ET-1- and NO-mediated signal transduction pathway in human brain capillary endothelial cells

Microglia at the Crossroads of Pathogen-Induced Neuroinflammation

Microglia are the resident tissue macrophages of the central nervous system (CNS). Recent findings point out that in the steady state the major role of microglia, is to instruct and regulate the correct function of the neuronal networks and different components of the neurovascular unit in the adult CNS, while providing immune surveillance. Paradoxically, during CNS infection immune activation of microglia generates an inflammatory milieu that contributes to the clearance of the pathogen but can, in the process, harm nearby cells of CNS. Most of the knowledge about the harmful effects of activated microglia on CNS has arisen from studies on neurodegenerative diseases. In this review we will focus on the beneficial role and detrimental functions of microglial cells on the neighboring cells of the CNS upon infection.

Characterization of endothelium-dependent and -independent processes in occipital artery of the rat: Relevance to control of blood flow to nodose sensory cells

Circulating factors access cell bodies of vagal afferents in nodose ganglia (NG) via the occipital artery (OA). Constrictor responses of OA segments closer in origin from the external carotid artery (ECA) differ from segments closer to NG. Our objective was to determine the role of endothelium in this differential vasoreactivity in rat OA segments. Vasoreactivity of OA segments (proximal segments closer to ECA, distal segments closer to NG) were examined in wire myographs. We evaluated (a) vasoconstrictor effects of 5-hydroxytryptamine (5-HT) in intact and endothelium-denuded OA segments in absence/presence of soluble guanylate cyclase (SGC) inhibitor ODQ, (b) vasodilator responses elicited by NO-donor MAHMA NONOate in intact or endothelium-denuded OA segments in absence/presence of ODQ, and (c) vasodilator responses elicited by endothelium-dependent vasodilator, acetylcholine (ACh), in intact OA segments in absence/presence of ODQ. Intact distal OA responded more to 5-HT than intact proximal OA. Endothelium denudation increased 5-HT potency in both OA segments, especially proximal OA. ODQ increased maximal responses of 5HT in both segments, particularly proximal OA. ACh similarly relaxed both OA segments, effects abolished by endothelial denudation and attenuated by ODQ. MAHMA NONOate elicited transient vasodilation in both segments. Effects of ODQ against ACh were segment-dependent whereas those against MAHMA NONOate were not. The endothelium regulates OA responsiveness in a segment-dependently fashion. Endothelial cells at the OA-ECA junction more strongly influence vascular tone than those closer to NG. Differential endothelial regulation of OA tone may play a role in controlling blood flow and access of circulating factors to NG.

The progression of pulmonary arterial hypertension induced by monocrotaline is characterized by lung nitrosative and oxidative stress, and impaired pulmonary artery reactivity

The time-course of pulmonary arterial hypertension in the monocrotaline (MCT) model was investigated. Male rats were divided into two groups: MCT (received a 60 mg/kg i.p. injection) and control (received saline). The MCT and control groups were further divided into three cohorts, based on the follow-up interval: 1, 2, and 3 weeks. Right ventricle (RV) catheterization was performed and RV hypertrophy (RVH) was estimated. The lungs were used for biochemical, histological, molecular, and immunohistochemical analysis, while pulmonary artery rings were used for vascular reactivity. MCT promoted lung perivascular edema, inflammatory cells exudation, greater neutrophils and lymphocytes profile, and arteriolar wall thickness, compared to CTR group. Increases in pulmonary artery pressure and in RVH were observed in the MCT 2- and 3-week groups. The first week was marked by the presence of nitrosative stress (50% moderate and 33% accentuated staining by nitrotyrosine). These alterations lead to an adaptation of NO production by NO synthase activity after 2 weeks. Oxidative stress was evident in the third week, probably by an imbalance between endothelin-1 receptors, resulting in extracellular matrix remodeling, endothelial dysfunction, and RVH. Also, it was found a reduced pulmonary arterial vasodilatory response to acetylcholine after 2 (55%) and 3 (45%) weeks in MCT groups. The relevance of this study is precisely to show that nitrosative and oxidative stress predominate in distinct time windows of the disease progression.

Mechanisms of Blood-Brain Barrier Disruption in Herpes Simplex Encephalitis

Herpes simplex encephalitis (HSE) is often caused by infection with herpes simplex virus 1 (HSV-1), a neurotropic double-stranded DNA virus. HSE infection always impacts the temporal and frontal lobes or limbic system, leading to edema, hemorrhage, and necrotic changes in the brain parenchyma. Additionally, patients often exhibit severe complications following antiviral treatment, including dementia and epilepsy. HSE is further associated with disruptions to the blood-brain barrier (BBB), which consists of microvascular endothelial cells, tight junctions, astrocytes, pericytes, and basement membranes. Following an HSV-1 infection, changes in BBB integrity and permeability can result in increased movement of viruses, immune cells, and/or cytokines into the brain parenchyma. This leads to an enhanced inflammatory response in the central nervous system and further damage to the brain. Thus, it is important to protect the BBB from pathogens to reduce brain damage from HSE. Here, we discuss HSE and the normal structure and function of the BBB. We also discuss growing evidence indicating an association between BBB breakdown and the pathogenesis of HSE, as well as future research directions and potential new therapeutic targets. Graphical Abstract During herpes simplex encephalitis, the functions and structures of each composition of BBB have been altered by different factors, thus the permeability and integrity of BBB have been broken. The review aim to explore the potential mechanisms and factors in the process, probe the next research targets and new therapeutic targets.

Long-term high-fat diet induces hippocampal microvascular insulin resistance and cognitive dysfunction

Insulin action on hippocampus improves cognitive function, and obesity and type 2 diabetes are associated with decreased cognitive function. Cerebral microvasculature plays a critical role in maintaining cerebral vitality and function by supplying nutrients, oxygen, and hormones such as insulin to cerebral parenchyma, including hippocampus. In skeletal muscle, insulin actively regulates microvascular opening and closure, and this action is impaired in the insulin-resistant states. To examine insulin's action on hippocampal microvasculature and parenchyma and the impact of diet-induced obesity, we determined cognitive function and microvascular insulin responses, parenchyma insulin responses, and capillary density in the hippocampus in 2- and 8-mo-old rats on chow diet and 8-mo-old rats on a long-term high-fat diet (6 mo). Insulin infusion increased hippocampal microvascular perfusion in rats on chow diet by ~80-90%. High-fat diet feeding completely abolished insulin-mediated microvascular responses and protein kinase B phosphorylation but did not alter the capillary density in the hippocampus. This was associated with a significantly decreased cognitive function assessed using both the two-trial spontaneous alternation behavior test and the novel object recognition test. As the microvasculature provides the needed endothelial surface area for delivery of nutrients, oxygen, and insulin to hippocampal parenchyma, we conclude that hippocampal microvascular insulin resistance may play a critical role in the development of cognitive impairment seen in obesity and diabetes. Our results suggest that improvement in hippocampal microvascular insulin sensitivity might help improve or reverse cognitive function in the insulin-resistant states.

Endothelin-1 modulates methacholine-induced cutaneous vasodilatation but not sweating in young human skin

KEY POINTS

Endothelin-1 (ET-1) is a potent endothelial-derived vasoconstrictor that may modulate cholinergic cutaneous vascular regulation. Endothelin receptors are also expressed on the human eccrine sweat gland, although it remains unclear whether ET-1 modulates cholinergic sweating. We investigated whether ET-1 attenuates cholinergic cutaneous vasodilatation and sweating through a nitric oxide synthase (NOS)-dependent mechanism. Our findings show that ET-1 attenuates methacholine-induced cutaneous vasodilatation through a NOS-independent mechanism. We also demonstrate that ET-1 attenuates cutaneous vasodilatation in response to sodium nitroprusside, suggesting that ET-1 diminishes the dilatation capacity of vascular smooth muscle cells. We show that ET-1 does not modulate methacholine-induced sweating at any of the administered concentrations. Our findings advance our knowledge pertaining to the peripheral control underpinning the regulation of cutaneous blood flow and sweating and infer that ET-1 may attenuate the heat loss responses of cutaneous blood flow, but not sweating.

ABSTRACT

The present study investigated the effect of endothelin-1 (ET-1) on cholinergic mechanisms of end-organs (i.e. skin blood vessels and sweat glands) for heat dissipation. We evaluated the hypothesis that ET-1 attenuates cholinergic cutaneous vasodilatation and sweating through a nitric oxide synthase (NOS)-dependent mechanism. Cutaneous vascular conductance (CVC) and sweat rate were assessed in three protocols: in Protocol 1 (n = 8), microdialysis sites were perfused with lactated Ringer solution (Control), 40 pm, 4 nm or 400 nm ET-1; in Protocol 2 (n = 11) sites were perfused with lactated Ringer solution (Control), 400 nm ET-1, 10 mm N(G) -nitro-l-arginine (l-NNA; a NOS inhibitor) or a combination of 400 nm ET-1 and 10 mm l-NNA; in Protocol 3 (n = 8), only two sites (Control and 400 nm ET-1) were utilized to assess the influence of ET-1 on the dilatation capacity of vascular smooth muscle cells (sodium nitroprusside; SNP). Methacholine (MCh) was co-administered in a dose-dependent manner (0.0125, 0.25, 5, 100, 2000 mm, each for 25 min) at all skin sites. ET-1 at 400 nm (P < 0.05) compared to lower doses (40 pm and 4 nm) (all P > 0.05) significantly attenuated increases in CVC in response to 0.25 and 5 mm MCh. A high dose of ET-1 (400 nm) co-infused with l-NNA further attenuated CVC during 0.25, 5 and 100 mm MCh administration relative to the ET-1 site (all P < 0.05). Cutaneous vasodilatation in response to SNP was significantly blunted after administration of 400 nm ET-1 (P < 0.05). We show that ET-1 attenuates cutaneous vasodilatation through a NOS-independent mechanism, possibly through a vascular smooth muscle cell-dependent mechanism, and methacholine-induced sweating is not altered by ET-1.

End o' the line revisited: moving on from nitric oxide to CGRP

When endothelin-1(ET-1) was discovered it was hailed as the prototypical endothelium-derived contracting factor (EDCF). However, over the years little evidence emerged convincingly demonstrating that the peptide actually contributes to moment-to-moment changes in vascular tone elicited by endothelial cells. This has been attributed to the profound inhibitory effect of nitric oxide (NO) on both the production (by the endothelium) and the action (on vascular smooth muscle) of ET-1. Hence, the peptide is likely to initiate acute changes in vascular diameter only under extreme conditions of endothelial dysfunction when the NO bioavailability is considerably reduced if not absent. The present essay discusses whether or not this concept should be revised, in particular in view of the potent inhibitory effect exerted by calcitonin gene related peptide (CGRP) released from sensorimotor nerves on vasoconstrictor responses to ET-1.

Effects of herbal compound 861 on collagen synthesis and degradation in rat mesangial cells exposed to high glucose

OBJECTIVE

To investigate the effects of Herbal Compound 861 (Cpd 861) on collagen synthesis and degradation in rat mesangial cells exposed to high glucose.

METHODS

The third to fifth passage of rat mesangial cells were exposed to high glucose and Cpd 861 at a concentration of 0.25-4.00 g/L for 24, 48 and 72 h, respectively. Benazepril (10(-7)-10(-3) mmol/L) was selected as positive control. The methyl thiazolyl tetrazolium colorimetric assay was used to evaluate the effect of Cpd 861 on cell proliferation. After incubation with Cpd 861 at a concentration of 2.00 g/L for 48 h, the protein secretions of collagen type IV, matrix metallopeptidase 9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1), transforming growth factor beta 1 (TGF-β1), and hepatocyte growth factor (HGF) were detected by enzyme-linked immunosorbent assay method. And rat mesangial cells were harvested to determine MMP-9, TIMP-1, TGF-β1 and HGF mRNA expression by reverse transcription polymerase chain reaction.

RESULTS

Cpd 861 inhibited cell proliferation induced by high glucose in a dose- and time-dependent manner. Compared with high glucose, collagen type IV production was decreased significantly by Cpd 861 (P<0.01). Cpd 861 increased the protein secretions and mRNA expressions of MMP-9 and HGF, whereas the protein secretions and mRNA expressions of TIMP-1 and TGF-β1 were reduced markedly (P<0.05). The ratio of MMP-9 to TIMP-1 was enhanced by Cpd 861 significantly. There was no significant difference in all above-mentioned effects between Cpd 861 (2.00 g/L) and benazepril (10(-5) mmol/L).

CONCLUSION

The anti-glomerulosclerosis mechanisms of Cpd 861 were partly attributed to its effects of inhibiting mesangial cell proliferation, decreasing collagen synthesis and enhancing collagen degradation.

Matrix Producing Cells in Chronic Kidney Disease: Origin, Regulation, and Activation

Chronic injury to the kidney causes kidney fibrosis with irreversible loss of functional renal parenchyma and leads to the clinical syndromes of chronic kidney disease (CKD) and end-stage renal disease (ESRD). Regardless of the type of initial injury, kidney disease progression follows the same pathophysiologic processes characterized by interstitial fibrosis, capillary rarefaction and tubular atrophy. Myofibroblasts play a pivotal role in fibrosis by driving excessive extracellular matrix (ECM) deposition. Targeting these cells in order to prevent the progression of CKD is a promising therapeutic strategy, however, the cellular source of these cells is still controversial. In recent years, a growing amount of evidence points to resident mesenchymal cells such as pericytes and perivascular fibroblasts, which form extensive networks around the renal vasculature, as major contributors to the pool of myofibroblasts in renal fibrogenesis. Identifying the cellular origin of myofibroblasts and the key regulatory pathways that drive myofibroblast proliferation and transdifferentiation as well as capillary rarefaction is the first step to developing novel anti-fibrotic therapeutics to slow or even reverse CKD progression and ultimately reduce the prevalence of ESRD. This review will summarize recent findings concerning the cellular source of myofibroblasts and highlight recent discoveries concerning the key regulatory signaling pathways that drive their expansion and progression in CKD.

Nitric oxide: orchestrator of endothelium-dependent responses

The present review first summarizes the complex chain of events, in endothelial and vascular smooth muscle cells, that leads to endothelium-dependent relaxations (vasodilatations) due to the generation of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS) and how therapeutic interventions may improve the bioavailability of NO and thus prevent/cure endothelial dysfunction. Then, the role of other endothelium-derived mediators (endothelium-derived hyperpolarizing (EDHF) and contracting (EDCF) factors, endothelin-1) and signals (myoendothelial coupling) is summarized also, with special emphasis on their interaction(s) with the NO pathway, which make the latter not only a major mediator but also a key regulator of endothelium-dependent responses.

The role of MAPK in drug-induced kidney injury

This paper focuses on the role that mitogen-activated protein kinases (MAPKs) play in drug-induced kidney injury. The MAPKs, of which there are four major classes (ERK, p38, JNK, and ERK5/BMK), are signalling cascades which have been found to be broadly conserved across a wide variety of organisms. MAPKs allow effective transmission of information from the cell surface to the cytosolic or nuclear compartments. Cross talk between the MAPKs themselves and with other signalling pathways allows the cell to modulate responses to a wide variety of external stimuli. The MAPKs have been shown to play key roles in both mediating and ameliorating cellular responses to stress including xenobiotic-induced toxicity. Therefore, this paper will discuss the specific role of the MAPKs in the kidney in response to injury by a variety of xenobiotics and the potential for therapeutic intervention at the level of MAPK signalling across different types of kidney disease.

Connexin channels provide a target to manipulate brain endothelial calcium dynamics and blood-brain barrier permeability

The cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) is an important factor determining the functional state of blood-brain barrier (BBB) endothelial cells but little is known on the effect of dynamic [Ca(2+)](i) changes on BBB function. We applied different agonists that trigger [Ca(2+)](i) oscillations and determined the involvement of connexin channels and subsequent effects on endothelial permeability in immortalized and primary brain endothelial cells. The inflammatory peptide bradykinin (BK) triggered [Ca(2+)](i) oscillations and increased endothelial permeability. The latter was prevented by buffering [Ca(2+)](i) with BAPTA, indicating that [Ca(2+)](i) oscillations are crucial in the permeability changes. Bradykinin-triggered [Ca(2+)](i) oscillations were inhibited by interfering with connexin channels, making use of carbenoxolone, Gap27, a peptide blocker of connexin channels, and Cx37/43 knockdown. Gap27 inhibition of the oscillations was rapid (within minutes) and work with connexin hemichannel-permeable dyes indicated hemichannel opening and purinergic signaling in response to stimulation with BK. Moreover, Gap27 inhibited the BK-triggered endothelial permeability increase in in vitro and in vivo experiments. By contrast, [Ca(2+)](i) oscillations provoked by exposure to adenosine 5' triphosphate (ATP) were not affected by carbenoxolone or Gap27 and ATP did not disturb endothelial permeability. We conclude that interfering with endothelial connexin hemichannels is a novel approach to limiting BBB-permeability alterations.

Cytocompatibility of electrospun nanofiber tubular scaffolds for small diameter tissue engineering blood vessels

A tubular scaffold was fabricated by using electrospun polymer solution blends of pNSR32 (recombinant spider silk protein), PCL (polycaprolactone) and Gt (gelatin). The physicochemical properties and cytocompatibility of these scaffolds were investigated. Afterwards, the pNSR32/PCL/Gt tubular scaffold (inner diameter=3mm) showed high porosity of 86.2 ± 2.9%, pore size of 2423 ± 979nm and average fibre diameter of 166 ± 85nm. Water uptake and contact angle of the scaffolds reached 112.0 ± 4.4% and 45.7 ± 13.7°, respectively. SDRAECs (Sprague Dawley Rat Aortic Endothelial Cells) grew and proliferated well and phenotype could be maintained on the composite scaffolds after they had been cultured on the composite scaffolds for 7 days. Compared with pure PCL scaffolds a greater density of viable cells was seen on the composites, especially the pNSR32/PCL/Gt scaffolds.

Effects of amlodipine on TGF-β-induced Smad2, 4 expressions in adriamycin toxicity of rat mesangial cells

Transforming growth factor-β (TGF-β) is closely associated with progressive renal fibrosis. A central component of TGF-β-stimulated mesangial cell fibrogenesis is the TGF-β family-specific Smad signal transduction pathway. This study investigated the expression of TGF-β-receptor--activated Smad2, its common partner Smad4, and the phosphorylated Smad2 (p-Smad2) in adriamycin-induced toxicity of cultured rat mesangial cells. This in vitro study showed that amlodipine (10(-9) to 10(-5) mol/l) had no effect on the toxicity of rat mesangial cells induced by adriamycin in the absence of TGF-β1. However, amlodipine (10(-7) to 10(-5) mol/l) reduced the toxicity of rat mesangial cells induced by TGF-β1 in the absence of adriamycin; moreover, amlodipine (10(-8) to 10(-5) mol/l) significantly reduced adriamycin-induced cytotoxicity when it was given in combination with TGF-β1; amlodipine (10(-6), 10(-5) mol/l) had no effect on Smad2 mRNA and protein expression induced by adriamycin + TGF-β1, but it (10(-6), 10(-5) mol/l) dramatically inhibited the down-regulation of p-Smad2 protein expression as well as Smad4 mRNA and protein expression induced by adriamycin + TGF-β1 in rat mesangial cells. Present study shows that amlodipine exerts a significant inhibition on adriamycin-induced toxicity in rat mesangial cells by affecting the expression of TGF-β/Smad signaling intermediates p-Smad2 and Smad4.

A conceptual framework for the molecular pathogenesis of progressive kidney disease

The data regarding the pathogenesis of progressive kidney disease implicate cytokine effects, physiological factors, and myriad examples of relatively nonspecific cellular dysfunction. The sheer volume of information being generated on this topic threatens to overwhelm our efforts to understand progression in chronic kidney disease or to derive rational strategies to treat it. Here, a conceptual framework is offered for organizing and considering these data. Disease is initiated by an injury that evokes a tissue-specific cellular response. Subsequent structural repair may be effective, or the new structure may be sufficiently changed that it requires an adaptive physiological response. If this adaptation is not successful, subsequent cycles of misdirected repair or maladaptation may lead to progressive nephron loss. To illustrate how this framework can be used to organize our approach to disease pathogenesis, the role of cytokines in proteinuria and progressive glomerular disease is discussed. Finally, this theoretical framework is reconsidered to examine its implications for the diagnosis and treatment of clinical conditions. Application of this schema could have significant relevance to both research inquiry and clinical practice.

Endothelin A receptors mediate relaxation of guinea pig internal anal sphincter through cGMP pathway

BACKGROUND

Endothelin (ET) modulates motility of the internal anal sphincter through unclear receptor subtypes.

METHODS

We measured relaxation of guinea pig internal anal sphincter strips caused by ET-related peptides and binding of (125)I-ET-1 to cell membranes prepared from the internal anal sphincter muscle. Visualization of (125)I-ET-1 binding sites in tissue was performed by autoradiography.

KEY RESULTS

In the guinea pig internal anal sphincter, ET-1 caused a marked relaxation insensitive to tetrodotoxin, atropine, or omega-conotoxin GVIA. ET-2 was as potent as ET-1. ET-3 caused a mild relaxation. The relative potencies for ETs to cause relaxation were ET-1 = ET-2 > ET-3. The ET-1-induced relaxation was inhibited by BQ-123, an ET(A) antagonist, but not by BQ-788, an ET(B) antagonist. These indicate that ET(A) receptors mediate the relaxation. The relaxant response of ET-1 was attenuated by LY 83583, KT 5823, Rp-8CPT-cGMPS, tetraethyl ammonium, 4-aminopyridine and N(omega)-nitro-L-arginine, but not significantly affected by N(G)-nitro-L-arginine methyl ester, N(G)-methyl-L-arginine, charybdotoxin, apamin, KT 5720, and Rp-cAMPS. These suggest the involvement of cyclic guanosine 3',5'-cyclic monophosphate (cGMP), and potassium channels. Autoradiography localized (125)I-ET-1 binding to the internal anal sphincter. Binding of (125)I-ET-1 to the cell membranes prepared from the internal anal sphincter revealed the presence of two subtypes of ET receptors, ET(A) and ET(B) receptors.

CONCLUSIONS & INFERENCES

Taken together, these results demonstrate that ET(A) receptors mediate relaxation of guinea pig internal anal sphincter through the cGMP pathway.

Renal fibrosis

Renal fibrosis, characterized by tubulointerstitial fibrosis and glomerulosclerosis, is the final manifestation of chronic kidney disease. Renal fibrosis is characterized by an excessive accumulation and deposition of extracellular matrix components. This pathologic result usually originates from both underlying complicated cellular activities such as epithelial-to-mesenchymal transition, fibroblast activation, monocyte/macrophage infiltration, and cellular apoptosis and the activation of signaling molecules such as transforming growth factor beta and angiotensin II. However, because the pathogenesis of renal fibrosis is extremely complicated and our knowledge regarding this condition is still limited, further studies are needed.

Changes in glomerular mesangium in kidneys with congenital nephrotic syndrome of the Finnish type

Congenital nephrotic syndrome of the Finnish type (NPHS1, CNF) is an autosomal recessive disease caused by mutations in a major podocyte protein, nephrin. NPHS1 is associated with heavy proteinuria and the development of glomerular scarring. We studied the cellular and molecular changes affecting the glomerular mesangium in NPHS1 kidneys. Marked hyperplasia of mesangial cells (MC) was mainly responsible for the early mesangial expansion in NPHS1 glomeruli. The levels of the proliferation marker, mindbomb homolog 1 and the major MC mitogen, platelet-derived growth factor, and its receptors, however, were quite normal. Only a small number of cells were positive for CD68 (marker for phagocytic cells) and CD34 (marker for mesenchymal precursor cells) in the NPHS1 mesangium. MCs strongly expressed alpha-smooth muscle actin, indicating myofibloblast transformation. The expression levels of the profibrotic mediators osteopontin and transforming growth factor beta were up-regulated in NPHS1 glomeruli by 3.2 and 1.6-fold, respectively, compared to the controls. The synthesis by MCs of the typical fibroblast products collagen I, fibronectin, and tenascin, however, was low, and the extracellular matrix increase was caused by the accumulation of a normal MC product, collagen IV. The results indicate that severe glomerular sclerosis can develop without major qualitative cellular or molecular changes in the mesangium.

Endothelin-1 impairs nitric oxide signaling in endothelial cells through a protein kinase Cdelta-dependent activation of STAT3 and decreased endothelial nitric oxide synthase expression

In an ovine model of persistent pulmonary hypertension of the newborn (PPHN), endothelin-1 (ET-1) expression is increased, while endothelial nitric oxide synthase (eNOS) expression is decreased. However, the molecular mechanisms by which ET-1 attenuates eNOS expression in endothelial cells are not completely understood. Thus, the goal of this study was to determine if the overexpression of ET-1 decreases eNOS expression in pulmonary arterial endothelial cells isolated from fetal lambs. To increase the ET-1 expression, cells were transfected with a plasmid coding for Prepro-ET-1, a precursor of ET-1. After overexpression of Prepro-ET-1, ET-1 levels in the culture medium were significantly increased (control = 805.3 +/- 69.8; Prepro-ET-1 overexpression = 1351 +/- 127.9). eNOS promoter activity, protein levels, and NO generation were all significantly decreased by the overexpression of Prepro-ET-1. The decrease in transcription correlated with increased activity of protein kinase Cdelta (PKCdelta) and STAT3. Further, DNA binding activity of STAT3 was also increased by Prepro-ET-1 overexpression. The increase in STAT3 activity and decrease in eNOS promoter activity were inhibited by the overexpression of dominant negative mutants of PKCdelta or STAT3. Further, a 2 bp mutation in the STAT3 binding site in the eNOS promoter inhibited STAT3 binding and led to enhanced promoter activity in the presence of Prepro-ET-1 overexpression. In conclusion, ET-1 secretion is increased by Prepro-ET-1 overexpression. This results in activation of PKCdelta, which phosphorylates STAT3, increasing its binding to the eNOS promoter. This in turn decreases eNOS promoter activity, protein levels, and NO production. Thus, ET-1 can reduce eNOS expression and NO generation in fetal pulmonary artery endothelial cells through PKCdelta-mediated activation of STAT3.

Role of aldose reductase in TGF-beta1-induced fibronectin synthesis in human mesangial cells

Accumulation of glomerular extracellular matrix (ECM) may result in glomerulosclerosis. Several lines of evidence indicate a key role for transforming growth factor-beta1 (TGF-beta1) in glomerular ECM synthesis and degradation, such as fibronectin (FN). Aldose reductase (AR) was proven to be one of the TGF-beta1 responsive genes in cultured rat mesangial cells using the SSH-PCR method and there were positive correlation between the AR and TGF-beta1 in our previous studies. So we assumed that AR could regulate FN synthesis. In this study, we explored the role of AR in FN production and possible mechanism involved. The expression of AR, FN and c-Jun proteins were analyzed by Western blot and the activity of activator protein-1 (AP-1) was assessed by electrophoretic mobility shift assay (EMSA). Our results showed that AR could mediate the TGF-beta1-induced FN production, which may associate with AP-1 activation.

Amelioration of hypoperfusion after traumatic brain injury by in vivo endothelin-1 knockout

Endothelin 1 (ET-1) is one of the most powerful vasoconstrictors in the brain. Its expression is upregulated after traumatic brain injury (TBI) and is a major factor in the ensuing hypoperfusion. Attenuation of ET-1 effects has been mainly achieved by blockade of its receptors. The result of a direct blockade of ET-1 mRNA synthesis is not known. We used the Marmarou's model to inflict injury to male Sprague-Dawley rats injected with antisense ET-1 oligodeoxynucleotides (ODNs) before injury. Laser Doppler flowmetry in noninjured rats (2 groups, i.e., untreated and animals that received cODNs) revealed a constant cerebral blood flow of approximately 14 mL.min-1.100 g-1, whereas the values from injured animals pretreated with control ODNs (cODNs) or from animals subjected to TBI alone were approximately 8.0 mL.min-1.100 g-1 during the 18-48 h time period post-TBI. After antisense ET-1 ODNs pretreatment, however, cerebral blood flow in injured animals was approximately 17 mL.min-1.100 g-1 during the 6-48 h time period. Antisense ET-1 ODNs-treated animals also had 19%-29% larger microvessel cross-sectional area and approximately one-third less ET-1 immunoreactivity in the 50-75% range after injury than did cODNs-treated animals after TBI. The results indicate that this direct in vivo approach is an effective therapeutic intervention for the restoration of cerebral blood flow after TBI.

Advanced oxidation protein products induce mesangial cell perturbation through PKC-dependent activation of NADPH oxidase

Mesangial deposition of extracellular matrix (ECM) is a hallmark of several glomerular diseases including diabetic nephropathy. Accumulation of advanced oxidation protein products (AOPPs) has been found in diabetes and chronic kidney disease and linked to mesangial ECM deposition and progressive glomerulosclerosis in these disorders. Although emerging evidence implicates AOPPs as the renal pathogenic factors, the underlying mechanisms have not been investigated. Here, using cultured rat mesangial cells (MCs) as a model, we identify AOPPs as the important mediators for activation of MC NADPH oxidase. Exposure of MCs to AOPPs, through membrane-associated phosphorylation of PKCα, induced rapid phosphorylation of cytosolic p47phox and its membrane translocation, enhanced interaction of p47phox with the membrane components p22phox and Nox4, and increased expression of these key regulatory subunits of NADPH oxidase. Challenge with AOPPs triggered cytosolic superoxide generation, resulting in upregulation of fibronectin and collagen IV genes and proteins and overexpression of TGF-β1 via a PKC-NADPH oxidase-dependent pathway, as these downstream events were blocked by the inhibitors of PKC, inhibitors of NADPH oxidase, or the cytosolic superoxide scavenger. These data provide new information for understanding the molecular basis underlying AOPP-induced MC perturbation and might be a central step toward development of new interventions.

RGC-32 mediates transforming growth factor-beta-induced epithelial-mesenchymal transition in human renal proximal tubular cells

Epithelial-mesenchymal transition (EMT) occurs in several disease states, including renal fibrosis and carcinogenesis. Myofibroblasts produced from EMT of renal tubular cells are responsible for the deposition of extracellular matrix components in a large portion of renal interstitial fibrosis. Transforming growth factor-beta (TGF-beta) plays an essential role in the EMT of renal tubular cells, but the molecular mechanism governing this process remains largely unknown. In this study, we found that RGC-32 (response gene to complement 32) is critical for TGF-beta-induced EMT of human renal proximal tubular cells (HPTCs). RGC-32 is not normally expressed in the HPTCs. However, TGF-beta stimulation markedly activates RGC-32 while inducing an EMT, as shown by the induction of smooth muscle alpha-actin (alpha-SMA) and extracellular matrix proteins collagen I and fibronectin, as well as the reduction of epithelial marker E-cadherin. TGF-beta function is mediated by several signaling pathways, but RGC-32 expression in HPTCs appears to be mainly regulated by Smad. Functionally, RGC-32 appears to mediate TGF-beta-induced EMT of HPTCs. Blockage of RGC-32 using short hairpin interfering RNA significantly inhibits TGF-beta induction of myofibroblast marker gene alpha-SMA while repressing the expression of E-cadherin. In contrast, overexpression of RGC-32 induces alpha-SMA expression while restoring E-cadherin. RGC-32 also inhibits the expression of another adherens junction protein, N-cadherin, suggesting that RGC-32 alone induces the phenotypic conversion of renal epithelial cells to myofibroblasts. Additional studies show that RGC-32 stimulates the production of extracellular matrix components fibronectin and collagen I. Mechanistically, RGC-32 induces EMT via the activation of other transcription factors such as Snail and Slug. RGC-32 knockdown inhibits the expression of Snail and Slug during TGF-beta-induced EMT. Taken together, our data demonstrate for the first time that RGC-32 plays a critical role in TGF-beta-induced EMT of renal tubular cells.

High glucose activates PKC-zeta and NADPH oxidase through autocrine TGF-beta1 signaling in mesangial cells

Conversion of normally quiescent mesangial cells into extracellular matrix-overproducing myofibroblasts in response to high ambient glucose and transforming growth factor (TGF)-beta(1) is central to the pathogenesis of diabetic nephropathy. Previously, we reported that mesangial cells respond to high glucose by generating reactive oxygen species (ROS) from NADPH oxidase dependent on protein kinase C (PKC) -zeta activation. We investigated the role of TGF-beta(1) in this action of high glucose on primary rat mesangial cells within 1-48 h. Both high glucose and exogenous TGF-beta(1) stimulated PKC-zeta kinase activity, as measured by an immune complex kinase assay and immunofluorescence confocal cellular imaging. In high glucose, Akt Ser473 phosphorylation appeared within 1 h and Smad2/3 nuclear translocation was prevented with neutralizing TGF-beta(1) antibodies. Neutralizing TGF-beta(1) antibodies, or a TGF-beta receptor kinase inhibitor (LY364947), or a phosphatidylinositol 3,4,5-trisphosphate (PI3) kinase inhibitor (wortmannin), prevented PKC-zeta activation by high glucose. TGF-beta(1) also stimulated cellular membrane translocation of PKC-alpha, -beta(1), -delta, and -epsilon, similar to high glucose. High glucose and TGF-beta(1) enhanced ROS generation by mesangial cell NADPH oxidase, as detected by 2,7-dichlorofluorescein immunofluorescence. This response was abrogated by neutralizing TGF-beta(1) antibodies, LY364947, or a specific PKC-zeta pseudosubstrate peptide inhibitor. Expression of constitutively active PKC-zeta in normal glucose caused upregulation of p22(phox), a likely mechanism of NADPH oxidase activation. We conclude that very early responses of mesangial cells to high glucose include autocrine TGF-beta(1) stimulation of PKC isozymes including PI3 kinase activation of PKC-zeta and consequent generation of ROS by NADPH oxidase.

Reduction of chronic allograft nephropathy by inhibition of extracellular signal-regulated kinase 1 and 2 signaling

Chronic allograft nephropathy (CAN), the most common cause of late kidney allograft failure, is not effectively prevented by immunosuppressive regimens. Activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) via MEK mediates actions of various growth factors, including transforming growth factor (TGF)-beta1, which plays a key role in CAN. Hence, we tested the therapeutic potential of MEK-ERK1/2 signaling disruption to prevent CAN. Kidneys from C57BL/6J (H-2(b)) mice were transplanted to bilaterally nephrectomized BALB/c (H-2(d)) mice. At 14 days after transplantation, the recipients were subjected to 28 days of treatment with the MEK inhibitor CI-1040. All six CI-1040-treated allografts survived, while two of seven grafts in the vehicle-treated group were lost. At the end of the experiment, the function and structure of grafts in the CI-1040-treated group were significantly preserved, as indicated by lower levels of serum creatinine or blood urea nitrogen than in the vehicle-treated group [30 +/- 6 vs. 94 +/- 39 microM creatinine (P = 0.0015) and 22 +/- 8 vs. 56 +/- 25 mM BUN (P = 0.0054)] and reduced CAN in the CI-1040-treated group compared with vehicle controls (CAN score = 4.2 vs. 10.3, P = 0.0119). The beneficial effects induced by CI-1040 were associated with reduction of ERK1/2 phosphorylation and TGFbeta1 levels in grafts. Also, CI-1040 potently suppressed not only TGFbeta biosynthesis in kidney cell cultures but also antiallograft immune responses in vitro and in vivo. Our data suggest that interference of MEK-ERK1/2 signaling with a pharmacological agent (e.g., CI-1040) has therapeutic potential to prevent CAN in kidney transplantation.

Nitric oxide and cardiovascular and renal effects

Nitric oxide (NO) has multiple protective effects for regulating the cardiovascular and renal systems. The major functions include endothelium-dependent relaxation, anti-inflammatory effects, as well as antihypertrophic and antithrombotic activities. Many of the activities mediated by NO are systematically antagonized by angiotensin-II (Ang II), a vasconstrictor peptide. Studies described in the review below have demonstrated that the balance between NO and Ang II activities rather than the absolute concentration of each molecule determines their effects on the physiology and pathophysiology of the cardiovascular and renal systems. NO donors have been used for years as therapeutic agents for a range of cardiovascular conditions including angina, myocardial infarction and for the reduction of arterial stiffness. An understanding of the mechanisms underlying the effects of these medications will enable the development of novel therapies to balance the effects of NO in the cardiovascular system.

Roles of PINCH-2 in regulation of glomerular cell shape change and fibronectin matrix deposition

The PINCH-1-integrin-linked kinase (ILK)-alpha-parvin (PIP) complex plays important roles in the regulation of glomerular cell behavior, including podocyte shape change, apoptosis, and mesangial fibronectin matrix deposition. In this study, we show that PINCH-2, a protein that is structurally related to PINCH-1 but encoded by a different gene, is coexpressed with PINCH-1 in podocytes. Treatment of podocytes with transforming growth factor (TGF)-beta1 elevated the level of PINCH-2, resulting in increased association of PINCH-2 with ILK and alpha-parvin and concomitant displacement of PINCH-1 from the PIP complex. To gain insights into the functional consequences of elevated PINCH-2 expression, we overexpressed PINCH-2 in podocytes by infection with an adenovirus encoding PINCH-2. Overexpression of PINCH-2 resulted in displacement of PINCH-1 from the PIP complex and compromised podocyte spreading. The PINCH-2-mediated displacement of PINCH-1, however, did not prompt apoptosis. Interestingly, the effect of PINCH-2 on podocyte spreading depends on differentiation status, as overexpression of PINCH-2 in podocytes that were not fully differentiated did not alter cell spreading. Finally, we show that overexpression of PINCH-2 in mesangial cells resulted in displacement of PINCH-1 from the PIP complex but impaired neither mesangial cell spreading nor fibronectin matrix deposition. These studies suggest that PINCH-2 can substitute for PINCH-1 in at least certain processes in glomerular cells (e.g., podocyte survival signaling and mesangial fibronectin matrix deposition), albeit that an aberrantly high level of PINCH-2 may contribute to TGF-beta1-induced alteration in podocyte shape modulation.

TGFbeta-induced RhoA activation and fibronectin production in mesangial cells require caveolae

Glomerular sclerosis of diverse etiologies is characterized by mesangial matrix accumulation, with transforming growth factor-beta (TGFbeta) an important pathogenic factor. The GTPase RhoA mediates TGFbeta-induced matrix accumulation in some settings. Here we study the role of the membrane microdomain caveolae in TGFbeta-induced RhoA activation and fibronectin upregulation in mesangial cells (MC). In primary rat MC, TGFbeta1 time dependently increased RhoA and downstream Rho kinase activation. Rho pathway inhibition blocked TGFbeta1-induced upregulation of fibronectin transcript and protein. TGFbeta1-induced RhoA activation was prevented by disrupting caveolae with cholesterol depletion and rescued by cholesterol repletion. Compared with wild types, RhoA/Rho kinase activation was absent in MC lacking caveolae. Reexpression of caveolin-1 (and caveolae) restored these responses. Phosphorylation of caveolin-1 on Y14, effected by Src kinases, has been implicated in signaling responses. Overexpression of nonphosphorylatable caveolin-1 Y14A prevented TGFbeta1-induced RhoA activation. TGFbeta1 also activated Src, and its inhibition blocked RhoA activation. Furthermore, TGFbeta1 led to association of RhoA and caveolin-1. This was prevented by Src or TGFbeta receptor I inhibition, and by caveolin-1 Y14A overexpression. Last, fibronectin upregulation by TGFbeta1 was blocked by Src inhibition, not seen in caveolin-1 knockout MC, and restored by caveolin-1 reexpression in the latter. TGFbeta1-induced collagen I accumulation also required caveolae. TGFbeta1-mediated Smad2/3 activation, however, did not require caveolae. We conclude that RhoA/Rho kinase mediates TGFbeta-induced fibronectin upregulation. This requires caveolae and caveolin-1 interaction with RhoA. Interference with caveolin/caveolae or RhoA signaling thus represents a potential target for the treatment of fibrotic renal disease.

Smad ubiquitination regulatory factor-2 in the fibrotic kidney: regulation, target specificity, and functional implication

Smad ubiquitination regulatory factor-2 (Smurf2) is an E3 ubiqutin ligase that plays a pivotal role in regulating TGF-beta signaling via selectively targeting key components of the Smad pathway for degradation. In this study, we have investigated the regulation of Smurf2 expression, its target specificity, and the functional implication of its induction in the fibrotic kidney. Immunohistochemical staining revealed that Smurf2 was upregulated specifically in renal tubules of kidney biopsies from patients with various nephropathies. In vitro, Smurf2 mRNA and protein were induced in human proximal tubular epithelial cells (HKC-8) upon TGF-beta1 stimulation. Ectopic expression of Smurf2 was sufficient to reduce the steady-state levels of Smad2, but not Smad1, Smad3, Smad4, and Smad7, in HKC-8 cells. Interestingly, Smurf2 was also able to downregulate the Smad transcriptional corepressors Ski, SnoN, and TG-interacting factor. Inhibition of the proteasomal pathway prevented Smurf2-mediated downregulation of Smad2 and Smad corepressors. Functionally, overexpression of Smurf2 enhanced the transcription of the TGF-beta-responsive promoter and augmented TGF-beta1-mediated E-cadherin suppression, as well as fibronectin and type I collagen induction in HKC-8 cells. These results indicate that Smurf2 specifically targets both positive and negative Smad regulators for destruction in tubular epithelial cells, thereby providing a complex fine-tuning of TGF-beta signaling. It appears that dysregulation of Smurf2 could contribute to an aberrant TGF-beta/Smad signaling in the pathogenesis of kidney fibrosis.

Sex and the renin-angiotensin system: inequality between the sexes in response to RAS stimulation and inhibition

The purpose of this review is to examine sex differences in response to stimulation and inhibition of the renin-angiotensin system (RAS). The RAS plays a prominent role in the development of chronic renal disease, and there are known sex differences not only in the expression level of components of the RAS but also in how males and females respond to perturbations of the RAS. In men, renal injury increases in parallel with increased activation of the RAS, while in women, increases in ANG II do not necessarily translate into increases in renal injury. Moreover, both epidemiological and experimental studies have noted sex differences in the therapeutic benefits following angiotensin-converting enzyme inhibitor and angiotensin receptor blocker treatment. Despite these differences, RAS inhibitors are the most commonly prescribed drugs for the treatment of chronic renal disease, irrespective of sex. This review will examine how males and females respond to stimulation and inhibition of the RAS, with a focus on renal disease.

Transforming growth factor-beta regulates house dust mite-induced allergic airway inflammation but not airway remodeling

RATIONALE

It is now believed that both chronic airway inflammation and remodeling contribute significantly to airway dysfunction and clinical symptoms in allergic asthma. Transforming growth factor (TGF)-beta is a powerful regulator of both the tissue repair and inflammatory responses, and numerous experimental and clinical studies suggest that it may play an integral role in the pathogenesis of asthma.

OBJECTIVES

We investigated the role of TGF-beta in the regulation of allergic airway inflammation and remodeling using a mouse model of house dust mite (HDM)-induced chronic allergic airway disease.

METHODS

We have previously shown that intranasal administration of an HDM extract (5 d/wk for 5 wk) elicits robust Th2-polarized airway inflammation and remodeling that is associated with increased airway hyperreactivity. Here, Balb/c mice were similarly exposed to HDM and concurrently treated with a pan-specific TGF-beta neutralizing antibody.

MEASUREMENTS AND MAIN RESULTS

We observed that anti-TGF-beta treatment in the context of either continuous or intermittent HDM exposure had no effect on the development of HDM-induced airway remodeling. To further confirm these findings, we also subjected SMAD3 knockout mice to 5 weeks of HDM and observed that knockout mice developed airway remodeling to the same extent as HDM-exposed littermate controls. Notably, TGF-beta neutralization exacerbated the eosinophilic infiltrate and led to increased airway hyperreactivity.

CONCLUSIONS

Collectively, these data suggest that TGF-beta regulates HDM-induced chronic airway inflammation but not remodeling, and furthermore, caution against the use of therapeutic strategies aimed at interfering with TGF-beta activity in the treatment of this disease.

ACE inhibitor reduces growth factor receptor expression and signaling but also albuminuria through B2-kinin glomerular receptor activation in diabetic rats

Diabetic nephropathy (DN) is associated with increased oxidative stress, overexpression and activation of growth factor receptors, including those for transforming growth factor-β1 (TGF-β-RII), platelet-derived growth factor (PDGF-R), and insulin-like growth factor (IGF1-R). These pathways are believed to represent pathophysiological determinants of DN. Beyond perfect glycemic control, angiotensin-converting enzyme inhibitors (ACEI) are the most efficient treatment to delay glomerulosclerosis. Since their mechanisms of action remain uncertain, we investigated the effect of ACEI on the glomerular expression of these growth factor pathways in a model of streptozotocin-induced diabetes in rats. The early phase of diabetes was found to be associated with an increase in glomerular expression of IGF1-R, PDGF-R, and TGF-β-RII and activation of IRS1, Erk 1/2, and Smad 2/3. These changes were significantly reduced by ACEI treatment. Furthermore, ACEI stimulated glutathione peroxidase activity, suggesting a protective role against oxidative stress. ACEI decreased ANG II production but also increased bradykinin bioavailability by reducing its degradation. Thus the involvement of the bradykinin pathway was investigated using coadministration of HOE-140, a highly specific nonpeptidic B2-kinin receptor antagonist. Almost all the previously described effects of ACEI were abolished by HOE-140, as was the increase in glutathione peroxidase activity. Moreover, the well-established ability of ACEI to reduce albuminuria was also prevented by HOE-140. Taken together, these data demonstrate that, in the early phase of diabetes, ACEI reverse glomerular overexpression and activation of some critical growth factor pathways and increase protection against oxidative stress and that these effects involve B2-kinin receptor activation.

The role of tubular epithelial-mesenchymal transition in progressive kidney disease

The accumulation of interstitial matrix represents the final common pathway of most forms of kidney disease. Much of this matrix is synthesized by interstitial myofibroblasts, recruited from resident fibroblasts and circulating precursors. In addition, a significant proportion is derived from epithelial-mesenchymal transition (EMT) of tubuloepithelial cells. The importance of EMT has been demonstrated in experimental models, where blockade of EMT attenuates renal fibrosis. Although a number of factors may initiate EMT in the kidney, the most potent is transforming growth factor-beta1 (TGF-beta1). Moreover, many other prosclerotic factors have effects on EMT indirectly, via induction of TGF-beta1. Signaling events in this pathway include activation of Smad/integrin-linked kinase (ILK) and connective tissue growth factor (CTGF). Basement membrane integrity is also a key regulator of EMT. In particular, overexpression of matrix metalloproteinase-2 has a key role in the initiation of EMT, membrane dissolution, and the interstitial transit of transformed mesenchymal cells. Endogenous inhibitors of EMT also play an important counterregulatory role both to prevent EMT and stimulate uncommitted cells to regain their tubular phenotype (mesenchymal-epithelial transition). Such inhibitors represent a potential therapeutic approach, offering a mechanism to slow or even redress established renal fibrosis.

Effect of adenosine in extracellular matrix synthesis in human and rat mesangial cells

Adenosine (ADO) is an intermediary metabolite of adenosine trisphosphate degradation and a vasoactive mediator. We showed previously that ADO induces contraction and proliferation in rat mesangial cells by a mechanism involving A1 and A2 receptors. The studies concerning the effect of ADO on extracellular matrix (ECM) accumulation in mesangial cells are scarce. The purpose of our study was to evaluate the effect of ADO and the effect of the selective stimulation of A1 and A2 ADO receptors on the expression of ECM components fibronectin and collagen type I, in human and rat renal mesangial cells. Cultured human and rat renal mesangial cells were subjected to selective stimulation of A1 and A2 ADO receptors for 24 and 48 h. Fibronectin and collagen type I expression was evaluated by Western blot; total collagen synthesis was measured by [3H]-proline incorporation into collagen proteins. ADO, A1 and A2 receptor stimulation induce increases in fibronectin expression in rat mesangial cells, and A1 receptor stimulation partially inhibits fibronectin expression in serum-stimulated rat mesangial cells, without any effect in human mesangial cells. A2 receptor stimulation reduces collagen type I expression in serum-stimulated mesangial cells. Neither ADO nor A1 or A2 receptor stimulation induce significant changes in total collagen synthesis. These data suggest that ADO is not a major regulator of ECM synthesis in rat and human mesangial cells.

Induction of IL-13 triggers TGF-beta1-dependent tissue fibrosis in chronic 2,4,6-trinitrobenzene sulfonic acid colitis

To investigate the immunopathogenesis of inflammation-associated fibrosis, we analyzed the chronic colitis and late-developing fibrosis occurring in BALB/c mice administered weekly doses of intrarectal 2,4,6-trinitrobenzene sulfonic acid. We showed first in this model that an initial Th1 response involving IL-12p70 and IFN-gamma subsides after 3 wk to be supplanted by an IL-23/IL-25 response beginning after 4-5 wk. This evolution is followed by gradually increasing production of IL-17 and cytokines ordinarily seen in a Th2 response, particularly IL-13, which reaches a plateau at 8-9 wk. In vitro stimulation studies suggest that this IL-13 production is dependent on IL-23 and IL-25, but not on IL-12p70. We then show that IL-13 production results in the induction of an IL-13R formerly thought to function only as a decoy receptor, IL-13Ralpha(2), and this receptor is critical to the production of TGF-beta(1) and the onset of fibrosis. Thus, if IL-13 signaling through this receptor is blocked by administration of soluble IL-13Ralpha(2)-Fc, or by administration of IL-13Ralpha(2)-specific small interfering RNA, TGF-beta(1) is not produced and fibrosis does not occur. These studies show that in chronic 2,4,6-trinitrobenzene sulfonic acid colitis, fibrosis is dependent on the development of an IL-13 response that acts through a novel cell surface-expressed IL-13R to induce TGF-beta(1). A similar mechanism may obtain in certain forms of human inflammatory bowel disease.

Specificity protein 1 and Smad-dependent regulation of human heme oxygenase-1 gene by transforming growth factor-beta1 in renal epithelial cells

Excess transforming growth factor-beta1 (TGF-beta1) in the kidney leads to increased cell proliferation and deposition of extracellular matrix, resulting in progressive kidney fibrosis. TGF-beta1, however, stabilizes and attenuates tissue injury through the activation of cytoprotective proteins, including heme oxygenase-1 (HO-1). HO-1 catabolizes pro-oxidant heme into substances with anti-oxidant, anti-apoptotic, anti-fibrogenic, vasodilatory and immune modulatory properties. Little is known regarding the molecular regulation of human HO-1 induction by TGF-beta1 except that it is dependent on de novo RNA synthesis and requires a group of structurally related proteins called Smads. It is not known whether other DNA binding proteins are required to initiate transcription of HO-1 and, furthermore, the promoter region(s) involved in TGF-beta1-mediated induction of HO-1 has not been identified. The purpose of this study was to further delineate the molecular regulation of HO-1 by TGF-beta1 in human renal proximal tubular cells. Actinomycin D and nuclear run-on studies demonstrate that TGF-beta1 augments HO-1 expression by increased gene transcription and does not involve increased mRNA stability. Using transient transfection, mithramycin A, small interfering RNA, electrophoretic mobility shift assays, and decoy oligonucleotide experiments, a TGF-beta1-responsive region is identified between 9.1 and 9.4 kb of the human HO-1 promoter. This approximately 280-bp TGF-beta1-responsive region contains a putative Smad binding element and specificity protein 1 binding sites, both of which are required for human HO-1 induction by TGF-beta1.

TNF-alpha, but not IFN-gamma, regulates CCN2 (CTGF), collagen type I, and proliferation in mesangial cells: possible roles in the progression of renal fibrosis

Connective tissue growth factor (CCN2) is a profibrotic factor acting downstream and independently of TGF-beta to mediate renal fibrosis. Although inflammation is often involved in the initiation and/or progression of fibrosis, the role of inflammatory cytokines in regulation of glomerular CCN2 expression, cellular proliferation, and extracellular matrix accumulation is unknown. We studied two such cytokines, TNF-alpha and IFN-gamma, for their effects on cultured mesangial cells in the presence or absence of TGF-beta, as a model for progressive renal fibrosis. Short-term treatment with TNF-alpha, like TGF-beta, significantly increased secreted CCN2 per cell, but unlike TGF-beta inhibited cellular replication. TNF-alpha combined with TGF-beta further increased CCN2 secretion and mRNA levels and reduced proliferation. Surprisingly, however, TNF-alpha treatment decreased baseline collagen type I protein and mRNA levels and largely blocked their stimulation by TGF-beta. Long-term treatment with TGF-beta or TNF-alpha alone no longer increased CCN2 protein levels. However, the combination synergistically increased CCN2. IFN-gamma had no effect on either CCN2 or collagen activity and produced a mild inhibition of TGF-beta-induced collagen only at a high concentration (500 U/ml). In summary, we report a strong positive regulatory role for TNF-alpha, but not IFN-gamma, in CCN2 production and secretion, including that driven by TGF-beta. The stimulation of CCN2 release by TNF-alpha, unlike TGF-beta, is independent of cellular proliferation and not linked to increased collagen type I accumulation. This suggests that the paradigm of TGF-beta-driven CCN2 with subsequent collagen production may be overridden by an as yet undefined inhibitory mechanism acting either directly or indirectly on matrix metabolism.

TGF-beta-activated kinase 1 and TAK1-binding protein 1 cooperate to mediate TGF-beta1-induced MKK3-p38 MAPK activation and stimulation of type I collagen

We have previously demonstrated that transforming growth factor-beta(1) (TGF-beta(1)) rapidly activates the mitogen-activated protein kinase kinase 3 (MKK3)-p38 MAPK signaling cascade, leading to the induction of type I collagen synthesis in mouse glomerular mesangial cells (Wang L, Ma R, Flavell RA, Choi ME. J Biol Chem 277: 47257-47262, 2002). In the present study, we investigated the functional role of upstream TGF-beta-activated kinase 1 (TAK1) and TAK1-binding protein 1 (TAB1) in the TGF-beta(1) signaling cascade. Rapid activation of endogenous TAK1 activity by TGF-beta(1) was observed in mouse mesangial cells. Transient overexpression of TAK1 with TAB1 enhanced the activation of MKK3 and p38 MAPK with or without TGF-beta(1) stimulation, whereas a dominant-negative mutant of TAK1 (TAK1DN) suppressed TGF-beta(1)-induced activation of MKK3 and p38 MAPK. Moreover, constitutive expression of TAK1DN reduced steady-state protein levels of MKK3 and p38 MAPK as well as MKK3 phosphorylation. Increased p38alpha MAPK activity by ectopic expression of either TAB1 or wild-type p38alpha MAPK resulted in enhanced TGF-beta(1)-induced type I collagen expression. In contrast, constitutive expression of TAK1DN inhibited collagen induction. Taken together, our data indicate that TAK1 and TAB1 play a pivotal role as upstream signal transducers activating the MKK3-p38 MAPK signaling cascade that leads to the induction of type I collagen expression by TGF-beta(1). In addition, our findings also suggest that TAK1 has a novel function in regulation of the steady-state protein levels of MKK3 and p38 MAPK.

Could Streptococcal Erythrogenic Toxin B Induce Inflammation prior to the Development of Immune Complex Deposits in Poststreptococcal Glomerulonephritis?

Acute poststreptococcal glomerulonephritis (APSGN) is a consequence of the immune response to streptococcal antigens with further in situ antigen-antibody interaction and deposition of circulating immune complexes, resulting in the activation of complement and the inflammatory process. These events are related to a previous antibody response. However, early renal events, when circulating streptococcal antigens bind to the kidney during streptococcal infection, remain unknown. Cationic streptococcal erythrogenic toxin type B (ETB) and its precursor (ETBP) are largely produced by nephritogenic streptococci and have high affinity for anionic glomerular structures. Renal deposition of ETB/ETBP makes conceivable a possible interaction between these streptococcal proteins with intrinsic glomerular cells or infiltrating leukocytes. Since ETB/ETBP are chemotactic for leukocytes and capable of inducing proliferation, cytokine and chemokine production, expression of adhesion molecules and apoptosis in renal cells and leukocytes, the early presence of these proteins could be a relevant event before and during antigen-antibody interaction takes place in renal tissues.

TGF-beta-regulated collagen type I accumulation: role of Src-based signals

Transforming growth factor-beta (TGF-beta) stimulates myofibroblast transdifferentiation, leading to type I collagen accumulation and fibrosis. We investigated the function of Src in TGF-beta-induced collagen I accumulation. In human mesangial cells, PTyr416 Src (activated Src) was 3.3-fold higher in TGF-beta-treated cells than in controls. Src activation by TGF-beta was blocked by rottlerin and by a dominant negative mutant of protein kinase Cdelta (PKCdelta), showing that TGF-beta activates Src by a PKCdelta-based mechanism. Pharmacological inhibitors and a dominant negative Src mutant prevented the increase in collagen type I secretion in cells exposed to TGF-beta. Similarly, on-target Src small interference RNA (siRNA) prevented type I collagen secretion in response to TGF-beta, but off-target siRNA complexes had no effect. It is well established in mesangial cells that upregulation of type I collagen by TGF-beta requires extracellular signal-regulated kinase 1/2 (ERK1/2), and we found that activation of ERK1/2 by TGF-beta requires Src. In conclusion, these results suggest that stimulation of collagen type I secretion by TGF-beta requires a PKCdelta-Src-ERK1/2 signaling motif.

cAMP inhibits transforming growth factor-beta-stimulated collagen synthesis via inhibition of extracellular signal-regulated kinase 1/2 and Smad signaling in cardiac fibroblasts

Cardiac fibroblasts produce and degrade extracellular matrix and are critical in regulating cardiac remodeling and hypertrophy. Cytokines such as transforming growth factor-beta (TGF-beta) play a fundamental role in the development of tissue fibrosis by stimulating matrix deposition and other profibrotic responses, but less is known about pathways that might inhibit fibrosis. Increased cAMP formation inhibits myofibroblast differentiation and collagen production by cardiac fibroblasts, but the mechanism of this inhibition is not known. We sought to characterize the signaling pathways by which cAMP-elevating agents alter collagen expression and myofibroblast differentiation. Treatment with 10 microM forskolin or isoproterenol increased cAMP production and cAMP response element binding protein (CREB) phosphorylation in cardiac fibroblasts and inhibited serum- or TGF-beta-stimulated collagen synthesis by 37% or more. These same cAMP-elevating agents blunted TGF-beta-stimulated expression of collagen I, collagen III, and alpha-smooth muscle actin. Forskolin or isoproterenol treatment blocked the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) induced by TGF-beta despite the fact that these cAMP-elevating agents stimulated ERK1/2 activation on their own. cAMP-elevating agents also attenuated the activation of c-Jun NH(2)-terminal kinase and reduced binding of the transcriptional coactivator CREB-binding protein 1 to transcriptional complexes containing Smad2, Smad3, and Smad4. Pharmacological inhibition of ERK completely blocked TGF-beta-stimulated collagen gene expression, but expression of an active mutant of MEK was additive with TGF-beta treatment. Thus, cAMP-elevating agents inhibit the profibrotic effects of TGF-beta in cardiac fibroblasts largely through inhibiting ERK1/2 phosphorylation but also by reducing Smad-mediated recruitment of transcriptional coactivators.

RACK1 Binds to Smad3 to Modulate Transforming Growth Factor-β1-stimulated α2(I) Collagen Transcription in Renal Tubular Epithelial Cells

Although it is clear that transforming growth factor-beta1 (TGF-beta1) is critical for renal fibrogenesis, the complexity of the involved mechanisms is increasingly apparent. TGF-beta1 stimulates phosphorylation of Smad2/3 and activates other signaling molecules as well. The molecular link between these other kinases and Smads is not known. We sought new binding partners for Smad3 in renal cells and identified receptor for activated protein kinase C 1 (RACK1) as a novel binding partner of Smad3. The linker region of Smad3 and the tryptophan-aspartic acid repeat 6 and 7 of RACK1 are sufficient for the association. RACK1 also interacts with Smad3 in the human kidney epithelial cell line, HKC. Silencing RACK1 increases transcriptional activity of TGF-beta1-responsive promoter sequences of the Smad binding element (SBE), p3TP-Lux, and alpha2(I) collagen. Conversely, overexpressed RACK1 negatively modulates alpha2(I) collagen transcriptional activity in TGF-beta1-stimulated cells. RACK1 did not affect phosphorylation of Smad3 at the C terminus or in the linker region. However, RACK1 reduced direct binding of Smad3 to the SBE motif. Mutating a RACK1 tyrosine at residue 246, but not at 228, decreased the inhibitory effect of RACK1 on both alpha2(I) collagen promoter activity and Smad binding to SBE induced by TGF-beta1. These results suggest that RACK1 modulates transcription of alpha2(I) collagen by TGF-beta1 through interference with Smad3 binding to the gene promoter.

Elevated endothelin-1 levels impair nitric oxide homeostasis through a PKC-dependent pathway

BACKGROUND

Endothelin-1 (ET-1) plays an important role in the maintenance of vascular tone and pathological states such as ischemia/reperfusion (I/R) injury, coronary vasospasm, and cardiac allograft vasculopathy. We assessed the effects of elevated ET-1 levels as seen after I/R to determine if ET-1 modulates nitric oxide (NO) production via the translocation of specific protein kinase C (PKC) isoforms.

METHODS AND RESULTS

Human saphenous vein endothelial cells (HSVECs) (n=8) were incubated with ET-1 or phosphate-buffered saline (PBS) for 24 hours. NO production was determined in the supernatant by measuring nitrate/nitrite levels. Protein expression of endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), caveolin-1 and PKC were determined. Lastly, PKC translocation and activity were assessed after exposure to the drug of interest. HSVECs exposed to ET-1 displayed decreased NO production. PKC inhibition reduced NO production, whereas PKC activation increased production. NO production was maintained when HSVECs exposed to ET-1 were treated with the PKC agonist, PMA. eNOS protein expression was reduced after ET-1 treatment. PKC inhibition also downregulated eNOS protein expression, whereas PMA upregulated expression. ET-1 exposure led to a significant increase in PKCdelta and PKCalpha translocation compared with control, whereas translocation of PKClambda was inhibited. ET-1 exposure significantly reduced overall PKC activity compared with control.

CONCLUSIONS

Our study demonstrates that high levels of ET-1 impair endothelial NO production via an isoform-specific PKC-mediated inhibition of eNOS expression. ET-1 antagonism with bosentan stimulates translocation of PKClambda and leads to increased PKC activity and NO production. ET-1 antagonism may provide a novel therapeutic strategy to improve vascular homeostasis.