Inhibition of capillary morphogenesis and associated apoptosis by dominant negative mutant transforming growth factor-beta receptors

Enhanced TGF-β Signaling Contributes to the Insulin-Induced Angiogenic Responses of Endothelial Cells

Angiogenesis, the development of new blood vessels, is a key process in disease. We reported that insulin promotes translocation of transforming growth factor β (TGF-β) receptors to the plasma membrane of epithelial and fibroblast cells, thus enhancing TGF-β responsiveness. Since insulin promotes angiogenesis, we addressed whether increased autocrine TGF-β signaling participates in endothelial cell responses to insulin. We show that insulin enhances TGF-β responsiveness and autocrine TGF-β signaling in primary human endothelial cells, by inducing a rapid increase in cell surface TGF-β receptor levels. Autocrine TGF-β/Smad signaling contributed substantially to insulin-induced gene expression associated with angiogenesis, including TGF-β target genes encoding angiogenic mediators; was essential for endothelial cell migration; and participated in endothelial cell invasion and network formation. Blocking TGF-β signaling impaired insulin-induced microvessel outgrowth from neonatal aortic rings and modified insulin-stimulated blood vessel formation in zebrafish. We conclude that enhanced autocrine TGF-β signaling is integral to endothelial cell and angiogenic responses to insulin.

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Insulin promotes enhanced autocrine TGF-β responsiveness in endothelial cells

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Autocrine TGF-β signaling contributes to insulin-induced angiogenesis gene expression

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Insulin-induced endothelial migration and sprouting require autocrine TGF-β signaling

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Enhanced autocrine TGF-β signaling is integral to angiogenic responses to insulin

The Role of Chemokines in Wound Healing

Wound healing is a multistep process with four overlapping but distinct stages: hemostasis, inflammation, proliferation, and remodeling. An alteration at any stage may lead to the development of chronic non-healing wounds or excessive scar formation. Impaired wound healing presents a significant health and economic burden to millions of individuals worldwide, with diabetes mellitus and aging being major risk factors. Ongoing understanding of the mechanisms that underly wound healing is required for the development of new and improved therapies that increase repair. Chemokines are key regulators of the wound healing process. They are involved in the promotion and inhibition of angiogenesis and the recruitment of inflammatory cells, which release growth factors and cytokines to facilitate the wound healing process. Preclinical research studies in mice show that the administration of CCL2, CCL21, CXCL12, and a CXCR4 antagonist as well as broad-spectrum inhibition of the CC-chemokine class improve the wound healing process. The focus of this review is to highlight the contributions of chemokines during each stage of wound healing and to discuss the related molecular pathologies in complex and chronic non-healing wounds. We explore the therapeutic potential of targeting chemokines as a novel approach to overcome the debilitating effects of impaired wound healing.

Development of the renal vasculature

The kidney vasculature has a unique and complex architecture that is central for the kidney to exert its multiple and essential physiological functions with the ultimate goal of maintaining homeostasis. An appropriate development and coordinated assembly of the different vascular cell types and their association with the corresponding nephrons is crucial for the generation of a functioning kidney. In this review we provide an overview of the renal vascular anatomy, histology, and current knowledge of the embryological origin and molecular pathways involved in its development. Understanding the cellular and molecular mechanisms involved in renal vascular development is the first step to advance the field of regenerative medicine.

Transforming Growth Factor-β Drives the Transendothelial Migration of Hepatocellular Carcinoma Cells

The entry of malignant hepatocytes into blood vessels is a key step in the dissemination and metastasis of hepatocellular carcinoma (HCC). The identification of molecular mechanisms involved in the transmigration of malignant hepatocytes through the endothelial barrier is of high relevance for therapeutic intervention and metastasis prevention. In this study, we employed a model of hepatocellular transmigration that mimics vascular invasion using hepatic sinusoidal endothelial cells and malignant hepatocytes evincing a mesenchymal-like, invasive phenotype by transforming growth factor (TGF)-β. Labelling of respective cell populations with various stable isotopes and subsequent mass spectrometry analyses allowed the “real-time” detection of molecular changes in both transmigrating hepatocytes and endothelial cells. Interestingly, the proteome profiling revealed 36 and 559 regulated proteins in hepatocytes and endothelial cells, respectively, indicating significant changes during active transmigration that mostly depends on cell–cell interaction rather than on TGF-β alone. Importantly, matching these in vitro findings with HCC patient data revealed a panel of common molecular alterations including peroxiredoxin-3, epoxide hydrolase, transgelin-2 and collectin 12 that are clinically relevant for the patient’s survival. We conclude that hepatocellular plasticity induced by TGF-β is crucially involved in blood vessel invasion of HCC cells.

Dichotomous roles of TGF-β in human cancer

Transforming growth factor-β (TGF-β) mediates numerous biological processes, including embryonic development and the maintenance of cellular homeostasis in a context-dependent manner. Consistent with its central role in maintaining cellular homeostasis, inhibition of TGF-β signaling results in disruption of normal homeostatic processes and subsequent carcinogenesis, defining the TGF-β signaling pathway as a tumor suppressor. However, once carcinogenesis is initiated, the TGF-β signaling pathway promotes cancer progression. This dichotomous function of the TGF-β signaling pathway is mediated through altering effects on both the cancer cells, by inducing apoptosis and inhibiting proliferation, and the tumor microenvironment, by promoting angiogenesis and inhibiting immunosurveillance. Current studies support inhibition of TGF-β signaling either alone, or in conjunction with anti-angiogenic therapy or immunotherapy as a promising strategy for the treatment of human cancers.

Flucytosine and Amphotericin B Coadministration Induces Dose-Related Renal Injury

Invasive fungal infections remain an important clinical problem, and despite recent approaches, they bring high morbidity and mortality. Combination therapies are the most effective; however, adverse effects need to be considered. In this study, we aimed to evaluate the nephrotoxicity induced by combined therapy of flucytosine (FL) and amphotericin B (AMF) at 3 different doses administered to mice for 14 days: 300 μg/kg AMF+50 mg/kg FL; 600 μg/kg AMF+100 mg/kg FL; 900 μg/kg AMF+150 mg/kg FL. Antifungal coadministration triggered nuclear translocation of NF-κB and upregulated nuclear factor kappa-light-chain-enhancer of activated B cells subunit p65 (NF-κB p65) messenger RNA mRNA level in dose-dependent manner. The immunopositivity of tumor necrosis factor-α and interleukin-6 (IL-6), together with IL-6 gene expression, increased both in tubular and glomerular cells. Amphotericin B–flucytosine cotreatment increased significantly the number of terminal deoxy-nucleotidyl transferase (TdT)-mediated dUTP nick end-labeling positive nuclei. Apoptotic cells in renal tubuli were confirmed by electron microscopy. Histopathological analysis revealed collagen accumulation at the glomerular level. Collagen was also evidenced in the glomeruli at the dose of 900 μg/kg AMF+150mg/kg FL by Masson-Goldner trichrome staining and electron microscopy. Moreover, antifungal cotherapy induced upregulation of transforming growth factor beta 1 (TGF-β1) gene expression in a dose-dependent manner. Inflammation and epithelial tubular apoptosis are associated with TGF-β1 activation and initiation of the early stage of glomerular fibrosis at higher doses, leading to tubule–interstitial fibrosis.

Broad-Spectrum Inhibition of the CC-Chemokine Class Improves Wound Healing and Wound Angiogenesis

Angiogenesis is involved in the inflammation and proliferation stages of wound healing, to bring inflammatory cells to the wound and provide a microvascular network to maintain new tissue formation. An excess of inflammation, however, leads to prolonged wound healing and scar formation, often resulting in unfavourable outcomes such as amputation. CC-chemokines play key roles in the promotion of inflammation and inflammatory-driven angiogenesis. Therefore, inhibition of the CC-chemokine class may improve wound healing. We aimed to determine if the broad-spectrum CC-chemokine inhibitor “35K” could accelerate wound healing in vivo in mice. In a murine wound healing model, 35K protein or phosphate buffered saline (PBS, control) were added topically daily to wounds. Cohorts of mice were assessed in the early stages (four days post-wounding) and in the later stages of wound repair (10 and 21 days post-wounding). Topical application of the 35K protein inhibited CC-chemokine expression (CCL5, CCL2) in wounds and caused enhanced blood flow recovery and wound closure in early-mid stage wounds. In addition, 35K promoted neovascularisation in the early stages of wound repair. Furthermore, 35K treated wounds had significantly lower expression of the p65 subunit of NF-κB, a key inflammatory transcription factor, and augmented wound expression of the pro-angiogenic and pro-repair cytokine TGF-β. These findings show that broad-spectrum CC-chemokine inhibition may be beneficial for the promotion of wound healing.

Vascular Growth Factors and Glomerular Disease

The glomerulus is a highly specialized microvascular bed that filters blood to form primary urinary filtrate. It contains four cell types: fenestrated endothelial cells, specialized vascular support cells termed podocytes, perivascular mesangial cells, and parietal epithelial cells. Glomerular cell-cell communication is critical for the development and maintenance of the glomerular filtration barrier. VEGF, ANGPT, EGF, SEMA3A, TGF-β, and CXCL12 signal in paracrine fashions between the podocytes, endothelium, and mesangium associated with the glomerular capillary bed to maintain filtration barrier function. In this review, we summarize the current understanding of these signaling pathways in the development and maintenance of the glomerulus and the progression of disease.

TGFβ Signaling in Tumor Initiation, Epithelial-to-Mesenchymal Transition, and Metastasis

Retaining the delicate balance in cell signaling activity is a prerequisite for the maintenance of physiological tissue homeostasis. Transforming growth factor-beta (TGFβ) signaling is an essential pathway that plays crucial roles during embryonic development as well as in adult tissues. Aberrant TGFβ signaling activity regulates tumor progression in a cancer cell-autonomous or non-cell-autonomous fashion and these effects may be tumor suppressing or tumor promoting depending on the cellular context. The fundamental role of this pathway in promoting cancer progression in multiple stages of the metastatic process, including epithelial-to-mesenchymal transition (EMT), is also becoming increasingly clear. In this review, we discuss the latest advances in the effort to unravel the inherent complexity of TGFβ signaling and its role in cancer progression and metastasis. These findings provide important insights into designing personalized therapeutic strategies against advanced cancers.

Role of TGFβ in regulation of the tumor microenvironment and drug delivery (review)

Deregulation of cell signaling homeostasis is a predominant feature of cancer initiation and progression. Transforming growth factor β (TGFβ) is a pleiotropic cytokine, which regulates numerous biological processes of various tissues in an autocrine and paracrine manner. Aberrant activity of TGFβ signaling is well known to play dual roles in cancer, depending on tumor stage and cellular context. The crucial roles of TGFβ in modulating the tumor microenvironment, its contribution to the accumulation of mechanical forces within the solid constituents of a tumor and its effects on the effective delivery of drugs are also becoming increasingly clear. In this review, we discuss the latest advances in the efforts to unravel the effects of TGFβ signaling in various components of the tumor microenvironment and how these influence the generation of forces and the efficacy of drugs. We also report the implications of tumor mechanics in cancer therapy and the potential usage of anti-TGFβ agents to enhance drug delivery and augment existing therapeutic approaches. These findings provide new insights towards the significance of targeting TGFβ pathway to enhance personalized tumor treatment.

Analysis and characterization of the functional TGFβ receptors required for BMP6-induced osteogenic differentiation of mesenchymal progenitor cells

Although BMP6 is highly capable of inducing osteogenic differentiation of mesenchymal progenitor cells (MPCs), the molecular mechanism involved remains to be fully elucidated. Using dominant negative (dn) mutant form of type I and type II TGFβ receptors, we demonstrated that three dn-type I receptors (dnALK2, dnALK3, dnALK6), and three dn-type II receptors (dnBMPRII, dnActRII, dnActRIIB), effectively diminished BMP6- induced osteogenic differentiation of MPCs. These findings suggested that ALK2, ALK3, ALK6, BMPRII, ActRII and ActRIIB are essential for BMP6-induced osteogenic differentiation of MPCs. However, MPCs in this study do not express ActRIIB. Moreover, RNA interference of ALK2, ALK3, ALK6, BMPRII and ActRII inhibited BMP6-induced osteogenic differentiation in MPCs. Our results strongly suggested that BMP6-induced osteogenic differentiation of MPCs is mediated by its functional TGFβ receptors including ALK2, ALK3, ALK6, BMPRII, and ActRII.

Role of the TGF-β/BMP-7/Smad pathways in renal diseases

TGF-β (transforming growth factor-β) and BMP-7 (bone morphogenetic protein-7), two key members in the TGF-β superfamily, play important but diverse roles in CKDs (chronic kidney diseases). Both TGF-β and BMP-7 share similar downstream Smad signalling pathways, but counter-regulate each other to maintain the balance of their biological activities. During renal injury in CKDs, this balance is significantly altered because TGF-β signalling is up-regulated by inducing TGF-β1 and activating Smad3, whereas BMP-7 and its downstream Smad1/5/8 are down-regulated. In the context of renal fibrosis, Smad3 is pathogenic, whereas Smad2 and Smad7 are renoprotective. However, this counter-balancing mechanism is also altered because TGF-β1 induces Smurf2, a ubiquitin E3-ligase, to target Smad7 as well as Smad2 for degradation. Thus overexpression of renal Smad7 restores the balance of TGF-β/Smad signalling and has therapeutic effect on CKDs. Recent studies also found that Smad3 mediated renal fibrosis by up-regulating miR-21 (where miR represents microRNA) and miR-192, but down-regulating miR-29 and miR-200 families. Therefore restoring miR-29/miR-200 or suppressing miR-21/miR-192 is able to treat progressive renal fibrosis. Furthermore, activation of TGF-β/Smad signalling inhibits renal BMP-7 expression and BMP/Smad signalling. On the other hand, overexpression of renal BMP-7 is capable of inhibiting TGF-β/Smad3 signalling and protects the kidney from TGF-β-mediated renal injury. This counter-regulation not only expands our understanding of the causes of renal injury, but also suggests the therapeutic potential by targeting TGF-β/Smad signalling or restoring BMP-7 in CKDs. Taken together, the current understanding of the distinct roles and mechanisms of TGF-β and BMP-7 in CKDs implies that targeting the TGF-β/Smad pathway or restoring BMP-7 signalling may represent novel and effective therapies for CKDs.

Heme oxygenase-1 as a target for TGF-β in kidney disease

Transforming growth factor-β (TGF-β) is a multifunctional regulatory cytokine that is implicated in a variety of kidney diseases, including diabetic nephropathy and chronic transplant rejection, where it promotes stimulation of the extracellular matrix deposition, cell proliferation, and migration. TGF-β exerts its biological functions largely via its downstream complex signaling molecules, Smad proteins. Paradoxically, TGF-β also is essential for normal homeostasis and suppression of inflammation through mechanisms that are yet to be fully elucidated. One feasible mechanism by which TGF-β may exert its beneficial properties is through induction of heme oxygenase-1 (HO-1). Induction of this redox-sensitive enzyme is known to be cytoprotective through its potent antioxidant, anti-inflammatory, and anti-apoptotic properties in different conditions including several kidney diseases. In this overview, recent advances in our understanding of the role of TGF-β in kidney disease, its molecular regulation of HO-1 expression, and the potential role of HO-1 induction as a therapeutic modality in TGF-β-mediated kidney diseases are highlighted.

TGF-β1 induces endothelial cell apoptosis by shifting VEGF activation of p38(MAPK) from the prosurvival p38β to proapoptotic p38α

TGF-β1 and VEGF, both angiogenesis inducers, have opposing effects on vascular endothelial cells. TGF-β1 induces apoptosis; VEGF induces survival. We have previously shown that TGF-β1 induces endothelial cell expression of VEGF, which mediates TGF-β1 induction of apoptosis through activation of p38 mitogen-activated protein kinase (MAPK). Because VEGF activates p38(MAPK) but protects the cells from apoptosis, this finding suggested that TGF-β1 converts p38(MAPK) signaling from prosurvival to proapoptotic. Four isoforms of p38(MAPK) -α, β, γ, and δ-have been identified. Therefore, we hypothesized that different p38(MAPK) isoforms control endothelial cell apoptosis or survival, and that TGF-β1 directs VEGF activation of p38(MAPK) from a prosurvival to a proapoptotic isoform. Here, we report that cultured endothelial cells express p38α, β, and γ. VEGF activates p38β, whereas TGF-β1 activates p38α. TGF-β1 treatment rapidly induces p38α activation and apoptosis. Subsequently, p38α activation is downregulated, p38β is activated, and the surviving cells become refractory to TGF-β1 induction of apoptosis and proliferate. Gene silencing of p38α blocks TGF-β1 induction of apoptosis, whereas downregulation of p38β or p38γ expression results in massive apoptosis. Thus, in endothelial cells p38α mediates apoptotic signaling, whereas p38β and p38γ transduce survival signaling. TGF-β1 activation of p38α is mediated by VEGF, which in the absence of TGF-β1 activates p38β. Therefore, these results show that TGF-β1 induces endothelial cell apoptosis by shifting VEGF signaling from the prosurvival p38β to the proapoptotic p38α.

Short-term serum deprivation confers sensitivity to taxanes in platinum-resistant human ovarian cancer cells

BACKGROUND

Based on the evidences showing that serum deprivation provokes apoptosis in a variety of cells, we have investigated the effect of serum deprivation on drug sensitivity.

METHODS

After human ovarian cancer cells were preincubated in 0.5 % serum containing medium for 12 hours, cellular drug sensitivities were determined by colony-forming assay.

RESULTS

Serum deprivation treatment resulted in significant increase in paclitaxel sensitivity by factors of mean ± SD, 148.6 ± 28.1 and 10.1 ± 1.0 (n = 3; P < 0.001) fold in platinum-resistant C13 and CP70 cells, respectively. Similarly, serum deprivation induced significant docetaxel sensitivity in these cell lines. However, no enhancement effect of serum deprivation was observed in platinum-sensitive 2008 and A2780 cells. Serum deprivation did not have any effect on the sensitivities to cisplatin, vincristin, and doxorubicin in all of these cells. More than 7-fold increase of apoptotic cells were observed in C13 or CP70 cells when they were treated by serum deprivation followed by paclitaxel compared with the treatment of either serum deprivation or paclitaxel alone. Confocal laser microscopy using rhodamine 123 and flow cytometric analysis with 3,3'-dihexyloxacarbocyanine iodide revealed that serum deprivation decreased mitochondrial membrane potential in C13 or CP70 cells, whereas no change was observed in 2008 and A2780 cells. This indicates that serum deprivation induced depolarization specifically in platinum-resistant cells. Electron microscopy revealed that serum deprivation caused regeneration of mitochondrial matrix structure in C13 or CP70 cells where mitochondria were usually destructed and disappeared.

DISCUSSIONS

These results indicate that serum deprivation confers taxane hypersensitivity specifically in platinum-resistant cells by recovering their impaired mitochondrial functions. The evidence might be clinically beneficial for the development of new chemotherapeutic technology, particularly for the patients with platinum-resistant ovarian cancer.

Vascular damage in the central nervous system: a multifaceted role for vascular-derived TGF-β

The brain function depends on a continuous supply of blood. The blood-brain barrier (BBB), which is formed by vascular cells and glia, separates components of the circulating blood from neurons and maintains the precisely regulated brain milieu required for proper neuronal function. A compromised BBB alters the transport of molecules between the blood and brain and has been associated with or shown to precede neurodegenerative disease. Blood components immediately leak into the brain after mechanical damage or as a consequence of a compromised BBB in brain disease changing the extracellular environment at sites of vascular damage. It is intriguing how blood-derived components alter the cellular and molecular constituents of the neurovascular interface after BBB opening. We recently identified an unexpected role for the blood protein fibrinogen, which is deposited in the nervous system promptly after vascular damage, as an initial scar inducer by promoting the availability of active TGF-β. Fibrinogen-bound latent TGF-β interacts with astrocytes, leading to active TGF-β formation and activation of the TGF-β/Smad signaling pathway. Here, we discuss the pleiotropic effects of potentially vascular-derived TGF-β on cells at the neurovascular interface and we speculate how these biological effects might contribute to degeneration and regeneration processes. Summarizing the effects of the components derived from the brain vascular system on nervous system regeneration might support the development of new therapeutic approaches.

Identification and analysis of type II TGF-β receptors in BMP-9-induced osteogenic differentiation of C3H10T1/2 mesenchymal stem cells

Our previous studies have demonstrated that bone morphogenetic protein 9 (BMP-9) is one of the most efficacious BMPs to induce osteoblast differentiation of mesenchymal stem cells (MSCs). However, the molecular mechanism underlying the BMP-9-induced osteogenic differentiation of MSCs remains to be fully elucidated. In this study, dominant negative (DN) type II TGF-β receptors were constructed and introduced into C3H10T1/2 stem cells, then in vitro and in vivo assays were carried out to analyze and identify the type II TGF-β receptors required for BMP-9-induced osteogenesis. We found that three DN type II TGF-β receptors, DN-BMPRII, DN-ActRII, and DN-ActRIIB, diminished BMP-9-induced alkaline phosphatase (ALP) activity, led to a decrease in BMP-9-induced Smad binding element (SBE)-controled reporter activity, reduced BMP-9-induced expressions of Smad6 and Smad7, and decreased BMP-9-induced mineralization in vitro and ectopic bone formation in vivo, finally resulted in decreased bone masses and immature osteogenesis. These findings strongly suggested that three wild-type II TGF-β receptors, BMPRII, ActRII and ActRIIB, may play a functional role in BMP-9-induced osteogenic differentiation of C3H10T1/2 cells. However, C3H10T1/2 stem cells can express BMPRII and ActRII, but not ActRIIB. Using RNA interference (RNAi), we found that luciferase reporter activity and ALP activity induced by BMP-9 were accordingly inhibited along with the knockdown of BMPRII and ActRII. Taken together, our results demonstrated that BMPRII and ActRII are the functional type II TGF-β receptors in BMP-9-induced osteogenic differentiation of C3H10T1/2 cells.

Trichostatin a prevents TGF-beta1-induced apoptosis by inhibiting ERK activation in human renal tubular epithelial cells

Histone deacetylase (HDAC) inhibitors have recently been reported to have possible reno-protective effects in the last few years. In this study, we found that tricostatin A (TSA), an HDAC inhibitor, prevented transforming growth factor beta1 (TGF-beta1)-induced apoptosis in cultured human renal proximal tubular epithelial cells (RPTECs). TGF-beta1-induced apoptosis via the activation of both caspase-8 and caspase-9 but did not activate the Fas receptor and did not alter Bcl-2 or Bax protein expression. TSA prevented TGF-beta1-induced apoptosis and the activation of caspase-8 and caspase-9 in RPTECs but did not inhibit the TGF-beta1-induced phosphorylation of Smad3 and p38 mitogen-activated protein kinase (MAPK). However, TSA inhibited the TGF-beta1-induced phosphorylation of extracellular signal regulated kinase (ERK), and the MAPK/ERK kinase inhibitor U0126, which specifically inhibits ERK, also prevented TGF-beta1-induced apoptosis. Our results show, for the first time, that TSA inhibits TGF-beta1-induced ERK activation and overrides pro-apoptotic signals like Smad3 and p38 in human RPTECs.

The hormetic morphogen theory of curvature and the morphogenesis and pathology of tubular and other curved structures

In vitro, morphogens such as transforming growth factor (TGF)-beta can up-and down-regulate cell growth at low and high concentrations respectively, i.e. they behave like hormetic agents. The hormetic morphogen theory of curvature proposes that in vivo tissue gradients of such morphogens secreted by source cells determine the fate of cells within their gradient fields (field cells) and that morphogen-induced amplitude modulation of field cell mitochondrial adenosine triphosphate (ATP) generation controls field cell growth along the morphogen gradients: At the high concentration end of gradients, field cell ATP generation and field cell growth is reduced. With declining concentrations along the rest of the gradients field cell ATP and growth is progressively less reduced until an equidyne point is reached, beyond which ATP generation and growth gradually increases. Thus, the differential growth rates along the gradients curve the tissue. Apoptosis at very high morphogen concentrations enables lumen and cavity formation of tubular, spherical, cystic, domed, and other curved biological structures. The morphogen concentration, the gradient slope and the hormesis responses of field cells determine the curvature of such structures during developmental morphogenesis, tissue remodeling and repair of injury. Aberrant hormetic morphogen signaling is associated with developmental abnormalities, vascular diseases, and tumor formation.

Identification of ARIA regulating endothelial apoptosis and angiogenesis by modulating proteasomal degradation of cIAP-1 and cIAP-2

Endothelial apoptosis is a pivotal process for angiogenesis during embryogenesis as well as postnatal life. By using a retrovirus-mediated signal sequence trap method, we identified a previously undescribed gene, termed ARIA (apoptosis regulator through modulating IAP expression), which regulates endothelial apoptosis and angiogenesis. ARIA was expressed in blood vessels during mouse embryogenesis, as well as in endothelial cells both in vitro and in vivo. ARIA is a unique protein with no homology to previously reported conserved domain structures. Knockdown of ARIA in HUVECs by using small interfering RNA significantly reduced endothelial apoptosis without affecting either cell migration or proliferation. ARIA knockdown significantly increased inhibitor of apoptosis (cIAP)-1 and cIAP-2 protein expression, although their mRNA expression was not changed. Simultaneous knockdown of cIAP-1 and cIAP-2 abolished the antiapoptotic effect of ARIA knockdown. Using yeast 2-hybrid screening, we identified the interaction of ARIA with 20S proteasome subunit alpha-7. Thereafter, we found that cIAP-1 and cIAP-2 were degraded by proteasomes in endothelial cells under normal condition. Overexpression of ARIA significantly reduced cIAP-1 expression, and this reduction was abolished by proteasomal inhibition in BAECs. Also, knockdown of ARIA demonstrated an effect similar to proteasomal inhibition with respect to not only expression but also subcellular localization of cIAP-1 and cIAP-2. In vivo angiogenesis studied by Matrigel-plug assay, mouse ischemic retinopathy model, and tumor xenograft model was significantly enhanced by ARIA knockdown. Together, our data indicate that ARIA is a unique factor regulating endothelial apoptosis, as well as angiogenesis, presumably through modulating proteasomal degradation of cIAP-1 and cIAP-2 in endothelial cells.

Transforming growth factor-beta 1 (TGF-beta1) induces angiogenesis through vascular endothelial growth factor (VEGF)-mediated apoptosis

VEGF and TGF-beta1 induce angiogenesis but have opposing effects on endothelial cells. VEGF protects endothelial cells from apoptosis; TGF-beta1 induces apoptosis. We have previously shown that VEGF/VEGF receptor-2 (VEGFR2) signaling mediates TGF-beta1 induction of apoptosis. This finding raised an important question: Does this mechanism stimulate or inhibit angiogenesis? Here we report that VEGF-mediated apoptosis is required for TGF-beta1 induction of angiogenesis. In vitro the apoptotic effect of TGF-beta1 on endothelial cells is rapid and followed by a long period in which the cells are refractory to apoptosis induction by TGF-beta1. Inhibition of VEGF/VEGFR2 signaling abrogates formation of cord-like structures by TGF-beta1 with an effect comparable to that of z-VAD, an apoptosis inhibitor. Similarly, genetic deficiency of VEGF abolishes TGF-beta1 upregulation of endothelial cell differentiation and formation of vascular structures in embryoid bodies. In vivo TGF-beta1 induces endothelial cell apoptosis as rapidly as in vitro. Inhibition of VEGF blocks TGF-beta1 induction of both apoptosis and angiogenesis, an effect similar to that of z-VAD. Thus, TGF-beta1 induction of angiogenesis requires a rapid and transient apoptotic effect mediated by VEGF/VEGFR2. This novel, unexpected role of VEGF and VEGFR2 indicates VEGF-mediated apoptosis as a potential target to control angiogenesis.

PPARgamma in Kidney Physiology and Pathophysiology

Involvement of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) in kidney physiology has been explored recently. Synthetic PPARγ ligands can ameliorate the diabetic kidney disease through different mechanisms, involving inhibition of mesangial cell growth, reduction of mesangial matrix, and cytokine production of glomerular cells as well as promoting endothelial cell survival within the kidney glomeruli. Activation of PPARγ has additional profibrotic consequences, which can contribute to wound healing in diabetic glomerulonephritis. Beside many beneficial effects, PPARγ activation, however, can lead to severe water retention, a common side effect of thiazolidinedione therapy. This unwanted effect is due to the activation of PPARγ in the mesonephric distal collecting system, where PPARγ positively regulates sodium and water resorbtion leading to the expansion of interstitial fluid volume. Recent studies indicate that PPARγ is also involved in the normal kidney development, renal lipid metabolism, and activation of the renin-angiotensin system. In this paper, we give a synopsis of the current knowledge on PPARγ functions in kidney phyisology and pathophysiology.

The role of the matricellular protein SPARC in the dynamic interaction between the tumor and the host

Tumor growth is essentially the result of an evolving cross-talk between malignant and surrounding stromal cells (fibroblasts, endothelial cells and inflammatory cells). This heterogeneous mass of extracellular matrix and intermingled cells interact through cell-cell and cell-matrix contacts. Malignant cells also secrete soluble proteins that reach neighbor stromal cells, forcing them to provide the soil on which they will grow and metastasize. Different studies including expression array analysis identified the matricellular protein SPARC as a marker of poor prognosis in different cancer types. Further evidence demonstrated that high SPARC levels are often associated with the most aggressive and highly metastatic tumors. Here we describe the most recent evidence that links SPARC with human cancer progression, the controversy regarding its role in certain human cancers and the physiological processes in which SPARC is involved: epithelial-mesenchymal transition, immune surveillance and angiogenesis. Its relevance as a potential target in cancer therapy is also discussed.

The role of the matricellular protein SPARC in the dynamic interaction between the tumor and the host

Tumor growth is essentially the result of an evolving cross-talk between malignant and surrounding stromal cells (fibroblasts, endothelial cells and inflammatory cells). This heterogeneous mass of extracellular matrix and intermingled cells interact through cell-cell and cell-matrix contacts. Malignant cells also secrete soluble proteins that reach neighbor stromal cells, forcing them to provide the soil on which they will grow and metastasize. Different studies including expression array analysis identified the matricellular protein SPARC as a marker of poor prognosis in different cancer types. Further evidence demonstrated that high SPARC levels are often associated with the most aggressive and highly metastatic tumors. Here we describe the most recent evidence that links SPARC with human cancer progression, the controversy regarding its role in certain human cancers and the physiological processes in which SPARC is involved: epithelial-mesenchymal transition, immune surveillance and angiogenesis. Its relevance as a potential target in cancer therapy is also discussed.

Role of the JAK-STAT pathway in protection of hydrogen peroxide preconditioning against apoptosis induced by oxidative stress in PC12 cells

The aim of this study was to investigate the role of JAK-STAT pathway in the cytoprotection afforded by preconditioning with H(2)O(2). It was shown that (1) Preconditioning with 100 micromol/L H(2)O(2) can markedly protect PC12 cells against apoptosis and cytotoxicity induced by 300 micromol/L H(2)O(2); (2) The expression and tyrosine phosphorylation of JAK2, not JAK1 were rapidly increased at 5 min after H(2)O(2) preconditioning; (3) The expression of STAT1 and STAT3 were significantly increased at 15 min after H(2)O(2) preconditioning, and the pTyr-STAT1 and pTyr-STAT3 were markedly increased at 60 min after H(2)O(2) preconditioning; (4) Pretreatment with the JAK inhibitor AG-490 (10 micromol/L) 20 min before H(2)O(2) preconditioning blocked not only the activation of JAK2, STAT1 and STAT3, but also the cytoprotection of H(2)O(2) preconditioning against apoptosis and cytotoxicity induced by oxidative stress. These findings suggested that preconditioning with H(2)O(2) activated the JAK-STAT pathway that played an important role in the cytoprotection induced by H(2)O(2) preconditioning.

TGFB1 and TGFBR1 polymorphisms and breast cancer risk in the Nurses' Health Study

BACKGROUND

Transforming growth factor beta 1 (TGFB1) forms a signaling complex with transforming growth factor beta receptors 1 and 2 and has been described as both a tumor suppressor and tumor promoter. Single nucleotide polymorphisms in TGFB1 and a microsatellite in TGFBR1 have been investigated for association with risk of breast cancer, with conflicting results.

METHODS

We examined polymorphisms in the promoter region of the TGFB1 gene as well as the TGFBR1*6A microsatellite in the Nurses' Health Study cohort.

RESULTS

No overall associations between the L10P polymorphism of TGFB1 or the TGFBR1 microsatellite were detected. However, we observed an inverse association between the -509 C/T polymorphism of TGFB1 (p-trend = 0.04), which was stronger and more significant among women with estrogen receptor positive breast cancer.

CONCLUSION

Polymorphisms in the promoter region of TGFB1 are not likely to be associated with large increases in breast cancer risk overall among Caucasian women.

The endothelial cell in ischemic acute kidney injury: implications for acute and chronic function

Recent evidence suggests that injury to the renal vasculature may play an important role in the pathogenesis of both early and chronic ischemic acute kidney injury (AKI). Established and new data support the suggestion that vascular injury, in particular, endothelial cell injury, participates in the extent and maintenance of AKI by pathways that are related to vascular tone. Early alterations in peritubular capillary blood flow during reperfusion has been documented and associated with loss of normal endothelial cell function, which can be replaced pharmacologically or with cell replacement interventions. Distorted peritubular capillary morphology is associated with loss of barrier function that may contribute to early alterations in vascular stasis. In addition, ischemia induces alterations in endothelial cells that may promote inflammation and procoagulant activity, thus contributing to vascular congestion. Reductions in microvasculature density may play a critical part in the progression of chronic kidney disease following initial recovery from ischemia/reperfusion-induced AKI. The exact nature of how capillary loss alters renal function and predisposes renal disease is thought to be due at least in part to hypoxia. Finally, the loss of endothelial cell function may represent an important therapeutic target in which nitric oxide, vascular trophic support, and/or endothelial progenitor cells may show potential importance in ameliorating the acute and/or chronic effects of ischemic AKI.

Vascular development is disrupted by endothelial cell-specific expression of the anti-apoptotic protein Bcl-2

Endothelial cell (EC) apoptosis has been detected in remodelling blood vessels in vivo, and inhibition of EC apoptosis appears to alter vascular morphogenesis in vitro, suggesting that EC apoptosis may play a role in blood vessel remodelling. However, apoptotic EC are difficult to quantify in vivo, and studies of the incidence of EC apoptosis and the sites at which it occurs in vivo have produced contradictory results. Therefore, the specific biological roles played by EC apoptosis remain unclear. Here, we have used a transgenic approach to determine the biological function of EC apoptosis in vivo. Anti-apoptotic Bcl-2 transgenes were expressed in mice under control of the EC-specific tie2 promoter. These transgenic mice died during the second half of gestation. While the development and remodelling of large vessels including aortic arch arteries and great veins proceeded normally, abnormally dense and disorganised networks of small vessels were present in the skin and internal organs. In addition, vessel organisation and lumen formation were disrupted in the placental labyrinth. This study provides direct experimental evidence that endothelial cell apoptosis plays an essential role during embryogenesis. Our results suggest that EC apoptosis plays an important role in determining the structure of the microcirculation but may be dispensable for large vessel development.

VEGF, a prosurvival factor, acts in concert with TGF-beta1 to induce endothelial cell apoptosis

VEGF and TGF-beta1 are potent angiogenesis inducers with opposing effects on endothelial cells. TGF-beta1 induces apoptosis; VEGF protects endothelial cells from apoptosis. We found that TGF-beta1 promotes endothelial cell expression of FGF-2, which up-regulates VEGF synthesis. Inhibition of VEGF signaling through VEGF receptor 2 (flk-1) abrogates TGF-beta1-induced apoptosis and p38(MAPK) activation. Inhibition of p38(MAPK) blocks TGF-beta1-induced apoptosis, showing that VEGF/flk-1-mediated activation of p38(MAPK) is required for TGF-beta1 induction of apoptosis. In the absence of TGF-beta1, VEGF activates p38(MAPK) and promotes endothelial cell survival. However, in context with TGF-beta1, VEGF/flk-1-mediated activation of p38(MAPK) results in apoptosis. Thus, cross-talk between TGF-beta1 and VEGF signaling converts VEGF/flk-1-activated p38(MAPK) into a proapoptotic signal. This finding illustrates an unexpected role of VEGF and indicates that VEGF can be pharmacologically converted into an apoptotic factor, a novel approach to antiangiogenesis therapy.

Stimulation of cyclooxygenase-2 expression by bone-derived transforming growth factor-beta enhances bone metastases in breast cancer

Cyclooxygenase-2 (COX-2), the rate-limiting enzyme of prostaglandin synthesis, has been implicated in invasiveness and distant metastases of cancer. Bone is one of the most common target sites of cancer metastasis. However, the role of COX-2 in bone metastasis is unclear. We examined the surgical specimens of bone metastases from patients with various types of cancers by using immunohistochemistry and observed evident COX-2 expression in these bone metastases. In a nude mouse model of bone metastasis, the MDA-MB-231 human breast cancer cells showed no COX-2 expression at orthotopic sites, whereas these cells, when metastasized to bone, intensely expressed COX-2, suggesting that the bone microenvironment induced COX-2 expression. Consistent with this notion, inhibition of bone resorption by the bisphosphonate ibandronate reduced COX-2 expression in MDA-MB-231 cells in bone. Transforming growth factor-beta (TGFbeta), one of the most abundant growth factors stored in bone, increased COX-2 expression and prostaglandin E2 production in MDA-MB-231 cells in culture. MDA-MB-231 cells overexpressing dominant-negative TGFbeta type II receptors showed decreased bone metastases and reduced osteoclastic bone resorption with impaired COX-2 expression. The COX-2 inhibitors, NS-398 and nimesulide, significantly suppressed bone metastases with decreased osteoclast number and increased apoptosis in MDA-MB-231 cells. These results suggest that bone-derived TGFbeta up-regulates COX-2 expression in breast cancer cells, thereby increasing prostaglandin E2 production, which in turn, stimulates osteoclastic bone destruction, leading to the progression of bone metastases. Our results also suggest that COX-2 is a potential therapeutic target for bone metastases in breast cancer.

CD44 Disruption Prevents Degeneration of the Capillary Network in Obstructive NephropathyviaReduction of TGF-β1–Induced Apoptosis

CD44 is a glycoprotein that is involved in inflammation and cell-cell/cell-matrix interactions, is upregulated in the kidney upon injury, and leads to fibrosis through enhancement of TGF-beta1 signaling. Absence of CD44 prevents development of renal fibrosis in unilateral ureteral obstruction (UUO). A hallmark of development of renal fibrosis is the degeneration of the capillary network. This study shows that CD44 is upregulated on capillary endothelial cells during UUO. For elucidation of the role of CD44 on peritubular endothelial cells in UUO, capillary network degeneration was compared in CD44+/+ and CD44-/- mice. As expected, degeneration of the capillary network was observed in CD44+/+ mice during UUO, associated with increased endothelial apoptosis. However, in the absence of CD44, degeneration of the network is prevented as a result of a decrease in the rate of apoptosis in endothelial cells. The divergence in endothelial apoptosis is not correlated to differential vascular endothelial growth factor or thrombospondin-1 expression. For further investigation of capillary regression, CD44+/+ and CD44-/- peritubular capillary endothelial cell lines were established. With the use of these cells, it is shown that interaction between CD44 and its ligand hyaluronic acid enhances the proapoptotic effect of TGF-beta1 but not thrombospondin-1 on endothelial cells, contributing to the degeneration of the capillary network. Blocking interaction between hyaluronic acid and CD44 therefore may be a potential therapeutic opportunity to preserve the capillary network and prevent the development of fibrosis in chronic renal disease.

The cyclin-dependent kinase inhibitor p21 is required for TGF-beta1-induced podocyte apoptosis

BACKGROUND

Reduced podocyte number is a critical determinant in the development of glomerulosclerosis. Transforming growth factor-beta1 (TGF-beta1) induces podocyte apoptosis, but the cell cycle events are not known. The cyclin-dependent kinase (CDK) inhibitor p21 increases in podocytes in diseases where TGF-beta increases. Accordingly, we studied the role of p21 in podocyte apoptosis.

METHODS

Immortalized and primary p21+/+ and p21-/- mouse podocytes were used. Apoptosis was measured by Hoechst 33342 staining and caspase-3 activity following the exposure to TGF-beta1 or puromycin aminonucleoside. p21 and specific Bcl-2-related family proteins levels were measured by Western blot analysis. To prove a role for p21, we reconstituted p21 expression in p21-/- podocytes utilizing an adenovirus vector.

RESULTS

TGF-beta1 increased the protein levels of p21 in p21+/+ podocytes, and this coincided with apoptosis. In contrast, TGF-beta1 did not induce apoptosis in p21-/- podocytes. Restoring p21 expression increased apoptosis in p21-/- podocytes following exposure to TGF-beta1. TGF-beta1 increased the protein levels of an anti-apoptotic Bcl-2 in p21-/- podocytes, but not in p21+/+ podocytes. Moreover, TGF-beta1 did not increase Bcl-2 expression in p21-/- podocytes in which p21 expression was restored. Finally, puromycin aminonucleoside also induced apoptosis in p21+/+ podocytes, but not in p21-/- podocytes.

CONCLUSION

Podocyte apoptosis induced by TGF-beta1 and puromycin aminonucleoside requires p21, and Bcl-2 plays a crucial role downstream of p21 in mediating this effect. These results suggest that p21 may play a critical role in the decrease in podocyte number in disease status accompanied by increased TGF-beta1.

Type I collagen is a molecular target for inhibition of angiogenesis by endogenous thrombospondin-1

Three-dimensional explant cultures of muscle tissue were used to characterize secreted proteins regulated by endogenous levels of the angiogenesis modulator thrombospondin (TSP)-1. Explants from TSP1 null mice exhibit enhanced neovascularization associated with increased endothelial outgrowth but decreased outgrowth of perivascular smooth muscle cells . The absence of endogenous TSP1 did not diminish activation of latent transforming growth factor-beta and moderately decreased matrix metalloproteinase levels. However, significant changes in other secreted proteins were observed. Endogenous TSP1 decreased mRNA levels for collagens Ialpha1, Ialpha2, and IIIalpha1 and laminin alpha4 and increased collagen IValpha1 mRNA expression. Endogenous TSP1 also decreased the level of type I collagen protein produced by the vascular outgrowths. Collagens Ialpha1, Ialpha2, and IIIalpha1 are known tumor endothelial markers, suggesting that TSP1 coordinately regulates a set of extracellular matrix genes that reverse the angiogenic switch. Suppression of collagen Ialpha1 or Ialpha2 mRNAs using antisense morpholinos inhibited outgrowth in TSP1 null explants and proliferation of TSP1 null endothelial cells, indicating that type I collagen synthesis is limiting for this neovascularization response.

Membrane type 1-matrix metalloproteinase induces endothelial cell morphogenic differentiation by a caspase-dependent mechanism

Membrane-type 1 matrix metalloproteinase (MT1-MMP) has been suggested to play an essential role in angiogenesis. Based on recent evidence suggesting that the sprouting and branching of capillaries during angiogenesis involves apoptosis, we investigated the involvement of this process in MT1-MMP-dependent morphogenic differentiation of EC into capillary-like structures. We found that MT1-MMP sensitizes EC to apoptosis, since reduction of MT1-MMP expression abolished vimentin fragmentation in apoptotic HUVECs while overexpression of the enzyme induced caspase-3 activity in BAECs subjected to pro-apoptotic treatments. MT1-MMP-mediated caspase-3 activation likely occurs through the mitochondrial pathway since it was abrogated by Bcl-2, but not by CrmA overexpression. Reduction of MT1-MMP expression in HUVECs reduced morphogenic differentiation that was correlated with diminished vimentin fragmentation, whereas its overexpression in BAECs stimulated both processes. Inactivation of the catalytic activity or removal of the cytoplasmic domain of MT1-MMP markedly reduced its ability to induce both morphogenic differentiation and caspase-3 activation. The inhibitory effects of the anti-apoptotic protein Bcl-2 and the caspase inhibitor zVAD-fmk further suggested the involvement of apoptosis during MT1-MMP-mediated morphogenic differentiation. Our results show that the ability of MT1-MMP to induce EC morphogenic differentiation involves its activation of a caspase-dependent mechanism.

Glomerular endothelial cell differentiation

BACKGROUND

Glomerular endothelial cells differ from most other endothelial cells in that they are extraordinarily flattened and highly fenestrated. In this differentiated form, they allow formation of glomerular ultrafiltrate at a prodigious rate.

METHODS

Molecular processes that dictate the development and differentiation of glomerular endothelium are reviewed.

RESULTS

During glomerular development, angioblasts already present in the metanephric blastema well before any organized angiogenic sprouts invade the capillary cleft of developing nephrons at the comma and S-shape stages in response to chemotactic and guiding cues from primitive podocytes. The angioblasts then undergo homotypic aggregation into precapillary cords as yet devoid of a lumen. Lumen development then proceeds through the loss of superfluous endothelial cells by apoptosis as well as flattening of the remaining viable endothelial cells. The final step, fenestration, is critically dependent on appropriate stimuli, most notably vascular endothelial growth factor A (VEGF-A), from differentiated podocytes. Current evidence suggests that the fenestrae of fully differentiated glomerular endothelium can be lost within hours if the VEGF-A stimulus is removed, and that the glomerular endotheliosis, loss of glomerular filtration rate (GFR) and proteinuria observed in preeclampsia are due to the circulating inhibitor of VEGF-A, soluble VEGF receptor 1 (VEGFR-1).

CONCLUSION

Differentiation of the glomerular endothelium is highly dependent on podocyte-derived stimuli and their loss leads to the derangements of glomerular function in preeclampsia.

Transforming growth factor-β in acute renal failure: receptor expression, effects on proliferation, cellularity, and vascularization after recovery from injury

Transforming growth factor (TGF)-β1and a number of TGF-β-responsive genes are transiently enhanced following induction of ischemic acute renal failure (ARF) in the rat. The mRNA and protein expression of TGF-β receptors were analyzed in postischemic rat kidneys by ribonuclease protection, in situ hybridization, and immunohistochemistry. TGF-βRI and -RII were enhanced within 3 days of ischemia-reperfusion (I/R) injury and remained elevated for up 7 days post-I/R; TGF-β receptor expression was localized primarily in regenerating tubules within the outer medulla. A neutralizing TGF-β antibody exacerbated cellular proliferation observed on day 3 postischemia but had no effect on day 1 or 2. TGF-β antibody treatment had no measurable effect on loss of renal function or the restoration of renal function during the recovery response for up to 35 days postsurgery. However, ischemic injury resulted in modest renal hypertrophy that is due, in part, to in an increase in the number of interstitial cells in the postischemic kidney. Immunohistochemistry showed that several of these cells stained positively for the fibroblast-specific marker, S100A4 positive. Anti-TGF-β treatment substantially attenuated the renal hypertrophy, interstitial cellularity, and S100A4-positive cells present at 35 days post-I/R. Finally, TGF-β immunoneutralization attenuated the loss of renal vascular density following recovery from I/R injury. These data suggest that the TGF-β/TβR system is enhanced in the postischemic kidney. However, the current study failed to identify a prominent role for this system in the repair of proximal tubules following ARF. In contrast, the activation of this system may play an important role in the long-term structure of the postischemic kidney by influencing microvascular structure and interstitial cellularity.

Myeloid-related proteins 8 and 14 induce a specific inflammatory response in human microvascular endothelial cells

Myeloid-related protein 8 (MRP8) and MRP14, S100 proteins secreted by activated phagocytes, bind specifically to endothelial cells. The endothelial response to MRP8/MRP14, however, is unknown. Using oligonucleotide microarray analysis, we show for the first time that MRP8/MRP14 induce a thrombogenic, inflammatory response in human microvascular endothelial cells by increasing the transcription of proinflammatory chemokines and adhesion molecules and by decreasing the expression of cell junction proteins and molecules involved in monolayer integrity. All changes on the gene expression level could be confirmed using biochemical and functional assays. We demonstrated that the expression of MRP8/MRP14 closely correlated with the inflammatory activity in systemic vasculitis, confirming the important role of these proteins for distinct inflammatory reactions in endothelia. MRP8/MRP14 may represent novel targets for anti-inflammatory strategies.

Rarefaction of peritubular capillaries following ischemic acute renal failure: a potential factor predisposing to progressive nephropathy

PURPOSE OF REVIEW

Long-term renal complications of acute renal failure have generally not been expected in patients that recover from acute renal failure. However, as the incidence of acute renal failure is rising, the incidence of long-term complications is likely to increase. As a corollary to ischemic acute renal failure, ischemic injury in the setting of transplant is a leading cause of delayed graft function. Unlike acute renal failure in native kidneys, delayed graft function is highly predictive of chronic nephropathy and organ failure. It is generally well accepted that acute reversible injuries mediated by ischemia render grafts susceptible toward future demise. The nature of the susceptibility that is conveyed to grafts following ischemic injury is not well understood.

RECENT FINDINGS

Evidence from animal models suggests that acute injury results in microvascular damage and vessel loss in the kidney, which, as opposed to tubular damage, is largely persistent. In addition, various studies of biopsies of renal transplants suggest that ischemia imposes an early and sustained loss in peritubular capillaries in the transplanted graft. The loss of peritubular capillaries has been associated with nephropathies of diverse etiologies and may represent a single, common pathway towards progressive damage.

SUMMARY

It is hypothesized that rarefaction of peritubular capillaries represents a critical event, following ischemic injury, that permanently alters renal function and predisposes patients to the development of chronic renal insufficiency. Factors that affect vascular reactivity or the structural dynamics of the kidney vascular system following injury may represent future treatment modalities following renal injury.

Expression of the type-1 repeats of thrombospondin-1 inhibits tumor growth through activation of transforming growth factor-beta

In the present study, the type-1 repeats of thrombospondin-1 (TSP-1) were transfected into A431 cells. Expression of all three type-1 repeats (3TSR) and expression of just the second type-1 repeat containing the transforming growth factor (TGF)-beta activating sequence KRFK (TSR2 + KRFK) significantly inhibited in vivo tumor angiogenesis and growth in nude mice. These tumors expressed increased levels of both active and total TGF-beta. A431 cells expressing the second type-1 repeat without the KRFK sequence (TSR2 - KRFK) produced tumors that were slightly larger than the 3TSR and TSR2 + KRFK tumors. These tumors expressed elevated levels of active TGF-beta but levels of total TGF-beta were not different from control tumors. Injection of the peptide, LSKL, which blocks TSP-1 activation of TGF-beta, reversed the growth inhibition observed with cells expressing TSR2 + KRFK to a level comparable to controls. Various residues in the WSHWSPW region and the VTCG sequence of both TSR2+/- KRFK were mutated. Although mutation of the VTCG sequence had no significant effect on tumor growth, mutation of the WSHWSPW sequence reduced inhibition of tumor growth. These findings suggest that the inhibition of tumor angiogenesis and growth by endogenous TSP-1 involves regulation of both active and total TGF-beta and the sequences KRFK and WSHWSPW in the second type-1 repeat.

Peroxisome proliferator-activated receptor-gamma ligands inhibit TGF-beta 1-induced fibronectin expression in glomerular mesangial cells

The thiazolidinedione (TZD) class of antidiabetic drugs, which are ligands for peroxisome proliferator-activated receptor (PPAR)-gamma, has been shown to possess potent anti-inflammatory and antineoplastic actions. Here, we show in mesangial cells that PPAR-gamma agonists inhibit fibronectin expression by transforming growth factor (TGF)-beta 1. TGF-beta 1 enhanced fibronectin mRNA expression, and this enhancement was abrogated by pretreatment with pioglitazone. Electrophoretic mobility shift assay identified that pioglitazone inhibited TGF-beta 1-induced DNA binding of activator protein-1 (AP-1). Pioglitazone inhibited AP-1 reporter activity but not Smad binding elements reporter activity without affecting TGF-beta 1-induced activation of mitogen-activated protein kinases (MAPKs) or Smad2. PPAR-gamma overexpression inhibited TGF-beta 1-induced fibronectin expression as well as the activation of AP-1. 15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), a natural PPAR-gamma ligand, also inhibited TGF-beta1-induced fibronectin expression by suppressing AP-1 activation by TGF-beta 1. 15d-PGJ(2) inhibited the TGF-beta 1-induced MAPK activation. Dominant-negative PPAR-gamma (Delta PPAR-gamma) completely abrogated the inhibitory effect of pioglitazone and incompletely blocked its effect of 15d-PGJ(2) on TGF-beta 1-induced AP-1 reporter activity. Delta PPAR-gamma overexpression did not affect the inhibitory effect of 15d-PGJ(2) on TGF-beta 1-induced MAPK activation. In conclusion, pioglitazone inhibits TGF-beta 1-induced fibronectin expression by inhibiting AP-1 activation dependent on PPAR-gamma, while 15d-PGJ(2) acts through a dual mechanism independent of and dependent on PPAR-gamma activation in mouse mesangial cells.

Intervention with Tranilast Attenuates Renal Pathology and Albuminuria in Advanced Experimental Diabetic Nephropathy

<i>Background/Aims:</i> Tubulointerstitial pathology with the accumulation of extracellular matrix are pathological hallmarks of diabetic nephropathy that are directly related to declining renal function. Tranilast (N-[3,4-dimethoxycinnamoyl]anthranilic acid), an inhibitor of transforming growth factor-β (TGF-β), used to treat hypertrophic scars has recently been shown in pilot studies to exert a beneficial effect in advanced diabetic nephropathy in humans. However, its effects on diabetic renal pathology are unknown. <i>Methods:</i> Studies were conducted using a transgenic model, the diabetic (mRen-2)27 rat, which develops many of the structural and functional characteristics of human diabetic nephropathy when diabetes is induced with streptozotocin (STZ). An experimental design was chosen to mimic, in part, the clinical context with drug therapy (tranilast 400 mg/kg/ day) initiated in established disease (8 weeks after STZ) and in the presence of persistent hyperglycaemia and hypertension. <i>Results:</i> At 16 weeks, diabetes was associated with progressive albuminuria, tubulointerstitial fibrosis and tubular atrophy. Without affecting blood pressure or blood glucose, tranilast treatment was associated with a 83% reduction in tubulointerstitial fibrosis (p < 0.001), a 58% reduction in tubular atrophy (p < 0.01) and near normalization of albuminuria (p < 0.05) in diabetic Ren-2 rats. In vitro studies in primary cultures of human renal cortical fibroblasts demonstrated a reduction in TGF-β-induced hydroxyproline incorporation and fibronectin synthesis with tranilast 100 µ<i>M</i>. <i>Conclusion:</i> Tranilast, when administered during the course of experimental diabetic nephropathy, attenuates tubulointerstitial pathology and albuminuria. These findings are consistent with the antagonist effects of tranilast on TGF-β actions in the diabetic kidney.

Endothelial cell apoptosis during glomerular capillary lumen formation in vivo

Transforming growth factor-beta (TGF-beta) stimulates endothelial cell apoptosis in vitro, and inhibition of TGF-beta1 leads to retention of undifferentiated endothelial cells in developing glomerular capillaries and reduced lumen formation in vivo. This study explored the question whether glomerular capillary lumen formation in vivo may involve TGF-beta1-dependent endothelial cell apoptosis. Neutralizing anti-TGF-beta1 or non-immune IgY were infused into the renal arteries of 3-d-old rats, and the kidneys were examined 2 d later. By transmission electron microscopy, endocapillary apoptotic cells were observed at a frequency of 0.10/loop in immature glomeruli of 3-d-old rat pups. In 5-d-old rat pups given neutralizing TGF-beta1 antibody or control IgY, the frequency of endocapillary apoptotic cells was 0.03 and 0.09/loop, respectively (P < 0.001, chi(2)). Dual labeling with TUNEL and anti-von Willebrand factor (vWF) antibody showed that apoptotic cells in immature glomeruli of 5-d-old rat pups are endothelial cells. Quantitative analysis showed significantly fewer TUNEL/vWF-labeled cells in glomeruli after anti-TGF-beta1 antibody infusion than in controls. No endocapillary apoptotic cells were observed in any group in C-shaped or S-shaped bodies, and the TUNEL assay revealed no glomerular apoptotic cells in kidneys from mature rats. These findings suggest that superfluous endothelial cells are cleared from immature glomerular capillaries by apoptosis, a process regulated by TGF-beta1. Taken together with the previous finding, that TGF-beta1 blockade blunts glomerular capillary lumen formation in vivo, it is proposed that TGF-beta1-dependent apoptosis serves to open capillary lumens in this vascular bed during glomerular development.

Antiangiogenic effects of butyric acid involve inhibition of VEGF/KDR gene expression and endothelial cell proliferation

The formation of new blood vessels from pre-existing ones is required for the growth of solid tumors and for metastasis. Interaction of tumor-secreted vascular endothelial growth factor (VEGF) with its receptor(s) on endothelial cells triggers endothelial cell proliferation and migration, which facilitate tumor angiogenesis. Butyric acid (BuA), a fermentation product of dietary fibers in the colon, is shown to alter gene expression and is postulated to be anticarcinogenic. The results presented in this paper indicate that BuA can be antiangiogenic in vivo by inhibiting angiogenesis in chorioallantoic membrane assay. BuA was not cytotoxic to endothelial cells but was a potent antiproliferative agent besides being proapoptotic to endothelial cells as verified by FACS analysis. Conditioned media from BuA-treated Ehrlich ascites tumor cells showed a 30% decrease in VEGF concentration when compared with untreated cells. The decrease in VEGF mRNA and its receptor, KDR mRNA levels in EAT and endothelial cells respectively, suggests that the VEGF-KDR system of angiogenesis is the molecular target for the antiangiogenic action of BuA.

TGF-beta signaling in renal disease

Since discovery over a decade ago of a role for the cytokine TGF-beta as key mediator of glomerular and tubulointerstitial pathobiology in chronic kidney diseases, studies of TGF-beta signaling in the kidney have focused on the molecular biology of fibrogenesis. In recent years, glomerular and tubular epithelial cell apoptosis and cellular transdifferentiation have been proposed as putative primary pathomechanisms that may underlie progression of renal disease. This review describes evidence in support of nonlinear models and functional roles of TGF-beta signaling in mediating apoptosis and epithelial-to-mesenchymal transdifferentiation (EMT) in chronic progressive renal disease. Emphasis is placed on cell context-dependent models of TGF-beta signaling providing a conceptual framework to consolidate seemingly distinct pathomechanisms of progression of glomerular and tubulointerstitial disease.