Inhibition of cholesterol biosynthesis disrupts lipid raft/caveolae and affects insulin receptor activation in 3T3-L1 preadipocytes

"MiR-7 controls cholesterol biosynthesis through posttranscriptional regulation of DHCR24 expression"

Dysregulation of cholesterol homeostasis is associated with several pathologies including cardiovascular diseases and neurological disorders such as Alzheimer's disease (AD). MicroRNAs (miRNAs) have emerged as key post-transcriptional regulators of cholesterol metabolism. We previously established the role of miR-7 in regulating insulin resistance and amyloidosis, which represents a common pathological feature between type 2 diabetes and AD. We show here an additional metabolic function of miR-7 in cholesterol biosynthesis. We found that miR-7 blocks the last steps of the cholesterol biosynthetic pathway in vitro by targeting relevant genes including DHCR24 and SC5D posttranscriptionally. Intracranial infusion of miR-7 on an adeno-associated viral vector reduced the expression of DHCR24 in the brain of wild-type mice, supporting in vivo miR-7 targeting. We also found that cholesterol regulates endogenous levels of miR-7 in vitro, correlating with transcriptional regulation through SREBP2 binding to its promoter region. In parallel to SREBP2 inhibition, the levels of miR-7 and hnRNPK (the host gene of miR-7) were concomitantly reduced in brain in a mouse model of Niemann Pick type C1 disease and in murine fatty liver, which are both characterized by intracellular cholesterol accumulation. Taken together, the results establish a novel regulatory feedback loop by which miR-7 modulates cholesterol homeostasis at the posttranscriptional level, an effect that could be exploited for therapeutic interventions against prevalent human diseases.

Caveolin-1 temporal modulation enhances antibody drug efficacy in heterogeneous gastric cancer

Resistance mechanisms and heterogeneity in HER2-positive gastric cancers (GC) limit Trastuzumab benefit in 32% of patients, and other targeted therapies have failed in clinical trials. Using patient samples, patient-derived xenografts (PDXs), partially humanized biological models, and HER2-targeted imaging technologies we demonstrate the role of caveolin-1 (CAV1) as a complementary biomarker in GC selection for Trastuzumab therapy. In retrospective analyses of samples from patients enrolled on Trastuzumab trials, the CAV1-high profile associates with low membrane HER2 density and low patient survival. We show a negative correlation between CAV1 tumoral protein levels – a major protein of cholesterol-rich membrane domains – and Trastuzumab-drug conjugate TDM1 tumor uptake. Finally, CAV1 depletion using knockdown or pharmacologic approaches (statins) increases antibody drug efficacy in tumors with incomplete HER2 membranous reactivity. In support of these findings, background statin use in patients associates with enhanced antibody efficacy. Together, this work provides preclinical justification and clinical evidence that require prospective investigation of antibody drugs combined with statins to delay drug resistance in tumors.

Clinical evidences have demonstrated limited efficacy of HER2-targeted therapies in patients with gastric cancer (GC). Here the authors show that survival benefit to anti-HER2 antibody Trastuzumab is reduced in GC patients with high levels of the caveolin-1 and that, in preclinical cancer models, antibody drug efficacy can be improved by modulating caveolin-1 levels with cholesterol-depleting drugs, statins.

High-fat diet induced alterations in plasma membrane cholesterol content impairs insulin receptor binding and signalling in mouse liver but is ameliorated by atorvastatin

A high-fat diet (HFD) impairs insulin binding and signalling and may contribute to the development of insulin resistance. In addition, in vitro studies have shown that alterations in plasma membrane cholesterol influence ligand binding and downstream signalling for several receptor-tyrosine kinases (RTKs), including the insulin receptor. Using an ex vivo approach, we explored the effects of a HFD on insulin binding and signalling in mouse liver and relate these to observed changes in plasma membrane cholesterol. Mice fed a HFD demonstrated decreased insulin signalling compared to mice fed a normal chow diet (ND), indicated by a 3-fold decrease in insulin binding (P < 0.001) and a similar decrease in insulin receptor phosphorylation (~2.5-fold; P < 0.0001). Interestingly, we also observed a marked decrease in the cholesterol content of liver plasma membranes in the HFD fed mice (P < 0.0001). These effects of the HFD were found to be ameliorated by atorvastatin treatment (P < 0.0001). However, in ND mice, atorvastatin had no influence on membrane cholesterol content or insulin binding and signalling. The influence of membrane cholesterol on insulin binding and signalling was also corroborated in HepG2 cells. To the best of our knowledge, this is the first demonstration of the effects of a HFD and atorvastatin treatment on changes in plasma membrane cholesterol content and the consequent effects on insulin binding and signalling. Collectively, these findings suggest that changes in membrane cholesterol content could be an important underlying reason for the long-known effects of a HFD on the development of insulin resistance.

Aurora A and AKT Kinase Signaling Associated with Primary Cilia

Dysregulation of kinase signaling is associated with various pathological conditions, including cancer, inflammation, and autoimmunity; consequently, the kinases involved have become major therapeutic targets. While kinase signaling pathways play crucial roles in multiple cellular processes, the precise manner in which their dysregulation contributes to disease is dependent on the context; for example, the cell/tissue type or subcellular localization of the kinase or substrate. Thus, context-selective targeting of dysregulated kinases may serve to increase the therapeutic specificity while reducing off-target adverse effects. Primary cilia are antenna-like structures that extend from the plasma membrane and function by detecting extracellular cues and transducing signals into the cell. Cilia formation and signaling are dynamically regulated through context-dependent mechanisms; as such, dysregulation of primary cilia contributes to disease in a variety of ways. Here, we review the involvement of primary cilia-associated signaling through aurora A and AKT kinases with respect to cancer, obesity, and other ciliopathies.

Evaluation of Cardiotonic Steroid Modulation of Cellular Cholesterol and Phospholipid

We have previously shown that 21-benzylidene digoxin (21-BD) increases the total cholesterol and phospholipid content on the membrane of HeLa cells. Lipid modulation caused by cardiotonic steroids (CTS) is still unexplored. Therefore, the aim of the present study was to evaluate the cholesterol and phospholipid modulation of the cell membrane caused by ouabain and 21-BD and the possible involvement of the caveolae on this modulation. For this, one cell line containing caveolae (HeLa) and other not containing (Caco-2) were used. The modulation of the lipid profile was evaluated by total cholesterol and phospholipids measurements, and identification of membrane phospholipids by HPTLC. The cholesterol distribution was evaluated by filipin staining. The caveolin-1 expression was evaluated by Western Blotting. Ouabain had no effect on the total membrane lipid content in both cell lines. However, 21-BD increased total membrane phospholipid content and had no effect on the membrane cholesterol content in Caco-2 cells. CTS were not able to alter the specific phospholipids content. In the filipin experiments, 21-BD provoked a remarkable redistribution of cholesterol to the perinuclear region of HeLa cells. In Caco-2 cells, it was observed only a slight increase in cholesterol, especially as intracellular vesicles. The caveolin-1 expression was not altered by any of the compounds. Our data mainly show different effects of two cardiotonic steroids. Ouabain had no effect on the lipid profile of cells, whereas 21-BD causes important changes in cholesterol and phospholipid content. Therefore, the modulation of cholesterol content in the plasma membrane of HeLa cells is not correlated with the expression of caveolin-1.

Statins Decrease Programmed Death-Ligand 1 (PD-L1) by Inhibiting AKT and β-Catenin Signaling

Retrospective observational studies have reported that statins improve clinical outcomes in patients previously treated with programmed cell death protein 1 (PD-1)-targeting monoclonal antibodies for malignant pleural mesothelioma (MPM) and advanced non-small cell lung cancer (NSCLC). In multiple mouse cancer models, de novo synthesis of mevalonate and cholesterol inhibitors was found to synergize with anti-PD-1 antibody therapy. In the present study, we investigated whether statins affect programmed death-ligand 1 (PD-L1) expression in cancer cells. Four statins, namely simvastatin, atorvastatin, lovastatin, and fluvastatin, decreased PD-L1 expression in melanoma and lung cancer cells. In addition, we found that AKT and β-catenin signaling involved PD-L1 suppression by statins. Our cellular and molecular studies provide inspiring evidence for extending the clinical evaluation of statins for use in combination with immune checkpoint inhibitor-based cancer therapy.

Primary cilia and lipid raft dynamics

Primary cilia, antenna-like structures of the plasma membrane, detect various extracellular cues and transduce signals into the cell to regulate a wide range of functions. Lipid rafts, plasma membrane microdomains enriched in cholesterol, sphingolipids and specific proteins, are also signalling hubs involved in a myriad of physiological functions. Although impairment of primary cilia and lipid rafts is associated with various diseases, the relationship between primary cilia and lipid rafts is poorly understood. Here, we review a newly discovered interaction between primary cilia and lipid raft dynamics that occurs during Akt signalling in adipogenesis. We also discuss the relationship between primary cilia and lipid raft-mediated Akt signalling in cancer biology. This review provides a novel perspective on primary cilia in the regulation of lipid raft dynamics.

Phospholipid exchange shows insulin receptor activity is supported by both the propensity to form wide bilayers and ordered raft domains

Insulin receptor (IR) is a membrane tyrosine kinase that mediates the response of cells to insulin. IR activity has been shown to be modulated by changes in plasma membrane lipid composition, but the properties and structural determinants of lipids mediating IR activity are poorly understood. Here, using efficient methyl-alpha-cyclodextrin mediated lipid exchange, we studied the effect of altering plasma membrane outer leaflet phospholipid composition upon the activity of IR in mammalian cells. After substitution of endogenous lipids with lipids having an ability to form liquid ordered (Lo) domains (sphingomyelins) or liquid disordered (Ld) domains (unsaturated phosphatidylcholines (PCs)), we found that the propensity of lipids to form ordered domains is required for high IR activity. Additional substitution experiments using a series of saturated PCs showed that IR activity increased substantially with increasing acyl chain length, which increases both bilayer width and the propensity to form ordered domains. Incorporating purified IR into alkyl maltoside micelles with increasing hydrocarbon lengths also increased IR activity, but more modestly than by increasing lipid acyl chain length in cells. These results suggest that the ability to form Lo domains as well as wide bilayer width contributes to increased IR activity. Inhibition of phosphatases showed that some of the lipid dependence of IR activity upon lipid structure reflected protection from phosphatases by lipids that support Lo domain formation. These results are consistent with a model in which a combination of bilayer width and ordered domain formation modulates IR activity via IR conformation and accessibility to phosphatases.

Cell cycle dependence on the mevalonate pathway: Role of cholesterol and non-sterol isoprenoids

The mevalonate pathway is responsible for the synthesis of isoprenoids, including sterols and other metabolites that are essential for diverse biological functions. Cholesterol, the main sterol in mammals, and non-sterol isoprenoids are in high demand by rapidly dividing cells. As evidence of its importance, many cell signaling pathways converge on the mevalonate pathway and these include those involved in proliferation, tumor-promotion, and tumor-suppression. As well as being a fundamental building block of cell membranes, cholesterol plays a key role in maintaining their lipid organization and biophysical properties, and it is crucial for the function of proteins located in the plasma membrane. Importantly, cholesterol and other mevalonate derivatives are essential for cell cycle progression, and their deficiency blocks different steps in the cycle. Furthermore, the accumulation of non-isoprenoid mevalonate derivatives can cause DNA replication stress. Identification of the mechanisms underlying the effects of cholesterol and other mevalonate derivatives on cell cycle progression may be useful in the search for new inhibitors, or the repurposing of preexisting cholesterol biosynthesis inhibitors to target cancer cell division. In this review, we discuss the dependence of cell division on an active mevalonate pathway and the role of different mevalonate derivatives in cell cycle progression.

One Raft to Guide Them All, and in Axon Regeneration Inhibit Them

Central nervous system damage caused by traumatic injuries, iatrogenicity due to surgical interventions, stroke and neurodegenerative diseases is one of the most prevalent reasons for physical disability worldwide. During development, axons must elongate from the neuronal cell body to contact their precise target cell and establish functional connections. However, the capacity of the adult nervous system to restore its functionality after injury is limited. Given the inefficacy of the nervous system to heal and regenerate after damage, new therapies are under investigation to enhance axonal regeneration. Axon guidance cues and receptors, as well as the molecular machinery activated after nervous system damage, are organized into lipid raft microdomains, a term typically used to describe nanoscale membrane domains enriched in cholesterol and glycosphingolipids that act as signaling platforms for certain transmembrane proteins. Here, we systematically review the most recent findings that link the stability of lipid rafts and their composition with the capacity of axons to regenerate and rebuild functional neural circuits after damage.

Primary cilia-dependent lipid raft/caveolin dynamics regulate adipogenesis

Primary cilia play a pivotal role in signal transduction and development and are known to serve as signaling hubs. Recent studies have shown that primary cilium dysfunction influences adipogenesis, but the mechanisms are unclear. Here, we show that mesenchymal progenitors C3H10T1/2 depleted of trichoplein, a key regulator of cilium formation, have significantly longer cilia than control cells and fail to differentiate into adipocytes. Mechanistically, the elongated cilia prevent caveolin-1- and/or GM3-positive lipid rafts from being assembled around the ciliary base where insulin receptor proteins accumulate, thereby inhibiting the insulin-Akt signaling. We further generate trichoplein knockout mice, in which adipogenic progenitors display elongated cilia and impair the lipid raft dynamics. The knockout mice on an extended high-fat diet exhibit reduced body fat and smaller adipocytes than wild-type (WT) mice. Overall, our results suggest a role for primary cilia in regulating adipogenic signal transduction via control of the lipid raft dynamics around cilia.

Lipid Raft Association Stabilizes VEGF Receptor 2 in Endothelial Cells

The binding of vascular endothelial growth factor A (VEGF) to VEGF receptor-2 (VEGFR-2) stimulates angiogenic signaling. Lipid rafts are cholesterol-dense regions of the plasma membrane that serve as an organizational platform for biomolecules. Although VEGFR2 has been shown to colocalize with lipid rafts to regulate its activation, the effect of lipid rafts on non-activated VEGFR2 has not been explored. Here, we characterized the involvement of lipid rafts in modulating the stability of non-activated VEGFR2 in endothelial cells using raft disrupting agents: methyl-β-cyclodextrin, sphingomyelinase and simvastatin. Disrupting lipid rafts selectively decreased the levels of non-activated VEGFR2 as a result of increased lysosomal degradation. The decreased expression of VEGFR2 translated to reduced VEGF-activation of the extracellular signal-regulated protein kinases (ERK). Overall, our results indicate that lipid rafts stabilize VEGFR2 and its associated signal transduction activities required for angiogenesis. Thus, modulation of lipid rafts may provide a means to regulate the sensitivity of endothelial cells to VEGF stimulation. Indeed, the ability of simvastatin to down regulate VEGFR2 and inhibit VEGF activity suggest a potential mechanism underlying the observation that this drug improves outcomes in the treatment of certain cancers.

Tm7sf2 Disruption Alters Radial Gene Positioning in Mouse Liver Leading to Metabolic Defects and Diabetes Characteristics

Tissue-specific patterns of radial genome organization contribute to genome regulation and can be established by nuclear envelope proteins. Studies in this area often use cancer cell lines, and it is unclear how well such systems recapitulate genome organization of primary cells or animal tissues; so, we sought to investigate radial genome organization in primary liver tissue hepatocytes. Here, we have used a NET47/Tm7sf2^–/– liver model to show that manipulating one of these nuclear membrane proteins is sufficient to alter tissue-specific gene positioning and expression. Dam-LaminB1 global profiling in primary liver cells shows that nearly all the genes under such positional regulation are related to/important for liver function. Interestingly, Tm7sf2 is a paralog of the HP1-binding nuclear membrane protein LBR that, like Tm7sf2, also has an enzymatic function in sterol reduction. Fmo3 gene/locus radial mislocalization could be rescued with human wild-type, but not TM7SF2 mutants lacking the sterol reductase function. One central pathway affected is the cholesterol synthesis pathway. Within this pathway, both Cyp51 and Msmo1 are under Tm7sf2 positional and expression regulation. Other consequences of the loss of Tm7sf2 included weight gain, insulin sensitivity, and reduced levels of active Akt kinase indicating additional pathways under its regulation, several of which are highlighted by mispositioning genes. This study emphasizes the importance for tissue-specific radial genome organization in tissue function and the value of studying genome organization in animal tissues and primary cells over cell lines.

Insulin Receptor Trafficking: Consequences for Insulin Sensitivity and Diabetes

Insulin receptor (INSR) has been extensively studied in the area of cell proliferation and energy metabolism. Impaired INSR activities lead to insulin resistance, the key factor in the pathology of metabolic disorders including type 2 diabetes mellitus (T2DM). The mainstream opinion is that insulin resistance begins at a post-receptor level. The role of INSR activities and trafficking in insulin resistance pathogenesis has been largely ignored. Ligand-activated INSR is internalized and trafficked to early endosome (EE), where INSR is dephosphorylated and sorted. INSR can be subsequently conducted to lysosome for degradation or recycled back to the plasma membrane. The metabolic fate of INSR in cellular events implies the profound influence of INSR on insulin signaling pathways. Disruption of INSR-coupled activities has been identified in a wide range of insulin resistance-related diseases such as T2DM. Accumulating evidence suggests that alterations in INSR trafficking may lead to severe insulin resistance. However, there is very little understanding of how altered INSR activities undermine complex signaling pathways to the development of insulin resistance and T2DM. Here, we focus this review on summarizing previous findings on the molecular pathways of INSR trafficking in normal and diseased states. Through this review, we provide insights into the mechanistic role of INSR intracellular processes and activities in the development of insulin resistance and diabetes.

Understanding toward the Biophysical Interaction of Polymeric Proanthocyanidins (Persimmon Condensed Tannins) with Biomembranes: Relevance for Biological Effects

Persimmon condensed tannins (PT) are highly polymerized (mDP = 26) and highly galloylated (72%) proanthocyanidins. Its pleiotropic effects in oxidation resistance, neuroprotection, hypolipidemia, and cardio-protection both in vitro and in vivo were widely reported. Because large proanthocyanidins are unlikely to be absorbed in the gastrointestinal tract, it is believed that the interaction of PT with biological membranes may play a crucial role in its biological activities. In the present study, the capacities of PT adsorbing to membrane, partitioning into membrane, and its influence on the membrane fluidity were investigated by fluorescence quenching, isothermal titration calorimetry (ITC) and fluorescence anisotropy measurements in a biomembrane-mimetic system composed of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE), sphingomyelin (SPM), and cholesterol (CHOL). Besides, the effects of PT on the morphology and integrity of the cell membrane were studied by scanning electron microscopy (SEM) and fluorescence staining in the 3T3-L1 cell model. The results suggested that PT could affect cell membrane rafts domains, destroy the cell membrane morphology, and regulate cell membrane fluidity, which might contribute to its biological effects.

Use of virus-like particles as a native membrane model to study the interaction of insulin with the insulin receptor

There is emerging evidence of the utility of virus-like particles (VLPs) as a novel model for the study of receptor-ligand interactions in a native plasma membrane environment. VLPs consist of a viral core protein encapsulated by portions of the cell membrane with membrane proteins and receptors expressed in their native conformation. VLPs can be generated in mammalian cells by transfection with the retroviral core protein (gag). In this study, we used Chinese hamster ovary (CHO T10) cells stably overexpressing the insulin receptor (IR) to generate IR bearing VLPs. The diameter and size uniformity of VLPs were estimated by dynamic light scattering and morphological features examined by scanning electron microscopy. The presence of high affinity IR on VLPs was demonstrated by competitive binding assays (K_D: 2.3 ± 0.4 nM, n = 3), which was similar to that on the parental CHO T10 cells (K_D: 2.1 ± 0.4 nM, n = 3). We also report that increases or decreases in membrane cholesterol content by treatment with methyl-β-cyclodextrin (MBCD) or cholesterol pre-loaded methyl-β-cyclodextrin (cMBCD), respectively, substantially decreased insulin binding (> 30%) to both VLPs and cells, and we speculate this is due to a change in receptor disposition. We suggest that this novel finding of decreases in insulin binding in response to changes in membrane cholesterol content may largely account for the unexplained decreases in insulin signalling events previously reported elsewhere. Finally, we propose VLPs as a viable membrane model for the study of insulin-IR interactions in a native membrane environment.

Antipsychotics Promote Metabolic Disorders Disrupting Cellular Lipid Metabolism and Trafficking

Antipsychotics frequently cause obesity and related metabolic disorders that current psychopharmacological/endocrinological theories do not explain consistently. An integrative/alternative theory implies metabolic alterations happening at the cellular level. Many observations in vitro and in vivo, and pivotal observations in humans, point towards chemical properties of antipsychotics, independent of receptor binding characteristics. Being amphiphilic weak bases, antipsychotics can disrupt lysosomal function, affecting cholesterol trafficking; moreover, by chemical mimicry, antipsychotics can inhibit cholesterol biosynthesis. These two molecular adverse effects may trigger a cascade of transcriptional and biochemical events, ultimately reducing available cholesterol while increasing cholesterol precursors and fatty acids. The macroscopic manifestation of these molecular alterations includes decreased high-density lipoprotein and increased very low-density lipoprotein and triglycerides that may translate into obesity and related metabolic disorders.

Cholesterol-enriched membrane microdomains are needed for insulin signaling and proliferation in hepatic cells

Hepatocyte proliferation during liver regeneration is a well-coordinated process regulated by the activation of several growth factor receptors, including the insulin receptor (IR). The IR can be localized in part to cholesterol-enriched membrane microdomains, but the role of such domains in insulin-mediated events in hepatocytes is not known. We investigated whether partitioning of IRs into cholesterol-enriched membrane rafts is important for the mitogenic effects of insulin in the hepatic cells. IR and lipid rafts were labeled in HepG2 cells and primary rat hepatocytes. Membrane cholesterol was depleted in vitro with metyl-β-cyclodextrin (MβCD) and in vivo with lovastatin. Insulin-induced calcium (Ca²⁺) signals studies were examined in HepG2 cells and in freshly isolated rat hepatocytes as well as in whole liver in vivo by intravital confocal imaging. Liver regeneration was studied by 70% partial hepatectomy (PH), and hepatocyte proliferation was assessed by PCNA staining. A subpopulation of IR was found in membrane microdomains enriched in cholesterol. Depletion of cholesterol from plasma membrane resulted in redistribution of the IR along the cells, which was associated with impaired insulin-induced nuclear Ca²⁺ signals, a signaling event that regulates hepatocyte proliferation. Cholesterol depletion also led to ERK1/2 hyper-phosphorylation. Lovastatin administration to rats decreased hepatic cholesterol content, disrupted lipid rafts and decreased insulin-induced Ca²⁺ signaling in hepatocytes, and delayed liver regeneration after PH. Therefore, membrane cholesterol content and lipid rafts integrity showed to be important for the proliferative effects of insulin in hepatic cells. NEW & NOTEWORTHY One of insulin's actions is to stimulate liver regeneration. Here we show that a subpopulation of insulin receptors is in a specialized cholesterol-enriched region of the cell membrane and this subfraction is important for insulin's proliferative effects.

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

BACKGROUND

Adult mesenchymal stem cells (MSCs) are an important resource for tissue growth, repair, and regeneration. To utilize MSCs more effectively, a clear understanding of how they react to environmental cues is essential. Currently, relatively little is known about how the composition of the plasma membranes affects stem cell phenotype and properties. The presence of lipid molecules, including cholesterol in particular, in the plasma membrane plays a crucial role in regulating a variety of physiological processes in cells. In this study, we examined the effects of perturbations in cholesterol/caveolin-1 (CAV-1)/caveolae homeostasis on the membrane properties and adhesive characteristics of MSCs. Findings from this study will contribute to the understanding of how cholesterol/CAV-1/caveolae regulates aspects of the cell membrane important to cell adhesion, substrate sensing, and microenvironment interaction.

METHODS

We generated five experimental MSC groups: 1) untreated MSCs; 2) cholesterol-depleted MSCs; 3) cholesterol-supplemented MSCs; 4) MSCs transfected with control, nonspecific small interfering (si)RNA; and 5) MSCs transfected with CAV-1 siRNA. Each cell group was analyzed for perturbation of cholesterol status and CAV-1 expression by performing Amplex Red cholesterol assay, filipin fluorescence staining, and real-time polymerase chain reaction (PCR). The membrane fluidity in the five experimental cell groups were measured using pyrene fluorescence probe staining followed by FACS analysis. Cell adhesion to collagen and fibronectin as well as cell surface integrin expression were examined.

RESULTS

Cholesterol supplementation to MSCs increased membrane cholesterol, and resulted in decreased membrane fluidity and localization of elevated numbers of caveolae and CAV-1 to the cell membrane. These cells showed increased expression of α1, α4, and β1 integrins, and exhibited higher adhesion rates to fibronectin and collagen. Conversely, knockdown of CAV-1 expression or cholesterol depletion on MSCs caused a parallel decrease in caveolae content and an increase in membrane fluidity due to decreased delivery of cholesterol to the cell membrane. Cells with depleted CAV-1 expression showed decreased cell surface integrin expression and slower adhesion to different substrates.

CONCLUSIONS

Our results demonstrate that perturbations in cholesterol/CAV-1 levels significantly affect the membrane properties of MSCs. These findings suggest that modification of membrane cholesterol and/or CAV-1 and caveolae may be used to manipulate the biological activities of MSCs.

Sterol targeting drugs reveal life cycle stage-specific differences in trypanosome lipid rafts

Cilia play important roles in cell signaling, facilitated by the unique lipid environment of a ciliary membrane containing high concentrations of sterol-rich lipid rafts. The African trypanosome Trypanosoma brucei is a single-celled eukaryote with a single cilium/flagellum. We tested whether flagellar sterol enrichment results from selective flagellar partitioning of specific sterol species or from general enrichment of all sterols. While all sterols are enriched in the flagellum, cholesterol is especially enriched. T. brucei cycles between its mammalian host (bloodstream cell), in which it scavenges cholesterol, and its tsetse fly host (procyclic cell), in which it both scavenges cholesterol and synthesizes ergosterol. We wondered whether the insect and mammalian life cycle stages possess chemically different lipid rafts due to different sterol utilization. Treatment of bloodstream parasites with cholesterol-specific methyl-β-cyclodextrin disrupts both membrane liquid order and localization of a raft-associated ciliary membrane calcium sensor. Treatment with ergosterol-specific amphotericin B does not. The opposite results were observed with ergosterol-rich procyclic cells. Further, these agents have opposite effects on flagellar sterol enrichment and cell metabolism in the two life cycle stages. These findings illuminate differences in the lipid rafts of an organism employing life cycle-specific sterols and have implications for treatment.

Changes in the plasma membrane in metabolic disease: impact of the membrane environment on G protein-coupled receptor structure and function

Drug development targeting GPCRs often utilizes model heterologous cell expression systems, reflecting an implicit assumption that the membrane environment has little functional impact on these receptors or on their responsiveness to drugs. However, much recent data have illustrated that membrane components can have an important functional impact on intrinsic membrane proteins. This review is directed toward gaining a better understanding of the structure of the plasma membrane in health and disease, and how this organelle can influence GPCR structure, function and regulation. It is important to recognize that the membrane provides a potential mode of lateral allosteric regulation of GPCRs and can affect the effectiveness of drugs and their biological responses in various disease states, which can even vary among individuals across the population. The type 1 cholecystokinin receptor is reviewed as an exemplar of a class A GPCR that is affected in this way by changes in the plasma membrane.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

Membrane lipid alterations in the metabolic syndrome and the role of dietary oils

The metabolic syndrome is a cluster of pathological conditions, including hypertension, hyperglycemia, hypertriglyceridemia, obesity and low HDL levels that is of great concern worldwide, as individuals with metabolic syndrome have an increased risk of type-2 diabetes and cardiovascular disease. Insulin resistance, the key feature of the metabolic syndrome, might be at the same time cause and consequence of impaired lipid composition in plasma membranes of insulin-sensitive tissues like liver, muscle and adipose tissue. Diet intervention has been proposed as a powerful tool to prevent the development of the metabolic syndrome, since healthy diets have been shown to have a protective role against the components of the metabolic syndrome. Particularly, dietary fatty acids are capable of modulating the deleterious effects of these conditions, among other mechanisms, by modifications of the lipid composition of the membranes in insulin-sensitive tissues. However, there is still scarce data based of high-level evidence on the effects of dietary oils on the effects of the metabolic syndrome and its components. This review summarizes the current knowledge on the effects of dietary oils on improving alterations of the components of the metabolic syndrome. It also examines their influence in the modulation of plasma membrane lipid composition and in the functionality of membrane proteins involved in insulin activity, like the insulin receptor, GLUT-4, CD36/FAT and ABCA-1, and their effect in the metabolism of glucose, fatty acids and cholesterol, and, in turn, the key features of the metabolic syndrome. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Disrupting Hepatocyte Cyp51 from Cholesterol Synthesis Leads to Progressive Liver Injury in the Developing Mouse and Decreases RORC Signalling

Development of mice with hepatocyte knockout of lanosterol 14α-demethylase (H^Cyp51−/−) from cholesterol synthesis is characterized by the progressive onset of liver injury with ductular reaction and fibrosis. These changes begin during puberty and are generally more aggravated in the knockout females. However, a subgroup of (pre)pubertal knockout mice (runts) exhibits a pronounced male prevalent liver dysfunction characterized by downregulated amino acid metabolism and elevated Casp12. RORC transcriptional activity is diminished in livers of all runt mice, in correlation with the depletion of potential RORC ligands subsequent to CYP51 disruption. Further evidence for this comes from the global analysis that identified a crucial overlap between hepatic Cyp51^−/− and Rorc^−/− expression profiles. Additionally, the reduction in RORA and RORC transcriptional activity was greater in adult H^Cyp51−/− females than males, which correlates well with their downregulated amino and fatty acid metabolism. Overall, we identify a global and sex-dependent transcriptional de-regulation due to the block in cholesterol synthesis during development of the Cyp51 knockout mice and provide in vivo evidence that sterol intermediates downstream of lanosterol may regulate the hepatic RORC activity.

A, Kazi RS, Banarjee R, Rathore R, MV V, HV T, Kumar Bhat M, MJ K. Methylglyoxal attenuates insulin signaling and downregulates the enzymes involved in cholesterol biosynthesis

Methylglyoxal (MG) is a highly reactive dicarbonyl known to be elevated under the hyperglycemic conditions of diabetes and is implicated in the development of diabetic complications.

Perturbed rhythmic activation of signaling pathways in mice deficient for Sterol Carrier Protein 2-dependent diurnal lipid transport and metabolism

Through evolution, most of the living species have acquired a time keeping system to anticipate daily changes caused by the rotation of the Earth. In all of the systems this pacemaker is based on a molecular transcriptional/translational negative feedback loop able to generate rhythmic gene expression with a period close to 24 hours. Recent evidences suggest that post-transcriptional regulations activated mostly by systemic cues play a fundamental role in the process, fine tuning the time keeping system and linking it to animal physiology. Among these signals, we consider the role of lipid transport and metabolism regulated by SCP2. Mice harboring a deletion of the Scp2 locus present a modulated diurnal accumulation of lipids in the liver and a perturbed activation of several signaling pathways including PPARα, SREBP, LRH-1, TORC1 and its upstream regulators. This defect in signaling pathways activation feedbacks upon the clock by lengthening the circadian period of animals through post-translational regulation of core clock regulators, showing that rhythmic lipid transport is a major player in the establishment of rhythmic mRNA and protein expression landscape.

Vaginal epithelial cells regulate membrane adhesiveness to co-ordinate bacterial adhesion

Vaginal epithelium is colonized by different bacterial strains and species. The bacterial composition of vaginal biofilms controls the balance between health and disease. Little is known about the relative contribution of the epithelial and bacterial cell surfaces to bacterial adhesion and whether and how adhesion is regulated over cell membrane regions. Here, we show that bacterial adhesion forces with cell membrane regions not located above the nucleus are stronger than with regions above the nucleus both for vaginal pathogens and different commensal and probiotic lactobacillus strains involved in health. Importantly, adhesion force ratios over membrane regions away from and above the nucleus coincided with the ratios between numbers of adhering bacteria over both regions. Bacterial adhesion forces were dramatically decreased by depleting the epithelial cell membrane of cholesterol or sub-membrane cortical actin. Thus, epithelial cells can regulate membrane regions to which bacterial adhesion is discouraged, possibly to protect the nucleus.

Transcriptional Regulation of Cytosolic Sulfotransferase 1C2 by Intermediates of the Cholesterol Biosynthetic Pathway in Primary Cultured Rat Hepatocytes

Cytosolic sulfotransferase 1C2 (SULT1C2) is expressed in the kidney, stomach, and liver of rats; however, the mechanisms regulating expression of this enzyme are not known. We evaluated transcriptional regulation of SULT1C2 by mevalonate (MVA)-derived intermediates in primary cultured rat hepatocytes using several cholesterol synthesis inhibitors. Blocking production of mevalonate with the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor pravastatin (30 μM), reduced SULT1C2 mRNA content by ∼40% whereas the squalene synthase inhibitor squalestatin (SQ1, 0.1 μM), which causes accumulation of nonsterol isoprenoids, increased mRNA content by 4-fold. Treatment with MVA (10 mM) strongly induced SULT1C2 mRNA by 12-fold, and this effect was blocked by inhibiting squalene epoxidase but not by more distal cholesterol inhibitors, indicating the effects of MVA are mediated by postsqualene metabolites. Using rapid amplification of cDNA ends (RACE), we characterized the 5' end of SULT1C2 mRNA and used this information to generate constructs for promoter analysis. SQ1 and MVA increased reporter activity by ∼1.6- and 3-fold, respectively, from a construct beginning 49 base pairs (bp) upstream from the longest 5'-RACE product (-3140:-49). Sequence deletions from this construct revealed a hepatocyte nuclear factor 1 (HNF1) element (-2558), and mutation of this element reduced basal (75%) and MVA-induced (30%) reporter activity and attenuated promoter activation following overexpression of HNF1α or 1β. However, the effects of SQ1 were localized to a more proximal promoter region (-281:-49). Collectively, our findings demonstrate that cholesterol biosynthetic intermediates influence SULT1C2 expression in rat primary hepatocytes. Further, HNF1 appears to play an important role in mediating basal and MVA-induced SULT1C2 transcription.

The Deleterious Effects of Oxidative and Nitrosative Stress on Palmitoylation, Membrane Lipid Rafts and Lipid-Based Cellular Signalling: New Drug Targets in Neuroimmune Disorders

Oxidative and nitrosative stress (O&NS) is causatively implicated in the pathogenesis of Alzheimer's and Parkinson's disease, multiple sclerosis, chronic fatigue syndrome, schizophrenia and depression. Many of the consequences stemming from O&NS, including damage to proteins, lipids and DNA, are well known, whereas the effects of O&NS on lipoprotein-based cellular signalling involving palmitoylation and plasma membrane lipid rafts are less well documented. The aim of this narrative review is to discuss the mechanisms involved in lipid-based signalling, including palmitoylation, membrane/lipid raft (MLR) and n-3 polyunsaturated fatty acid (PUFA) functions, the effects of O&NS processes on these processes and their role in the abovementioned diseases. S-palmitoylation is a post-translational modification, which regulates protein trafficking and association with the plasma membrane, protein subcellular location and functions. Palmitoylation and MRLs play a key role in neuronal functions, including glutamatergic neurotransmission, and immune-inflammatory responses. Palmitoylation, MLRs and n-3 PUFAs are vulnerable to the corruptive effects of O&NS. Chronic O&NS inhibits palmitoylation and causes profound changes in lipid membrane composition, e.g. n-3 PUFA depletion, increased membrane permeability and reduced fluidity, which together lead to disorders in intracellular signal transduction, receptor dysfunction and increased neurotoxicity. Disruption of lipid-based signalling is a source of the neuroimmune disorders involved in the pathophysiology of the abovementioned diseases. n-3 PUFA supplementation is a rational therapeutic approach targeting disruptions in lipid-based signalling.

In vitro Hypolipidemic and Antioxidant Effects of Leaf and Root Extracts of Taraxacum Officinale

Adipose tissue dysfunction constitutes a primary defect in obesity and might link this disease to severe chronic health problems. We aimed to evaluate the antioxidant activity of three extracts from Taraxacum officinale (dandelion) as well as their effects on mature 3T3-L1 adipocytes concerning intracellular lipid accumulation and cytotoxicity, this would give indications regarding therapeutic interest of dandelion as potential anti-obesity candidate. Antioxidant activities of extracts from dandelion roots and leaves were evaluated in vitro using 1,1-diphenyl-2-picrylhyorazyl (DPPH) and Ferric Reducing Antioxidant Power (FRAP) methods at the concentration range used in cellular assays (300–600 µg/mL). The influence of the extracts on mature 3T3-L1 adipocyte viability was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Lipid content was determined by Oil-red-O staining. The extracts showed effective antioxidant activity correlating with total flavonoid and polyphenol contents. However, the functionality level was weakly associated with the antioxidant activity. Further, our data demonstrated that mature 3T3-L1 adipocytes reduced in size and number when incubated with the extracts, which suggests a significant increase in lipolysis activity. Particularly, leaf extract and crude powdered root of dandelion reduced triglyceride accumulation in mature 3T3-L1 adipocytes to a greater extent that the extract from the root. Our study shows anti-lipogenic effects of dandelion extracts on adipocytes as well as radical scavenging and reducing activity. Importantly, along with previous results indicating that cell populations cultivated in the presence of the dandelion extracts decrease in 3T3-L1 adipogenesis capacity, these results suggests that these extracts might represent a treatment option for obesity-related diseases by affecting different processes during the adipocyte life cycle.

Phytochemical regulation of Fyn and AMPK signaling circuitry

During the past decades, phytochemical terpenoids, polyphenols, lignans, flavonoids, and alkaloids have been identified as antioxidative and cytoprotective agents. Adenosine monophosphate-activated protein kinase (AMPK) is a kinase that controls redox-state and oxidative stress in the cell, and serves as a key molecule regulating energy metabolism. Many phytochemicals directly or indirectly alter the AMPK pathway in distinct manners, exerting catabolic metabolism. Some of them are considered promising in the treatment of metabolic diseases such as type II diabetes, obesity, and hyperlipidemia. Another important kinase that regulates energy metabolism is Fyn kinase, a member of the Src family kinases that plays a role in various cellular responses such as insulin signaling, cell growth, oxidative stress and apoptosis. Phytochemical inhibition of Fyn leads to AMPK-mediated protection of the cell in association with increased antioxidative capacity and mitochondrial biogenesis. The kinases may work together to form a signaling circuitry for the homeostasis of energy conservation and expenditure, and may serve as targets of phytochemicals. This review is intended as a compilation of recent advancements in the pharmacological research of phytochemicals targeting Fyn and AMPK circuitry, providing information for the prevention and treatment of metabolic diseases and the accompanying tissue injuries.

Cholesterol in myelin biogenesis and hypomyelinating disorders

The largest pool of free cholesterol in mammals resides in myelin membranes. Myelin facilitates rapid saltatory impulse propagation by electrical insulation of axons. This function is achieved by ensheathing axons with a tightly compacted stack of membranes. Cholesterol influences myelination at many steps, from the differentiation of myelinating glial cells, over the process of myelin membrane biogenesis, to the functionality of mature myelin. Cholesterol emerged as the only integral myelin component that is essential and rate-limiting for the development of myelin in the central and peripheral nervous system. Moreover, disorders that interfere with sterol synthesis or intracellular trafficking of cholesterol and other lipids cause hypomyelination and neurodegeneration. This review summarizes recent results on the roles of cholesterol in CNS myelin biogenesis in normal development and under different pathological conditions. This article is part of a Special Issue entitled Brain Lipids.

Cholesterol depletion by methyl-β-cyclodextrin augments tamoxifen induced cell death by enhancing its uptake in melanoma

BACKGROUND

Despite modern advances in treatment, skin cancer is still one of the most common causes of death in the western countries. Chemotherapy plays an important role in melanoma management. Tamoxifen has been used either alone or in- combination with other chemotherapeutic agents to treat melanoma. However, response rate of tamoxifen as a single agent has been comparatively low. In the present study, we investigated whether treatment with methyl-β-cyclodextrin (MCD), a cholesterol depleting agent, increases the efficacy of tamoxifen in melanoma cells.

METHODS

This was a two-part study that incorporated in vitro effects of tamoxifen and MCD combination by analyzing cell survival, apoptosis and cell cycle analysis and in vivo antitumor efficacy on tumor isografts in C57BL/6J mice.

RESULTS

MCD potentiated tamoxifen induced anticancer effects by causing cell cycle arrest and induction of apoptosis. Sensitization to tamoxifen was associated with down regulation of antiapoptotic protein Bcl-2, up-regulation of proapoptotic protein Bax, reduced caveolin-1 (Cav-1) and decreased pAkt/pERK levels. Co-administration of tamoxifen and MCD caused significant reduction in tumor volume and tumor weight in mice due to enhancement of drug uptake in the tumor. Supplementation with cholesterol abrogated combined effect of tamoxifen and MCD.

CONCLUSION

Our results emphasize a potential synergistic effect of tamoxifen with MCD, and therefore, may provide a unique therapeutic window for improvement in melanoma treatment.

Comprehensive gas chromatography-electron ionisation mass spectrometric analysis of fatty acids and sterols using sequential one-pot silylation: quantification and isotopologue analysis

RATIONALE

Fatty acids and sterol lipids play crucial roles in several biological processes and several biological facts underline the interconnection between these lipid classes. Therefore, it is of interest to develop a comprehensive method analysing both classes in the form of their most favourable derivatives suitable for quantification and isotopologue analysis.

METHODS

Lipids were derivatised by a sequential one-pot procedure using N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MtBSTFA) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). No clean-up or concentration steps were necessary. The prepared samples were directly available for gas chromatography-electron ionisation mass spectrometric (GC-EI-MS) analysis on a standard column. For quantification, the SIM mode was used and for isotopologue analysis scheduled scan mode was applied.

RESULTS

Development of a sequential one-pot derivatisation for GC-EI-MS allowing comprehensive analysis of fatty acids and sterols as their most favourable derivatives. Validation carried out using human plasma, comparison with certified NIST plasma. LLOQ of usually 3.3 ng/mL achieved. Isotopologue analysis of 2-[(13)C]-acetate incorporation in HL-60 cells proving feasibility of method.

CONCLUSIONS

The presented method successfully combines two consecutive silylation reactions in one pot, enabling the analysis of both fatty acids and sterols in a comprehensive analytical method. The method has great potential for the quantification of lipids as well as the comprehensive study of both biochemical pathways, using [(13)C]-flux analysis.

An association of metabolic syndrome constellation with cellular membrane caveolae

Metabolic syndrome (MetS) is a cluster of metabolic abnormalities that can predispose an individual to a greater risk of developing type-2 diabetes and cardiovascular diseases. The cluster includes abdominal obesity, dyslipidemia, hypertension, and hyperglycemia - all of which are risk factors to public health. While searching for a link among the aforementioned malaises, clues have been focused on the cell membrane domain caveolae, wherein the MetS-associated active molecules are colocalized and interacted with to carry out designated biological activities. Caveola disarray could induce all of those individual metabolic abnormalities to be present in animal models and humans, providing a new target for therapeutic strategy in the management of MetS.

Desmosterol and DHCR24: unexpected new directions for a terminal step in cholesterol synthesis

3β-Hydroxysterol Δ(24)-reductase (DHCR24) catalyzes the conversion of desmosterol to cholesterol. This ultimate step of cholesterol biosynthesis appears to be remarkable in its diverse functions and the number of diseases it is implicated in from vascular disease to Hepatitis C virus (HCV) infection to cancer to Alzheimer's disease. This review summarizes the present knowledge on the DHCR24 gene, sterol Δ(24)-reductase protein and the regulation of both. In addition, the functions of desmosterol, DHCR24 and their roles in human diseases are discussed. It is apparent that DHCR24 exerts more complex effects than what would be expected based on the enzymatic activity of sterol Δ(24)-reduction alone, such as its influence in modulating oxidative stress. Increasing information about DHCR24 membrane association, processing, enzymatic regulation and interaction partners will provide further fundamental insights into DHCR24 and its many and varied biological roles.

Loss of caveolin-1 expression in knock-in mouse model of Huntington's disease suppresses pathophysiology in vivo

Loss of cholesterol homeostasis and altered vesicle trafficking have been detected in Huntington's disease (HD) cellular and animal models, yet the role of these dysfunctions in pathophysiology of HD is unknown. We demonstrate here that defects in caveolar-related cholesterol trafficking directly contribute to the mechanism of HD in vivo. We generated new mouse models that express mutant Huntington's protein (mhtt), but have partial or total loss of caveolin-1 (Cav1) expression. Fluorescence resonance energy transfer dequenching confirms a direct interaction between mhtt and Cav1. Mhtt-expressing neurons exhibited cholesterol accumulation and suppressed caveolar-related post-Golgi trafficking from endoplasmic reticulum/Golgi to plasma membrane. Loss or reduction of Cav1 expression in a knock-in HD mouse model rescues the cholesterol phenotype in neurons and significantly delays the onset of motor decline and development of neuronal inclusions. We propose that aberrant interaction between Cav1 and mhtt leads to altered cholesterol homeostasis and plays a direct causative role in the onset of HD pathophysiology in vivo.

From evolution to revolution: miRNAs as pharmacological targets for modulating cholesterol efflux and reverse cholesterol transport

There has been strong evolutionary pressure to ensure that an animal cell maintains levels of cholesterol within tight limits for normal function. Imbalances in cellular cholesterol levels are a major player in the development of different pathologies associated to dietary excess. Although epidemiological studies indicate that elevated levels of high-density lipoprotein (HDL)-cholesterol reduce the risk of cardiovascular disease, recent genetic evidence and pharmacological therapies to raise HDL levels do not support their beneficial effects. Cholesterol efflux as the first and probably the most important step in reverse cholesterol transport is an important biological process relevant to HDL function. Small non-coding RNAs (microRNAs), post-transcriptional control different aspects of cellular cholesterol homeostasis including cholesterol efflux. miRNA families miR-33, miR-758, miR-10b, miR-26 and miR-106b directly modulates cholesterol efflux by targeting the ATP-binding cassette transporter A1 (ABCA1). Pre-clinical studies with anti-miR therapies to inhibit some of these miRNAs have increased cellular cholesterol efflux, reverse cholesterol transport and reduce pathologies associated to dyslipidemia. Although miRNAs as therapy have benefits from existing antisense technology, different obstacles need to be solved before we incorporate such research into clinical care. Here we focus on the clinical potential of miRNAs as therapeutic target to increase cholesterol efflux and reverse cholesterol transport as a new alternative to ameliorate cholesterol-related pathologies.

Probucol and the cholesterol synthesis inhibitors simvastatin and triparanol regulate I ks channel function differently

Channels responsible for slowly activating delayed-rectifier potassium current (I(Ks)) are composed of KCNQ1 and KCNE1 subunits, and these channels play a role in the repolarization of cardiac action potentials. Recently, we showed that the antihyperlipidemic drug probucol, which induces QT prolongation, decreases the I(Ks) after 24-h treatment. In the present study, we investigated the effects of three cholesterol-lowering agents (probucol, an enhancer of cholesterol efflux; simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor; and triparanol, a 3β-hydroxysterol-▵24-reductase inhibitor) on cholesterol synthesis, the KCNQ1 current (I KCNQ1), and the I(Ks) to clarify the differences in the modes of action of these agents on the I(Ks). Probucol did not inhibit cholesterol synthesis and had no effect on I KCNQ1, while I(Ks) decreased after 24-h treatment. Simvastatin inhibited cholesterol synthesis and decreased I KCNQ1 and I(Ks). Additionally, the activation kinetics of I(Ks) became faster, compared with that of control I(Ks). Triparanol inhibited cholesterol synthesis but did not reduce I KCNQ1 and I(Ks). However, the activation kinetics of I(Ks) became faster. Our data indicated that the mechanism by which probucol inhibits I(Ks) was not mediated by the inhibition of cholesterol synthesis but depended on an interaction with the KCNQ1/KCNE1 complex. Meanwhile, the reduction in cholesterol induced by simvastatin and triparanol is one of the mechanisms that affects the kinetics of I(ks).

Insulin receptor activation through its accumulation in lipid rafts by mild electrical stress

Insulin resistance is due to the reduced cellular response to insulin in peripheral tissues. The interaction of insulin with its receptor is the first step in insulin action and thus the identified target of insulin resistance. It has been well established that defects or mutations in the insulin receptor (IR) cause insulin resistance. Therefore, an IR activator might be a novel therapeutic approach for insulin resistance. Our previous report showed that mild electrical stress (MES) enhanced the insulin-induced signaling pathway. However, the molecular mechanism of the effect of MES remains unclear. We assessed the effect of MES, which is characterized by low-intensity direct current, on insulin signaling in vitro and in vivo. Here, we showed that MES activated the insulin signaling in an insulin-independent manner and improved insulin resistance in peripheral tissues of high fat-fed mice. Moreover, we found that MES increased the localization of IR in lipid rafts and enhanced the level of phosphorylated Akt in insulin-resistant hepatic cells. Ablation of lipid rafts disrupted the effect of MES on Akt activation. Our findings indicate that MES has potential as an activator of IR in an insulin-independent manner, and might be beneficial for insulin resistance in type 2 diabetes.

Cholesterol metabolism and the pathogenesis of non-alcoholic steatohepatitis

Emerging experimental and human evidence has linked altered hepatic cholesterol homeostasis and free cholesterol (FC) accumulation to the pathogenesis of non-alcoholic steatohepatits (NASH). This review focuses on cellular mechanisms of cholesterol toxicity involved in liver injury and on alterations in cholesterol homeostasis promoting hepatic cholesterol overload in NASH. FC accumulation injures hepatocytes directly, by disrupting mitochondrial and endoplasmic reticulum (ER) membrane integrity, triggering mitochondrial oxidative injury and ER stress, and by promoting generation of toxic oxysterols, and indirectly, by inducing adipose tissue dysfunction. Accumulation of oxidized LDL particles may also activate Kupffer and hepatic stellate cells, promoting liver inflammation and fibrogenesis. Hepatic cholesterol accumulation is driven by a deeply deranged cellular cholesterol homeostasis, characterized by elevated cholesterol synthesis and uptake from circulating lipoproteins and by a reduced cholesterol excretion. Extensive dysregulation of cellular cholesterol homeostasis by nuclear transcription factors sterol regulatory binding protein (SREBP)-2, liver X-receptor (LXR)-α and farnesoid X receptor (FXR) plays a key role in hepatic cholesterol accumulation in NASH. The therapeutic implications and opportunities for normalizing cellular cholesterol homeostasis in these patients are also discussed.

Mild electrical stimulation and heat shock ameliorates progressive proteinuria and renal inflammation in mouse model of Alport syndrome

Alport syndrome is a hereditary glomerulopathy with proteinuria and nephritis caused by defects in genes encoding type IV collagen in the glomerular basement membrane. All male and most female patients develop end-stage renal disease. Effective treatment to stop or decelerate the progression of proteinuria and nephritis is still under investigation. Here we showed that combination treatment of mild electrical stress (MES) and heat stress (HS) ameliorated progressive proteinuria and renal injury in mouse model of Alport syndrome. The expressions of kidney injury marker neutrophil gelatinase-associated lipocalin and pro-inflammatory cytokines interleukin-6, tumor necrosis factor-α and interleukin-1β were suppressed by MES+HS treatment. The anti-proteinuric effect of MES+HS treatment is mediated by podocytic activation of phosphatidylinositol 3-OH kinase (PI3K)-Akt and heat shock protein 72 (Hsp72)-dependent pathways in vitro and in vivo. The anti-inflammatory effect of MES+HS was mediated by glomerular activation of c-jun NH₂-terminal kinase 1/2 (JNK1/2) and p38-dependent pathways ex vivo. Collectively, our studies show that combination treatment of MES and HS confers anti-proteinuric and anti-inflammatory effects on Alport mice likely through the activation of multiple signaling pathways including PI3K-Akt, Hsp72, JNK1/2, and p38 pathways, providing a novel candidate therapeutic strategy to decelerate the progression of patho-phenotypes in Alport syndrome.