Fibrosis and angiogenesis

Chemokine-mediated angiogenesis: an essential link in the evolution of airway fibrosis?

Angiogenesis may be an important factor in the development of fibrotic lung disease. Prior studies have strongly suggested a role for angiogenic vascular remodeling in pulmonary fibrosis, and emerging evidence indicates that new vessel formation is critical in airway fibrosis. Bronchiolitis obliterans syndrome is a fibrotic occlusion of distal airways that is largely responsible for the morbidity and mortality of patients after lung transplantation. In this issue, Belperio et al. demonstrate a role for CXC chemokine receptor 2 in the regulation of angiogenesis-mediated airway fibroproliferation. By integrating an understanding of neovascularization into the study of events that occur between inflammation and fibrosis, it becomes increasingly possible to rationally design therapies that can halt conditions of maladaptive fibrosis.

Combination of interferon-beta and angiotensin-converting enzyme inhibitor, perindopril, attenuates the murine liver fibrosis development

Recent studies have revealed that both interferon (IFN) and angiotensin-converting enzyme inhibitor (ACE-I) exert an anti-fibrotic effect. The aim of this study was to examine the combined effect of the ACE-I and IFN on the murine hepatic fibrosis development. A model of CCl(4)-induced hepatic fibrosis was used to assess the effect of the clinically used ACE-I, perindopril (PE), and IFN-beta. The PE and IFN were administered after 2-week treatment with CCl(4), and the hepatic indices of fibrosis were assessed at 8 weeks. Single treatment with either PE or IFN at the clinically available comparable doses significantly attenuated liver fibrogenesis associated with suppression of the hepatic hydroxyproline and serum fibrosis markers. The number of alpha-smooth muscle actin-positive cells, and the hepatic alpha1(I)-procollagen mRNA were also markedly inhibited. The inhibitory effect of PE was more potent than IFN, and the combination treatment with PE and IFN almost completely attenuated liver fibrosis development. In vitro, the angiotensin-II (AT-II) type 1 receptor blocker and IFN suppressed the AT-II-induced proliferation and alpha1(I)-procollagen mRNA expression of the activated hepatic stellate cells. The combination treatment of the clinically used PE and IFN may provide a new strategy for anti-liver fibrosis therapy.

Serum bFGF and VEGF correlate respectively with bowel wall thickness and intramural blood flow in Crohn's disease

Serum levels of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF)--two factors known to promote tissue repair, fibroblast proliferation, and angiogenesis--were measured in Crohn's disease patients and correlated with bowel wall thickness (BWT), measured by conventional grey scale ultrasonography, and with the ileal intramural vessel flow, measured by contrast-enhanced color Doppler imaging. Serum samples were obtained from 25 patients with active Crohn's disease and 22 healthy volunteers, all sex- and age-matched. Serum bFGF and VEGF levels were measured by ELISA assay. All the patients were examined with conventional transabdominal bowel sonography. Color Doppler of the intramural enteric vessels was then performed after the intravenous injection of Levovist, a galactose-based sonographic contrast agent. In Crohn's disease patients, serum bFGF and VEGF were significantly higher compared with healthy volunteers. A positive correlation between serum bFGF and BWT and between serum VEGF and color Doppler signal intensity was found. The raised serum bFGF levels in Crohn's disease patients with intestinal strictures compared with patients with other phenotypes (fistulizing, inflammatory), together with the correlation observed between serum bFGF and BWT, suggests a possible involvement of bFGF in the process of transmural fibrogenesis in Crohn's disease. The higher levels of VEGF in those patients with increased intramural blood flow suggests that VEGF may be considered a marker of angiogenesis in this condition.

Early growth response gene 1-mediated apoptosis is essential for transforming growth factor beta1-induced pulmonary fibrosis

Fibrosis and apoptosis are juxtaposed in pulmonary disorders such as asthma and the interstitial diseases, and transforming growth factor (TGF)-β₁ has been implicated in the pathogenesis of these responses. However, the in vivo effector functions of TGF-β₁ in the lung and its roles in the pathogenesis of these responses are not completely understood. In addition, the relationships between apoptosis and other TGF-β₁–induced responses have not been defined. To address these issues, we targeted bioactive TGF-β₁ to the murine lung using a novel externally regulatable, triple transgenic system. TGF-β₁ produced a transient wave of epithelial apoptosis that was followed by mononuclear-rich inflammation, tissue fibrosis, myofibroblast and myocyte hyperplasia, and septal rupture with honeycombing. Studies of these mice highlighted the reversibility of this fibrotic response. They also demonstrated that a null mutation of early growth response gene (Egr)-1 or caspase inhibition blocked TGF-β₁–induced apoptosis. Interestingly, both interventions markedly ameliorated TGF-β₁–induced fibrosis and alveolar remodeling. These studies illustrate the complex effects of TGF-β₁ in vivo and define the critical role of Egr-1 in the TGF-β₁ phenotype. They also demonstrate that Egr-1–mediated apoptosis is a prerequisite for TGF-β₁–induced fibrosis and remodeling.

Tumstatin peptide, an inhibitor of angiogenesis, prevents glomerular hypertrophy in the early stage of diabetic nephropathy

In the early stage of diabetic nephropathy (one of the major microvascular complications of diabetes) glomerular hyperfiltration and hypertrophy are observed. It is clinically important to regulate glomerular hypertrophy for preventing glomerulosclerosis. The number of glomerular endothelial cells is known to be increased in diabetic nephropathy associated with enlarged glomerular tufts, suggesting that the mechanism is similar to that of angiogenesis. Tumstatin peptide is an angiogenesis inhibitor derived from type IV collagen and inhibits in vivo neovascularization induced by vascular endothelial growth factor (VEGF), one of the mediators of glomerular hypertrophy in diabetic nephropathy. Here, we show the effect of tumstatin peptide in inhibiting alterations in early diabetic nephropathy. Glomerular hypertrophy, hyperfiltration, and albuminuria were suppressed by tumstatin peptide (1 mg/kg) in streptozotocin-induced diabetic mice. Glomerular matrix expansion, the increase of total glomerular cell number and glomerular endothelial cells (CD31 positive), and monocyte/macrophage accumulation was inhibited by tumstatin peptide. Increase in renal expression of VEGF, flk-1, and angiopoietin-2, an antagonist of angiopoietin-1, was inhibited by tumstatin treatment in diabetic mice. Alteration of glomerular nephrin expression, a podocyte protein crucial for maintaining glomerular filtration barrier, was recovered by tumstatin in diabetic mice. Taken together, these results demonstrate the potential use of antiangiogenic tumstatin peptide as a novel therapeutic agent in early diabetic nephropathy.

Regulation of TGFβ1-mediated growth inhibition and apoptosis by RUNX2 isoforms in endothelial cells

Runx transcription factors regulate viral growth, hematopoiesis, bone formation, angiogenesis, and gastric epithelial development through specific DNA-binding motifs on target gene promoters. Vascular endothelial cells (ECs) express RUNX genes that are activated by angiogenic factors. The RUNX2 gene also activates the vascular endothelial growth factor promoter. Alternatively spliced forms of RUNX genes have been described, but their functions in angiogenesis have not been elucidated. In this study, expression of a novel alternatively spliced variant of RUNX2 (RUNX2Delta8), lacking the region encoded by exon 8, was detected in aortic tissue undergoing angiogenesis in vitro and in ECs. Expression of RUNX2 and RUNX2Delta8 increased in vascular sprouts concomitant with expression of cellular proteases and cytokines known to mediate angiogenesis. RUNX2 DNA-binding activity was expressed in proliferating but not quiescent ECs. Ectopic expression of RUNX2 in ECs increased cell sprouting, cell proliferation, DNA synthesis, and phosphorylation of phosphorylated retinoblastoma relative to control transfectants while RUNX2, but not RUNX2Delta8 transfectants, acquired resistance to growth inhibition by transforming growth factor (TGFbeta1). Furthermore, RUNX2Delta8-transfected cells were more sensitive to TGFbeta1-induced apoptosis than RUNX2 transfectants. Consistent with these data, the RUNX2 gene was a strong repressor of the promoter of the cyclin-dependent kinase inhibitor, p21(CIP1), while RUNX2Delta8 was a competitive inhibitor of RUNX2 and exhibited weak repression activity. These results support the hypothesis that ECs regulate growth and apoptosis, in part, by alternative splicing events in the RUNX2 transcription factor to affect the TGFbeta1 signaling pathway. The exon 8 domain of RUNX2 may contribute to the strong repression activity of RUNX2 for some target gene promoters.

Inflammatory cytokines, angiogenesis, and fibrosis in the rat peritoneum

Peritonitis, a common complication of peritoneal dialysis, is followed by acute changes in the function of the peritoneum. The role of inflammatory cytokines in these processes is not clearly identified. We used adenoviral-mediated gene transfer to transiently overexpress interleukin (IL)-1 beta (AdIL-1 beta) or tumor necrosis factor (TNF)-alpha (AdTNF-alpha) in the rat peritoneum then used a modified equilibrium test to study the histological and functional changes. Overexpression of IL-1 beta or TNF-alpha led to an acute inflammatory response. Both inflammatory cytokines induced an early expression of the angiogenic cytokine, vascular endothelial growth factor, along with increased expression of the profibrotic cytokine, transforming growth factor-beta1, along with fibronectin expression and collagen deposition in peritoneal tissues. Both inflammatory cytokines induced angiogenesis, increased solute permeability, and ultrafiltration dysfunction at earlier time points. Changes in structure and function seen in AdTNF-alpha-treated animals returned to normal by 21 days after infection, whereas AdIL-1 beta-treated animals had persistently increased vasculature with submesothelial thickening and fibrosis. This was associated with up-regulation TIMP-1. TNF-alpha or IL-1 beta both induce acute changes in the peritoneum that mimic those seen in peritoneal dialysis patients who experience an episode of peritonitis. These functional changes were associated with early angiogenesis that resolved rapidly after exposure to TNF-alpha. IL-1 beta exposure, however, led to a different response with sustained vascularization and fibrosis. IL-1 beta inhibition may be a therapeutic goal in acute peritonitis to prevent peritoneal damage.

Thrombospondin 2 inhibits microvascular endothelial cell proliferation by a caspase-independent mechanism

The matricellular protein thrombospondin 2 (TSP2) regulates a variety of cell-matrix interactions. A prominent feature of TSP2-null mice is increased microvascular density, particularly in connective tissues synthesized after injury. We investigated the cellular basis for the regulation of angiogenesis by TSP2 in cultures of murine and human fibroblasts and endothelial cells. Fibroblasts isolated from murine and human dermis synthesize TSP2 mRNA and secrete significant amounts of immunoreactive TSP2, whereas endothelial cells from mouse lung and human dermis did not synthesize TSP2 mRNA or protein. Recombinant mouse TSP2 inhibited growth of human microvascular endothelial cells (HMVECs) mediated by basic fibroblast growth factor, insulin-like growth factor-1, epidermal growth factor, and vascular endothelial growth factor (VEGF). HMVECs exposed to TSP2 in the presence of these growth factors had a decreased proportion of cells in S and G2/M phases. HMVECs cultured with a combination of basic fibroblast growth factor, insulin-like growth factor-1, and epidermal growth factor displayed an increased proportion of nonviable cells in the presence of TSP2, but the addition of VEGF blocked this TSP2-mediated impairment of cell viability. TSP2-mediated inhibition of DNA synthesis by HMVECs in the presence of VEGF was not affected by the broad-spectrum caspase inhibitor zVAD-fmk. Similar findings were obtained with TSP1. Taken together, these observations indicate that either TSP2 or TSP1 can inhibit HMVEC proliferation by inhibition of cell cycle progression and induction of cell death, but the mechanisms responsible for TSP2-mediated inhibition of cell cycle progression are independent from those leading to cell death.

Antiangiogenic and antifibrotic gene therapy in a chronic infusion model of peritoneal dialysis in rats

To identify the relative importance of peritoneal fibrosis and angiogenesis in peritoneal membrane dysfunction, adenoviral mediated gene transfer of angiostatin, a recognized angiogenesis inhibitor, and decorin, a transforming growth factor-beta-inhibiting proteoglycan, were used in a daily infusion model of peritoneal dialysis. A peritoneal catheter and subcutaneous port were inserted in rats. Five and fourteen d after insertion, adenovirus-expressing angiostatin, decorin, or AdDL70, a null control virus, were administered. Daily infusion of 4.25% Baxter Dianeal was initiated 7 d after catheter insertion and continued until day 35. Three initial doses of lipopolysaccharide were administered on days 8, 10, and 12 to promote an inflammatory response. Net ultrafiltration was used as a measure of membrane function, and peritoneum-associated vasculature and mesenteric collagen content was quantified. Ultrafiltration dysfunction, angiogenesis, and fibrosis were observed in daily infusion control animals. Animals treated with AdAngiostatin demonstrated an improvement in net ultrafiltration (-3.1 versus -7.8 ml for control animals; P = 0.0004) with a significant reduction in vessel density. AdDecorin-treated animals showed a reduction in mesenteric collagen content (1.8 versus 2.9 microg/mg; P = 0.04); however, AdDecorin treatment had no effect on net ultrafiltration. In a rodent model of peritoneal membrane failure, net ultrafiltration was significantly improved and peritoneal-associated blood vessels were significantly reduced by using adenovirus-mediated gene transfer of angiostatin. Decorin, a transforming growth factor-beta-inhibiting proteoglycan, reduced collagen content but did not affect net ultrafiltration. Improvement in the function of the peritoneum as a dialysis membrane after treatment with angiostatin has implications for treatment of peritoneal membrane dysfunction seen in patients on long-term dialysis.

Angiogenic and angiostatic factors in systemic sclerosis: increased levels of vascular endothelial growth factor are a feature of the earliest disease stages and are associated with the absence of fingertip ulcers

To examine whether the lack of sufficient neoangiogenesis in systemic sclerosis (SSc) is caused by a decrease in angiogenic factors and/or an increase in angiostatic factors, the potent proangiogenic molecules vascular endothelial growth factor (VEGF) and basic fibroblast growth factor, and the angiostatic factor endostatin were determined in patients with SSc and in healthy controls. Forty-three patients with established SSc and nine patients with pre-SSc were included in the study. Serum levels of VEGF, basic fibroblast growth factor and endostatin were measured by ELISA. Age-matched and sex-matched healthy volunteers were used as controls. Highly significant differences were found in serum levels of VEGF between SSc patients and healthy controls, whereas no differences could be detected for endostatin and basic fibroblast growth factor. Significantly higher levels of VEGF were detected in patients with Scl-70 autoantibodies and in patients with diffuse SSc. Patients with pre-SSc and short disease duration showed significant higher levels of VEGF than healthy controls, indicating that elevated serum levels of VEGF are a feature of the earliest disease stages. Patients without fingertip ulcers were found to have higher levels of VEGF than patients with fingertip ulcers. Levels of endostatin were associated with the presence of giant capillaries in nailfold capillaroscopy, but not with any other clinical parameter. The results show that the concentration of VEGF is already increased in the serum of SSc patients at the earliest stages of the disease. VEGF appears to be protective against ischemic manifestations when concentrations of VEGF exceed a certain threshold level.

Extracellular matrix-derived peptide binds to alpha(v)beta(3) integrin and inhibits angiogenesis

Angiogenesis is associated with several pathological disorders as well as with normal physiological maintenance. Components of vascular basement membrane are speculated to regulate angiogenesis in both positive and negative manner. Recently, we reported that tumstatin (the NC1 domain of alpha 3 chain of type IV collagen) and its deletion mutant tum-5 possess anti-angiogenic activity. In the present study, we confirm that the anti-angiogenic activity of tumstatin and tum-5 is independent of disulfide bond requirement. This property of tum-5 allowed us to use overlapping synthetic peptide strategy to identify peptide sequence(s) which possess anti-angiogenic activity. Among these peptides, only the T3 peptide (69-88 amino acids) and T7 peptide (74-98 amino acids) inhibited proliferation and induced apoptosis specifically in endothelial cells. The peptides, similar to tumstatin and the tum-5 domain, bind and function via alpha(v)beta(3) in an RGD-independent manner. Restoration of a disulfide bond between two cysteines within the peptide did not alter the anti-angiogenic activity. Additionally, these studies show that tumstatin peptides can inhibit proliferation of endothelial cells in the presence of vitronectin, fibronectin, and collagen I. Anti-angiogenic effect of the peptides was further confirmed in vivo using a Matrigel plug assay in C57BL/6 mice. Collectively, these experiments suggest that the anti-angiogenic activity of tumstatin is localized to a 25-amino acid region of tumstatin and it is independent of disulfide bond linkage. Structural features and potency of the tumstatin peptide make it highly feasible as a potential anti-cancer drug.

Identification of the anti-angiogenic site within vascular basement membrane-derived tumstatin

Components of vascular basement membrane are involved in regulating angiogenesis. Recently, tumstatin (the NC1 domain of alpha3 chain of type IV collagen) was identified as possessing anti-angiogenic activity. In the present study, the anti-angiogenic activity of tumstatin was localized to the putative 54-132-amino acid Tum-5 domain, and the activity mediated by alpha(v)beta(3) integrin interaction in an RGD-independent manner. The recombinant Tum-5 produced in Escherichia coli and Pichia Pastoris specifically inhibited proliferation and caused apoptosis of endothelial cells with no significant effect on nonendothelial cells. Tum-5 also inhibited tube formation of endothelial cells on Matrigel and induced G1 endothelial cell cycle arrest. Moreover, anti-angiogenic effect of Tum-5 was also examined in vivo using both a Matrigel plug assay in C57BL/6 mice and human prostate cancer (PC-3) xenografts in nude mice. The in vivo results demonstrate that Tum-5 at 1 mg/kg significantly inhibited growth of PC-3 tumors in association with a decrease in CD31 positive vasculature. These in vivo studies also show that, at molar equivalents, human Tum-5 is at least 10-fold more active than human endostatin. In addition, these studies for the first time suggest that through the action of endogenous inhibitors, alpha(v)beta(3) integrin may also function as a negative regulator of angiogenesis. Taken together, these findings demonstrate that Tum-5, a domain derived from tumstatin, is an effective inhibitor of tumor-associated angiogenesis and a promising candidate for the treatment of cancer.

Tubulointerstitial renal disease

Tubulointerstitial damage, in progressive chronic renal disease of all types, arises because of a complex interplay between factors in the tubular lumen, tubular epithelial cells, peritubular capillaries, resident and infiltrating interstitial cells and extracellular matrix. Particularly in proteinuric renal disease, tubular epithelial cells play a central role in orchestrating these events. In response to mediators arising systemically, in the tubular lumen or from other renal cells, tubular epithelial cells undergo a complex series of structural and functional changes and produce a bewildering number of soluble and fixed mediators, which in turn lead to interstitial inflammation and fibrosis. Knowledge of these interactions has increased exponentially over the past decade, and has defined a number of new targets for treatment. Both expansion and consolidation of this knowledge is needed to determine which of these targets holds the most promise for future treatment.