State of actin in gastric parietal cells

Hidden Acid Retention with Normal Serum Bicarbonate Level in Chronic Kidney Disease

Management of metabolic acidosis is crucial for preserving bone, muscle, and renal health, as evidenced by the results of several interventional studies conducted on patients with chronic kidney disease (CKD). Considering the continuity of CKD progression over time, it is reasonable to deduce that a subclinical form of metabolic acidosis may exist prior to the manifestation of overt metabolic acidosis. Covert H⁺ retention with normal serum bicarbonate level in patients with CKD may result in maladaptive responses that contribute to kidney function deterioration, even in the early stages of the disease. The loss of adaptive compensatory mechanisms of urinary acid excretion may be a key factor in this process. Early modulation of these responses could be an important therapeutic strategy in preventing CKD progression. However, to date, the optimal approach for alkali therapy in subclinical metabolic acidosis in CKD remains uncertain. There is a lack of established guidelines on when to initiate alkali therapy, potential side effects of alkali agents, and the optimal blood bicarbonate levels based on evidence-based practices. Therefore, further research is necessary to address these concerns and establish more robust guidelines for the use of alkali therapy in patients with CKD. Herein, we provide an overview of recent developments on this subject and examine the potential therapeutic approaches that interventional treatments may present for patients with hidden H⁺ retention, exhibiting normal serum bicarbonate levels - commonly described as subclinical or eubicarbonatemic metabolic acidosis in patients with CKD.

Mechanisms of Metabolic Acidosis-Induced Kidney Injury in Chronic Kidney Disease

Retrospective analyses and single-center prospective studies identify chronic metabolic acidosis as an independent and modifiable risk factor for progression of CKD. In patients with CKD, untreated chronic metabolic acidosis often leads to an accelerated reduction in GFR. Mechanisms responsible for this reduction include adaptive responses that increase acid excretion but lead to a decline in kidney function. Metabolic acidosis in CKD stimulates production of intrakidney paracrine hormones including angiotensin II, aldosterone, and endothelin-1 (ET-1) that mediate the immediate benefit of increased kidney acid excretion, but their chronic upregulation promotes inflammation and fibrosis. Chronic metabolic acidosis also stimulates ammoniagenesis that increases acid excretion but also leads to ammonia-induced complement activation and deposition of C3 and C5b-9 that can cause tubule-interstitial damage, further worsening disease progression. These effects, along with acid accumulation in kidney tissue, combine to accelerate progression of kidney disease. Treatment of chronic metabolic acidosis attenuates these adaptive responses; reduces levels of angiotensin II, aldosterone, and ET-1; reduces ammoniagenesis; and diminishes inflammation and fibrosis that may lead to slowing of CKD progression.

Involvement of median preoptic nucleus and medullary noradrenergic neurons in cardiovascular and sympathetic responses of hemorrhagic rats

The infusion of hypertonic saline solution (HSS) is known to be beneficial to the treatment of hypovolemic hemorrhage (HH). The central mechanism of HSS-induced cardiovascular and autonomic recovery of animals subjected to HH remains unclear. Hence, the present study evaluated the involvement of median preoptic nucleus (MnPO) and medullary noradrenergic neurons (A1 and A2) in HSS-induced cardiovascular and sympathetic responses in hemorrhagic rats. The wistar rats were subjected to specific lesion of noradrenergic neurons through the nanoinjections of anti-DβH-saporin into caudal ventrolateral medulla (A1 neurons) and nucleus of the solitary tract (A2 neurons). After recovery, mean arterial pressure (MAP) and renal sympathetic nervous activity were recorded. The HH was performed through blood withdrawal until a MAP of 60 mmHg was attained. In sham rats, HSS infusion (3M NaCl) reestablished MAP without change in HH-induced sympathoinhibition. The muscimol (agonist of GABAA receptor) was nanoinjected in MnPO during HH and MnPO inhibition abolished the recovery of MAP and HSS-induced sympathoinhibition. Simultaneous lesions of A1 and A2 abolished MAP restoration and sympathoinhibition after HSS infusion. These results suggest that the recovery of MAP and HSS-induced sympathoinhibition in hemorrhaged rats depend on intact neural projections from A1 and A2 to MnPO.

The biology of the ABCA3 lipid transporter in lung health and disease

The lipid transporter, ATP-binding cassette class A3 (ABCA3), is a highly conserved multi-membrane-spanning protein that plays a critical role in the regulation of pulmonary surfactant homeostasis. Mutations in ABCA3 have been increasingly recognized as one of the causes of inherited pulmonary diseases. These monogenic disorders produce familial lung abnormalities with pathological presentations ranging from neonatal surfactant-deficiency-induced respiratory failure to childhood or adult diffuse parenchymal lung diseases for which specific treatment modalities remain limited. More than 200 ABCA3 mutations have been reported to date with approximately three quarters of patients presenting as compound heterozygotes. Recent advances in our understanding of the molecular basis underlying normal ABCA3 biosynthesis and processing and of the mechanisms of alveolar epithelial cell dysregulation caused by the expression of its mutant forms are beginning to emerge. These insights and the role of environmental factors and modifier genes are discussed in the context of the considerable variability in disease presentation observed in patients with identical ABCA3 gene mutations. Moreover, the opportunities afforded by an enhanced understanding of ABCA3 biology for targeted therapeutic strategies are addressed.

Surfactant protein D attenuates sub-epithelial fibrosis in allergic airways disease through TGF-β

Background

Surfactant protein D (SP-D) can regulate both innate and adaptive immunity. Recently, SP-D has been shown to contribute to the pathogenesis of airway allergic inflammation and bleomycin-induced pulmonary fibrosis. However, in allergic airways disease, the role of SP-D in airway remodeling remains unknown. The objective of this study was to determine the contribution of functional SP-D in regulating sub-epithelial fibrosis in a mouse chronic house dust mite model of allergic airways disease.

Methods

C57BL/6 wild-type (WT) and SP-D−/− mice (C57BL/6 background) were chronically challenged with house dust mite antigen (Dermatophagoides pteronyssinus, Dp). Studies with SP-D rescue and neutralization of TGF-β were conducted. Lung histopathology and the concentrations of collagen, growth factors, and cytokines present in the airspace and lung tissue were determined. Cultured eosinophils were stimulated by Dp in presence or absence of SP-D.

Results

Dp-challenged SP-D−/− mice demonstrate increased sub-epithelial fibrosis, collagen production, eosinophil infiltration, TGF-β1, and IL-13 production, when compared to Dp-challenged WT mice. By immunohistology, we detected an increase in TGF-β1 and IL-13 positive eosinophils in SP-D−/− mice. Purified eosinophils stimulated with Dp produced TGF-β1 and IL-13, which was prevented by co-incubation with SP-D. Additionally, treatment of Dp challenged SP-D−/− mice with exogenous SP-D was able to rescue the phenotypes observed in SP-D−/− mice and neutralization of TGF-β1 reduced sub-epithelial fibrosis in Dp-challenged SP-D−/− mice.

Conclusion

These data support a protective role for SP-D in the pathogenesis of sub-epithelial fibrosis in a mouse model of allergic inflammation through regulation of eosinophil-derived TGF-β.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-014-0143-9) contains supplementary material, which is available to authorized users.

Myosin IIB and F-actin control apical vacuolar morphology and histamine-induced trafficking of H-K-ATPase-containing tubulovesicles in gastric parietal cells

Selective inhibitors of myosin or actin function and confocal microscopy were used to test the role of an actomyosin complex in controlling morphology, trafficking, and fusion of tubulovesicles (TV) containing H-K-ATPase with the apical secretory canaliculus (ASC) of primary-cultured rabbit gastric parietal cells. In resting cells, myosin IIB and IIC, ezrin, and F-actin were associated with ASC, whereas H-K-ATPase localized to intracellular TV. Histamine caused fusion of TV with ASC and subsequent expansion resulting from HCl and water secretion; F-actin and ezrin remained associated with ASC whereas myosin IIB and IIC appeared to dissociate from ASC and relocalize to the cytoplasm. ML-7 (inhibits myosin light chain kinase) caused ASC of resting cells to collapse and most myosin IIB, F-actin, and ezrin to dissociate from ASC. TV were unaffected by ML-7. Jasplakinolide (stabilizes F-actin) caused ASC to develop large blebs to which actin, myosin II, and ezrin, as well as tubulin, were prominently localized. When added prior to stimulation, ML-7 and jasplakinolide prevented normal histamine-stimulated transformations of ASC/TV and the cytoskeleton, but they did not affect cells that had been previously stimulated with histamine. These results indicate that dynamic pools of actomyosin are required for maintenance of ASC structure in resting cells and for trafficking of TV to ASC during histamine stimulation. However, the dynamic pools of actomyosin are not required once the histamine-stimulated transformation of TV/ASC and cytoskeleton has occurred. These results also show that vesicle trafficking in parietal cells shares mechanisms with similar processes in renal collecting duct cells, neuronal synapses, and skeletal muscle.

Dietary management of chronic kidney disease: protein restriction and beyond

PURPOSE OF REVIEW

More kidney protective strategies are needed to reduce the burden of complete kidney failure from chronic kidney disease (CKD). Clinicians sometimes use protein restriction as kidney protection despite its demonstrated lack of effectiveness in the only large-scale study. Small-scale studies support that dietary acid reduction is kidney-protective, including when done with base-inducing foods like fruits and vegetables. We review these studies in light of current kidney-protective recommendations.

RECENT FINDINGS

Animal models of CKD show that acid-inducing dietary protein exacerbates and base-inducing protein ameliorates nephropathy progression, and that increased intake of acid-inducing but not base-inducing dietary protein exacerbates progression. Clinical studies show that dietary acid reduction with Na-based alkali reduces kidney injury and slows nephropathy progression in patients with CKD and reduced glomerular filtration rate (GFR); base-inducing fruits and vegetables reduce kidney injury in patients with reduced GFR; and base-inducing fruits and vegetables improve metabolic acidosis in CKD.

SUMMARY

Protein type rather than amount might more importantly affect nephropathy progression. Base-inducing foods might be another way to reduce dietary acid, a strategy shown in small studies to slow nephropathy progression. Further studies will determine if CKD patients should be given base-inducing food as part of their management.

Role of the Median Preoptic Nucleus in Arterial Pressure Regulation and Sodium and Water Homeostasis during High Dietary Salt Intake

Changes in the osmolality and level of angiotensin II (ANG II) are important peripheral signals modulating appropriate central sympathetic output and maintaining a normal arterial pressure during high salt intake. The median preoptic nucleus (MnPO) receives reciprocal inputs from the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT), the circumventricular organs that have been shown to be necessary in multiple central effects of changes in the osmolality and circulating ANG II directed toward the maintenance of sodium and water homeostasis. We, therefore, hypothesized that the MnPO is a crucial part of the central neuronal mechanisms mediating the blood pressure control by altered osmolality and/or ANG II signaling during chronic high dietary salt intake. Male Sprague-Dawley rats were randomly assigned to either sham (operation), or electrolytic lesion of the MnPO. After a 7-day recovery, rats were instrumented with radiotelemetric transducers and aortic flow probes for the measurement of the mean arterial pressure + heart rate (HR) and cardiac output (CO), respectively. Femoral venous catheters were also implanted to collect blood for the measurements of plasma osmolality and sodium concentration, as well as plasma renin activity. Rats were given another 10 days to recover and then were subjected to a 28-day-long study protocol that included a 7-day control period (1.0% NaCl diet), followed by 14 days of high salt (4.0% NaCl), and a 7-day recovery period (1.0% NaCl). The data showed, that despite a slight increase in the MAP observed in both MnPO- (n = 12) and sham-lesioned (n = 8) rats during the high-salt period, there were no significant differences between the MAP, HR, and CO in the two groups throughout the study protocol. These findings do not support the hypothesis that the MnPO is necessary to maintain normal blood pressure during high dietary salt intake. However, MnPO-lesioned rats showed less sodium balance than sham-lesioned rats during the first 4 days of high salt intake. Although, these results may be explained partly by the plasma hyperosmolarity and hypernatremia observed in MnPO-lesioned rats; they also shed light on the role of the MnPO in central neuronal control of renal sodium handling during chronic high dietary salt intake.

Segmental allergen challenge alters multimeric structure and function of surfactant protein D in humans

RATIONALE

Surfactant protein D (SP-D), a 43-kD collectin, is synthesized and secreted by airway epithelia as a dodecamer formed by assembly of four trimeric subunits. We have previously shown that the quaternary structure of SP-D can be altered during inflammatory lung injury through its modification by S-nitrosylation, which in turn alters its functional behavior producing a proinflammatory response in effector cells.

OBJECTIVES

We hypothesized that alterations in structure and function of SP-D may occur in humans with acute allergic inflammation.

METHODS

Bronchoalveolar lavage (BAL) fluid was collected from 15 nonsmoking patients with mild intermittent allergic asthma before and 24 hours after segmental provocation with saline, allergen, LPS, and mixtures of allergen and LPS. Structural modifications of SP-D were analyzed by native and sodium dodecyl sulfate gel electrophoresis.

MEASUREMENTS AND MAIN RESULTS

The multimeric structure of native SP-D was found to be disrupted after provocation with allergen or a mixture of allergen and LPS. Interestingly, under reducing conditions, sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that 7 of 15 patients with asthma developed an abnormal cross-linked SP-D band after segmental challenge with either allergen or a mixture of allergen with LPS but not LPS alone. Importantly, patients with asthma with cross-linked SP-D demonstrated significantly higher levels of BAL eosinophils, nitrogen oxides, IL-4, IL-5, IL-13, and S-nitrosothiol-SP-D compared with patients without cross-linked SP-D.

CONCLUSIONS

We conclude that segmental allergen challenge results in changes of SP-D multimeric structure and that these modifications are associated with an altered local inflammatory response in the distal airways.

Surfactant protein D binding to Aspergillus fumigatus hyphae is calcineurin-sensitive

Surfactant protein D (SP-D) plays a central role in pulmonary innate immune responses to microbes and allergens, often enhancing clearance of inhaled material. Although SP-D functions during bacterial and viral infections are well established, much less is known about its possible roles during invasive fungal infections. Aspergillus fumigatus is a prominent fungal pathogen in immunocompromised individuals, and can cause allergic or invasive aspergillosis. SP-D has been shown to be protective against both of these disease modalities. The moieties present on the fungal surface responsible for SP-D binding remain largely unclear, although cell wall 1,3-beta-D-glucan is bound by SP-D in other fungal species. There is little information regarding the interaction of SP-D with A. fumigatus hyphae which are responsible for the invasive form of disease. Here, we show that SP-D binding to A. fumigatus hyphae is sensitive to the activity of the calcium-activated protein phosphatase calcineurin. Deletion of the catalytic subunit calcineurin A (DeltacnaA) or pharmacologic inhibition of calcineurin through FK506 abrogated SP-D binding. In contrast, SP-D binding to Cruptococcus neoformans was calcineurin-independent. Pharmacologic inhibition of A. fumigatus cell wall components by caspofungin (inhibits 1,3-beta-D-glucan synthesis) and nikkomycin Z (inhibits chitin synthesis) increased SP-D binding to the wild-type strain. In contrast, SP-D binding increased in the DeltacnaA strain only after nikkomycin Z treatment. We conclude that SP-D binding to A. fumigatus hyphae is calcineurin-sensitive, presumably as a consequence of calcineurin's role in regulating production of key cell wall binding partners, such as 1,3-beta-D-glucan. Elucidation of the interaction between lung innate immune factors and A. fumigatus could lead to the development of novel therapeutic interventions.

Surfactant protein D increases phagocytosis of hypocapsular Cryptococcus neoformans by murine macrophages and enhances fungal survival

Cryptococcus neoformans is a facultative intracellular opportunistic pathogen and the leading cause of fungal meningitis in humans. In the absence of a protective cellular immune response, the inhalation of C. neoformans cells or spores results in pulmonary infection. C. neoformans cells produce a polysaccharide capsule composed predominantly of glucuronoxylomannan, which constitutes approximately 90% of the capsular material. In the lungs, surfactant protein A (SP-A) and SP-D contribute to immune defense by facilitating the aggregation, uptake, and killing of many microorganisms by phagocytic cells. We hypothesized that SP-D plays a role in C. neoformans pathogenesis by binding to and enhancing the phagocytosis of the yeast. Here, the abilities of SP-D to bind to and facilitate the phagocytosis and survival of the wild-type encapsulated strain H99 and the cap59Delta mutant hypocapsular strain are assessed. SP-D binding to cap59Delta mutant cells was approximately sixfold greater than binding to wild-type cells. SP-D enhanced the phagocytosis of cap59Delta cells by approximately fourfold in vitro. To investigate SP-D binding in vivo, SP-D(-/-) mice were intranasally inoculated with Alexa Fluor 488-labeled cap59Delta or H99 cells. By confocal microscopy, a greater number of phagocytosed C. neoformans cells in wild-type mice than in SP-D(-/-) mice was observed, consistent with in vitro data. Interestingly, SP-D protected C. neoformans cells against macrophage-mediated defense mechanisms in vitro, as demonstrated by an analysis of fungal viability using a CFU assay. These findings provide evidence that C. neoformans subverts host defense mechanisms involving surfactant, establishing a novel virulence paradigm that may be targeted for therapy.

Control of gastric acid secretion in health and disease

Recent milestones in the understanding of gastric acid secretion and treatment of acid-peptic disorders include the (1) discovery of histamine H(2)-receptors and development of histamine H(2)-receptor antagonists, (2) identification of H(+)K(+)-ATPase as the parietal cell proton pump and development of proton pump inhibitors, and (3) identification of Helicobacter pylori as the major cause of duodenal ulcer and development of effective eradication regimens. This review emphasizes the importance and relevance of gastric acid secretion and its regulation in health and disease. We review the physiology and pathophysiology of acid secretion as well as evidence regarding its inhibition in the management of acid-related clinical conditions.

Review: Surfactant protein D: A lung specific biomarker in COPD?

A major impediment in the development of novel drugs for chronic obstructive pulmonary disease (COPD) has been the scarcity of a well-validated, robust, and easily obtainable intermediate end point such as serum biomarkers. To date the best serum biomarkers in COPD have been non-speci“c pro-in”ammatory molecules synthesized largely by extra-pulmonary organs. In COPD, an ideal biomarker would be one that (1) was produced mostly in the lungs (and was reliably measurable in the peripheral circulation using commercially available kits), (2) changed with the clinical status of patients or with relevant exposures; and (3) had inherent functional attributes that suggested a possible causal role in the pathogenesis of the disease. In this paper, we review one promising systemic biomarker that ful“lls some of these criteria, surfactant protein D (SPD).

Acidosis-sensing glutamine pump SNAT2 determines amino acid levels and mammalian target of rapamycin signalling to protein synthesis in L6 muscle cells

Wasting of lean tissue as a consequence of metabolic acidosis is a serious problem in patients with chronic renal failure. A possible contributor is inhibition by low pH of the System A (SNAT2) transporter, which carries the amino acid L-glutamine (L-Gln) into muscle cells. The aim of this study was to determine the effect of selective SNAT2 inhibition on intracellular amino acid profiles and amino acid-dependent signaling through mammalian target of rapamycin in L6 skeletal muscle cells. Inhibition of SNAT2 with the selective competitive substrate methylaminoisobutyrate, metabolic acidosis (pH 7.1), or silencing SNAT2 expression with small interfering RNA all depleted intracellular L-Gln. SNAT2 inhibition also indirectly depleted other amino acids whose intracellular concentrations are maintained by the L-Gln gradient across the plasma membrane, notably the anabolic amino acid L-leucine. Consequently, SNAT2 inhibition strongly impaired signaling through mammalian target of rapamycin to ribosomal protein S6 kinase, ribosomal protein S6, and 4E-BP1, leading to impairment of protein synthesis comparable with that induced by rapamycin. It is concluded that even though SNAT2 is only one of several L-Gln transporters in muscle, it may determine intracellular anabolic amino acid levels, regulating the amino acid signaling that affects protein mass, nucleotide/nucleic acid metabolism, and cell growth.

Increased surfactant protein-D and foamy macrophages in smoking-induced mouse emphysema

BACKGROUND AND OBJECTIVE

The molecular mechanisms underlying COPD remain undetermined. The lungs of surfactant protein-D (SP-D) deficient mice show emphysema and an excessive number of foamy macrophages. This study aims to elucidate roles of SP-D and foamy macrophages in smoking-induced mouse emphysema.

METHODS

Twenty B6C3F1 mice were exposed to cigarette smoke (2 cigarettes/day/mouse for 6 months). The mice were killed, and formalin-fixed, paraffin-embedded lung sections were carried out on seven mice, BAL was carried out on six mice, and seven mice were used to make lung homogenates. In in vitro studies, A549 cells were transduced with the SP-D expression plasmid and treated with cigarette smoke extract to evaluate cell viability.

RESULTS

Emphysema was induced in the mice by chronic cigarette smoke exposure. Increased expression of matrix metalloproteinase-9 and -12 was observed, and foamy alveolar macrophages accumulated in the smoke-exposed lungs. Immunostaining of BAL cells revealed the major source of matrix metalloproteinase-12 to be foamy alveolar macrophages. Furthermore, SP-D was elevated in emphysema lungs. Expression of transcription factors, Fra-1, junB and C/EBPbeta (which induce SP-D) were significantly elevated in emphysema lungs. The in vitro expression of SP-D gene in A549 cells prolonged cell survival following exposure to cigarette smoke condensate.

CONCLUSIONS

The accumulation of foamy alveolar macrophages may play a key role in the development of smoking-induced emphysema. Increased SP-D may play a protective role in the development of smoking-induced emphysema, in part by preventing alveolar cell death.

Understanding ERM proteins--the awesome power of genetics finally brought to bear

In epithelial cells, the Ezrin, Radixin and Moesin (ERM) proteins are involved in many cellular functions, including regulation of actin cytoskeleton, control of cell shape, adhesion and motility, and modulation of signaling pathways. However, discerning the specific cellular roles of ERMs has been complicated by redundancy between these proteins. Recent genetic studies in model organisms have identified unique roles for ERM proteins. These include the regulation of morphogenesis and maintenance of integrity of epithelial cells, stabilization of intercellular junctions, and regulation of the Rho small GTPase. These studies also suggest that ERMs have roles in actomyosin contractility and vesicular trafficking in the apical domain of epithelial cells. Thus, genetic analysis has enhanced our understanding of these widely expressed membrane-associated proteins.

CFTR surface expression and chloride currents are decreased by inhibitors of N-WASP and actin polymerization

The cystic fibrosis transmembrane conductance regulator (CFTR) undergoes rapid turnover at the plasma membrane in various cell types. The ubiquitously expressed N-WASP promotes actin polymerization and regulates endocytic trafficking of other proteins in response to signaling molecules such as Rho-GTPases. In the present study we investigated the effects of wiskostatin, an N-WASP inhibitor, on the surface expression and activity of CFTR. We demonstrate, using surface biotinylation methods, that the steady-state surface CFTR pool in stably transfected BHK cells was dramatically decreased following wiskostatin treatment with a corresponding increase in the amount of intracellular CFTR. Similar effects were observed for latrunculin B, a specific actin-disrupting reagent. Both reagents strongly inhibited macroscopic CFTR-mediated Cl(-) currents in two cell types including HT29-Cl19A colonic epithelial cells. As previously reported, CFTR internalization from the cell surface was strongly inhibited by a cyclic-AMP cocktail. This effect of cyclic-AMP was only partially blunted in the presence of wiskostatin, which raises the possibility that these two factors modulate different steps in CFTR traffic. In kinetic studies wiskostatin appeared to accelerate the initial rate of CFTR endocytosis as well as inhibit its recycling back to the cell surface over longer time periods. Our studies implicate a role for N-WASP-mediated actin polymerization in regulating CFTR surface expression and channel activity.

Cyclic stretch-induced reorganization of the cytoskeleton and its role in enhanced gene transfer

Cyclic stretch is known to alter a number of cellular and subcellular processes, including those involved in nonviral gene delivery. We have previously shown that moderate equibiaxial cyclic stretch (10% change in basement membrane area, 0.5 Hz, 50% duty cycle) of human pulmonary A549 cells enhances gene transfer and expression of reporter plasmid DNA in vitro, and that this phenomena may be due to alterations in cytoplasmic trafficking. Although the path by which plasmid DNA travels through the cytoplasm toward the nucleus is not well understood, the cytoskeleton and the constituents of the cytoplasm are known to significantly hinder macromolecular diffusion. Using biochemical techniques and immunofluorescence microscopy, we show that both the microfilament and microtubule networks are significantly reorganized by equibiaxial cyclic stretch. Prevention of this reorganization through the use of cytoskeletal stabilizing compounds mitigates the stretch-induced increase in gene expression, however, depolymerization in the absence of stretch is not sufficient to increase gene expression. These results suggest that cytoskeletal reorganization plays an important role in stretch-induced gene transfer and expression.

Surfactant protein D augments bacterial association but attenuates major histocompatibility complex class II presentation of bacterial antigens

Surfactant protein D (SP-D) is a secreted pattern recognition molecule associated with lung surfactant and mediates the clearance of pathogens in multiple ways. SP-D is an established part of the innate immune system, but it also modulates the adaptive immune response by interacting with both antigen-presenting cells and T cells. In a previous study, antigen presentation by bone marrow-derived dendritic cells was enhanced by SP-D. As dendritic cell function varies depending on the tissue of origin, we extended these studies to antigen-presenting cells isolated from mouse lung. Flow cytometric studies showed that SP-D binds calcium dependently and specifically to lung CD11c-positive cells. Opsonization of fluorescently labeled Escherichia coli by SP-D enhanced uptake by lung dendritic cells. SP-D facilitated the association of E. coli and antigen-presenting cells by increasing the frequency of CD11+ cells associated with E. coli by up to 10-fold. In contrast to the effect on bone marrow-derived dendritic cells, SP-D decreased the antigen presentation of ovalbumin, expressed in E. coli, to ovalbumin-specific major histocompatibility complex class II-specific T-cell hybridomas by 30-50%. The reduction of antigen presentation did not depend on whether the dendritic cells were isolated from the lungs of nonstimulated mice or mice that had been exposed to LPS aerosols. Our results show that SP-D increases the opsonization of pathogens, but decreases the antigen presentation by lung dendritic cells, and thereby, potentially dampens the activation of T cells and an adaptive immune response against bacterial antigens--during both steady-state conditions and inflammation.

Immunohistochemical study about the Flt-1/VEGFR1 expression in the gastrointestinal tract of mouse, rat, dog, swine and monkey

Fms-like tyrosine kinase 1 (Flt-1) performs a subordinate effector role in mesenchymal angiogenesis and potentially serves an equally important functional role as a self-contained receptor in epithelial cells. In both endothelial cells and epithelial cells, Flt-1/vascular endothelial growth factor receptor 1 (VEGFR1) downstream signalling is involved in regulating cellular processes such as cytoskeletal changes and cellular survival protection. Cellular renewal of the gastrointestinal mucosa is based on these processes and might involve Flt-1/VEGFR1 pathway activities; the molecular mechanisms regulating these cellular dynamics remain unclear. This study was performed to investigate the presence and distribution of Flt-1/VEGFR1 in epithelial cells of the gastrointestinal tract by immunohistochemistry (IHC). Gastrointestinal tissues were taken from eight anatomical sites from mouse, rat, dog, swine and monkey. Present results revealed a cytosolic Flt-1/VEGFR1 staining pattern in mucosal epithelial cells for all investigated species. Non-epithelial structures also displayed a distinct Flt-1/VEGFR1 positivity and included vascular smooth muscle walls, enteric smooth muscle layers, the enteric nervous system and capillary endothelial cells. Diverse intensities of the Flt-1/VEGFR1 binding reaction within each species were observed in the intestinal mucosa with a strong immunoreaction in enterocytes and with a low protein expression in the ileum in most species. Crypt cells in the large intestine were mostly negative for Flt-1/VEGFR1. A peculiar and mainly intranuclear antibody binding reaction was found in Brunner's gland epithelial cells of mouse and rat whereas Brunner's glands of dog, swine and monkey remained completely negative. These results indicate a potential involvement of Flt-1/VEGFR1 in normal restitution of gastrointestinal structures in the species studied. Additionally, intranuclear Flt-1/VEGFR1 antibody binding in Brunner's glands of rodents may suggest a nuclear translocation of the transmembrane VEGFR1 which has not previously been described.

Helicobacter felis-induced gastritis was suppressed in mice overexpressing thioredoxin-1

Thioredoxin-1 (TRX-1) is a redox-active protein involved in scavenging reactive oxygen species and regulating redox-sensitive transcription factors. TRX-1 is induced in various inflammatory conditions and shows cytoprotective action. We investigated the roles of TRX-1 in the host defense mechanism against Helicobacter felis (H. felis) infection. Transgenic (TG) mice overexpressing human TRX-1 and wild-type (WT) mice were orally inoculated with H. felis. After 2 months, histology, oxidative damage, and gene expression of several cytokines, including macrophage inflammatory protein-2 (MIP-2), a murine equivalent to interleukin (IL)-8, in the gastric mucosa were investigated. Furthermore, the effects of TRX-1 on oxidative stress and neutrophil migration were studied both in vivo and in vitro. The gastric mucosa was thickened in H. felis-infected WT mice, but not in infected TRX-1-TG mice. Histologically, all H. felis-infected WT mice developed moderate-to-severe gastritis, whereas the development of gastritis was significantly suppressed in infected TRX-1-TG mice. Oxidative damage markers, 8-hydroxy-2'-deoxyguanosine and malondialdehyde, increased in the stomach of infected WT mice, but not TRX-1-TG mice. Upregulation of IL-1beta and tumor necrosis factor-alpha gene expression in H. felis-infected TRX-1-TG mice was significantly lower than in WT mice. However, upregulation of MIP-2 and IL-7 was not different between the two groups. TRX-1 suppressed oxidative cytotoxicity and DNA damage, and inhibited neutrophil migration both in vivo and in vitro. The present study suggests that overexpression of TRX-1 suppresses H. felis-induced gastritis by inhibiting chemotaxis of neutrophils and reducing oxidative stress.

Histone deacetylase HDAC8 associates with smooth muscle alpha-actin and is essential for smooth muscle cell contractility

Although originally characterized as nuclear enzymes controlling the stability of nucleosomes, histone deacetylases (HDACs) may also exert their activity within the cytosol. Recently, we have demonstrated that HDAC8, a class I HDAC, is a novel, prominently cytosolic marker of smooth muscle differentiation. As HDAC8 displays a striking stress fiber-like pattern of distribution and is coexpressed in vivo with smooth muscle alpha-actin (alpha-SMA) and smooth muscle myosin heavy chain, we have explored the possible participation of this HDAC in smooth muscle cytoskeleton regulation. Cell fractionation assays performed with primary human smooth muscle cells (HSMCs) showed that HDAC8, in contrast to HDAC1 and HDAC3, was enriched in cytoskeleton-bound protein fractions and insoluble cell pellets, suggesting an association of HDAC8 with the cystoskeleton. Coimmunoprecipitation experiments using HSMCs, NIH-3T3 cells, and human prostate tissue lysates further demonstrated that HDAC8 associates with alpha-SMA but not with beta-actin. HDAC8 silencing through RNA interference strongly reduced the capacity of HSMCs to contract collagen lattices. Mock transfections had no effect on HSMC contractily, and transfections with small interfering RNAs (siRNAs) specific for HDAC6, a cytosolic HDAC that functions as an alpha-tubulin deacetylase, resulted in a weak contraction inhibition. Although mock- and HDAC6 siRNA-transfected HSMCs showed no noticeable morphological changes, HDAC8 siRNA-transfected HSMCs displayed a size reduction with diminished cell spreading after replating. Altogether, our findings indicate that HDAC8 associates with the smooth muscle actin cytoskeleton and may regulate the contractile capacity of smooth muscle cells.

Neutrophil Serine Proteinases Inactivate Surfactant Protein D by Cleaving within a Conserved Subregion of the Carbohydrate Recognition Domain

Surfactant protein D (SP-D) plays important roles in innate immunity including the defense against bacteria, fungi, and respiratory viruses. Because SP-D specifically interacts with neutrophils that infiltrate the lung in response to acute inflammation and infection, we examined the hypothesis that the neutrophil-derived serine proteinases (NSPs): neutrophil elastase, proteinase-3, and cathepsin G degrade SP-D. All three human NSPs specifically cleaved recombinant rat and natural human SP-D dodecamers in a time- and dose-dependent manner, which was reciprocally dependent on calcium concentration. The NSPs generated similar, relatively stable, disulfide cross-linked immunoreactive fragments of approximately 35 kDa (reduced), and sequencing of a major catheptic fragment definitively localized the major sites of cleavage to a highly conserved subregion of the carbohydrate recognition domain. Cleavage markedly reduced the ability of SP-D to promote bacterial aggregation and to bind to yeast mannan in vitro. Incubation of SP-D with isolated murine neutrophils led to the generation of similar fragments, and cleavage was inhibited with synthetic and natural serine proteinase inhibitors. In addition, neutrophils genetically deficient in neutrophil elastase and/or cathepsin G were impaired in their ability to degrade SP-D. Using a mouse model of acute bacterial pneumonia, we observed the accumulation of SP-D at sites of neutrophil infiltration coinciding with the appearance of approximately 35-kDa SP-D fragments in bronchoalveolar lavage fluids. Together, our data suggest that neutrophil-derived serine proteinases cleave SP-D at sites of inflammation with potential deleterious effects on its biological functions.

Small molecule mitochondrial F1F0 ATPase hydrolase inhibitors as cardioprotective agents. Identification of 4-(N-arylimidazole)-substituted benzopyran derivatives as selective hydrolase inhibitors

In this paper we show that 4-aryl-CH2-imidazole-substituted benzopyran compounds with 3S,4R-stereochemistry are cardioprotective by inhibiting the F1F0 mitochondrial ATP hydrolase. Compounds (e.g., 13) with 3R,4S-stereochemistry act as mitochondrial KATP openers. This resulted from an inversion of stereochemistry for the F1F0 mitochondrial ATP hydrolase vs mitochondrial KATP. Structure-activity relationships for the inhibition of mitochondrial ATP hydrolase are also delineated. It is not clear how 13 (3R,4S) can selectively inhibit the hydrolytic activity of the F1F0 mitochondrial enzyme without interfering with the synthase activity.

Rab11b resides in a vesicular compartment distinct from Rab11a in parietal cells and other epithelial cells

The Rab11 family of small GTPases is composed of three members, Rab11a, Rab11b, and Rab25. While recent work on Rab11a and Rab25 has yielded some insights into their function, Rab11b has received little attention. Therefore, we sought to examine the distribution of endogenous Rab11b in epithelial cells. In rabbit gastric parietal cells, unlike Rab11a, Rab11b did not colocalize or coisolate with H(+)/K(+)-ATPase. In MDCK cells, endogenous Rab11b localized to an apical pericentrisomal region distinct from Rab11a. The microtubule agents nocodazole and taxol dramatically alter Rab11a's localization in the cell, while effects on Rab11b's distribution were less apparent. These results indicate that in contrast to Rab11a, the Rab11b compartment in the apical region is not as dependent upon microtubules. While Rab11a is known to regulate transferrin trafficking in nonpolarized cells and IgA trafficking in polarized cells, Rab11b exhibited little colocalization with either of these cargoes. Thus, while Rab11a and Rab11b share high sequence homology, they appear to reside within distinct vesicle compartments.

Cell biology of acid secretion by the parietal cell

Acid secretion by the gastric parietal cell is regulated by paracrine, endocrine, and neural pathways. The physiological stimuli include histamine, acetylcholine, and gastrin via their receptors located on the basolateral plasma membranes. Stimulation of acid secretion typically involves an initial elevation of intracellular calcium and/or cAMP followed by activation of a cAMP-dependent protein kinase cascade that triggers the translocation and insertion of the proton pump enzyme, H,K-ATPase, into the apical plasma membrane of parietal cells. Whereas the H,K-ATPase contains a plasma membrane targeting motif, the stimulation-mediated relocation of the H,K-ATPase from the cytoplasmic membrane compartment to the apical plasma membrane is mediated by a SNARE protein complex and its regulatory proteins. This review summarizes the progress made toward an understanding of the cell biology of gastric acid secretion. In particular we have reviewed the early signaling events following histaminergic and cholinergic activation, the identification of multiple factors participating in the trafficking and recycling of the proton pump, and the role of the cytoskeleton in supporting the apical pole remodeling, which appears to be necessary for active acid secretion by the parietal cell. Emphasis is placed on identifying protein factors that serve as effectors for the mechanistic changes associated with cellular activation and the secretory response.

Different actions of protein kinase C isoforms alpha and epsilon on gastric acid secretion

1. The phorbol ester TPA, an activator of protein kinase C (PKC), inhibits cholinergic stimulation of gastric acid secretion but increases basal H(+) secretion. 2. Since these contradictory findings suggest the action of different PKC isozymes we analysed the role of calcium-dependent PKC-alpha, and calcium-independent PKC-epsilon in gastric acid secretion. 3. Inhibition of PKC-alpha by the indolocarbazole Gö 6976 revealed that about 28% of carbachol-induced acid secretion was inhibited by PKC-alpha. In the presence of Gö 6976 approximately 64% of the carbachol-induced signal transduction is mediated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), and 14% is conveyed by PKC-epsilon as deduced from the inhibition with the bisindolylmaleimide Ro 31-8220. 4. Inhibition of carbachol-induced acid secretion by TPA was accompanied by a decrease in CaMKII activity. 5. The stimulation of basal acid secretion by TPA was biphasic with a peak at a very low concentration (10 pM), resulting in an activation of the calcium-sensor CaMKII. The activation was determined with a phosphospecific polyclonal antibody against active CaMKII. The TPA-induced increase of H(+) secretion was sensitive to the cell-permeable Ca(2+)-chelator BAPTA/AM, Ro 31-8220, and the CaMKII-inhibitor KN-62, but not to Gö 6976. 6. Since TPA induced the translocation of PKC-epsilon but not of PKC-alpha in resting parietal cells, PKC-epsilon seems to be at least responsible for an initial elevation of free intracellular calcium to initiate TPA-induced acid secretion. 7. Our data indicate the different roles of two PKC isoforms: PKC-epsilon activation appears to facilitate cholinergic stimulation of H(+)-secretion likely by increasing intracellular calcium. In contrast, PKC-alpha activation attenuates acid secretion accompanied by a down-regulation of CaMKII activity.

Perturbation of gastric mucosa in mice expressing the temperature-sensitive mutant of SV40 large T antigen. Potential for establishment of an immortalised parietal cell line

Gastric parietal cells have a unique secretory membrane system that undergoes a profound transformation when the parietal cell is stimulated to secrete acid. Understanding this process has been hindered by the lack of an immortalised parietal cell line. Here we have explored a strategy for the development of a parietal cell line by the generation of transgenic mice bearing the temperature-sensitive mutant of the SV40 large T antigen (SV40 tsA58) under the control of the regulatory sequences of the gastric H+/K+ ATPase beta-subunit (H/Kbeta-tsA58). Three H/ Kbeta-tsA58 transgenic mouse lines were established, namely 218, 224 and 228, all of which expressed the tsA58 T antigen in the gastric mucosa. Unexpectedly, the gastric mucosae of all lines were hypertrophic indicating that the temperature-sensitive large T antigen was partially active at 37 degrees C. Immunofluorescence together with light and electron microscopic studies revealed that mature parietal and zymogenic cells were absent in H/Kbeta-tsA58 transgenic lines 218 and 224, and small undifferentiated cells were the dominant cell type in the gastric units. On the other hand, a few mature parietal cells were detected in line 228 together with an increased proportion of undifferentiated cells and, normally rare, pre-parietal cells. As line 228 represented a rich source of pre-parietal cells, gastric cells from line 228 were isolated and cultured at 33 degrees C, the permissive temperature for tsA58. Gastric epithelial cells, expressing the T antigen, were maintained in culture for over 6 weeks. Upon a temperature shift to 39 C the cultured gastric cells developed characteristics of differentiated parietal cells, including the presence of a nascent canaliculus and dramatically increased production of the gastric H+/K+ ATPase beta-subunit. Therefore, this system shows the potential to generate an immature parietal cell line that can be induced to differentiate in vitro.

Regulation of acid secretion and paracellular permeability by F-actin in the bullfrog, Rana catesbeiana

Many studies have implicated F-actin in the regulation of gastric acid secretion using cytochalasin D (CD) to disrupt apical actin filaments in oxyntic cells. However, it is known that CD also affects mucosal permeability by disrupting tight junction structure. Here we investigated the contribution of F-actin to mucosal permeability and acid secretion in the stomach using CD. Stomachs were mounted in Ussing chambers and acid secretion (stimulated or inhibited), transepithelial resistance (TER), mannitol flux, bicarbonate transport, and dual mannitol/sodium fluxes were determined with or without CD. H(+) back diffusion was predicted from its diffusion coefficient. Incubation with CD resulted in a significant reduction in stimulated acid secretion. TER was unchanged in stimulated tissues but significantly reduced in inhibited tissues. Mannitol flux, bicarbonate transport, and H(+)-back diffusion increased significantly with CD. However, the rates of bicarbonate and H(+) flux were not large enough to account for the inhibition of acid secretion. These findings demonstrate that actin filaments regulate paracellular permeability and play an essential role in the regulation of acid secretion in the stomach.

Regulation of gastric epithelial cell development revealed in H(+)/K(+)-ATPase beta-subunit- and gastrin-deficient mice

The gastric H(+)/K(+)-ATPase is essential for normal development of parietal cells. Here we have directly assessed the role of the H(+)/K(+)-ATPase beta-subunit (H/K-beta) on epithelial cell development by detailed quantitation of the epithelial cell types of the gastric mucosa of H/K-beta-deficient mice. H/K-beta-deficient mice had a 3.1-fold increase in the number of immature cells per gastric unit; however, the numbers of surface mucous and parietal cells were similar to those in the gastric units of wild-type mice. The effect of elevated gastrin levels in the H/K-beta-deficient mice was determined by producing mice that are also deficient in gastrin. We demonstrated that the increased production of immature cells and resulting hypertrophy is caused by the overproduction of gastrin. However, the depletion of zymogenic cells, which is another feature of H/K-beta-deficient mice, is independent of hypergastrinemia. Significantly, parietal cells of H/K-beta- and gastrin-deficient mice had abnormal secretory membranes and were devoid of resting tubulovesicular membranes. Together these data suggest a homeostatic mechanism limiting the number of immature cells that can develop into end-stage epithelial cells and indicate a direct role for H/K-beta in the development of mature parietal cells.

Induction of macrophage matrix metalloproteinase biosynthesis by surfactant protein D

Recent studies strongly suggest that surfactant protein D (SP-D) plays important roles in pulmonary host defense and the regulation of immune and inflammatory reactions in the lung. Although SP-D can bind to alveolar macrophages and can elicit their chemotaxis, relatively little is known about the direct cellular consequences of SP-D on the function of these cells. Because matrix metalloproteinases (MMPs) are synthesized in increased amounts in response to various proinflammatory stimuli, we investigated the capacity of SP-D to modulate the production of MMPs by freshly isolated human alveolar macrophages. Unexpectedly we found that recombinant rat SP-D dodecamers selectively induce the biosynthesis of collagenase-1 (MMP-1), stromelysin (MMP-3), and macrophage elastase (MMP-12) without significantly increasing the production of tumor necrosis factor alpha and interleukin-1beta. SP-D did not alter the production of these MMPs by fibroblasts. Phosphatidylinositol, a surfactant-associated ligand that interacts with the carboxyl-terminal neck and carbohydrate recognition domains of SP-D, inhibited the SP-D-dependent increase in MMP biosynthesis. A trimeric, recombinant protein consisting of only the neck and carbohydrate recognition domain did not augment metalloproteinase production, suggesting that the stimulatory effect on MMP production depends on an appropriate spatial presentation of trimeric lectin domains. Although SP-D dodecamers can selectively augment metalloproteinase activity in vitro, this effect may be competitively inhibited by tissue inhibitors of metalloproteinases or surfactant-associated ligands in vivo.

Functionally distinct pools of actin in secretory cells

Acid secretion by the gastric parietal cell is controlled through movement of vesicles containing the proton pump, the H(+)-K(+)-ATPase (HK). We have used latrunculin B (Lat B), which binds to monomeric actin, to investigate actin turnover in the stimulated parietal cell. In isolated gastric glands, relatively high concentrations of Lat B were required to inhibit acid accumulation (ED(50) approximately 70 microM). Cultured parietal cells stimulated in the presence of low Lat B (0.1--1 microM) have reduced lamellipodia formation and some aberrant punctate phalloidin-stained structures, but translocation of HK and vacuolar swelling appeared unaffected. High Lat B (10--50 microM) resulted in gross changes in actin organization (punctate phalloidin-stained structures throughout the cell and nucleus) and reduced translocation of HK and vacuolar swelling. Resting parietal cells treated with high Lat B showed minor effects on morphology and F-actin staining. If resting cells treated with high Lat B were washed immediately before stimulation, they exhibited a normal stimulated morphology. These data suggest distinct pools of parietal cell actin: a pool highly susceptible to Lat B primarily involved in motile function of cultured cells; and a Lat B-resistant pool, most likely microvillar filaments, that is essential for secretion. Furthermore, the stimulation process appears to accentuate the effects of Lat B, most likely through Lat B binding to monomer actin liberated by the turnover of the motile actin filament pool.

A model of the gastric gland ejection cycle: low ejection fractions require reduction of the glandular dead space

This paper was inspired by the reported results of authors from Uppsala and Lund that gastric glands in rats rhythmically contract 3-7 cycles per minute and develop luminal pressures more than 10 mmHg. To ensure that pepsinogen is not retained in the acid-rich section of the gland, ejection fractions would need to be more than 50% of the gland volume. We have tried to calculate the ejection fraction of such contractions. Dimensions of human gastric glands were measured on the fresh frozen samples of macroscopically and histologically normal gastric mucosa. In total, 18 specimens (from nine persons) were measured under the microscope. The density of glands was 135 +/- 11 (mean +/- S.D.) glands per mm( 2) of gastric mucosa. A typical gastric gland is a tubular structure 1.2 +/- 0.22 mm long and 0.03-0.05 mm wide. We have used 1 mm for length and 0.03 mm for the gland diameter to calculate that each gland approximates a volume of 707 pl, suggesting that the total glandular volume for 15 million glands reaches 10.6 ml. Further calculations based on one to five contractions per minute on an average and on the total volume of gastric glands of 10 ml showed that only ejection fractions less than 10% deliver daily volumes less than 3 l. The presented model of the gastric gland activity is based on the idea that the low ejection fractions require a reduction of the glandular dead space. The reduced luminal pressure during the gland relaxation might cause backflux of hydrophobic viscoelastic mucus through the gland aperture. Repeated glandular contractions and relaxations would move the mucus all the way to the gland bottom, filling the gland cavity below the neck with an axial semisolid mucous cylinder. This filling would reduce the gland dead space. During contractions, the gland would eject mainly the peripheral, the more liquid part of its content. The decreasing luminal pressure in the relaxing gland would pull the outlet mucus inside, protecting gland apertures from the gastric juice.

Vesicular trafficking machinery, the actin cytoskeleton, and H+-K+-ATPase recycling in the gastric parietal cell

Gastric HCl secretion by the parietal cell involves the secretagogue-regulated re-cycling of the H+-K+-ATPase at the apical membrane. The trafficking of the H+-K+-ATPase and the remodelling of the apical membrane during this process are likely to involve the co-ordination of the function of vesicular trafficking machinery and the cytoskeleton. This review summarizes the progress made in the identification and characterization of components of the vesicular trafficking machinery that are associated with the H+-K+-ATPase and of components of the actin-based cytoskeleton that are associated with the apical membrane of the parietal cell. Since many of these proteins are also expressed at the apical pole of other epithelial cells, the parietal cell may represent a model system to characterize the protein- protein interactions that regulate apical membrane trafficking in many other epithelial cells.

Neuronal nitric oxide strongly suppresses sympathetic outflow in high-salt Dahl rats

OBJECTIVE

To investigate the effects of a selective inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitroindazole, on peripheral sympathetic outflow in Dahl rats.

DESIGN AND METHODS

Dahl salt-sensitive and salt-resistant rats were fed either a regular-salt (0.4% NaCl) or a high-salt (8% NaCl) diet for 4 weeks. In chronically instrumented conscious rats, renal sympathetic nerve activity (RSNA) was measured in both baroreceptor-loaded and baroreceptor-unloaded states. The baroreceptor unload was performed by decreasing arterial pressure with occlusion of the inferior vena cava.

RESULTS

7-Nitroindazole (307 micromol/kg intraperitoneally) increased resting RSNA from 24 +/- 3% to 38 +/- 6% with an increase in mean arterial pressure of 15 +/- 3 mmHg, and increased baroreceptor-unloaded RSNA from 100% to 278 +/- 16% in salt-sensitive Dahl rats receiving a high-salt diet However, 7-nitroindazole did not increase resting RSNA, but did increase baroreceptor-unloaded RSNA from 100% to 179 +/- 15%, 177 +/- 15%, and 133 +/- 4% in salt-sensitive Dahl rats receiving a regular-salt diet, salt-resistant Dahl rats receiving a high-salt diet, and salt-resistant Dahl rats receiving a regular-salt diet, respectively. The high-salt diet significantly increased the baroreceptor-unloaded RSNA more than the regular-salt diet did, in both salt-sensitive and salt-resistant rats. After administration of the vehicle for 7-nitroindazole (peanut oil), L-arginine (100 micromol/kg per min for 10 min) decreased both resting and baroreceptor-unloaded RSNA, whereas after pretreatment with 7-nitroindazole, the L-arginine-induced suppression was reversed, in Dahl salt-sensitive rats receiving a high-salt diet.

CONCLUSIONS

Neuronal nitric oxide may suppress the sympathetic discharge generated before baroreflex-mediated inhibition in all rats. This neuronal nitric oxide-mediated suppression was enhanced by the salt load in both salt-resistant and salt-sensitive Dahl rats. Finally, the neuronal nitric oxide-mediated suppression in tonic peripheral sympathetic outflow may be greatly enhanced in salt-sensitive hypertension.

Diverse regulation of microfilament assembly, production of TNF-alpha, and reactive oxygen intermediates by actin modulating substances and inhibitors of ADP-ribosylation in human monocytes stimulated with LPS

Lipopolysaccharide (LPS), a potent activator of human monocytes, induced F-actin polymerization in a concentration- and time-dependent manner. To test whether cytoskeletal events participate in the control of the LPS-induced ROI and TNF-alpha production, three natural occurring actin-modulating substances, cytochalasin D (Cyt D), latrunculin B (Lat B), and jasplakinolide (JK), were used. Here we show that treatment of monocytes with Cyt D, Lat B, or JK led to a rearrangement of the actin cytoskeleton, which upon addition of LPS was further modified. Cyt D and Lat B induced generation of ROI in the absence of LPS and enhanced the LPS-triggered respiratory burst. JK also proved to be a potent activator of ROI-production but only in the presence of LPS. TNF-alpha production was hardly affected by the three substances. There was no correlation between a specific state of Cyt D-, Lat B-, or JK-modified actin polymerization and ROI-production. Inhibitors of ADP-ribosylation proved to be activators of F-actin polymerization. They were shown to prevent ROI- and TNF-alpha production and to reduce the capability of LPS to mediate maximal F-actin assembly. At concentrations at which inhibition was greatest, maximal blockage of ROI and TNF-alpha production was observed. These findings may argue for a role of ADP-ribosylation in the transduction pathways mediating the biological responses, with involvement in the assembly of actin-containing cytoskeletal microfilaments.

A proposed mechanism for the potentiation of cAMP-mediated acid secretion by carbachol

Acid secretion in isolated rabbit gastric glands was monitored by the accumulation of [(14)C]aminopyrine. Stimulation of the glands with carbachol synergistically augmented the response to dibutyryl cAMP. The augmentation persisted even after carbachol was washed out and was resistant to chelated extracellular Ca(2+) and to inhibitors of either protein kinase C or calmodulin kinase II. Cytochalasin D at 10 microM preferentially blocked the secretory effect of carbachol and its synergism with cAMP, whereas it had no effect on histamine- or cAMP-stimulated acid secretion within 15 min. Cytochalasin D inhibited the carbachol-stimulated intracellular Ca(2+) concentration ([Ca(2+)](i)) increase due to release from the Ca(2+) store. Treatment of the glands with cytochalasin D redistributed type 3 inositol 1,4,5-trisphosphate receptor (the major subtype in the parietal cell) from the fraction containing membranes of large size to the microsomal fraction, suggesting a dissociation of the store from the plasma membrane. These findings suggest that intracellular Ca(2+) release by cholinergic stimulation is critical for determining synergism with cAMP in parietal cell activation and that functional coupling between the Ca(2+) store and the receptor is maintained by actin microfilaments.

Serological diagnosis of idiopathic pulmonary alveolar proteinosis

Previously, we reported the specific occurrence of neutralizing autoantibodies against granulocyte-macrophage colony-stimulating factor (GM-CSF) in the bronchoalveolar lavage fluid from 11 Japanese patients with idiopathic pulmonary alveolar proteinosis (I-PAP). The autoantibody was also detected in sera from all 5 I-PAP patients examined. To determine that the existence of the autoantibody is not limited to the Japanese patients, we examined sera from 24 I-PAP patients in five countries and showed that the autoantibody was consistently and specifically present in such patients. Thus, detection of the autoantibody in sera can be used for diagnosis of I-PAP. To establish a simple and convenient method for diagnosis of I-PAP, we developed a novel latex agglutination test using latex beads coupled with recombinant human GM-CSF. GM-CSF binding proteins isolated from the sera using the latex beads were identified as the autoantibodies of IgG(1) and IgG(2). The titer of the autoantibody determined by this test correlated with that determined by ELISA. Agglutination was positive in 300-fold diluted sera from all 24 I-PAP patients, but negative in sera from four secondary PAP patients, two congenital PAP patients, 40 patients with other lung diseases, and 38 of 40 normal subjects. These results establish that the latex agglutination test is a reliable method for serological diagnosis of I-PAP with high sensitivity (100%) and specificity (98%).

Regulation and function of p38 protein kinase in isolated canine gastric parietal cells

We examined the regulation and functional role of p38 kinase in gastric acid secretion. p38 kinase was immunoprecipitated from cell lysates of highly purified gastric parietal cells in primary culture, and its activity was quantitated by in vitro kinase assay. Carbachol effects were dose- and time-dependent, with a maximal 10-fold stimulatory effect detected after 30 min of incubation. SB-203580, a highly selective inhibitor of p38 kinase, blocked carbachol induction of p38 kinase activity, with maximal inhibition at 10 microM. Stimulation by carbachol was unaffected by preincubation of parietal cells with the intracellular Ca(2+) chelator BAPTA-AM, but incubation of cells in Ca(2+)-free medium led to a 50% inhibition of carbachol induction of p38 kinase activity. Because some of the effects of carbachol are mediated by the small GTP-binding protein Rho, we examined the role of Rho in carbachol induction of p38 kinase activity. We tested the effect of exoenzyme C3 from Clostridium botulinum (C3), a toxin known to ADP-ribosylate and specifically inactivate Rho. C3 led to complete ADP-ribosylation of Rho, and it inhibited carbachol induction of p38 kinase by 50%. We then tested the effect of SB-203580 and C3 on carbachol-stimulated uptake of [(14)C]aminopyrine (AP). Inhibition of p38 kinase by SB-203580 led to a dose-dependent increase in AP uptake induced by carbachol, with maximal (threefold) effect at 10 microM SB-203580. Similarly, preincubation of parietal cells with C3 led to a twofold increase in AP uptake induced by carbachol. Thus carbachol induces a cascade of events in parietal cells that results in activation of p38 kinase through signaling pathways that are at least in part dependent on Rho activation and on the presence of extracellular Ca(2+). p38 kinase appears to inhibit gastric acid secretion.

The cytoskeleton of digestive epithelia in health and disease

The mammalian cell cytoskeleton consists of a diverse group of fibrillar elements that play a pivotal role in mediating a number of digestive and nondigestive cell functions, including secretion, absorption, motility, mechanical integrity, and mitosis. The cytoskeleton of higher-eukaryotic cells consists of three highly abundant major protein families: microfilaments (MF), microtubules (MT), and intermediate filaments (IF), as well as a growing number of associated proteins. Within digestive epithelia, the prototype members of these three protein families are actins, tubulins, and keratins, respectively. This review highlights the important structural, regulatory, functional, and unique features of the three major cytoskeletal protein groups in digestive epithelia. The emerging exciting biological aspects of these protein groups are their involvement in cell signaling via direct or indirect interaction with a growing list of associated proteins (MF, MT, IF), the identification of several disease-causing mutations (IF, MF), the functional role that they play in protection from environmental stresses (IF), and their functional integration via several linker proteins that bridge two or potentially all three of these groups together. The use of agents that target specific cytoskeletal elements as therapeutic modalities for digestive diseases offers potential unique areas of intervention that remain to be fully explored.

Gastric H(+),K(+)-adenosine triphosphatase beta subunit is required for normal function, development, and membrane structure of mouse parietal cells

BACKGROUND & AIMS

Parietal cells of the gastric mucosa contain a complex and extensive secretory membrane system that harbors gastric H(+),K(+)-adenosine triphosphatase (ATPase), the enzyme primarily responsible for acidification of the gastric lumen. We have produced mice deficient in the H(+),K(+)-ATPase beta subunit to determine the role of the protein in the biosynthesis of this membrane system and the biology of gastric mucosa.

METHODS

Mice deficient in the H(+), K(+)-ATPase beta subunit were produced by gene targeting.

RESULTS

The stomachs of H(+),K(+)-ATPase beta subunit-deficient mice were achlorhydric. Histological and immunocytochemical analyses with antibodies to the H(+),K(+)-ATPase alpha subunit revealed that parietal cell development during ontogeny was retarded in H(+), K(+)-ATPase beta subunit-deficient mice. In 15-day-old mice, cells with secretory canaliculi were observed in wild-type but not in H(+), K(+)-ATPase beta subunit-deficient mice. Parietal cells of H(+), K(+)-ATPase beta subunit-deficient mice 17 days and older contained an abnormal canaliculus that was dilated and contained fewer and shorter microvilli than normal. In older parietal cells, the abnormal canaliculus was massive (25 micrometer in diameter) and contained few microvilli. We did not observe typical tubulovesicular membranes in any parietal cell from H(+),K(+)-ATPase beta subunit-deficient mice. Histopathologic alterations were only observed in the stomach.

CONCLUSIONS

The H(+),K(+)-ATPase beta subunit is required for acid-secretory activity of parietal cells in vivo, normal development and cellular homeostasis of the gastric mucosa, and attainment of the normal structure of the secretory membranes.

Development of the actin and the cytokeratin cytoskeletons of parietal cells during differentiation of the rat gastric mucosa

Available evidence strongly suggests that microfilaments and cytokeratin intermediate filaments (IF) play a role in the reorganization of the luminal pole required for the secretion of acid by parietal cells. To correlate the organization of both cytoskeletal systems with the differentiation of the secretory membranes of parietal cells, the distribution of F-actin and cytokeratin was studied during the ontogenic development of the rat. Primitive parietal cells were detected with parietal cells autoantibodies and ultrastructurally by transmission electron microscopy (TEM). The distribution of IF and of F-actin in differentiating parietal cells was determined using anticytokeratin antibodies and FITC-phalloidin, respectively. Development of both cytoskeletal systems was followed by TEM. Ultrastructurally, parietal cells are identified from day 19 on, by the presence of an incipient canaliculus, which later enlarges and fills with microvilli. No intracellular tubulovesicular system is observed. Using parietal cells autoantibodies these cells are detected from day 20 on. Immunocytochemistry and TEM demonstrate that parietal cells possess organized cytokeratin and actin cytoskeletons, which develop further as differentiation proceeds. At birth, parietal cells show an ultrastructure and a distribution of IF and microfilaments similar to that of differentiated cells. In newly born rats, the F-actin cytoskeleton redistributes after suckling. This reorganization results from an enlargement of the canalicular lumen, filled with microvilli rich in actin. Thus, functional maturation of parietal cells is paralleled by the development of organized IF and F-actin cytoskeletons associated to the secretory surface.

Glycoprotein-340 binds surfactant protein-A (SP-A) and stimulates alveolar macrophage migration in an SP-A-independent manner

Glycoprotein-340 (gp-340) was first identified as a surfactant protein (SP)-D-binding molecule purified from lung lavage of patients with alveolar proteinosis (Holmskov, et al., J. Biol. Chem. 1997;272:13743). In purifying SP-A from proteinosis lavage, we isolated a protein that copurifies with SP-A and SP-D and that was later found by protein sequencing to be gp-340. We have shown that soluble gp-340 binds SP-A in a calcium-dependent manner independent of the lectin activity of SP-A. To examine the functional significance of this interaction, we tested the ability of soluble gp-340 to block SP-A binding to and stimulation of the chemotaxis of alveolar macrophages. We found that gp-340 does not affect the binding of SP-A to alveolar macrophages over a wide range of SP-A concentrations, nor does it inhibit the ability of SP-A to stimulate macrophage chemotaxis. We also found that gp-340 alone stimulates the random migration (chemokinesis) of alveolar macrophages in a manner independent of SP-A-stimulated chemotaxis. These results suggest that gp-340 is not a cell-surface receptor necessary for SP-A stimulation of chemotaxis, and show that gp-340 can directly affect macrophage function.

Structure, biologic properties, and expression of surfactant protein D (SP-D)

Surfactant protein D (SP-D) is a member of the family of collagenous host defense lectins, designated collectins. There is increasing evidence that SP-D, like SP-A, is an important component of the innate immune response to microbial challenge, and that it may participate in other aspects of immune and inflammatory regulation within the lung. SP-D binds to glycoconjugates and/or lipid moieties expressed by a wide variety of microorganisms and certain other organic particles, in vitro. Although binding may facilitate microbial clearance through aggregation or other direct effects on the organism, SP-D also has the capacity to modulate leukocyte function, and in some circumstances, to enhance their killing of microorganisms.

Altered surfactant homeostasis and alveolar type II cell morphology in mice lacking surfactant protein D

Surfactant protein D (SP-D) is one of two collectins found in the pulmonary alveolus. On the basis of homology with other collectins, potential functions for SP-D include roles in innate immunity and surfactant metabolism. The SP-D gene was disrupted in embryonic stem cells by homologous recombination to generate mice deficient in SP-D. Mice heterozygous for the mutant SP-D allele had SP-D concentrations that were approximately 50% wild type but no other obvious phenotypic abnormality. Mice totally deficient in SP-D were healthy to 7 months but had a progressive accumulation of surfactant lipids, SP-A, and SP-B in the alveolar space. By 8 weeks the alveolar phospholipid pool was 8-fold higher than wild-type littermates. There was also a 10-fold accumulation of alveolar macrophages in the null mice, and many macrophages were both multinucleated and foamy in appearance. Type II cells in the null mice were hyperplastic and contained giant lamellar bodies. These alterations in surfactant homeostasis were not associated with detectable changes in surfactant surface activity, postnatal respiratory function, or survival. The findings in the SP-D-deficient mice suggest a role for SP-D in surfactant homeostasis.