Hypoxia-inducible factor signaling provides protection in Clostridium difficile-induced intestinal injury

BACKGROUND & AIMS

Clostridium difficile is the leading cause of nosocomial infectious diarrhea. Antibiotic resistance and increased virulence of strains have increased the number of C difficile-related deaths worldwide. The innate host response mechanisms to C difficile are not resolved; we propose that hypoxia-inducible factor (HIF-1) has an innate, protective role in C difficile colitis. We studied the impact of C difficile toxins on the regulation of HIF-1 and evaluated the role of HIF-1alpha in C difficile-mediated injury/inflammation.

METHODS

We assessed HIF-1alpha mRNA and protein levels and DNA binding in human mucosal biopsy samples and Caco-2 cells following exposure to C difficile toxins. We used the mouse ileal loop model of C difficile toxin-induced intestinal injury. Mice with targeted deletion of HIF-1alpha in the intestinal epithelium were used to assess the effects of HIF-1alpha signaling in response to C difficile toxin.

RESULTS

Mucosal biopsy specimens and Caco-2 cells exposed to C difficile toxin had a significant increase in HIF-1alpha transcription and protein levels. Toxin-induced DNA binding was also observed in Caco-2 cells. Toxin-induced HIF-1alpha accumulation was attenuated by nitric oxide synthase inhibitors. In vivo deletion of intestinal epithelial HIF-1alpha resulted in more severe, toxin-induced intestinal injury and inflammation. In contrast, stabilization of HIF-1alpha with dimethyloxallyl glycine attenuated toxin-induced injury and inflammation. This was associated with induction of HIF-1-regulated protective factors (such as vascular endothelial growth factor-alpha, CD73, and intestinal trefoil factor) and down-regulation of proinflammatory molecules such as tumor necrosis factor and Cxcl1.

CONCLUSIONS

HIF-1alpha protects the intestinal mucosa from C difficile toxins. The innate protective actions of HIF-1alpha in response to C difficile toxins be developed as therapeutics for C difficile-associated disease.

Innate immunity: cytoplasmic DNA sensing by the AIM2 inflammasome

Cytoplasmic double-stranded DNA triggers cell death and secretion of the pro-inflammatory cytokine IL-1beta in macrophages. Recent reports now describe the mechanism underlying this observation. Upon sensing of DNA, the HIN-200 family member AIM2 triggers the assembly of the inflammasome, culminating in caspase-1 activation, IL-1beta maturation and pyroptotic cell death.

The inflammasome recognizes cytosolic microbial and host DNA and triggers an innate immune response

The innate immune system recognizes nucleic acids during infection and tissue damage. Whereas viral RNA is detected by endosomal toll-like receptors (TLR3, TLR7, TLR8) and cytoplasmic RIG-I and MDA5, endosomal TLR9 and cytoplasmic DAI bind DNA, resulting in the activation of nuclear factor-kappaB and interferon regulatory factor transcription factors. However, viruses also trigger pro-inflammatory responses, which remain poorly defined. Here we show that internalized adenoviral DNA induces maturation of pro-interleukin-1beta in macrophages, which is dependent on NALP3 and ASC, components of the innate cytosolic molecular complex termed the inflammasome. Correspondingly, NALP3- and ASC-deficient mice display reduced innate inflammatory responses to adenovirus particles. Inflammasome activation also occurs as a result of transfected cytosolic bacterial, viral and mammalian (host) DNA, but in this case sensing is dependent on ASC but not NALP3. The DNA-sensing pro-inflammatory pathway functions independently of TLRs and interferon regulatory factors. Thus, in addition to viral and bacterial components or danger signals in general, inflammasomes sense potentially dangerous cytoplasmic DNA, strengthening their central role in innate immunity.

The inflammasome: a danger sensing complex triggering innate immunity

The NOD-like receptors (NLR) are a family of intracellular sensors of microbial motifs and 'danger signals' that have emerged as being crucial components of the innate immune responses and inflammation. Several NLRs (NALPs and IPAF) form a caspase-1-activating multiprotein complex, termed inflammasome, that processes proinflammatory cytokines including IL-1beta. Amongst the various inflammasomes, the NALP3 inflammasome is particularly qualified to sense a plethora of diverse molecules, ranging from bacterial muramyldipeptide to monosodium urate crystals. The important role of the NALP3 inflammasome is emphasized by the identification of mutations in the NALP3 gene that are associated with a susceptibility to inflammatory disorders. These and other issues related to the inflammasome are discussed in this review.

Reovirus decreases azoxymethane-induced aberrant crypt foci and colon cancer in a rodent model

Reovirus type 3 Dearing has demonstrated oncolytic efficacy in vitro and in vivo against a variety of cancer cell lines, tumor xenografts and syngeneic cancer models. In this study, we investigated the effectiveness of reovirus against aberrant crypt foci (ACF) and colon cancer induced by the carcinogen azoxymethane (AOM) in an immunocompetent rat model. Sprague-Dawley rats received 15 mg/kg AOM intraperitoneally once per week for 4 weeks and reovirus was administered rectally once a week for 5 weeks starting 20 weeks after the last dose of AOM. Two weeks after completion of reovirus therapy, animals were examined for tumor burden in the colon and other tissues. Reovirus-treated animals showed a decrease in total ACF numbers (P=0.014), in large ACFs (P=0.0069) and in tumor number (P=0.03) compared to vehicle-treated animals. Fewer obstructing tumors in the colon (P=0.07) and duodenum (P=0.03) and reduced hepatic metastases were also noted. In addition, a tumor cell line derived from hepatic metastases was found to be susceptible to reovirus in vitro. Our results show that repeated rectal reovirus administration had some efficacy in the treatment and prevention of AOM-induced ACFs, colon cancers and metastases.

The characterization of alpha5-integrin expression on tubular epithelium during renal injury

The hallmark of progressive chronic kidney disease is the deposition of extracellular matrix proteins and tubulointerstitial fibrosis. Integrins mediate cell-extracellular matrix interaction and may play a role tubular epithelial injury. Murine primary tubular epithelial cells (TECs) express alpha(5)-integrin, a fibroblast marker and the natural receptor for fibronectin. Microscopy localized alpha(5)-integrin on E-cadherin-positive cells, confirming epithelial expression. The expression of alpha(5)-integrin increased in TECs grown on fibronectin and occurred in parallel with an upregulation of alpha-smooth muscle actin (alphaSMA), a marker of epithelial-mesenchymal transition (EMT). Exposure of TECs to transforming growth factor (TGF)-beta also increased TEC alpha(5)-integrin expression in association with alphaSMA and EMT. Knock-down of alpha5-integrin expression with short interfering RNA attenuated the TGF-beta induction of alphaSMA but did not alter morphologic EMT. Rather, alpha5-integrin was necessary for epithelial cell migration on fibronectin but not type IV collagen during cell spreading and epithelial wound healing in vitro. Immunohistochemistry revealed basolateral tubular epithelial alpha(5)-integrin expression in mouse kidneys after unilateral ureteric obstruction but not in contralateral control kidneys. In patient biopsies of nondiabetic kidney disease, alpha(5)-integrin expression was increased significantly in the renal interstitium. Focal basolateral staining was also detected in injured, but not in normal, tubular epithelium. In summary, these data show that TECs are induced to express alpha(5)-integrin during EMT and tubular epithelial injury in vitro and in vivo. These results increase our understanding of the biology of integrins during EMT and tubular injury in chronic kidney disease.

Isolation of neutrophils from mouse liver: A novel method to study effector leukocytes during inflammation

Neutrophils are phagocytic leukocytes that represent one of the first lines of defense during infection and injury. Neutrophils emigrate into tissues during inflammation and are phenotypically different compared to cells in the circulation. To further understand the biology of tissue-recruited neutrophils, we have developed a reliable method to isolate these cells from inflamed liver. Acute liver inflammation was induced in mice by systemic treatment with adenovirus vectors. Two hours following adenovirus treatment, livers were enzymatically digested and leukocytes isolated by Percoll density gradient centrifugation. Neutrophils were then purified by negative immunomagnetic separation. Neutrophils isolated in this manner were 95% pure as determined by flow cytometry and more than 97% viable by propidium iodide staining. In order to carry out molecular studies, we extracted high quality genomic DNA and RNA from isolated neutrophils. PCR was used to successfully amplify sample genes from isolated neutrophil DNA. Isolated neutrophil RNA was used in a ribonuclease protection assay to evaluate chemokine gene expression. Neutrophils were shown to express multiple chemokine mRNA transcripts including MIP-1 beta, MIP-2 and IP-10. This work describes a novel method to isolate highly pure, viable neutrophils from pathologically inflamed tissue for subsequent detailed cellular and molecular analysis.

Akt/protein kinase B activation by adenovirus vectors contributes to NFkappaB-dependent CXCL10 expression

In gene therapy, the innate immune system is a significant barrier to the effective application of adenovirus (Ad) vectors. In kidney epithelium-derived (REC) cells, serotype 5 Ad vectors induce the expression of the chemokine CXCL10 (IP-10), a response that is dependent on NFkappaB. Compared to the parental vector AdLuc, transduction with the RGD-deleted vector AdL.PB resulted in reduced CXCL10 activation despite increasing titers, implying that RGD-alpha(V) integrin interactions contribute to adenovirus induction of inflammatory genes. Akt, a downstream effector of integrin signaling, was activated within 10 min of transduction with Ad vectors in a dose-dependent manner. Akt activation was not present following transduction with AdL.PB, confirming the importance of capsid-alpha(V) integrin interactions in Ad vector Akt activation. Inhibition of the phosphoinositide-3-OH kinase/Akt pathway by Wortmannin or Ly294002 compounds decreased Ad vector induction of CXCL10 mRNA. Similarly, adenovirus-mediated overexpression of the dominant negative AktAAA decreased CXCL10 mRNA expression compared to the reporter vector AdLacZ alone. The effect of Akt on CXCL10 mRNA expression occurred via NFkappaB-dependent transcriptional activation, since AktAAA overexpression and Ly294002 both inhibited CXCL10 and NFkappaB promoter activation in luciferase reporter experiments. These results show that Akt plays a role in the Ad vector activation of NFkappaB and CXCL10 expression. Understanding the mechanism underlying the regulation of host immunomodulatory genes by adenovirus vectors will lead to strategies that will improve the efficacy and safety of these agents for clinical use.

Neutrophils interact with adenovirus vectors via Fc receptors and complement receptor 1

Neutrophils are effectors of the innate immune response to adenovirus vectors. Following the systemic administration of Cy2-labeled AdLuc in mice, flow cytometry and PCR analysis of liver leukocytes revealed that 25% of recruited neutrophils interacted with adenovirus vectors. In vitro, flow cytometry of human neutrophils incubated with Cy2-labeled AdLuc also demonstrated a significant interaction with adenovirus vectors. Fluorescence and electron microscopy confirmed vector internalization by neutrophils. The AdLuc-neutrophil interaction reduced vector transduction efficiency by more than 50% in coincubation assays in epithelium-derived cells. Adenovirus vector uptake by neutrophils occurred independently of coxsackievirus adenovirus receptor (CAR) and capsid RGD motifs, since neutrophils do not express CAR and uptake of the RGD-deleted vector AdL.PB* was similar to that of AdLuc. Furthermore, both AdLuc and AdL.PB* activated neutrophils and induced similar degrees of L-selectin shedding. Neutrophil uptake of AdLuc was dependent on the presence of complement and antibodies, since the interaction between AdLuc and neutrophils was significantly reduced when they were incubated in immunoglobulin G-depleted or heat-inactivated human serum. Blocking of complement receptor 1 (CD35) but not complement receptor 3 (CD11b/CD18) significantly reduced neutrophil uptake of AdLuc. Blocking of Fc gammaRI (CD64), Fc gammaRII (CD32), and Fc gammaRIII (CD16) individually or together also reduced neutrophil uptake of AdLuc, although less than blocking of CD35 alone. Combined CR1 and Fc receptor blockade synergistically inhibited neutrophil-AdLuc interactions close to baseline. These results demonstrate opsonin-dependent adenovirus vector interactions with neutrophils and their corresponding receptors.

Use of a murine secreted alkaline phosphatase as a non-immunogenic reporter gene in mice

BACKGROUND

The development of any vector system as a gene delivery system requires its optimization in vitro and in vivo. Preliminary studies frequently involve the use of a reporter gene, which allows for the rapid and simple assay of vector function through monitoring expression levels of the reporter gene. However, evaluation of vector efficacy can be compromised by immune responses directed against immunogenic reporter proteins.

METHODS

We have cloned a murine secreted alkaline phosphatase (mSEAP), and explored its use as a reporter gene in the context of an early region 1 (E1)-deleted adenovirus (Ad) vector. Studies involved characterization of gene expression in vitro and in vivo, and immunological responses after gene delivery to mice.

RESULTS

In tissue culture, we show that mSEAP is easily measured quantitatively using a sensitive, commercially available chemiluminescent assay, or visualized directly using histological staining. The level of transgene expression from AdmSEAP was similar to that observed for an Ad vector encoding the human placental secreted alkaline phosphatase (hSEAP). After intravenous administration in mice, AdmSEAP continued to express at high levels for the duration of the experiment (1 month), whereas expression from AdhSEAP declined to background levels over the course of the experiment. Although cytotoxic T-lymphocytes were not detected against either the murine or human SEAP proteins in mice, antibodies were readily detected against the human protein. No antibodies were detected to mSEAP.

CONCLUSIONS

Taken together, these data illustrate that mSEAP is a sensitive, non-immunogenic reporter gene for preclinical mouse studies.

Soluble fibronectin induces chemokine gene expression in renal tubular epithelial cells

BACKGROUND

Increasing proteinuria in kidney disease is associated with an increased risk of renal failure. Urinary proteins such as albumin induce inflammatory signaling and gene expression in tubular epithelial cells (TECs). Fibronectin is an extracellular matrix protein that can exist in soluble form and is excreted in the urine of patients with glomerular disease.

METHODS

To explore the impact of soluble fibronectin on tubular epithelium, murine TECs were stimulated with soluble fibronectin and chemokine mRNA was determined by RNase protection assay.

RESULTS

Fibronectin induced the expression of inflammatory chemokine genes, including monocyte chemoattractant protein-1 (MCP-1) (CCL2) and macrophage inflammatory protein-2 (MIP-2) within 2 hours in a dose-dependent manner. Phosphorylation of Src family tyrosine kinases was also increased in TECs following exposure to fibronectin. Src tyrosine kinases were involved in the fibronectin activation of MCP-1 since the Src inhibitors SU6656 and PP2 effectively reduced the induction of this chemokine. Fibronectin also induced the phosphorylation of extracellular signal-regulated protein kinase (ERK1/2) within minutes in TECs. The ERK kinase (MEK1/2) inhibitor U0126 inhibited the fibronectin induction of MCP-1 mRNA suggesting that ERK1/2 was also involved in this inflammatory pathway. Furthermore, fibronectin also induced phosphorylation of IkappaBalpha within 20 minutes in TECs. The nuclear factor-kappaB (NF-kappaB) inhibitors N-acetyl-L-cysteine (NAC) and pyrrolidinecarbodithioic acid (PDTC) effectively blocked fibronectin induction of MCP-1 mRNA.

CONCLUSION

Soluble fibronectin activates MCP-1 gene expression in TECs via Src tyrosine kinases, ERK1/2 and NF-kappaB. These data provide further support to the concept that proteinuria per se contributes to the tubulointerstitial injury observed in glomerular disease.

The chemokine GRO-alpha (CXCL1) confers increased tumorigenicity to glioma cells

The chemokine GRO-alpha (CXCL1) has been found to mediate the proliferation of glia progenitor cells during neural development. As malignant gliomas are thought to arise from glia progenitors or their differentiated counterparts, astrocytes or oligodendrocytes, we have investigated whether GRO-alpha regulates the tumor characteristics of glioma cells. We found first that resected glioma specimens were strongly immunoreactive for GRO-alpha expression in cells with the morphology of tumor cells. In culture, the U251 glioma line transfected to overexpress GRO-alpha had elevated levels of motility and invasiveness. GRO-alpha transfectants increased their expression of several proteins associated with migratory behavior, including matrix metalloproteinase-2, beta1-integrin and SPARC. The implantation of GRO-alpha glioma clones into the brain of nude mice caused the early demise of mice and this was associated with the formation of larger intracerebral tumors when compared with mice implanted with vector control lines. These results implicate GRO-alpha in gliomas and suggest that the dysregulation of a glia proliferative factor contributes to tumorigenesis. Targeting GRO-alpha may be a useful therapeutic tool to control brain tumor biology.

Immune Responses to Adeno-Associated Virus Vectors

One of the biggest challenges in optimizing viral vectors for gene therapy relates to the immune response of the host. Adeno-associated virus (AAV) vectors are associated with low immunogenicity and toxicity, resulting in vector persistence and long-term transgene expression. The inability of AAV vectors to efficiently transduce or activate antigen presenting cells (APCs) may account for their decreased immunogenicity. AAV mediated gene therapy however, leads to the development of antibodies against the vector capsid. Anti-AAV antibodies have neutralizing effects that decrease the efficiency of in vivo gene therapy and can prevent vector re-administration. Furthermore, recent studies have shown that AAV vectors can elicit both cellular and humoral immune responses against the transgene product. Both cell-mediated response and humoral response to the delivered gene depend on a number of variables; including the nature of the transgene, the promoter used, the route and site of administration, vector dose and host factors. The response of the host to the vector, in terms of antigen-specific immunity, will play a substantial role in clinical outcome. It is therefore important to understand both, why AAV vectors are able to escape immunity and the circumstances and mechanisms that lead to the induction of immune responses. This review will summarize innate and adaptive immune responses to AAV vectors, discuss possible mechanisms and outline strategies, such as capsid modifications, use of alternative serotypes, or immunosuppression, which have been used to circumvent them.

The induction of inflammation by adenovirus vectors used for gene therapy

The ability to repair or enhance an individual's genetic make-up provides the sublime opportunity to ameliorate or eliminate many clinical disorders that affect mankind. Gene therapy is thus a revolutionary clinical strategy that may potentially treat an array of genetic and non-genetic diseases, as well as a novel method for drug delivery and vaccination. To these ends, adenovirus vectors are currently the most promising means to deliver specific genes of interest into target cells of the patient. A major limitation of the use of adenovirus vectors in clinical trials, however, is the rapidly induced inflammatory response against these infectious particles. This review aims to describe the cellular and molecular mechanisms involved in the adenovirus-mediated inflammatory response.

The Innate Immune Response to Adenovirus Vectors

Gene therapy is a clinical strategy that may potentially treat an array of genetic and nongenetic diseases, as well as a novel method for drug delivery and vaccination. To these ends, adenovirus vectors are a promising means to deliver specific genes of interest into the patient. A major limitation of the use of adenovirus vectors is the host immune response. Adenovirus vectors induce the innate arm of the immune system that results in inflammation of transduced tissues and efficient clearance of administered vectors. Unlike adaptive immunity, the innate response is mediated by the adenovirus particle and does not require viral transcription. In vivo, the innate immune response involves the induction of cytokines and activation of effector leukocytes that comprise the host response to these agents. A number of interactions with leukocytes and with epithelial and endothelial cells are essential in triggering the host response to adenovirus vectors. Signal transduction via MAP kinases and NF-kappaB-mediated gene transcription are triggered during early virus-cell interactions and are key events in the innate recognition of adenovirus vector transduction. This review aims to describe data examining cellular and molecular mechanisms involved in the adenovirus-mediated innate immune response.

Helper-dependent adenovirus vectors elicit intact innate but attenuated adaptive host immune responses in vivo

Helper-dependent adenovirus (HD-Ad) vectors with all adenoviral genes deleted mediate very long-term expression of therapeutic transgenes in a variety of animal models of disease. These vectors are associated with reduced toxicity and improved safety relative to traditional early region 1 deletion first-generation Ad (FG-Ad) vectors. Many studies have clearly demonstrated that FG-Ad vectors induce innate and adaptive immune responses in vivo; however, a comprehensive analysis of host immune responses to HD-Ad vectors has not yet been performed. In DBA/2 mice, intravenous injection of HD-Ad vectors encoding LacZ (HD-AdLacZ) or a murine secreted alkaline phosphatase (HD-AdSEAP) induced an early expression of inflammatory cytokine and chemokine genes in the liver, including interferon-inducible protein 10, macrophage inflammatory protein 2, and tumor necrosis factor alpha, and were expressed in a pattern similar to that induced by FG-Ad vectors encoding AdSEAP. Like AdSEAP, and consistent with the pattern of cellular gene expression, HD-AdLacZ and HD-AdSEAP induced the recruitment of CD11b-positive leukocytes to the transduced liver within hours of administration. AdSEAP also induced a second phase of liver inflammation, consisting of inflammatory gene expression and CD3-positive lymphocytic infiltrates 7 days posttransduction. In contrast, beyond 24 h no infiltrates or expression of inflammatory genes was detected in the livers of mice receiving HD-AdSEAP. Despite the lack of liver inflammation at 7 days, Ad-specific cytotoxic T lymphocytes could be detected in mice receiving HD-AdSEAP. This lack of liver inflammation was not due to reduced transduction since levels of transgene expression and the amounts of vector DNA in the liver were equivalent in mice receiving HD-AdSEAP and AdSEAP. These results demonstrate that HD-Ad vectors induce intact innate but attenuated adaptive immune responses in vivo.

Molecular basis of the inflammatory response to adenovirus vectors

Adenovirus vectors are extensively studied in experimental and clinical models as agents for gene therapy. Recent generations of helper-dependent adenovirus vectors have the majority of viral genes removed and result in vectors with a large carrying capacity, reduced host adaptive immune responses and improved gene transfer efficiency. Adenovirus vectors, however, activate innate immune responses shortly after administration in vivo. Unlike the adaptive response, the innate response to adenovirus vectors is transcription independent and is caused by the viral particle or capsid. This response results in inflammation of transduced tissues and substantial loss of vector genomes in the first 24 h. The adenovirus capsid activates a number of signaling pathways following cell entry including p38 mitogen-activated protein kinase and extracellular signal-regulated kinase (ERK) that ultimately lead to expression of proinflammatory genes. Various cytokines, chemokines and leukocyte adhesion molecules are induced by the adenovirus particle in a wide range of cell types providing a molecular basis for the inflammatory properties of these vectors. An understanding of the innate response to adenovirus vectors is essential to overcome the last remaining hurdle to improve the safety and effectiveness of these agents.

The role of capsid-endothelial interactions in the innate immune response to adenovirus vectors

Adenovirus (Ad) vectors can produce inflammatory responses at high doses. Intravenous administration of an Ad vector expressing green fluorescent protein (AdGFP) to naive mice induced a biphasic pattern of liver cytokine/chemokine gene expression over 7 days. Tumor necrosis factor alpha (TNF-alpha), macrophage inflammatory protein 2 (MIP-2), and interferon gamma-inducible protein 10 (IP-10) genes were upregulated, with two distinct peaks of mRNA expression occurring at 6 hr and 5 days. The administration of transcription-defective AdGFP particles induced the early but not the late peak of chemokine/cytokine gene expression, confirming that Ad vector-induced inflammation is capsid dependent in the early phase and transcription dependent in the late phase. To determine the role of adenoviral capsid motifs in the early phase, capsid-modified Ad vectors were employed. The intravenous administration of the RGD-deleted Ad vector AdL.PB*, the fiber mutant AdL.F*, or the double mutant AdL.F*PB* induced similar levels of cytokine/chemokine expression compared with the wild-type vector AdLuc. Kupffer cell blockade significantly reduced liver TNF-alpha, MIP-2, and IP-10 gene expression and liver inflammation after the administration of AdL.PB* or AdL.F*PB*. Fluorescence microscopy of AdLuc- and AdL.PB*-transduced liver at 1 hr revealed localization of Ad vectors to liver sinusoids in Kupffer cell-depleted mice. AdL.PB* induced less E-selectin and VCAM-1 gene expression in liver, confirming reduced endothelial activation in mice receiving RGD-deleted Ad vectors. In vitro studies of endothelial cells demonstrated reduced transduction and endothelial activation by AdL.PB* compared with AdLuc. These results demonstrate that adenovirus capsid RGD motifs are required for efficient transduction and endothelial cell activation. Altering vector tropism represents a feasible strategy to modulate the innate response to Ad vectors in nontargeted tissues.

The role of selectins and integrins in adenovirus vector-induced neutrophil recruitment to the liver

Adenovirus vectors for human gene therapy induce early host inflammatory responses in transduced tissues that limit gene transfer efficiency and can result in significant morbidity. The present study aimed to elucidate the cellular mechanisms underlying the acute inflammation induced by adenovirus vectors in the liver. Leukocyte rolling and adhesion in response to an intravenously administered adenovirus vector was examined by intravital microscopy in mouse liver. Adenovirus vectors significantly increased leukocyte rolling and adhesion in the postsinusoidal venules within minutes of transduction. Unlike other inflammatory states in the liver, no leukocyte retention was seen in the sinusoids in response to adenovirus vector administration. Inhibition of P-selectin, alpha(4)-integrin, and E-selectin was necessary to completely block leukocyte rolling and subsequent adhesion. The administration of an anti-alpha(4)-integrin antibody alone significantly reduced leukocyte adhesion. In contrast, adenovirus vector-induced leukocyte adhesion was unchanged in CD18-knockout mice. Depletion of circulating neutrophils eliminated leukocyte rolling and adhesion in response to adenovirus vector transduction in the liver. In conclusion, adenovirus vectors induce rapid neutrophil-mediated inflammation in the post-sinusoidal venules by selectins and alpha(4)-integrin but surprisingly not by CD18.

Complement factor B gene regulation: synergistic effects of TNF-alpha and IFN-gamma in macrophages

Complement factor B (Bf) plays an important role in activating the alternative complement pathway. The inflammatory cytokines, in particular TNF-alpha and IFN-gamma, are critical in the regulation of Bf gene expression in macrophages. In this study, we investigated the mechanisms of Bf gene regulation by TNF-alpha and IFN-gamma in murine macrophages. Northern analysis revealed that Bf mRNA expression was synergistically up-regulated by TNF-alpha and IFN-gamma in MH-S cells. Truncations of the 5' Bf promoter identified a region between -556 and -282 bp that mediated TNF-alpha responsiveness as well as the synergistic effect of TNF-alpha and IFN-gamma on Bf expression. Site-directed mutagenesis of a NF-kappaB-binding element in this region (-433 to -423 bp) abrogated TNF-alpha responsiveness and decreased the synergistic effect of TNF-alpha and IFN-gamma on Bf expression. EMSAs revealed nuclear protein binding to this NF-kappaB cis-binding element on TNF-alpha stimulation. Supershift analysis revealed that both p50 and p65 proteins contribute to induction of Bf by TNF-alpha. An I-kappaB dominant negative mutant blocked Bf induction by TNF-alpha and reduced the synergistic induction by TNF-alpha and IFN-gamma. In addition, the proteasome inhibitor MG132, which blocks NF-kappaB induction, blocked TNF-alpha-induced Bf promoter activity and the synergistic induction of Bf promoter activity by TNF-alpha and IFN-gamma. LPS was found to induce Bf promoter activity through the same NF-kappaB cis-binding site. These findings suggest that a NF-kappaB cis-binding site between -433 and -423 bp is required for TNF-alpha responsiveness and for TNF-alpha- and IFN-gamma-stimulated synergistic responsiveness of the Bf gene.

Differential activation of innate immune responses by adenovirus and adeno-associated virus vectors

Adenovirus vectors induce acute inflammation of infected tissues due to activation of the innate immune system and expression of numerous chemokines and cytokines in transduced target cells. In contrast, adeno-associated virus (AAV) vectors are not associated with significant inflammation experimentally or clinically. We tested the ability of AAV vectors to induce the expression of chemokines in vitro and to activate the innate immune system in vivo. In human HeLa cells and murine renal epithelium-derived cells (REC cells) the adenovirus vector AdlacZ induced the expression of multiple inflammatory chemokines including RANTES, interferon-inducible protein 10 (IP-10), interleukin-8 (IL-8), MIP-1beta, and MIP-2 in a dose-dependent manner. The use of AAVlacZ did not induce the expression of these chemokines above baseline levels despite 40-fold-greater titers than AdlacZ and greater amounts of intracellular AAVlacZ genomes according to Southern and slot blot analysis. This finding confirmed that the lack of AAVlacZ induction of chemokine was not due to reduced transduction. In DBA/2 mice, the intravenous administration of 2.5 x 10(11) particles of AAVlacZ resulted in the rapid induction of liver tumor necrosis factor alpha (TNF-alpha), RANTES, IP-10, MIP-1beta, MCP-1, and MIP-2 mRNAs. However, 6 h following injection, chemokine mRNA levels returned to baseline. As expected, administration of 10-fold less AdlacZ caused an induction of liver TNF-alpha and chemokine mRNAs that persisted for more than 24 h posttransduction. Whereas intravenous administration of 2.5 x 10(11) particles of AAVlacZ triggered a transient infiltration of neutrophils and CD11b(+) cells into liver, this response stood in contrast to widespread inflammation and toxicity induced by AdlacZ. Kupffer cell depletion abolished AAVlacZ but not AdlacZ-induced chemokine expression and neutrophil infiltration. In summary, these results show that AAV vectors activate the innate immune system to a lesser extent than do adenovirus vectors and offer a possible explanation for the reduced inflammatory properties of AAV compared to adenovirus vectors.

Adenovirus vector-induced inflammation: capsid-dependent induction of the C-C chemokine RANTES requires NF-kappa B

Adenovirus vectors for gene therapy activate responses in the host that result in acute inflammation of transduced tissues. Our previous studies in vivo demonstrate that chemokines, including the C-C chemokine RANTES (regulated on activation, normal T cell expressed and secreted), contribute to the acute inflammation induced by adenovirus vectors. Various first-generation adenovirus vectors, including adCMV beta gal, were equally capable of inducing the expression of RANTES 3 hr after transduction in epithelial HeLa and REC cells. Deletional analysis of the human RANTES promoter revealed that induction by adCMV beta gal required the elements spanning base pairs -90 to -25 of the gene. Electrophoretic mobility shift assays demonstrated that nuclear extracts from adCMV beta gal-transduced HeLa cells bound to an NF-kappa B site at position -54. Overexpression of I-kappa B alpha suppressed adCMV beta gal induction of RANTES, confirming that this process was dependent on the nuclear translocation of NF-kappa B. The coxsackievirus-adenovirus receptor (CAR)-independent, serotype 3 adenovirus was equally capable of inducing the expression of RANTES in HeLa cells. This observation suggested that binding to CAR was not specifically required in adenovirus vector-induced RANTES expression. The use of RGD peptides to block adCMV beta gal interactions with alpha(v)-integrins reduced RANTES expression but also transduction efficiency. In CAR-deficient P815 cells, binding of adCMV beta gal to alpha(v)-integrins without efficient cell transduction did not result in increased RANTES expression. Expression of human CAR in P815 cells increased the binding and transduction efficiency of adCMV beta gal and resulted in RANTES expression in these cells. These results suggest that the induction of RANTES by adenovirus vectors is dependent on efficient interaction with its cell surface receptors and vector internalization. Understanding the biology of the host response to adenovirus vectors will impact the design of future generations of these agents aimed at reducing their immunogenicity and improving their safety.

Activation of p38 and ERK signaling during adenovirus vector cell entry lead to expression of the C-X-C chemokine IP-10

The use of adenovirus vectors for human gene therapy is limited by potent inflammatory responses that result in significant morbidity. In kidney-derived epithelial cells (REC), activation of extracellular signal-regulated kinase 1/2 (ERK) and p38 kinase (p38) pathways occurred within 20 min of transduction with the serotype 5 adenovirus vector AdCMV beta gal. Inhibition of ERK and p38 with U0126 and SB203580, respectively, reduced the expression of IP-10 mRNA following transduction with AdCMV beta gal. To determine the role of the coxsackievirus-adenovirus receptor (CAR) or alpha(v) integrins in the activation of ERK and p38 and the expression of IP-10, REC cells were transduced with the fiber-modified and RGD-deleted adenovirus vectors AdL.F(RAEK-HA) and AdL.PB(HA), respectively. Compared with the wild-type capsid vector Ad5Luc, transduction with AdL.F(RAEK-HA) and AdL.PB(HA) resulted in reduced ERK-p38 activation and less IP-10 mRNA expression. The decreased IP-10 expression induced by the tropism-modified vectors was due to diminished transduction, since increasing multiplicity of infection resulted in increased IP-10 expression. Inhibition of adenovirus penetration with bafilomycin A1 or ammonium chloride attenuated the activation of ERK-p38 and IP-10 mRNA expression following infection, suggesting that endosomal escape was required to trigger these pathways. In vivo, direct inhibition of ERK and p38 signaling pathways inhibited adenovirus vector-induced IP-10 expression in mouse liver 1 h following transduction. These results demonstrate the importance of signaling via ERK and p38 in the early host response to adenovirus vectors and will permit the development of novel strategies to improve the safety and efficacy of these agents in human gene therapy.

Diabetes mellitus increases endothelin-1 gene transcription in rat kidney

BACKGROUND

Mesangial cell hypertrophy and increased extracellular matrix (ECM) contribute to mesangial expansion in early progressive diabetic nephropathy. Previous studies suggest that the growth factor endothelin-1 (ET-1) is not only up-regulated in diabetes, but may mediate the effects of hyperglycemia on mesangial cell hypertrophy and ECM synthesis. In models of diabetes mellitus, the mechanisms underlying increased ET-1 peptide and mRNA remain unknown. Therefore, our purpose is to determine whether ET-1 gene activity increases in kidneys of streptozotocin (SZT)-treated rats.

METHODS

Male Sprague-Dawley rats were injected with either SZT or vehicle. Parameters including glucose, body weight, 24-hour urine volume, urinary protein, and urinary ET-1 excretion were recorded. All rats were sacrificed at 12 weeks postinjection. Prepro-ET-1 mRNA from whole kidneys was determined using both RNase protection and reverse transcription-polymerase chain reaction (RT-PCR). The abundance of ET-1 peptide in primary cultured mesangial cells was detected by indirect immunofluorescence following treatment with 5.6, 11.2, or 22.5 mmol/L D-glucose for 24 hours. Cellular ET-1 mRNA was measured using RT-PCR in control cells at time 0 and also following exposure to increasing concentrations of glucose for 24 hours. Rat mesangial cells were transfected with a luciferase reporter construct containing the rat ET-1 promoter (pET1. Luc), and relative ET-1 promoter activity was measured after a 24-hour exposure to 5.6 and 22.5 mmol/L of D- or L-glucose.

RESULTS

After 12 weeks of hyperglycemia, diabetic rats gained less weight (344 +/- 23.9 vs. 548.75 +/- 15.08 g), had increased urinary volume (158.6 +/- 24.32 vs. 8.38 +/- 1.56 mL/day), and had marked proteinuria (101.7 +/- 12.2 vs. 14.1 +/- 2.8 mg/day) compared with controls. Total urinary ET-1 peptide increased 26.4-fold in diabetic versus control rats (17.5083 +/- 5.405 vs. 0.6635 +/- 0.343 ng/day). ET-1 mRNA extracted from whole rat kidneys was increased 2.1-fold in diabetic versus control animals. Primary cultured rat mesangial cells demonstrated a significant increase in immunofluorescence labeling of ET-1 peptide and ET-1 mRNA in response to increasing concentrations of glucose. Furthermore, transfected mesangial cells exposed to 22.5 mmol/L D-glucose showed a 1.6-fold increase in ET-1 promoter activity relative to those treated with 5.6 mmol/L glucose.

CONCLUSION

Glucose increases ET-1 gene expression in the kidney of the SZT-treated rat model of diabetes mellitus. Furthermore, high glucose induces ET-1 expression in primary cultured rat mesangial cells and directly enhances ET-1 promoter activity. The greater relative increase in peptide compared with transcription suggests the potential participation of other mechanisms such as increased mRNA stability, protein stability, and/or enhanced translational efficiency.

Adenovirus vector-induced expression of the C-X-C chemokine IP-10 is mediated through capsid-dependent activation of NF-kappaB

The use of adenovirus vectors for gene therapy has been limited by well-defined cellular and humoral immune responses. We have previously shown that adenovirus vectors rapidly induce the expression of the C-X-C chemokine, interferon-inducible protein 10 (IP-10), in vivo. Various first-generation, type 5 adenovirus vectors, including adCMVbetagal and UV-psoralen-inactivated adenovirus, equally induced the expression of IP-10 mRNA as early as 3 h following infection in mouse renal epithelial cells (REC). Luciferase reporter experiments using deletional mutants of the murine IP-10 5'-flanking region revealed that transcriptional activation of the IP-10 promoter by adCMVbetagal was dependent on the -161- to -96-bp region upstream of the transcription start site. In electrophoretic mobility shift assays, adCMVbetagal, adCMV-GFP, FG140, and transcription-defective adenovirus induced protein binding to oligonucleotides containing a consensus sequence for NF-kappaB at position -113 of the IP-10 promoter. Supershift assays confirmed an increase in binding activity of NF-kappaB p65 but not p50 or cRel in REC cells infected with various replication-deficient adenoviruses. Coinfection of REC cells with adCMVbetagal and an adenoviral vector expressing IkappaBalpha resulted in suppression of adCMVbetagal-induced expression of IP-10 at 6 and 16 h, further strengthening the conclusion that adenovirus-induced activation of IP-10 is dependent on NF-kappaB. The induction of IP-10 appeared to be direct because infection with adenovirus vectors failed to induce the expression of the potent IP-10 stimulators, interferon gamma and tumor necrosis factor alpha. Together, these findings demonstrate that adenovirus vectors directly induce the expression of IP-10 through capsid dependent activation of NF-kappaB.

Adenoviral gene therapy leads to rapid induction of multiple chemokines and acute neutrophil-dependent hepatic injury in vivo

Replication-deficient adenoviruses are known to induce acute injury and inflammation of infected tissues, thus limiting their use for human gene therapy. However, molecular mechanisms triggering this response have not been fully defined. To characterize this response, chemokine expression was evaluated in DBA/2 mice following the intravenous administration of various adenoviral vectors. Administration of adCMVbeta gal, adCMV-GFP, or FG140 intravenously rapidly induced a consistent pattern of C-X-C and C-C chemokine expression in mouse liver in a dose-dependent fashion. One hour following infection with 10(10) PFU of adCMVbeta gal, hepatic levels of MIP-2 mRNA were increased >60-fold over baseline. MCP-1 and IP-10 mRNA levels were also increased immediately following infection with various adenoviral vectors, peaking at 6 hr with >25- and >100-fold expression, respectively. Early induction of RANTES and MIP-1beta mRNA by adenoviral vectors also occurred, but to a lesser degree. The induction of chemokines occurred independently of viral gene expression since psoralen-inactivated adenoviral particles produced an identical pattern of chemokine gene transcription within the first 16 hr of administration. The expression of chemokines correlated as expected with the influx of neutrophils and CD11b+ cells into the livers of infected animals. At high titers, all adenoviral vectors caused significant hepatic necrosis and apoptosis following systemic administration to DBA/2 mice. To investigate the role of neutrophils in this adenovirus-induced hepatic injury, animals were pretreated with neutralizing anti-MIP-2 antibodies or depleted of neutrophils. MIP-2 antagonism and neutrophil depletion both resulted in reduced serum ALT/AST levels and attenuation of the adenovirus-induced hepatic injury histologically, confirming that this early injury is largely due to chemokine production and neutrophil recruitment. Our findings further clarify the early immune response against replication-deficient adenoviral vectors and suggest a strategy to prevent adenovirus-mediated inflammation and tissue injury by interfering with chemokine or neutrophil function.

Fas ligand gene transfer to the vessel wall inhibits neointima formation and overrides the adenovirus-mediated T cell response

Proliferation of vascular smooth muscle cells (VSMCs) in response to injury plays a key role in the pathogenesis of vascular disorders. Fas ligand (FasL) induces apoptosis in Fas-bearing cells, and its expression on activated T cells contributes to the regulation of the immune response and physiological cell turnover. Here, we show that a replication-defective adenovirus encoding FasL (Ad-FasL) induced apoptosis in Fas-bearing VSMCs. When introduced locally to balloon-injured rat carotid arteries, a well characterized model of a VSMC-derived lesion, Ad-FasL functioned as a potent inhibitor of neointima formation. In rats immunized with an empty adenoviral vector, robust T cell infiltration of the vessel wall was detected after local delivery of a beta-galactosidase-expressing virus (Ad-betagal), whereas T cell infiltrates were not detected after local delivery of Ad-FasL. Prior immunization prevented beta-galactosidase expression from Ad-betagal, whereas the expression of the FasL transgene was unaffected. When Ad-betagal and Ad-FasL were delivered together to preimmunized animals, T cell infiltration was reduced and beta-galactosidase expression was restored. These data demonstrate that Fas ligand gene transfer can effectively inhibit injury-induced vessel lesion formation and can allow adenovirus-harboring cells to evade immune destruction.

Ex vivo adenovirus-mediated gene delivery leads to long-term expression in pancreatic islet transplants

BACKGROUND

Replication-deficient adenovirus, one of the most efficient vectors in gene therapy, has been limited by transient transgene expression due to its episomal location and loss during cell division, as well as a host immune response against viral proteins.

METHODS

Murine pancreatic islets were infected ex vivo with ad5-cytomegalovirus (CMV)-beta-galactosidase and transplanted into diabetic recipients with normalization of glucose metabolism.

RESULTS

High levels of beta-galactosidase activity were detectable histologically for at least 20 weeks after transplant, and beta-galactosidase and viral mRNA were also present that long. Sera from transplanted animals did not significantly inhibit ad5-CMV-interleukin-2-Ig infection of HeLa cells in vitro, whereas sera from intravenously delivered ad5-CMV-beta-galactosidase drastically diminished HeLa cell infection, suggesting the presence of reduced levels of antibodies in transplanted animals as compared with intravenously infected animals. Immunofluorescent staining of islet isografts infected with ad5-CMV-beta-galactosidase revealed the presence of CD8+ and CD4+ T lymphocytes at all time points, however, no islet destruction was seen.

CONCLUSIONS

Treatment of islet isografts ex vivo with ad5-CMV-beta-galactosidase results in prolonged transgene expression, possibly due to an attenuated immune response against adenovirus.

Adenovirus-mediated expression of Fas ligand induces hepatic apoptosis after Systemic administration and apoptosis of ex vivo-infected pancreatic islet allografts and isografts

Fas ligand (FasL) mediates apoptosis of Fas-bearing cells and is expressed on a limited number of tissues, predominantly activated T lymphocytes. We describe the construction and biological activity of a replication-deficient type-5 adenovirus encoding murine FasL under the control of the cytomegalovirus (CMV) promoter (adCMV-FasL). In vitro, Jurkat cells undergo apoptosis when co-incubated with adCMV-FasL-infected COS cells. Systemic administration of adCMV-FasL to Wistar rats or DBA/2J mice results in widespread hepatic apoptosis and death in a dose-dependent manner within 72 hr, an effect not seen in lpr mice, or animals administered equivalent doses of adCMV-beta gal. Murine pancreatic islets also undergo apoptosis when infected ex vivo with adCMV-FasL, resulting in uniform primary nonfunction when transplanted into syngeneic or allogeneic diabetic recipients. These results indicate that adCMV-FasL is a potentially useful tool to study Fas/FasL biology.

Contrast-induced encephalopathy and seizures in a patient with chronic renal insufficiency

Radiographic contrast agents are associated with a number of adverse effects, including central nervous system effects and seizures. Almost all contrast agents are primarily filtered and excreted by the kidneys, and they accumulate in patients with end-stage renal disease. Brain retention of contrast associated with high doses is a rare event, having been reported only twice in the literature. We report a case of a 49-year-old male on chronic hemodialysis who developed brain retention of contrast resulting in seizures and encephalopathy after receiving large doses of meglumine/sodium diatrizoate during coronary angiography. He was treated successfully with hemodialysis and suffered no permanent neurologic sequelae. Patients with end-stage renal disease may be at increased risk of adverse effects from contrast when administered in high doses.