Sympathetic activity regulates epithelial proliferation and wound healing via adrenergic receptor α2A

Innervation of the intestinal mucosa by the sympathetic nervous system is well described but the effects of adrenergic receptor stimulation on the intestinal epithelium remain equivocal. We therefore investigated the effect of sympathetic neuronal activation on intestinal cells in mouse models and organoid cultures, to identify the molecular routes involved. Using publicly available single-cell RNA sequencing datasets we show that the α2A isoform is the most abundant adrenergic receptor in small intestinal epithelial cells. Stimulation of this receptor with norepinephrine or a synthetic specific α2A receptor agonist promotes epithelial proliferation and stem cell function, while reducing differentiation in vivo and in intestinal organoids. In an anastomotic healing mouse model, adrenergic receptor α2A stimulation resulted in improved anastomotic healing, while surgical sympathectomy augmented anastomotic leak. Furthermore, stimulation of this receptor led to profound changes in the microbial composition, likely because of altered epithelial antimicrobial peptide secretion. Thus, we established that adrenergic receptor α2A is the molecular delegate of intestinal epithelial sympathetic activity controlling epithelial proliferation, differentiation, and host defense. Therefore, this receptor could serve as a newly identified molecular target to improve mucosal healing in intestinal inflammation and wounding.

The Multifaceted Role of Serotonin in Intestinal Homeostasis

The monoamine serotonin, 5-hydroxytryptamine (5-HT), is a remarkable molecule with conserved production in prokaryotes and eukaryotes and a wide range of functions. In the gastrointestinal tract, enterochromaffin cells are the most important source for 5-HT production. Some intestinal bacterial species are also able to produce 5-HT. Besides its role as a neurotransmitter, 5-HT acts on immune cells to regulate their activation. Several lines of evidence indicate that intestinal 5-HT signaling is altered in patients with inflammatory bowel disease. In this review, we discuss the current knowledge on the production, secretion, and signaling of 5-HT in the intestine. We present an inventory of intestinal immune and epithelial cells that respond to 5-HT and describe the effects of these signaling processes on intestinal homeostasis. Further, we detail the mechanisms by which 5-HT could affect inflammatory bowel disease course and describe the effects of interventions that target intestinal 5-HT signaling.

Neuronal innervation of the intestinal crypt

Mucosal damage is a key feature of inflammatory bowel diseases (IBD) and healing of the mucosa is an endpoint of IBD treatment that is often difficult to achieve. Autonomic neurons of the parasympathetic and sympathetic nervous system may influence intestinal epithelial cell growth and modulating epithelial innervation could for that reason serve as an interesting therapeutic option to improve mucosal healing. Understanding of the biological processes triggered by nonspecific and specific epithelial adrenergic and cholinergic receptor activation is of key importance. At present, with rising technological advances, bioelectronic neuromodulation as treatment modality has gained momentum. We discuss the current view on state-of-the-art innervation of the intestinal crypt and its impact on epithelial cell growth and differentiation. Furthermore, we outline bioelectronic technology and review its relevance to wound healing processes.

Acetylcholine-producing T cells augment innate immune-driven colitis but are redundant in T cell-driven colitis

Clinical trials suggest that vagus nerve stimulation presents an alternative approach to classical immune suppression in Crohn's disease. T cells capable of producing acetylcholine (ChAT⁺ T cells) in the spleen are essential mediators of the anti-inflammatory effect of vagus nerve stimulation. Besides the spleen, ChAT⁺ T cells are found abundantly in Peyer's patches of the small intestine. However, the role of ChAT⁺ T cells in colitis pathogenesis is unknown. Here, we made use of CD4^creChAT^fl/fl mice (CD4ChAT^-/- mice) lacking ChAT expression specifically in CD4⁺ T cells. Littermates (ChAT^fl/fl mice) served as controls. In acute dextran sulfate sodium (DSS)-induced colitis (7 days of 2% DSS in drinking water), CD4ChAT^-/- mice showed attenuated colitis and lower intestinal inflammatory cytokine levels compared with ChAT^fl/fl mice. In contrast, in a resolution model of DSS-induced colitis (5 days of 2% DSS followed by 7 days without DSS), CD4ChAT^-/- mice demonstrated a worsened colitis recovery and augmented colonic histological inflammation scores and inflammatory cytokine levels as compared with ChAT^fl/fl mice. In a transfer colitis model using CD4⁺CD45RB^high T cells, T cells from CD4ChAT^-/- mice induced a similar level of colitis compared with ChAT^fl/fl T cells. Together, our results indicate that ChAT⁺ T cells aggravate the acute innate immune response upon mucosal barrier disruption in an acute DSS-induced colitis model, whereas they are supporting the later resolution process of this innate immune-driven colitis. Surprisingly, ChAT expression in T cells seems redundant in the context of T cell-driven colitis.NEW & NOTEWORTHY By using different mouse models of experimental colitis, we provide evidence that in dextran sulfate sodium-induced colitis, ChAT⁺ T cells capable of producing acetylcholine worsen the acute immune response, whereas they support the later healing phase of this innate immune-driven colitis.

Painful interactions: Microbial compounds and visceral pain

Visceral pain, characterized by abdominal discomfort, originates from organs in the abdominal cavity and is a characteristic symptom in patients suffering from irritable bowel syndrome, vulvodynia or interstitial cystitis. Most organs in which visceral pain originates are in contact with the external milieu and continuously exposed to microbes. In order to maintain homeostasis and prevent infections, the immune- and nervous system in these organs cooperate to sense and eliminate (harmful) microbes. Recognition of microbial components or products by receptors expressed on cells from the immune and nervous system can activate immune responses but may also cause pain. We review the microbial compounds and their receptors that could be involved in visceral pain development.

Loss of intestinal sympathetic innervation elicits an innate immune driven colitis

BACKGROUND

Both the parasympathetic and sympathetic nervous system exert control over innate immune responses. In inflammatory bowel disease, sympathetic innervation in intestinal mucosa is reduced. Our aim was to investigate the role of sympathetic innervation to the intestine on regulation of the innate immune responses.

METHODS

In lipopolysaccharide (LPS)-stimulated macrophages, we evaluated the effect of adrenergic receptor activation on cytokine production and metabolic profile. In vivo, the effect of sympathetic denervation on mucosal innate immune responses using 6-hydroxydopamine (6-OHDA), or using surgical transection of the superior mesenteric nerve (sympathectomy) was tested in Rag1^-/- mice that lack T- and B-lymphocytes.

RESULTS

In murine macrophages, adrenergic β2 receptor activation elicited a dose-dependent reduction of LPS-induced cytokines, reduced LPS-induced glycolysis and increased maximum respiration. Sympathectomy led to a significantly decreased norepinephrine concentration in intestinal tissue. Within 14 days after sympathectomy, mice developed clinical signs of colitis, colon oedema and excess colonic cytokine production. Both 6-OHDA and sympathectomy led to prominent goblet cell depletion and histological damage of colonic mucosa.

CONCLUSIONS

We conclude that the sympathetic nervous system plays a regulatory role in constraining innate immune cell reactivity towards microbial challenges, likely via the adrenergic β2 receptor.

Reversal of visceral hypersensitivity in rat by Menthacarin® , a proprietary combination of essential oils from peppermint and caraway, coincides with mycobiome modulation

BACKGROUND

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder associated with altered gastrointestinal microflora and increased nociception to colonic distension. This visceral hypersensitivity can be reversed in our rat maternal separation model by fungicides. Menthacarin^® is a proprietary combination of essential oils from Mentha x piperita L. and Carum carvi. Because these oils exhibit antifungal and antibacterial properties, we investigated whether Menthacarin^® can reverse existing visceral hypersensitivity in maternally separated rats.

METHODS

In non-handled and maternally separated rats, we used the visceromotor responses to colorectal distension as measure for visceral sensitivity. We evaluated this response before and 24 hours after water-avoidance stress and after 7 days treatment with Menthacarin^® or control. The pre- and post-treatment mycobiome and microbiome were characterized by sequencing of fungal internal transcribed spacer 1 (ITS-1) and bacterial 16s rDNA regions. In vitro antifungal and antimicrobial properties of Menthacarin^® were studied with radial diffusion assay.

KEY RESULTS

Menthacarin^® inhibited in vitro growth of yeast and bacteria. Water-avoidance caused visceral hypersensitivity in maternally separated rats, and this was reversed by treatment. Multivariate analyses of ITS-1 and 16S high throughput data showed that maternal separation, induced changes in the myco- and microbiome. Menthacarin^® treatment of non-handled and maternally separated rats shifted the mycobiomes to more similar compositions.

CONCLUSIONS & INFERENCES

The development of visceral hypersensitivity in maternally separated rats and the Menthacarin^® -mediated reversal of hypersensitivity is associated with changes in the mycobiome. Therefore, Menthacarin^® may be a safe and effective treatment option that should be tested for IBS.

Neuronal control of experimental colitis occurs via sympathetic intestinal innervation

BACKGROUND

Vagus nerve stimulation is currently clinically evaluated as a treatment for inflammatory bowel disease. However, the mechanism by which this therapeutic intervention can have an immune-regulatory effect in colitis remains unclear. We determined the effect of intestine-specific vagotomy or intestine-specific sympathectomy of the superior mesenteric nerve (SMN) on dextran sodium sulfate (DSS)-induced colitis in mice. Furthermore, we tested the efficacy of therapeutic SMN stimulation to treat DSS-induced colitis in rats.

METHODS

Vagal and SMN fibers were surgically dissected to achieve intestine-specific vagotomy and sympathectomy. Chronic SMN stimulation was achieved by implantation of a cuff electrode. Stimulation was done twice daily for 5 minutes using a biphasic pulse (10 Hz, 200 μA, 2 ms). Disease activity index (DAI) was used as a clinical parameter for colitis severity. Colonic cytokine expression was measured by quantitative PCR and ELISA.

KEY RESULTS

Intestine-specific vagotomy had no effect on DSS-induced colitis in mice. However, SMN sympathectomy caused a significantly higher DAI compared to sham-operated mice. Conversely, SMN stimulation led to a significantly improved DAI compared to sham stimulation, although no other parameters of colitis were affected significantly.

CONCLUSIONS & INFERENCES

Our results indicate that sympathetic innervation regulates the intestinal immune system as SMN denervation augments, and SMN stimulation ameliorates DSS-induced colitis. Surprisingly, intestine-specific vagal nerve denervation had no effect in DSS-induced colitis.

Intestinal Fungal Dysbiosis Is Associated With Visceral Hypersensitivity in Patients With Irritable Bowel Syndrome and Rats

BACKGROUND & AIMS

Visceral hypersensitivity is one feature of irritable bowel syndrome (IBS). Bacterial dysbiosis might be involved in the activation of nociceptive sensory pathways, but there have been few studies of the role of the mycobiome (the fungal microbiome) in the development of IBS. We analyzed intestinal mycobiomes of patients with IBS and a rat model of visceral hypersensitivity.

METHODS

We used internal transcribed spacer 1-based metabarcoding to compare fecal mycobiomes of 18 healthy volunteers with those of 39 patients with IBS (with visceral hypersensitivity or normal levels of sensitivity). We also compared the mycobiomes of Long-Evans rats separated from their mothers (hypersensitive) with non-handled (normally sensitive) rats. We investigated whether fungi can cause visceral hypersensitivity using rats exposed to fungicide (fluconazole and nystatin). The functional relevance of the gut mycobiome was confirmed in fecal transplantation experiments: adult maternally separated rats were subjected to water avoidance stress (to induce visceral hypersensitivity), then given fungicide and donor cecum content via oral gavage. Other rats subjected to water avoidance stress were given soluble β-glucans, which antagonize C-type lectin domain family 7 member A (CLEC7A or DECTIN1) signaling via spleen-associated tyrosine kinase (SYK), a SYK inhibitor to reduce visceral hypersensitivity, or vehicle (control). The sensitivity of mast cells to fungi was tested with mesenteric windows (ex vivo) and the human mast cell line HMC-1.

RESULTS

α diversity (Shannon index) and mycobiome signature (stability selection) of both groups of IBS patients differed from healthy volunteers, and the mycobiome signature of hypersensitive patients differed from that of normally sensitive patients. We observed mycobiome dysbiosis in rats that had been separated from their mothers compared with non-handled rats. Administration of fungicide to hypersensitive rats reduced their visceral hypersensitivity to normal levels of sensitivity. Administration of cecal mycobiomes from rats that had been separated from their mothers (but not non-handled mycobiome) restored hypersensitivity to distension. Administration of soluble β-glucans or a SYK inhibitor reduced visceral hypersensitivity, compared with controls. Particulate β-glucan (a DECTIN-1 agonist) induced mast cell degranulation in mesenteric windows and HMC-1 cells responded to fungal antigens by release of histamine.

CONCLUSIONS

In an analysis of patients with IBS and controls, we associated fungal dysbiosis with IBS. In studies of rats, we found fungi to promote visceral hypersensitivity, which could be reduced by administration of fungicides, soluble β-glucans, or a SYK inhibitor. The intestinal fungi might therefore be manipulated for treatment of IBS-related visceral hypersensitivity.

In Vitro Functionality of Human Fetal Liver Cells and Clonal Derivatives under Proliferative Conditions

Mature human hepatocytes are not suitable for large-scale in vitro applications that rely on hepatocyte function, due to their limited availability and insufficient proliferation capacity in vitro. In contrast, human fetal liver cells (HFLC) can be easily expanded in vitro. In this study we evaluated the hepatic function of HFLCs under proliferative conditions, to determine whether HFLCs can replace mature hepatocytes for in vitro applications. HFLCs were isolated from fetal livers of 16 weeks gestation. Hepatic functions of HFLCs were determined in primary culture and after expansion in vitro. Clonal derivatives were selected and tested for hepatic functionality. Results were compared to primary mature human hepatocytes in vitro. No differences were observed between primary HFLCs and mature human hepatocytes in albumin production and mRNA levels of various liver-specific genes. Ureagenesis was 4.4-fold lower and ammonia elimination was absent in HFLCs. Expanding HFLCs decreased hepatic functions and increased cell stretching. In contrast, clonal derivatives had stable functionality and morphology and responded to differentiation stimuli. Although their hepatic functions were higher than in passaged HFLCs, functionality was at least 20 times lower compared to mature human hepatocytes. HFLCs cannot replace mature human hepatocytes in in vitro applications requiring extensive in vitro expansion, because this is associated with decreased hepatic functionality. Selecting functional subpopulations can, at least partly, prevent this. In addition, defining conditions that support hepatic differentiation is necessary to obtain HFLC cultures suitable for in vitro hepatic applications.

Biliverdin Reductase inhibitors did not improve severe unconjugated hyperbilirubinemia in vivo

We aimed to identify potent biliverdin reductase (BVRA) inhibitors as a novel concept for the treatment of severe unconjugated hyperbilirubinemia. 1280 FDA-approved compounds were screened in vitro for their ability to inhibit human and rat BVRA activity and 26 compounds were identified as BVRA inhibitors. Montelukast and Disulfiram were selected as potentially clinically applicable drugs and tested to reduce serum unconjugated bilirubin (UCB) levels in the Ugt1a1-deficient rat, a model for chronic unconjugated hyperbilirubinemia. Oral administration of Disulfiram was toxic in the Ugt1a1-deficient rat (weight loss, transaminase elevation). Oral Montelukast administration led to low serum concentrations and did not alter serum UCB levels. Intraperitoneal injections of Montelukast resulted in concentrations up to 110 μmol/L in serum and 400 μmol/L in the liver. Still, serum UCB levels remained unaltered. This first study on biliverdin reductase inhibition as a novel concept for treatment of unconjugated hyperbilirubinemia identified putative in vitro BVRA inhibitors. Montelukast, the clinically most suitable inhibitor, did not result in reduction of serum UCB in the Ugt1a1-deficient rat. The proposed treatment strategy will not result in amelioration of severe unconjugated hyperbilirubinemia in humans without the identification or development of more potent BVRA inhibitors.

Acetylcholine-producing T cells in the intestine regulate antimicrobial peptide expression and microbial diversity

The cholinergic anti-inflammatory pathway reduces systemic tumor necrosis factor (TNF) via acetylcholine-producing memory T cells in the spleen. These choline acetyltransferase (ChAT)-expressing T cells are also found in the intestine, where their function is unclear. We aimed to characterize these cells in mouse and human intestine and delineate their function. We made use of the ChAT-enhanced green fluorescent protein (eGFP) reporter mice. CD4^Cre mice were crossed to ChAT^fl/fl mice to achieve specific deletion of ChAT in CD4⁺ T cells. We observed that the majority of ChAT-expressing T cells in the human and mouse intestine have characteristics of Th17 cells and coexpress IL17A, IL22, and RORC The generation of ChAT-expressing T cells was skewed by dendritic cells after activation of their adrenergic receptor β₂ To evaluate ChAT T cell function, we generated CD4-specific ChAT-deficient mice. CD4ChAT^-/- mice showed a reduced level of epithelial antimicrobial peptides lysozyme, defensin A, and ang4, which was associated with an enhanced bacterial diversity and richness in the small intestinal lumen in CD4ChAT^-/- mice. We conclude that ChAT-expressing T cells in the gut are stimulated by adrenergic receptor activation on dendritic cells. ChAT-expressing T cells may function to mediate the host AMP secretion, microbial growth and expansion.

The SCFA butyrate stimulates the epithelial production of retinoic acid via inhibition of epithelial HDAC

In the intestinal mucosa, retinoic acid (RA) is a critical signaling molecule. RA is derived from dietary vitamin A (retinol) through conversion by aldehyde dehydrogenases (aldh). Reduced levels of short-chain fatty acids (SCFAs) are associated with pathological microbial dysbiosis, inflammatory disease, and allergy. We hypothesized that SCFAs contribute to mucosal homeostasis by enhancing RA production in intestinal epithelia. With the use of human and mouse epithelial cell lines and primary enteroids, we studied the effect of SCFAs on the production of RA. Functional RA conversion was analyzed by Adlefluor activity assays. Butyrate (0-20 mM), in contrast to other SCFAs, dose dependently induced aldh1a1 or aldh1a3 transcript expression and increased RA conversion in human and mouse epithelial cells. Epithelial cell line data were replicated in intestinal organoids. In these organoids, butyrate (2-5 mM) upregulated aldh1a3 expression (36-fold over control), whereas aldh1a1 was not significantly affected. Butyrate enhanced maturation markers (Mucin-2 and villin) but did not consistently affect stemness markers or other Wnt target genes (lgr5, olfm4, ascl2, cdkn1). In enteroids, the stimulation of RA production by SCFA was mimicked by inhibitors of histone deacetylase 3 (HDAC3) but not by HDAC1/2 inhibitors nor by agonists of butyrate receptors G-protein-coupled receptor (GPR)43 or GPR109A, indicating that butyrate stimulates RA production via HDAC3 inhibition. We conclude that the SCFA butyrate inhibits HDAC3 and thereby supports epithelial RA production.

Adverse Effects of Genistein in a Mucopolysaccharidosis Type I Mouse Model

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disorder characterized by diminished degradation of the glycosaminoglycans heparan sulfate (HS) and dermatan sulfate (DS). Patients present with a variety of symptoms, including severe skeletal disease. Current therapeutic strategies have only limited effects on bone disease. The isoflavone genistein has been studied as a potential therapy for the mucopolysaccharidoses because of its putative ability to inhibit GAG synthesis and subsequent accumulation. Cell, animal, and clinical studies, however, showed variable outcomes. To determine the effects of genistein on MPS I-related bone disease, wild-type (WT) and MPS I mice were fed a genistein-supplemented diet (corresponding to a dose of approximately 160 mg/kg/day) for 8 weeks. HS and DS levels in bone and plasma remained unchanged after genistein supplementation, while liver HS levels were decreased in genistein-fed MPS I mice as compared to untreated MPS I mice. Unexpectedly, genistein-fed mice exhibited significantly decreased body length and femur length. In addition, 60% of genistein-fed MPS I mice developed a scrotal hernia and/or scrotal hydrocele, manifestations, which were absent in WT or untreated MPS I mice. In contrast to studies in MPS III mice, our study in MPS I mice demonstraes no beneficial but even potential adverse effects of genistein supplementation. Our results urge for a cautious approach on the use of genistein, at least in patients with MPS I.

Lynch syndrome: the patients' perspective

People with Lynch syndrome have a high lifetime risk for the development of colorectal, endometrial and several other types of cancer. Lynch syndrome is caused by germline mutations in genes encoding DNA mismatch repair proteins. In this review, issues that concern Lynch patients are highlighted from the patients' perspective. Both authors are affected by Lynch syndrome and are active in Lynch patient organizations. The goal of this review is to assist heath care providers in the improvement of care for individuals who share our disorder. Institutional and/or national guidelines that should lead to the identification of Lynch patients have been developed in many countries. However, adherence to these guidelines is poor and the consequence is severe underdiagnosis of Lynch syndrome. An important task of patient organizations is therefore to increase awareness of Lynch syndrome among the general public and health care providers. Because diagnosis of Lynch syndrome based on family history is difficult, the use of molecular and or histological techniques that permit unequivocal diagnosis should be more aggressively promoted. Since Lynch syndrome encompasses a broad spectrum of cancers, a multidisciplinary treatment and screening protocol for all Lynch patients is necessary. Lynch patients must be seen by a team of specialists that are knowledgeable in the various manifestations of Lynch syndrome. Because tumors with mismatch repair deficiency have specific properties, identification of effective chemotherapy regimens, specifically targeted to patients with deficiencies in DNA repair mechanisms, must be developed. The high lifetime risk of developing cancer in Lynch patients warrants lifestyle advice and research into chemopreventive measures that reduce the risk of cancer in this vulnerable group. Implementation of these recommendations will result in greatly improved quality of life for people affected with Lynch syndrome, it is therefore important that health care providers and patient organizations work together to achieve these goals.

Phase 1 and phase 2 drug metabolism and bile acid production of HepaRG cells in a bioartificial liver in absence of dimethyl sulfoxide

The human liver cell line HepaRG has been recognized as a promising source for in vitro testing of metabolism and toxicity of compounds. However, currently the hepatic differentiation of these cells relies on exposure to dimethylsulfoxide (DMSO), which, as a side effect, has a cytotoxic effect and represses an all-round hepatic functionality. The AMC-bioartificial liver (AMC-BAL) is a three-dimensional bioreactor that has previously been shown to upregulate various liver functions of cultured cells. We therefore cultured HepaRG cells in the AMC-BAL without DMSO and characterized the drug metabolism. Within 14 days of culture, the HepaRG-AMC-BALs contained highly polarized viable liver-like tissue with heterogeneous expression of CYP3A4. We found a substantial metabolism of the tested substrates, ranging from 26% (UDP-glucuronosyltransferase 1A1), 47% (CYP3A4), to 240% (CYP2C9) of primary human hepatocytes. The CYP3A4 activity could be induced 2-fold by rifampicin, whereas CYP2C9 activity remained equally high. The HepaRG-AMC-BAL secreted bile acids at 43% the rate of primary human hepatocytes and demonstrated hydroxylation, conjugation, and transport of bile salts. Concluding, culturing HepaRG cells in the AMC-BAL yields substantial phase 1 and phase 2 drug metabolism, while maintaining high viability, rendering DMSO addition superfluous for the promotion of drug metabolism. Therefore, AMC-BAL culturing makes the HepaRG cells more suitable for testing metabolism and toxicity of drugs.

Human liver endothelial cells, but not macrovascular or microvascular endothelial cells, engraft in the mouse liver

Liver cell transplantation has had limited clinical success so far, partly due to poor engraftment of hepatocytes. Instead of hepatocytes. other cell types, such as endothelial cells, could be used in ex vivo liver gene therapy. The goal of the present study was to compare the grafting and repopulation capacity of human endothelial cells derived from various tissues. Human endothelial cells were isolated from adult and fetal livers using anti-human CD31 antibody-conjugated magnetic beads. Human macrovascular endothelial cells were obtained from umbilical vein. Human microvascular endothelial cells were isolated from adipose tissue. Cells were characterized using flow cytometry. Liver engraftment and repopulation of endothelial cells was studied after intrasplenic transplantation in monocrotaline-treated immunodeficient mice. Following transplantation, human liver endothelial cells engrafted throughout the mouse liver. With immunoscanning electron microscopy, fenestrae in engrafted human liver endothelial cells were identified, a characteristic feature of liver sinusoidal endothelial cells. In contrast, CD31-negative liver cells, human macrovascular and microvascular endothelial cells were not capable of repopulating mouse liver. Characterization of human liver, macrovascular, and microvascular endothelial cells demonstrated expression of CD31, CD34, and CD146 but not CD45. Our study shows that only human liver endothelial cells, but not macro- and microvascular endothelial cells, have the unique capacity to engraft and repopulate the mouse liver. These results indicate that mature endothelial cells cannot transdifferentiate in vivo and thus do not exhibit phenotypic plasticity. Our results have set a basis for further research to the potential of human liver endothelial cells in liver-directed cell and gene therapy.

DLK1, a serum marker for hepatoblastoma in young infants

Hepatoblastoma is a malignant pediatric liver tumor. The currently used diagnostic serum marker for hepatoblastoma, α-fetoprotein (AFP), is not always reliable in infants with hepatoblastoma, due to the physiologically elevated levels of AFP in this age group. In this report, we show that Delta-like 1 homolog (DLK1), a protein highly expressed during fetal development, but almost completely absent after birth, and an established liver-stem cell marker, is a new candidate serum marker of hepatoblastoma, especially in young infants.

A diet containing the soy phytoestrogen genistein causes infertility in female rats partially deficient in UDP glucuronyltransferase

Soy beans contain genistein, a natural compound that has estrogenic effects because it binds the estrogen receptor with relatively high affinity. Genistein is therefore the most important environmental estrogen in the human diet. Detoxification of genistein is mediated through conjugation by UDP-glucuronyltransferase 1 and 2 (UGT1 and UGT2) isoenzymes. Gunn rats have a genetic deficiency in UGT1 activity, UGT2 activities are not affected. Because our Gunn rats stopped breeding after the animal chow was changed to a type with much higher soy content, we examined the mechanism behind this soy diet induced infertility. Gunn and control rats were fed diets with and without genistein. In these rats, plasma levels of genistein and metabolites, fertility and reproductive parameters were determined. Enzyme assays showed reduced genistein UGT activity in Gunn rats, as compared to wild type rats. Female Gunn rats were completely infertile on a genistein diet, wild type rats were fertile. Genistein diet caused a persistent estrus, lowered serum progesterone and inhibited development of corpora lutea in Gunn rats. Concentrations of total genistein in Gunn and control rat plasma were identical and within the range observed in humans after soy consumption. However, Gunn rat plasma contained 25% unconjugated genistein, compared to 3.6% in control rats. This study shows that, under conditions of reduced glucuronidation, dietary genistein exhibits a strongly increased estrogenic effect. Because polymorphisms that reduce UGT1 expression are prevalent in the human population, these results suggest a cautionary attitude towards the consumption of large amounts of soy or soy supplements.

Cellular localization and biochemical analysis of mammalian CDC50A, a glycosylated β-subunit for P4 ATPases

CDC50 proteins are β-subunits for P4 ATPases, which upon heterodimerization form a functional phospholipid translocation complex. Emerging evidence in mouse models and men links mutations in P4 ATPase genes with human disease. This study analyzed the tissue distribution and cellular localization of CDC50A, the most abundant and ubiquitously expressed CDC50 homologue in the mouse. The authors have raised antibodies that detect mouse and human CDC50A and studied CDC50A localization and glycosylation status in mouse liver cells. CDC50A is a terminal-glycosylated glycoprotein and is expressed in hepatocytes and liver sinusoidal endothelial cells, where it resides in detergent-resistant membranes. In pancreas and stomach, CDC50A localized to secretory vesicles, whereas in the kidney, CDC50A localized to the apical region of proximal convoluted tubules of the cortex. In WIF-B9 cells, CDC50A partially costains with the trans-Golgi network. Data suggest that CDC50A is present as a fully glycosylated protein in vivo, which presumes interaction with distinct P4 ATPases.

Complementary functions of the flippase ATP8B1 and the floppase ABCB4 in maintaining canalicular membrane integrity

BACKGROUND & AIMS

Progressive familial intrahepatic cholestasis can be caused by mutations in ABCB4 or ATP8B1; each encodes a protein that translocates phospholipids, but in opposite directions. ABCB4 flops phosphatidylcholine from the inner to the outer leaflet, where it is extracted by bile salts. ATP8B1, in complex with the accessory protein CDC50A, flips phosphatidylserine in the reverse direction. Abcb4(-/-) mice lack biliary secretion of phosphatidylcholine, whereas Atp8b1-deficient mice have increased excretion of phosphatidylserine into bile. Each system is thought to have a role protecting the canalicular membrane from bile salts.

METHODS

To investigate the relationship between the mechanisms of ABCB4 and ATP8B1, we expressed the transporters separately and together in cultured cells and studied viability and phospholipid transport. We also created mice with disruptions in ABCB4 and ATP8B1 (double knockouts) and studied bile formation and hepatic damage in mice fed bile salts.

RESULTS

Overexpression of ABCB4 was toxic to HEK293T cells; the toxicity was counteracted by coexpression of the ATP8B1-CDC50A complex. In Atp8b1-deficient mice, bile salts induced extraction of phosphatidylserine and ectoenzymes from the canalicular membrane; this process was not observed in the double-knockout mice.

CONCLUSIONS

ATP8B1 is required for hepatocyte function, particularly in the presence of ABCB4. This is most likely because the phosphatidylserine flippase complex of ATP8B1-CDC50A counteracts the destabilization of the membrane that occurs when ABCB4 flops phosphatidylcholine. Lipid asymmetry is therefore important for the integrity of the canalicular membrane; ABCB4 and ATP8B1 cooperate to protect hepatocytes from bile salts.

Synthetic gene regulation circuits for control of cell expansion

A major drawback in the analysis of primary cells and in regenerative sciences concerns the limited number and homogeneity of cells. This limitation could be overcome by in vitro cell expansion that retains the properties of the cell types of interest. However, for most primary differentiated cells the proliferation capacity is finite and/or proliferation is associated with dedifferentiation of cells. We have developed a flexible cell expansion strategy that allows strict and reliable control of cell proliferation. This system relies on synthetic gene modules that employ positive feedback loops based on Tetracycline control. These gene modules were constructed and transduced by lentiviral vectors. We succeeded in the generation of murine and importantly also of human endothelial cell lines. The key feature of the established cell lines is that their proliferation status can be strictly controlled while the expression of relevant markers is maintained. This strict control of proliferation was observed in cell clones and in cell pools and was even maintained when two independent immortalizing genes were simultaneously employed. Thus, this strategy is flexible, easy to handle, and reliable. Most importantly, it allows expansion of human cells with a primary-like phenotype.

Separating lentiviral vector injection and induction of gene expression in time, does not prevent an immune response to rtTA in rats

Background

Lentiviral gene transfer can provide long-term expression of therapeutic genes such as erythropoietin. Because overexpression of erythropoietin can be toxic, regulated expression is needed. Doxycycline inducible vectors can regulate expression of therapeutic transgenes efficiently. However, because they express an immunogenic transactivator (rtTA), their utility for gene therapy is limited. In addition to immunogenic proteins that are expressed from inducible vectors, injection of the vector itself is likely to elicit an immune response because viral capsid proteins will induce “danger signals” that trigger an innate response and recruit inflammatory cells.

Methodology and Principal Findings

We have developed an autoregulatory lentiviral vector in which basal expression of rtTA is very low. This enabled us to temporally separate the injection of virus and the expression of the therapeutic gene and rtTA. Wistar rats were injected with an autoregulatory rat erythropoietin expression vector. Two or six weeks after injection, erythropoietin expression was induced by doxycycline. This resulted in an increase of the hematocrit, irrespective of the timing of the induction. However, most rats only responded once to doxycycline administration. Antibodies against rtTA were detected in the early and late induction groups.

Conclusions

Our results suggest that, even when viral vector capsid proteins have disappeared, expression of foreign proteins in muscle will lead to an immune response.

[Gluttony and penance--laxatives and 'liver stones']

Gluttony is not only a mortal sin, it is also an important cause of medical problems. After sinning a penance must be paid and for this mortal sin the most obvious penance is laxation. Alternative medicine provides help: numerous types of laxative that claim to have positive effects on mental health, detoxification and aid in weight loss are to be found on the internet. The most surprising claim is that laxatives expel gall stones. These 'liver-cleansing' treatments result in the excretion of soft, stone-like structures in the faeces which may be seen by patients as being gall stones. Such 'liver stones' have been described in the literature and it is understood that they develop from the olive oil that is taken with the course of laxatives. That passing such stones is not associated with a reduction in gall stones is hardly surprising. Although laxation has been regarded as beneficial since ancient times, it is not effective in removing gall stones.

Doxycycline regulated lentiviral vectors

Lentiviral vectors are a powerful tool to achieve regulated expression of transgenes in vivo and in vitro. The doxycycline-inducible system is well characterized and can be used to regulate expression mediated by lentiviral vectors. Because many different doxycycline-inducible lentiviral vectors have been described, choosing the best vector system can be difficult. This chapter can be used as a guide to select the optimal system for a particular application.

Novel immortalized human fetal liver cell line, cBAL111, has the potential to differentiate into functional hepatocytes

Background

A clonal cell line that combines both stable hepatic function and proliferation capacity is desirable for in vitro applications that depend on hepatic function, such as pharmacological or toxicological assays and bioartificial liver systems. Here we describe the generation and characterization of a clonal human cell line for in vitro hepatocyte applications.

Results

Cell clones derived from human fetal liver cells were immortalized by over-expression of telomerase reverse transcriptase. The resulting cell line, cBAL111, displayed hepatic functionality similar to the parental cells prior to immortalization, and did not grow in soft agar. Cell line cBAL111 expressed markers of immature hepatocytes, like glutathione S transferase and cytokeratin 19, as well as progenitor cell marker CD146 and was negative for lidocaine elimination. On the other hand, the cBAL111 cells produced urea, albumin and cytokeratin 18 and eliminated galactose. In contrast to hepatic cell lines NKNT-3 and HepG2, all hepatic functions were expressed in cBAL111, although there was considerable variation in their levels compared with primary mature hepatocytes. When transplanted in the spleen of immunodeficient mice, cBAL111 engrafted into the liver and partly differentiated into hepatocytes showing expression of human albumin and carbamoylphosphate synthetase without signs of cell fusion.

Conclusion

This novel liver cell line has the potential to differentiate into mature hepatocytes to be used for in vitro hepatocyte applications.

Reduction of liver macrophage transduction by pseudotyping lentiviral vectors with a fusion envelope from Autographa californica GP64 and Sendai virus F2 domain

Background

Lentiviral vectors are well suited for gene therapy because they can mediate long-term expression in both dividing and nondividing cells. However, lentiviral vectors seem less suitable for liver gene therapy because systemically administered lentiviral vectors are preferentially sequestered by liver macrophages. This results in a reduction of available virus and might also increase the immune response to the vector and vector products.

Reduction of macrophage sequestration is therefore essential for efficient lentiviral liver gene therapy.

Results

Fusions were made of Autographa californica GP64 and the hepatocyte specific Sendai Virus envelope proteins. Lentiviral vectors were produced with either wild type GP64, Sendai-GP64, or both wild type GP64 and Sendai-GP64 and tested in vitro and in vivo for hepatocyte and macrophage gene transfer.

Sendai-GP64 pseudotyped vectors showed specific gene transfer to HepG2 hepatoma cells, with no detectable transduction of HeLa cervical carcinoma cells, and a decreased affinity for RAW mouse macrophages. Co-expression of wild type GP64 and Sendai-GP64 resulted in improved viral titers while retaining increased affinity for HepG2 cells.

In vivo, the Sendai-GP64 vectors also showed decreased transduction of murine liver macrophages.

Conclusion

We demonstrate reduced macrophage transduction in vitro and in vivo with GP64/Sendai chimeric envelope proteins.

Autoregulatory lentiviral vectors allow multiple cycles of doxycycline-inducible gene expression in human hematopoietic cells in vivo

The efficient control of gene expression in vivo from lentiviral vectors remains technically challenging. To analyze inducible gene expression in a human setting, we generated 'human immune system' (HIS) mice by transplanting newborn BALB/c Rag2(-/-)IL-2Rgamma(c)(-/-) immunodeficient mice with human hematopoietic stem cells transduced with a doxycycline-inducible lentiviral vector. We compared several methods of doxycycline delivery to mice, and could accurately measure doxycycline in vivo using a new sensitive detection assay. Two different lentiviral vector designs with constitutive (TRECMV-V14) or autoregulatory (TREAuto-V14) expression of an optimized reverse tetracycline transactivator were used to transduce human hematopoietic stem cells. After transplantation into immunodeficient mice, we analyzed the expression of the green fluorescent protein (GFP) reporter gene in the human hematopoiesis-derived cells that develop and accumulate in the generated HIS mice. We show efficient inducible GFP expression in adult HIS mice containing TREAuto-V14-transduced human cells, whereas GFP expression is poor with the TRECMV-V14 vector. Multiple cycles of doxycycline exposure in the TREAuto-V14 group result in repeated cycles of GFP expression with no loss of intensity. These findings are of major interest for gene therapy and basic research settings that require inducible gene expression.

Small animal models of hepatocyte transplantation

In this chapter, we describe techniques used to determine the efficiency of hepatocyte transplantation in animal models of liver disease. We have included the Gunn rat as a model of an inherited liver disease without hepatocyte damage and Abcb4 knockout mice as a model for an inherited liver disease with hepatocyte damage. Immunodeficient mice are included as an animal model for human hepatocyte transplantation.We describe problems that can be encountered in the maintenance and breeding of Gunn rats and immunodeficient Rag2/gamma common knockout mice. Protocols for the collection of bile in rats and mice are described, and we have also detailed the detection of green fluorescent protein (GFP)-labelled human hepatocytes in immunodeficient mice in this chapter.

Engineering physiologically controlled pacemaker cells with lentiviral HCN4 gene transfer

BACKGROUND

Research on biological pacemakers for the heart has so far mainly focused on short-term gene and cell therapies. To develop a clinically relevant biological pacemaker, long-term function and incorporation of autonomic modulation are crucial. Lentiviral vectors can mediate long-term gene expression, while isoform 4 of the Hyperpolarization-activated Cyclic Nucleotide-gated channel (encoded by HCN4) contributes to pacemaker function and responds maximally to cAMP, the second messenger in autonomic modulation.

MATERIAL AND METHODS

Action potential (AP) properties and pacemaker current (I(f)) were studied in single neonatal rat ventricular myocytes that overexpressed HCN4 after lentiviral gene transduction. Autonomic responsiveness and cycle length stability were studied using extracellular electrograms of confluent cultured monolayers.

RESULTS

Perforated patch-clamp experiments demonstrated that HCN4-transduced single cardiac myocytes exhibited a 10-fold higher I(f) than non-transduced single myocytes, along with slow diastolic depolarization, comparable to pacemaker cells of the sinoatrial node, the dominant native pacemaker. HCN4-transduced monolayers exhibited a 47% increase in beating rate, compared to controls. Upon addition of DBcAMP, HCN4-transduced monolayers had beating rates which were 54% faster than baseline and significantly more regular than controls.

CONCLUSIONS

Lentiviral vectors efficiently transduce cardiac myocytes and mediate functional gene expression. Because HCN4-transduced myocytes demonstrate an increase in spontaneous beating rate and responsiveness to autonomic modulation, this approach may be useful to create a biological pacemaker.

Alteration of viral lipid composition by expression of the phospholipid floppase ABCB4 reduces HIV vector infectivity

Background

The presence of cholesterol in the Human Immunodeficiency Virus (HIV) lipid envelop is important for viral function as cholesterol depleted viral particles show reduced infectivity. However, it is less well established whether other viral membrane lipids are also important for HIV infection.

The ABCB4 protein is a phosphatidyl choline (PC) floppase that mediates transport of PC from the inner to the outer membrane leaflet. This property enabled us to modulate the lipid composition of HIV vectors and study the effects on membrane composition and infection efficiency.

Results

Virus generated in the presence of ABCB4 was enriched in PC and cholesterol but contained less sphingomyelin (SM). Viral titers were reduced 5.9 fold. These effects were not observed with an inactive ABCB4 mutant. The presence of the ABC transport inhibitor verapamil abolished the effect of ABCB4 expression on viral titers.

The ABCB4 mediated reduction in infectivity was caused by changes in the viral particles and not by components co purified with the virus because virus made in the presence of ABCB4 did not inhibit virus made without ABCB4 in a competition assay.

Incorporation of the envelope protein was not affected by the expression of ABCB4. The inhibitory effect of ABCB4 was independent of the viral envelope as the effect was observed with two different envelope proteins.

Conclusion

Our data indicate that increasing the PC content of HIV particles reduces infectivity.

Preferential gene transfer of lentiviral vectors to liver-derived cells, using a hepatitis B peptide displayed on GP64

One of the problems that limit the efficiency of viral gene therapy is the lack of specificity of viral particle binding. The development of techniques to target viral particles to specific cell types is therefore important. Because GP64 can efficiently pseudotype lentiviral vectors, we investigated the possibility of using GP64 for lentiviral vector particle targeting. A peptide derived from the hepatitis B virus (HBV) PreS1 protein, with known affinity for an unidentified receptor expressed on hepatocytes, was inserted at amino acid position 278 of the GP64 protein (PreS1-GP64). The GP64 and PreS1-GP64 proteins were expressed and incorporated into lentiviral particles at comparable levels. Flow cytometry measurements confirmed surface display of the PreS1 peptide. The highest titers of PreS1-GP64-pseudotyped lentiviral vectors were observed on liver-derived cell lines. Gene transfer of PreS1-GP64 lentiviral vectors was inhibited by coincubation with an antibody directed against the PreS1 peptide. These data suggest that the PreS1 peptide is involved in viral attachment to the cell surface. The insertion of targeting peptides into the GP64 envelope protein represents a potential approach for the targeting of lentiviral vectors to specific cell types.

The sterol transporting heterodimer ABCG5/ABCG8 requires bile salts to mediate cholesterol efflux

The ATP binding cassette transporters ABCG5 and ABCG8 are indispensable for hepatobiliary cholesterol transport. In this study, we investigated the specificity of the heterodimer for cholesterol acceptors. Dog gallbladder epithelial cells were mono- or double-transfected with lentiviral mouse Abcg5 and Abcg8 vectors. Double-transfected cells showed increased efflux to different bile salt (BS) species, while mono-transfected cells did not show enhanced efflux. The efflux was initiated at micellar concentrations and addition of phosphatidylcholine increased efflux. Cholesterol secretion was highly BS dependent, whereas other cholesterol acceptors such as ApoAI, HDL or methyl-beta-cyclodextrin did not elicit Abcg5/g8 dependent cholesterol secretion.

Domain-wide regulation of gene expression in the human genome

Transcription factor complexes bind to regulatory sequences of genes, providing a system of individual expression regulation. Targets of distinct transcription factors usually map throughout the genome, without clustering. Nevertheless, highly and weakly expressed genes do cluster in separate chromosomal domains with an average size of 80-90 genes. We therefore asked whether, besides transcription factors, an additional level of gene expression regulation exists that acts on chromosomal domains. Here we show that identical green fluorescent protein (GFP) reporter constructs integrated at 90 different chromosomal positions obtain expression levels that correspond to the activity of the domains of integration. These domains are up to 80 genes long and can exert an eightfold effect on the expression levels of integrated genes. 3D-FISH shows that active domains of integration have a more open chromatin structure than integration domains with weak activity. These results reveal a novel domain-wide regulatory mechanism that, together with transcription factors, exerts a dual control over gene transcription.

Biological pacing by gene and cell therapy

At present, cardiac rhythm disorders such as sick sinus syndrome (SSS) or AV nodal block (AVB) are usually treated by electronic pacemakers. These devices have significant shortcomings, including lack of autonomic modulation, and the need for repetitive procedures for battery replacement or lead repositioning. Biological pacemakers as replacement or complement to electronic pacemakers have been the subject of increasing research interest. This research has resulted in many encouraging preclinical studies. Various approaches in the field of gene and cell therapy have been developed by different groups and this combined effort makes it increasingly realistic that this therapy will eventually find its way to clinical applicability. (Neth Heart J 2007;15:318-22.).

Gene therapy to create biological pacemakers

Old age and a variety of cardiovascular disorders may disrupt normal sinus node function. Currently, this is successfully treated with electronic pacemakers, which, however, leave room for improvement. During the past decade, different strategies to initiate pacemaker function by gene therapy were developed. In the search for a biological pacemaker, various approaches were explored, including beta(2)-adrenergic receptor overexpression, down regulation of the inward rectifier current, and overexpression of the pacemaker current. The most recent advances include overexpression of bioengineered ion channels and genetically modified stem cells. This review considers the strengths and the weaknesses of the different approaches and discusses some of the different viral vectors currently used.

Nuclear receptors Nur77, Nurr1, and NOR-1 expressed in atherosclerotic lesion macrophages reduce lipid loading and inflammatory responses

OBJECTIVE

Atherosclerosis is an inflammatory disease in which macrophage activation and lipid loading play a crucial role. In this study, we investigated expression and function of the NR4A nuclear receptor family, comprising Nur77 (NR4A1, TR3), Nurr1 (NR4A2), and NOR-1 (NR4A3) in human macrophages.

METHODS AND RESULTS

Nur77, Nurr1, and NOR-1 are expressed in early and advanced human atherosclerotic lesion macrophages primarily in areas of plaque activation/progression as detected by in situ-hybridization and immunohistochemistry. Protein expression localizes to the nucleus. Primary and THP-1 macrophages transiently express NR4A-factors in response to lipopolysaccharide and tumor necrosis factor alpha. Lentiviral overexpression of Nur77, Nurr1, or NOR-1 reduces expression and production of interleukin (IL)-1beta and IL-6 proinflammatory cytokines and IL-8, macrophage inflammatory protein-1alpha and -1beta and monocyte chemoattractant protein-1 chemokines. In addition, NR4A-factors reduce oxidized-low-density lipoprotein uptake, consistent with downregulation of scavenger receptor-A, CD36, and CD11b macrophage marker genes. Knockdown of Nur77 or NOR-1 with gene-specific lentiviral short-hairpin RNAs resulted in enhanced cytokine and chemokine synthesis, increased lipid loading, and augmented CD11b expression, demonstrating endogenous NR4A-factors to inhibit macrophage activation, foam-cell formation, and differentiation.

CONCLUSIONS

NR4A-factors are expressed in human atherosclerotic lesion macrophages and reduce human macrophage lipid loading and inflammatory responses, providing further evidence for a protective role of NR4A-factors in atherogenesis.

Adeno-associated Virus Vector Serotypes Mediate Sustained Correction of Bilirubin UDP Glucuronosyltransferase Deficiency in Rats

Crigler-Najjar (CN) patients have no bilirubin UDP glucuronosyltransferase (UGT1A1) activity and suffer brain damage because of bilirubin toxicity. Vectors based on adeno-associated virus (AAV) serotype 2 transduce liver cells with relatively low efficiency. Recently, AAV serotypes 1, 6, and 8 have been shown to be more efficient for liver cell transduction. We compared AAV serotypes 1, 2, 6, and 8 for correction of UGT1A1 deficiency in the Gunn rat model of CN disease. Adult Gunn rats were injected with CMV-UGT1A1 AAV vectors. Serum bilirubin was decreased over the first year by 64% for AAV1, 16% for AAV2, 25% for AAV6, and 35% for AAV8. Antibodies to UGT1A1 were detected after injection of all AAV serotypes. An AAV1 UGT1A1 vector with the liver-specific albumin promoter corrected serum bilirubin levels but did not induce UGT1A1 antibodies. Two years after injection of AAV vectors all animals had large lipid deposits in the liver. These lipid deposits were not seen in age-matched control animals. AAV1 vectors are promising candidates for CN gene therapy because they can mediate a reduction in serum bilirubin levels in Gunn rats that would be therapeutic in humans.

Immune response to lentiviral bilirubin UDP-glucuronosyltransferase gene transfer in fetal and neonatal rats

Gene therapy for inherited disorders might cause an immune response to the therapeutic protein. A solution would be to introduce the gene in the fetal or neonatal period, which should lead to tolerization. Lentiviral vectors mediate long-term gene expression, and are well suited for gene therapy early in development. A model for fetal or neonatal gene therapy is the inherited disorder of bilirubin metabolism, Crigler-Najjar disease (CN). The absence of bilirubin UDP-glucoronyltransferase (UGT1A1) activity in CN patients causes high serum levels of unconjugated bilirubin and brain damage in infancy. CN is attractive for the development of gene therapy because the mutant Gunn rat closely mimics the human disease. Injection of UGT1A1 lentiviral vectors corrected the hyperbilirubinemia for more than a year in rats injected as fetuses and for up to 18 weeks in rats injected the day of birth. UGT1A1 gene transfer was confirmed by the presence of bilirubin glucuronides in bile. All animals injected with UGT1A1 lentiviral vectors developed antibodies to UGT1A1. Animals injected with green fluorescent protein (GFP) lentiviral vectors did not develop antibodies to GFP. Our results indicate that fetal and neonatal gene therapy with immunogenic proteins such as UGT1A1 does not necessarily lead to tolerization.

Endothelial KLF2 links local arterial shear stress levels to the expression of vascular tone-regulating genes

Lung Krüppel-like factor (LKLF/KLF2) is an endothelial transcription factor that is crucially involved in murine vasculogenesis and is specifically regulated by flow in vitro. We now show a relation to local flow variations in the adult human vasculature: decreased LKLF expression was noted at the aorta bifurcations to the iliac and carotid arteries, coinciding with neointima formation. The direct involvement of shear stress in the in vivo expression of LKLF was determined independently by in situ hybridization and laser microbeam microdissection/reverse transcriptase-polymerase chain reaction in a murine carotid artery collar model, in which a 4- to 30-fold induction of LKLF occurred at the high-shear sites. Dissection of the biomechanics of LKLF regulation in vitro demonstrated that steady flow and pulsatile flow induced basal LKLF expression 15- and 36-fold at shear stresses greater than approximately 5 dyne/cm2, whereas cyclic stretch had no effect. Prolonged LKLF induction in the absence of flow changed the expression of angiotensin-converting enzyme, endothelin-1, adrenomedullin, and endothelial nitric oxide synthase to levels similar to those observed under prolonged flow. LKLF repression by siRNA suppressed the flow response of endothelin-1, adrenomedullin, and endothelial nitric oxide synthase (P < 0.05). Thus, we demonstrate that endothelial LKLF is regulated by flow in vivo and is a transcriptional regulator of several endothelial genes that control vascular tone in response to flow.

Lentiviral shRNA silencing of murine bone marrow cell CCR2 leads to persistent knockdown of CCR2 function in vivo

A major barrier in hematopoietic gene function studies is posed by the laborious and time-consuming generation of knockout mice with an appropriate genetic background. Here we present a novel lentivirus-based strategy for the in situ generation of hematopoietic knockdowns. A short hairpin RNA (shRNA) was designed targeting murine CC-chemokine receptor 2 (CCR2), which was able to specifically blunt CCR2 expression at the mRNA, protein, and functional levels in vitro. Reconstitution of irradiated recipient mice with autologous bone marrow that had been ex vivo transduced with shRNA lentivirus led to persistent down-regulation of CCR2 expression, which translated into a 70% reduction in CCR2-dependent recruitment of macrophages to an inflamed peritoneal cavity without noticeable side effects on related chemokine receptors or general inflammation status. These findings clearly demonstrate the potential of shRNA lentivirus-infected bone marrow transplantation as a rapid and effective method to generate hematopoietic knockdowns for leukocyte gene function studies.

Comparison of single regulated lentiviral vectors with rtTA expression driven by an autoregulatory loop or a constitutive promoter

Regulated expression of a therapeutic gene is crucial for safe and efficacious gene therapy. Many inducible regulatory systems use a constitutive promoter to express a regulatory protein, such as rtTA in the Tet-On system, which may restrict their use because of cytotoxicity and immunogenicity. Autoregulatory expression of rtTA provides extremely low levels of rtTA when transgene expression is off, with rapid transgene induction upon addition of doxycycline. Lentiviral vectors efficiently transfer genes to dividing and non-dividing cells with long-term gene expression both in vitro and in vivo. We compared regulatory function in a single lentiviral vector where rtTA was either expressed from a constitutive promoter or placed in an autoregulatory loop. Autoregulatory expression of rtTA was superior to constitutive promoter expression, resulting in higher viral titers, undetectable levels of both rtTA and transgene expression in the absence of doxycycline, improved induction kinetics and increased induction levels in all cells tested. We further expanded the utility of the autoregulatory vector by using an improved rtTA variant with an increased sensitivity to doxycycline. This lentiviral vector with doxycycline-regulated transgene expression may be useful for gene therapy applications and in experimental settings where strict temporal expression of a transgene is required.

Kupffer Cells and Not Liver Sinusoidal Endothelial Cells Prevent Lentiviral Transduction of Hepatocytes

Lentiviral vectors can stably transduce dividing and nondividing cells in vivo and are best suited to long-term correction of inherited liver diseases. Intraportal administration of lentiviral vectors expressing green fluorescent protein (Lenti-GFP) in mice resulted in a higher transduction of nonparenchymal cells than hepatocytes (7.32 +/- 3.66% vs 0.22 +/- 0.08%, respectively). Therefore, various treatments were explored to increase lentiviral transduction of hepatocytes. Lenti-GFP was injected into the common bile duct, which led to transduction of biliary epithelium and hepatocytes at low efficiency. Transient removal of the sinusoidal endothelial cell layer by cyclophosphamide to increase accessibility to hepatocytes did not improve hepatocyte transduction (0.42 +/- 0.36%). Inhibition of Kupffer cell function by gadolinium chloride led to a significant decrease in GFP-positive nonparenchymal cells (2.15 +/- 3.14%) and a sevenfold increase in GFP-positive hepatocytes compared to nonpretreated mice (1.48 +/- 2.01%). These findings suggest that sinusoidal endothelial cells do not significantly limit lentiviral transduction of hepatocytes, while Kupffer cells sequester lentiviral particles thereby preventing hepatocyte transduction. Therefore, the use of agents that inhibit Kupffer cell function may be important for lentiviral vector treatment of liver disease.