homeostasis and thrombosis regulation, proliferation, and vascular inflammation. Diverse stressors affect functions in both ECs and VSMCs and abnormalities of functions in these cells play a crucial role in cardiovascular disease initiation and progression. Toll-like receptors (TLRs) are important detectors of pathogen-associated molecular patterns derived from various microbes and viruses as well as damage-associated molecular patterns derived from damaged cells and perform innate immune responses. Among TLRs, several studies reveal that TLR3 plays a key role in initiation, development and/or protection of diseases, and an emerging body of evidence indicates that TLR3 presents components of the vasculature, including ECs and VSMCs, and plays a functional role. An agonist of TLR3, polyinosinic-polycytidylic acid [poly (I:C)], affects ECs, including cell death, inflammation, chemoattractant, adhesion, permeability, and hemostasis. Poly (I:C) also affects VSMCs including inflammation, proliferation, and modulation of vascular tone. Moreover, alterations of vascular function induced by certain molecules and/or interventions are exerted through TLR3 signaling. Hence, we present the association between TLR3 and vascular function according to the latest studies.

Flotillins affect LPS-induced TLR4 signaling by modulating the trafficking and abundance of CD14

Lipopolysaccharide (LPS) induces a strong pro-inflammatory reaction of macrophages upon activation of Toll-like receptor 4 (TLR4) with the assistance of CD14 protein. Considering a key role of plasma membrane rafts in CD14 and TLR4 activity and the significant impact exerted on that activity by endocytosis and intracellular trafficking of the both LPS acceptors, it seemed likely that the pro-inflammatory reaction could be modulated by flotillins. Flotillin-1 and -2 are scaffolding proteins associated with the plasma membrane and also with endo-membranes, affecting both the plasma membrane dynamics and intracellular protein trafficking. To verify the above hypothesis, a set of shRNA was used to down-regulate flotillin-2 in Raw264 cells, which were found to also become deficient in flotillin-1. The flotillin deficiency inhibited strongly the TRIF-dependent endosomal signaling of LPS-activated TLR4, and to a lower extent also the MyD88-dependent one, without affecting the cellular level of TLR4. The flotillin depletion also inhibited the pro-inflammatory activity of TLR2/TLR1 and TLR2/TLR6 but not TLR3. In agreement with those effects, the depletion of flotillins down-regulated the CD14 mRNA level and the cellular content of CD14 protein, and also inhibited constitutive CD14 endocytosis thereby facilitating its shedding. Ultimately, the cell-surface level of CD14 was markedly diminished. Concomitantly, CD14 recycling was enhanced via EEA1-positive early endosomes and golgin-97-positive trans-Golgi network, likely to compensate for the depletion of the cell-surface CD14. We propose that the paucity of surface CD14 is the reason for the down-regulated signaling of TLR4 and the other TLRs depending on CD14 for ligand binding.

Molecular characterization and function of the lipid raft protein Lvflotillin-1A from Litopenaeus vannamei

White spot syndrome virus (WSSV) can cause a contagious, high virulent and pandemic disease for crustaceans, especially shrimps. However, the molecular mechanism of WSSV pathogenesis remains unclear. Flotillins are lipid raft-associated proteins, which mainly include flotillin-1 and flotillin-2. They are involved in the formation of large heteromeric protein complexes engaged in diverse signalling pathways at the membrane-cytosol interface. They defined a clathrin-independent endocytic pathway in mammalian cells. Our previous studies suggested that shrimp flotillin-2 might mediate endocytosis involved in WSSV infection. To further explore the function of shrimp flotillin, a flotillin-1 homologous, Lvflotillin-1A was identified and characterized in Litopenaeus vanamei. The transcription of Lvflotillin-1A showed a significant decline at 12h post-infection, followed by complete recovery and a slight up-regulation after the WSSV challenge. Gene silencing revealed that inhibition of Lvflotillin-1A raised the virus infection, suggesting Lvflotillin-1A might play an important role in shrimp immunity. Furthermore, co-immunoprecipitation and immunofluorescence illustrated that Lvflotillin-1A and Lvflotillin-2 could form hetero-oligomers, and co-expression promoted the accumulation of intracellular vesicles. The study revealed that WSSV might up-regulate Lvflotillin-2 expression and alter the subcellular location of Lvflotillin-1 protein to facilitate virus infection. These results will provide information for understanding the interaction between WSSV and shrimp.

Deciphering the relationship between caveolae-mediated intracellular transport and signalling events

The caveolae-mediated transport across polarized epithelial cell barriers has been largely deciphered in the last decades and is considered the second essential intracellular transfer mechanism, after the clathrin-dependent endocytosis. The basic cell biology knowledge was supplemented recently, with the molecular mechanisms beyond caveolae generation implying the key contribution of the lipid-binding proteins (the structural protein Caveolin and the adapter protein Cavin), along with the bulb coat stabilizing molecules PACSIN-2 and Eps15 homology domain protein-2. The current attention is focused also on caveolae architecture (such as the bulb coat, the neck, the membrane funnel inside the bulb, and the associated receptors), and their specific tasks during the intracellular transport of various cargoes. Here, we resume the present understanding of the assembly, detachment, and internalization of caveolae from the plasma membrane lipid raft domains, and give an updated view on transcytosis and endocytosis, the two itineraries of cargoes transport via caveolae. The review adds novel data on the signalling molecules regulating caveolae intracellular routes and on the transport dysregulation in diseases. The therapeutic possibilities offered by exploitation of Caveolin-1 expression and caveolae trafficking, and the urgent issues to be uncovered conclude the review.

Potential depression and antidepressant-response biomarkers in human lymphoblast cell lines from treatment-responsive and treatment-resistant subjects: roles of SSRIs and omega-3 polyunsaturated fatty acids

While several therapeutic strategies exist for depression, most antidepressant drugs require several weeks before reaching full biochemical efficacy and remission is not achieved in many patients. Therefore, biomarkers for depression and drug-response would help tailor treatment strategies. This study made use of banked human lymphoblast cell lines (LCLs) from normal and depressed subjects; the latter divided into remitters and non-remitters. Due to the fact that previous studies have shown effects on growth factors, cytokines, and elements of the cAMP-generating system as potential biomarkers for depression and antidepressant action, these were examined in LCLs. Initial gene and protein expression profiles for signaling cascades related to neuroendocrine and inflammatory functions differ among the three groups. Growth factor genes, including VEGFA and BDNF were significantly down-regulated in cells from depressed subjects. In addition, omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been reported to act as both antidepressants and anti-inflammatories, but the mechanisms for these effects are not established. Here we showed that n-3 PUFAs and escitalopram (selective serotonin reuptake inhibitors, SSRIs) treatment increased adenylyl cyclase (AC) and BDNF gene expression in LCLs. These data are consistent with clinical observations showing that n-3 PUFA and SSRI have antidepressant affects, which may be additive. Contrary to observations made in neuronal and glial cells, n-3 PUFA treatment attenuated cAMP accumulation in LCLs. However, while lymphoblasts show paradoxical responses to neurons and glia, patient-derived lymphoblasts appear to carry potential depression biomarkers making them an important tool for studying precision medicine in depressive patients. Furthermore, these data validate usefulness of n-3 PUFAs in treatment for depression.

Flotillin-Dependent Membrane Microdomains Are Required for Functional Phagolysosomes against Fungal Infections

Lipid rafts form signaling platforms on biological membranes with incompletely characterized role in immune response to infection. Here we report that lipid-raft microdomains are essential components of phagolysosomal membranes of macrophages and depend on flotillins. Genetic deletion of flotillins demonstrates that the assembly of both major defense complexes vATPase and NADPH oxidase requires membrane microdomains. Furthermore, we describe a virulence mechanism leading to dysregulation of membrane microdomains by melanized wild-type conidia of the important human-pathogenic fungus Aspergillus fumigatus resulting in reduced phagolysosomal acidification. We show that phagolysosomes with ingested melanized conidia contain a reduced amount of free Ca²⁺ ions and that inhibition of Ca²⁺-dependent calmodulin activity led to reduced lipid-raft formation. We identify a single-nucleotide polymorphism in the human FLOT1 gene resulting in heightened susceptibility for invasive aspergillosis in hematopoietic stem cell transplant recipients. Collectively, flotillin-dependent microdomains on the phagolysosomal membrane play an essential role in protective antifungal immunity.

Low-density lipoprotein receptor-related protein 6 regulates cardiomyocyte-derived paracrine signaling to ameliorate cardiac fibrosis

Rationale: Maladaptive cardiac remodeling is a critical step in the progression of heart failure. Low-density lipoprotein receptor-related protein 6 (LRP6), a co-receptor of Wnt, has been implicated in cardiac protection. We aimed to study the role of cardiomyocyte-expressed LRP6 in cardiac remodeling under chronic pressure overload.

Methods: Cardiac parameters were analyzed in inducible cardiac-specific LRP6 overexpressing and control mice subjected to transverse aortic constriction (TAC).

Results: Cardiac LRP6 was increased at an early phase after TAC. Cardiomyocyte-specific LRP6 overexpression improved cardiac function and inhibited cardiac hypertrophy and fibrosis four weeks after TAC. The overexpression significantly inhibited β-catenin activation, likely contributing to the inhibitory effect on cardiac hypertrophy after TAC. LRP6 overexpression reduced the expression and secretion of Wnt5a and Wnt11 by cardiomyocytes, and knockdown of Wnt5a and Wnt11 greatly inhibited cardiac fibrosis and dysfunction under pressure overload in vitro and in vivo. Cardiomyocyte-expressed LRP6 interacted with cathepsin D (CTSD, a protease) and promoted the degradation of Wnt5a and Wnt11, inhibiting cardiac fibrosis and dysfunction induced by TAC. The protease inhibitor leupeptin attenuated the interaction between LRP6 and CTSD, enhanced the expression of Wnt5a and Wnt11, and deteriorated cardiac function and fibrosis in cardiomyocyte-specific LRP6-overexpressing mice under pressure overload. Mutants from human patients, P1427Q of LRP6 and G316R of CTSD significantly inhibited the interaction between LRP6 and CTSD and increased Wnt5a and Wnt11 expression.

Conclusion: Cardiomyocyte-expressed LRP6 promoted the degradation of Wnt5a and Wnt11 by regulating CTSD and inhibited cardiac fibrosis under pressure overload. Our study demonstrated a novel role of LRP6 as an anti-fibrosis regulator.

Characterization of raft microdomains in bovine mammary tissue during lactation: How they are modulated by fatty acid treatments

The objective of the current study was first to characterize lipid raft microdomains isolated as detergent-resistant membranes (DRM) from mammary gland tissue, and second to determine how dietary fatty acids (FA) such as conjugated linoleic acid (CLA), 19:1 cyclo, and long-chain n-3 polyunsaturated FA affect lipid raft markers of mammary cells, and to finally establish relationships between these markers and lactation performance in dairy cows. Eight Holstein cows were used in a replicated 4 × 4 Latin square design with periods of 28 d. For the first 14 d, cows received daily an abomasal infusion of (1) 406 g of a saturated FA supplement (112 g of 16:0 + 230 g of 18:0) used as a control; (2) 36 g of a CLA supplement (13.9 g of trans-10,cis-12 18:2) + 370 g of saturated FA; (3) 7 g of Sterculia fetida oil (3.1 g of 19:1 cyclo, STO) + 399 g of saturated FA; or (4) 406 g of fish oil (55.2 g of cis-5,cis-8,cis-11,cis-14,cis-17 20:5 + 59.3 g of cis-4,cis-7,cis-10,cis-13,cis-16,cis-19 22:6, FO). Mammary biopsies were harvested on d 14 of each infusion period and were followed by a 14-d washout interval. Cholera toxin subunit B, which specifically binds to ganglioside M-1 (GM-1), a lipid raft marker, was used to assess its distribution in DRM. Infusions of CLA, STO, and FO were individually compared with the control, and significance was declared at P ≤ 0.05. Milk fat yield was decreased with CLA and FO, but was not affected by STO. Milk lactose yield was decreased with CLA and STO, but was not affected by FO. Mammary tissue shows a strong GM-1-signal enrichment in isolated DRM from mammary gland tissue. Caveolin (CAV) and flotillin (FLOT) are 2 proteins considered as lipid raft markers and they are present in DRM from mammary gland tissue. Distributions of GM-1, CAV-1, and FLOT-1 showed an effect of treatments determined by their subcellular distributions in sucrose gradient fractions. Regardless of treatments, data showed positive relationships between the yield of milk fat, protein, and lactose, and the abundance GM-1 in DRM fraction. Milk protein yield was positively correlated with relative proportion of FLOT-1 in the soluble fraction, whereas lactose yield was positively correlated with relative proportion of CAV-1 in the DRM fractions. Infusion of CLA decreased mRNA abundance of CAV-1, FLOT-1, and FLOT-2. Regardless of treatments, a positive relationship was observed between fat yield and mRNA abundance of FLOT-2. In conclusion, although limited to a few markers, results of the current experiment raised potential links between variation in specific biologically active component of raft microdomains in bovine mammary gland and lactation performances in dairy cows.

A highly efficient hybrid peptide ameliorates intestinal inflammation and mucosal barrier damage by neutralizing lipopolysaccharides and antagonizing the lipopolysaccharide-receptor interaction

Intestinal inflammatory disorders, such as inflammatory bowel disease, are major contributors to mortality and morbidity in humans and animals worldwide. While some native peptides have great potential as therapeutic agents against intestinal inflammation, potential cytotoxicity, anti-inciting action, and suppression of anti-inflammatory activity may limit their development as anti-inflammatory agents. Peptide hybridization is an effective approach for the design and engineering of novel functional peptides because hybrid peptides combine the advantages and benefits of various native peptides. In the present study, a novel hybrid anti-inflammatory peptide that combines the active center of Cecropin A (C) and the core functional region of LL-37 (L) was designed [C-L peptide; C (1-8)-L (17-30)] through in silico analysis to reduce cytotoxicity and improve the anti-inflammatory activity of the parental peptides. The resulting C-L peptide exhibited lower cytotoxicity than either C or L peptides alone. C-L also exerted a protective effect against lipopolysaccharide (LPS)-induced inflammatory responses in RAW264.7 macrophages and in the intestines of a mouse model. The hybrid peptide exhibited increased anti-inflammatory activity compared to the parental peptides. C-L plays a role in protecting intestinal tissue from damage, LPS-induced weight loss, and leukocyte infiltration. In addition, C-L reduces the expression levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), IL-1β, and interferon-gamma (IFN-γ), as well as reduces cell apoptosis. It also reduced mucosal barrier damage caused by LPS. The anti-inflammatory effects of the hybrid peptide were mainly attributed to its LPS-neutralizing activity and antagonizing the activation of LPS-induced Toll-like receptor 4-myeloid differentiation factor 2 (TLR4/MD2). The peptide also affected the TLR4-(nuclear factor κB) signaling pathway, modulating the inflammatory response upon LPS stimulation. Collectively, these findings suggest that the newly designed peptide, C-L, could be developed into a novel anti-inflammatory agent for animals or humans.

Flotillins: At the Intersection of Protein S-Palmitoylation and Lipid-Mediated Signaling

Flotillin-1 and flotillin-2 are ubiquitously expressed, membrane-associated proteins involved in multifarious cellular events from cell signaling, endocytosis, and protein trafficking to gene expression. They also contribute to oncogenic signaling. Flotillins bind the cytosolic leaflet of the plasma membrane and endomembranes and, upon hetero-oligomerization, serve as scaffolds facilitating the assembly of multiprotein complexes at the membrane-cytosol interface. Additional functions unique to flotillin-1 have been discovered recently. The membrane-binding of flotillins is regulated by S-palmitoylation and N-myristoylation, hydrophobic interactions involving specific regions of the polypeptide chain and, to some extent, also by their oligomerization. All these factors endow flotillins with an ability to associate with the sphingolipid/cholesterol-rich plasma membrane domains called rafts. In this review, we focus on the critical input of lipids to the regulation of the flotillin association with rafts and thereby to their functioning. In particular, we discuss how the recent developments in the field of protein S-palmitoylation have contributed to the understanding of flotillin1/2-mediated processes, including endocytosis, and of those dependent exclusively on flotillin-1. We also emphasize that flotillins affect directly or indirectly the cellular levels of lipids involved in diverse signaling cascades, including sphingosine-1-phosphate and PI(4,5)P₂. The mutual relations between flotillins and distinct lipids are key to the regulation of their involvement in numerous cellular processes.

Endocytosis Controls siRNA Efficiency: Implications for siRNA Delivery Vehicle Design and Cell-Specific Targeting

While small interfering RNAs (siRNAs) are commonly used for laboratory studies, development of siRNA therapeutics has been slower than expected, due, in part, to a still limited understanding of the endocytosis and intracellular trafficking of siRNA-containing complexes. With the recent characterization of multiple clathrin-/caveolin-independent endocytic pathways, that is, those mediated by Graf1, Arf6, and flotillin, it has become clear that the endocytic mechanism influences subsequent intracellular processing of the internalized cargo. To explore siRNA delivery in light of these findings, we developed a novel assay that differentiates uptake by each of the endocytic pathways and can be used to determine whether endocytosis by a pathway leads to the initiation of RNA interference (RNAi). Using Lipofectamine 2000 (LF2K), we determined the endocytosis pathway leading to active silencing (whether by clathrin, caveolin, Arf6, Graf1, flotillin, or macropinocytosis) across multiple cell types (HeLa, H1299, HEK293, and HepG2). We showed that LF2K is internalized by Graf1-, Arf6-, or flotillin-mediated endocytosis for the initiation of RNAi, depending on cell type. In addition, we found that a portion of siRNA-containing complexes is internalized by pathways that do not lead to initiation of silencing. Inhibition of these pathways enhanced intracellular levels of siRNAs with concomitant enhancement of silencing.

Protein phosphatase 2A-mediated flotillin-1 dephosphorylation up-regulates endothelial cell migration and angiogenesis regulation

Endothelial cells have key functions in endothelial barrier integrity and in responses to angiogenic signals that promote cell proliferation, cell migration, cytoskeletal reorganization, and formation of new blood vessels. These functions highly depend on protein-protein interactions in cell-cell junction and cell attachment complexes and on interactions with cytoskeletal proteins. Protein phosphatase 2A (PP2A) dephosphorylates several target proteins involved in cytoskeletal dynamics and cell adhesion. Our goal was to find new interacting and substrate proteins of the PP2A-B55α holoenzyme in bovine pulmonary endothelial cells. Using LC-MS/MS analysis, we identified flotillin-1 as a protein that binds recombinant GSH S-transferase-tagged PP2A-B55α. Immunoprecipitation experiments, proximity ligation assays, and immunofluorescent staining confirmed the interaction between these two endogenous proteins in endothelial cells. Originally, flotillins were described as regulatory proteins for axon regeneration, but they appear to function in many cellular processes, such as membrane receptor signaling, endocytosis, and cell adhesion. Ser³¹⁵ is a known PKC-targeted site in flotillin-1. Utilizing phosphomutants of flotillin-1 and the NanoBiT luciferase assay, we show here that phosphorylation/dephosphorylation of Ser³¹⁵ in flotillin-1 significantly affects its interaction with PP2A-B55α and that PP2A-B55α dephosphorylates phospho-Ser³¹⁵ Spreading, attachment, migration, and in vitro tube formation rates of S315A variant-overexpressing cells were faster than those of nontransfected or S315D-transfected cells. These results indicate that the PP2A-flotillin-1 interaction identified here affects major physiological activities of pulmonary endothelial cells.

Moxifloxacin suppresses airway inflammation and modulates expression of caveolin-1 and flotillin-1 in airway smooth muscle cells of asthmatic rats

Background

Moxifloxacin (MXF) possesses anti-inflammatory properties on asthmatic airway smooth muscle cells (ASMCs) beyond their antimicrobial effects, but the mechanisms are still unknown. This study was to investigate effects of MXF on expression of caveolin-1 (Cav-1) and flotillin-1 (FLOT1) in ASMCs in asthmatic rats.

Methods

ASMCs were collected from the airway and cultured in vitro. Cells from normal rats were treated with normal saline (Group N); cells from asthmatic rats were incubated with normal saline (Group A) or MXF (20 mg/L) (Group M); Cav-1 expression was up-regulated by transferring Cav-1 expressing lentivirus (Group L) and FLOT1 expression down-regulated by using siRNA in cells from asthmatic rats (Group S). The expressions of Cav-1, FLOT1 and p65 NF-κB were measured by Western blotting and quantificational real-time polymerase chain reaction (qRT-PCR), and interleukin-8 (IL-8) and eotaxin contents were measured by enzyme-linked immunosorbent assay (ELISA).

Results

Compared with normal control, Cav-1 expression significantly decreased in asthmatic groups (P<0.01); MXF up-regulated Cav-1 expression in asthmatic groups (P<0.01). However, compared with normal control, the expression of FLOT1 and p65 NF-κB dramatically increased in asthmatic groups (P<0.01); MXF down-regulated the expression of FLOT1 and p65 NF-κB in asthmatic groups (P<0.01); meanwhile, the expressions of FLOT1 and p65 NF-κB decreased after up-regulation of Cav-1 expression in asthmatic groups (P=0.01). Compared with asthmatic groups, the IL-8 and eotaxin contents significantly decreased in MXF Groups, Cav-1 up-regulation asthmatic groups and FLOT1 down-regulation asthmatic groups (P<0.01).

Conclusions

MXF can modulate the airway inflammation, upregulate Cav-1 expression, downregulate the expression of FLOT1 and p65 NF-κB in asthmatic rat ASMCs, which may be related to the anti-inflammatory effects of MXF in asthmatic ASMCs.

Flotillin-mediated endocytosis and ALIX-syntenin-1-mediated exocytosis protect the cell membrane from damage caused by necroptosis

Necroptosis is a form of regulated necrosis that is implicated in various human diseases including Alzheimer's disease. Necroptosis requires the translocation of the pseudokinase MLKL from the cytosol to the plasma membrane after its phosphorylation by the kinase RIPK3. Using protein cross-linking followed by affinity purification, we detected the lipid raft-associated proteins flotillin-1 and flotillin-2 and the ESCRT-associated proteins ALIX and syntenin-1 in membrane-localized MLKL immunoprecipitates. Phosphorylated MLKL was removed from membranes through either flotillin-mediated endocytosis followed by lysosomal degradation or ALIX-syntenin-1-mediated exocytosis. Thus, cells undergoing necroptosis need to overcome these independent suppressive mechanisms before plasma membrane disruption can occur.

Identification and characterization of the lamprey Flotillin-1 gene with a role in cell adhesion

Flotillin-1 is a kind of localize into specific cholesterol rich microdomains in cellular membranes and highly conserved lipid rafts marker protein widely distributed in animals and plants. It provides a platform for the reaction of many proteins in signal transduction, as scaffolding plays an important role in transmembrane signaling and cell adhesion. Here, Flotillin-1 protein from lamprey was identified and characterized (designated as L-Flotillin-1). After a partial cDNA sequence of L-Flotillin-1 was identified in a lamprey supraneural body cDNA library, the full-length cDNA was obtained using 3'- and 5'-rapid amplification of cDNA ends (RACE). L-Flotillin-1 encodes 424 amino acids and contains a prohibitin domain and a flotillin repetitive area. The L-Flotillin-1 protein was primarily distributed in kidney, supraneural body, gill, heart, liver and intestine via real-time PCR and immunohistochemistry assays. Immunofluorescence and western blot results showed that L-Flotillin-1 was considered to be used as a marker protein of lamprey lipid rafts and exosomes. Furthermore, overexpression of pEGFP-N1-L-Flotillin-1 induced the up-regulation of vascular cell adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1) mRNA levels. These results indicated that the L-Flotillin-1 gene encodes Flotillin-1 protein that was used as a conserved marker protein and may play an important role in cell adhesion, providing clues for understanding the universal functions of Flotillin-1 proteins in other species and suggesting that these proteins could serve as pattern recognition molecules in immunotherapy. We revealed that Flotillin-1 protein of lamprey overexpression in human cells plays a prevalent role in cell migration and provide new thought of treatment to diseases.

Sirtuin1 protects endothelial Caveolin-1 expression and preserves endothelial function via suppressing miR-204 and endoplasmic reticulum stress

Sirtuin1 (Sirt1) is a class III histone deacetylase that regulates a variety of physiological processes, including endothelial function. Caveolin1 (Cav1) is also an important determinant of endothelial function. We asked if Sirt1 governs endothelial Cav1 and endothelial function by regulating miR-204 expression and endoplasmic reticulum (ER) stress. Knockdown of Sirt1 in endothelial cells, and in vivo deletion of endothelial Sirt1, induced endothelial ER stress and miR-204 expression, reduced Cav1, and impaired endothelium-dependent vasorelaxation. All of these effects were reversed by a miR-204 inhibitor (miR-204 I) or with overexpression of Cav1. A miR-204 mimic (miR-204 M) decreased Cav1 in endothelial cells. In addition, high-fat diet (HFD) feeding induced vascular miR-204 and reduced endothelial Cav1. MiR-204-I protected against HFD-induced downregulation of endothelial Cav1. Moreover, pharmacologic induction of ER stress with tunicamycin downregulated endothelial Cav1 and impaired endothelium-dependent vasorelaxation that was rescued by overexpressing Cav1. In conclusion, Sirt1 preserves Cav1-dependent endothelial function by mitigating miR-204-mediated vascular ER stress.

Caveolae and Caveolin-1 Integrate Reverse Cholesterol Transport and Inflammation in Atherosclerosis

Lipid disorder and inflammation play critical roles in the development of atherosclerosis. Reverse cholesterol transport is a key event in lipid metabolism. Caveolae and caveolin-1 are in the center stage of cholesterol transportation and inflammation in macrophages. Here, we propose that reverse cholesterol transport and inflammation in atherosclerosis can be integrated by caveolae and caveolin-1.

Class-A scavenger receptor function and expression in the rainbow trout (Oncorhynchus mykiss) epithelial cell lines RTgutGC and RTgill-W1

Class A scavenger receptors (SR-As) are cell surface receptors that bind a range of ligands, including modified low-density lipoproteins (mLDLs) and nucleic acids. Due to their ability to bind extracellular dsRNA, SR-As play an important role in the viral dsRNA initiated immune pathway. Most research on SR-As has focused on mammalian models, and there has been limited research on SR-As in fish. Thus, the presence of functional class A scavenger receptors (SR-As) were investigated in the rainbow trout cell lines, RTgutGC and RTgill-W1. SR-A ligand binding was assessed using fluorescently labeled acetylated-low density lipoprotein (acLDL) and synthetic dsRNA, polyinosinic:polycytidylic acid (poly IC), in combination with a series of known SR-A competitive ligands: fucoidan, dextran sulfate (DxSO4) and polyinosinic acid (poly I). Both cell lines were able to bind acLDL, which was blocked by SR-A competitive ligands. In RTgutGC, acLDL and poly IC competed for binding to the same surface receptor; however, in RTgill-W1 they did not. Poly IC-fluorescein binding was blocked by SR-A competitive ligands in RTgutGC but not RTgill-W1, suggesting an SR-A dependent dsRNA uptake mechanism in RTgutGC and an SR-A-independent update mechanism in RTgill-W1. Both cell lines responded to extracellular dsRNA treatment with the up-regulation of interferons (IFNs) and interferon stimulated genes (ISGs) as measured by quantitative (q)RT-PCR; however, RTgutGC expressed significantly higher transcript levels for both IFNs and ISGs compared with RTgill-W1 following extracellular poly IC treatment. Expression of SR-As, specifically a SCARA4-like sequence, was identified at the transcript level in both cell lines. These results suggest that both RTgill-W1 and RTgutGC express functional SR-As that are able to bind the classic SR-A ligand, acLDL. Although they both express SCARA4, the full SR-A expression profile; however, is likely different between the cell lines, as dsRNA uptake appears to be SR-A dependent in RTgutGC but SR-A-independent in RTgill-W1. Also, dsRNA uptake via SR-As appears to mediate a more robust antiviral response compared with a SR-A independent method of uptake. This study is the first to identify functional SR-As in rainbow trout epithelial cells, and contributes not only to a better understanding of modified LDL transport but also innate immunity in these economically important animals.