Effective treatment of familial hypercholesterolaemia in the mouse model using adenovirus-mediated transfer of the VLDL receptor gene

Acyl-CoA thioesterase 12 suppresses YAP-mediated hepatocarcinogenesis by limiting glycerolipid biosynthesis

Cancer cells use acetate to support the higher demand for energy and lipid biosynthesis during uncontrolled cell proliferation, as well as for acetylation of regulatory proteins. Acyl-CoA thioesterase 12 (Acot12) is the enzyme that hydrolyzes acetyl-CoA to acetate in liver cytosol and is downregulated in hepatocellular carcinoma (HCC). A mechanistic role for Acot12 in hepatocarcinogenesis was assessed in mice in response to treatment with diethylnitrosamine(DEN)/carbon tetrachloride (CCl4) administration or prolonged feeding of a diet that promotes non-alcoholic steatohepatitis (NASH). Relative to controls, Acot12-/- mice exhibited accelerated liver tumor formation that was characterized by the hepatic accumulation of glycerolipids, including lysophosphatidic acid (LPA), and that was associated with reduced Hippo signaling and increased yes-associated protein (YAP)-mediated transcriptional activity. In Acot12-/- mice, restoration of hepatic Acot12 expression inhibited hepatocarcinogenesis and YAP activation, as did knockdown of hepatic YAP expression. Excess LPA produced due to deletion of Acot12 signaled through LPA receptors (LPARs) coupled to Gα12/13 subunits to suppress YAP phosphorylation, thereby promoting its nuclear localization and transcriptional activity. These findings identify a protective role for Acot12 in suppressing hepatocarcinogenesis by limiting biosynthesis of glycerolipids including LPA, which preserves Hippo signaling.

A viral biomolecular condensate coordinates assembly of progeny particles

Biomolecular condensates formed by phase separation can compartmentalize and regulate cellular processes1,2. Emerging evidence has suggested that membraneless subcellular compartments in virus-infected cells form by phase separation3-8. Although linked to several viral processes3-5,9,10, evidence that phase separation contributes functionally to the assembly of progeny particles in infected cells is lacking. Here we show that phase separation of the human adenovirus 52-kDa protein has a critical role in the coordinated assembly of infectious progeny particles. We demonstrate that the 52-kDa protein is essential for the organization of viral structural proteins into biomolecular condensates. This organization regulates viral assembly such that capsid assembly is coordinated with the provision of viral genomes needed to produce complete packaged particles. We show that this function is governed by the molecular grammar of an intrinsically disordered region of the 52-kDa protein, and that failure to form condensates or to recruit viral factors that are critical for assembly results in failed packaging and assembly of only non-infectious particles. Our findings identify essential requirements for coordinated assembly of progeny particles and demonstrate that phase separation of a viral protein is critical for production of infectious progeny during adenovirus infection.

VLDL receptor gene therapy for reducing atherogenic lipoproteins

Over the past 40 years, there has been considerable research into the management and treatment of atherogenic lipid disorders. Although the majority of treatments and management strategies for cardiovascular disease (CVD) center around targeting low-density lipoprotein cholesterol (LDL-C), there is mounting evidence for the residual CVD risk attributed to high triglyceride (TG) and lipoprotein(a) (Lp(a)) levels despite the presence of lowered LDL-C levels. Among the biological mechanisms for clearing TG-rich lipoproteins, the VLDL receptor (VLDLR) plays a key role in the trafficking and metabolism of lipoprotein particles in multiple tissues, but it is not ordinarily expressed in the liver. Since VLDLR is capable of binding and internalizing apoE-containing TG-rich lipoproteins as well as Lp(a), hepatic VLDLR expression has the potential for promoting clearance of these atherogenic particles from the circulation and managing the residual CVD risk not addressed by current lipid lowering therapies. This review provides an overview of VLDLR function and the potential for developing a genetic medicine based on liver-targeted VLDLR gene expression.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

Adenovirus-mediated ubiquitination alters protein-RNA binding and aids viral RNA processing

Viruses promote infection by hijacking the ubiquitin machinery of the host to counteract or redirect cellular processes. Adenovirus encodes two early proteins, E1B55K and E4orf6, that together co-opt a cellular ubiquitin ligase complex to overcome host defences and promote virus production. Adenovirus mutants lacking E1B55K or E4orf6 display defects in viral RNA processing and protein production, but previously identified substrates of the redirected ligase do not explain these phenotypes. Here, we used a quantitative proteomics approach to identify substrates of E1B55K/E4orf6-mediated ubiquitination that facilitate RNA processing. While all currently known cellular substrates of E1B55K and E4orf6 are degraded by the proteasome, we uncovered RNA-binding proteins as high-confidence substrates that are not decreased in overall abundance. We focused on two RNA-binding proteins, RALY and hnRNP-C, which we confirm are ubiquitinated without degradation. Knockdown of RALY and hnRNP-C increased levels of viral RNA splicing, protein abundance and progeny production during infection with E1B55K-deleted virus. Furthermore, infection with E1B55K-deleted virus resulted in an increased interaction of hnRNP-C with viral RNA and attenuation of viral RNA processing. These data suggest that viral-mediated ubiquitination of RALY and hnRNP-C relieves a restriction on viral RNA processing and reveal an unexpected role for non-degradative ubiquitination in the manipulation of cellular processes during virus infection.

Review of the scientific evolution of gene therapy for the treatment of homozygous familial hypercholesterolaemia: past, present and future perspectives

Familial hypercholesterolaemia (FH) is a devastating genetic disease that leads to extremely high cholesterol levels and severe cardiovascular disease, mainly caused by mutations in any of the main genes involved in low-density lipoprotein cholesterol (LDL-C) uptake. Among these genes, mutations in the LDL receptor (LDLR) are responsible for 80%–90% of the FH cases. The severe homozygous variety (HoFH) is not successfully treated with standard cholesterol-lowering therapies, and more aggressive strategies must be considered to mitigate the effects of this disease, such as weekly/biweekly LDL apheresis. However, development of new therapeutic approaches is needed to cure HoFH. Because HoFH is mainly due to mutations in theLDLR, this disease has been proposed as an ideal candidate for gene therapy. Several preclinical studies have proposed that the transference of functional copies of theLDLRgene reduces circulating LDL-C levels in several models of HoFH, which has led to the first clinical trials in humans. Additionally, the recent development of clustered regularly interspaced short palindromic repeat/CRISPR-associated 9 technology for genome editing has opened the door to therapies aimed at directly correcting the specific mutation in the endogenousLDLRgene. In this article, we review the genetic basis of the FH disease, paying special attention to the severe HoFH as well as the challenges in its diagnosis and clinical management. Additionally, we discuss the current therapies for this disease and the new emerging advances in gene therapy to target a definitive cure for this disease.

The Reelin Receptors Apolipoprotein E receptor 2 (ApoER2) and VLDL Receptor

Apolipoprotein E receptor 2 (ApoER2) and VLDL receptor belong to the low density lipoprotein receptor family and bind apolipoprotein E. These receptors interact with the clathrin machinery to mediate endocytosis of macromolecules but also interact with other adapter proteins to perform as signal transduction receptors. The best characterized signaling pathway in which ApoER2 and VLDL receptor (VLDLR) are involved is the Reelin pathway. This pathway plays a pivotal role in the development of laminated structures of the brain and in synaptic plasticity of the adult brain. Since Reelin and apolipoprotein E, are ligands of ApoER2 and VLDLR, these receptors are of interest with respect to Alzheimer’s disease. We will focus this review on the complex structure of ApoER2 and VLDLR and a recently characterized ligand, namely clusterin.

MLN64 induces mitochondrial dysfunction associated with increased mitochondrial cholesterol content

MLN64 is a late endosomal cholesterol-binding membrane protein that has been implicated in cholesterol transport from endosomal membranes to the plasma membrane and/or mitochondria, in toxin-induced resistance, and in mitochondrial dysfunction. Down-regulation of MLN64 in Niemann-Pick C1 deficient cells decreased mitochondrial cholesterol content, suggesting that MLN64 functions independently of NPC1. However, the role of MLN64 in the maintenance of endosomal cholesterol flow and intracellular cholesterol homeostasis remains unclear. We have previously described that hepatic MLN64 overexpression increases liver cholesterol content and induces liver damage. Here, we studied the function of MLN64 in normal and NPC1-deficient cells and we evaluated whether MLN64 overexpressing cells exhibit alterations in mitochondrial function. We used recombinant-adenovirus-mediated MLN64 gene transfer to overexpress MLN64 in mouse liver and hepatic cells; and RNA interference to down-regulate MLN64 in NPC1-deficient cells. In MLN64-overexpressing cells, we found increased mitochondrial cholesterol content and decreased glutathione (GSH) levels and ATPase activity. Furthermore, we found decreased mitochondrial membrane potential and mitochondrial fragmentation and increased mitochondrial superoxide levels in MLN64-overexpressing cells and in NPC1-deficient cells. Consequently, MLN64 expression was increased in NPC1-deficient cells and reduction of its expression restore mitochondrial membrane potential and mitochondrial superoxide levels. Our findings suggest that MLN64 overexpression induces an increase in mitochondrial cholesterol content and consequently a decrease in mitochondrial GSH content leading to mitochondrial dysfunction. In addition, we demonstrate that MLN64 expression is increased in NPC cells and plays a key role in cholesterol transport into the mitochondria.

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MLN64 overexpression induces an increase in mitochondrial cholesterol content.

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MLN64 protein expression is increased in NPC cells.

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Down-regulation of MLN64 restores mitochondrial membrane potential and superoxide levels in NPC cells.

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MLN64 overexpression produces mitochondrial dysfunction.

Carboxy-terminal deletion of the HDL receptor reduces receptor levels in liver and steroidogenic tissues, induces hypercholesterolemia, and causes fatal heart disease

The HDL receptor SR-BI mediates the transfer of cholesteryl esters from HDL to cells and controls HDL abundance and structure. Depending on the genetic background, loss of SR-BI causes hypercholesterolemia, anemia, reticulocytosis, splenomegaly, thrombocytopenia, female infertility, and fatal coronary heart disease (CHD). The carboxy terminus of SR-BI (⁵⁰⁵QEAKL⁵⁰⁹) must bind to the cytoplasmic adaptor PDZK1 for normal hepatic-but not steroidogenic cell-expression of SR-BI protein. To determine whether SR-BI's carboxy terminus is also required for normal protein levels in steroidogenic cells, we introduced into SR-BI's gene a ⁵⁰⁷Ala/STOP mutation that produces a truncated receptor (SR-BIΔCT). As expected, the dramatic reduction of hepatic receptor protein in SR-BIΔCT mice was similar to that in PDZK1 knockout (KO) mice. Unlike SR-BI KO females, SR-BIΔCT females were fertile. The severity of SR-BIΔCT mice's hypercholesterolemia was intermediate between those of SR-BI KO and PDZK1 KO mice. Substantially reduced levels of the receptor in adrenal cortical cells, ovarian cells, and testicular Leydig cells in SR-BIΔCT mice suggested that steroidogenic cells have an adaptor(s) functionally analogous to hepatic PDZK1. When SR-BIΔCT mice were crossed with apolipoprotein E KO mice (SR-BIΔCT/apoE KO), pathologies including hypercholesterolemia, macrocytic anemia, hepatic and splenic extramedullary hematopoiesis, massive splenomegaly, reticulocytosis, thrombocytopenia, and rapid-onset and fatal occlusive coronary arterial atherosclerosis and CHD (median age of death: 9 wk) were observed. These results provide new insights into the control of SR-BI in steroidogenic cells and establish SR-BIΔCT/apoE KO mice as a new animal model for the study of CHD.

A core viral protein binds host nucleosomes to sequester immune danger signals

Viral proteins mimic host protein structure and function to redirect cellular processes and subvert innate defenses. Small basic proteins compact and regulate both viral and cellular DNA genomes. Nucleosomes are the repeating units of cellular chromatin and play an important part in innate immune responses. Viral-encoded core basic proteins compact viral genomes, but their impact on host chromatin structure and function remains unexplored. Adenoviruses encode a highly basic protein called protein VII that resembles cellular histones. Although protein VII binds viral DNA and is incorporated with viral genomes into virus particles, it is unknown whether protein VII affects cellular chromatin. Here we show that protein VII alters cellular chromatin, leading us to hypothesize that this has an impact on antiviral responses during adenovirus infection in human cells. We find that protein VII forms complexes with nucleosomes and limits DNA accessibility. We identified post-translational modifications on protein VII that are responsible for chromatin localization. Furthermore, proteomic analysis demonstrated that protein VII is sufficient to alter the protein composition of host chromatin. We found that protein VII is necessary and sufficient for retention in the chromatin of members of the high-mobility-group protein B family (HMGB1, HMGB2 and HMGB3). HMGB1 is actively released in response to inflammatory stimuli and functions as a danger signal to activate immune responses. We showed that protein VII can directly bind HMGB1 in vitro and further demonstrated that protein VII expression in mouse lungs is sufficient to decrease inflammation-induced HMGB1 content and neutrophil recruitment in the bronchoalveolar lavage fluid. Together, our in vitro and in vivo results show that protein VII sequesters HMGB1 and can prevent its release. This study uncovers a viral strategy in which nucleosome binding is exploited to control extracellular immune signaling.

Sleeping Beauty Transposon Vectors in Liver-directed Gene Delivery of LDLR and VLDLR for Gene Therapy of Familial Hypercholesterolemia

Plasmid-based Sleeping Beauty (SB) transposon vectors were developed and used to deliver genes for low-density lipoprotein and very-low-density lipoprotein receptors (LDLR and VLDLR, respectively) or lacZ reporter into liver of an LDLR-deficient mouse model of familial hypercholesterolemia (FH). SB transposase, SB100x, was used to integrate the therapeutic transposons into mice livers for evaluating the feasibility of the vectors in reducing high blood cholesterol and the progression of atherosclerosis. Hydrodynamic gene delivery of transposon-VLDLR into the livers of the mice resulted in initial 17-19% reductions in plasma cholesterol, and at the later time points, in a significant stabilization of the cholesterol level for the 6.5-month duration of the study compared to the control mice. Transposon-LDLR-treated animals also demonstrated a trend of stabilization in the cholesterol levels in the long term. Vector-treated mice had slightly less lipid accumulation in the liver and reduced aortic atherosclerosis. Clinical chemistry and histological analyses revealed normal liver function and morphology comparable to that of the controls during the follow-up with no safety issues regarding the vector type, transgenes, or the gene transfer method. The study demonstrates the safety and potential benefits of the SB transposon vectors in the treatment of FH.

Human adenovirus 52 uses sialic acid-containing glycoproteins and the coxsackie and adenovirus receptor for binding to target cells

Most adenoviruses attach to host cells by means of the protruding fiber protein that binds to host cells via the coxsackievirus and adenovirus receptor (CAR) protein. Human adenovirus type 52 (HAdV-52) is one of only three gastroenteritis-causing HAdVs that are equipped with two different fiber proteins, one long and one short. Here we show, by means of virion-cell binding and infection experiments, that HAdV-52 can also attach to host cells via CAR, but most of the binding depends on sialylated glycoproteins. Glycan microarray, flow cytometry, surface plasmon resonance and ELISA analyses reveal that the terminal knob domain of the long fiber (52LFK) binds to CAR, and the knob domain of the short fiber (52SFK) binds to sialylated glycoproteins. X-ray crystallographic analysis of 52SFK in complex with 2-O-methylated sialic acid combined with functional studies of knob mutants revealed a new sialic acid binding site compared to other, known adenovirus:glycan interactions. Our findings shed light on adenovirus biology and may help to improve targeting of adenovirus-based vectors for gene therapy.

ATP Synthase β-Chain Overexpression in SR-BI Knockout Mice Increases HDL Uptake and Reduces Plasma HDL Level

HDL cholesterol is known to be inversely correlated with cardiovascular disease due to its diverse antiatherogenic functions. SR-BI mediates the selective uptake of HDL-C. SR-BI knockout diminishes but does not completely block the transport of HDL; other receptors may be involved. Ectopic ATP synthase β-chain in hepatocytes has been previously characterized as an apoA-I receptor, triggering HDL internalization. This study was undertaken to identify the overexpression of ectopic ATP synthase β-chain on DIL-HDL uptake in primary hepatocytes in vitro and on plasma HDL levels in SR-BI knockout mice. Human ATP synthase β-chain cDNA was delivered to the mouse liver by adenovirus and GFP adenovirus as control. The adenovirus-mediated overexpression of β-chain was identified at both mRNA and protein levels on mice liver and validated by its increasing of DiL-HDL uptake in primary hepatocytes. In response to hepatic overexpression of β-chain, plasma HDL-C levels and cholesterol were reduced in SR-BI knockout mice, compared with the control. The present data suggest that ATP synthase β-chain can serve as the endocytic receptor of HDL, and its overexpression can reduce plasma HDL-C.

Comparative reactivity of remnant-like lipoprotein particles (RLP) and low-density lipoprotein (LDL) to LDL receptor and VLDL receptor: effect of a high-dose statin on VLDL receptor expression

BACKGROUND

Comparison of the reactivity of remnant-like lipoprotein particles (RLP) and LDL particles to LDL receptor and VLDL receptor has not been investigated.

METHODS

LDL receptor- or VLDL receptor-transfected ldlA-7, HepG2 and L6 cells were used. Human LDL and rabbit β-VLDL were isolated by ultracentrifugation. Human RLP was isolated using an immunoaffinity mixed gel. The effect of statin on lipoprotein receptors was examined.

RESULTS

Both LDL receptor and VLDL receptor recognized RLP. In LDL receptor transfectants, RLP, β-VLDL and LDL all bound to LDL receptor. Cold RLP competed efficiently with DiI-β-VLDL; however, cold LDL competed weakly. In VLDL receptor transfectants, RLP and β-VLDL bound to VLDL receptor, but not LDL. RLP bound to VLDL receptor with higher affinity than β-VLDL because of higher apolipoprotein E in RLP. LDL receptor expression was induced in HepG2 by the low concentration of statin while VLDL receptor expression was induced in L6 myoblasts at higher concentration.

CONCLUSIONS

RLP are bound to hepatic LDL receptor more efficiently than LDL, which may explain the mechanism by which statins prevent cardiovascular risk by primarily reducing plasma RLP rather than by reducing LDL. Additionally, a high-dose of statins also may reduce plasma RLP through muscular VLDL receptor.

RNAi-mediated knockdown of HMG CoA reductase enhances gene expression from physiologically regulated low-density lipoprotein receptor therapeutic vectors in vivo

The development of novel strategies to enhance gene expression from therapeutic vectors may prove advantageous for complementation gene therapy. This applies to therapeutic expression of the low-density lipoprotein receptor (LDLR) gene to treat familial hypercholesterolaemia (FH), where appropriate gene regulation could enhance therapeutic effect. We have previously reported that LDLR genomic DNA expression vectors can be regulated in vivo by pravastatin. In the current study, we investigated whether targeted knockdown of the mevalonate pathway in conjunction with LDLR delivery would lead to enhanced LDLR transgene expression and improved phenotype recovery. We demonstrated here that knockdown of HMG CoA reductase (HMGCR) by up to 70% using small interfering RNAs (siRNAs) led to a significant increase in binding and internalisation of LDL particles in vitro in mouse and human cells. In vivo co-injection of LDLR promoter luciferase expression plasmids with siRNAs or microRNA (miRNA) expression vectors targeting mouse Hmgcr led to at least a 10-fold increase in luciferase expression. Injection of Ldlr(-/-) mice with pLDLR-LDLR expression plasmids led to a significant reduction in plasmid LDL cholesterol, which was further enhanced by co-injection with miRNA expression vectors targeted to mouse Hmgcr. Our data suggest that targeted knockdown of HMGCR may enhance gene therapy outcomes for FH.

Constitutive androstane receptor activation decreases plasma apolipoprotein B-containing lipoproteins and atherosclerosis in low-density lipoprotein receptor-deficient mice

OBJECTIVE

The goal of this study was to determine the impact of the nuclear receptor constitutive androstane receptor (CAR) on lipoprotein metabolism and atherosclerosis in hyperlipidemic mice.

METHODS AND RESULTS

Low-density lipoprotein receptor-deficient (Ldlr(-/-)) and apolipoprotein E-deficient (ApoE(-/-)) mice fed a Western-type diet were treated weekly with the Car agonist 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) or the vehicle only for 8 weeks. In Ldlr(-/-) mice, treatment with TCPOBOP induced a decrease in plasma triglyceride and intermediate-density lipoprotein/low-density lipoprotein cholesterol levels (≈30% decrease in both cases after 2 months, P<0.01). These mice also showed a significant reduction in the production of very-low-density lipoproteins associated with a decrease in hepatic triglyceride content and the repression of several genes involved in lipogenesis. TCPOBOP treatment also induced a marked increase in the very-low-density lipoprotein receptor in the liver, which probably contributed to the decrease in intermediate-density lipoprotein/low-density lipoprotein levels. Atherosclerotic lesions in the aortic valves of TCPOBOP-treated Ldlr(-/-) mice were also reduced (-60%, P<0.001). In ApoE(-/-) mice, which lack the physiological apoE ligand for the very-low-density lipoprotein receptor, the effect of TCPOBOP on plasma cholesterol levels and the development of atherosclerotic lesions was markedly attenuated.

CONCLUSIONS

CAR is a potential target in the prevention and treatment of hypercholesterolemia and atherosclerosis.

LDLR-Gene therapy for familial hypercholesterolaemia: problems, progress, and perspectives

Coronary artery diseases (CAD) inflict a heavy economical and social burden on most populations and contribute significantly to their morbidity and mortality rates. Low-density lipoprotein receptor (LDLR) associated familial hypercholesterolemia (FH) is the most frequent Mendelian disorder and is a major risk factor for the development of CAD. To date there is no cure for FH. The primary goal of clinical management is to control hypercholesterolaemia in order to decrease the risk of atherosclerosis and to prevent CAD. Permanent phenotypic correction with single administration of a gene therapeutic vector is a goal still needing to be achieved. The first ex vivo clinical trial of gene therapy in FH was conducted nearly 18 years ago. Patients who had inherited LDLR gene mutations were subjected to an aggressive surgical intervention involving partial hepatectomy to obtain the patient's own hepatocytes for ex vivo gene transfer with a replication deficient LDLR-retroviral vector. After successful re-infusion of transduced cells through a catheter placed in the inferior mesenteric vein at the time of liver resection, only low-level expression of the transferred LDLR gene was observed in the five patients enrolled in the trial. In contrast, full reversal of hypercholesterolaemia was later demonstrated in in vivo preclinical studies using LDLR-adenovirus mediated gene transfer. However, the high efficiency of cell division independent gene transfer by adenovirus vectors is limited by their short-term persistence due to episomal maintenance and the cytotoxicity of these highly immunogenic viruses. Novel long-term persisting vectors derived from adeno-associated viruses and lentiviruses, are now available and investigations are underway to determine their safety and efficiency in preparation for clinical application for a variety of diseases. Several novel non-viral based therapies have also been developed recently to lower LDL-C serum levels in FH patients. This article reviews the progress made in the 18 years since the first clinical trial for gene therapy of FH, with emphasis on the development, design, performance and limitations of viral based gene transfer vectors used in studies to ameliorate the effects of LDLR deficiency.

IL-22 induces an acute-phase response

IL-22 is made by a unique set of innate and adaptive immune cells, including the recently identified noncytolytic NK, lymphoid tissue-inducer, Th17, and Th22 cells. The direct effects of IL-22 are restricted to nonhematopoietic cells, its receptor expressed on the surface of only epithelial cells and some fibroblasts in various organs, including parenchymal tissue of the gut, lung, skin, and liver. Despite this cellular restriction on IL-22 activity, we demonstrate that IL-22 induces effects on systemic biochemical, cellular, and physiological parameters. By utilizing adenoviral-mediated delivery of IL-22 and systemic administration of IL-22 protein, we observed that IL-22 modulates factors involved in coagulation, including fibrinogen levels and platelet numbers, and cellular constituents of blood, such as neutrophil and RBC counts. Furthermore, we observed that IL-22 induces thymic atrophy, body weight loss, and renal proximal tubule metabolic activity. These cellular and physiological parameters are indicative of a systemic inflammatory state. We observed that IL-22 induces biochemical changes in the liver including induction of fibrinogen, CXCL1, and serum amyloid A that likely contribute to the reported cellular and physiological effects of IL-22. Based on these findings, we propose that downstream of its expression and impact in local tissue inflammation, circulating IL-22 can further induce changes in systemic physiology that is indicative of an acute-phase response.

Gene therapy in a humanized mouse model of familial hypercholesterolemia leads to marked regression of atherosclerosis

Background

Familial hypercholesterolemia (FH) is an autosomal codominant disorder caused by mutations in the low-density lipoprotein receptor (LDLR) gene. Homozygous FH patients (hoFH) have severe hypercholesterolemia leading to life threatening atherosclerosis in childhood and adolescence. Mice with germ line interruptions in the Ldlr and Apobec1 genes (Ldlr^−/−Apobec1^−/−) simulate metabolic and clinical aspects of hoFH, including atherogenesis on a chow diet.

Methods/Principal Findings

In this study, vectors based on adeno-associated virus 8 (AAV8) were used to deliver the gene for mouse Ldlr (mLDLR) to the livers of Ldlr^−/−Apobec1^−/− mice. A single intravenous injection of AAV8.mLDLR was found to significantly reduce plasma cholesterol and non-HDL cholesterol levels in chow-fed animals at doses as low as 3×10⁹ genome copies/mouse. Whereas Ldlr^−/−Apobec1^−/− mice fed a western-type diet and injected with a control AAV8.null vector experienced a further 65% progression in atherosclerosis over 2 months compared with baseline mice, Ldlr^−/−Apobec1^−/− mice treated with AAV8.mLDLR realized an 87% regression of atherosclerotic lesions after 3 months compared to baseline mice. Immunohistochemical analyses revealed a substantial remodeling of atherosclerotic lesions.

Conclusions/Significance

Collectively, the results presented herein suggest that AAV8-based gene therapy for FH may be feasible and support further development of this approach. The pre-clinical data from these studies will enable for the effective translation of gene therapy into the clinic for treatment of FH.

Gene therapy for dyslipidemia: a review of gene replacement and gene inhibition strategies

Despite numerous technological and pharmacological advances and more detailed knowledge of molecular etiologies, cardiovascular diseases remain the leading cause of morbidity and mortality worldwide claiming over 17 million lives a year. Abnormalities in the synthesis, processing and catabolism of lipoprotein particles can result in severe hypercholesterolemia, hypertriglyceridemia or low HDL-C. Although a plethora of antidyslipidemic pharmacological agents are available, these drugs are relatively ineffective in many patients with Mendelian lipid disorders, indicating the need for new and more effective interventions. In vivo somatic gene therapy is one such intervention. This article summarizes current strategies being pursued for the development of clinical gene therapy for dyslipidemias that cannot effectively be treated with existing drugs.

Long-term physiologically regulated expression of the low-density lipoprotein receptor in vivo using genomic DNA mini-gene constructs

Familial hypercholesterolemia (FH) is a condition caused by mutations in the low-density lipoprotein receptor (LDLR) gene. Expression of LDLR is highly regulated and excess receptor expression is cytotoxic. To incorporate essential gene regulation into a gene therapy vector for FH, we generated vectors in which the expression of therapeutic human LDLR gene, or luciferase reporter gene, is driven by 10 kb of human LDLR genomic DNA encompassing the promoter region including elements essential for physiologically regulated expression. Using luciferase expression and specific LDL binding and internalization assays, we have shown in vitro that the genomic promoter element confers long-term, physiologically regulated gene expression and complementation of receptor deficiency in culture for 240 cell-generations. This was demonstrated in the presence of sterols or statins, modifiers of LDLR promoter activity. In vivo, we demonstrate efficient liver-specific delivery and expression of luciferase following hydrodynamic tail-vein injection and confirm that expression from the LDLR promoter element is sensitive to statin administration. We also demonstrate long-term LDLR expression from the 10-kb promoter element up to 9 months following delivery. The vector system that we describe provides the efficient delivery, long-term expression, and physiological regulation required for a successful gene therapy intervention for FH.

A neuronal VLDLR variant lacking the third complement-type repeat exhibits high capacity binding of apoE containing lipoproteins

Very-low-density lipoprotein receptor (VLDLR) is a multi ligand apolipoprotein E (apoE) receptor and is involved in brain development through Reelin signaling. Different forms of VLDLR can be generated by alternative splicing. VLDLR-I contains all exons. VLDLR-II lacks an O-linked sugar domain encoded by exon 16, while VLDLR-III lacks the third complement-type repeat in the ligand binding domain encoded by exon 4. We quantitatively compared lipoprotein binding to human VLDLR variants and analyzed their mRNA expression in both human cerebellum and mouse brain. VLDLR-III exhibited the highest capacity in binding to apoE enriched beta-VLDL in vitro and was more effective in removing apoE containing lipoproteins from the circulation than other variants in vivo. In human cerebellum, the major species was VLDLR-II, while the second most abundant species was a newly identified VLDLR-IV which lacks both exon 4 and 16. VLDLR-I was present at low levels. In adult mice, exon 4 skipping varied between 30 and 47% in different brain regions, while exon 16 skipping ranged by 51-76%. Significantly higher levels of VLDLR proteins were found in mouse cerebellum and cerebral cortex than other regions. The deletions of exon 4 and exon 16 frequently occurred in primary neurons, indicating that newly identified variant VLDLR-IV is abundant in neurons. In contrast, VLDLR mRNA lacking exon 4 was not detectable in primary astrocytes. Such cell type-specific splicing patterns were found in both mouse cerebellum and cerebral cortex. These results suggest that a VLDLR variant lacking the third complement-type repeat is generated by neuron-specific alternative splicing. Such differential splicing may result in different lipid uptake in neurons and astrocytes.

Gene delivery to the liver

Viral gene transfer to the liver has proven extremely effective in animal models and is currently being evaluated in clinical trials for a variety of metabolic disorders. In rodents, a single tail vein injection of an adenoviral vector can transduce most hepatocytes in vivo. This provides a convenient model for assessing vector design as well as for evaluating the effects of specific transgenes in genetic mouse models of human disease. Protocols for optimized in vivo hepatic gene transfer are described.

Adenoviral low density lipoprotein receptor attenuates progression of atherosclerosis and decreases tissue cholesterol levels in a murine model of familial hypercholesterolemia

Familial hypercholesterolemia is an autosomal codominant disease characterized by high concentrations of pro-atherogenic lipoproteins and premature atherosclerosis secondary to low density lipoprotein receptor (LDLr) deficiency. In the current study, the effects of gene transfer with 5 x 10(10) particles of E1E3E4-deleted adenoviral vectors expressing the LDLr (AdLDLr) or VLDLr (AdVLDLr) under control of the hepatocyte-specific human alpha(1)-antitrypsin promoter and 4 copies of the human apo E enhancer in C57BL/6 LDLr(-/-) mice were investigated. Evaluation was performed in both sexes and in mice fed either standard chow or an atherogenic diet containing 0.2% cholesterol and 10% coconut oil. Compared to control mice, AdLDLr and AdVLDLr persistently decreased plasma non-HDL cholesterol in both sexes and on both diets. Six months after LDLr gene transfer in mice fed the atherogenic diet, average intimal area was 2.5-fold (p<0.01) and 3.2-fold (p<0.001) lower in male and female mice, respectively, compared to controls. In mice fed standard chow, intimal area was reduced 22-fold (p<0.001) and 21-fold (p<0.001) after LDLr gene transfer in male and female mice, respectively. We show that non-HDL lipoproteins are more atherogenic in female mice, independent of sex differences of plasma HDL cholesterol levels, and that saturated fat does not have an effect on atherosclerosis independent of plasma cholesterol levels. Finally, quantification of tissue cholesterol levels indicates that AdLDLr does not induce cholesterol accumulation in the liver and reduces cholesterol content in the myocardium, quadriceps muscle and kidney. In conclusion, hepatocyte-specific LDLr gene transfer significantly improves cholesterol homeostasis in LDLr(-/-) mice.

Delivery and long-term expression of a 135 kb LDLR genomic DNA locus in vivo by hydrodynamic tail vein injection

BACKGROUND

The delivery of a complete genomic DNA locus in vivo may prove advantageous for complementation gene therapy, especially when physiological regulation of gene expression is desirable. Hydrodynamic tail vein injection has been shown to be a highly efficient means of non-viral delivery of plasmid DNA to the liver. Here, we apply hydrodynamic tail vein injection to deliver and express large genomic DNA inserts > 100 kb in vivo.

METHODS

Firstly, a size series (12-172 kb) of bacterial artificial chromosome (BAC) plasmids, carrying human genomic DNA inserts, episomal retention elements, and the enhanced green fluorescent protein (EGFP) reporter gene, was delivered to mice by hydrodynamic tail vein injection. Secondly, an episomal BAC vector carrying the whole genomic DNA locus of the human low-density lipoprotein receptor (LDLR) gene, and an expression cassette for the LacZ reporter gene, was delivered by the same method.

RESULTS

We show that the efficiency of delivery is independent of vector size, when an equal number of plasmid molecules are used. We also show, by LacZ reporter gene analysis, that BAC delivery within the liver is widespread. Finally, BAC-end PCR, RT-PCR and immunohistochemistry demonstrate plasmid retention and long-term expression (4 months) of human LDLR in transfected hepatocytes.

CONCLUSION

This is the first demonstration of somatic delivery and long-term expression of a genomic DNA transgene > 100 kb in vivo and shows that hydrodynamic tail vein injection can be used to deliver and express large genomic DNA transgenes in the liver.

Overexpression of the cholesterol-binding protein MLN64 induces liver damage in the mouse

AIM: To examine the in vivo phenotype associated with hepatic metastatic lymph node 64 (MLN64) over-expression.

METHODS: Recombinant-adenovirus-mediated MLN64 gene transfer was used to overexpress MLN64 in the livers of C57BL/6 mice. We measured the effects of MLN64 overexpression on hepatic cholesterol content, bile flow, biliary lipid secretion and apoptosis markers. For in vitro studies cultured CHO cells with transient MLN64 overexpression were utilized and apoptosis by TUNEL assay was measured.

RESULTS: Livers from Ad.MLN64-infected mice exhibited early onset of liver damage and apoptosis. This response correlated with increases in liver cholesterol content and biliary bile acid concentration, and impaired bile flow. We investigated whether liver MLN64 expression could be modulated in a murine model of hepatic injury. We found increased hepatic MLN64 mRNA and protein levels in mice with chenodeoxycholic acid-induced liver damage. In addition, cultured CHO cells with transient MLN64 overexpression showed increased apoptosis.

CONCLUSION: In summary, hepatic MLN64 over-expression induced damage and apoptosis in murine livers and altered cholesterol metabolism. Further studies are required to elucidate the relevance of these findings under physiologic and disease conditions.

Modulation of lipoprotein receptor functions by intracellular adaptor proteins

Members of the low density lipoprotein (LDL) receptor gene family are critically involved in a wide range of physiological processes including lipid and vitamin homeostasis, cellular migration, neurodevelopment, and synaptic plasticity, to name a few. Lipoprotein receptors exert these diverse biological functions by acting as cellular uptake receptors or by inducing intracellular signaling cascades. It was discovered that a short sequence in the intracellular region of all lipoprotein receptors, Asn-Pro-X-Tyr (NPXY) is important for mediating either endocytosis or signal transduction events, and that this motif serves as a binding site for phosphotyrosine-binding (PTB) domain containing scaffold proteins. These molecular adaptors connect the transmembrane receptors with the endocytosis machinery and regulate cellular trafficking, or function as assembly sites for dynamic multi-protein signaling complexes. Whereas the LDL receptor represents the archetype of an endocytic lipoprotein receptor, the structurally closely related apolipoprotein E receptor 2 (apoER2) and very low density lipoprotein (VLDL) receptor activate a kinase-dependent intracellular signaling cascade after binding to the neuronal signaling molecule Reelin. This review focuses on two related PTB domain containing adaptor proteins that mediate these divergent lipoprotein receptor responses, ARH (autosomal recessive hypercholesterolemia protein) and Dab1 (disabled-1), and discusses the structural and molecular basis of this different behaviour.

Sustained phenotypic correction in a mouse model of hypoalphalipoproteinemia with a helper-dependent adenovirus vector

We examined the efficacy and host response to the adenovirus (Ad)-mediated delivery of human apolipoprotein A-I (APOA1) gene to the liver of APOA1(-/-) mice. Administration of a first-generation vector (FGAd-AI) resulted in a transient appearance of APOA1 in plasma and induced an anti-APOA1 antibody titer, whereas treatment with a helper-dependent vector (HDAd-AI) resulted in sustained APOA1 expression without inducing an antibody titer. With these results, we studied the effects of FGAd vectors on APOAI expression by HDAd-AI vector. Co-treatment with an FGAd vector inhibited HDAd-AI- mediated APOA1 expression independent of transgene cassettes, but only FGAd-AI induced a humoral response. Furthermore, APOA1 mRNA levels in mice co-treated with FGAd vectors were much lower than those expected from the vector copy number, suggesting that DNA of FGAd vectors interferes with the HDAd-AI vector's APOA1 promoter. A single treatment with an HDAd-AI vector produced a supraphysiological plasma APOA1 level that gradually declined to about half the normal human level over the course of 2 years, associated with a plasma cholesterol level that is persistently higher than that in controls. This investigation provides the proof of principle that liver-directed HDAd gene delivery is effective for the long-term phenotypic correction of monogenic hypoalphalipoproteinemia.

Effects of hepatic expression of the high-density lipoprotein receptor SR-BI on lipoprotein metabolism and female fertility

The etiology of human female infertility is often uncertain. The sterility of high-density lipoprotein (HDL) receptor-negative (SR-BI(-/-)) female mice suggests a link between female infertility and abnormal lipoprotein metabolism. SR-BI(-/-) mice exhibit elevated plasma total cholesterol [with normal-sized and abnormally large HDL and high unesterified to total plasma cholesterol (UC:TC) ratio]. We explored the influence of hepatic SR-BI on female fertility by inducing hepatic SR-BI expression in SR-BI(-/-) animals by adenovirus transduction or stable transgenesis. For transgenes, we used both wild-type SR-BI and a double-point mutant, Q402R/Q418R (SR-BI-RR), which is unable to bind to and mediate lipid transfer from wild-type HDL normally, but retains virtually normal lipid transport activities with low-density lipoprotein. Essentially wild-type levels of hepatic SR-BI expression in SR-BI(-/-) mice restored to nearly normal the HDL size distribution and plasma UC:TC ratio, whereas approximately 7- to 40-fold overexpression dramatically lowered plasma TC and increased biliary cholesterol secretion. In contrast, SR-BI-RR overexpression had little effect on SR-BI(+/+) mice, but in SR-BI(-/-) mice, it substantially reduced levels of abnormally large HDL and normalized the UC:TC ratio. In all cases, hepatic transgenic expression restored female fertility. Overexpression in SR-BI(-/-) mice of lecithin:cholesterol acyl transferase, which esterifies plasma HDL cholesterol, did not normalize the UC:TC ratio, probably because the abnormal HDL was a poor substrate, and did not restore fertility. Thus, hepatic SR-BI-mediated lipoprotein metabolism influences murine female fertility, raising the possibility that dyslipidemia might contribute to human female infertility and that targeting lipoprotein metabolism might complement current assisted reproductive technologies.

Gene therapy for lipoprotein disorders

Existing approaches to the treatment of refractory hypercholesterolaemia, severe hypertriglyceridaemia, low levels of high-density lipoprotein cholesterol and certain inherited disorders of intracellular lipid metabolism are ineffective in a substantial number of patients. Somatic gene therapy is considered to be a potential approach to the therapy of several of these lipid disorders. In many cases preclinical proof-of-principle studies have already been performed, and in one (homozygous familial hypercholesterolaemia) a clinical trial has been conducted. Other clinical gene therapy trials for dyslipidaemia are likely to be initiated within the next several years.

MR and fluorescent imaging of low-density lipoprotein receptors

RATIONALE AND OBJECTIVES

Over-expression of low-density lipoprotein receptors (LDLRs) occurs in many types of malignancies and is related to the requirement for lipids for rapid proliferation of the tumors. On the other hand, LDLRs that are unable to bind LDL are found on hepatocytes of patients with familial hypercholesterolemia (FH), a genetic disease that leads to premature atherosclerosis and death. The highly selective binding of LDL to LDLR makes these particles ideal carriers of therapeutic and diagnostic contrast agents into the targeted cells. The objectives of this paper are to examine whether a prototype contrast agent (PTIR267) with dual detection properties is suitable for labeling of LDL particles for in vivo detection of LDLR by magnetic resonance imaging (MRI) and for in vitro monitoring of cellular localization by confocal fluorescence microscopy.

MATERIALS AND METHODS

PTIR267 is a lipophilic GdDTPA derivative conjugated to a fluorescent dye. The conjugated dye molecule makes the probe sufficiently water soluble to allow labeling of LDL by a brief incubation of LDL with PTIR267 dissolved in PBS at 37 degrees C (mole ratio LDL: PTIR267 = 0.09:1). The molar relaxivity of PTIR267 in saline is 26 mM(-1)s(-1). Specific LDLR-mediated uptake of PTIR267-labeled LDL was demonstrated in vitro by confocal fluorescence imaging of B16 melanoma cells using confocal fluorescence imaging. In vivo uptake of PTIR267-labeled LDL by a subcutaneously implanted B16 melanoma in mice leads to 30% decrease in longitudinal relaxation time (T(1)) in the tumor. In vivo uptake of PTIR267-labeled LDL leads to 70% decrease in T(1) in a normal C57BL/6 mouse liver; however, in the liver of LDL receptor gene knockout (LDLr-/-) mice with C57BL/6 background, only 12% decrease in T(1) is observed.

CONCLUSIONS

The dual fluorescence and MR imaging properties of PTIR267, combined with the ease of LDL labeling, suggest that it will be a useful tool for optimization of LDLR-targeted cancer diagnosis or therapy and for monitoring the efficacy of gene therapy of FH.

Low-density lipoprotein receptor gene therapy using helper-dependent adenovirus produces long-term protection against atherosclerosis in a mouse model of familial hypercholesterolemia

We tested the efficacy of low-density lipoprotein receptor (LDLR) therapy using helper-dependent adenovirus (HD-Ad), comparing it with that of very low-density lipoprotein receptor (VLDLR), an LDLR homolog. We treated high cholesterol diet fed LDLR-/- mice with a single intravenous injection of HD-Ad expressing monkey LDLR (1.5 x 10(13) or 5 x 10(12) VP/kg) or VLDLR. Throughout the 24-week experiment, plasma cholesterol of LDLR-treated mice was lower than that of VLDLR-treated mice, which was in turn lower than that of PBS-treated mice. Anti-LDLR antibodies developed in 2/10 mice treated with high-dose HD-Ad-LDLR but in none (0/14) of the other treatment groups. HD-Ad-treated mice displayed significant retardation of atherosclerotic lesion progression. We next tested the long-term efficacy of low-dose HD-Ad-LDLR injected into 12-week-old LDLR-/- mice. After 60 weeks, atherosclerosis lesions covered approximately 50% of the surface of aortas of control mice, whereas aortas of treated mice were essentially lesion-free. The lipid lowering effect of HD-Ad-LDLR lasted at least 108 weeks (>2 years) when all control mice had died. In addition to retarding lesion progression, treatment caused lesion remodeling from a vulnerable-looking to a more stable-appearing phenotype. In conclusion, HD-Ad-mediated LDLR gene therapy is effective in conferring long-term protection against atherosclerosis in a mouse model of familial hypercholesterolemia.

Strain-specific rate of shutdown of CMV enhancer activity in murine liver confirmed by use of persistent [E1−, E2b−] adenoviral vectors

The systemic delivery of [E1(-)] adenoviral (Ad) vectors encoding a transgene results in efficient viral uptake and abundant transgene expression in the liver. However, [E1(-)]Ad vector persistence is transient due to cytotoxic T lymphocyte (CTL)-mediated loss of the Ad-infected cells. Our laboratory has previously demonstrated that additional modifications to the [E1(-)]Ad vector genome, by deletion of the Ad E2b genes, significantly decreased virus-genome-derived gene expression and simultaneously improved the long-term performance of the resultant [E1(-), E2b(-)]Ad vector. In this study, we confirmed that [E1(-), E2b(-)]Ad vector genomes could persist equally well in C57Bl/6 or Balb/c mouse hepatocytes. Despite vector genome persistence, we observed a strain-dependent variability in the duration of CMV enhancer/promoter-driven transgene expression in the liver. While Balb/c mice rapidly shut down [E1(-), E2b(-)]Ad-derived transgene expression, C57Bl/6 mice allowed for prolonged transgene expression. This occurred even when both strains were crossed into a severe combined immune-deficient background, demonstrating that host adaptive immune responses are not responsible for the phenomenon. Furthermore, differential methylation of the CMV enhancer/promoter was also not demonstrated in either strain of mouse, eliminating this mechanism as causative. Thus, alternative mechanisms for this phenomenon are discussed.

Low-Density Lipoprotein (LDL) Receptor/Transferrin Fusion Protein:In VivoProduction and Functional Evaluation as a Potential Therapeutic Tool for Lowering Plasma LDL Cholesterol

A soluble form of human low-density lipoprotein receptor (LDL-R) fused in frame with rabbit transferrin (LDL-Rs(hu)/Tf(rab)) is assessed in vivo as a therapeutic tool for lowering plasma LDL cholesterol. The cDNA encoding LDL-Rs(hu)/Tf(rab) is expressed in mice, using a hydrodynamics-based gene transfer procedure. The transgene is transcribed in the liver of transduced animals and the corresponding protein is secreted into the bloodstream. Circulating LDL-Rs(hu)/Tf(rab) binds LDL specifically, thus indicating that it is correctly processed through the cellular compartments in vivo. More importantly, the expression of LDL-Rs(hu)/Tf(rab) allows the removal of injected human (125)I-labeled LDL ((123)I-LDL) from the bloodstream of transduced CD1 mice, which show faster LDL plasma clearance, anticipating by approximately 90 min the same clearance value observed in control animals. A similar effect is observed in transduced LDL-R(-/-) mice, in which the clearance of injected human LDL depends solely on the presence of circulating LDL-Rs(hu) /Tf(rab). In these animals the extent of plasma LDL clearance is directly related to the concentration of LDL-Rs(hu)/Tf(rab) in the blood. Finally, LDL-Rs(hu)/Tf(rab) does not alter the pattern of LDL organ distribution: in transduced animals, as well as in control animals, liver and bladder are the predominantly labeled organs after (123)I-LDL injection. However, LDL-Rs(hu)/Tf(rab) has a quantitative effect on LDL tissue deposition: in treated animals LDL-Rs(hu)/Tf(rab) determines an increase in radioactivity in the liver at early times after (123)I-LDL injection and a progressive labeling of the bladder, starting 20 min after injection.

The Very Low-density Lipoprotein (VLDL) Receptor: Characterization and Functions as a Peripheral Lipoprotein Receptor

The very low-density lipoprotein (VLDL) receptor is a member of the low-density lipoprotein (LDL) receptor family. In vitro and in vivo studies have shown that VLDL receptor binds triglyceride (TG)-rich lipoproteins but not LDL, and functions as a peripheral remnant lipoprotein receptor. VLDL receptor is expressed abundantly in fatty acid-active tissues (heart, skeletal muscle and fat), the brain and macrophages. It is likely that VLDL receptor functions in concert with lipoprotein lipase (LPL), which hydrolyses TG in VLDL and chylomicron. In contrast to the LDL receptor, VLDL receptor binds apolipoprotein (apo) E2/2 VLDL particles as well as apoE3/3 VLDL, and the expression is not down-regulated by intracellular lipoproteins. Recently, various functions of the VLDL receptor have been reported in lipoprotein metabolism, metabolic syndrome/atherosclerosis, cardiac fatty acid metabolism, neuronal migration and angiogenesis/tumor growth. Gene therapy of VLDL receptor into the liver showed a benefit effect for lipoprotein metabolism in both LDL receptor knockout and apoE mutant mice. Beyond its function as a peripheral lipoprotein receptor, possibilities of its physiological function have been extended to include signal transduction, angiogenesis and tumor growth.

Hepatic overexpression of caveolins increases bile salt secretion in mice

Caveolins are cholesterol-binding proteins involved in the regulation of several intracellular processes, including cholesterol transport. Because hepatocytes express caveolin-1 and caveolin-2, these proteins might modulate hepatic lipid metabolism and biliary lipid secretion. Our aim was to investigate the potential physiologic role of caveolins in hepatic cholesterol and bile salt (BS) metabolism and transport using adenoviral gene transfer. C57BL/6 mice were infected with recombinant human caveolin-1 and caveolin-2 adenoviruses. Mice infected with adenovirus lacking the transgene were used as controls. Hepatic caveolin expression was evaluated by immunochemical methods. Reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting were used to assess messenger RNA (mRNA) levels and protein mass of BS transporters (sodium taurocholate cotransporting polypeptide [Ntcp] and bile salt export pump [Bsep]). Serum, liver, biliary, and fecal biochemical determinations and BS maximal secretory rate (SRm) were performed by standard methods. Ad.Cav-1- and Ad.Cav-2-infected mice exhibited a 10- and 7-fold increase in hepatic caveolin-1 and caveolin-2 protein expression, respectively. Caveolin-1-overexpressing mice had a significant increase in plasma high-density lipoprotein (HDL) cholesterol and hepatic free cholesterol content, whereas total plasma cholesterol and triglyceride levels remained unchanged. Hepatic caveolin-1 and/or caveolin-2 overexpression significantly increased bile flow and secretion of all biliary lipids. Caveolin-1-overexpressing mice showed a 2.5-fold increase in taurocholate (TC) SRm, indicating increased canalicular BS transport capacity. BS pool size and fecal BS excretion remained within the normal range in mice with Cav-1 overexpression. No changes were seen in the protein mass of BS transporters Ntcp and Bsep. In conclusion, our findings indicate that caveolins may play an important role in regulating hepatic BS and cholesterol metabolism.

Gene therapy applications for spine fusion

OBJECTIVE

This article reviews the potential utilization of various growth factors to enhance spinal fusion and outlines the principles of gene therapy and its application to spinal fusion surgery.

SUMMARY OF BACKGROUND DATA

Gene therapy offers an exciting new way to potentially deliver growth factors locally in a targeted fashion with physiologic doses. In its current definition, gene therapy is defined as the use of nucleic acid transfer, either RNA or DNA, to treat or prevent a disease. The scope of gene therapy has expanded beyond its initial application as a method of replacing genetic defects, and its potential to facilitate spinal fusions is currently being evaluated.

CONCLUSIONS

Gene therapy strategies for spine fusion are appealing because the setting is uniquely suited for genetic manipulation. The intervention is locally applied. Only a short duration of transgene response by the cells is necessary to establish a spine fusion, and a variety of osteoinductive growth factors have been identified and are available for use. Attempts at spine fusion using gene therapy in the lower animals have been successful using both in vivo and ex vivo approaches. Before human clinical trials can be established, further testing is required in more challenging animal models of bone induction such as nonhuman primates. Should a successful clinical program of gene therapy for spine fusion be established, the use of autograft and its associated morbidities could be eliminated. In fact, gene therapy offers the potential for minimally invasive applications that could bypass the need for an open procedure altogether. It is likely that gene therapy will be a powerful therapeutic tool for the spine surgeon in the new millennium.

A tetracycline-regulated adenoviral expression system for in vivo delivery of transgenes to lung and liver

BACKGROUND

Recombinant adenoviruses are an established tool for somatic gene transfer to multiple cell types in animals as well as in tissue culture. However, generation of adenoviruses expressing transgenes that are potentially toxic to the host cell line represents a practical problem. The aim of this study was to construct an adenoviral expression system that prevents transgene expression during the generation and propagation of the virus, and allows efficient gene transfer to lung and liver, major target organs of gene therapy.

METHODS

Using the tet-off system we constructed tetracycline (tet) regulatable recombinant adenoviruses expressing the marker gene LacZ (Adtet-off.LacZ) as well as a secretory protein, human group IIA secretory phospholipase A(2) (Adtet-off.hsPLA(2)). Expression (Western blot, activity assay) was tested in vitro (HeLa cells), and in vivo by gene transfer to lung and liver.

RESULTS

Without addition of tetracycline we demonstrated expression of LacZ (Adtet-off.LacZ) and sPLA(2) (Adtet-off.hsPLA(2)) in HeLa cells. Providing additional tet-transactivator (tTA) protein either by stable transfection or coinfection with a tTA-expressing adenovirus resulted in a further increase of LacZ and sPLA(2) expression. Transgene expression in vitro was eliminated by the addition of tetracycline to the culture medium. Adtet-off.LacZ and Adtet-off.hsPLA(2) allowed successful gene transfer in vivo to lung and liver. While the expression was highly efficient within the lungs, however, additional tTA was necessary to achieve high-level expression within liver.

CONCLUSIONS

Tet-regulatable adenoviral expression systems may facilitate the construction of recombinant adenoviruses encoding potentially toxic transgenes and permit regulated transgene expression.

Gene therapy for cerebral vascular disease: update 2003

Gene therapy is a promising strategy for cerebrovascular diseases. Several genes that encode vasoactive products have been transferred via cerebrospinal fluid for the prevention of vasospasm after subarachnoid hemorrhage. Transfer of neuroprotective genes, including targeting of proinflammatory mediators, is a current strategy of gene therapy for ischemic stroke. Stimulation of growth of collateral vessels, stabilization of atherosclerotic plaques, inhibition of thrombosis, and prevention of restenosis are important objectives of gene therapy for coronary and limb arteries, but application of these approaches to carotid and intracranial arteries has received little attention. Several fundamental advances, including development of safer vectors, are needed before gene therapy achieves an important role in the treatment of cerebrovascular disease and stroke.

Infectious delivery of a 135-kb LDLR genomic locus leads to regulated complementation of low-density lipoprotein receptor deficiency in human cells

The ability to deliver efficiently a complete genomic DNA locus to human and rodent cells will likely find widespread application in functional genomic studies and novel gene therapy protocols. In contrast to a cDNA expression cassette, the use of a complete genomic DNA locus delivers a transgene intact with its native promoter, the exons, all the intervening introns, and the regulatory regions. The presence of flanking, noncoding genomic DNA sequences could prove critical for prolonged and appropriate gene expression. We have recently developed a technology for the rapid conversion of bacterial artificial chromosome (BAC) clones into high-capacity herpes simplex virus-based amplicon vectors. Here, we express the human low-density lipoprotein receptor (LDLR), mutated in familial hypercholesterolemia (FH), from a 135-kb BAC insert. The infectious LDLR genomic locus vectors were shown to express at physiologically appropriate levels in three contexts. First, the LDLR locus was expressed appropriately in the ldl(-/-)a7 Chinese hamster ovary (CHO) cell line immediately following infectious delivery; second, the locus was maintained within a replicating episomal vector and expressed at broadly physiological levels in CHO cells for 3 months following infectious delivery; and third, the locus was efficiently expressed in human fibroblasts derived from FH patients. Finally, we show that the infectious LDLR locus retains classical expression regulation by sterol levels in human cells. This long-term expression and physiological regulation of LDLR prepares the way for in vivo functional studies of infectious delivery of BAC inserts.

Familial hypercholesterolemia--improving treatment and meeting guidelines

Familial hypercholesterolemia (FH) is a common, inherited disorder that affects around one in 500 individuals in the heterozygous form. By the year 2001, more people in the US had FH than were infected by the human immunodeficiency virus. The disease is caused by mutations within the low-density lipoprotein (LDL) receptor gene. FH is associated with elevated plasma LDL-cholesterol (LDL-C) levels, xanthomatosis, early onset of atherosclerosis and premature cardiac death. Patients with heterozygous FH commonly have plasma LDL-C levels that are two-fold higher than normal, while homozygotes have four- to five-fold elevations in plasma LDL-C. Although FH patients have a high risk of developing premature coronary heart disease (CHD), they remain underdiagnosed and undertreated. Early detection of FH is critical to prolonging the life of these patients. Once identified, patients with heterozygous FH can be placed on a diet and drug management program. As the most efficacious and well-tolerated agents, hydroxy methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are usually the drugs of first choice; bile acid sequestrants, niacin, and occasionally fibrates may be used as supplemental agents. Statins may also provide a realistic option for the treatment of some FH homozygotes with genes that produce partially functional LDL receptors. However, a number of patients are still failing to reach treatment guidelines even with the most effective of the currently available statins. The development of new more efficacious statins or the use of new combination therapies such as statins with the cholesterol absorption inhibitor, ezetimibe may help to reduce the current problem of undertreatment in FH patients.

A review on the diagnosis, natural history, and treatment of familial hypercholesterolaemia

BACKGROUND

Familial hypercholesterolaemia (FH) affects approximately 1 in 500 people (10 million world-wide) and the elevated serum cholesterol concentrations lead to a more than 50% risk of fatal or non-fatal coronary heart disease by age 50 years in men and at least 30% in women aged 60 years. Based on a systematic literature search, we review the natural history of FH, describe the diagnostic criteria, and consider the effectiveness of treatment.

METHODS

A comprehensive review was conducted of the literature on the diagnosis of FH, the morbidity and mortality related to treated and untreated FH, and the evidence on the effectiveness of treatment of FH in adults and children. Treatment options have changed since statin treatment became available, and we have not considered pre-statin therapy studies of treatment effectiveness.

FINDINGS AND DISCUSSION

A clinical diagnosis of FH is widely used, but a definitive diagnosis can be made by genetic screening, although mutations are currently only detected in 30-50% of patients with a clinical diagnosis. Under-diagnosis of FH has been reported world-wide ranging from less than 1% to 44%. The relative risk of death of FH patients not treated with statins is between three and fourfold but treatment is effective, and delays or prevents the onset of coronary heart disease. Early detection and treatment is important. Aggressive LDL therapy is more effective in the regression of the carotid intima media thickness than conventional LDL therapy. Diagnosis at birth is problematic, and should be delayed until at least 2 years of age. Statins are not generally recommended for the treatment of children up to adolescence. Resins may be used but poor adherence is a problem. Technical advances in mutation detection, and the identification of other genes that cause FH, are likely to have important implications for the cost effectiveness of genetic diagnosis of FH.

Hepatic overexpression of sterol carrier protein-2 inhibits VLDL production and reciprocally enhances biliary lipid secretion

We examined in vivo a role for sterol carrier protein-2 (SCP-2) in the regulation of lipid secretion across the hepatic sinusoidal and canalicular membranes. Recombinant adenovirus Ad.rSCP2 was used to overexpress SCP-2 in livers of mice. We determined plasma, hepatic, and biliary lipid concentrations; hepatic fatty acid (FA) and cholesterol synthesis; hepatic and biliary phosphatidylcholine (PC) molecular species; and VLDL triglyceride production. In Ad.rSCP2 mice, there was marked inhibition of hepatic fatty acids and cholesterol synthesis to <62% of control mice. Hepatic triglyceride contents were decreased, while cholesterol and phospholipids concentrations were elevated in Ad.rSCP2 mice. Hepatic VLDL triglyceride production fell in Ad.rSCP2 mice to 39% of control values. As expected, biliary cholesterol, phospholipids, bile acids outputs, and biliary PC hydrophobic index were significantly increased in Ad.rSCP2 mice. These studies indicate that SCP-2 overexpression in the liver markedly inhibits lipid synthesis as well as VLDL production, and alters hepatic lipid contents. In contrast, SCP-2 increased biliary lipid secretion and the proportion of hydrophobic PC molecular species in bile. These effects suggest a key regulatory role for SCP-2 in hepatic lipid metabolism and the existence of a reciprocal relationship between the fluxes of lipids across the sinusoidal and canalicular membranes.