Biomedical subjects

Dean Sheppard

Publications and source records attributed to Dean Sheppard.

At least 19 recordsLinked to original sources

PubMed2007

Alphav beta6 integrin regulates renal fibrosis and inflammation in Alport mouse.

The transforming growth factor (TGF)-beta-inducible integrin alpha v beta6 is preferentially expressed at sites of epithelial remodeling and has been shown to bind and activate latent precursor TGF-beta. Herein, we show that alpha v beta6 is overexpressed in human kidney epithelium in membranous glomerulonephritis, diabetes mellitus, IgA nephropathy, Goodpasture's syndrome, and Alport syndrome renal epithelium. To assess the potential regulatory role of alpha v beta6 in renal disease, we studied the effects of function-blocking alpha v beta6 monoclonal antibodies (mAbs) and genetic ablation of the beta6 subunit on kidney fibrosis in Col4A3-/- mice, a mouse model of Alport syndrome. Expression of alpha v beta6 in Alport mouse kidneys was observed primarily in cortical tubular epithelial cells and in correlation with the progression of fibrosis. Treatment with alpha v beta6-blocking mAbs inhibited accumulation of activated fibroblasts and deposition of interstitial collagen matrix. Similar inhibition of renal fibrosis was observed in beta6-deficient Alport mice. Transcript profiling of kidney tissues showed that alpha v beta6-blocking mAbs significantly inhibited disease-associated changes in expression of fibrotic and inflammatory mediators. Similar patterns of transcript modulation were produced with recombinant soluble TGF-beta RII treatment, suggesting shared regulatory functions of alpha v beta6 and TGF-beta. These findings demonstrate that alpha v beta6 can contribute to the regulation of renal fibrosis and suggest this integrin as a potential therapeutic target.

Animals↗

PubMed2006

The Integrin alpha9beta1 contributes to granulopoiesis by enhancing granulocyte colony-stimulating factor receptor signaling.

The integrin alpha9beta1 is widely expressed on neutrophils, smooth muscle, hepatocytes, endothelia, and some epithelia. We now show that mice lacking this integrin have a dramatic defect in neutrophil development, with decreased numbers of granulocyte precursors in bone marrow and impaired differentiation of bone marrow cells into granulocytes. In response to granulocyte colony-stimulating factor (G-CSF), alpha9-deficient bone marrow cells or human bone marrow cells incubated with alpha9beta1-blocking antibody demonstrated decreased phosphorylation of signal transducer and activator of transcription 3 and extracellular signal-regulated protein kinase. These effects depended on the alpha9 subunit cytoplasmic domain, which was required for formation of a physical complex between alpha9beta1 and ligated G-CSF receptor. Integrin alpha9beta1 was required for granulopoiesis and played a permissive role in the G-CSF-signaling pathway, suggesting that this integrin could play an important role in disorders of granulocyte development and other conditions characterized by defective G-CSF signaling.

Animals↗

PubMed2006

Integrin alphavbeta5 regulates lung vascular permeability and pulmonary endothelial barrier function.

Increased lung vascular permeability is an important contributor to respiratory failure in acute lung injury (ALI). We found that a function-blocking antibody against the integrin alphavbeta5 prevented development of lung vascular permeability in two different models of ALI: ischemia-reperfusion in rats (mediated by vascular endothelial growth factor [VEGF]) and ventilation-induced lung injury (VILI) in mice (mediated, at least in part, by transforming growth factor-beta [TGF-beta]). Knockout mice homozygous for a null mutation of the integrin beta5 subunit were also protected from lung vascular permeability in VILI. In pulmonary endothelial cells, both the genetic absence and blocking of alphavbeta5 prevented increases in monolayer permeability induced by VEGF, TGF-beta, and thrombin. Furthermore, actin stress fiber formation induced by each of these agonists was attenuated by blocking alphavbeta5, suggesting that alphavbeta5 regulates induced pulmonary endothelial permeability by facilitating interactions with the actin cytoskeleton. These results identify integrin alphavbeta5 as a central regulator of increased pulmonary vascular permeability and a potentially attractive therapeutic target in ALI.

Amides↗

PubMed2006

Alveolar epithelial cell mesenchymal transition develops in vivo during pulmonary fibrosis and is regulated by the extracellular matrix.

Mechanisms leading to fibroblast accumulation during pulmonary fibrogenesis remain unclear. Although there is in vitro evidence of lung alveolar epithelial-to-mesenchymal transition (EMT), whether EMT occurs within the lung is currently unknown. Biopsies from fibrotic human lungs demonstrate epithelial cells with mesenchymal features, suggesting EMT. To more definitively test the capacity of alveolar epithelial cells for EMT, mice expressing beta-galactosidase (beta-gal) exclusively in lung epithelial cells were generated, and their fates were followed in an established model of pulmonary fibrosis, overexpression of active TGF-beta1. beta-gal-positive cells expressing mesenchymal markers accumulated within 3 weeks of in vivo TGF-beta1 expression. The increase in vimentin-positive cells within injured lungs was nearly all beta-gal-positive, indicating epithelial cells as the main source of mesenchymal expansion in this model. Ex vivo, primary alveolar epithelial cells cultured on provisional matrix components, fibronectin or fibrin, undergo robust EMT via integrin-dependent activation of endogenous latent TGF-beta1. In contrast, primary cells cultured on laminin/collagen mixtures do not activate the TGF-beta1 pathway and, if exposed to active TGF-beta1, undergo apoptosis rather than EMT. These data reveal alveolar epithelial cells as progenitors for fibroblasts in vivo and implicate the provisional extracellular matrix as a key regulator of epithelial transdifferentiation during fibrogenesis.

Animals↗

PubMed2006

Ligation of protease-activated receptor 1 enhances alpha(v)beta6 integrin-dependent TGF-beta activation and promotes acute lung injury.

Activation of latent TGF-beta by the alpha(v)beta6 integrin is a critical step in the development of acute lung injury. However, the mechanism by which alpha(v)beta6-mediated TGF-beta activation is regulated has not been identified. We show that thrombin, and other agonists of protease-activated receptor 1 (PAR1), activate TGF-beta in an alpha(v)beta6 integrin-specific manner. This effect is PAR1 specific and is mediated by RhoA and Rho kinase. Intratracheal instillation of the PAR1-specific peptide TFLLRN increases lung edema during high-tidal-volume ventilation, and this effect is completely inhibited by a blocking antibody against the alpha(v)beta6 integrin. Instillation of TFLLRN during high-tidal-volume ventilation is associated with increased pulmonary TGF-beta activation; however, this is not observed in Itgb6-/- mice. Furthermore, Itgb6-/- mice are also protected from ventilator-induced lung edema. We also demonstrate that pulmonary edema and TGF-beta activity are similarly reduced in Par1-/- mice following bleomycin-induced lung injury. These results suggest that PAR1-mediated enhancement of alpha(v)beta6-dependent TGF-beta activation could be one mechanism by which activation of the coagulation cascade contributes to the development of acute lung injury, and they identify PAR1 and the alpha(v)beta6 integrin as potential therapeutic targets in this condition.

Amides↗

PubMed2006

Activation of transforming growth factor-beta by the integrin alphavbeta8 delays epithelial wound closure.

Transforming growth factor (TGF)-beta family members regulate multiple aspects of wound repair through effects on cell proliferation, matrix production, and tissue inflammation, but the effects of TGF-beta on wound closure itself have been controversial. We found that blocking antibodies to TGF-beta enhanced the degree of closure of scratch wounds in primary airway epithelial monolayers, while addition of exogenous TGF-beta1 inhibited the degree of closure, suggesting that endogenous activation of TGF-beta normally serves as a brake on the degree of wound closure. Although these cells secreted large amounts of TGF-beta2 and small amounts of TGF-beta1, blockade of TGF-beta1 enhanced the degree of wound closure, whereas blockade of TGF-beta2 had no effect. TGF-beta1 (but not TGF-beta2) can be activated by two members of the integrin family, alphavbeta6 and alphavbeta8, which are both expressed on airway epithelial cells. Wounding induced activation of TGF-beta through effects of both integrins, but antibodies against alphavbeta8 enhanced the degree of wound closure, whereas antibodies against alphavbeta6 did not.

Antibodies, Monoclonal↗

PubMed2006

Induction of a homeostatic circuit in lung tissue by microbial compounds.

TGFbeta presented and activated by integrin alphavbeta6 expressed on alveolar epithelial cells (AEC) continuously inhibits the functionality of alveolar macrophages (AM). Despite this inhibition, AM retain their ability to respond to inhaled microorganisms. Herein we describe a homeostatic circuit through which the effects of microbial products on macrophages transiently circumvent this inhibition by repressing alphavbeta6 expression on AEC. Subsequent production of matrix metalloproteinases by activated AM activates latent TGFbeta, reinduces alphavbeta6 expression, and thereby reinstates tonic inhibition of AM function. Our results reveal how AM can be activated while minimizing their potential to inflict collateral damage to the adjacent lung tissue and indicate that tissue-specific microenvironmental factors shape organ-specific defense strategies against microbial invasion.

Animals↗

PubMed2006

ADAM33 is not essential for growth and development and does not modulate allergic asthma in mice.

A disintegrin and metalloprotease 33 (ADAM33) is a transmembrane protease and integrin ligand that has been identified as an asthma susceptibility gene product. To determine whether ADAM33 plays important roles in mammalian development and the modulation of allergic airway dysfunction, we generated ADAM33-null mice by gene targeting. ADAM33-null mice were born at expected Mendelian ratios, and both male and females developed normally and were fertile. No anatomical or histological abnormalities were detected in any tissues. In an animal model of allergic asthma, ADAM33-null mice showed normal allergen-induced airway hyperreactivity, immunoglobulin E production, mucus metaplasia, and airway inflammation. Our results demonstrate that ADAM33 is not essential for growth or reproduction in the mouse and does not modulate baseline or allergen-induced airway responsiveness.

ADAM Proteins↗

PubMed2006

Pulmonary emphysema: when more is less.

Pulmonary emphysema results from the loss of intricate alveolar architecture and progressive simplification of small and highly effective gas-exchanging units into large, inefficient cyst-like spaces. Because of the loss of alveolar gas-exchanging units and the capillary bed within them, blood oxygen levels eventually fall and pressures within the pulmonary circulation rise. Recent insights from genetically manipulated mouse models have refined our understanding of the molecular events that prevent or promote the development of pulmonary emphysema. Capitalizing on an improved molecular understanding of emphysema with improved therapeutics has the potential to enhance both the survival and quality of life of patients with this common lung disease.

Animals↗

PubMed2006

Alpha9beta1: a novel osteoclast integrin that regulates osteoclast formation and function.

UNLABELLED: We identified a previously unknown integrin, alpha(9)beta(1), on OCLs and their precursors. Antibody to alpha(9) inhibited OCL formation in human marrow cultures, and OCLs from alpha(9) knockout mice had a defect in actin ring reorganization and an impaired bone resorption capacity. INTRODUCTION: Integrins play important roles in osteoclast (OCL) formation and function. Mature OCLs mainly express alpha(v)beta(3) integrin, a heterodimer adhesion receptor that has been implicated in osteoclastic bone resorption. We identified ADAM8, a disintegrin and metalloproteinase, as a novel stimulator of OCL differentiation and showed that the disintegrin domain of ADAM8 mediated its effects on OCL formation. Because the disintegrin domain of ADAM8 does not bind Arg-Gly-Asp (RGD) sequences, we determined which integrin bound ADAM8 and characterized its role in OCL formation and activity. MATERIALS AND METHODS: Chinese hamster ovary cells (CHO) expressing different integrin subunits were tested for their capacity to bind the disintegrin domain of ADAM8. Mouse or human bone marrow cells and purified OCL precursors were tested for alpha(9)beta(1) integrin expression by Western blot, immunocytochemistry, and real-time RT-PCR. A monoclonal antibody to human alpha(9) was used to block alpha(9)beta(1) on OCL precursors stimulated by 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] or RANKL. Vertebrae of 7-day-old alpha(9)(-/-) mice and wildtype (WT) littermates were compared using bone histomorphometry and 3D microCT analysis. RESULTS: Alpha(9) integrin was expressed by mouse and human bone marrow-derived OCLs and their precursors. Importantly, the anti-alpha(9) antibody inhibited human OCL formation stimulated by 1alpha,25(OH)(2)D(3) or RANKL dose-dependently. Furthermore, analysis of OCLs formed in marrow cultures from alpha(9)(-/-) mice showed that the OCLs formed were more contracted and formed significantly less bone resorption pits on dentin slices. Histologic analysis of alpha(9)(-/-) vertebrae showed thickened trabecular regions and retained cartilage within vertebral bodies of alpha(9)(-/-) mice. 3D microCT analysis of alpha(9)(-/-) vertebrae also showed a significant increase in trabecular bone volume/total tissue volume and a tendency for decreased trabecular separation compared with WT mice. CONCLUSIONS: These results support a previously unknown role for alpha(9)beta(1) integrin in OCL formation and function.

ADAM Proteins↗

PubMed2006

Transforming growth factor beta: a central modulator of pulmonary and airway inflammation and fibrosis.

The requirement for precise geometric organization of endothelial cells and epithelial cells makes the gas-exchange region of the lung especially vulnerable to the adverse consequences of toxic products released from inflammatory cells. However, as a filter for large volumes of atmospheric gas, the lung is continually exposed to microorganisms and other toxic insults that require robust inflammatory defense. Enhanced production of extracellular matrix proteins is one important mechanism for restricting tissue damage, but excessive matrix production also has serious adverse effects on gas exchange. The amazing ability of the lung to recover from a barrage of environmental insults depends on precisely regulating both inflammation and extracellular matrix production in space and time. Below I review some of the evidence implicating members of the transforming growth factor beta family as critical mediators of this delicate dance and describe examples of how disruption of this balance by alterations in the magnitude of spatially restricted transforming growth factor beta activation can contribute to pathologic consequences of alveolar and airway injury and inflammation.

Animals↗

PubMed2005

Population stratification confounds genetic association studies among Latinos.

In the United States, asthma prevalence and mortality are the highest among Puerto Ricans and the lowest among Mexicans. Case-control association studies are a powerful strategy for identifying genes of modest effect in complex diseases. However, studies of complex disorders in admixed populations such as Latinos may be confounded by population stratification. We used ancestry informative markers (AIMs) to identify and correct for population stratification among Mexican and Puerto Rican subjects participating in case-control studies of asthma. Three hundred and sixty-two subjects with asthma (Mexican: 181, Puerto Rican: 181) and 359 ethnically matched controls (Mexican: 181, Puerto Rican: 178) were genotyped for 44 AIMs. We observed a greater than expected degree of association between pairs of AIMs on different chromosomes in Mexicans (P < 0.00001) and Puerto Ricans (P < 0.00002) providing evidence for population substructure and/or recent admixture. To assess the effect of population stratification on association studies of asthma, we measured differences in genetic background of cases and controls by comparing allele frequencies of the 44 AIMs. Among Puerto Ricans but not in Mexicans, we observed a significant overall difference in allele frequencies between cases and controls (P = 0.0002); of 44 AIMs tested, 8 (18%) were significantly associated with asthma. However, after adjustment for individual ancestry, only two of these markers remained significantly associated with the disease. Our findings suggest that empirical assessment of the effects of stratification is critical to appropriately interpret the results of case-control studies in admixed populations.

Alleles↗

PubMed2005

Mfge8 is critical for mammary gland remodeling during involution.

Apoptosis is a critical process in normal mammary gland development and the rapid clearance of apoptotic cells prevents tissue injury associated with the release of intracellular antigens from dying cells. Milk fat globule-EGF-factor 8 (Mfge8) is a milk glycoprotein that is abundantly expressed in the mammary gland epithelium and has been shown to facilitate the clearance of apoptotic lymphocytes by splenic macrophages. We report that mice with disruption of Mfge8 had normal mammary gland development until involution. However, abnormal mammary gland remodeling was observed postlactation in Mfge8 mutant mice. During early involution, Mfge8 mutant mice had increased numbers of apoptotic cells within the mammary gland associated with a delay in alveolar collapse and fat cell repopulation. As involution progressed, Mfge8 mutants developed inflammation as assessed by CD45 and CD11b staining of mammary gland tissue sections. With additional pregnancies, Mfge8 mutant mice developed progressive dilatation of the mammary gland ductal network. These data demonstrate that Mfge8 regulates the clearance of apoptotic epithelial cells during mammary gland involution and that the absence of Mfge8 leads to inflammation and abnormal mammary gland remodeling.

Animals↗

PubMed2005

ADAM disintegrin-like domain recognition by the lymphocyte integrins alpha4beta1 and alpha4beta7.

The ADAM (a disintegrin and metalloprotease) family of proteins possess both proteolytic and adhesive domains. We have established previously that the disintegrin domain of ADAM28, an ADAM expressed by human lymphocytes, is recognized by the integrin alpha4beta1. The present study characterizes the integrin binding properties of the disintegrin-like domains of human ADAM7, ADAM28 and ADAM33 with the integrins alpha4beta1, alpha4beta7 and alpha9beta1. Cell-adhesion assays demonstrated that, similar to ADAM28, the ADAM7 disintegrin domain supported alpha4beta1-dependent Jurkat cell adhesion, whereas the ADAM33 disintegrin domain did not. The lymphocyte integrin alpha4beta7 was also found to recognize both disintegrin domains of ADAM7 and ADAM28, but not of ADAM33. This is the first demonstration that mammalian disintegrins are capable of interacting with alpha4beta7. All three disintegrin domains supported alpha9beta1-dependent cell adhesion. Recognition by both alpha4beta1 and alpha4beta7 of ADAM7 and ADAM28 was activation-dependent, requiring either the presence of Mn2+ or an activating monoclonal antibody for cell attachment. Charge-to-alanine mutagenesis experiments revealed that the same residues within an individual ADAM disintegrin domain function in recognizing multiple integrins. However, the residues within a specific region of each ADAM disintegrin-like domain required for integrin binding were distinct. These results establish that ADAM7 and ADAM28 are recognized by the leucocyte integrins alpha4beta1, alpha4beta7 and alpha9beta1. ADAM33 exclusively supported only alpha9beta1-dependent adhesion.

ADAM Proteins↗

PubMed2005

Interleukin-1beta decreases expression of the epithelial sodium channel alpha-subunit in alveolar epithelial cells via a p38 MAPK-dependent signaling pathway.

Acute lung injury (ALI) is a devastating syndrome characterized by diffuse alveolar damage, elevated airspace levels of pro-inflammatory cytokines, and flooding of the alveolar spaces with protein-rich edema fluid. Interleukin-1beta (IL-1beta) is one of the most biologically active cytokines in the distal airspaces of patients with ALI. IL-1beta has been shown to increase lung epithelial and endothelial permeability. In this study, we hypothesized that IL-1beta would decrease vectorial ion and water transport across the distal lung epithelium. Therefore, we measured the effects of IL-1beta on transepithelial current, resistance, and sodium transport in primary cultures of alveolar epithelial type II (ATII) cells. IL-1beta significantly reduced the amiloride-sensitive fraction of the transepithelial current and sodium transport across rat ATII cell monolayers. Moreover, IL-1beta decreased basal and dexamethasone-induced epithelial sodium channel alpha-subunit (alpha ENaC) mRNA levels and total and cell-surface protein expression. The inhibitory effect of IL-1beta on alpha ENaC expression was mediated by the activation of p38 MAPK in both rat and human ATII cells and was independent of the activation of alpha v beta6 integrin and transforming growth factor-beta. These results indicate that IL-1beta may contribute to alveolar edema in ALI by reducing distal lung epithelial sodium absorption. This reduction in ion and water transport across the lung epithelium is in large part due to a decrease in alpha ENaC expression through p38 MAPK-dependent inhibition of alpha ENaC promoter activity and to an alteration in ENaC trafficking to the apical membrane of ATII cells.

Animals↗

PubMed2005

Genetic admixture and asthma-related phenotypes in Mexican American and Puerto Rican asthmatics.

Genetic association studies in admixed populations may be biased if individual ancestry varies within the population and the phenotype of interest is associated with ancestry. However, recently admixed populations also offer potential benefits in association studies since markers informative for ancestry may be in linkage disequilibrium across large distances. In particular, the enhanced LD in admixed populations may be used to identify alleles that underlie a genetically determined difference in a phenotype between two ancestral populations. Asthma is known to have different prevalence and severity among ancestrally distinct populations. We investigated several asthma-related phenotypes in two ancestrally admixed populations: Mexican Americans and Puerto Ricans. We used ancestry informative markers to estimate the individual ancestry of 181 Mexican American asthmatics and 181 Puerto Rican asthmatics and tested whether individual ancestry is associated with any of these phenotypes independently of known environmental factors. We found an association between higher European ancestry and more severe asthma as measured by both forced expiratory volume at 1 second (r=-0.21, p=0.005) and by a clinical assessment of severity among Mexican Americans (OR: 1.55; 95% CI 1.25 to 1.93). We found no significant associations between ancestry and severity or drug responsiveness among Puerto Ricans. These results suggest that asthma severity may be influenced by genetic factors differentiating Europeans and Native Americans in Mexican Americans, although differing results for Puerto Ricans require further investigation.

Adolescent↗

PubMed2005

Integrin-mediated activation of latent transforming growth factor beta.

Members of the integrin family recognize a variety of spatially-restricted extracellular ligands. Classically, ligation of integrins activates cytoplasmic signals in the integrin-expressing cell and contributes to cell adhesion, migration, proliferation and survival. At least two members of this family, alphavbeta6 and alphavbeta8 perform an additional function, activation of latent complexes of transforming growth factor beta. In effect, this process allows integrins on one cell to activate signals on adjacent (in the case of alphavbeta6) or nearby cells (in the case of alphavbeta8). Integrin-mediated TGFbeta activation has been shown to play important roles in modulating tissue fibrosis, acute lung injury and pulmonary emphysema. Given the important roles that TGFbeta plays in modulating epithelial cell growth, epithelial-to-mesenchymal transformation and tumor invasion and metastasis, integrin-mediated TGFbeta activation is likely to play important roles in tumor growth and metastasis.

Animals↗

PubMed2005

Transcriptional activation of integrin beta6 during the epithelial-mesenchymal transition defines a novel prognostic indicator of aggressive colon carcinoma.

We used a spheroid model of colon carcinoma to analyze integrin dynamics as a function of the epithelial-mesenchymal transition (EMT), a process that provides a paradigm for understanding how carcinoma cells acquire a more aggressive phenotype. This EMT involves transcriptional activation of the beta6 integrin subunit and a consequent induction of alphavbeta6 expression. This integrin enhances the tumorigenic properties of colon carcinoma, including activation of autocrine TGF-beta and migration on interstitial fibronectin. Importantly, this study validates the clinical relevance of the EMT. Kaplan-Meier analysis of beta6 expression in 488 colorectal carcinomas revealed a striking reduction in median survival time of patients with high beta6 expression. Elevated receptor expression did not simply reflect increasing tumor stage, since log-rank analysis showed a more significant impact on the survival of patients with early-stage, as opposed to late-stage, disease. Cox regression analysis confirmed that this integrin is an independent variable for these tumors. These findings define the alphavbeta6 integrin as an important risk factor for early-stage disease and a novel therapeutic candidate for colorectal cancer.

Animals↗