Abstract
Hirschsprung disease and Waardenburg syndrome are human genetic diseases characterized by distinct neural crest defects. Patients with Hirschsprung disease suffer from gastrointestinal motility disorders, whereas Waardenburg syndrome consists of defective melanocyte function, deafness, and craniofacial abnormalities. Mutations responsible for Hirschsprung disease and Waardenburg syndrome have been identified, and some patients have been described with characteristics of both disorders. Here, we demonstrate that PAX3, which is often mutated in Waardenburg syndrome, is required for normal enteric ganglia formation. Pax3 can bind to and activate expression of the c-RET gene, which is often mutated in Hirschsprung disease. Pax3 functions with Sox10 to activate transcription of c-RET, and SOX10 mutations result in Waardenburg-Hirschsprung syndrome. Thus, Pax3, Sox10, and c-Ret are components of a neural crest development pathway, and interruption of this pathway at various stages results in neural crest–related human genetic syndromes.
Authors
Deborah Lang, Fabian Chen, Rita Milewski, Jun Li, Min Min Lu, Jonathan A. Epstein
Abstract
Renal prostaglandin (PG) synthesis is mediated by cyclooxygenase-1 and -2 (COX1 and COX2). After dehydration, the maintenance of normal renal function becomes particularly dependent upon PG synthesis. The present studies were designed to examine the potential link between medullary COX1 and COX2 expression in hypertonic stress. In response to water deprivation, COX2, but not COX1, mRNA levels increase significantly in the renal medulla, specifically in renal medullary interstitial cells (RMICs). Water deprivation also increases renal NF-κB–driven reporter expression in transgenic mice. NF-κB activity and COX2 expression could be induced in cultured RMICs with hypertonic sodium chloride and mannitol, but not urea. RMIC COX2 expression was also induced by driving NF-κB activation with a constitutively active IκB kinase α (IKKα). Conversely, introduction of a dominant-negative IκB mutant reduced COX2 expression after hypertonicity or IKKα induction. RMICs failed to survive hypertonicity when COX2 was downregulated using a COX2-selective antisense or blocked with the selective nonsteroidal anti-inflammatory drug (NSAID) SC58236, reagents that did not affect cell survival in isotonic media. In rabbits treated with SC58236, water deprivation induced apoptosis of medullary interstitial cells in the renal papilla. These results demonstrate that water deprivation and hypertonicity activate NF-κB. The consequent increase in COX2 expression favors RMIC survival in hypertonic conditions. Inhibition of RMIC COX2 could contribute to NSAID-induced papillary injury.
Authors
Chuan-Ming Hao, Fiona Yull, Timothy Blackwell, Martin Kömhoff, Linda S. Davis, Matthew D. Breyer
Abstract
The Golgi complex and the trans-Golgi network are critical cellular organelles involved in the endocytic and biosynthetic pathways of protein trafficking. Lipids have been implicated in the regulation of membrane-protein trafficking, vesicular fusion, and targeting. We have explored the role of cytosolic group IV phospholipase A2 (cPLA2) in membrane-protein trafficking in kidney epithelial cells. Adenoviral expression of cPLA2 in LLC-PK1 kidney epithelial cells prevents constitutive trafficking to the plasma membrane of an aquaporin 2-green fluorescent protein chimera, with retention of the protein in the rough endoplasmic reticulum. Plasma membrane Na+-K+-ATPase α-subunit localization is markedly reduced in cells expressing cPLA2, whereas the trafficking of a Cl–/HCO3– anion exchanger to the plasma membrane is not altered in these cells. Expression of cPLA2 results in dispersion of giantin and β-COP from their normal, condensed Golgi localization, and in marked disruption of the Golgi cisternae. cPLA2 is present in Golgi fractions from noninfected LLC-PK1 cells and rat kidney cortex. The distribution of tubulin and actin was not altered by cPLA2, indicating that the microtubule and actin cytoskeleton remain intact. Total cellular protein synthesis is unaffected by the increase in cPLA2 activity. Thus cPLA2 plays an important role in determining Golgi architecture and selective control of constitutive membrane-protein trafficking in renal epithelial cells.
Authors
Gabriel J. Choukroun, Vladimir Marshansky, Corinne E. Gustafson, Mary McKee, Roger J. Hajjar, Anthony Rosenzweig, Dennis Brown, Joseph V. Bonventre
Abstract
The pharynx is the primary reservoir for strains of group A Streptococcus (GAS) associated both with pharyngitis (streptococcal sore throat) and with invasive or “flesh-eating” soft tissue infections. We now report that CD44, a hyaluronic acid-binding protein that mediates human cell-cell– and cell-extracellular matrix–binding interactions, functions as a receptor for GAS colonization of the pharynx in vivo. We found that attachment of GAS to murine epithelial keratinocytes was mediated by binding of the GAS hyaluronic acid capsular polysaccharide to CD44. In studies of transgenic mice with a selective defect in epithelial expression of CD44, GAS adherence to CD44-deficient keratinocytes in vitro was reduced compared with adherence to keratinocytes expressing normal levels of CD44. After intranasal inoculation, GAS colonized the oropharynx of wild-type mice but failed to colonize transgenic mice deficient in CD44 expression. GAS colonization of wild-type mice could be blocked by coadministration of mAb to CD44 or by pretreatment of the animals with exogenous hyaluronic acid. These results provide evidence that CD44 serves as a receptor for GAS colonization of the pharynx and support the potential efficacy of disrupting the interaction between the GAS hyaluronic acid capsule and CD44 as a novel approach to preventing pharyngeal infection.
Authors
Colette Cywes, Ivan Stamenkovic, Michael R. Wessels
Abstract
VEGF is a secreted mitogen associated with angiogenesis and is also a potent vascular permeability factor. The biological role of VEGF in the ischemic brain remains unknown. This study was undertaken to investigate whether VEGF enhances cerebral microvascular perfusion and increases blood-brain barrier (BBB) leakage in the ischemic brain. Using magnetic resonance imaging (MRI), three-dimensional laser-scanning confocal microscope, and functional neurological tests, we measured the effects of administrating recombinant human VEGF165 (rhVEGF165) on angiogenesis, functional neurological outcome, and BBB leakage in a rat model of focal cerebral embolic ischemia. Late (48 hours) administration of rhVEGF165 to the ischemic rats enhanced angiogenesis in the ischemic penumbra and significantly improved neurological recovery. However, early postischemic (1 hour) administration of rhVEGF165 to ischemic rats significantly increased BBB leakage, hemorrhagic transformation, and ischemic lesions. Administration of rhVEGF165 to ischemic rats did not change BBB leakage and cerebral plasma perfusion in the contralateral hemisphere. Our results indicate that VEGF can markedly enhance angiogenesis in the ischemic brain and reduce neurological deficits during stroke recovery and that inhibition of VEGF at the acute stage of stroke may reduce the BBB permeability and the risk of hemorrhagic transformation after focal cerebral ischemia.
Authors
Zheng Gang Zhang, Li Zhang, Quan Jiang, Ruilan Zhang, Kenneth Davies, Cecylia Powers, Nicholas van Bruggen, Michael Chopp
Genetic characterization of rebounding HIV-1 after cessation of highly active antiretroviral therapy
Abstract
Despite prolonged treatment with highly active antiretroviral therapy (HAART), infectious HIV-1 continues to replicate and to reside latently in resting memory CD4+ T lymphocytes, creating a major obstacle to HIV-1 eradication. It is therefore not surprising to observe a prompt viral rebound after discontinuation of HAART. The nature of the rebounding virus, however, remains undefined. We now report on the genetic characterization of rebounding viruses in eight patients in whom plasma viremia was undetectable throughout about 3 years of HAART. Taking advantage of the extensive length polymorphism in HIV-1 env, we found that in five patients who did not show HIV-1 replication during treatment, the rebound virus was identical to those isolated from the latent reservoir. In three other patients, two of whom had been free of plasma viremia but had showed some residual viral replication, the rebound virus was genetically different from the latent reservoir virus, corresponding instead to minor viral variants detected during the course of treatment in lymphoid tissues. We conclude that in cases with apparent complete HIV-1 suppression by HAART, viral rebound after cessation of therapy could have originated from the activation of virus from the latent reservoir. In patients with incomplete suppression by chemotherapy, however, the viral rebound is likely triggered by ongoing, low-level replication of HIV-1, perhaps occurring in lymphoid tissues.
Authors
Linqi Zhang, Chris Chung, Bor-Shen Hu, Tian He, Yong Guo, Alexandria J. Kim, Eva Skulsky, Xia Jin, Arlene Hurley, Bharat Ramratnam, Martin Markowitz, David D. Ho
Peroxisome proliferator–activated receptor γ coactivator-1 promotes cardiac mitochondrial biogenesis
Abstract
Cardiac mitochondrial function is altered in a variety of inherited and acquired cardiovascular diseases. Recent studies have identified the transcriptional coactivator peroxisome proliferator–activated receptor γ coactivator-1 (PGC-1) as a regulator of mitochondrial function in tissues specialized for thermogenesis, such as brown adipose. We sought to determine whether PGC-1 controlled mitochondrial biogenesis and energy-producing capacity in the heart, a tissue specialized for high-capacity ATP production. We found that PGC-1 gene expression is induced in the mouse heart after birth and in response to short-term fasting, conditions known to increase cardiac mitochondrial energy production. Forced expression of PGC-1 in cardiac myocytes in culture induced the expression of nuclear and mitochondrial genes involved in multiple mitochondrial energy-transduction/energy-production pathways, increased cellular mitochondrial number, and stimulated coupled respiration. Cardiac-specific overexpression of PGC-1 in transgenic mice resulted in uncontrolled mitochondrial proliferation in cardiac myocytes leading to loss of sarcomeric structure and a dilated cardiomyopathy. These results identify PGC-1 as a critical regulatory molecule in the control of cardiac mitochondrial number and function in response to energy demands.
Authors
John J. Lehman, Philip M. Barger, Attila Kovacs, Jeffrey E. Saffitz, Denis M. Medeiros, Daniel P. Kelly
Abstract
MMP activity with disruption of structural collagen has been implicated in the pathophysiology of dilated cardiomyopathy. To examine the role of this enzyme in cardiac function, a transgenic mouse was created that constitutively expressed human collagenase (MMP-1) in the heart. At 6 months of age, these animals demonstrated compensatory myocyte hypertrophy with an increase in the cardiac collagen concentration due to elevated transcription of type III collagen. Chronic myocardial expression of MMP-1 produced loss of cardiac interstitial collagen coincident with a marked deterioration of systolic and diastolic function at 12 months of age. This is the first animal model demonstrating that direct disruption of the extracellular matrix in the heart reproduces the changes observed in the progression of human heart failure.
Authors
Henry E. Kim, Seema S. Dalal, Erik Young, Marianne J. Legato, Myron L. Weisfeldt, Jeanine D’Armiento
Abstract
In North America, liver disease due to alcohol consumption is an important cause of death in adults, although its pathogenesis remains obscure. Despite the fact that resident hepatic macrophages are known to contribute to early alcohol-induced liver injury via oxidative stress, the exact source of free radicals has remained a mystery. To test the hypothesis that NADPH oxidase is the major source of oxidants due to ethanol, we used p47phox knockout mice, which lack a critical subunit of this major source of reactive oxygen species in activated phagocytes. Mice were treated with ethanol chronically, using a Tsukamoto-French protocol, for 4 weeks. In wild-type mice, ethanol caused severe liver injury via a mechanism involving gut-derived endotoxin, CD14 receptor, production of electron spin resonance–detectable free radicals, activation of the transcription factor NF-κB, and release of cytotoxic TNF-α from activated Kupffer cells. In NADPH oxidase–deficient mice, neither an increase in free radical production, activation of NF-κB, an increase in TNF-α mRNA, nor liver pathology was observed. These data strongly support the hypothesis that free radicals from NADPH oxidase in hepatic Kupffer cells play a predominant role in the pathogenesis of early alcohol-induced hepatitis by activating NF-κB, which activates production of cytotoxic TNF-α.
Authors
Hiroshi Kono, Ivan Rusyn, Ming Yin, Erwin Gäbele, Shunhei Yamashina, Anna Dikalova, Maria B. Kadiiska, Henry D. Connor, Ronald P. Mason, Brahm H. Segal, Blair U. Bradford, Steven M. Holland, Ronald G. Thurman
Abstract
Antithrombin is a plasma protease inhibitor that inhibits thrombin and contributes to the maintenance of blood fluidity. Using targeted gene disruption, we investigated the role of antithrombin in embryogenesis. Mating mice heterozygous for antithrombin gene (ATIII) disruption, ATIII+/–, yielded the expected Mendelian distribution of genotypes until 14.5 gestational days (gd). However, approximately 70% of the ATIII–/– embryos at 15.5 gd and 100% at 16.5 gd had died and showed extensive subcutaneous hemorrhage. Histological examination of those embryos revealed extensive fibrin(ogen) deposition in the myocardium and liver, but not in the brain or lung. Furthermore, no apparent fibrin(ogen) deposition was detected in the extensive hemorrhagic region, suggesting that fibrinogen might be decreased due to consumptive coagulopathy and/or liver dysfunction. These findings suggest that antithrombin is essential for embryonic survival and that it plays an important role in regulation of blood coagulation in the myocardium and liver.
Authors
Kazuhiro Ishiguro, Tetsuhito Kojima, Kenji Kadomatsu, Yukiko Nakayama, Akira Takagi, Misao Suzuki, Naoki Takeda, Masafumi Ito, Koji Yamamoto, Tadashi Matsushita, Kazuo Kusugami, Takashi Muramatsu, Hidehiko Saito
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