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Interaction between neuronal nitric oxide synthase and inhibitory G protein activity in heart rate regulation in conscious mice.

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Abstract

Nitric oxide (NO) synthesized within mammalian sinoatrial cells has been shown to participate in cholinergic control of heart rate (HR). However, it is not known whether NO synthesized within neurons plays a role in HR regulation. HR dynamics were measured in 24 wild-type (WT) mice and 24 mice in which the gene for neuronal NO synthase (nNOS) was absent (nNOS-/- mice). Mean HR and HR variability were compared in subsets of these animals at baseline, after parasympathetic blockade with atropine (0.5 mg/kg i.p.), after beta-adrenergic blockade with propranolol (1 mg/kg i.p.), and after combined autonomic blockade. Other animals underwent pressor challenge with phenylephrine (3 mg/kg i.p.) after beta-adrenergic blockade to test for a baroreflex-mediated cardioinhibitory response. The latter experiments were then repeated after inactivation of inhibitory G proteins with pertussis toxin (PTX) (30 microgram/kg i.p.). At baseline, nNOS-/- mice had higher mean HR (711+/-8 vs. 650+/-8 bpm, P = 0.0004) and lower HR variance (424+/-70 vs. 1,112+/-174 bpm2, P = 0.001) compared with WT mice. In nNOS-/- mice, atropine administration led to a much smaller change in mean HR (-2+/-9 vs. 49+/-5 bpm, P = 0.0008) and in HR variance (64+/-24 vs. -903+/-295 bpm2, P = 0.02) than in WT mice. In contrast, propranolol administration and combined autonomic blockade led to similar changes in mean HR between the two groups. After beta-adrenergic blockade, phenylephrine injection elicited a fall in mean HR and rise in HR variance in WT mice that was partially attenuated after treatment with PTX. The response to pressor challenge in nNOS-/- mice before PTX administration was similar to that in WT mice. However, PTX-treated nNOS-/- mice had a dramatically attenuated response to phenylephrine. These findings suggest that the absence of nNOS activity leads to reduced baseline parasympathetic tone, but does not prevent baroreflex-mediated cardioinhibition unless inhibitory G proteins are also inactivated. Thus, neuronally derived NO and cardiac inhibitory G protein activity serve as parallel pathways to mediate autonomic slowing of heart rate in the mouse.

Authors

P Jumrussirikul, J Dinerman, T M Dawson, V L Dawson, U Ekelund, D Georgakopoulos, L P Schramm, H Calkins, S H Snyder, J M Hare, R D Berger

Paternal mutation of the sulfonylurea receptor (SUR1) gene and maternal loss of 11p15 imprinted genes lead to persistent hyperinsulinism in focal adenomatous hyperplasia.

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Congenital hyperinsulinism, or persistent hyperinsulinemic hypoglycemia of infancy (PHHI), is a glucose metabolism disorder characterized by unregulated secretion of insulin and profound hypoglycemia. From a morphological standpoint, there are two types of histopathological lesions, a focal adenomatous hyperplasia of islet cells of the pancreas in approximately 30% of operated sporadic cases, and a diffuse form. In sporadic focal forms, specific losses of maternal alleles (LOH) of the imprinted chromosomal region 11p15, restricted to the hyperplastic area of the pancreas, were observed. Similar mechanisms are observed in embryonal tumors and in the Beckwith-Wiedemann syndrome (BWS), also associated with neonatal but transient hyperinsulinism. However, this region also contains the sulfonylurea receptor (SUR1) gene and the inward rectifying potassium channel subunit (KIR6.2) gene, involved in recessive familial forms of PHHI, but not known to be imprinted. Although the parental bias in loss of maternal alleles did not argue in favor of their direct involvement, the LOH may also unmask a recessive mutation leading to persistent hyperinsulinism. We now report somatic reduction to hemizygosity or homozygosity of a paternal SUR1 constitutional heterozygous mutation in four patients with a focal form of PHHI. Thus, this somatic event which leads both to beta cell proliferation and to hyperinsulinism can be considered as the somatic equivalent, restricted to a microscopic focal lesion, of constitutional uniparental disomy associated with unmasking of a heterozygous parental mutation leading to a somatic recessive disorder.

Authors

V Verkarre, J C Fournet, P de Lonlay, M S Gross-Morand, M Devillers, J Rahier, F Brunelle, J J Robert, C Nihoul-Fékété, J M Saudubray, C Junien

A mouse model of myosin binding protein C human familial hypertrophic cardiomyopathy.

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Familial hypertrophic cardiomyopathy can be caused by mutations in genes encoding sarcomeric proteins, including the cardiac isoform of myosin binding protein C (MyBP-C), and multiple mutations which cause truncated forms of the protein to be made are linked to the disease. We have created transgenic mice in which varying amounts of a mutated MyBP-C, lacking the myosin and titin binding domains, are expressed in the heart. The transgenically encoded, truncated protein is stable but is not incorporated efficiently into the sarcomere. The transgenic muscle fibers showed a leftward shift in the pCa2+-force curve and, importantly, their power output was reduced. Additionally, expression of the mutant protein leads to decreased levels of endogenous MyBP-C, resulting in a striking pattern of sarcomere disorganization and dysgenesis.

Authors

Q Yang, A Sanbe, H Osinska, T E Hewett, R Klevitsky, J Robbins

Reduced microvascular thrombosis and improved outcome in acute murine stroke by inhibiting GP IIb/IIIa receptor-mediated platelet aggregation.

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Treatment options in acute stroke are limited by a dearth of safe and effective regimens for recanalization of an occluded cerebrovascular tributary, as well as by the fact that patients present only after the occlusive event is established. We hypothesized that even if the site of major arterial occlusion is recanalized after stroke, microvascular thrombosis continues to occur at distal sites, reducing postischemic flow and contributing to ongoing neuronal death. To test this hypothesis, and to show that microvascular thrombosis occurs as an ongoing, dynamic process after the onset of stroke, we tested the effects of a potent antiplatelet agent given both before and after the onset of middle cerebral arterial (MCA) occlusion in a murine model of stroke. After 45 min of MCA occlusion and 23 h of reperfusion, fibrin accumulates in the ipsilateral cerebral hemisphere, based upon immunoblotting, and localizes to microvascular lumena, based upon immunostaining. In concordance with these data, there is a nearly threefold increase in the ipsilateral accumulation of 111In-labeled platelets in mice subjected to stroke compared with mice not subjected to stroke. When a novel inhibitor of the glycoprotein IIb/IIIa receptor (SDZ GPI 562) was administered immediately before MCA occlusion, platelet accumulation was reduced 48%, and fibrin accumulation was reduced by 47% by immunoblot densitometry. GPI 562 exhibited a dose-dependent reduction of cerebral infarct volumes measured by triphenyltetrazolium chloride staining, as well as improvement in postischemic cerebral blood flow, measured by laser doppler. GPI 562 caused a dose-dependent increase in tail vein bleeding time, but intracerebral hemorrhage (ICH) was not significantly increased at therapeutic doses; however, there was an increase in ICH at the highest doses tested. When given immediately after withdrawal of the MCA occluding suture, GPI 562 was shown to reduce cerebral infarct volumes by 70%. These data support the hypothesis that in ischemic regions of brain, microvascular thrombi continue to accumulate even after recanalization of the MCA, contributing to postischemic hypoperfusion and ongoing neuronal damage.

Authors

T F Choudhri, B L Hoh, H G Zerwes, C J Prestigiacomo, S C Kim, E S Connolly Jr, G Kottirsch, D J Pinsky

Role of the stress-activated protein kinases in endothelin-induced cardiomyocyte hypertrophy.

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The signal transduction pathways governing the hypertrophic response of cardiomyocytes are not well defined. Constitutive activation of the stress-activated protein kinase (SAPK) family of mitogen-activated protein (MAP) kinases or another stress-response MAP kinase, p38, by overexpression of activated mutants of various components of the pathways is sufficient to induce a hypertrophic response in cardiomyocytes, but it is not clear what role these pathways play in the response to physiologically relevant hypertrophic stimuli. To determine the role of the SAPKs in the hypertrophic response, we used adenovirus-mediated gene transfer of SAPK/ERK kinase-1 (KR) [SEK-1(KR)], a dominant inhibitory mutant of SEK-1, the immediate upstream activator of the SAPKs, to block signal transmission down the SAPK pathway in response to the potent hypertrophic agent, endothelin-1 (ET-1). SEK-1(KR) completely inhibited ET-1-induced SAPK activation without affecting activation of the other MAP kinases implicated in the hypertrophic response, p38 and extracellular signal-regulated protein kinases (ERK)-1/ERK-2. Expression of SEK-1(KR) markedly inhibited the ET-1-induced increase in protein synthesis. In contrast, the MAPK/ERK kinase inhibitor, PD98059, which blocks ERK activation, and the p38 inhibitor, SB203580, had no effect on ET-1-induced protein synthesis. ET-1 also induced a significant increase in atrial natriuretic factor mRNA expression as well as in the percentage of cells with highly organized sarcomeres, responses which were also blocked by expression of SEK-1(KR). In summary, inhibiting activation of the SAPK pathway abrogated the hypertrophic response to ET-1. These data are the first demonstration that the SAPKs are necessary for the development of agonist-induced cardiomyocyte hypertrophy, and suggest that in response to ET-1, they transduce critical signals governing the hypertrophic response.

Authors

G Choukroun, R Hajjar, J M Kyriakis, J V Bonventre, A Rosenzweig, T Force

Matrilysin expression and function in airway epithelium.

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We report that matrilysin, a matrix metalloproteinase, is constitutively expressed in the epithelium of peribronchial glands and conducting airways in normal lung. Matrilysin expression was increased in airway epithelial cells and was induced in alveolar type II cells in cystic fibrosis. Other metalloproteinases (collagenase-1, stromelysin-1, and 92-kD gelatinase) were not produced by normal or injured lung epithelium. These observations suggest that matrilysin functions in injury-mediated responses of the lung. Indeed, matrilysin expression was increased in migrating airway epithelial cells in wounded human and mouse trachea. In human tissue, epithelial migration was reduced by > 80% by a hydroxamate inhibitor, and in mouse tissue, reepithelialization in trachea from matrilysin-null mice was essentially blocked. In vivo observations and cell culture studies demonstrated that matrilysin was secreted lumenally by lung epithelium, but upon activation or while migrating over wounds, some matrilysin was released basally. The constitutive production of matrilysin in conducting airways, its upregulation after injury, its induction by alveolar epithelium, and its release into both lumenal and matrix compartments suggest that this metalloproteinase serves multiple functions in intact and injured lung, one of which is to facilitate reepithelialization.

Authors

S E Dunsmore, U K Saarialho-Kere, J D Roby, C L Wilson, L M Matrisian, H G Welgus, W C Parks

Reduced binding and phagocytosis of Pneumocystis carinii by alveolar macrophages from persons infected with HIV-1 correlates with mannose receptor downregulation.

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The macrophage mannose receptor, a pattern recognition molecule and component of innate immunity, mediates binding and phagocytosis of Pneumocystis carinii and likely represents an important clearance mechanism in the lungs of immunocompetent hosts. The purpose of this study was to examine the ability of alveolar macrophages from HIV-infected individuals to bind and phagocytose P. carinii, and to investigate the role of the macrophage mannose receptor in mediating this interaction. Compared with healthy individuals, alveolar macrophage phagocytosis of P. carinii from HIV+ persons was reduced up to 74% (P = 0.02), primarily reflecting a reduction in the number of organisms associated with each macrophage (P = 0.019). Furthermore, macrophages from HIV+ individuals demonstrated up to an 80% (P < 0.05) reduction in mannose receptor surface expression and endocytosis. Mannose receptor affinity was unaltered, and mRNA levels were modestly reduced (P < 0.05). Cells from HIV+ individuals with CD4(+) counts < 200 cells/mm3 (representing individuals at high clinical risk for P. carinii pneumonia) demonstrated the lowest levels of P. carinii phagocytosis and mannose receptor endocytosis. In vitro HIV infection of alveolar macrophages from healthy individuals reduced mannose receptor endocytosis to 53.2% (P < 0.05) and P. carinii binding and phagocytosis to 67.4% (P < 0.05) of control. Our studies suggest that HIV infection may alter innate immunity in the lungs, and that impaired alveolar macrophage mannose receptor-mediated binding and phagocytosis of P. carinii may contribute to the susceptibility of HIV-infected individuals to this opportunistic pulmonary pathogen.

Authors

H Koziel, Q Eichbaum, B A Kruskal, P Pinkston, R A Rogers, M Y Armstrong, F F Richards, R M Rose, R A Ezekowitz

Effects of mutations in the human uncoupling protein 3 gene on the respiratory quotient and fat oxidation in severe obesity and type 2 diabetes.

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Human uncoupling protein 3 (UCP3) is a mitochondrial transmembrane carrier that uncouples oxidative ATP phosphorylation. With the capacity to participate in thermogenesis and energy balance, UCP3 is an important obesity candidate gene. A missense polymorphism in exon 3 (V102I) was identified in an obese and diabetic proband. A mutation introducing a stop codon in exon 4 (R143X) and a terminal polymorphism in the splice donor junction of exon 6 were also identified in a compound heterozygote that was morbidly obese and diabetic. Allele frequencies of the exon 3 and exon 6 splice junction polymorphisms were determined and found to be similar in Gullah-speaking African Americans and the Mende tribe of Sierra Leone, but absent in Caucasians. Moreover, in exon 6-splice donor heterozygotes, basal fat oxidation rates were reduced by 50%, and the respiratory quotient was markedly increased compared with wild-type individuals, implicating a role for UCP3 in metabolic fuel partitioning.

Authors

G Argyropoulos, A M Brown, S M Willi, J Zhu, Y He, M Reitman, S M Gevao, I Spruill, W T Garvey

A novel phenotype related to partial loss of function mutations of the follicle stimulating hormone receptor.

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A single natural loss of function mutation of the follicle stimulating hormone receptor (FSHR) has been described to date. Present in the Finnish population it markedly impairs receptor function, blocking follicle development at the primary stage and presenting as primary amenorrhea with atrophic ovaries. When Western European women with this phenotype were examined for FSHR mutations the result was negative, suggesting that other etiologies corresponding to this clinical pattern are markedly more frequent. We now describe a novel phenotype related to mutations provoking a partial loss of function of the FSHR. A woman with secondary amenorrhea had very high plasma gonadotropin concentrations (especially FSH), contrasting with normal sized ovaries and antral follicles up to 5 mm at ultrasonography. Histological and immunohistochemical examination of the ovaries showed normal follicular development up to the small antral stage and a disruption at further stages. The patient was found to carry compound heterozygotic mutations of the FSHR gene: Ile160Thr and Arg573Cys substitutions located, respectively, in the extracellular domain and in the third intracellular loop of the receptor. The mutated receptors, when expressed in COS-7 cells, showed partial functional impairment, consistent with the clinical and histological observations: the first mutation impaired cell surface expression and the second altered signal transduction of the receptor. This observation suggests that a limited FSH effect is sufficient to promote follicular growth up to the small antral stage. Further development necessitates strong FSH stimulation. The contrast between very high FSH levels and normal sized ovaries with antral follicles may thus be characteristic of such patients.

Authors

I Beau, P Touraine, G Meduri, A Gougeon, A Desroches, C Matuchansky, E Milgrom, F Kuttenn, M Misrahi

Cloning and identification of human Sca as a novel inhibitor of osteoclast formation and bone resorption.

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Abstract

Increased osteoclast activity is responsible for the enhanced bone destruction in postmenopausal osteoporosis, Paget's disease, bone metastasis, and hypercalcemia of malignancy. However, the number of known inhibitory factors that block osteoclast formation and bone resorption are limited. Therefore, we used an expression-cloning approach to identify novel factors produced by osteoclasts that inhibit osteoclast activity. A candidate clone was identified and isolated from a human osteoclast-like multinucleated cell (MNC) cDNA library, named osteoclast inhibitory peptide-1 (OIP-1), and the cDNA sequence was determined. This sequence matched that of the recently identified human stem cell antigen, was structurally similar to the mouse Ly-6 gene family, and the sequence predicted it was a glycosyl phosphatidyl inositol (GPI)-anchored protein that had a cleavable COOH-terminal peptide. Western blot analysis of conditioned media from 293 cells transfected with the OIP-1 cDNA clone confirmed that OIP-1 was released into the media as a membrane-bound GPI-linked protein. Interestingly, both recombinant OIP-1 expressed in Escherichia coli (which does not have GPI linker) and OIP-1 expressed by mammalian cells significantly reduced osteoclast-like MNC formation induced by 1,25-dihydroxyvitamin D3 or PTH-related protein in mouse and human bone marrow cultures, and inhibited 45Ca release from prelabeled bone in fetal rat organ cultures. In contrast, recombinant OIP-1 did not inhibit the growth of a variety of other cell types. These data indicate that OIP-1 is a novel, specific inhibitor of osteoclast formation and bone resorption.

Authors

S J Choi, R D Devlin, C Menaa, H Chung, G D Roodman, S V Reddy

The effect of novel polymorphisms in the interleukin-6 (IL-6) gene on IL-6 transcription and plasma IL-6 levels, and an association with systemic-onset juvenile chronic arthritis.

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During active disease, patients with systemic-onset juvenile chronic arthritis (S-JCA) demonstrate a rise and fall in serum interleukin-6 (IL-6) that parallels the classic quotidian fever. To investigate the possibility that this cytokine profile results from a difference in the control of IL-6 expression, we examined the 5' flanking region of the IL-6 gene for polymorphisms. A G/C polymorphism was detected at position -174. In a group of 383 healthy men and women from a general practice in North London, the frequency of the C allele was 0.403 (95% confidence interval 0.37-0.44). In comparison, 92 patients with S-JCA had a different overall genotype frequency, especially those with onset of disease at < 5 yr of age. This was mainly due to the statistically significant lower frequency of the CC genotype in this subgroup. When comparing constructs of the 5' flanking region (-550-+61 bp) in a luciferase reporter vector transiently transfected into HeLa cells, the -174C construct showed 0.624+/-0.15-fold lower expression than the -174G construct. After stimulation with LPS or IL-1, expression from the -174C construct did not significantly change after 24 h, whereas expression from the -174G construct increased by 2.35+/-0.10- and 3.60+/-0.26-fold, respectively, compared with the unstimulated level. Plasma levels of IL-6 were also measured in 102 of the healthy subjects, and the C allele was found to be associated with significantly lower levels of plasma IL-6. These results suggest that there is a genetically determined difference in the degree of the IL-6 response to stressful stimuli between individuals. The reduced frequency of the potentially protective CC genotype in young S-JCA patients may contribute to its pathogenesis. Similarly the individual's IL-6 genotype may be highly relevant in other conditions where IL-6 has been implicated, such as atherosclerosis.

Authors

D Fishman, G Faulds, R Jeffery, V Mohamed-Ali, J S Yudkin, S Humphries, P Woo

The negative inotropic effect of beta3-adrenoceptor stimulation is mediated by activation of a nitric oxide synthase pathway in human ventricle.

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Beta1- and beta2-adrenoceptors in heart muscle cells mediate the catecholamine-induced increase in the force and frequency of cardiac contraction. Recently, in addition, we demonstrated the functional expression of beta3-adrenoceptors in the human heart. Their stimulation, in marked contrast with that of beta1- and beta2-adrenoceptors, induces a decrease in contractility through presently unknown mechanisms. In the present study, we examined the role of a nitric oxide (NO) synthase pathway in mediating the beta3-adrenoceptor effect on the contractility of human endomyocardial biopsies. The negative inotropic effects of a beta3-adrenoceptor agonist, BRL 37344, and also of norepinephrine in the presence of alpha- and beta1-2-blockade were inhibited both by a nonspecific blocker of NO, methylene blue, and two NO synthase (NOS) inhibitors, L-N-monomethyl-arginine and L-nitroarginine-methyl ester. The effect of the NOS inhibitors was reversed by an excess of L-arginine, the natural substrate of NOS, but not by D-arginine. Moreover, the effects of the beta3-adrenoceptor agonist on contractility were associated with parallel increases in the production of NO and intracellular cGMP, which were also inhibited by NOS inhibitors. Immunohistochemical staining of human ventricular biopsies showed the expression of the endothelial constitutive (eNOS), but not the inducible (iNOS) isoform of NOS in both ventricular myocytes and endothelial cells. These results demonstrate that beta3-adrenoceptor stimulation decreases cardiac contractility through activation of an NOS pathway. Changes in the expression of this pathway may alter the balance between positive and negative inotropic effects of catecholamines on the heart potentially leading to myocardial dysfunction.

Authors

C Gauthier, V Leblais, L Kobzik, J N Trochu, N Khandoudi, A Bril, J L Balligand, H Le Marec

Requirement of Stat3 but not Stat1 activation for epidermal growth factor receptor- mediated cell growth In vitro.

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Stimulation of epidermal growth factor receptor (EGFR) by ligand(s) leads to activation of signaling molecules including Stat1 and Stat3, two members of the signal transducers and activators of transcription (STAT) protein family. Activation of Stat1 and Stat3 was constitutive in transformed squamous epithelial cells, which produce elevated levels of TGF-alpha, and was enhanced by the addition of exogenous TGF-alpha. Targeting of Stat3 using antisense oligonucleotides directed against the translation initiation site, resulted in significant growth inhibition. In addition, cells stably transfected with dominant negative mutant Stat3 constructs failed to proliferate in vitro. In contrast, targeting of Stat1 using either antisense or dominant-negative strategies had no effect on cell growth. Thus, TGF-alpha/EGFR-mediated autocrine growth of transformed epithelial cells is dependent on activation of Stat3 but not Stat1.

Authors

J R Grandis, S D Drenning, A Chakraborty, M Y Zhou, Q Zeng, A S Pitt, D J Tweardy

Autoreactive T cells to platelet GPIIb-IIIa in immune thrombocytopenic purpura. Role in production of anti-platelet autoantibody.

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T cell proliferative responses to platelet membrane GPIIb-IIIa were examined in 14 patients with chronic immune thrombocytopenic purpura (ITP), 7 systemic lupus erythematosus (SLE) patients with or without thrombocytopenia, and 10 healthy donors. Although peripheral blood T cells from all subjects failed to respond to the protein complex in its native state, reduced GPIIb-IIIa stimulated T cells from three ITP patients and one SLE patient with thrombocytopenia, and tryptic peptides of GPIIb-IIIa stimulated T cells from nearly all subjects. The specificity of the responses for GPIIb-IIIa was confirmed by activation of GPIIb-IIIa-primed T cells by a recombinant GPIIbalpha fragment in secondary cultures. Characterization of T cell response induced by modified GPIIb-IIIa showed that the response was restricted by HLA-DR, the responding T cells had a CD4(+) phenotype, and the proliferation was accelerated only in ITP patients, suggesting in vivo activation of these T cells. In vitro IgG anti-GPIIb-IIIa synthesis in PBMC cultures was induced by modified GPIIb-IIIa specifically in ITP patients with platelet-associated anti-GPIIb-IIIa antibody. Anti-GPIIb-IIIa antibody produced in supernatants was absorbed by incubation with normal platelets. In summary, CD4(+) and HLA-DR-restricted T cells to GPIIb-IIIa are involved in production of anti-platelet autoantibody in ITP patients and are related to the pathogenic process in chronic ITP.

Authors

M Kuwana, J Kaburaki, Y Ikeda

Central nervous system nitric oxide synthase activity regulates insulin secretion and insulin action.

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Systemic inhibition of nitric oxide synthase (NOS) with NG-monomethyl-L-arginine (L-NMMA) causes acute insulin resistance (IR), but the mechanism is unknown. We tested whether L-NMMA-induced IR occurs via NOS blockade in the central nervous system (CNS). Six groups of Sprague-Dawley rats were studied after chronic implantation of an intracerebroventricular (ICV) catheter into the lateral ventricle and catheters into the carotid artery and jugular vein. Animals were studied after overnight food deprivation, awake, unrestrained, and unstressed; all ICV infusion of L-NMMA or D-NMMA (control) were performed with artificial cerebrospinal fluid. ICV administration of L-NMMA resulted in a 30% rise in the basal glucose level after 2 h, while ICV D-NMMA had no effect on glucose levels. Insulin, epinephrine, and norepinephrine levels were unchanged from baseline in both groups. Tracer (3H-3-glucose)-determined glucose disposal rates during 2 h euglycemic hyperinsulinemic (300 microU/ml) clamps performed after ICV administration of L-NMMA were reduced by 22% compared with D-NMMA. Insulin secretory responses to a hyperglycemic clamp and to a superimposed arginine bolus were reduced by 28% in L-NMMA-infused rats compared with D-NMMA. In conclusion, ICV administration of L-NMMA causes hyperglycemia via the induction of defects in insulin secretion and insulin action, thus recapitulating abnormalities observed in type 2 diabetes. The data suggest the novel concept that central NOS-dependent pathways may control peripheral insulin action and secretion. This control is not likely to be mediated via adrenergic mechanisms and could occur via nonadrenergic, noncholinergic nitrergic neural and/or endocrine pathways. These data support previously published data suggesting that CNS mechanisms may be involved in the pathogenesis of some forms of insulin resistance and type 2 diabetes independent of adiposity.

Authors

R Shankar, J S Zhu, B Ladd, D Henry, H Q Shen, A D Baron

Local overexpression of TIMP-1 prevents aortic aneurysm degeneration and rupture in a rat model.

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Abstract

Although matrix metalloproteinases (MMPs) are expressed in abundance in arterial aneurysms, their contribution to arterial wall degeneration, dilation, and rupture has not been determined. We investigated MMP function in a rat model of aneurysm associated with arterial dilation, elastin loss, medial invasion by mononuclear inflammatory cells, and MMP upregulation. Rupture was correlated with increased gelatinase B (MMP-9) and activated gelatinase A (MMP-2). Syngeneic rat smooth muscle cells retrovirally transfected with tissue inhibitor of matrix metalloproteinases (TIMP)-1 cDNA (LTSN) or with the vector alone as a control (LXSN) were seeded onto the luminal surface of the vessels. The seeding of LTSN cells resulted in TIMP-1 local overexpression. The seeding with LTSN cells, but not LXSN cells, decreased MMP-9, activated MMP-2 and 28-kD caseinase and elastase activity, preserved elastin in the media, and prevented aneurysmal degeneration and rupture. We conclude that MMP overexpression is responsible for aneurysmal degeneration and rupture in this rat model and that local pharmacological blockade might be a reasonable strategy for controlling the formation of aneurysms in humans.

Authors

E Allaire, R Forough, M Clowes, B Starcher, A W Clowes

Augmentation of lung liquid clearance via adenovirus-mediated transfer of a Na,K-ATPase beta1 subunit gene.

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Abstract

Previous studies have suggested that alveolar Na,K-ATPases play an important role in active Na+ transport and lung edema clearance. We reasoned that overexpression of Na,K-ATPase subunit genes could increase Na,K-ATPase function in lung epithelial cells and edema clearance in rat lungs. To test this hypothesis we produced replication deficient human type 5 adenoviruses containing cDNAs for the rat alpha1 and beta1 Na,K-ATPase subunits (adMRCMValpha1 and adMRCMVbeta1, respectively). As compared to controls, adMRCMVbeta1 increased beta1 subunit expression and Na,K-ATPase function by 2. 5-fold in alveolar type 2 epithelial cells and rat airway epithelial cell monolayers. No change in Na,K-ATPase function was noted after infection with adMRCMValpha1. Rat lungs infected with adMRCMVbeta1, but not adMRCMValpha1, had increased beta1 protein levels and lung liquid clearance 7 d after tracheal instillation. Alveolar epithelial permeability to Na+ and mannitol was mildly increased in animals infected with adMRCMVbeta1 and a similar Escherichia coli lacZ-expressing virus. Our data shows, for the first time, that transfer of the beta1 Na,K-ATPase subunit gene augments Na,K-ATPase function in epithelial cells and liquid clearance in rat lungs. Conceivably, overexpression of Na,K-ATPases could be used as a strategy to augment lung liquid clearance in patients with pulmonary edema.

Authors

P Factor, F Saldias, K Ridge, V Dumasius, J Zabner, H A Jaffe, G Blanco, M Barnard, R Mercer, R Perrin, J I Sznajder

Apoptosis mediated by Fas but not tumor necrosis factor receptor 1 prevents chronic disease in mice infected with murine cytomegalovirus.

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Abstract

The role of Fas- and TNF-receptor 1 (TNF-R1)-mediated apoptosis in the clearance of virally infected cells and in the regulation of the immune response was analyzed after murine cytomegalovirus (MCMV) infection of C57BL/6 (B6)-+/+ mice, Fas-mutant B6-lpr/lpr mice, TNF-R1 knockout B6-tnfr0/0 mice, and double-deficient B6-tnfr0/0 lpr/lpr mice. There was approximately equivalent clearance of MCMV in B6-+/+, B6-tnfr0/0, and B6-lpr/lpr mice, and by day 28 no infectious virus could be detected in the liver, kidney, lung, or peritoneal exudate. However, delayed virus clearance was observed in B6-tnfr0/0 lpr/lpr mice. An acute inflammatory response occurred in the liver, lung, and kidney of all mice, which was most severe 7 d after MCMV infection, but resolved by day 28 in B6-+/+ and B6-tnfr0/0 mice, but not in B6-lpr/lpr or B6-tnfr0/0 lpr/lpr mice. These results indicate that apoptosis mediated by either Fas or TNF-R1 is sufficient for rapid clearance of the virus. However, apoptosis induced by Fas, but not TNF-R1, is required for the downmodulation of the immune response to the virus and prevention of a chronic inflammatory reaction.

Authors

M Fleck, E R Kern, T Zhou, J Podlech, W Wintersberger, C K Edwards 3rd, J D Mountz

Transgenic expression of replication-restricted enteroviral genomes in heart muscle induces defective excitation-contraction coupling and dilated cardiomyopathy.

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Abstract

Numerous studies have implicated Coxsackievirus in acute and chronic heart failure. Although enteroviral nucleic acids have been detected in selected patients with dilated cardiomyopathy, the significance of such persistent nucleic acids is unknown. To investigate the mechanisms by which restricted viral replication with low level expression of Coxsackieviral proteins may be able to induce cardiomyopathy, we generated transgenic mice which express a replication-restricted full-length Coxsackievirus B3 (CVB3) cDNA mutant (CVB3DeltaVP0) in the heart driven by the cardiac myocyte-specific myosin light chain-2v (MLC-2v) promoter. CVB3DeltaVP0 was generated by mutating infectious CVB3 cDNA at the VP4/VP2 autocatalytic cleavage site from Asn-Ser to Lys-Ala. Cardiac-specific expression of this cDNA leads to synthesis of positive- and negative-strand viral RNA in the heart without formation of infectious viral progeny. Histopathologic analysis of transgenic hearts revealed typical morphologic features of myocardial interstitial fibrosis and in some cases degeneration of myocytes, thus resembling dilated cardiomyopathy in humans. There was also an increase in ventricular atrial natriuretic factor mRNA levels, demonstrating activation of the embryonic program of gene expression typical of ventricular hypertrophy and failure. Echocardiographic analysis demonstrated the presence of left ventricular dilation and decreased systolic function in the transgenic mice compared with wild-type littermates, evidenced by increased ventricular end-diastolic and end-systolic dimensions and decreased fractional shortening. Analysis of isolated myocytes from transgenic mice demonstrate that there is defective excitation-contraction coupling and a decrease in the magnitude of isolated cell shortening. These data demonstrate that restricted replication of enteroviral genomes in the heart can induce dilated cardiomyopathy with excitation-contraction coupling abnormalities similar to pressure overload models of dilated cardiomyopathy.

Authors

R Wessely, K Klingel, L F Santana, N Dalton, M Hongo, W Jonathan Lederer, R Kandolf, K U Knowlton

Serum from patients with type 2 diabetes with neuropathy induces complement-independent, calcium-dependent apoptosis in cultured neuronal cells.

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Abstract

We hypothesized that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that promotes complement-independent, calcium-dependent apoptosis in neuronal cell lines. Neuronal cells were cultured in the presence of complement-inactivated sera obtained from patients with type 2 diabetes with and without neuropathy and healthy adult control patients. Serum from diabetic patients with neuropathy was associated with a significantly greater induction of apoptosis, compared to serum from diabetic patients without neuropathy and controls. In the presence of calcium channel antagonists, induction of apoptosis was reduced by approximately 50%. Pretreatment of neuronal cells with serum from diabetic patients with neuropathy was associated with a significant increase in elevated K+-evoked cytosolic calcium concentration. Serum-induced enhancement in cytosolic calcium and calcium current density was blocked by treatment with trypsin and filtration of the serum using a 100,000-kd molecular weight filter. Treatment with an anti-human IgG antibody was associated with intense fluorescence on the surface of neuronal cells exposed to sera from patients with type 2 diabetes mellitus with neuropathy. We conclude that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that induces complement-independent, calcium-dependent apoptosis in neuronal cells.

Authors

S Srinivasan, M J Stevens, H Sheng, K E Hall, J W Wiley