SR-B1's Next Top Model: Structural Perspectives on the Functions of the HDL Receptor

Biomimetic high-density lipoprotein nanoparticles for the delivery of nucleic acid-based therapeutics

The field of delivering nucleic acids (NAs) via high-density lipoprotein-mimicking nanoparticles (HDL NPs) has shown promising advancements over the past two decades. HDL NPs are designed to efficiently bind NAs, safeguard them from degradation, and help navigate through various biological barriers to deliver them into the target cell's cytosol. Some HDL NPs allow direct cytosolic delivery of NAs by a selective mechanism with the involvement of HDL's natural receptor scavenger receptor class B type I (SR-B1). In contrast, others rely on endocytic uptake of the entire NA-loaded HDL NP. Owing to their highly biocompatible nature, ability to target clinically relevant receptors, and fine tunability, NA-loaded HDL NPs are applied to treat cancer, cardiovascular diseases, and brain malignancies. They are also emerging as potent vaccines against cancers and infectious diseases. This review focuses on various architectures of NA-loaded HDL NPs, their mechanisms for NA cellular uptake, and their therapeutic efficacy in vivo. It comprehensively covers the latest nanocarriers for NA delivery that contain HDL's apolipoproteins (ApoA-I, ApoE) or their mimetic peptides, which define the unique functional and targeting capabilities of HDL NPs.

Keratinocyte SR-B1 expression and targeting in cytokine-driven skin inflammation

BACKGROUND

Strategies to treat inflammatory skin conditions require identifying new targets involved in interactions between overlying epithelial and underlying dermal immune cells. Scavenger receptor class B type 1 (SR-B1) is a cell surface receptor that binds high-density lipoproteins (HDL) and mediates inflammatory responses in immune and endothelial cells. The SR-B1 receptor is also expressed in keratinocytes, but its role in inflammatory skin diseases remains unexplored.

METHODS

To investigate keratinocyte SR-B1 in the setting of inflammation, we measured its expression in skin biopsy samples obtained from patients with psoriasis; human skin explants exposed to the inflammatory cytokine, interleukin-17A (IL-17A); and mouse skin exposed to the pro-inflammatory agent, imiquimod (IMQ). We also evaluated the effects of SR-B1 knockdown on primary keratinocyte responses to IL-17A. Finally, we employed a synthetic HDL-nanoparticle (HDL NP) to investigate the therapeutic potential of targeting SR-B1 in IL-17A-stimulated keratinocytes and in male C57BL/6 mice with IMQ-induced skin inflammation.

RESULTS

Our data show SR-B1 expression is increased in diseased human skin and in both human and mouse models of skin inflammation. SR-B1 knockdown in keratinocytes exacerbates the inflammatory response to IL-17A, whereas targeting SR-B1 with HDL NP attenuates this response. In the IMQ murine model, topical application of HDL NPs improves the skin phenotype, normalizes SR-B1 expression, and reduces molecular and cellular markers of inflammation.

CONCLUSIONS

Overall, SR-B1 plays a role in skin inflammation and HDL NP-mediated targeting of SR-B1 in keratinocytes may offer a targeted new therapy for inflammatory skin disease.

Combined action of dietary-based approaches and therapeutic agents on cholesterol metabolism and main related diseases

BACKGROUND

Dyslipidaemia is among the major causes of severe diseases and, despite being well-established, the hypocholesterolaemic therapies still face significant concerns about potential side effects (such as myopathy, myalgia, liver injury digestive problems, or mental fuzziness in some people taking statins), interaction with other drugs or specific foods. Accordingly, this review describes the latest developments in the most effective therapies to control and regulate dyslipidaemia.

SCOPE AND APPROACH

Herein, the metabolic dynamics of cholesterol and their integration with the current therapies: statins, bile acid sequestrants, fibrates, niacin, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors, reconstituted high-density lipoprotein (rHDL), or anti-inflammatory and immune-modulating therapies), were compared focusing their effectiveness, patients' adhesion and typical side-effects. Likewise, the interaction of these therapies with recommended dietary habits, focusing functional foods and nutraceuticals uptake were also considered.

KEY FINDINGS AND CONCLUSIONS

Since none of the current therapeutic alternatives represent an ideal solution (mainly due to side-effects or patients' tolerance), the potential adjuvant action of selected diets (and other healthy habits) was proposed as a way to improve the cholesterol-lowering effectiveness, while reducing the adverse effects caused by dose-increase or continuous uptake of alternating therapeutic agents. In general, the relevance of well-adapted diets must be acknowledged and their potential effects must be exhorted among patients, who need to be aware of the associated multifactorial advantages.

Role of Scavenger Receptor B1 (SR-B1) in Improving Food Benefits for Human Health

Scavenger receptor class B member 1 (SR-B1) is a multiligand receptor with a broad range of functions spanning from the uptake of cholesteryl esters from high-density lipoproteins (HDLs) and transport of micronutrients such as fat-soluble vitamins and carotenoids across cell membranes to roles in tumor progression, pathogen recognition, and inflammatory responses. As a target of exposome factors such as environmental stressors and unhealthy lifestyle choices, as well as aging, dysregulated expression and activity of SR-B1 can negatively impact human health. Intriguingly, not only is SR-B1 a major determinant of nutrient homeostasis and, hence, metabolic health status, but these same nutrients and some phytochemicals have also demonstrated their ability to modulate SR-B1. Therefore, an integrated approach that, taking into account human health, nutrition, and food technology sciences, aims to produce foods with health-promoting effects should take advantage of the multifaceted properties of SR-B1. Improved functional foods and novel nanoparticle-based delivery systems, rich in nutrients and phytochemicals, with precise targeting to SR-B1 in specific tissues or structures could represent a strategic advance to improve human health and promote well-being.

Activating transcription factor-3 orchestrates the modulation of vascular anti-contractile activity and relaxation by governing the secretion of HDL-bound sphingosine-1-phosphate in perivascular adipose tissue

BACKGROUND AND PURPOSE

Perivascular adipose tissues (PVATs) play a critical role in modulating vascular homeostasis and protecting against cardiovascular dysfunction-mediated blood pressure dysregulation. We demonstrated that the activating transcription factor-3 (Atf3) gene in the PVAT is crucial for improving vascular wall tension abnormalities; however, its protective mechanism remains unclear. Herein, we aim to determine whether ATF3 regulates PVAT-derived relaxing factor (PVDRF) biosynthesis and if its secretion contributes to vasorelaxation.

EXPERIMENTAL APPROACH

This study employed an in vivo animal model using global Atf3-deficient mice, in vitro blood vessel myography, and biochemical analyses to evaluate ATF3-mediated PVDRF release and reactivity in the vasculature.

KEY RESULTS

Wild-type (WT) mouse thoracic aortic PVAT extracts significantly induced resting tone dilation and attenuated vasoconstrictor-induced contractile responses compared to Atf3-/- mice. Heat-stable PVAT extracts from WT mice caused sustained and reproducible vasodilation without tachyphylaxis in control aortic rings. Biochemical evaluation of PVDRF release revealed that Atf3-/- mice had lower sphingosine-1-phosphate (S1P) and HDL cholesterol (HDL-C) levels than WT mice. Furthermore, PVAT extracts from WT mice induced long-lasting vasorelaxation, which was significantly inhibited by the S1P3 receptor antagonist TY52156 and scavenger receptor class B type 1 receptor antagonist glyburide.

CONCLUSION AND IMPLICATIONS

ATF3 within the PVAT can modulate vascular function by strengthening sphingosine kinase 1 (sphk1)-S1P-S1P3 receptor lipid signalling and stimulating S1P binding to HDL to form the vasodilator HDL-S1P. ATF3 is an essential modulator for maintaining the physiological function of PVAT, providing a novel target for treatment of obesity-related cardiovascular diseases.

High-density lipoprotein cholesterol: how studying the 'good cholesterol' could improve cardiovascular health

High cholesterol levels are associated with an increased risk of cardiovascular disease, specifically atherosclerosis, a leading cause of death worldwide. Atherosclerosis occurs when cholesterol and fat build up in plaques along blood vessel walls, restricting blood flow and preventing nutrients and oxygen from diffusing in and out of the bloodstream. High-density lipoprotein cholesterol (HDL) particles prevent the build-up of such plaques, removing excess cholesterol from the peripheral tissues and delivering it to the liver, where it can be removed from the body. This pathway is known as reverse cholesterol transport (RCT). Because HDL plays a key role in preventing plaque buildup, understanding how this molecule and RCT function in the body could help us develop much-needed new atherosclerosis therapies and prevention strategies. However, HDL metabolism is complex, and research on HDL has been less favoured than research investigating a much better-understood molecule, low-density lipoprotein cholesterol, as a treatment target. More specifically, the receptors involved in the process of taking up HDL within the liver and their relationships to one another, along with the mechanism of whole, or holoparticle uptake of HDL remain to be clarified. In this review, we discuss several outstanding mysteries in HDL metabolism, consider why previous clinical trials to improve cardiovascular health by modulating HDL levels have been unsuccessful and argue that understanding HDL metabolism is essential for crafting interventions to reduce cardiovascular disease risk.

Sticky Business: Correlating Oligomeric Features of Class B Scavenger Receptors to Lipid Transport

PURPOSE OF THE REVIEW

Atherosclerotic plaques result from imbalanced lipid metabolism and maladaptive chronic immune responses. Class B scavenger receptors are lipid transporters and regulators of their metabolism. The purpose of this review is to explore recent structural findings of these membrane-associated receptors, with particular focus on their higher-order oligomeric organization and impact on lipid transport.

RECENT FINDINGS

Class B scavenger receptors have evidence for oligomerization, with recent efforts placed on identifying residues and motifs responsible for mediating this process. The first studies correlating scavenger receptor oligomerization to function are described. This review highlights two emerging hypotheses regarding the function of scavenger receptor oligomerization. The first is a hydrophobic channel created by self-association of receptors to promote transport. The second hypothesis suggests that homo-oligomerization stabilizes receptors, prevents internalization and thereby promotes transport indirectly. Novel computational and in vitro experimental techniques with purified receptors are also described.

Comparative analysis of Scarb1 and Cd36 in grass carp (Ctenopharyngodon idellus): Implications for DHA uptake

The polyunsaturated fatty acid docosahexaenoic acid (DHA) significantly influences fish growth and lipid metabolism. Nevertheless, the specific mechanism by which DHA is transported and exerts its effects remains unclear. Scavenger receptor class B type I (SCARB1) is essential for maintaining cellular cholesterol levels and regulating the immune system in mammals, as well as facilitating the uptake of fatty acids (FAs). Another class B scavenger receptor, cluster-determinant 36 (CD36), is involved in promoting the uptake and transport of long-chain fatty acids. However, the molecular characteristics of the grass carp scarb1 gene have not yet been reported, and the potential role of Scarb1 and Cd36 in mediating DHA transport and metabolism remains uncertain. This study aimed to investigate the effects of Scarb1 and Cd36 on DHA transport. Initially, grass carp scarb1-1 and scarb1-2 were cloned. Predictions were made regarding their structural characteristics, including number and presence of transmembrane domains and glycosylation sites. Furthermore, gene structure analysis revealed that scarb1-1 has two additional exons in the 3'-region compared to scarb1-2. The multiple sequence alignment indicated that Scarb1 exhibits conserved motifs and amino acid residues across vertebrates. mRNA expression of scarb1-1 was the highest in the intestine, while scarb1-2 was highest expressed in adipose tissue, with both having lower expression levels in muscle tissue. Scarb1-1 was primarily localized on the cell membrane, whereas Scarb1-2 was found in both the cell membrane and cytoplasm. After overexpression of grass carp Scarb1-1, Scarb1-2, and Cd36 in HEK 293 T cells, DHA incubation showed that only Cd36 significantly increased cellular DHA relative content, suggesting a potential role of Cd36 in DHA transport. These findings will serve as a basis for further research on fatty acid transport in fish.

Magnetic Nanoparticles: A Comprehensive Review from Synthesis to Biomedical Frontiers

Nanotechnology has opened new doors of exploration, particularly in materials science and healthcare. Magnetic nanoparticles (MNP), the tiny magnets, because of their various properties, have the potential to bring about radical changes in the field of medicine. The distinctive surface chemistry, nontoxicity, biocompatibility, and, in particular, the inducible magnetic moment of magnetic materials has attracted a great deal of interest in morphological structures from a variety of scientific domains. This review presents a concise overview of MNPs and their crucial properties and synthesis routes. It also aims to highlight the continuous synthesis methods available for MNP production. In recent years, the use of computational methods for understanding the behavior of nanoparticles has been on the rise. Thus, we also discuss the numerical models developed to understand how magnetic nanoparticles can be used in magnetic hyperthermia and targeting the Circle of Wilis. With the increasing use of MNPs in biomedical applications, it becomes necessary to understand the mechanisms of toxicity, which are elucidated in this review. The review focuses on the biomedical applications of MNPs in drug delivery, theranostics, and MRI contrasting agents. We anticipate that this article will broaden the perspective on magnetic nanoparticles and help to understand their functionality and applicability better.

Dynamic and Energetic Aspects of Carotenoids In-and-Around Model Lipid Membranes Revealed in Molecular Modelling

In contrast to plants, humans are unable to synthesise carotenoids and have to obtain them from diet. Carotenoids fulfil several crucial biological functions in the organism; however, due to poor solubility in water, their bioavailability from plant-based food is low. The processes of carotenoid absorption and availability in the human body have been intensively studied. The recent experimental findings concerning these processes are briefly presented in the introductory part of this review, together with a summary of such topics as carotenoid carriers, body transport and tissue delivery, to finally report on molecular-level studies of carotenoid binding by membrane receptors. The main message of the review is contained in the section describing computational investigations of carotenoid intercalation and dynamic behaviour in lipid bilayers. The relevance of these computational studies lies in showing the direct link between the microscopic behaviour of molecules and the characteristics of their macroscopic ensembles. Furthermore, studying the interactions between carotenoids and lipid bilayers, and certainly proteins, on the molecular- and atomic-level using computational methods facilitates the interpretation and explanation of their macroscopic properties and, hopefully, helps to better understand the biological functions of carotenoids.

An innovative viewpoint on the existing and prospectiveness of SR-B1

Scavenger Receptor Class B Type 1 (SR-B1), a receptor protein expressed on the cell membrane, plays a crucial role in the metabolism and transport of cholesterol and other lipids, contributing significantly to the homeostasis of lipid levels within the body. Bibliometric analysis involves the application of mathematical and statistical methods to quantitatively analyze different types of documents. It involves the analysis of structural and temporal trends in scholarly articles, coupled with the identification of subject emphasis and variations. Through a bibliometric analysis, this study examines the historical background, current research trends, and future directions in the exploration of SR-B1. By offering insights into the research status and development of SR-B1, this paper aims to assist researchers in identifying novel pathways and areas of investigation in this field of study. Following the screening process, it can be concluded that research on SR-B1 has consistently remained a topic of significant interest over the past 17 years. Interestingly, SR-B1 has recently garnered attention in areas beyond its traditional research focus, including the field of cancer. The primary objective of this review is to provide a concise and accessible overview of the development process of SR-B1 that can help readers who are not well-versed in SR-B1 research quickly grasp its key aspects. Furthermore, this review aims to offer insights and suggestions to researchers regarding potential future research directions and areas of emphasis relating to SR-B1.

Development and validation of a purification system for functional full-length human SR-B1 and CD36

Scavenger receptor class B type 1 (SR-B1) and CD36 are both members of the class B scavenger receptor family that play important roles in lipoprotein metabolism and atherosclerotic disease. SR-B1 is the primary receptor for high-density lipoproteins, while CD36 is the receptor responsible for the internalization of oxidized low-density lipoproteins. Despite their importance, class B scavenger receptor structure has only been studied by functional domain or peptide fragments-there are currently no reports of utilizing purified full-length protein. Here we report the successful expression and purification of full-length human SR-B1 and CD36 using an Spodoptera frugiperda insect cell system. We demonstrate that both SR-B1 and CD36 retained their normal functions in Spodoptera frugiperda cells, including lipoprotein binding, lipid transport, and the formation of higher order oligomers in the plasma membrane. Purification schemes for both scavenger receptors were optimized and their purity was confirmed by SDS-PAGE. Both purified scavenger receptors were assessed for stability by thermal shift assay and shown to maintain stable melting temperatures up to 6 weeks post-purification. Microscale thermophoresis was used to demonstrate that purified SR-B1 and CD36 were able to bind their native lipoprotein ligands. Further, there was no difference in affinity of SR-B1 for high-density lipoprotein or CD36 for oxidized low-density lipoprotein, when comparing glycosylated and deglycosylated receptors. These studies mark a significant step forward in creating physiologically relevant tools to study scavenger receptor function and lay the groundwork for future functional studies and determination of receptor structure.

Scavenger receptor class B type I is required for efficient glucose uptake and metabolic homeostasis in adipocytes

Obesity is a worldwide epidemic and places individuals at a higher risk for developing comorbidities that include cardiovascular disease and type 2 diabetes. Adipose tissue contains adipocytes that are responsible for lipid metabolism and reducing misdirected lipid storage. Adipocytes facilitate this process through insulin-mediated uptake of glucose and its subsequent metabolism into triglycerides for storage. During obesity, adipocytes become insulin resistant and have a reduced ability to mediate glucose import, thus resulting in whole-body metabolic dysfunction. Scavenger receptor class B type I (SR-BI) has been implicated in glucose uptake in skeletal muscle and adipocytes via its native ligands, apolipoprotein A-1 and high-density lipoproteins. Further, SR-BI translocation to the cell surface in adipocytes is sensitive to insulin stimulation. Using adipocytes differentiated from ear mesenchymal stem cells isolated from wild-type and SR-BI knockout (SR-BI -/- ) mice as our model system, we tested the hypothesis that SR-BI is required for insulin-mediated glucose uptake and regulation of energy balance in adipocytes. We demonstrated that loss of SR-BI in adipocytes resulted in inefficient glucose uptake regardless of cell surface expression levels of glucose transporter 4 compared to WT adipocytes. We also observed reduced glycolytic capacity, increased lipid biosynthesis, and dysregulated expression of lipid metabolism genes in SR-BI -/- adipocytes compared to WT adipocytes. These results partially support our hypothesis and suggest a novel role for SR-BI in glucose uptake and metabolic homeostasis in adipocytes.

Novel receptor, mutation, vaccine, and establishment of coping mode for SARS-CoV-2: current status and future

Since the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its resultant pneumonia in December 2019, the cumulative number of infected people worldwide has exceeded 670 million, with over 6.8 million deaths. Despite the marketing of multiple series of vaccines and the implementation of strict prevention and control measures in many countries, the spread and prevalence of SARS-CoV-2 have not been completely and effectively controlled. The latest research shows that in addition to angiotensin converting enzyme II (ACE2), dozens of protein molecules, including AXL, can act as host receptors for SARS-CoV-2 infecting human cells, and virus mutation and immune evasion never seem to stop. To sum up, this review summarizes and organizes the latest relevant literature, comprehensively reviews the genome characteristics of SARS-CoV-2 as well as receptor-based pathogenesis (including ACE2 and other new receptors), mutation and immune evasion, vaccine development and other aspects, and proposes a series of prevention and treatment opinions. It is expected to provide a theoretical basis for an in-depth understanding of the pathogenic mechanism of SARS-CoV-2 along with a research basis and new ideas for the diagnosis and classification, of COVID-19-related disease and for drug and vaccine research and development.

LDL Transcytosis by the Arterial Endothelium-Atherosclerosis by a Thousand Cuts?

PURPOSE OF REVIEW

The accumulation of LDL in the arterial intima is an initiating event in atherosclerosis. After decades of controversy, it is now clear that transcytosis of LDL across an intact endothelial monolayer contributes to its intimal deposition. We review recent observations in this field and address the question of whether LDL transcytosis can be manipulated therapeutically.

RECENT FINDINGS

The development of a live-cell imaging method for studying transcytosis using total internal reflection fluorescence (TIRF) microscopy has catalyzed recent discoveries. LDL transcytosis is mediated by SR-BI and ALK1. Estrogen down-regulates SR-BI and inhibits LDL transcytosis, while the nuclear structural protein HMGB1 promotes LDL transcytosis. LDL transcytosis by ALK1 is independent of the receptor's kinase activity and is antagonized by BMP9, ALK1's canonical ligand. Inflammation stimulates LDL transcytosis. Identifying the function and mechanisms of LDL transcytosis may ultimately permit its therapeutic manipulation.

New Insights on the Uptake and Trafficking of Coenzyme Q

Coenzyme Q (CoQ) is an essential lipid with many cellular functions, such as electron transport for cellular respiration, antioxidant protection, redox homeostasis, and ferroptosis suppression. Deficiencies in CoQ due to aging, genetic disease, or medication can be ameliorated by high-dose supplementation. As such, an understanding of the uptake and transport of CoQ may inform methods of clinical use and identify how to better treat deficiency. Here, we review what is known about the cellular uptake and intracellular distribution of CoQ from yeast, mammalian cell culture, and rodent models, as well as its absorption at the organism level. We discuss the use of these model organisms to probe the mechanisms of uptake and distribution. The literature indicates that CoQ uptake and distribution are multifaceted processes likely to have redundancies in its transport, utilizing the endomembrane system and newly identified proteins that function as lipid transporters. Impairment of the trafficking of either endogenous or exogenous CoQ exerts profound effects on metabolism and stress response. This review also highlights significant gaps in our knowledge of how CoQ is distributed within the cell and suggests future directions of research to better understand this process.

Highlighting In Vitro the Role of Brain-like Endothelial Cells on the Maturation and Metabolism of Brain Pericytes by SWATH Proteomics

Within the neurovascular unit, brain pericytes (BPs) are of major importance for the induction and maintenance of the properties of the blood-brain barrier (BBB) carried by the brain microvessel endothelial cells (ECs). Throughout barriergenesis, ECs take advantage of soluble elements or contact with BPs to maintain BBB integrity and the regulation of their cellular homeostasis. However, very few studies have focused on the role of ECs in the maturation of BPs. The aim of this study is to shed light on the proteome of BPs solocultured (hBP-solo) or cocultured with ECs (hBP-coc) to model the human BBB in a non-contact manner. We first generated protein libraries for each condition and identified 2233 proteins in hBP-solo versus 2492 in hBP-coc and 2035 common proteins. We performed a quantification of the enriched proteins in each condition by sequential window acquisition of all theoretical mass spectra (SWATH) analysis. We found 51 proteins enriched in hBP-solo related to cell proliferation, contractility, adhesion and extracellular matrix element production, a protein pattern related to an immature cell. In contrast, 90 proteins are enriched in hBP-coc associated with a reduction in contractile activities as observed in vivo in ‘mature’ BPs, and a significant gain in different metabolic functions, particularly related to mitochondrial activities and sterol metabolism. This study highlights that BPs take advantage of ECs during barriergenesis to make a metabolic switch in favor of BBB homeostasis in vitro.

A short amphipathic alpha helix in scavenger receptor BI facilitates bidirectional HDL-cholesterol transport

During reverse cholesterol transport, high-density lipoprotein (HDL) carries excess cholesterol from peripheral cells to the liver for excretion in bile. The first and last steps of this pathway involve the HDL receptor, scavenger receptor BI (SR-BI). While the mechanism of SR-BI-mediated cholesterol transport has not yet been established, it has long been suspected that cholesterol traverses through a hydrophobic tunnel in SR-BI’s extracellular domain. Confirmation of a hydrophobic tunnel is hindered by the lack of a full-length SR-BI structure. Part of SR-BI’s structure has been resolved, encompassing residues 405 to 475, which includes the C-terminal transmembrane domain and its adjacent extracellular region. Within the extracellular segment is an amphipathic helix (residues 427–436, referred to as AH(427–436)) that showed increased protection from solvent in NMR-based studies. Homology models predict that hydrophobic residues in AH(427–436) line a core cavity in SR-BI’s extracellular region that may facilitate cholesterol transport. Therefore, we hypothesized that hydrophobic residues in AH(427–436) are required for HDL cholesterol transport. Here, we tested this hypothesis by mutating individual residues along AH(427–436) to a charged residue (aspartic acid), transiently transfecting COS-7 cells with plasmids encoding wild-type and mutant SR-BI, and performing functional analyses. We found that mutating hydrophobic, but not hydrophilic, residues in AH(427–436) impaired SR-BI bidirectional cholesterol transport. Mutating phenylalanine-430 was particularly detrimental to SR-BI’s functions, suggesting that this residue may facilitate important interactions for cholesterol delivery within the hydrophobic tunnel. Our results support the hypothesis that a hydrophobic tunnel within SR-BI mediates cholesterol transport.