Use of cyclodextrins to manipulate plasma membrane cholesterol content: evidence, misconceptions and control strategies

Hydroxypropyl-Beta Cyclodextrin Barrier Prevents Respiratory Viral Infections: A Preclinical Study

The emergence and mutation of pathogenic viruses have been occurring at an unprecedented rate in recent decades. The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has developed into a global public health crisis due to extensive viral transmission. In situ RNA mapping has revealed angiotensin-converting enzyme 2 (ACE2) expression to be highest in the nose and lower in the lung, pointing to nasal susceptibility as a predominant route for infection and the cause of subsequent pulmonary effects. By blocking viral attachment and entry at the nasal airway using a cyclodextrin-based formulation, a preventative therapy can be developed to reduce viral infection at the site of entry. Here, we assess the safety and antiviral efficacy of cyclodextrin-based formulations. From these studies, hydroxypropyl beta-cyclodextrin (HPBCD) and hydroxypropyl gamma-cyclodextrin (HPGCD) were then further evaluated for antiviral effects using SARS-CoV-2 pseudotypes. Efficacy findings were confirmed with SARS-CoV-2 Delta variant infection of Calu-3 cells and using a K18-hACE2 murine model. Intranasal pre-treatment with HPBCD-based formulations reduced viral load and inflammatory signaling in the lung. In vitro efficacy studies were further conducted using lentiviruses, murine hepatitis virus (MHV), and influenza A virus subtype H1N1. These findings suggest HPBCD may be used as an agnostic barrier against transmissible pathogens, including but not limited to SARS-CoV-2.

Shear Stress and Sub-Femtomolar Levels of Ligand Synergize to Activate ALK1 Signaling in Endothelial Cells

Endothelial cells (ECs) respond to concurrent stimulation by biochemical factors and wall shear stress (SS) exerted by blood flow. Disruptions in flow-induced responses can result in remodeling issues and cardiovascular diseases, but the detailed mechanisms linking flow-mechanical cues and biochemical signaling remain unclear. Activin receptor-like kinase 1 (ALK1) integrates SS and ALK1-ligand cues in ECs; ALK1 mutations cause hereditary hemorrhagic telangiectasia (HHT), marked by arteriovenous malformation (AVM) development. However, the mechanistic underpinnings of ALK1 signaling modulation by fluid flow and the link to AVMs remain uncertain. We recorded EC responses under varying SS magnitudes and ALK1 ligand concentrations by assaying pSMAD1/5/9 nuclear localization using a custom multi-SS microfluidic device and a custom image analysis pipeline. We extended the previously reported synergy between SS and BMP9 to include BMP10 and BMP9/10. Moreover, we demonstrated that this synergy is effective even at extremely low SS magnitudes (0.4 dyn/cm2) and ALK1 ligand range (femtogram/mL). The synergistic response to ALK1 ligands and SS requires the kinase activity of ALK1. Moreover, ALK1's basal activity and response to minimal ligand levels depend on endocytosis, distinct from cell-cell junctions, cytoskeleton-mediated mechanosensing, or cholesterol-enriched microdomains. However, an in-depth analysis of ALK1 receptor trafficking's molecular mechanisms requires further investigation.

Regulatory role of cholesterol in modulating actin dynamics and cell adhesive interactions in the trabecular meshwork

The trabecular meshwork (TM) tissue plays a crucial role in maintaining intraocular pressure (IOP) homeostasis. Increased TM contractility and stiffness are directly correlated with elevated IOP. Although cholesterol is known to be a determinant of glaucoma occurrence and elevated IOP, the underlying mechanisms remain elusive. In this study, we used human TM (HTM) cells to unravel the effects of cholesterol on TM stiffness. We achieved this by performing acute cholesterol depletion with Methyl-β-cyclodextrin (MβCD) and cholesterol enrichment/replenishment with MβCD cholesterol complex (CHOL). Interestingly, cholesterol depletion triggered notable actin depolymerization and decreased focal adhesion formation, while enrichment/replenishment promoted actin polymerization, requiring the presence of actin monomers. Using a specific reporter of phosphatidylinositol 4,5-bisphosphate (PIP2), we demonstrated that cholesterol depletion decreases PIP2 levels on the cell membrane, whereas enrichment increases them. Given the critical role of PIP2 in actin remodeling and focal adhesion formation, we postulate that cholesterol regulates actin dynamics by modulating PIP2 levels on the membrane. Furthermore, we showed that cholesterol levels regulate integrin α5β1 and αVβ3 distribution and activation, subsequently altering cell-extracellular matrix (ECM) interactions. Notably, the depletion of cholesterol, as a major lipid constituent of the cell membrane, led to a decrease in HTM cell membrane tension, which was reversed upon cholesterol replenishment. Overall, our systematic exploration of cholesterol modulation on TM stiffness highlights the critical importance of maintaining appropriate membrane and cellular cholesterol levels for achieving IOP homeostasis.

Cholesterol-Mediated Anchoring of Phospholipids onto Proteinosomes for Switching Membrane Permeability

Modulated membrane functionalization is a necessary and overarching step for hollow microcompartments toward their application as nanoreactors or artificial cells. In this study, we show a way to generate phospholipid hybrid proteinosomes that could show superposed virtues of liposomes and proteinosomes. In comparison to pure proteinosomes, both the membrane fluidity and permeability are improved obviously after forming the phospholipid hybrid proteinosomes. Specifically, the integration of phospholipids also endows the hybrid proteinosomes demonstrating a stepwise release of the encapsulants of FITC-dextran (70 and 150 kDa) triggered sequentially by phospholipase and protease, and then a modulated cascaded enzymatic reaction between two different populations of proteinosomes are achieved. Therefore, it is anticipated that such constructed phospholipid hybrid proteinosomes could be employed as an improved microcompartmental model for further advanced artificial cell design toward achieving logic signal communication within the various artificial cellular populations as well as potential applications in the field of microreactors.

Exploring the role of cyclodextrins as a cholesterol scavenger: a molecular dynamics investigation of conformational changes and thermodynamics

This study presents a comprehensive analysis of the cholesterol binding mechanism and conformational changes in cyclodextrin (CD) carriers, namely βCD, 2HPβCD, and MβCD. The results revealed that the binding of cholesterol to CDs was spontaneous and thermodynamically favorable, with van der Waals interactions playing a dominant role, while Coulombic interactions have a negligible contribution. The solubility of cholesterol/βCD and cholesterol/MβCD complexes was lower compared to cholesterol/2HPβCD complex due to stronger vdW and Coulombic repulsion between water and CDs. Hydrogen bonding was found to have a minor role in the binding process. The investigation of mechanisms and kinetics of binding demonstrated that cholesterol permeates into the CD cavities completely. Replicas consideration indicated that while the binding to 2HPβCD occurred perpendicularly and solely through positioning cholesterol's oxygen toward the primary hydroxyl rim (PHR), the mechanism of cholesterol binding to βCD and MβCD could take place with the orientation of oxygen towards both rims. Functionalization resulted in decreased cavity polarity, increased constriction tendency, and altered solubility and configuration of the carrier. Upon cholesterol binding, the CDs expanded, increasing the cavity volume in cholesterol-containing systems. The effects of cholesterol on the relative shape anisotropy (κ2) and asphericity parameter (b) in cyclodextrins were investigated. βCD exhibited a spherical structure regardless of cholesterol presence, while 2HPβCD and MβCD displayed more pronounced non-sphericity in the absence of cholesterol. Loading cholesterol transformed 2HPβCD and MβCD into more spherical shapes, with increased probabilities of higher κ2. MβCD showed a higher maximum peak of κ2 compared to 2HPβCD after cholesterol loading, while 2HPβCD maintained a significant maximum peak at 0.2 for b.

Endocytosis inhibitors block SARS-CoV-2 pseudoparticle infection of mink lung epithelium

Introduction

Both spill over and spill back of SARS-CoV-2 virus have been reported on mink farms in Europe and the United States. Zoonosis is a public health concern as dangerous mutated forms of the virus could be introduced into the human population through spillback.

Methods

The purpose of our study was to determine the SARS-CoV-2 entry mechanism using the mink lung epithelial cell line (Mv1Lu) and to block entry with drug inhibitors.

Results

Mv1Lu cells were susceptible to SARS-CoV-2 viral pseudoparticle infection, validating them as a suitable disease model for COVID-19. Inhibitors of TMPRSS2 and of endocytosis, two pathways of viral entry, were tested to identify those that blocked infection. TMPRSS2 inhibitors had minimal impact, which can be explained by the apparent lack of activity of this enzyme in the mink and its localization within the cell, not on the cell surface.

Discussion

Dyngo4a, a small molecule endocytosis inhibitor, significantly reduced infection, supporting the conclusion that the entry of the SARS-CoV-2 virus into Mv1Lu cells occurs primarily through endocytosis. The small molecule inhibitors that were effective in this study could potentially be used therapeutically to prevent SARS-CoV-2 infection in mink populations. This study will facilitate the development of therapeutics to prevent zoonotic transmission of SARS-CoV-2 variants to other animals, including humans.

ANO1, CaV1.2, and IP3R form a localized unit of EC-coupling in mouse pulmonary arterial smooth muscle

Pulmonary arterial (PA) smooth muscle cells (PASMC) generate vascular tone in response to agonists coupled to Gq-protein receptor signaling. Such agonists stimulate oscillating calcium waves, the frequency of which drives the strength of contraction. These Ca2+ events are modulated by a variety of ion channels including voltage-gated calcium channels (CaV1.2), the Tmem16a or Anoctamin-1 (ANO1)-encoded calcium-activated chloride (CaCC) channel, and Ca2+ release from the sarcoplasmic reticulum through inositol-trisphosphate receptors (IP3R). Although these calcium events have been characterized, it is unclear how these calcium oscillations underly a sustained contraction in these muscle cells. We used smooth muscle-specific ablation of ANO1 and pharmacological tools to establish the role of ANO1, CaV1.2, and IP3R in the contractile and intracellular Ca2+ signaling properties of mouse PA smooth muscle expressing the Ca2+ biosensor GCaMP3 or GCaMP6. Pharmacological block or genetic ablation of ANO1 or inhibition of CaV1.2 or IP3R, or Ca2+ store depletion equally inhibited 5-HT-induced tone and intracellular Ca2+ waves. Coimmunoprecipitation experiments showed that an anti-ANO1 antibody was able to pull down both CaV1.2 and IP3R. Confocal and superresolution nanomicroscopy showed that ANO1 coassembles with both CaV1.2 and IP3R at or near the plasma membrane of PASMC from wild-type mice. We conclude that the stable 5-HT-induced PA contraction results from the integration of stochastic and localized Ca2+ events supported by a microenvironment comprising ANO1, CaV1.2, and IP3R. In this model, ANO1 and CaV1.2 would indirectly support cyclical Ca2+ release events from IP3R and propagation of intracellular Ca2+ waves.

Identification and in vivo detection of side-chain hydroxylated metabolites of 4β-hydroxycholesterol

Oxysterols are oxidized derivatives of cholesterol that are formed by enzymatic processes or through the action of reactive oxygen species. Several of these bioactive lipids have been shown to be affected and/or play a role in inflammatory processes. 4β-hydroxycholesterol is one of the major oxysterols in mice and humans and its levels are affected by inflammatory diseases. However, apart from its long half-life, little is known about its catabolism. By incubating 4β-hydroxycholesterol with mouse mitochondria-enriched liver fractions, as well as 25-hydroxycholesterol and 27-hydroxycholesterol with recombinant CYP3A4, we identified 4β,25-dihydroxycholesterol and 4β,27-dihydroxycholesterol as 4β-hydroxycholesterol metabolites. Supporting the biological relevance of this metabolism, we detected both metabolites after incubation of J774, primary mouse peritoneal macrophages and PMA-differentiated THP-1 cells with 4β-hydroxycholesterol. Across our experiments, the incubation of cells with lipopolysaccharides differentially affected the levels of the 25- and 27-hydroxylated metabolites of 4β-hydroxycholesterol. Finally, 4β,27-dihydroxycholesterol was also detected in mice liver and plasma after intraperitoneal administration of 4β-hydroxycholesterol. To our knowledge, this is the first report of the in vitro and in vivo detection and quantification of 4β-hydroxycholesterol metabolites.

Cholesterol modulation of interactions between psychostimulants and dopamine transporters

The dopamine transporter (DAT) is a key site of action for cocaine and amphetamines. Dysfunctional DAT is associated with aberrant synaptic dopamine transmission and enhanced drug-seeking and taking behavior. Studies in cultured cells and ex vivo suggest that DAT function is sensitive to membrane cholesterol content. Although it is largely unknown whether psychostimulants alter cholesterol metabolism in the brain, emerging evidence indicates that peripheral cholesterol metabolism is altered in patients with psychostimulant use disorder and circulating cholesterol levels are associated with vulnerability to relapse. Cholesterol interacts with sphingolipids forming lipid raft microdomains on the membrane. These cholesterol-rich lipid raft microdomains serve to recruit and assemble other lipids and proteins to initiate signal transduction. There are two spatially and functionally distinct populations of the DAT segregated by cholesterol-rich lipid raft microdomains and cholesterol-scarce non-raft microdomains on the plasma membrane. These two DAT populations are differentially regulated by DAT blockers (e.g. cocaine), substrates (e.g. amphetamine), and protein kinase C providing distinct cholesterol-dependent modulation of dopamine uptake and efflux. In this chapter, we summarize the impact of depletion and addition of membrane cholesterol on DAT conformational changes between the outward-facing and the inward-facing states, lipid raft-associated DAT localization, basal and induced DAT internalization, and DAT function. In particular, we focus on how the interactions of the DAT with cocaine and amphetamine are influenced by membrane cholesterol. Lastly, we discuss the therapeutic potential of cholesterol-modifying drugs as a new avenue to normalize DAT function and dopamine transmission in patients with psychostimulant use disorder.

Interplay of Cholesterol and Actin in Neurotransmitter GPCR Signaling: Insights from Chronic Cholesterol Depletion Using Statin

Serotonin1A receptors are important neurotransmitter receptors in the G protein-coupled receptor (GPCR) family and modulate a variety of neurological, behavioral, and cognitive functions. We recently showed that chronic cholesterol depletion by statins, potent inhibitors of HMG-CoA reductase (the rate-limiting enzyme in cholesterol biosynthesis), leads to polymerization of the actin cytoskeleton that alters lateral diffusion of serotonin1A receptors. However, cellular signaling by the serotonin1A receptor under chronic cholesterol depletion remains unexplored. In this work, we explored signaling by the serotonin1A receptor under statin-treated condition. We show that cAMP signaling by the receptor is reduced upon lovastatin treatment due to reduction in cholesterol as well as polymerization of the actin cytoskeleton. To the best of our knowledge, these results constitute the first report describing the effect of chronic cholesterol depletion on the signaling of a G protein-coupled neuronal receptor. An important message arising from these results is that it is prudent to include the contribution of actin polymerization while analyzing changes in membrane protein function due to chronic cholesterol depletion by statins. Notably, our results show that whereas actin polymerization acts as a negative regulator of cAMP signaling, cholesterol could act as a positive modulator. These results assume significance in view of reports highlighting symptoms of anxiety and depression in humans upon statin administration and the role of serotonin1A receptors in anxiety and depression. Overall, these results reveal a novel role of actin polymerization induced by chronic cholesterol depletion in modulating GPCR signaling, which could act as a potential therapeutic target.

Cell membrane targetable NIR fluorescent polarity probe for selective visualization of cancer cells and early tumor

The development of a sensitive method for early cancer diagnosis is very important because the early diagnosis of cancer is crucial in preventing the spread of cancer cells and improving patient survival rates. Recent studies showed that cancer cell membranes have lower polarity than normal cell membranes, which provides a new approach for cancer diagnosis at the cell membrane level. We developed herein a highly sensitive cell membrane polarity probe (Cal-M) for early diagnosis of cancer. This probe has low cytotoxicity, good photostability, near-infrared (NIR) fluorescence emission (>700 nm), large Stokes shift, high sensitivity for polarity, excellent cell membrane localization performance, and the ability to selectively light up cancer cells. Using this probe staining, the fluorescence of cancer cells is ∼63 times higher than that of normal cells, demonstrating excellent sensitivity and selectivity of Cal-M. This probe was also successfully used to detect polarity changes on cancer cell membranes and selectively visualize tumors in mice. Notably, the tumor could be visualized sensitively with a size as small as 1.37 mm3, indicating that Cal-M is promising for early diagnosis of tumors.

Temperature activated transient receptor potential ion channels from Antarctic fishes

Antarctic notothenioid fishes (cryonotothenioids) live in waters that range between -1.86°C and an extreme maximum +4°C. Evidence suggests these fish sense temperature peripherally, but the molecular mechanism of temperature sensation in unknown. Previous work identified transient receptor potential (TRP) channels TRPA1b, TRPM4 and TRPV1a as the top candidates for temperature sensors. Here, cryonotothenioid TRPA1b and TRPV1a are characterized using Xenopus oocyte electrophysiology. TRPA1b and TRPV1a showed heat-evoked currents with Q10s of 11.1 ± 2.2 and 20.5 ± 2.4, respectively. Unexpectedly, heat activation occurred at a threshold of 22.9 ± 1.3°C for TRPA1b and 32.1 ± 0.6°C for TRPV1a. These fish have not experienced such temperatures for at least 15 Myr. Either (1) another molecular mechanism underlies temperature sensation, (2) these fishes do not sense temperatures below these thresholds despite having lethal limits as low as 5°C, or (3) native cellular conditions modify the TRP channels to function at relevant temperatures. The effects of osmolytes, pH, oxidation, phosphorylation, lipids and accessory proteins were tested. No conditions shifted the activity range of TRPV1a. Oxidation in combination with reduced cholesterol significantly dropped activation threshold of TRPA1b to 11.3 ± 2.3°C, it is hypothesized the effect may be due to lipid raft disruption.

Caveolin-3 loss linked with the P104L LGMD-1C mutation modulates skeletal muscle mTORC1 signalling and cholesterol homeostasis

BACKGROUND

Caveolins are the principal structural components of plasma membrane caveolae. Dominant pathogenic mutations in the muscle-specific caveolin-3 (Cav3) gene isoform, such as the limb girdle muscular dystrophy type 1C (LGMD-1C) P104L mutation, result in dramatic loss of the Cav3 protein and pathophysiological muscle weakness/wasting. We hypothesize that such muscle degeneration may be linked to disturbances in signalling events that impact protein turnover. Herein, we report studies assessing the effects of Cav3 deficiency on mammalian or mechanistic target of rapamycin complex 1 (mTORC1) signalling in skeletal muscle cells.

METHODS

L6 myoblasts were stably transfected with Cav3P104L or expression of native Cav3 was abolished by CRISPR/Cas9 genome editing (Cav3 knockout [Cav3KO]) prior to performing subcellular fractionation and immunoblotting, analysis of real-time mitochondrial respiration or fixed cell immunocytochemistry. Skeletal muscle from wild-type and Cav3-/- mice was processed for immunoblot analysis of downstream mTORC1 substrate phosphorylation.

RESULTS

Cav3 was detected in lysosomal-enriched membranes isolated from L6 myoblasts and observed by confocal microscopy to co-localize with lysosomal-specific markers. Cav3P104L expression, which results in significant (~95%) loss of native Cav3, or CRISPR/Cas9-mediated Cav3KO, reduced amino acid-dependent mTORC1 activation. The decline in mTORC1-directed signalling was detected by immunoblot analysis of L6 muscle cells and gastrocnemius Cav3-/- mouse muscle as judged by reduced phosphorylation of mTORC1 substrates that play key roles in the initiation of protein synthesis (4EBP1S65 and S6K1T389 ). S6K1T389 and 4EBP1S65 phosphorylation reduced by over 75% and 80% in Cav3KO muscle cells and by over 90% and 30% in Cav3-/- mouse skeletal muscle, respectively. The reduction in protein synthetic capacity in L6 muscle cells was confirmed by analysis of puromycylated peptides using the SUnSET assay. Cav3 loss was also associated with a 26% increase in lysosomal cholesterol, and pharmacological manipulation of lysosomal cholesterol was effective in replicating the reduction in mTORC1 activity observed in Cav3KO cells. Notably, re-expression of Cav3 in Cav3KO myoblasts normalized lysosomal cholesterol content, which coincided with a recovery in protein translation and an associated increase in mTORC1-directed phosphorylation of downstream targets.

CONCLUSIONS

Our findings indicate that Cav3 can localize on lysosomal membranes and is a novel regulator of mTORC1 signalling in muscle. Cav3 deficiency associated with the Cav3P104L mutation impairs mTORC1 activation and protein synthetic capacity in skeletal muscle cells, which may be linked to disturbances in lysosomal cholesterol trafficking and contribute to the pathology of LGMD-1C.

Cyclodextrin-Mediated Cholesterol Depletion Induces Adiponectin Secretion in 3T3-L1 Adipocytes

Adipocytes store a significant amount of cholesterol and triglycerides. However, whether cholesterol modulates adipocyte function remains largely unknown. We modulated the cholesterol level in adipocytes to examine its effect on the secretion of adiponectin, an important hormone specifically secreted by adipocytes. Treating differentiated 3T3-L1 adipocytes with 4 mM methyl-β-cyclodextrin (MβCD), a molecule with a high affinity for cholesterol, rapidly depleted cholesterol in adipocytes. Interestingly, MβCD treatment increased adiponectin in the medium without affecting its intracellular level, suggesting a modulation of secretion. By contrast, cholesterol addition did not affect adiponectin secretion, suggesting that cholesterol-depletion-induced intracellular cholesterol trafficking, but not reduced cholesterol level, accounted for MβCD-induced adiponectin secretion. MβCD-induced adiponectin secretion was reduced after 10 μg/mL U18666A treatment that suppressed cholesterol transport out of late endosomes/lysosomes. Depleting Niemann-Pick type C1 (NPC1) or NPC2 proteins, which mediate endosomal/lysosomal cholesterol export, consistently reduced MβCD-induced adiponectin secretion. Furthermore, treatment with 1 μM bafilomycin A1, which neutralized acidic endosomes/lysosomes, also attenuated MβCD-induced adiponectin secretion. Finally, MβCD treatment redistributed cellular adiponectin to lower-density fractions in sucrose gradient fractionation. Our results show that MβCD-mediated cholesterol depletion elevates the secretion of adiponectin, highlighting the involvement of endosomes and lysosomes in adiponectin secretion in adipocytes.

Cholesterol and Ceramide Facilitate Membrane Fusion Mediated by the Fusion Peptide of the SARS-CoV-2 Spike Protein

SARS-CoV-2 entry into host cells is mediated by the Spike (S) protein of the viral envelope. The S protein is composed of two subunits: S1 that induces binding to the host cell via its interaction with the ACE2 receptor of the cell surface and S2 that triggers fusion between viral and cellular membranes. Fusion by S2 depends on its heptad repeat domains that bring membranes close together and its fusion peptide (FP) that interacts with and perturbs the membrane structure to trigger fusion. Recent studies have suggested that cholesterol and ceramide lipids from the cell surface may facilitate SARS-CoV-2 entry into host cells, but their exact mode of action remains unknown. We have used a combination of in vitro liposome-liposome and in situ cell-cell fusion assays to study the lipid determinants of S-mediated membrane fusion. Our findings reveal that both cholesterol and ceramide lipids facilitate fusion, suggesting that targeting these lipids could be effective against SARS-CoV-2. As a proof of concept, we examined the effect of chlorpromazine (CPZ), an antipsychotic drug known to perturb membrane structure. Our results show that CPZ effectively inhibits S-mediated membrane fusion, thereby potentially impeding SARS-CoV-2 entry into the host cell.

Membrane Cholesterol Interactions with Proteins in Hypercholesterolemia-Induced Endothelial Dysfunction

PURPOSE OF REVIEW

The goal of this review is to highlight work identifying mechanisms driving hypercholesterolemia-mediated endothelial dysfunction. We specifically focus on cholesterol-protein interactions and address specific questions related to the impact of hypercholesterolemia on cellular cholesterol and vascular endothelial function. We describe key approaches used to determine the effects of cholesterol-protein interactions in mediating endothelial dysfunction under dyslipidemic conditions.

RECENT FINDINGS

The benefits of removing the cholesterol surplus on endothelial function in models of hypercholesterolemia is clear. However, specific mechanisms driving cholesterol-induced endothelial dysfunction need to be determined. In this review, we detail the latest findings describing cholesterol-mediated endothelial dysfunction, highlighting our studies indicating that cholesterol suppresses endothelial Kir2.1 channels as a major underlying mechanism. The findings detailed in this review support the targeting of cholesterol-induced suppression of proteins in restoring endothelial function in dyslipidemic conditions. The identification of similar mechanisms regarding other cholesterol-endothelial protein interactions is warranted.

Clec12a inhibits MSU-induced immune activation through lipid raft expulsion

Monosodium uric acid (MSU) crystal, the etiological agent of gout, has been shown to trigger innate immune responses via multiple pathways. It is known that MSU-induced lipid sorting on plasma membrane promotes the phosphorylation of Syk and eventually leads to the activation of phagocytes. However, whether this membrane lipid-centric mechanism is regulated by other processes is unclear. Previous studies showed that Clec12a, a member of the C-type lectin receptor family, is reported to recognize MSU and suppresses this crystalline structure-induced immune activation. How this scenario is integrated into the lipid sorting-mediated inflammatory responses by MSU, and particularly, how Clec12a intercepts lipid raft-originated signaling cascade remains to be elucidated. Here, we found that the ITIM motif of Clec12a is dispensable for its inhibition of MSU-mediated signaling; instead, the transmembrane domain of Clec12a disrupts MSU-induced lipid raft recruitment and thus attenuates downstream signals. Single amino acid mutagenesis study showed the critical role of phenylalanine in the transmembrane region for the interactions between C-type lectin receptors and lipid rafts, which is critical for the regulation of MSU-mediated lipid sorting and phagocyte activation. Overall, our study provides new insights for the molecular mechanisms of solid particle-induced immune activation and may lead to new strategies in inflammation control.

Lipid rafts and human diseases: why we need to target gangliosides

Gangliosides are functional components of membrane lipid rafts that control critical functions in cell communication. Many pathologies involve raft gangliosides, which therefore represent an approach of choice for developing innovative therapeutic strategies. Beginning with a discussion of what a disease is (and is not), this review lists the major human pathologies that involve gangliosides, which includes cancer, diabetes, and infectious and neurodegenerative diseases. In most cases, the problem is due to a protein whose binding to gangliosides either creates a pathological condition or impairs a physiological function. Then, I draw up an inventory of the different molecular mechanisms of protein-ganglioside interactions. I propose to classify the ganglioside-binding domains of proteins into four categories, which I name GBD-1, GBD-2, GBD-3, and GBD-4. This structural and functional classification could help to rationalize the design of innovative molecules capable of disrupting the binding of selected proteins to gangliosides without generating undesirable effects. The biochemical specificities of gangliosides expressed in the human brain must also be taken into account to improve the reliability of animal models (or any animal-free alternative) of Alzheimer's and Parkinson's diseases.

Enhanced Membrane Fluidization and Cholesterol Displacement by 1-Heptanol Inhibit Mast Cell Effector Functions

Signal transduction by the high-affinity IgE receptor (FcεRI) depends on membrane lipid and protein compartmentalization. Recently published data show that cells treated with 1-heptanol, a cell membrane fluidizer, exhibit changes in membrane properties. However, the functional consequences of 1-heptanol-induced changes on mast cell signaling are unknown. This study shows that short-term exposure to 1-heptanol reduces membrane thermal stability and dysregulates mast cell signaling at multiple levels. Cells treated with 1-heptanol exhibited increased lateral mobility and decreased internalization of the FcεRI. However, this did not affect the initial phosphorylation of the FcεRI-β chain and components of the SYK/LAT1/PLCγ1 signaling pathway after antigen activation. In contrast, 1-heptanol inhibited SAPK/JNK phosphorylation and effector functions such as calcium response, degranulation, and cytokine production. Membrane hyperfluidization induced a heat shock-like response via increased expression of the heat shock protein 70, increased lateral diffusion of ORAI1-mCherry, and unsatisfactory performance of STIM1-ORAI1 coupling, as determined by flow-FRET. Furthermore, 1-heptanol inhibited the antigen-induced production of reactive oxygen species and potentiated stress-induced plasma membrane permeability by interfering with heat shock protein 70 activity. The combined data suggest that 1-heptanol-mediated membrane fluidization does not interfere with the earliest biochemical steps of FcεRI signaling, such as phosphorylation of the FcεRI-β chain and components of the SYK/LAT/PLCγ1 signaling pathway, instead inhibiting the FcεRI internalization and mast cell effector functions, including degranulation and cytokine production.

Regulation of cholesterol homeostasis in osteoporosis mechanisms and therapeutics

Osteoporosis is a metabolic bone disease that affects hundreds of millions of people worldwide and is characterized by excessive loss of bone protein and mineral content. The incidence and mortality of osteoporosis increase with age, creating a significant medical and economic burden globally. The importance of cholesterol levels has been reported in the development of diseases including osteoporosis. It is important to note that key enzymes and molecules involved in cholesterol homeostasis are closely related to bone formation. Excessive cholesterol may cause osteoporosis, cholesterol and its metabolites affect bone homeostasis by regulating the proliferation and stimulation of osteoblasts and osteoclasts. Therefore, antagonism of elevated cholesterol levels may be a potential strategy to prevent osteoporosis. There is sufficient evidence to support the use of bisphosphonates and statin drugs for osteoporosis in the clinic. Therefore, in view of the aggravation of the aging problem, we summarize the intracellular mechanism of cholesterol homeostasis and its relationship with osteoporosis (including cholesterol and cholesterol oxidation products (COPs) in osteoporosis). Furthermore, the current clinical cholesterol-lowering drugs for osteoporosis were also summarized, as are new and promising therapies (cell-based therapies (e.g., stem cells) and biomaterial-delivered target drug therapies for osteoporosis as well).

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

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

Differences in proteome perturbations caused by the Wolbachia strain wAu suggest multiple mechanisms of Wolbachia-mediated antiviral activity

Some strains of the inherited bacterium Wolbachia have been shown to be effective at reducing the transmission of dengue virus (DENV) and other RNA viruses by Aedes aegypti in both laboratory and field settings and are being deployed for DENV control. The degree of virus inhibition varies between Wolbachia strains. Density and tissue tropism can contribute to these differences but there are also indications that this is not the only factor involved: for example, strains wAu and wAlbA are maintained at similar intracellular densities but only wAu produces strong DENV inhibition. We previously reported perturbations in lipid transport dynamics, including sequestration of cholesterol in lipid droplets, with strains wMel/wMelPop in Ae. aegypti. To further investigate the cellular basis underlying these differences, proteomic analysis of midguts was carried out on Ae. aegypti lines carrying strains wAu and wAlbA: with the hypothesis that differences in perturbations may underline Wolbachia-mediated antiviral activity. Surprisingly, wAu-carrying midguts not only showed distinct proteome perturbations when compared to non-Wolbachia carrying and wAlbA-carrying midguts but also wMel-carrying midguts. There are changes in RNA processing pathways and upregulation of a specific set of RNA-binding proteins in the wAu-carrying line, including genes with known antiviral activity. Lipid transport and metabolism proteome changes also differ between strains, and we show that strain wAu does not produce the same cholesterol sequestration phenotype as wMel. Moreover, in contrast to wMel, wAu antiviral activity was not rescued by cyclodextrin treatment. Together these results suggest that wAu could show unique features in its inhibition of arboviruses compared to previously characterized Wolbachia strains.

Mutant APC reshapes Wnt signaling plasma membrane nanodomains by altering cholesterol levels via oncogenic β-catenin

Although the role of the Wnt pathway in colon carcinogenesis has been described previously, it has been recently demonstrated that Wnt signaling originates from highly dynamic nano-assemblies at the plasma membrane. However, little is known regarding the role of oncogenic APC in reshaping Wnt nanodomains. This is noteworthy, because oncogenic APC does not act autonomously and requires activation of Wnt effectors upstream of APC to drive aberrant Wnt signaling. Here, we demonstrate the role of oncogenic APC in increasing plasma membrane free cholesterol and rigidity, thereby modulating Wnt signaling hubs. This results in an overactivation of Wnt signaling in the colon. Finally, using the Drosophila sterol auxotroph model, we demonstrate the unique ability of exogenous free cholesterol to disrupt plasma membrane homeostasis and drive Wnt signaling in a wildtype APC background. Collectively, these findings provide a link between oncogenic APC, loss of plasma membrane homeostasis and CRC development.

Efficient Secretory Production of δ-Tocotrienol by Combining Pathway Modularization and Transportation Engineering

The vitamin E component δ-tocotrienol has shown impressive activities in radioprotection, neuroprotection, and cholesterol reduction. Its production is limited by the low content in plants and difficulty in separation from other tocotrienols. Fermentative production using a microbial cell factory that exclusively produces and secretes δ-tocotrienol is a promising alternative approach. Assembly of the δ-tocotrienol synthetic pathway in Saccharomyces cerevisiae followed by comprehensive pathway engineering led to the production of 73.45 mg/L δ-tocotrienol. Subsequent addition of 2-hydroxypropyl-β-cyclodextrin (CD) and overexpression of the transcription factor PDR1 significantly elevated δ-tocotrienol titer to 241.7 mg/L (63.65 mg/g dry cell weight) in shake flasks, with 30.4% secreted. By properly adding CD and the in situ extractant olive oil, 181.12 mg/L of δ-tocotrienol was collected as an extracellular product, accounting for 85.6% of the total δ-tocotrienol production. This process provides not only a promising δ-tocotrienol cell factory but also insights into yeast engineering toward secretory production of other terpenoids.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

CONCLUSION

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

Involvement of Lipid Rafts in the Invasion of Opportunistic Bacteria Serratia into Eukaryotic Cells

Cell membrane rafts form signaling platforms on the cell surface, controlling numerous protein-protein and lipid-protein interactions. Bacteria invading eukaryotic cells trigger cell signaling to induce their own uptake by non-phagocytic cells. The aim of this work was to reveal the involvement of membrane rafts in the penetration of the bacteria Serratia grimesii and Serratia proteamaculans into eukaryotic cells. Our results show that the disruption of membrane rafts by MβCD in the three cell lines tested, M-HeLa, MCF-7 and Caco-2, resulted in a time-dependent decrease in the intensity of Serratia invasion. MβCD treatment produced a more rapid effect on the bacterial susceptibility of M-HeLa cells compared to other cell lines. This effect correlated with a faster assembly of the actin cytoskeleton upon treatment with MβCD in M-HeLa cells in contrast to that in Caco-2 cells. Moreover, the 30 min treatment of Caco-2 cells with MβCD produced an increase in the intensity of S. proteamaculans invasion. This effect correlated with an increase in EGFR expression. Together with the evidence that EGFR is involved in S. proteamaculans invasion but not in S. grimesii invasion, these results led to the conclusion that an increase in EGFR amount on the plasma membrane with the undisassembled rafts of Caco-2 cells after 30 min of treatment with MβCD may increase the intensity of S. proteamaculans but not of S. grimesii invasion. Thus, the MβCD-dependent degradation of lipid rafts, which enhances actin polymerization and disrupts signaling pathways from receptors on the host cell's surface, reduces Serratia invasion.

The ensured proliferative capacity of myoblast in serum-reduced conditions with Methyl-β-cyclodextrin

To produce muscle fibers for cultured meat on a large scale, it is important to expand myoblasts in a serum-reduced or serum-free medium to avoid cost, ethical, and environmental issues. Myoblasts such as C2C12 cells differentiate quickly into myotubes and lose their ability to proliferate when the serum-rich medium is replaced with a serum-reduced medium. This study demonstrates that Methyl-β-cyclodextrin (MβCD), a starch-derived agent that depletes cholesterol, can inhibit further differentiation of myoblasts at the MyoD-positive stage by reducing plasma membrane cholesterol on C2C12 cells and primary cultured chick muscle cells. Furthermore, MβCD efficiently blocks cholesterol-dependent apoptotic cell death of myoblasts, which is one of the mechanisms by which it inhibits the differentiation of C2C12 myoblast cells, as dead cells of myoblast are necessary for the fusion of adjacent myoblasts during the differentiation process into myotubes. Importantly, MβCD maintains the proliferative capacity of myoblasts only under differentiation conditions with a serum-reduced medium, suggesting that its mitogenic effect is due to its inhibitory effect on myoblast differentiation into myotube. In conclusion, this study provides significant insights into ensuring the proliferative capacity of myoblasts in a future serum-free condition for cultured meat production.

Cholesterol-load evokes robust calcium response in macrophages: An early event toward cholesterol-induced macrophage death

Macrophages in atherosclerotic lesions accumulate large amounts of unesterified cholesterol. Excess cholesterol load leads to cell death of macrophages, which is associated with the progression of atherosclerotic lesions. Calcium depletion in the endoplasmic reticulum (ER) and subsequent pro-apoptotic aberrant calcium signaling are key events in cholesterol-induced macrophage death. Although these concepts imply cytoplasmic calcium events in cholesterol-loaded macrophages, the mechanisms linking cholesterol accumulation to cytoplasmic calcium response have been poorly investigated. Based on our previous finding that extracellularly applied cholesterol evoked robust calcium oscillations in astrocytes, a type of glial cells in the brain, we hypothesized that cholesterol accumulation in macrophages triggers cytoplasmic calcium elevation. Here, we showed that cholesterol application induces calcium transients in THP-1-derived and peritoneal macrophages. Inhibition of inositol 1,4,5-trisphosphate receptors (IP3Rs) and l-type calcium channels (LTCCs) prevented cholesterol-induced calcium transients and ameliorated cholesterol-induced macrophage death. These results suggest that cholesterol-induced calcium transients through IP3Rs and LTCCs are crucial mechanisms underlying cholesterol-induced cell death of macrophages.

Myeloid-derived suppressor cells deficient in cholesterol biosynthesis promote tumor immune evasion

Cancer immunotherapy targeting myeloid-derived suppressor cells (MDSCs) is one of the most promising anticancer strategies. Metabolic reprogramming is vital for MDSC activation, however, the regulatory mechanisms of cholesterol metabolic reprogramming in MDSCs remains largely unexplored. Using the receptor-interacting protein kinase 3 (RIPK3)-deficient MDSC model, a previously established tumor-infiltrating MDSC-like model, we found that the cholesterol accumulation was significantly decreased in these cells. Moreover, the phosphorylated AKT-mTORC1 signaling was reduced, and downstream SREBP2-HMGCR-mediated cholesterol synthesis was blunted. Interestingly, cholesterol deficiency profoundly elevated the immunosuppressive activity of MDSCs. Mechanistically, cholesterol elimination induced nuclear accumulation of LXRβ, thereby promoting LXRβ-RXRα heterodimer binding of a novel composite element in the promoter of Arg1. Furthermore, itraconazole enhanced the immunosuppressive activity of MDSCs to boost tumor growth by suppressing the RIPK3-AKT-mTORC1 pathway and impeding cholesterol synthesis. Our findings demonstrate that RIPK3 deficiency leads to cholesterol abrogation in MDSCs, which facilitates tumor-infiltrating MDSC activation, and highlight the therapeutic potential of targeting cholesterol synthesis to overcome tumor immune evasion.

Hydroxypropyl-β-Cyclodextrin Depletes Membrane Cholesterol and Inhibits SARS-CoV-2 Entry into HEK293T-ACEhi Cells

Vaccination has drastically decreased mortality due to coronavirus disease 19 (COVID-19), but not the rate of acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Alternative strategies such as inhibition of virus entry by interference with angiotensin-I-converting enzyme 2 (ACE2) receptors could be warranted. Cyclodextrins (CDs) are cyclic oligosaccharides that are able to deplete cholesterol from membrane lipid rafts, causing ACE2 receptors to relocate to areas devoid of lipid rafts. To explore the possibility of reducing SARS-CoV-2 entry, we tested hydroxypropyl-β-cyclodextrin (HPβCD) in a HEK293T-ACE2^hi cell line stably overexpressing human ACE2 and Spike-pseudotyped SARS-CoV-2 lentiviral particles. We showed that HPβCD is not toxic to the cells at concentrations up to 5 mM, and that this concentration had no significant effect on cell cycle parameters in any experimental condition tested. Exposure of HEK293T-ACE^hi cells to concentrations of HPβCD starting from 2.5 mM to 10 mM showed a concentration-dependent reduction of approximately 50% of the membrane cholesterol content. In addition, incubation of HEK293T-ACE^hi cells with HIV-S-CoV-2 pseudotyped particles in the presence of increasing concentrations of HPβCD (from 0.1 to 10 mM) displayed a concentration-dependent effect on SARS-CoV-2 entry efficiency. Significant effects were detected at concentrations at least one order of magnitude lower than the lowest concentration showing toxic effects. These data indicate that HPβCD is a candidate for use as a SARS-CoV-2 prophylactic agent.

Pooled genome-wide CRISPR activation screening for rapamycin resistance genes in Drosophila cells

Loss-of-function and gain-of-function genetic perturbations provide valuable insights into gene function. In Drosophila cells, while genome-wide loss-of-function screens have been extensively used to reveal mechanisms of a variety of biological processes, approaches for performing genome-wide gain-of-function screens are still lacking. Here, we describe a pooled CRISPR activation (CRISPRa) screening platform in Drosophila cells and apply this method to both focused and genome-wide screens to identify rapamycin resistance genes. The screens identified three genes as novel rapamycin resistance genes: a member of the SLC16 family of monocarboxylate transporters (CG8468), a member of the lipocalin protein family (CG5399), and a zinc finger C2H2 transcription factor (CG9932). Mechanistically, we demonstrate that CG5399 overexpression activates the RTK-Akt-mTOR signaling pathway and that activation of insulin receptor (InR) by CG5399 requires cholesterol and clathrin-coated pits at the cell membrane. This study establishes a novel platform for functional genetic studies in Drosophila cells.

FACI is a novel clathrin adaptor protein 2-binding protein that facilitates low-density lipoprotein endocytosis

BACKGROUND

Cholesterol plays a vital role in multiple physiological processes. Cellular uptake of cholesterol is mediated primarily through endocytosis of low-density lipoprotein (LDL) receptor. New modifiers of this process remain to be characterized. Particularly, the role of fasting- and CREB-H-induced (FACI) protein in cholesterol homeostasis merits further investigation.

METHODS

Interactome profiling by proximity labeling and affinity purification - mass spectrometry was performed. Total internal reflection fluorescence microscopy and confocal immunofluorescence microscopy were used to analyze protein co-localization and interaction. Mutational analysis was carried out to define the domain and residues required for FACI localization and function. Endocytosis was traced by fluorescent cargos. LDL uptake in cultured cells and diet-induced hypercholesterolemia in mice were assessed.

RESULTS

FACI interacted with proteins critically involved in clathrin-mediated endocytosis, vesicle trafficking, and membrane cytoskeleton. FACI localized to clathrin-coated pits (CCP) on plasma membranes. FACI contains a conserved DxxxLI motif, which mediates its binding with the adaptor protein 2 (AP2) complex. Disruption of this motif of FACI abolished its CCP localization but didn't affect its association with plasma membrane. Cholesterol was found to facilitate FACI transport from plasma membrane to endocytic recycling compartment in a clathrin- and cytoskeleton-dependent manner. LDL endocytosis was enhanced in FACI-overexpressed AML12 cells but impaired in FACI-depleted HeLa cells. In vivo study indicated that hepatic FACI overexpression alleviated diet-induced hypercholesterolemia in mice.

CONCLUSIONS

FACI facilitates LDL endocytosis through its interaction with the AP2 complex.

Tyrosine-derived polymeric surfactant nanospheres insert cholesterol in cell membranes

HYPOTHESIS

The design of biodegradable tyrosine-derived polymeric surfactants (TyPS) through the use of calculated thermodynamic parameters could lead to phospholipid membrane surface modifiers capable of controlling cellular properties such as viability. Delivery of cholesterol by TyPS nanospheres into membrane phospholipid domains could provide further controlled modulation of membrane physical and biological properties.

EXPERIMENT

Calculated Hansen solubility parameters (∂_T) and hydrophile:lipophile balances (HLB) were applied to design and synthesize a small family of diblock and triblock TyPS with different hydrophobic blocks and PEG hydrophilic blocks. Self-assembled TyPS/cholesterol nanospheres were prepared in aqueous media via co-precipitation. Cholesterol loading and Langmuir film balance surface pressures of phospholipid monolayers were obtained. TyPS and TyPS/cholesterol nanosphere effects on human dermal cell viability were evaluated by cell culture using poly(ethylene glycol) (PEG) and Poloxamer 188 as controls.

FINDINGS

Stable TyPS nanospheres incorporated between 1% and 5% cholesterol. Triblock TyPS formed nanosphere with dimensions significantly smaller than diblock TyPS nanospheres. In accord calculated thermodynamic parameters, cholesterol binding increased with increasing TyPS hydrophobicity. TyPS inserted into phospholipid monolayer films in a manner consistent with their thermodynamic properties and TyPS/cholesterol nanospheres delivered cholesterol into the films. Triblock TyPS/cholesterol nanospheres increased human dermal cell viability, which was indicative of potentially beneficial TyPS effects on cell membrane surface properties.

Exploring Receptor Binding Affinities and Hepatic Cell Association of N-Acetyl-d-Galactosamine-Modified β-Cyclodextrin-Based Polyrotaxanes for Liver-Targeted Therapies

Acid-degradable polyrotaxanes (PRXs) containing threading β-cyclodextrins (β-CDs) are promising candidates for therapeutic applications of β-CDs in metabolic diseases with cholesterol overload or imbalance. To improve cellular uptake specificity and efficiency of PRXs in hepatocytes, N-acetyl-d-galactosamine (GalNAc)-modified PRXs were developed to facilitate asialoglycoprotein receptor (ASGR)-mediated endocytosis. Binding affinity studies revealed that the dissociation constant (K_D) values between recombinant ASGR and GalNAc-PRXs decreased with an increase in the number of modified GalNAc units. Additionally, the K_D values for GalNAc-PRXs were smaller than those for GalNAc-modified β-CD and amylose, suggesting that the PRX backbone structure improves the binding affinity with ASGR. However, the intracellular uptake levels of GalNAc-PRXs in HepG2 cells increased with a decrease in the number of modified GalNAc units, which was opposite to the trend observed in the binding affinity study. We found that GalNAc-PRXs had a large number of GalNAc units localized in recycling endosomes, resulting in the low intracellular uptake. The cholesterol-reducing abilities of GalNAc-PRXs were assessed using cholesterol-overloaded HepG2 cells. GalNAc-PRXs with a small number of GalNAc units were demonstrated to show superior cholesterol-reducing effects compared to previously designed acid-degradable PRX and clinically tested β-CD derivatives. Thus, we conclude that GalNAc modification is a promising molecular design for the therapeutic application of β-CD-threaded PRXs in various metabolic diseases with cholesterol overload or imbalance in the liver.

Investigation of 2-Hydroxypropyl-β-Cyclodextrin Treatment in a Neuronal-Like Cell Model of Niemann-Pick Type C Using Quantitative Proteomics

Niemann-Pick, type C (NPC) is a fatal, neurovisceral lysosomal storage disorder with progressive neurodegeneration and no FDA-approved therapy. Significant efforts have been focused on the development of therapeutic options, and 2-hydroxypropyl-β-cyclodextrin (HP-b-CD) has emerged as a promising candidate. In cell culture, HP-b-CD ameliorates cholesterol storage in endo/lysosomes, a hallmark of the disorder. Furthermore, in animal studies, treatment with HP-b-CD delays neurodegeneration and extends lifespan. While HP-b-CD has been promising in vitro and in vivo, a clear understanding of the mechanism(s) of action is lacking. Utilizing a neuron-like cell culture model of SH-SY5Y differentiated cells and U18666A to induce the NPC phenotype, we report here a large-scale mass-spectrometry-based proteomic study to evaluate proteome changes upon treatment with these small molecules. In this study, we show that differentiated SH-SY5Y cells display morphological changes representative of neuronal-like cells along with increased levels of proliferation markers. Inhibition of the NPC cholesterol transporter 1 protein by U18666A resulted in increased levels of known NPC markers including SCARB2/LIMP2 and LAMP2. Finally, investigation of HP-b-CD treatment was performed where we observe that, although HP-b-CD reduces cholesterol storage, levels of NPC1 and NPC2 are not normalized to control levels. This finding further supports the need for a proteostasis strategy for NPC drug development. Moreover, proteins that were dysregulated in the U18666A model of NPC and normalized to control levels suggest that HP-b-CD promotes exocytosis in this neuron-like model. Utilizing state of the art mass spectrometry analysis, these data demonstrate newly reported changes with pharmacological perturbations related to NPC disease and provide insight into the mechanisms of HP-b-CD as a potential therapeutic.

Modeling maternal cholesterol exposure reveals a reduction of neural progenitor proliferation using human cerebral organoids

Maternal obesity raises the risk of high-cholesterol exposure for their offspring. Studies in cohorts and animal models report that maternal obesity could increase the risk of neurodevelopmental disorders in offspring including intellectual disabilities and autism spectrum disorders (ASDs). However, whether exposure to high cholesterol is responsible for brain developmental defects, as well as its underlying mechanism, is still unclear. Here, we constructed a cholesterol exposure model utilizing human pluripotent stem cell (hPSC)-derived cerebral organoids by exogenously adding cholesterol into the culture system. We observed enlargement of endosomes, decreased neural progenitor proliferation, and premature neural differentiation in brain organoids with the treatment of cholesterol. Moreover, in comparison with published transcriptome data, we found that our single-cell sequencing results showed a high correlation with ASD, indicating that high cholesterol during maternal might mediate the increased risk of ASD in the offspring. Our results reveal a reduction of neural progenitor proliferation in a cholesterol exposure model, which might be a promising indicator for prenatal diagnosis and offer a dynamic human model for maternal environment exposure.

Characterization of Complexes between Imidacloprid and β-Cyclodextrin: Evaluation of the Toxic Activity in Algae and Rotifers

The development of new formulations can be driven by the knowledge of host–guest complexes using cyclodextrins which have the ability to include guest molecules within their hydrophobic cavities, improving the physicochemical properties of the guest. To rationally explore new pesticide formulations, the effects of cyclodextrins on the properties of such guest molecules need to be explored. Imidacloprid is a neonicotinoid systemic insecticide used worldwide. In this study, the inclusion complexes of Imidacloprid (IMI) with β-cyclodextrin (β-CD) were prepared in the solid state by co-precipitation and the physical mixing method, with a stoichiometry of 1:1 and 1:2 molar ratios. The obtained products, Imidacloprid:β-cyclodextrin inclusion complex (IMI:β-CD), were characterized in the solid state by Fourier transform-infrared (FT-IR) spectroscopy and X-ray powder diffractometry (XRD). In solution, the 1:1 stoichiometry for the inclusion complexes was established by the Job plot method, and the binding constant of IMI:β-CD was determined by UV–vis titration. The toxicity was determined in producers and primary consumers of the freshwater trophic chain, the green alga Raphidocelis subcapitata and the rotifer Brachionus calyciflorus, respectively. The results indicated that Imidacloprid forms inclusion complexes with CDs showing improved physicochemical properties compared to free Imidacloprid. The formation of the inclusion complex reduced the chronic toxicity in rotifers when IMI concentrations were close to those of environmental concern (tenths/hundredths of micromoles/L). Therefore, CD inclusion complexes could provide important advantages to be considered for the future industrial production of new formulations.

Cholesterol Is a Regulator of CAV1 Localization and Cell Migration in Oral Squamous Cell Carcinoma

Cholesterol plays an important role in cancer progression, as it is utilized in membrane biogenesis and cell signaling. Cholesterol-lowering drugs have exhibited tumor-suppressive effects in oral squamous cell carcinoma (OSCC), suggesting that cholesterol is also essential in OSCC pathogenesis. However, the direct effects of cholesterol on OSCC cells remain unclear. Here, we investigated the role of cholesterol in OSCC with respect to caveolin-1 (CAV1), a cholesterol-binding protein involved in intracellular cholesterol transport. Cholesterol levels in OSCC cell lines were depleted using methyl-β-cyclodextrin and increased using the methyl-β-cyclodextrin-cholesterol complex. Functional analysis was performed using timelapse imaging, and CAV1 expression in cholesterol-manipulated cells was investigated using immunofluorescence and immunoblotting assays. CAV1 immunohistochemistry was performed on surgical OSCC samples. We observed that cholesterol addition induced polarized cell morphology, along with CAV1 localization at the trailing edge, and promoted cell migration. Moreover, CAV1 was upregulated in the lipid rafts and formed aggregates in the plasma membrane in cholesterol-added cells. High membranous CAV1 expression in tissue specimens was associated with OSCC recurrence. Therefore, cholesterol promotes the migration of OSCC cells by regulating cell polarity and CAV1 localization to the lipid raft. Furthermore, membranous CAV1 expression is a potential prognostic marker for OSCC patients.

Atorvastatin differentially regulates the interactions of cocaine and amphetamine with dopamine transporters

The function of the dopamine transporter (DAT) is regulated by membrane cholesterol content. A direct, acute removal of membrane cholesterol by methyl-β-cyclodextrin (MβCD) has been shown to reduce dopamine (DA) uptake and release mediated by the DAT. This is of particular interest because a few widely prescribed statins that lower peripheral cholesterol levels are blood-brain barrier (BBB) penetrants, and therefore could alter DAT function through brain cholesterol modulation. The goal of this study was to investigate the effects of prolonged atorvastatin treatment (24 h) on DAT function in neuroblastoma 2A cells stably expressing DAT. We found that atorvastatin treatment effectively lowered membrane cholesterol content in a concentration-dependent manner. Moreover, atorvastatin treatment markedly reduced DA uptake and abolished cocaine inhibition of DA uptake, independent of surface DAT levels. These deficits induced by atorvastatin treatment were reversed by cholesterol replenishment. However, atorvastatin treatment did not change amphetamine (AMPH)-induced DA efflux. This is in contrast to a small but significant reduction in DA efflux induced by acute depletion of membrane cholesterol using MβCD. This discrepancy may involve differential changes in membrane lipid composition resulting from chronic and acute cholesterol depletion. Our data suggest that the outward-facing conformation of DAT, which favors the binding of DAT blockers such as cocaine, is more sensitive to atorvastatin-induced cholesterol depletion than the inward-facing conformation, which favors the binding of DAT substrates such as AMPH. Our study on statin-DAT interactions may have clinical implications in our understanding of neurological side effects associated with chronic use of BBB penetrant statins.

Anti-inflammatory therapy of atherosclerosis: focusing on IKKβ

Chronic low-grade inflammation has been identified as a major contributor in the development of atherosclerosis. Nuclear Factor-κappa B (NF-κB) is a critical transcription factors family of the inflammatory pathway. As a major catalytic subunit of the IKK complex, IκB kinase β (IKKβ) drives canonical activation of NF-κB and is implicated in the link between inflammation and atherosclerosis, making it a promising therapeutic target. Various natural product derivatives, extracts, and synthetic, show anti-atherogenic potential by inhibiting IKKβ-mediated inflammation. This review focuses on the latest knowledge and current research landscape surrounding anti-atherosclerotic drugs that inhibit IKKβ. There will be more opportunities to fully understand the complex functions of IKKβ in atherogenesis and develop new effective therapies in the future.

Cortisol Rapidly Facilitates Glucocorticoid Receptor Translocation to the Plasma Membrane in Primary Trout Hepatocytes

Glucocorticoids (GCs) stimulate rapid cell signalling by activating the membrane-anchored intracellular glucocorticoid receptor (GR). However, the recruitment of the GR to the plasma membrane to facilitate nongenomic signalling is far from clear. As cytosolic free calcium ([Ca²⁺]i) is involved in intracellular protein dynamics, we tested the hypothesis that acute elevation in cortisol levels rapidly stimulates GR translocation to the plasma membrane via a calcium-dependent process in rainbow trout (Oncorhynchus mykiss) hepatocytes. To test this, we monitored temporal changes in intracellular GR distribution in response to cortisol exposure. Immunofluorescence labelling showed that the GR was present in cytosolic and nuclear compartments in trout hepatocytes. However, upon cortisol exposure, the GR rapidly (within 5 min) formed punctate and colocalized with caveolin-1, suggesting plasma membrane localization of the receptor. This redistribution of the GR to the plasma membrane was transient and lasted for 30 min and was evident even upon exposure to cortisol-BSA, a membrane-impermeable analogue of the steroid. The rapid cortisol-mediated GR translocation to the plasma membrane involved F-actin polymerization and was completely abolished in the presence of either EGTA or Cpd5J-4, a calcium release-activated calcium (CRAC) channel blocker. Additionally, the modulation of the biophysical properties of the plasma membrane by cholesterol or methyl β-cyclodextrin, which led to changes in ([Ca²⁺]i) levels, modified GR translocation to the plasma membrane. Altogether, acute cortisol-mediated rise in ([Ca²⁺]i) levels rapidly stimulated the translocation of intracellular GR to the plasma membrane, and we propose this as a mechanism promoting the nongenomic action of the GR for hepatocyte stress resistance.

How clathrin-coated pits control nanoparticle avidity for cells

The paramount relevance of clathrin-coated pits (CCPs) to receptor-mediated endocytosis of nanoparticles, extracellular vesicles, and viruses has made them the focus of many studies; however, the role of CCP geometry in the ligand-receptor interactions between multivalent nanoparticles and cells has not been investigated. We hypothesized the general dependence of nanoparticle binding energy on local membrane curvature to be expandable to the specific case of ligand-functionalized nanoparticles binding cell membranes, in the sense that membrane structures whose curvature matches that of the particle (e.g., CCPs) signficantly contribute to binding avidity. We investigated this hypothesis with nanoparticles that bind multivalently to angiotensin II receptor type 1, which is subject to clathrin-mediated endocytosis. When we used cholesterol extraction to prevent the action of CCPs, we found a 67 to 100-fold loss in avidity. We created a theoretical model that predicts this decrease based on the loss of ligand-receptor interactions when CCPs, which perfectly match nanoparticle geometry, are absent. Our findings shed new light on how cells "see" nanoparticles. The presence or absence of CPPs is so influential on how cells interact with nanoparticles that the number of particles required to be visible to cells changes by two orders of magnitude depending on CCP presence.

Lysosomal Targeting of β-Cyclodextrin

β-Cyclodextrin (β-CD) and derivatives are approved therapeutics in >30 clinical settings. β-CDs have also shown promise as therapeutics for treatment of some lysosomal storage disorders, such as Niemann-Pick disease type C, and other disease states which involve metabolite accumulation in the lysosome. In these cases, β-CD activity relies on transport to the lysosome, wherein it can bind hydrophobic substrate and effect extraction. The post-translational attachment of N-glycans terminated in mannose-6-phosphate (M6P) residues is the predominant method by which lysosomal enzymes are targeted to the lysosome. In this work we covalently attach a synthetic biantennary bis-M6P-terminated N-glycan to β-CD and study the effect of the added glycans in a mammalian cell line. The formation of a host guest complex with a Cy5 fluorophore allows study of both cellular internalisation and transport to the lysosome by fluorescence microscopy. Results indicate that the rates of both internalisation and lysosomal transport are increased by the attachment of M6P-glycans to β-CD, indicating that M6P-glycan conjugation may improve the therapeutic effectiveness of β-CD for the treatment of disorders involving hydrophobic metabolite accumulation in the lysosome.

The Antifungal Antibiotic Filipin as a Diagnostic Tool of Cholesterol Alterations in Lysosomal Storage Diseases and Neurodegenerative Disorders

Cholesterol is the most considerable member of a family of polycyclic compounds understood as sterols, and represents an amphipathic molecule, such as phospholipids, with the polar hydroxyl group located in position 3 and the rest of the molecule is completely hydrophobic. In cells, it is usually present as free, unesterified cholesterol, or as esterified cholesterol, in which the hydroxyl group binds to a carboxylic acid and thus generates an apolar molecule. Filipin is a naturally fluorescent antibiotic that exerts a primary antifungal effect with low antibacterial activity, interfering with the sterol stabilization of the phospholipid layers and favoring membrane leakage. This polyene macrolide antibiotic does not bind to esterified sterols, but only to non-esterified cholesterol, and it is commonly used as a marker to label and quantify free cholesterol in cells and tissues. Several lines of evidence have indicated that filipin staining could be a good diagnostic tool for the cholesterol alterations present in neurodegenerative (e.g., Alzheimer's Disease and Huntington Disease) and lysosomal storage diseases (e.g., Niemann Pick type C Disease and GM1 gangliosidosis). Here, we have discussed the uses and applications of this fluorescent molecule in lipid storage diseases and neurodegenerative disorders, exploring not only the diagnostic strength of filipin staining, but also its limitations, which over the years have led to the development of new diagnostic tools to combine with filipin approach.

Alterations in Cholesterol and Phosphoinositides Levels in the Intracellular Cholesterol Trafficking Disorder NPC

Lipid mistrafficking is a biochemical hallmark of Niemann-Pick Type C (NPC) disease and is classically characterized with endo/lysosomal accumulation of unesterified cholesterol due to genetic mutations in the cholesterol transporter proteins NPC1 and NPC2. Storage of this essential signaling lipid leads to a sequence of downstream events, including oxidative stress, calcium imbalance, neuroinflammation, and progressive neurodegeneration, another hallmark of NPC disease. These observations have been validated in a growing number of studies ranging from NPC cell cultures and animal models to patient specimens. In recent reports, alterations in the levels of another class of critical signaling lipids, namely phosphoinositides, have been described in NPC disease. Focusing on cholesterol and phosphoinositides, the chapter begins by reviewing the interactions of NPC proteins with cholesterol and their role in cholesterol transport. It then continues to describe the modulation of cholesterol efflux in NPC disease. The chapter concludes with a summary of findings related to the functional consequences of perturbations in phosphoinositides in this fatal disease.

The Interplay Between Cholesterol and Amyloid-β on HT22 Cell Viability, Morphology, and Receptor Tyrosine Kinase Signaling

BACKGROUND

There is a lack of understanding in the molecular and cellular mechanisms of Alzheimer's disease that has hindered progress on therapeutic development. The focus has been on targeting toxic amyloid-β (Aβ) pathology, but these therapeutics have generally failed in clinical trials. Aβ is an aggregation-prone protein that has been shown to disrupt cell membrane structure in molecular biophysics studies and interfere with membrane receptor signaling in cell and animal studies. Whether the lipid membrane or specific receptors are the primary target of attack has not been determined.

OBJECTIVE

This work elucidates some of the interplay between membrane cholesterol and Aβ42 on HT22 neuronal cell viability, morphology, and platelet-derived growth factor (PDGF) signaling pathways.

METHODS

The effects of cholesterol depletion by methyl-β-cyclodextrin followed by treatment with Aβ and/or PDGF-AA were assessed by MTT cell viability assays, western blot, optical and AFM microscopy.

RESULTS

Cell viability studies show that cholesterol depletion was mildly protective against Aβ toxicity. Together cholesterol reduction and Aβ42 treatment compounded the disruption of the PDGFα receptor activation. Phase contrast optical microscopy and live cell atomic force microscopy imaging revealed that cytotoxic levels of Aβ42 caused morphological changes including cell membrane damage, cytoskeletal disruption, and impaired cell adhesion; cell damage was ameliorated by cellular cholesterol depletion.

CONCLUSIONS

Cholesterol depletion impacted the effects of Aβ42 on HT22 cell viability, morphology, and receptor tyrosine kinase signaling.

Sensory axons induce epithelial lipid microdomain remodeling and determine the distribution of junctions in the epidermis

Epithelial cell properties are determined by the polarized distribution of membrane lipids, the cytoskeleton, and adhesive junctions. Epithelia are often profusely innervated, but little work has addressed how neurites affect epithelial organization. We previously found that basal keratinocytes in the zebrafish epidermis enclose axons in ensheathment channels sealed by autotypic junctions. Here we characterized how axons remodel cell membranes, the cytoskeleton, and junctions in basal keratinocytes. At the apical surface of basal keratinocytes, axons organized lipid microdomains quantitatively enriched in reporters for PI(4,5)P2 and liquid-ordered (Lo) membranes. Lipid microdomains supported the formation of cadherin-enriched, F-actin protrusions, which wrapped around axons, likely initiating ensheathment. In the absence of axons, cadherin-enriched microdomains formed on basal cells but did not organize into contiguous domains. Instead, these isolated domains formed heterotypic junctions with periderm cells, a distinct epithelial cell type. Thus, axon endings dramatically remodel polarized epithelial components and regulate epidermal adhesion.

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

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

PI(4,5)P2 and Cholesterol: Synthesis, Regulation, and Functions

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) is the most abundant membrane phosphoinositide and cholesterol is an essential component of the plasma membrane (PM). Both lipids play key roles in a variety of cellular functions including as signaling molecules and major regulators of protein function. This chapter provides an overview of these two important lipids. Starting from a brief description of their structure, synthesis, and regulation, the chapter continues to describe the primary functions and signaling processes in which PI(4,5)P₂ and cholesterol are involved. While PI(4,5)P₂ and cholesterol can act independently, they often act in concert or affect each other's impact. The chapters in this volume on "Cholesterol and PI(4,5)P₂ in Vital Biological Functions: From Coexistence to Crosstalk" focus on the emerging relationship between cholesterol and PI(4,5)P₂ in a variety of biological systems and processes. In this chapter, the next section provides examples from the ion channel field demonstrating that PI(4,5)P₂ and cholesterol can act via common mechanisms. The chapter ends with a discussion of future directions.

Role of Lysosomal Cholesterol in Regulating PI(4,5)P2-Dependent Ion Channel Function

Lysosomes are central regulators of cellular growth and signaling. Once considered the acidic garbage can of the cell, their ever-expanding repertoire of functions include the regulation of cell growth, gene regulation, metabolic signaling, cell migration, and cell death. In this chapter, we detail how another of the lysosome's crucial roles, cholesterol transport, plays a vital role in the control of ion channel function and neuronal excitability through its ability to influence the abundance of the plasma membrane signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂). This chapter will introduce the biosynthetic pathways of cholesterol and PI(4,5)P₂, discuss the molecular mechanisms through which each lipid distinctly regulates ion channels, and consider the interdependence of these lipids in the control of ion channel function.