Purinergic agonists, but not cAMP, stimulate coupled granule fusion and Cl- conductance in HT29-Cl.16E

Relevance of human fat distribution on lipid and lipoprotein metabolism and cardiovascular disease risk

PURPOSE OF REVIEW

Upper body abdominal and lower body gluteofemoral fat depot masses display opposing associations with plasma lipid and lipoprotein and cardiovascular disease (CVD) risk profiles. We review developments on adipose tissue fatty acid metabolism in the context of body fat distribution and how that might be related to adverse lipid and lipoprotein profiles and CVD risk.

RECENT FINDINGS

Recent data have confirmed the paradoxical relationship of upper abdominal and lower body gluteofemoral adiposity and CVD risk. Mechanistically, this is likely to reflect the different ways fat depots handle lipid storage and release, which impacts directly and indirectly on lipid and lipoprotein metabolism. The upper body enhances immediate fat storage pathway with rapid uptake of dietary-derived fatty acids, whereas the lower body fat depot has a reduced lipid turnover accommodating a slower fat redistribution. Body fat distribution and the fat depots' ability to undergo appropriate expansion when fat storage is required, rather than overall body fatness, appear as the important determinant of metabolic health.

SUMMARY

A focus on fat distribution in overweight people, preferably using precise imaging methods, rather than quantifying total body fatness, is likely to provide the medical community with better tools to stratify and treat patients with obesity-related complications.

Role of ion channels in the functional response of conjunctival goblet cells to dry eye

Optimal vision requires an ocular surface with a stable tear film whose many critical tasks include providing >70% of the eye's refractive power. However, for millions, tear film instability produces uncomfortable sight-impairing dry eye. Despite the multitude of etiologies for dry eye, a universal hallmark is hyperosmolarity of the tear film. Presently, knowledge of how the ocular surface responds to hyperosmolarity remains incomplete with little understood about the role of ion channels. This bioelectric analysis focused on conjunctival goblet cells whose release of tear-stabilizing mucin is a key adaptive response to dry eye. In freshly excised rat conjunctiva, perforated-patch recordings demonstrated that a ≥10% rise in osmolarity triggers goblet cells to rapidly generate a ~15-mV hyperpolarization due to the oxidant-dependent activation of ATP-sensitive K⁺ (K_ATP) channels. High-resolution membrane capacitance measurements used to monitor exocytosis revealed that this hyperpolarization results in an approximately fourfold boost in exocytotic activity evoked by cholinergic input, which in vivo occurs via a neural reflex and depends chiefly on calcium influxing down its electro-gradient. We discovered that this adaptive response is transient. During 30-80 min of hyperosmolarity, development of a depolarizing nonspecific cation conductance fully counterbalances the K_ATP-driven hyperpolarization and thereby eliminates the exocytotic boost. We conclude that hyperosmotic-induced hyperpolarization is a previously unappreciated mechanism by which goblet cells respond to transient ocular dryness. Loss of this voltage increase during long-term dryness/hyperosmolarity may account for the clinical conundrum that goblet cells in chronically dry eyes can remain filled with mucin even though the tear film is hyperosmotic and mucin-deficient.

Proteomics analysis of human tears from aqueous-deficient and evaporative dry eye patients

Despite the high global prevalence of dry eye syndrome (DES), the fundamental processes underlying this pathology remain largely unexplored. Therefore, this study endeavoured to investigate in-depth the tear proteome of DES patients employing the mass spectrometry (MS)-based proteomic strategies. Eighty patients were recruited and subdivided into three major DES subgroups, which are the aqueous-deficient (DRYaq), evaporative (DRYlip) and a combination of the two (DRYaqlip), as well as healthy subjects (CTRL). Discovery proteomics strategy was employed to identify large number of significantly differentially expressed tear proteins in DRYlip vs. CTRL, DRYaq vs. CTRL and DRYaqlip vs. CTRL with 22, 58 and 67 proteins, respectively. Biological functional analysis demonstrated for the first time that various metabolic processes were highly expressed in DRYaq and DRYaqlip, which might modulate various other known processes, especially the inflammatory and immune processes. Targeted proteomics strategy verified that 13 major proteins were differentially expressed in specific DES subgroups, comprising of PRR4, ZG16B, SCGB2A1, DMBT1, PROL1, LACRT, ALDH3A1, ENO1, TF, S100A8, S100A9, PEBP1 and ORM1. In conclusion, this study had explored in-depth the pathology of DES by unravelling various new fundamental processes and the major proteins responsible for the maintenance of tear film stability.

Novel insights into the function and dynamics of extracellular matrix in liver fibrosis

Emerging evidence suggests that altered components and posttranslational modifications of proteins in the extracellular matrix (ECM) may both initiate and drive disease progression. The ECM is a complex grid consisting of multiple proteins, most of which play a vital role in containing the essential information needed for maintenance of a sophisticated structure anchoring the cells and sustaining normal function of tissues. Therefore, the matrix itself may be considered as a paracrine/endocrine entity, with more complex functions than previously appreciated. The aims of this review are to 1) explore key structural and functional components of the ECM as exemplified by monogenetic disorders leading to severe pathologies, 2) discuss selected pathological posttranslational modifications of ECM proteins resulting in altered functional (signaling) properties from the original structural proteins, and 3) discuss how these findings support the novel concept that an increasing number of components of the ECM harbor signaling functions that can modulate fibrotic liver disease. The ECM entails functions in addition to anchoring cells and modulating their migratory behavior. Key ECM components and their posttranslational modifications often harbor multiple domains with different signaling potential, in particular when modified during inflammation or wound healing. This signaling by the ECM should be considered a paracrine/endocrine function, as it affects cell phenotype, function, fate, and finally tissue homeostasis. These properties should be exploited to establish novel biochemical markers and antifibrotic treatment strategies for liver fibrosis as well as other fibrotic diseases.

Purinergic signalling and cancer

Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.

Purinergic signalling in the gastrointestinal tract and related organs in health and disease

Purinergic signalling plays major roles in the physiology and pathophysiology of digestive organs. Adenosine 5'-triphosphate (ATP), together with nitric oxide and vasoactive intestinal peptide, is a cotransmitter in non-adrenergic, non-cholinergic inhibitory neuromuscular transmission. P2X and P2Y receptors are widely expressed in myenteric and submucous enteric plexuses and participate in sympathetic transmission and neuromodulation involved in enteric reflex activities, as well as influencing gastric and intestinal epithelial secretion and vascular activities. Involvement of purinergic signalling has been identified in a variety of diseases, including inflammatory bowel disease, ischaemia, diabetes and cancer. Purinergic mechanosensory transduction forms the basis of enteric nociception, where ATP released from mucosal epithelial cells by distension activates nociceptive subepithelial primary afferent sensory fibres expressing P2X3 receptors to send messages to the pain centres in the central nervous system via interneurons in the spinal cord. Purinergic signalling is also involved in salivary gland and bile duct secretion.

JNK is a novel regulator of intercellular adhesion

c-Jun N-terminal Kinase (JNK) is a family of protein kinases, which are activated by stress stimuli such as inflammation, heat stress and osmotic stress, and regulate diverse cellular processes including proliferation, survival and apoptosis. In this review, we focus on a recently discovered function of JNK as a regulator of intercellular adhesion. We summarize the existing knowledge regarding the role of JNK during the formation of cell-cell junctions. The potential mechanisms and implications for processes requiring dynamic formation and dissolution of cell-cell junctions including wound healing, migration, cancer metastasis and stem cell differentiation are also discussed.

Interleukin-18 stimulates fibronectin expression in primary human cardiac fibroblasts via PI3K-Akt-dependent NF-kappaB activation

Fibronectin (FN), a key component of the extracellular matrix, is upregulated in cardiac tissue during myocardial hypertrophy and failure. Here we show that interleukin (IL)-18, a proinflammatory and pro-hypertrophic cytokine, stimulates FN expression in adult human cardiac fibroblasts (HCF), an effect blocked by either the IL-18BP:Fc chimera or IL-18 neutralizing antibodies. IL-18 stimulated FN promoter-reporter activity in HCF, a response attenuated by mutation of an NF-kappaB binding site in the FN promoter. Overexpression of p65 stimulated FN transcription. IL-18 stimulated in vitro (p65, p50) and in vivo NF-kappaB DNA binding activities, and induced kappaB-dependent reporter gene activity. These effects were inhibited by adenoviral transduction of dominant negative (dn) p65 (Ad.dnp65) and dnIKK2 (Ad.dnIKK2). Investigation of signaling intermediates revealed that IL-18 stimulated PI3 kinase activity (blocked by wortmannin, LY294002, or Ad.dnPI3Kp85), and Akt phosphorylation and kinase activity (blocked by SH-5 or Ad.dnAkt). Furthermore, targeting MyD88, IRAK1, TRAF6, PI3K, Akt, and NF-kappaB by RNA interference or dn expression vectors blunted IL-18 mediated FN transcription and mRNA expression. Conversely, FN stimulated IL-18 expression. These data provide the first evidence that IL-18 and FN stimulate each other's expression in HCF, and suggest a role for IL-18, FN and their crosstalk in myocardial hypertrophy and remodeling, disease states characterized by enhanced FN expression and fibrosis.

Transcriptional regulation of stellate cell activation

The identification of activated hepatic stellate cells and related cell types as key fibrogenic effectors during liver injury has led to intense evaluation of transcriptional events underlying their behavior. While initial studies focused on characterizing interactions between transcription factors and regulatory regions within gene promoters, epigenetic mechanisms have emerged as major determinants of gene activation and repression, in particular histone acetylation and promoter methylation, as well as other complex conditional interactions that underlie global changes in gene expression. Three examples are provided that illustrate how stellate cell activation may be controlled by widely divergent regulatory pathways, including alternative splicing of a growth inhibitory transcription factor (Kruppel-like factor-6), epigenetic regulation of a factor regulating stellate cell survival (nuclear factor kappaB), and regulation of a transcription factor whose expression maintains stellate cell quiescence (LIM homeobox gene 2 [Lhx2]). These complex cascades illustrate how clarifying the finely tuned interdependent layers of transcriptional, translational, post-translational and epigenetic gene regulation in stellate cells is raising new prospects for therapy of hepatic fibrosis.

Methods for detecting internalized, FM 1-43 stained particles in epithelial cells and monolayers

The membrane dye FM 1-43 has frequently been used to quantify exocytosis in neurons. In epithelia, intense lateral intracellular space staining and fluctuations in baseline labeling produced inconsistent results. Membrane retrieved in the presence of FM 1-43 retains the dye, however, and cells that undergo compensatory endocytosis during and following evoked exocytosis contain punctate, fluorescent particles after washout of external stain. As an alternative measure of trafficking, we quantified the fluorescent puncta retained after dye washout and tested our method on both coverslip-grown cell clusters and filter-grown intact monolayers. Images for analysis were acquired using serial sectioning with either epifluorescence or confocal microscopy. Tests with an intestinal goblet cell line that exhibits basal and ATP-stimulated granule trafficking confirmed that 1), the algorithm identified the same number of internalized particles with either epifluorescence or confocal microscopy acquired images; 2), low density clusters exhibited significantly more internalized particles per cell than either filter-grown monolayers or high density clusters; 3), ATP stimulation significantly increased the number of internalized particles in all preparations; and 4), the number of particles internalized was comparable to capacitance measurements of exocytosis. This method provides a single technique for quantifying membrane trafficking in both monolayers and unpolarized cells.

Inhibitory effects of Ligusticum chuanxiong on the proliferation of rat hepatic stellate cells

BACKGROUND AND AIMS

Platelet-derived growth factor (PDGF) is a very potent mitogen for hepatic stellate cells (HSC) in hepatic fibrogenesis. Ligusticum chuanxiong Hort. (LC), a traditional Chinese herb used for cerebrovascular diseases, has been shown to exert anti-inflammatory and free radical scavenging effects. The aims of the present study were to investigate the effects of LC extract on the proliferation-related biomarkers in a rat HSC cell line (HSC-T6) stimulated with PDGF.

METHODS

DNA synthesis via bromodeoxyuridine (BrdU) incorporation, cell cycle related proteins and apoptosis markers were determined to evaluate the inhibitory effects of LC.

RESULTS

The results revealed that LC extract (25-100 microg/mL) concentration-dependently decreased the PDGF-induced cell proliferation as well as alpha-smooth muscle actin expression in HSC. The inhibitory activity of LC on HSC was associated with: (i) inhibition of BrdU incorporation; (ii) induction of apoptosis with the activation of caspase-3, up-regulation of cell cycle inhibitory proteins p21 and p27, and down-regulation of cell cycle stimulatory proteins cyclins D1 and D2; and (iii) increased phosphorylation of mitogen-activated protein kinases (JNK). LC at the studied concentrations showed no direct cytotoxicity on primary hepatocytes.

CONCLUSION

The results suggest that LC significantly inhibited PDGF-activated HSC proliferation, possibly through apoptotic mechanisms and the potential of LC as an antifibrotic agent warrants further investigation.

The front line of enteric host defense against unwelcome intrusion of harmful microorganisms: mucins, antimicrobial peptides, and microbiota

The intestinal tract is a complex ecosystem that combines resident microbiota and the cells of various phenotypes with complex metabolic activities that line the epithelial wall. The intestinal cells that make up the epithelium provide physical and chemical barriers that protect the host against the unwanted intrusion of microorganisms that hijack the cellular molecules and signaling pathways of the host and become pathogenic. Some of the organisms making up the intestinal microbiota also have microbicidal effects that contribute to the barrier against enteric pathogens. This review describes the two cell lineages present in the intestinal epithelium: the goblet cells and the Paneth cells, both of which play a pivotal role in the first line of enteric defense by producing mucus and antimicrobial peptides, respectively. We also analyze recent insights into the intestinal microbiota and the mechanisms by which some resident species act as a barrier to enteric pathogens. Moreover, this review examines whether the cells producing mucins or antimicrobial peptides and the resident microbiota act in partnership and whether they function individually and/or synergistically to provide the host with an effective front line of defense against harmful enteric pathogens.

Nuclear export of retinoid X receptor alpha in response to interleukin-1beta-mediated cell signaling: roles for JNK and SER260

As the obligate heterodimer partner to class II nuclear receptors, the retinoid X receptor alpha (RXRalpha) plays a vital physiological role in the regulation of multiple hepatic functions, including bile formation, intermediary metabolism, and endobiotic/xenobiotic detoxification. Many RXRalpha-regulated genes are themselves suppressed in inflamed liver via unknown mechanisms, which constitute a substantial component of the negative hepatic acute phase response. In this study we show that RXRalpha, generally considered a stable nuclear resident protein, undergoes rapid nuclear export in response to signals initiated by the pro-inflammatory cytokine interleukin-1beta (IL-1beta), a central activator of the acute phase response. Within 30 min of exposure to IL-1beta, nuclear levels of RXRalpha are markedly suppressed in human liver-derived HepG2 cells, temporally coinciding with its appearance in the cytoplasm. The nuclear residence of RXRalpha is maintained by inhibiting c-jun N-terminal kinase (JNK, curcumin or SP600125) or CRM-1-mediated nuclear export (Leptomycin B). Pretreatment with the proteasome inhibitor MG132 blocks IL-1beta-mediated reductions in nuclear RXRalpha levels while increasing accumulation in the cytoplasm. Mutational studies identify one residue, serine 260, a JNK phosphoacceptor site whose phosphorylation status had an unknown role in RXRalpha function, as critical for IL-1beta-mediated nuclear export of transfected human RXRalpha-green fluorescent fusion constructs. These findings indicate that inflammation-mediated cell signaling leads to rapid and profound reductions in nuclear RXRalpha levels, via a multistep, JNK-dependent mechanism involving Ser260, nuclear export, and proteasomal degradation. Thus, inflammation-meditated cell signaling targets RXRalpha for nuclear export and degradation; a potential mechanism that explains the broad suppression of RXRalpha-dependent gene expression in the inflamed liver.

Splanchnic lipolysis in human obesity

Elevated FFA concentrations have been shown to reproduce some of the metabolic abnormalities of obesity. It has been hypothesized that visceral adipose tissue lipolysis releases excess FFAs into the portal vein, exposing the liver to higher FFA concentrations. We used isotope dilution/hepatic vein catheterization techniques to examine whether intra-abdominal fat contributes a greater portion of hepatic FFA delivery in visceral obesity. Obese women (n = 24) and men (n = 20) with a range of obesity phenotypes, taken together with healthy, lean women (n = 12) and men (n = 12), were studied. Systemic, splanchnic, and leg FFA kinetics were measured. The results showed that plasma FFA concentrations were approximately 20% greater in obese men and obese women. The contribution of splanchnic lipolysis to hepatic FFA delivery ranged from less than 10% to almost 50% and increased as a function of visceral fat in women (r = 0.49, P = 0.002) and in men (r = 0.52, P = 0.002); the slope of the relationship was greater in women than in men (P < 0.05). Leg and splanchnic tissues contributed a greater portion of systemic FFA release in obese men and women than in lean men and women. We conclude that the contribution of visceral adipose tissue lipolysis to hepatic FFA delivery increases with increasing visceral fat in humans and that this effect is greater in women than in men.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Increased vesicle recycling in response to osmotic cell swelling. Cause and consequence of hypotonicity-provoked ATP release

Osmotic swelling of Intestine 407 cells leads to an immediate increase in cell surface membrane area as determined using the fluorescent membrane dye FM 1-43. In addition, as measured by tetramethylrhodamine isothiocyanate (TRITC)-dextran uptake, a robust (>100-fold) increase in the rate of endocytosis was observed, starting after a discrete lag time of 2-3 min and lasting for approximately 10-15 min. The hypotonicity-induced increase in membrane surface area, like the cell swelling-induced release of ATP (Van der Wijk, T., De Jonge, H. R., and Tilly, B. C. (1999) Biochem. J. 343, 579-586), was diminished after 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester loading or cytochalasin B treatment. Uptake of TRITC-dextrans, however, was not affected. Treatment of the cells with the vesicle-soluble N-ethylmaleimide-sensitive factor attachment protein receptor-specific protease Clostridium botulinum toxin F not only nearly eliminated the hypotonicity-induced increase in membrane surface area but also strongly diminished the release of ATP, indicating the involvement of regulated exocytosis. Both the ATP hydrolase apyrase and the MEK inhibitor PD098059 diminished the osmotic swelling-induced increase in membrane surface area as well as the subsequent uptake of TRITC-dextrans. Taken together, the results indicate that extracellular ATP is required for the hypotonicity-induced vesicle recycling and suggest that a positive feedback loop, involving purinergic activation of the Erk-1/2 pathway, may contribute to the release of ATP from hypo-osmotically stimulated cells.

Niflumic acid inhibits ATP-stimulated exocytosis in a mucin-secreting epithelial cell line

ATP is an efficacious secretagogue for mucin and chloride in the epithelial cell line HT29-Cl.16E. Mucin release has been measured as [3H]glucosamine-labeled product in extracellular medium and as single-cell membrane capacitance increases indicative of exocytosis-related increases in membrane area. The calcium-activated chloride channel blocker niflumic acid, also reported to modulate secretion, was used to probe for divergence in the purinergic signaling of mucin exocytosis and channel activation. With the use of whole cell patch clamping, ATP stimulated a transient capacitance increase of 15 +/- 4%. Inclusion of niflumic acid significantly reduced the ATP-stimulated capacitance change to 3 +/- 1%, although normalized peak currents were not significantly different. Ratiometric imaging was used to assess intracellular calcium (Cai2+) dynamics during stimulation. In the presence of niflumic acid, the ATP-stimulated peak change in Cai2+ was unaffected, but the initial response and overall time to Cai2+ peak were significantly affected. Excluding external calcium before ATP stimulation or including the capacitative calcium entry blocker LaCl3 during stimulation muted the initial calcium transient similar to that observed with niflumic acid and significantly reduced peak capacitance change, suggesting that a substantial portion of the ATP-stimulated mucin exocytosis in HT29-Cl.16E depends on a rapid, brief calcium influx through the plasma membrane. Niflumic acid interferes with this influx independent of a chloride channel blockade effect.

Role of luminal ATP in regulating electrogenic Na(+) absorption in guinea pig distal colon

Extracellular ATP regulates a variety of functions in epithelial tissues by activating the membrane P2-receptor. The purpose of this study was to investigate the autocrine/paracrine regulation by luminal ATP of electrogenic amiloride-sensitive Na(+) absorption in the distal colon from guinea pigs treated with aldosterone by measuring the amiloride-sensitive short-circuit current (I(sc)) and (22)Na(+) flux in vitro with the Ussing chamber technique. ATP added to the luminal side inhibited the amiloride-sensitive I(sc) and (22)Na(+) absorption to a similar degree. The concentration dependence of the inhibitory effect of ATP on amiloride-sensitive I(sc) had an IC(50) value of 20-30 microM, with the maximum inhibition being approximately 50%. The effects of different nucleotides and of a nucleoside were also studied, the order of potency being ATP = UTP > ADP > adenosine. The effects of ATP were slightly, but significantly, reduced in the presence of suramin in the luminal solution. The inhibitory effect of luminal ATP was more potent in the absence of both Mg2+ and Ca2+ from the luminal solution. Pretreatment of the tissue with ionomycin or thapsigargin in the absence of serosal Ca2+ did not affect the percent inhibition of amiloride-sensitive I(sc) induced by ATP. Mechanical perturbation with a hypotonic luminal solution caused a reduction in amiloride-sensitive I(sc), this effect being prevented by the presence of hexokinase, an ATP-scavenging enzyme. These results suggest that ATP released into the luminal side by hypotonic stimulation could exert an inhibitory effect on the electrogenic Na(+) absorption. This effect was probably mediated by a P2Y(2) receptor on the apical membrane of colonic epithelial cells, and a change in the intracellular Ca2+ concentration may not be necessary for this process.

Cytokine regulation of periportal fibrosis in humans infected with Schistosoma mansoni: IFN-gamma is associated with protection against fibrosis and TNF-alpha with aggravation of disease

Hepatic periportal fibrosis, which affects 5-10% of subjects infected by Schistosoma mansoni, is caused by the T cell-dependent granuloma that develop around schistosome eggs. Experimental models of infection have shown that granuloma and fibrosis are tightly regulated by cytokines. However, it is unknown why advanced periportal fibrosis occurs only in certain subjects. The goal of the present study was to evaluate the cytokine response of S. mansoni-infected subjects with advanced liver disease in an attempt to relate susceptibility to periportal fibrosis with an abnormal production of cytokines that regulate granuloma and fibrosis. Fibrosis was evaluated by ultrasound on 795 inhabitants of a Sudanese village in which S. mansoni is endemic: advanced periportal fibrosis was observed in 12% of the population; 35% of the affected subjects exhibited signs of portal hypertension. Age (odds ratio (OR), 11.5), gender (OR, 4.2), and infection levels (OR, 2.2) were significantly (p < or = 0.01) associated with hepatic fibrosis. Cytokines produced by egg-stimulated blood mononuclear cells from 99 subjects were measured (75 with no or mild fibrosis; 24 subjects with advanced fibrosis). Multivariate analysis of cytokine levels showed that high IFN-gamma levels were associated with a marked reduction of the risk of fibrosis (p = 0.01; OR, 0.1); in contrast, high TNF-alpha levels were associated with an increased risk (p = 0.05; OR, 4.6) of periportal fibrosis. Moreover, infection levels were negatively associated with IFN-gamma production. These results with observations in experimental models strongly suggest that IFN-gamma plays a key role in the protection of S. mansoni-infected patients against periportal fibrosis, whereas TNF-alpha may aggravate the disease.

Activated rat pancreatic stellate cells express intercellular adhesion molecule-1 (ICAM-1) in vitro

INTRODUCTION

Activated pancreatic stellate cells (PSCs) have recently been implicated in the pathogenesis of pancreatic fibrosis.

AIMS

To examine the role of PSCs in pancreatic inflammation by determining whether activated PSCs express intercellular adhesion molecule-1 (ICAM-1).

METHODOLOGY

Culture-activated rat PSCs were treated with interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), ethanol, or acetaldehyde. ICAM-1 expression was analyzed by flow cytometry. The induction of mRNA was assessed by Northern blot analysis. The binding activity of transcription factors was examined by electrophoretic mobility shift assay. The activation of mitogen-activated protein kinases was assessed by Western blotting with use of antiphosphospecific antibodies. The adhesion of MOLT-4 cells to activated PSCs was also assessed.

RESULTS

Culture-activated PSCs expressed ICAM-1. The expression was increased in response to IL-1 beta and TNF-alpha but not to alcohol, with comparable mRNA induction. IL-1 beta and TNF-alpha increased the nuclear factor-kappa B (NF-kappa B)-specific and activator protein-1-specific DNA binding activity, whereas the NF-IL6 activity was not altered. Alcohol did not increase NF-kappa B binding activity. IL-1 beta and TNF-alpha activated extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase/stress-activated protein kinase, and p38 mitogen-activated protein kinase. Inducible ICAM-1 expression was blocked by pyrrolidine dithiocarbamate, a specific inhibitor of NF-kappa B activation, but not by inhibitors of mitogen-activated protein kinase pathways. IL-1 beta and TNF-alpha increased the ICAM-1-mediated binding of MOLT-4 cells to activated PSCs, indicating a role of ICAM-1 in the adhesion of leukocytes to PSCs.

CONCLUSION

Our results suggest that activated PSCs express ICAM-1 mainly through the activation of NF-kappa B, thus playing a role in the pathogenesis of pancreatic inflammation.

Sphingosine-1-phosphate stimulates human Caco-2 intestinal epithelial proliferation via p38 activation and activates ERK by an independent mechanism

Sphingosine-1-phosphate (S-1-P) has been identified as an extracellular mediator and an intracellular second messenger that may modulate cell motility, adhesion, proliferation, and differentiation and cancer cell invasion. Widely distributed, S-1-P is most abundant in the intestine. Although S-1-P is likely to modulate various intracellular pathways, activation of the mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase 1 (ERK1), ERK2, and p38 is among the best-characterized S-1-P effects. Because the MAPKs regulate proliferation, we hypothesized that S-1-P might stimulate intestinal epithelial cell proliferation by MAPK activation. Human Caco-2 intestinal epithelial cells were cultured on a fibronectin matrix because fibronectin is an important constituent of the gut mucosal basement membrane. We assessed ERK1, ERK2, and p38 activation by Western blotting with antibodies specific for their active forms and proliferation by Coulter counting at 24 h. Specific MAP kinase kinase (MEK) and p38 inhibitors PD98059 (20 microM) and SB202190 and SB203580 (10 and 20 microM) were used to probe the role of ERK and p38 in S-1-P-mediated proliferation. Three or more similar studies were pooled for the analysis. S-1-P stimulated Caco-2 proliferation and dose-responsively activated ERK1, ERK2, and p38. Proliferation peaked at 5 microM, yielding a cell number 166.3 +/- 2.7% of the vehicle control (n = 6, P < 0.05). S-1-P also maximally stimulated ERK1, ERK2, and p38 at 5 microM, to 164.4 +/- 19.9%, 232.2 +/- 38.5%, and 169.2 +/- 20.5% of the control, respectively. Although MEK inhibition prevented S-1-P activation of ERK1 and ERK2 and slightly but significantly inhibited basal Caco-2 proliferation, MEK inhibition did not block the S-1-P mitogenic effect. However, pretreatment with 10 microM SB202190 or SB203580 (putative p38 inhibitors) attenuated the stimulation of proliferation by S-1-P. Twenty micromolars of SB202190 or SB203580 completely blocked the mitogenic effect of S-1-P. Ten to twenty micromolars of SB202190 and SB203580 also dose-dependently ablated the effects of 5 microM S-1-P on heat shock protein 27 accumulation, a downstream consequence of p38 MAPK activation. Consistent with the reports in some other cell types, S-1-P appears to activate ERK1, ERK2, and p38 and to stimulate proliferation. However, in contrast to the mediation of the S-1-P effects in some other cell types, S-1-P appears to stimulate human intestinal epithelial proliferation by activating p38. ERK activation by S-1-P is not required for its mitogenic effect.

Peroxisome proliferator-activated receptors and hepatic stellate cell activation

The present study examined the roles of peroxisome proliferator-activated receptors (PPAR) in activation of hepatic stellate cells (HSC), a pivotal event in liver fibrogenesis. RNase protection assay detected mRNA for PPARgamma1 but not that for the adipocyte-specific gamma2 isoform in HSC isolated from sham-operated rats, whereas the transcripts for neither isoforms were detectable in HSC from cholestatic liver fibrosis induced by bile duct ligation (BDL). Semi-quantitative reverse transcriptase-polymerase chain reaction confirmed a 70% reduction in PPARgamma mRNA level in HSC from BDL. Nuclear extracts from BDL cells showed an expected diminution of binding to PPAR-responsive element, whereas NF-kappaB and AP-1 binding were increased. Treatment of cultured-activated HSC with ligands for PPARgamma (10 microm 15-deoxy-Delta(12,14)-PGJ(2) (15dPGJ(2)); 0.1 approximately 10 microm BRL49653) inhibited DNA and collagen synthesis without affecting the cell viability. Suppression of HSC collagen by 15dPGJ(2) was abrogated 70% by the concomitant treatment with a PPARgamma antagonist (GW9662). HSC DNA and collagen synthesis were inhibited by WY14643 at the concentrations known to activate both PPARalpha and gamma (>100 microm) but not at those that only activate PPARalpha (<10 microm) or by a synthetic PPARalpha-selective agonist (GW9578). 15dPGJ(2) reduced alpha1(I) procollagen, smooth muscle alpha-actin, and monocyte chemotactic protein-1 mRNA levels while inducing matrix metalloproteinase-3 and CD36. 15dPGJ(2) and BRL49653 inhibited alpha1(I) procollagen promoter activity. Tumor necrosis factor alpha (10 ng/ml) reduced PPARgamma mRNA, and this effect was prevented by the treatment with 15dPGJ(2). These results demonstrate that HSC activation is associated with the reductions in PPARgamma expression and PPAR-responsive element binding in vivo and is reversed by the treatment with PPARgamma ligands in vitro. These findings implicate diminished PPARgamma signaling in molecular mechanisms underlying activation of HSC in liver fibrogenesis and the potential therapeutic value of PPARgamma ligands for liver fibrosis.

Regulated trafficking of the CFTR chloride channel

The cystic fibrosis transmembrane conductance regulator (CFTR), the ABC transporter encoded by the cystic fibrosis gene, is localized in the apical membrane of epithelial cells where it functions as a cyclic AMP-regulated chloride channel and as a regulator of other ion channels and transporters. Whereas a key role of cAMP-dependent phosphorylation in CFTR-channel gating has been firmly established, more recent studies have provided clear evidence for the existence of a second level of cAMP regulation, i.e. the exocytotic recruitment of CFFR to the plasma membrane and its endocytotic retrieval. Regulated trafficking of the CFTR Cl- channel has sofar been demonstrated only in a subset of CFTR-expressing cell types. However, with the introduction of more sensitive methods to measure CFTR cycling and submembrane localization, it might turn out to be a more general phenomenon that could contribute importantly to both the regulation of CFTR-mediated chloride transport itself and to the regulation of other transporters and CFTR-modulated cellular functions. This review aims to summarize the present state of knowledge regarding polarized and regulated CFTR trafficking and endosomal recycling in epithelial cells, to discuss present gaps in our understanding of these processes at the cellular and molecular level, and to consider its possible implications for cystic fibrosis.

The in vitro manipulation of carbohydrate metabolism: a new strategy for deciphering the cellular defence mechanisms against nitric oxide attack

This study was aimed at examining the effects of manipulating the carbohydrate source of the culture medium on the cellular sensitivity of epithelial cells to an oxidative attack. Our rationale was that substituting galactose for glucose in culture media would remove the protection afforded by glucose utilization in two major metabolic pathways, i.e. anaerobic glycolysis and/or the pentose phosphate pathway (PPP), which builds up cellular reducing power. Indeed, we show that the polarized human colonic epithelial cell line HT29-Cl.16E was sensitive to the deleterious effects of the NO donor PAPANONOate [3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine] only in galactose-containing medium. In such medium NO attack led to cytotoxic and apoptotic cell death, associated with formation of derivatives of NO auto-oxidation (collectively termed NOx) and peroxynitrite, leading to intracellular GSH depletion and nitrotyrosine formation. The addition of 2-deoxyglucose, a non-glycolytic substrate, to galactose-fed cells protected HT29-Cl. 16E cells from NO attack and maintained control GSH levels through its metabolic utilization in the PPP, as shown by (14)CO(2) production from 2-deoxy[1-(14)C]glucose. Therefore, increasing the availability of reducing equivalents without interfering with energy metabolism is able to prevent NO-induced cell injury. Finally, this background provides the conceptual framework for establishing nutritional manipulation of cellular metabolic pathways that could provide new means for (i) deciphering the mechanisms of cell injury by reactive nitrogen species and reactive oxygen species at the whole-cell level and (ii) establishing the hierarchy of intracellular defence mechanisms against these attacks.

Chronic pancreatitis

In the past year, numerous important papers were published on chronic pancreatitis, its causes, and its diagnosis; the cause of fibrosis; and pain in pancreatic cancer. More than 750 mutations have been described in the cystic fibrosis transmembrane regulator (CFTR) gene. Some mutations cause relatively mild reductions in CFTR function and may lead to disease in one organ without clinical involvement of other organs. Two groups of investigators recently reported that "idiopathic" chronic pancreatitis may be the sole manifestation of some CFTR mutations. Some recent reports may enhance our understanding of pancreatic fibrogenesis and may lead to therapies for painful chronic pancreatitis. Pancreatic stellate cells are vitamin A-containing cells that resemble hepatic stellate cells and were recently isolated from rat and human pancreas. They respond to inflammatory cytokines by producing collagen. Two studies show that endoscopic ultrasonography (EUS) correlates well with endoscopic retrograde cholangiopancreatography in moderate to severe chronic pancreatitis. However, in patients who have a few nondiagnostic abnormalities on EUS, these results have poor correlation with the results of endoscopic retrograde cholangiopancreatography and the secretin test. The clinical significance of these abnormalities is unclear, and the diagnosis of chronic pancreatitis should not be based on EUS findings alone. Painful chronic pancreatitis is a complex and difficult management problem. A recent study of alcoholic chronic pancreatitis suggests that the best predictors of pain relief are an intermittent pattern of pain and the presence of surgically correctable complications (eg, pseudocysts or biliary obstruction). An American Gastroenterological Association technical review of painful chronic pancreatitis emphasized the lack of controlled studies supporting any form of therapy. Further evidence that longstanding chronic pancreatitis is a premalignant condition has been provided by recent epidemiologic, pathologic, and molecular biology studies.

Intracellular signaling pathways in stellate cell activation

Pathological fibrogenesis in the liver is mediated by activated stellate cells. These cells have a myofibroblastic phenotype with the ability to proliferate and synthesize large quantities of extracellular matrix components. A number of factors have been proposed to initiate and perpetuate the fibrogenic process in stellate cells, including inflammatory cytokines, alterations in the extracellular matrix, growth factors, and oxidative stress. Some recent research has focused on the intracellular signaling pathways that are stimulated by these factors in stellate cells, including mitogen-activated protein kinases, phosphatidylinositol 3-kinase, focal adhesion kinase, and protein kinase C. This paper will summarize the experimental evidence that implicates these pathways in stellate cell activation, focusing on the effects of exposure to platelet-derived growth factor, tumor necrosis factor-alpha, and fibronectin. Implications for alcohol-induced hepatic fibrosis and future directions for research will also be discussed.

Stellate cell activation in alcoholic fibrosis--an overview

There has been remarkable progress in our understanding of how chronic alcohol ingestion may lead to hepatic injury and scarring, or fibrosis. Hepatic fibrosis represents the liver's wound healing response and is characterized by accumulation of interstitial matrix, or scar. Fibrosis in the liver results from the activation of stellate cells, or resident mesenchymal cells. Stellate cell activation is a dramatic phenotype transition whose net effect is the replacement of normal liver matrix by scar. Features of stellate cell activation include increased cell accumulation from proliferation and directed migration, increased matrix production, enhanced contractility, accelerated degradation of the normal liver matrix, release of profibrogenic cytokines, and loss of cellular vitamin A. Alcohol may enhance fibrogenesis through stimulation of stellate cells by hypoxia, generation of lipid peroxides from damaged hepatocytes, production of acetaldehyde that may have direct fibrogenic activity, and through activation of Kupffer cells or resident macrophages. Unanswered questions remain to be studied, but the clarification of underlying mechanisms of fibrosis portends continued progress in our ability to treat alcoholic liver fibrosis.

Differential regulation of IL-6 promoter activity in a human ovarian-tumor cell line transfected with various p53 mutants: involvement of AP-1

In human ovarian carcinomas, the p53 tumor-suppressor gene is frequently mutated. Interleukin-6 (IL-6) in these tumors is known to stimulate tumor-cell proliferation. In order to evaluate the effect of several p53 phenotypes on the IL-6 promoter activity, the human ovarian wild-type (wt)-p53 cell line A2780 was stably transfected with an empty plasmid (CMV) or (m)-175-, m-248- or m-273-p53. Electrophoretic mobility-shift assays revealed differences in activator protein-1 (AP-1) DNA-binding activity in the various clones. The CMV and m-273 clone had comparable amounts of AP-1. The m-175 clone displayed the least and m-248 the most pronounced AP-1 binding. Supershift analysis of AP-1/DNA complexes with antibodies against the AP-1 sub-units, c-Fos, FosB, Fra-1, Fra-2, c-Jun, JunB, and JunD, revealed that the AP-1/DNA complexes in the various clones had different compositions. Fra proteins were basically present only in m-175 and m-248 AP-1. IL-6-promoter activity was evaluated in the presence and absence of the AP-1 binding site which showed that the m-175-transfected clone has a transcriptional suppressing AP-1, whereas the CMV and the m-273 clones have an activating AP-1. Exposure of the p53 clones to tumor-necrosis factor-alpha (TNF-alpha) clearly altered the AP-1/DNA complex composition. IL-6-promoter activity was enhanced by TNF-alpha irrespective of the presence of an AP-1 binding site, while the degree of activation differed in the various clones, being most pronounced in the m-175 and m-248 clones. The results demonstrate that the basic and activated IL-6-promoter activity is differently regulated in the various p53 clones, possibly due to alterations in the AP-1 composition.

Purinergic and cholinergic agonists induce exocytosis from the same granule pool in HT29-Cl.16E monolayers

Several secretagogues induce mucin secretion in epithelial monolayers, as determined by measuring released granule contents. To assess whether different agonists act on the same granule pool, capacitance changes in intact monolayers of the goblet cell line HT29-Cl.16E were measured by a novel impedance method. Apical ATP (purinergic agonist) and basolateral carbachol (cholinergic agonist) induce rapid exocytosis with maximal capacitance changes within 3 min. The maximal levels of exocytosis that can be induced by optimal concentrations of either agonist are the same and produce a 30-40% increase in total monolayer capacitance. When ATP and carbachol are applied simultaneously, the magnitude of exocytosis is unchanged from the single-secretagogue level. The recovery of capacitance to baseline (endocytosis) is significantly faster after ATP stimulation than after carbachol stimulation. When ATP and carbachol are applied sequentially at doses that give maximal exocytosis, the magnitude of the capacitance increase produced by the second secretagogue is less than or equal to that of the capacitance decrease during the recovery period. Together, these data suggest that purinergic and cholinergic agonists act on the same granule pool.

UV irradiation activates JNK and increases alphaI(I) collagen gene expression in rat hepatic stellate cells

Hepatic stellate cells (HSCs) become activated into myofibroblast-like cells during the early stages of hepatic injury associated with fibrogenesis. The subsequent dysregulation of alphaI(I) collagen gene expression is a central pathogenetic step during the development of cirrhosis. Our recent study in rat HSCs (Davis, B. H., Chen, A., and Beno, D. (1996) J. Biol. Chem. 271, 11039-11042) found that ERK1,2 activation might be required for maximal alphaI(I) collagen gene expression. However, the role of the parallel JNK cascade in regulating alphaI(I) collagen gene expression was unknown. In this study, we initially found that UV irradiation of HSCs activated JNK but not ERK1,2. Furthermore, UV irradiation increased endogenous alpha I(I) collagen mRNA abundance and stimulated alpha I(I) collagen gene transcription in HSCs. The effect of the activation of JNK and Jun on alpha I(I) collagen gene expression was further evaluated via transfection of chloramphenicol acetyltransferase reporter plasmids with various sizes of truncated 5' upstream promoter sequence (UPS) of the alphaI(I) collagen gene. This revealed that dominant negative transcription factor JUN suppressed alpha I(I) collagen gene transcription in HSCs maintained in media with 20% serum and constitutively activated JUN increased alphaI(I) collagen gene transcription in HSCs cultured in media with 0.4% serum. UV activated JNK utilized a distal GC box in the 5'-UPS of the collagen gene to regulate gene transcription. This observation was confirmed by site-directed mutagenesis. In co-transfection experiments, the col-chloramphenicol acetyltransferase reporter with a mutagenized GC box was not suppressed by dn-JUN and was not stimulated by activated JUN or by UV irradiation. Southwestern blotting analyses and gel shift assays with basic transcription element-binding protein antiserum suggested that the GC box was bound by basic transcription element-binding protein, a recently described DNA-binding protein. In conclusion, the current study combined with our previous report suggests that ERK1,2 and JNK cascades regulate alphaI(I) collagen expression in HSCs through different regions of the 5'-UPS of the gene. The distal GC box in the 5'-UPS of the alphaI(I) collagen gene may play a central role in receiving extracellular signals through the JNK pathway.

System for dynamic measurements of membrane capacitance in intact epithelial monolayers

Dynamic measurements of exocytosis have been difficult to perform in intact epithelial monolayers. We have designed a system that estimates with +/-1% accuracy (99% confidence) the total membrane capacitance of monolayers represented by a lumped model. This impedance measurement and analysis system operates through a conventional transepithelial electrophysiology clamp, performing all signal measurements as frequently as every 5 s. Total membrane capacitance (the series combination of apical and basolateral membranes) is the inverse of one of three unique coefficients that describe the monolayer impedance. These coefficients are estimated using a weighted, nonlinear, least-squares algorithm. Using the estimated coefficients, solution ranges for individual membrane parameters are calculated, frequently providing results within +/-20% of true values without additional electrophysiological measurements. We determined the measurement system specifications and statistical significance of estimated parameters using 1) analytical testing with circuit simulation software and equation-generated data; 2) a system noise analysis combined with Monte Carlo simulations; and 3) analog model circuits for calibration of the electronic system and to check equation-generated results. Finally, the time course of capacitance changes associated with purinergically stimulated mucin exocytosis are quantified in monolayers of the colonic goblet cell-like cell line HT29-CI.16E.