Mechanisms by which bradykinin promotes fibrosis in vascular smooth muscle cells: role of TGF-beta and MAPK

Bradykinin attenuates endothelial-mesenchymal transition following cardiac ischemia-reperfusion injury

AIMS

Endothelial-mesenchymal transition (EndMT) is a crucial pathological process contributing to cardiac fibrosis. Bradykinin has been found to protect the heart against fibrosis. Whether bradykinin regulates EndMT has not been determined.

MATERIALS AND METHODS

Rats were subjected to ligation of the left anterior descending coronary artery for 1 h and subsequent reperfusion to induce cardiac ischemia-reperfusion (IR) injury. Bradykinin (0.5 μg/h) was infused by an osmotic pump implanted subcutaneously at the onset of reperfusion. Fourteen days later, the functional, histological, and molecular analyses were performed to investigate the changes in cardiac fibrosis and EndMT. Human coronary artery endothelial cells were utilized to determine the molecular mechanisms in vitro.

RESULTS

Bradykinin treatment improved cardiac function and decreased fibrosis following cardiac IR injury, accompanied by ameliorated EndMT and increased nitric oxide (NO) production. In vitro experiments found that bradykinin mitigated transforming growth factor β1 (TGFβ1)-induced EndMT. Significantly, the bradykinin B2 receptor antagonist or endothelial nitric oxide synthase inhibitor abolished the effects of bradykinin on EndMT inhibition, indicating that the bradykinin B2 receptor and NO might mediate the effects of bradykinin on EndMT inhibition.

CONCLUSION

Bradykinin plays an essential role in the process of cardiac fibrosis. Bradykinin preserves the cellular signature of endothelial cells, preventing them from EndMT following cardiac IR injury, possibly mediated by bradykinin B2 receptor activation and NO production.

TGFβ1 Regulates Cellular Composition of In Vitro Cardiac Perivascular Niche Based on Cardiospheres

The cardiac perivascular niche is a cellular microenvironment of a blood vessel. The principles of niche regulation are still poorly understood. We studied the effect of TGFβ1 on cells forming the cardiac perivascular niche using 3D cell culture (cardiospheres). Cardiospheres contained progenitor (c-Kit), endothelial (CD31), and mural (αSMA) cells, basement membrane proteins (laminin) and extracellular matrix proteins (collagen I, fibronectin). TGFβ1 treatment decreased the length of CD31+ microvasculature, VE cadherin protein level, and proportion of NG2+ cells, and increased proportion of αSMA+ cells and transgelin/SM22α protein level. We supposed that this effect is related to the stabilizing function of TGFβ1 on vascular cells: decreased endothelial cell proliferation, as shown for HUVEC, and activation of mural cell differentiation.

Role of platelet factor 4 in arteriovenous fistula maturation failure: What do we know so far?

The rate of arteriovenous fistula (AVF) maturation failure remains unacceptably high despite continuous efforts on technique improvement and careful pre-surgery planning. In fact, half of all newly created AVFs are unable to be used for hemodialysis (HD) without a salvage procedure. While vascular stenosis in the venous limb of the access is the culprit, the underlying factors leading to vascular narrowing and AVF maturation failure are yet to be determined. We have recently demonstrated that AVF non-maturation is associated with post-operative medial fibrosis and fibrotic stenosis, and post-operative intimal hyperplasia (IH) exacerbates the situation. Multiple pathological processes and signaling pathways are underlying the stenotic remodeling of the AVF. Our group has recently indicated that a pro-inflammatory cytokine platelet factor 4 (PF4/CXCL4) is upregulated in veins that fail to mature after AVF creation. Platelet factor 4 is a fibrosis marker and can be detected in vascular stenosis tissue, suggesting that it may contribute to AVF maturation failure through stimulation of fibrosis and development of fibrotic stenosis. Here, we present an overview of the how PF4-mediated fibrosis determines AVF maturation failure.

Molecular Pathogenesis and the Possible Role of Mitochondrial Heteroplasmy in Thoracic Aortic Aneurysm

Thoracic aortic aneurysm (TAA) is a life-threatening condition associated with high mortality, in which the aortic wall is deformed due to congenital or age-associated pathological changes. The mechanisms of TAA development remain to be studied in detail, and are the subject of active research. In this review, we describe the morphological changes of the aortic wall in TAA. We outline the genetic disorders associated with aortic enlargement and discuss the potential role of mitochondrial pathology, in particular mitochondrial DNA heteroplasmy, in the disease pathogenesis.

Dynamic Crosstalk between Vascular Smooth Muscle Cells and the Aged Extracellular Matrix

Vascular aging is accompanied by the fragmentation of elastic fibers and collagen deposition, leading to reduced distensibility and increased vascular stiffness. A rigid artery facilitates elastin to degradation by MMPs, exposing vascular cells to greater mechanical stress and triggering signaling mechanisms that only exacerbate aging, creating a self-sustaining inflammatory environment that also promotes vascular calcification. In this review, we highlight the role of crosstalk between smooth muscle cells and the vascular extracellular matrix (ECM) and how aging promotes smooth muscle cell phenotypes that ultimately lead to mechanical impairment of aging arteries. Understanding the underlying mechanisms and the role of associated changes in ECM during aging may contribute to new approaches to prevent or delay arterial aging and the onset of cardiovascular diseases.

Transforming growth factor-beta and liver injury in an arginine vasopressin-induced pregnant rat model

Objective

Approximately 30% of preeclamptic pregnancies exhibit abnormal liver function tests. We assessed liver injury-associated enzyme levels and circulating transforming growth factor beta (TGF-β) levels in an arginine vasopressin (AVP)-induced pregnant Sprague-Dawley rat model.

Methods

Pregnant and non-pregnant Sprague-Dawley rats (n=24) received AVP (150 ng/hr) subcutaneously via mini-osmotic pumps for 18 days. Blood pressure was measured, urine samples were collected, and all animals were euthanized via isoflurane. Blood was collected to measure circulating levels of TGF-β1-3 isomers and liver injury enzymes in pregnant AVP (PAVP), pregnant saline (PS), non-pregnant AVP (NAVP), and non-pregnant saline (NS) rats.

Results

The PAVP group showed significantly higher systolic and diastolic blood pressure than both saline-treated groups. The weight per pup was significantly lower in the AVP-treated group than in the saline group (p<0.05). Circulating TGF-β1-3 isomer levels were significantly higher in the PAVP rats than in the NS rats. However, similar TGF-β1 and TGF-β3 levels were noted in the PS and PAVP rats, while TGF-β2 levels were significantly higher in the PAVP rats. Circulating liver-type arginase-1 and 5'-nucleotidase levels were higher in the PAVP rats than in the saline group.

Conclusion

This is the first study to demonstrate higher levels of TGF-β2, arginase, and 5'-nucleotidase activity in PAVP than in PS rats. AVP may cause vasoconstriction and increase peripheral resistance and blood pressure, thereby elevating TGF-β and inducing the preeclampsia-associated inflammatory response. Future studies should explore the mechanisms through which AVP dysregulates liver injury enzymes and TGF-β in pregnant rats.

Vascular Cells Proteome Associated with Bradykinin and Leptin Inflammation and Oxidative Stress Signals

Among the primary contributors to cardiovascular diseases are inflammation and oxidative imbalance within the vessel walls as well as the fibrosis of rat aortic smooth muscle cell (RASMC). Bradykinin (BK) and leptin are inflammatory modulators that are linked to vascular injury. In this study, we employed tandem LC-MS/MS to identify protein signatures that encompass protein abundance in RASMC treated with BK or leptin followed by systems biology analyses to gain insight into the biological pathways and processes linked to vascular remodeling. In the study, 1837 proteins were identified in control untreated RASMC. BK altered the expression of 72 (4%) and 120 (6.5%) proteins, whereas leptin altered the expression of 189 (10.2%) and 127 (6.5%) proteins after 24 and 48 h, respectively, compared to control RASMC. BK increased the protein abundance of leptin receptor, transforming growth factor-β. On the other hand, leptin increased the protein abundance of plasminogen activator inhibitor 1 but decreased the protein abundance of cofilin. BK and leptin induced the expression of inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) and pathway analysis revealed the activation of mitogen-activated protein kinases (MAPKs) and AKT pathways. The proteome profile in response to BK and leptin revealed mechanistic interplay of multiple processes that modulate inflammation and oxidative stress signals in the vasculature.

TGF-β in fibrosis by acting as a conductor for contractile properties of myofibroblasts

Myofibroblasts are non-muscle contractile cells that play a key physiologically role in organs such as the stem villi of the human placenta during physiological pregnancy. They are able to contract and relax in response to changes in the volume of the intervillous chamber. Myofibroblasts have also been observed in several diseases and are involved in wound healing and the fibrotic processes affecting several organs, such as the liver, lungs, kidneys and heart. During the fibrotic process, tissue retraction rather than contraction is correlated with collagen synthesis in the extracellular matrix, leading to irreversible fibrosis and, finally, apoptosis of myofibroblasts. The molecular motor of myofibroblasts is the non-muscle type IIA and B myosin (NMMIIA and NMMIIB). Fibroblast differentiation into myofibroblasts is largely governed by the transforming growth factor-β1 (TGF-β1). This system controls the canonical WNT/β-catenin pathway in a positive manner, and PPARγ in a negative manner. The WNT/β-catenin pathway promotes fibrosis, while PPARγ prevents it. This review focuses on the contractile properties of myofibroblasts and the conductor, TGF-β1, which together control the opposing interplay between PPARγ and the canonical WNT/β-catenin pathway.

Organ and tissue fibrosis: Molecular signals, cellular mechanisms and translational implications

Fibrosis denotes excessive scarring, which exceeds the normal wound healing response to injury in many tissues. Although the extracellular matrix deposition appears unstructured disrupting the normal tissue architecture and subsequently impairing proper organ function, fibrogenesis is a highly orchestrated process determined by defined sequences of molecular signals and cellular response mechanisms. Persistent injury and parenchymal cell death provokes tissue inflammation, macrophage activation and immune cell infiltration. The release of biologically highly active soluble mediators (alarmins, cytokines, chemokines) lead to the local activation of collagen producing mesenchymal cells such as pericytes, myofibroblasts or Gli1 positive mesenchymal stem cell-like cells, to a transition of various cell types into myofibroblasts as well as to the recruitment of fibroblast precursors. Clinical observations and experimental models highlighted that fibrosis is not a one-way road. Specific mechanistic principles of fibrosis regression involve the resolution of chronic tissue injury, the shift of inflammatory processes towards recovery, deactivation of myofibroblasts and finally fibrolysis of excess matrix scaffold. The thorough understanding of common principles of fibrogenic molecular signals and cellular mechanisms in various organs - such as liver, kidney, lung, heart or skin - is the basis for developing improved diagnostics including biomarkers or imaging techniques and novel antifibrotic therapeutics.

Deriving vascular smooth muscle cells from mesenchymal stromal cells: Evolving differentiation strategies and current understanding of their mechanisms

Vascular smooth muscle cells (VSMCs) play essential roles in regulating blood vessel form and function. Regeneration of functional vascular smooth muscle tissue to repair vascular diseases is an area of intense research in tissue engineering and regenerative medicine. For functional vascular smooth muscle tissue regeneration to become a practical therapy over the next decade, the field will need to have access to VSMC sources that are effective, robust and safe. While pluripotent stem cells hold good future promise to this end, more immediate translation is expected to come from approaches that generate functional VSMCs from adult sources of multipotent adipose-derived and bone marrow-derived mesenchymal stromal cells (ASCs and BMSCs). The research to this end is extensive and is dominated by studies relating to classical biochemical signalling molecules used to induce differentiation of ASCs and BMSCs. However, prolonged use of the biochemical induction factors is costly and can cause potential endotoxin contamination in the culture. Over recent years several non-traditional differentiation approaches have been devised to mimic defined aspects of the native micro-environment in which VSMCs reside to contribute to the differentiation of VSMC-like cells from ASCs and BMSCs. In this review, the promises and limitations of several non-traditional culture approaches (e.g., co-culture, biomechanical, and biomaterial stimuli) targeting VSMC differentiation are discussed. The extensive crosstalk between the underlying signalling cascades are delineated and put into a translational context. It is expected that this review will not only provide significant insight into VSMC differentiation strategies for vascular smooth muscle tissue engineering applications, but will also highlight the fundamental importance of engineering the cellular microenvironment on multiple scales (with consideration of different combinatorial pathways) in order to direct cell differentiation fate and obtain cells of a desired and stable phenotype. These strategies may ultimately be applied to different sources of stem cells in the future for a range of biomaterial and tissue engineering disciplines.

Vasculopathy in the setting of cardiorenal syndrome: roles of protein-bound uremic toxins

Chronic kidney disease (CKD) often leads to and accelerates the progression of cardiovascular disease (CVD), while CVD also causes kidney dysfunction. This bidirectional interaction leads to the development of a complex syndrome known as cardiorenal syndrome (CRS). CRS not only involves both the heart and the kidney but also the vascular system through a vast array of contributing factors. In addition to hemodynamic, neurohormonal, mechanical, and biochemical factors, nondialyzable protein-bound uremic toxins (PBUTs) are also key contributing factors that have been demonstrated through in vitro, in vivo, and clinical observations. PBUTs are ineffectively removed by hemodialysis because their complexes with albumins are larger than the pores of the dialysis membranes. PBUTs such as indoxyl sulfate and p-cresyl sulfate are key determinate and predictive factors for the progression of CVD in CKD patients. In CRS, both vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) exhibit significant dysfunction that is associated with the progression of CVD. PBUTs influence proliferation, calcification, senescence, migration, inflammation, and oxidative stress in VSMCs and ECs through various mechanisms. These pathological changes lead to arterial remodeling, stiffness, and atherosclerosis and thus reduce heart perfusion and impair left ventricular function, aggravating CRS. There is limited literature about the effect of PBUT on the vascular system and their contribution to CRS. This review summarizes current knowledge on how PBUTs influence vasculature, clarifies the relationship between uremic toxin-related vascular disease and CRS, and highlights the potential therapeutic strategies of uremic vasculopathy in the setting of CRS.

Drug Treatment of Hypertension: Focus on Vascular Health

Hypertension, the most common preventable risk factor for cardiovascular disease and death, is a growing health burden. Serious cardiovascular complications result from target organ damage including cerebrovascular disease, heart failure, ischaemic heart disease and renal failure. While many systems contribute to blood pressure (BP) elevation, the vascular system is particularly important because vascular dysfunction is a cause and consequence of hypertension. Hypertension is characterised by a vascular phenotype of endothelial dysfunction, arterial remodelling, vascular inflammation and increased stiffness. Antihypertensive drugs that influence vascular changes associated with high BP have greater efficacy for reducing cardiovascular risk than drugs that reduce BP, but have little or no effect on the adverse vascular phenotype. Angiotensin converting enzyme ACE inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) improve endothelial function and prevent vascular remodelling. Calcium channel blockers also improve endothelial function, although to a lesser extent than ACEIs and ARBs. Mineralocorticoid receptor blockers improve endothelial function and reduce arterial stiffness, and have recently become more established as antihypertensive drugs. Lifestyle factors are essential in preventing the adverse vascular changes associated with high BP and reducing associated cardiovascular risk. Clinicians and scientists should incorporate these factors into treatment decisions for patients with high BP, as well as in the development of new antihypertensive drugs that promote vascular health.

Vascular Fibrosis in Aging and Hypertension: Molecular Mechanisms and Clinical Implications

Aging is the primary risk factor underlying hypertension and incident cardiovascular disease. With aging, the vasculature undergoes structural and functional changes characterized by endothelial dysfunction, wall thickening, reduced distensibility, and arterial stiffening. Vascular stiffness results from fibrosis and extracellular matrix (ECM) remodelling, processes that are associated with aging and are amplified by hypertension. Some recently characterized molecular mechanisms underlying these processes include increased expression and activation of matrix metalloproteinases, activation of transforming growth factor-β1/SMAD signalling, upregulation of galectin-3, and activation of proinflammatory and profibrotic signalling pathways. These events can be induced by vasoactive agents, such as angiotensin II, endothelin-1, and aldosterone, which are increased in the vasculature during aging and hypertension. Complex interplay between the “aging process” and prohypertensive factors results in accelerated vascular remodelling and fibrosis and increased arterial stiffness, which is typically observed in hypertension. Because the vascular phenotype in a young hypertensive individual resembles that of an elderly otherwise healthy individual, the notion of “early” or “premature” vascular aging is now often used to describe hypertension-associated vascular disease. We review the vascular phenotype in aging and hypertension, focusing on arterial stiffness and vascular remodelling. We also highlight the clinical implications of these processes and discuss some novel molecular mechanisms of fibrosis and ECM reorganization.

Transforming growth factor-beta 1 produced by vascular smooth muscle cells predicts fibrosis in the gastrocnemius of patients with peripheral artery disease

Background

Lower leg ischemia, myopathy, and limb dysfunction are distinguishing features of peripheral artery disease (PAD). The myopathy of PAD is characterized by myofiber degeneration in association with extracellular matrix expansion, and increased expression of transforming growth factor-beta 1 (TGF-β1; a pro-fibrotic cytokine). In this study, we evaluated cellular expression of TGF-β1 in gastrocnemius of control (CTRL) and PAD patients and its relationship to deposited collagen, fibroblast accumulation and limb hemodynamics.

Methods

Gastrocnemius biopsies were collected from PAD patients with claudication (PAD-II; N = 25) and tissue loss (PAD-IV; N = 20) and from CTRL patients (N = 20). TGF-β1 in slide-mounted specimens was labeled with fluorescent antibodies and analyzed by quantitative wide-field, fluorescence microscopy. We evaluated co-localization of TGF-β1 with vascular smooth muscle cells (SMC) (high molecular weight caldesmon), fibroblasts (TE-7 antigen), macrophages (CD163), T cells (CD3) and endothelial cells (CD31). Collagen was stained with Masson Trichrome and collagen density was determined by quantitative bright-field microscopy with multi-spectral imaging.

Results

Collagen density increased from CTRL to PAD-II to PAD-IV specimens (all differences p < 0.05) and was prominent around microvessels. TGF-β1 expression increased with advancing disease (all differences p < 0.05), correlated with collagen density across all specimens (r = 0.864; p < 0.001), associated with fibroblast accumulation, and was observed exclusively in SMC. TGF-β1 expression inversely correlated with ankle-brachial index across PAD patients (r = −0.698; p < 0.001).

Conclusions

Our findings support a progressive fibrosis in the gastrocnemius of PAD patients that is caused by elevated TGF-β1 production in the SMC of microvessels in response to tissue hypoxia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0790-3) contains supplementary material, which is available to authorized users.

Mechanisms of bradykinin-induced expression of connective tissue growth factor and nephrin in podocytes

Diabetic nephropathy (DN) is the main cause of morbidity and mortality in diabetes and is characterized by mesangial matrix deposition and podocytopathy, including podocyte loss. The risk factors and mechanisms involved in the pathogenesis of DN are still not completely defined. In the present study, we aimed to understand the cellular mechanisms through which activation of B2 kinin receptors contribute to the initiation and progression of DN. Stimulation of cultured rat podocytes with bradykinin (BK) resulted in a significant increase in ROS generation, and this was associated with a significant increase in NADPH oxidase (NOX)1 and NOX4 protein and mRNA levels. BK stimulation also resulted in a signicant increase in the phosphorylation of ERK1/2 and Akt, and this effect was inhibited in the presence of NOX1 and Nox4 small interfering (si)RNA. Furthermore, podocytes stimulated with BK resulted in a significant increase in protein and mRNA levels of connective tissue growth factor (CTGF) and, at the same time, a significant decrease in protein and mRNA levels of nephrin. siRNA targeted against NOX1 and NOX4 significantly inhibited the BK-induced increase in CTGF. Nephrin expression was increased in response to BK in the presence of NOX1 and NOX4 siRNA, thus implicating a role for NOXs in modulating the BK response in podocytes. Moreover, nephrin expression in response to BK was also significantly increased in the presence of siRNA targeted against CTGF. These findings provide novel aspects of BK signal transduction pathways in pathogenesis of DN and identify novel targets for interventional strategies.

Wnt16 attenuates TGFβ-induced chondrogenic transformation in vascular smooth muscle

OBJECTIVE

Phenotypic plasticity of vascular smooth muscle cells (VSMCs) contributes to cardiovascular disease. Chondrocyte-like transformation of VSMCs associates with vascular calcification and underlies the formation of aortic cartilaginous metaplasia induced in mice by genetic loss of matrix Gla protein (MGP). Previous microarray analysis identified a dramatic downregulation of Wnt16 in calcified MGP-null aortae, suggesting an antagonistic role for Wnt16 in the chondrogenic transformation of VSMCs.

APPROACH AND RESULTS

Wnt16 is significantly downregulated in MGP-null aortae, before the histological appearance of cartilaginous metaplasia, and in primary MGP-null VSMCs. In contrast, intrinsic TGFβ is activated in MGP-null VSMCs and is necessary for spontaneous chondrogenesis of these cells in high-density micromass cultures. TGFβ3-induced chondrogenic transformation in wild-type VSMCs associates with Smad2/3-dependent Wnt16 downregulation, but Wnt16 does not suppress TGFβ3-induced Smad activation. In addition, TGFβ3 inhibits Notch signaling in wild-type VSMCs, and this pathway is downregulated in MGP-null aortae. Exogenous Wnt16 stimulates Notch activity and attenuates TGFβ3-induced downregulation of Notch in wild-type VSMCs, prevents chondrogenesis in MGP-null and TGFβ3-treated wild-type VSMCs, and stabilizes expression of contractile markers of differentiated VSMCs.

CONCLUSIONS

We describe a novel TGFβ-Wnt16-Notch signaling conduit in the chondrocyte-like transformation of VSMCs and identify endogenous TGFβ activity in MGP-null VSMCs as a critical mediator of chondrogenesis. Our proposed model suggests that the activated TGFβ pathway inhibits expression of Wnt16, which is a positive regulator of Notch signaling and a stabilizer of VSMC phenotype. These data advance the comprehensive mechanistic understanding of VSMC transformation and may identify a novel potential therapeutic target in vascular calcification.

Balance between the two kinin receptors in the progression of experimental focal and segmental glomerulosclerosis in mice

Focal and segmental glomerulosclerosis (FSGS) is one of the most important renal diseases related to end-stage renal failure. Bradykinin has been implicated in the pathogenesis of renal inflammation, whereas the role of its receptor 2 (B2RBK; also known as BDKRB2) in FSGS has not been studied. FSGS was induced in wild-type and B2RBK-knockout mice by a single intravenous injection of Adriamycin (ADM). In order to further modulate the kinin receptors, the animals were also treated with the B2RBK antagonist HOE-140 and the B1RBK antagonist DALBK. Here, we show that the blockage of B2RBK with HOE-140 protects mice from the development of FSGS, including podocyte foot process effacement and the re-establishment of slit-diaphragm-related proteins. However, B2RBK-knockout mice were not protected from FSGS. These opposite results were due to B1RBK expression. B1RBK was upregulated after the injection of ADM and this upregulation was exacerbated in B2RBK-knockout animals. Furthermore, treatment with HOE-140 downregulated the B1RBK receptor. The blockage of B1RBK in B2RBK-knockout animals promoted FSGS regression, with a less-inflammatory phenotype. These results indicate a deleterious role of both kinin receptors in an FSGS model and suggest a possible cross-talk between them in the progression of disease.

Phosphorylation of Fli1 at threonine 312 by protein kinase C delta promotes its interaction with p300/CREB-binding protein-associated factor and subsequent acetylation in response to transforming growth factor beta

Previous studies have shown that transforming growth factor beta (TGF-beta)-induced collagen gene expression involves acetylation-dependent dissociation from the human alpha2(I) collagen (COL1A2) promoter of the transcriptional repressor Fli1. The goal of this study was to elucidate the regulatory steps preceding the acetylation of Fli1. We first showed that TGF-beta induces Fli1 phosphorylation on a threonine residue(s). The major phosphorylation site was localized to threonine 312 located in the DNA binding domain of Fli1. Using several independent approaches, we demonstrated that Fli1 is directly phosphorylated by protein kinase C delta (PKC delta). Additional experiments showed that in response to TGF-beta, PKC delta is recruited to the collagen promoter to phosphorylate Fli1 and that this step is a prerequisite for the subsequent interaction of Fli1 with p300/CREB-binding protein-associated factor (PCAF) and an acetylation event. The phosphorylation of endogenous Fli1 preceded its acetylation in response to TGF-beta stimulation, and the blockade of PKC delta abrogated both the phosphorylation and acetylation of Fli1 in dermal fibroblasts. Promoter studies showed that a phosphorylation-deficient mutant of Fli1 exhibited an increased inhibitory effect on the COL1A2 gene, which could not be reversed by the forced expression of PCAF or PKC delta. These data strongly suggest that the phosphorylation-acetylation cascade triggered by PKC delta represents the primary mechanism whereby TGF-beta regulates the transcriptional activity of Fli1 in the context of the collagen promoter.

Albumin-stimulated TGFbeta-1 in renal tubular cells is associated with activation of MAP kinase

BACKGROUND

Proteinuric renal diseases are often associated with progressive tubulointerstitial fibrosis that usually defines the degree and rate of progression of renal failure. Glomerular filtration of excess albumin, the dominant protein in proteinuria, into proximal tubule could provide the stimulus to induce certain fibrogenic cytokines from proximal tubular cells (PTC), which may account for fibrosis in the interstitium. To explore this hypothesis we tested the effect of bovine albumin in PTC in culture on the expression and secretion of transforming growth factor (TGF) beta-1, a prominent fibrogenic cytokine.

METHODS

TGFbeta-1 expressed by cultured PTC was measured by enzyme-linked immunosorbent assay (ELISA) and indirectly by reverse-transcription polymerase chain reaction (RT-PCR). Relative messenger ribonucleic acid (mRNA) levels were measured in ethidium bromides stained gels, by comparison to transcripts for 18s ribosomal RNA. Activated mitogen-activated protein (MAP) kinase was estimated by Western blot with phosphotyrosine-specific antibody.

RESULTS

Following incubation of PTC with albumin determination of TGF beta-1 mRNA in PTC and TGF beta-protein in culture medium both indicated a time- and dose-dependent increase. MAP kinase (p44/42) was activated within 5 min of exposure to albumin. Inhibition of the MAP kinase cascade by PD98059 attenuated the effect of albumin on TGF beta-1 expression.

CONCLUSIONS

These observations suggest that overexpression of TGF beta-1 by PTC in response to albumin is regulated through a MAP kinase signaling pathway. This mechanism may play a role in the development of interstitial fibrosis in proteinuric states.

Tissue kallikrein reverses insulin resistance and attenuates nephropathy in diabetic rats by activation of phosphatidylinositol 3-kinase/protein kinase B and adenosine 5'-monophosphate-activated protein kinase signaling pathways

We previously reported that iv delivery of the human tissue kallikrein (HK) gene reduced blood pressure and plasma insulin levels in fructose-induced hypertensive rats with insulin resistance. In the current study, we evaluated the potential of a recombinant adeno-associated viral vector expressing the HK cDNA (rAAV-HK) as a sole, long-term therapy to correct insulin resistance and prevent renal damage in streptozotocin-induced type-2 diabetic rats. Administration of streptozotocin in conjunction with a high-fat diet induced systemic hypertension, diabetes, and renal damage in rats. Delivery of rAAV-HK resulted in a long-term reduction in blood pressure, and fasting plasma insulin was significantly lower in the rAAV-HK group than in the control group. The expression of phosphatidylinositol 3-kinase p110 catalytic subunit and the levels of phosphorylation at residue Thr-308 of Akt, insulin receptor B, and AMP-activated protein kinases were significantly decreased in organs from diabetic animals. These changes were significantly attenuated after rAAV-mediated HK gene therapy. Moreover, rAAV-HK significantly decreased urinary microalbumin excretion, improved creatinine clearance, and increased urinary osmolarity. HK gene therapy also attenuated diabetic renal damage as assessed by histology. Together, these findings demonstrate that rAAV-HK delivery can efficiently attenuate hypertension, insulin resistance, and diabetic nephropathy in streptozotocin-induced diabetic rats.

Kinin infusion prevents renal inflammation, apoptosis, and fibrosis via inhibition of oxidative stress and mitogen-activated protein kinase activity

The progression of renal disease displays several characteristics, including proteinuria, apoptosis, inflammation, and fibrosis. In this study, we investigated the effect of long-term infusion of kinin in protection against salt-induced renal damage in Dahl salt-sensitive rats. Dahl salt-sensitive rats were fed a high-salt diet for 2 weeks and were then infused with bradykinin (500 ng/h) via subcutaneously implanted minipumps for 3 weeks. Kinin infusion attenuated salt-induced impaired renal function as evidenced by reduced proteinuria, serum creatinine, and blood urea nitrogen levels without apparent effect on blood pressure. Morphological analysis indicated that kinin administration reduced salt-induced glomerular sclerosis, tubular dilatation, luminal protein cast formation, and interlobular arterial thickness. Kinin also significantly lowered collagen I, III, and IV deposition and their mRNA levels. Moreover, kinin reduced interstitial monocyte/macrophage accumulation, as well as tubular cell apoptosis and caspase-3 activity. Protection of renal injury by kinin was associated with increased renal NO levels and reduced nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate oxidase activities and superoxide generation. Suppression of oxidative stress by kinin was accompanied by reduced transforming growth factor-beta1 protein and mRNA levels, as well as decreased phosphorylation of mitogen-activated protein kinases. This is the first study to demonstrate that kinin infusion can directly protect against salt-induced renal injury without blood pressure reduction by inhibiting apoptosis, inflammation, and fibrosis via suppression of oxidative stress, transforming growth factor-beta1 expression, and mitogen-activated protein kinase activation.

Microarray and phosphokinase screenings leading to studies on ERK and JNK regulation of connective tissue growth factor expression by angiotensin II 1a and bradykinin B2 receptors in Rat1 fibroblasts

Rat1 fibroblasts stably transfected with the rat angiotensin II (AngII) AT1a and bradykinin (BK) B2 receptor cDNAs gained the ability to bind Ang II and BK. Wild-type Rat1 cells bound neither ligand. Exposure to either effector led to characteristic Galphai and Galphaq signal cascades, the release of arachidonic acid (ARA), and the intracellular accumulation of inositol phosphates (IP). Microarray analyses in response to BK or AngII showed that both receptors markedly induce the CCN family genes, CTGF (CCN2) and Cyr61 (CCN1), as well as the vasculature-related genes, Cnn1 and Egr1. Real time PCR confirmed the increased expression of connective tissue growth factor (CTGF) mRNA. Combined sequence-based analysis of gene promoter regions with statistical prevalence analyses identified CREB, SRF, and ATF-1, downstream targets of ERK, and JNK, as prominent products of genes that are regulated by ligand binding to the BK or AngII receptors. The binding of AngII or BK markedly stimulated the phosphorylation and thus the activation of ERK2, JNK, and p38MAPK. A BKB2R and an AT1aR chimera which displayed only negligible G-protein-related signaling were constructed. Both mutant receptors continued to activate these kinases and stimulate CTGF expression. Inhibitors of ERK1/2 and JNK but not p38MAPK inhibited the BK- and AngII-stimulated expression of CTGF in cells expressing either the WT or mutant receptors, illustrating that ERK and JNK participate in the control of CTGF expression in a manner that appears to be independent of G-protein. Conversely, addition of BK or AngII to the cell line expressing WT AT1aR and BKB2R downregulated the expression of collagen alpha1(I) (COL1A1) mRNA. However, these effectors did not have this effect in cells expressing the mutant receptors. Thus, a robust G-protein related response is necessary for BK or AngII to affect COL1A1 expression.

Effects of transforming growth factor-beta in the development of inflammatory pseudotumour-like lesions in a murine model

Alterations in transforming growth factor (TGF)-beta signalling have been frequently implicated in human cancer, and an important mechanism underlying its pro-oncogenic nature is suppression of the host antitumour immune response. Considering the immunosuppressive effect of TGF-beta, we asked whether human tumour cells, known to secrete TGF-beta in culture, would survive and grow when implanted into the peritoneal cavity of immunocompetent mice. Therefore, we developed a xenogeneic model where mice were intraperitoneally (i.p.) injected with a TGF-beta-secreting human colorectal adenocarcinoma cell line, LISP-A10. Although animals did not develop macroscopic tumours, the recovery and isolation of human tumour cells was achieved when an inflammatory environment was locally induced by the administration of complete Freund's adjuvant (CFA). This procedure significantly increased TGF-beta concentrations in the peritoneal fluid and was accompanied by impaired activation of the host-specific immune response against LISP-A10 cells. Furthermore, inflammatory lesions resembling human inflammatory pseudotumours (IPTs) were observed on the surface of i.p. organs. These lesions could be induced by either injection of LISP-A10 cells, cells-conditioned medium or recombinant TGF-beta but only after administration of CFA. In addition, host cyclooxygenase-2 and kinin receptors played an important role in the induction of TGF-beta-mediated IPT-like lesions in our experimental model.

+9/+9 Homozygosity of the bradykinin receptor gene polymorphism is associated with reduced fat-free mass in chronic obstructive pulmonary disease

BACKGROUND

The etiology of muscle wasting in chronic obstructive pulmonary disease (COPD) is incompletely understood. We previously showed that the D rather than the I polymorphic variant of the angiotensin-converting enzyme (ACE) gene is associated with preserved quadriceps strength in COPD. If the ACE D allele influences skeletal muscle through increased ACE-related kinin degradation [and reduced activity at the bradykinin type 2 receptor (BK(2)R)], we might expect a similar association with the +9 BK(2)R genotype in this population as well.

OBJECTIVE

The objective was to test the hypothesis that the BK(2)R gene polymorphism is a determinant of fat-free mass and quadriceps strength in patients with COPD.

DESIGN

In a cross-sectional design we determined BK(2)R genotype, fat-free mass, and quadriceps strength in 110 COPD patients with a mean (+/-SD) predicted forced expiratory volume in 1 s of 34.3 +/- 16.4% and in 104 healthy age-matched control subjects.

RESULTS

The mean (+/-SD) fat-free mass index (in kg/m(2)) was significantly lower in 37 patients homozygous for the +9 allele than in carriers of the -9 allele (15.7 +/- 1.8 compared with 16.7 +/- 2.3; P = 0.038); the same pattern was true for quadriceps maximal voluntary force (30.8 +/- 10.4 and 36.4 +/- 12.8 kg; P = 0.02), respectively. No significant effect of BK(2)R genotype on inspiratory muscle strength or on any variable in control subjects was observed. There was no interaction between the effect of the BK(2)R and ACE genotypes on quadriceps strength.

CONCLUSIONS

The genotype associated with reduced BK(2)R expression is associated with reduced fat-free mass and quadriceps strength in COPD. However, alterations in the activity at the BK(2)R do not seem to account for the previously identified association of quadriceps strength with ACE genotype.

Bradykinin B2receptor antagonism attenuates inflammation, mast cell infiltration and fibrosis in remote myocardium after infarction in rats

Bradykinin may interfere with myocardial remodelling by promoting inflammation and mast cell activation or, alternatively, by counteracting angiotensin II-dependent collagen accumulation. The aim of the present study was to investigate the role of bradykinin B2 receptor antagonism in inflammatory and mast cell infiltration, fibroplasia and fibrosis accumulation following myocardial infarction (MI). Myocardial infarction was produced by the ligature of the left coronary artery in male Wistar rats that were 10 weeks of age. Immediately after MI, rats received the B2 receptor antagonist Hoe140 (0.5 microg/kg per min, s.c.) or saline over a period of 3 days, 1 week or 4 weeks, constituting three separate groups and their respective controls. Coronal myocardial tissue sections underwent haematoxylin and eosin, Giemsa and picrosirius red staining, as well as immunohistochemistry for alpha-smooth muscle actin (SMA). Morphometric studies were undertaken in three different myocardial regions: MI, remote non-infarcted subendocardium (non-MI SE) and remote non-infarcted interventricular septum (non-MI IVS). The MI size was comparable between Hoe140-treated groups and their respective controls (day 3: 42 +/- 4%, n = 8, vs 43 +/- 3%, n = 6; week 1: 37 +/- 5%, n = 5, vs 39 +/- 2%, n = 5; week 4: 35 +/- 3%, n = 9, vs 36 +/- 3%, n = 7). At day 3, Hoe140 treatment reduced inflammatory cell reaction within the MI (585 +/- 59 vs 995 +/- 170 cells/mm2; P = 0.02), non-MI SE (77 +/- 12 vs 214 +/- 57 cells/mm2; P = 0.02) and non-MI IVS (93 +/- 16 vs 135 +/- 14 cells/mm2; P = 0.03) regions. Mast cells were reduced within the non-MI IVS region (0.8 +/- 0.1 vs 2.5 +/- 0.4 cells/mm2; P = 0.006), but not within the MI region. In non-MI SE, mast cells were rarely found. At week 1, Hoe140 treatment reduced alpha-SMA-positive myofibroblast infiltration within the MI (2535 +/- 383 vs 5636 +/- 968 cells/mm2; P = 0.01) and non-MI SE (222 +/- 33 vs 597 +/- 162 cells/mm2; P = 0.03) regions. In the non-MI IVS region, alpha-SMA-positive myofibroblasts were rarely found. At week 4, Hoe140 treatment reduced collagen volume fraction within the MI (37 +/- 4 vs 53 +/- 4%; P = 0.03), non-MI SE (1.3 +/- 0.2 vs 2.6 +/- 0.3%; P = 0.001) and non-MI IVS (1.1 +/- 0.2 vs 1.8 +/- 0.2%; P = 0.01) regions. Bradykinin promotes inflammation, fibroplasia and fibrosis after MI. Mast cells may have a role in fibrosis deposition through a bradykinin-related mechanism.

Mechanisms of low-density lipoprotein-induced expression of connective tissue growth factor in human aortic endothelial cells

Hyperlipidemia is a recognized risk factor for atherosclerotic vascular disease. The underlying mechanisms that link lipoproteins and vascular disease are undefined. Connective tissue growth factor (CTGF) is emerging as a key determinant of progressive fibrotic diseases, and its expression is upregulated by diabetes. To define the mechanisms through which low-density lipoproteins (LDL) promote vascular injury, we evaluated whether LDL can modulate the expression of CTGF and collagen IV in human aortic endothelial cells (HAECs). Treatment of HAECs with LDL (50 microg/ml) for 24 h produced a significant increase in the mRNA and the protein levels of CTGF and collagen IV compared with unstimulated controls. To explore the mechanisms by which LDL regulates CTGF and collagen IV expression in HAECs, we determined first if CTGF and collagen IV are downstream targets for regulation by transforming growth factor-beta (TGF-beta). The results demonstrated that TGF-beta produced a concentration-dependent increase in the protein levels of CTGF. To assess whether the induction of CTGF in response to LDL is mediated via autocrine activation of TGF-beta, HAECs were treated with LDL for 24 h in the presence and absence of anti-TGF-beta neutralizing antibodies (anti-TGF-beta NA). The results demonstrated that the increase in CTGF induced by LDL was significantly inhibited by the anti-TGF-beta NA. To investigate the upstream mediators of TGF-beta on activity of CTGF in response to LDL, HAECs were treated with LDL for 24 h in the presence and absence of cell-permeable MAPK inhibitors. Inhibition of p38(mapk) activities did not affect LDL-induced TGF-beta1, CTGF, and collagen IV expression. On the other hand, SP-600125, a specific inhibitor of c-Jun NH(2)-terminal kinase, suppressed LDL-induced TGF-beta, CTGF, and collagen IV expression, and PD-98059, a selective inhibitor of p44/42(mapk), suppressed LDL-induced TGF-beta and CTGF expression. These findings are the first to implicate the MAPK pathway and TGF-beta as key players in LDL signaling, leading to CTGF and collagen IV expression in HAECs. The data also point to a potential mechanistic pathway through which lipoproteins may promote vascular injury.

Research progress of vasculopathy in portal hypertension

Portal hypertension, one of the vascular diseases, not only has lesions in liver, but also changes in vascular structures and functions of extrahepatic portal system, systemic system and pulmonary circulation. The pathological changes of vasculopathy in portal hypertension include remodeling of arterialized visceral veins, intimal injury of visceral veins and destruction of contractile structure in visceral arterial wall. The mechanisms of vasculopathy in portal hypertension may be attributed to the changes of hemodynamics in portal system, immune response, gene modulation, vasoactive substances, and intrahepatic blood flow resistance. Portal hypertension can cause visceral hyperdynamic circulation, and the development and progression of visceral vasculopathy, while visceral vasculopathy can promote the development and progression of portal hypertension and visceral hyperdynamic circulation in turn. The aforementioned three factors interact in the pathogenesis of hepatic cirrhosis-induced portal hypertension and are involved in hemorrhage due to varicose vein rupture.

Increased circulating levels of tissue kallikrein in systemic sclerosis correlate with microvascular involvement

BACKGROUND

In systemic sclerosis (SSc) the lack of an angiogenic response to hypoxia may be due to inappropriate synthesis of angiogenic and angiostatic factors. Tissue kallikrein (t-kallikrein), regulating the kallikrein-kinin system and acting on the microcirculation, is a potent angiogenic agent, and kallistatin is its natural inhibitor.

OBJECTIVE

To evaluate, in patients with SSc, t-kallikrein and kallistatin levels and their correlation with clinical features and measures of microvascular involvement.

PATIENTS AND METHODS

Serum levels of t-kallikrein and kallistatin (ELISA) and t-kallikrein skin expression (immunohistochemistry) were studied in patients with SSc, and evaluated for subset (dSSc or lSSc), clinical and immunological features, and microvascular involvement (ulcers, telangiectasias, nailfold videocapillaroscopy).

RESULTS

Circulating levels of t-kallikrein were higher in SSc than in controls (p<0.001). T-kallikrein did not differ between lSSc and dSSc, although it was higher in lSSc than in controls (p<0.001).T-kallikrein levels were higher in patients with early and active capillaroscopic pattern than in those with late pattern (p = 0.019 and 0.023). Patients with giant capillaries and capillary microhaemorrhages had higher t-kallikrein concentrations than patients with architectural derangement (p = 0.04). No differences in kallistatin levels were detected between patients with SSc and controls, or between lSSc and dSSc. In early SSc skin, the presence of t-kallikrein was found in endothelial and in perivascular inflammatory cells, while no staining in skin of advanced SSc was detected.

CONCLUSION

T-kallikrein levels are increased in patients with SSc, particularly in lSSc, and are associated with early and active capillaroscopic patterns. T-kallikrein may play a part in SSc microvascular changes.

Lysophosphatidic acid inhibits TGF-β-mediated stimulation of type I collagen mRNA stability via an ERK-dependent pathway in dermal fibroblasts

Lysophosphatidic acid (LPA) is a serum-derived pleiotropic mediator with a potential role in wound repair. Since extracellular matrix (ECM) deposition is a critical part of wound healing, this study was designed to examine whether LPA is involved in ECM regulation. Using human dermal fibroblasts, we demonstrate that LPA counteracts transforming growth factor-beta (TGF-beta) stimulation of type I collagen mRNA and protein. This factor elicits its inhibitory effects at the posttranscriptional level via destabilization of type I collagen mRNA. Furthermore, using the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059, we show that the extracellular signal-regulated kinase (ERK) pathway is a negative regulator of the TGF-beta-induced stabilization of type I collagen mRNA, and that the activation of the ERK pathway by LPA mediates their inhibitory effects on collagen production. In conclusion, this study describes a novel function for LPA as an antagonist of TGF-beta induced ECM deposition. These findings may be relevant to physiologic wound repair and may be useful in designing therapeutic agents to prevent excessive scarring.

Prevention of cardiac fibrosis and left ventricular dysfunction in diabetic cardiomyopathy in rats by transgenic expression of the human tissue kallikrein gene

Diabetic cardiomyopathy includes fibrosis. Kallikrein (KLK) can inhibit collagen synthesis and promote collagen breakdown. We investigated cardiac fibrosis and left ventricular (LV) function in transgenic rats (TGR) expressing the human kallikrein 1 (hKLK1) gene in streptozotocin (STZ) -induced diabetic conditions. Six weeks after STZ injection, LV function was determined in male Sprague-Dawley (SD) rats and TGR(hKLK1) (n=10/group) by a Millar tip catheter. Total collagen content (Sirius Red staining) and expression of types I, III, and VI collagen were quantified by digital image analysis. SD-STZ hearts demonstrated significantly higher total collagen amounts than normoglycemic controls, reflected by the concomitant increment of collagen types I, III, and VI. This correlated with a significant reduction of LV function vs. normoglycemic controls. In contrast, surface-specific content of the extracellular matrix, including collagen types I, III, and VI expression, was significantly lower in TGR(hKLK1)-STZ, not exceeding the content of SD and TGR(hKLK1) controls. This was paralleled by a preserved LV function in TGR(hKLK1)-STZ animals. The kallikrein inhibitor aprotinin and the bradykinin (BK) B2 receptor antagonist icatibant reduced the beneficial effects on LV function and collagen content in TGR(hKLK1)-STZ animals. Transgenic expression of hKLK1 counteracts the progression of LV contractile dysfunction and extracellular matrix remodeling in STZ-induced diabetic cardiomyopathy via a BK B2 receptor-dependent pathway.

Mechanisms of angiotensin II-induced expression of B2 kinin receptors

Although the primary roles of the kallikreinkinin system and the renin-angiotensin system are quite divergent, they are often intertwined under pathophysiological conditions. We examined the effect of ANG II on regulation of B(2) kinin receptors (B2KR) in vascular cells. Vascular smooth muscle cells (VSMC) were treated with ANG II in a concentration (10(-9)-10(-6) M)- and time (0-24 h)-dependent manner, and B2KR protein and mRNA levels were measured by Western blots and PCR, respectively. A threefold increase in B2KR protein levels was observed as early as 6 h, with a peak response at 10(-7) M. ANG II (10(-7) M) also increased B2KR mRNA levels twofold 4 h after stimulation. Actinomycin D suppressed the increase in B2KR mRNA and protein levels induced by ANG II. To elucidate the receptor subtype involved in mediating this regulation, VSMC were pretreated with losartan (AT(1) receptor antagonist) and/or PD-123319 (AT(2) receptor antagonist) at 10 microM for 30 min, followed by ANG II (10(-7) M) stimulation. Losartan completely blocked the ANG II-induced B2KR increase, whereas PD-123319 had no effect. In addition, expression of B2KR mRNA levels was decreased in AT(1A) receptor knockout mice. Finally, to determine whether ANG II stimulates B2KR expression via activation of the MAPK pathway, VSMC were pretreated with an inhibitor of p42/p44(mapk) (PD-98059) and/or an inhibitor of p38(mapk) (SB-202190), followed by ANG II (10(-7) M) for 24 h. Selective inhibition of the p42/p44(mapk) pathway significantly blocked the ANG II-induced increase in B2KR expression. These findings demonstrate that ANG II regulates expression of B2KR in VSMC and provide a rationale for studying the interaction between ANG II and bradykinin in the pathogenesis of vascular dysfunction.

Plasma prekallikrein: a risk marker for hypertension and nephropathy in type 1 diabetes

The relevance and significance of the plasma kallikrein/kinin system as a risk factor for the development of vascular complications in diabetic patients was explored in a cross-sectional study. We measured the circulating levels of plasma prekallikrein (PK) activity, factor XII, and high-molecular weight kininogen in the plasma of 636 type 1 diabetic patients from the Diabetes Control and Complications Trial/Epidemiology and Diabetes Intervention and Complications Study cohort. The findings demonstrated that type 1 diabetic patients with blood pressure > or =140/90 mmHg have increased PK levels compared with type 1 diabetic patients with blood pressure <140/90 (1.53 +/- 0.07 vs. 1.27 +/- 0.02 units/ml; P < 0.0001). Regression analysis also determined that plasma PK levels positively and significantly correlated with diastolic (DBP) and systolic blood pressures (SBP) as continuous variables (r = 0.17 and 0.18, respectively; P < 0.0001). In multivariate regression analysis, the semipartial r(2) value for PK was 2.93% for SBP and 2.92% for DBP (P < 0.0001). A positive correlation between plasma PK levels and the urinary albumin excretion rate (AER) was also observed (r = 0.16, P < 0.0001). In categorical analysis, patients with macroalbuminuria had a significantly higher level of plasma PK than normoalbuminuric patients (1.45 +/- 0.08 vs. 1.27 +/- 0.02 units/ml; P < 0.01), whereas microalbuminuric patients had an intermediate PK value (1.38 +/- 0.05 units/ml; P = NS). Among patients in the microalbuminuric subgroup, we observed a positive and independent correlation between PK and AER in univariate and multivariate regression analysis (r = 0.27, P < 0.03; n = 63). We concluded that in type 1 diabetes, 1) PK levels are elevated in association with increased blood pressure; 2) PK levels are independently correlated with AER and are categorically elevated in patients with macroalbuminuria; and 3) although the positive correlation between PK and AER within the subgroups of patients with microalbuminuria suggest that PK could be a marker for progressive nephropathy, longitudinal studies will be necessary to address this issue.

Bradykinin reduces growth factor-induced glomerular ERK1/2 phosphorylation

Several experimental data report both mitogenic and antimitogenic effects of bradykinin (BK). To conciliate these apparent opposite effects, we hypothesized that, depending on cell context activation, BK could reduce the mitogenic effect of growth factors. Therefore, in the present study we assessed the existence of possible negative cross talk between BK and potential pathogenic growth factors in freshly isolated rat glomeruli (IG). Next, we determined whether this cross talk could be pharmacologically recruited during angiotensin-converting enzyme (ACE) inhibition in the diabetic rat. In IG from normal rats, BK, via activation of the B(2) kinin receptor (B(2)R), causes a transient stimulation of ERK1/2 phosphorylation, whereas it inhibits ERK1/2 phosphorylation induced by IGF-1, PDGF-BB, VEGF, or basic FGF. The reduction of growth factor-induced ERK1/2 phosphorylation is abolished by an inhibitor of tyrosine phosphatase. In glomeruli from diabetic rats, hyperglycemia increased the phosphorylation level of ERK-1/2 as well as oxidative stress. The reversal of these events by ACE inhibition is mediated via B(2)R activation. These observations are consistent with a potential therapeutic role of BK and B(2)R during glomerulosclerosis.

Hybrid formation between the intracellular faces of the bradykinin B2 and angiotensin II AT1 receptors and signal transduction

Most frequently, the physiologic functions of the angiotensin II (Ang II) type 1 receptor (AT1R) and bradykinin B2 receptor (BKB2R) are antagonistic, particularly with respect to the regulation of vascular tone. Despite major differences in their physiologic actions, the receptors share sequence similarities. Both link to Galpha(i) and Galpha(q) and transduce very similar signal paths, not only those relating to the traditional G-protein associated second messengers, but also those involved in transactivation mechanisms involving receptor tyrosine kinases. With respect to these paths, some differences in signaling may be accounted for by cell type specificity. However, alternative signal cascades for these two receptors are becoming increasingly evident. One such is the recruitment of signaling molecules upon receptor translocation and internalization. The AT1R translocates into clathrin-coated pits and internalizes upon recruitment of beta-arrestin 2 which then recruits ASK1 and JNK3. The BKB2R translocates and internalizes mainly via caveolae. Another signaling divergence may be due to the direct activation of small G-proteins by both receptors. AT1R activates the RhoA, Rac1, Cdc42 while BKB2R couples only with Rac1 and Cdc42. Both receptors may serve as docking stations for intracellular proteins. One such example is the YIPP motif within the C-terminus of the ATIR which associates with the JAK/STAT pathway. Another potential alternative is the activation of tyrosine/serine kinase phosphatases by BK. This mechanism may directly oppose some of the protein tyrosine/ serine kinase paths activated by AT1R. These alternative mechanisms in sum are potentially responsible for the diversion in signal transduction between these two receptors. Regardless of the route of action, our results suggest that in Rat-1 fibroblasts stably transfected with BKB2R, BK slightly decreases connective tissue growth factor (CTGF) mRNA level while in ATIR transfected cells Ang II increases CTGF mRNA markedly. To determine whether mutant hybrids can be formed between these two receptors which encompass some of the function of the donor receptor but bind the ligand of the recipient receptor, a series of hybrids were formed with BKB2R the recipient and AT1R the donor receptor. Some of these hybrids show resistance to exchanges with the AT1R and form receptors which either do not bind (IC1 exchanges) or demonstrate poor function but normal internalization (proximal C-terminus exchanges). However, other hybrids have proven very functional. For example, the IC2, IC3 and distal C-terminus of the BKB2R IC face can be replaced simultaneously with the AT1R resulting in an hybrid which binds BK, continues to signal, is internalized and resensitized. Formation of this and other less extensive hybrids is discussed. Some of these hybrids possess the capacity to function as the AT1R as exemplified by their ability to upregulate CTGF expression as wild-type (WT) AT1R.

PKC-MEK-MAPK-dependent signal transduction pathway mediates the stimulation of lysyl oxidase expression by serum and PDGF in rat aortic smooth muscle cells

Lysyl oxidase (LO) plays a critical role in the stabilization and insolubilization of fibrous structural proteins of the extracellular matrix and has been implicated in the suppression of Ras-induced tumorigenesis. Several prior reports demonstrate that the expression of this catalyst is strongly influenced by a variety of effectors of cell function and is responsive to the growth state of fibrogenic cells. Using specific inhibitors of components of signal transduction pathways, the present study reveals that a PKC-MEK-MAPK-dependent pathway is critical to the enhanced expression of the LO gene in response to variations in the levels of the serum component of the growth medium and in response to platelet-derived growth factor (PDGF). PDGF is shown to be the major component of fetal bovine serum, which stimulates the activity of a LO promoter construct.

In vivo bradykinin B2 receptor activation reduces renal fibrosis

Angiotensin-converting enzyme (ACE) inhibitors reduce the progression of various fibrotic renal diseases both in humans and in animal models. Unilateral ureteral obstruction (UUO) is an animal model of accelerated renal tubulointerstitial fibrosis that is attenuated by ACE inhibition. Although ACE inhibitors increase bradykinin concentrations in addition to their effect on angiotensin II formation, the role of bradykinin in renal fibrosis has not been studied. We show here that genetic ablation (B2(-/-) mice) or pharmacological blockade of the bradykinin B2 receptor increases UUO-induced interstitial fibrosis in mice, whereas transgenic rats expressing increased endogenous bradykinin show reduced UUO-induced interstitial fibrosis. The increased interstitial fibrosis in B2(-/-) mice was accompanied by a decreased activity of plasminogen activators (PAs) and metalloproteinase-2 (MMP-2), enzymes involved in ECM degradation, suggesting that the protective effects of bradykinin involve activation of a B2 receptor/PA/MMP-2 cascade. This ability of bradykinin to increase PA activity was confirmed in primary culture proximal tubular cells. Thus, in both mice and rats, bradykinin B2 receptor activation reduces renal tubulointerstitial fibrosis in vivo, most likely by increasing ECM degradation.

Identification of prolylcarboxypeptidase as the cell matrix-associated prekallikrein activator

Investigations determined that the cell matrix-associated prekallikrein (PK) activator is prolylcarboxypeptidase. PK activation on human umbilical vein endothelial cell (HUVEC) matrix is inhibited by antipain (IC(50)=50 microM) but not anti-factor XIIa antibody, 3 mM benzamidine, 5 mM iodoacetic acid or iodoacetamide, or 3 mM N-ethylmaleimide. Corn trypsin inhibitor (IC(50)=100 nM) or Fmoc-aminoacylpyrrolidine-2-nitrile (IC(50)=100 microM) blocks matrix-associated PK activation. Angiotensin II (IC(50)=100 microM) or bradykinin (IC(50)=3 mM), but not angiotensin 1-7 or bradykinin 1-5, inhibits matrix-associated PK activation. ECV304 cell matrix PK activator also is blocked by 100 microM angiotensin II, 1 microM corn trypsin inhibitor, and 50 microM antipain, but not angiotensin 1-7. 1 mM angiotensin II or 300 microM Fmoc-aminoacylpyrrolidine-2-nitrile indirectly blocks plasminogen activation by inhibiting kallikrein formation for single chain urokinase activation. On immunoblot, prolylcarboxypeptidase antigen is associated with HUVEC matrix. These studies indicate that prolylcarboxypeptidase is the matrix PK activator.

B2 receptor activation reduces Erk1 and Erk2 phosphorylation induced by insulin-like growth factor-1, platelet-derived growth factor-BB, and high glucose in rat isolated glomeruli

Several experimental data document an activation of the mitogen-activated protein kinases Erk1 and Erk2 by bradykinin (BK), an agonist of the kinin B2 receptor (B2R). In contrast, other reports showed an inhibitory modulation of mitogenesis by BK. Therefore, we explored in the isolated glomeruli the effect of B2R activation on the signaling of insulin-like growth factor-1 (IGF-1), platelet-derived growth factor-BB (PDGF-BB), and high glucose (HG), three factors that are believed to be involved in the development of glomerulosclerosis via the phosphorylation of Erk1 and Erk2. We observed that the activation of B2R negatively modulates the phosphorylation of Erk1 and Erk2 induced by IGF-1, PDGF-BB, and HG in the glomerulus. These effects are consistent with the hypothesis of a protective role for BK in the kidney during development of glomerulosclerosis and renal pathologies associated with a hyperproliferative state.

Role of p38 MAPK in transforming growth factor beta stimulation of collagen production by scleroderma and healthy dermal fibroblasts

Transforming growth factor beta has been implicated as a mediator of excessive extracellular matrix deposition in scar tissue and fibrosis, including systemic sclerosis. To further characterize the mechanism of collagen gene expression in systemic sclerosis and healthy skin fibroblasts, we examined the role of p38 MAPK signaling in collagen gene regulation by transforming growth factor beta. Treatment of dermal fibroblasts with transforming growth factor beta resulted in a prolonged activation of p38 MAPK. Furthermore, a specific inhibitor of p38 suppressed transforming growth factor beta stimulation of collagen type I mRNA and the alpha2(I) collagen promoter activity. To further probe the role of p38 in collagen regulation by transforming growth factor beta, we utilized an expression vector containing p38alpha cDNA. Ectopic expression of p38alpha enhanced COL1A2 promoter activity and potentiated transforming growth factor beta stimulation of this promoter. The p38 response element in the COL1A2 promoter overlapped with the previously characterized transforming growth factor beta response element. Consistent with these observations, collagen type I mRNA and protein levels were increased in transforming-growth-factor-beta-stimulated fibroblasts transduced with an adenoviral vector expressing p38alpha. To determine the possible role of p38 in abnormal collagen production by systemic sclerosis fibroblasts, p38 protein levels were compared in systemic sclerosis and healthy skin fibroblasts. Both cell types exhibited similar total levels of p38 MAPK and similar kinetics of p38 activation in response to transforming growth factor beta. In conclusion, this study demonstrates a costimulatory role for p38 MAPK in transforming growth factor beta induction of the collagen type I gene. Expression levels and activation status of p38 are not consistently elevated in systemic sclerosis fibroblasts suggesting that the p38 MAPK pathway is not dysregulated in systemic sclerosis fibroblasts.

Regulation of B(2)-kinin receptors by glucose in vascular smooth muscle cells

The development of vascular disease is accelerated in hyperglycemic states. Vascular injury plays a pivotal role in the progression of atherosclerotic vascular disease in diabetes, which is characterized by increased vascular smooth muscle cell (VSMC) proliferation and extracellular matrix accumulation. We previously reported that diabetes alters the activity of the kallikrein-kinin system and results in the upregulation of kinin receptors in the vessel wall. To determine whether glucose can directly influence the regulation of kinin receptors, the independent effect of high glucose (25 mM) on B(2)-kinin receptors (B2KR) in VSMC was examined. A threefold increase in B2KR protein levels and a 40% increase in B2KR surface receptors were observed after treatment with high glucose after 24 h. The mRNA levels of B2KR were also significantly increased by high glucose as early as 4 h later. To elucidate the cellular mechanisms by which glucose regulates B2KR, we examined the role of protein kinase C (PKC). High glucose increased total PKC activity and resulted in the translocation of conventional PKC isoforms (beta(1) and beta(2)), novel (epsilon), and atypical (zeta) PKC isoforms into the membrane. Inhibition of PKC activity prevented the increase in B2KR levels induced by ambient high glucose. These findings provide the first evidence that glucose regulates the expression of B(2) receptors in VSMC and provide a rationale to further study the interaction between glucose and kinins on the pathogenesis of atherosclerotic vascular disease in diabetes.