Anti-latent TGF-beta binding protein-1 antibody or synthetic oligopeptides inhibit extracellular matrix expression induced by stretch in cultured rat mesangial cells

Recapitulation of Human Neural Microenvironment Signatures in iPSC-Derived NPC 3D Differentiation

Brain microenvironment plays an important role in neurodevelopment and pathology, where the extracellular matrix (ECM) and soluble factors modulate multiple cellular processes. Neural cell culture typically relies on heterologous matrices poorly resembling brain ECM. Here, we employed neurospheroids to address microenvironment remodeling during neural differentiation of human stem cells, without the confounding effects of exogenous matrices. Proteome and transcriptome dynamics revealed significant changes at cell membrane and ECM during 3D differentiation, diverging significantly from the 2D differentiation. Structural proteoglycans typical of brain ECM were enriched during 3D differentiation, in contrast to basement membrane constituents in 2D. Moreover, higher expression of synaptic and ion transport machinery was observed in 3D cultures, suggesting higher neuronal maturation in neurospheroids. This work demonstrates that 3D neural differentiation as neurospheroids promotes the expression of cellular and extracellular features found in neural tissue, highlighting its value to address molecular defects in cell-ECM interactions associated with neurological disorders.

Qingxuan Jiangya Decoction Mitigates Renal Interstitial Fibrosis in Spontaneously Hypertensive Rats by Regulating Transforming Growth Factor-β1/Smad Signaling Pathway

Qingxuan Jiangya Decoction (QXJYD) is a traditional Chinese medicine commonly used in the clinical treatment of hypertension. Earlier studies had shown that QXJYD could inhibit the elevation of blood pressure in spontaneously hypertensive rats (SHRs) and prevent remodeling of arterial vessels. This study examines the therapeutic efficacy of QXJYD against elevated blood pressure using the SHR model, as well as the mechanisms behind its antihypertensive activity and protection against renal fibrosis. The results showed that QXJYD significantly attenuated the increase in blood pressure in SHRs and mitigated the development of renal interstitial fibrosis. In addition, QXJYD also robustly decreased the excess accumulation of extracellular matrix and attenuated the elevated expression of MMPs. The antihypertensive effects and renal protection of QXJYD were determined to be strongly associated with inhibition of TGF-β1/Smad signaling pathway.

Pulmonary Hypoplasia Induced by Oligohydramnios: Findings from Animal Models and a Population-Based Study

Pulmonary hypoplasia is a substantial cause of death in newborn infants, and oligohydramnios is one of the most commonly associated abnormalities. Lung growth is influenced by physical factors such as the intrauterine space, lung liquid volume and pressure, and fetal breathing movements. During lung development, the main physical force experienced by the lungs is stretching induced by breathing movements and the lung fluid in the airspaces. Oligohydramnios reduces the intrathoracic cavity size, thus disrupting fetal lung growth and leading to pulmonary hypoplasia. The exact mechanism by which oligohydramnios alters the respiratory system structure and the effect of oligohydramnios on long-term respiratory outcomes remain unknown. In this review, we summarize the effects of oligohydramnios on lung development, discuss the mechanisms of oligohydramnios-induced pulmonary hypoplasia identified in various animal studies, and describe the long-term respiratory outcomes in childhood of oligohydramnios-exposed fetuses reported by a population-based study.

Secretory leukocyte protease inhibitor gene deletion alters bleomycin-induced lung injury, but not development of pulmonary fibrosis

Idiopathic pulmonary fibrosis is a progressive, fatal disease with limited treatment options. Protease-mediated transforming growth factor-β (TGF-β) activation has been proposed as a pathogenic mechanism of lung fibrosis. Protease activity in the lung is tightly regulated by protease inhibitors, particularly secretory leukocyte protease inhibitor (SLPI). The bleomycin model of lung fibrosis was used to determine the effect of increased protease activity in the lungs of Slpi(-/-) mice following injury. Slpi(-/-), and wild-type, mice received oropharyngeal administration of bleomycin (30 IU) and the development of pulmonary fibrosis was assessed. Pro and active forms of matrix metalloproteinase (MMP)-2 and MMP-9 were measured. Lung fibrosis was determined by collagen subtype-specific gene expression, hydroxyproline concentration, and histological assessment. Alveolar TGF-β activation was measured using bronchoalveolar lavage cell pSmad2 levels and global TGF-β activity was assessed by pSmad2 immunohistochemistry. The active-MMP-9 to pro-MMP-9 ratio was significantly increased in Slpi(-/-) animals compared with wild-type animals, demonstrating enhanced metalloproteinase activity. Wild-type animals showed an increase in TGF-β activation following bleomycin, with a progressive and sustained increase in collagen type I, alpha 1 (Col1α1), III, alpha 1(Col3α1), IV, alpha 1(Col4α1) mRNA expression, and a significant increase in total lung collagen 28 days post bleomycin. In contrast Slpi(-/-) mice showed no significant increase of alveolar TGF-β activity following bleomycin, above their already elevated levels, although global TGF-β activity did increase. Slpi(-/-) mice had impaired collagen gene expression but animals demonstrated minimal reduction in lung fibrosis compared with wild-type animals. These data suggest that enhanced proteolysis does not further enhance TGF-β activation, and inhibits sustained Col1α1, Col3α1, and Col4α1 gene expression following lung injury. However, these changes do not prevent the development of lung fibrosis. Overall, these data suggest that the absence of Slpi does not markedly modify the development of lung fibrosis following bleomycin-induced lung injury.

Regulation of skeletal growth and mineral acquisition by the GH/IGF-1 axis: Lessons from mouse models

The growth hormone (GH) and its downstream mediator, the insulin-like growth factor-1 (IGF-1), construct a pleotropic axis affecting growth, metabolism, and organ function. Serum levels of GH/IGF-1 rise during pubertal growth and associate with peak bone acquisition, while during aging their levels decline and associate with bone loss. The GH/IGF-1 axis was extensively studied in numerous biological systems including rodent models and cell cultures. Both hormones act in an endocrine and autocrine/paracrine fashion and understanding their distinct and overlapping contributions to skeletal acquisition is still a matter of debate. GH and IGF-1 exert their effects on osteogenic cells via binding to their cognate receptor, leading to activation of an array of genes that mediate cellular differentiation and function. Both hormones interact with other skeletal regulators, such as sex-steroids, thyroid hormone, and parathyroid hormone, to facilitate skeletal growth and metabolism. In this review we summarized several rodent models of the GH/IGF-1 axis and described key experiments that shed new light on the regulation of skeletal growth by the GH/IGF-1 axis.

Regulation of transforming growth factor-β1 activation and expression in the tissue remodeling involved in chronic rhinosinusitis

Transforming growth factor-β1 (TGF-β1) plays a key role in the tissue remodeling processes involved in chronic rhinosinusitis (CRS), with the biological functions of secreted TGF-β1 regulated by multiple proteins. Among these regulators, latency-associated peptide and latent TGF-β-binding protein inhibit TGF-β1 function, whereas different proteases and integrins activate it. Progress in understanding the factors responsible for the bioactivity and expression of TGF-β1 has revealed that the dysregulation of TGF-β1 activation and expression is closely associated with the chronic respiratory inflammatory diseases involved in CRS. This review of the regulation of TGF-β1 activation and expression provides insight into the mechanism responsible for the different CRS subtypes, which will help further the investigation of novel therapy targets for the treatment of CRS.

Angiotensin II type 1 receptor blocker attenuates the activation of ERK and NADPH oxidase by mechanical strain in mesangial cells in the absence of angiotensin II

It has been reported that mechanical strain activates extracellular signal-regulated protein kinases (ERK) without the involvement of angiotensin II (Ang II) in cardiomyocytes. We examined the effects of mechanical strain on ERK phosphorylation levels in the absence of Ang II using rat mesangial cells. The ratio of phosphorylated ERK (p-ERK) to total ERK expression was increased by cyclic mechanical strain in a time- and elongation strength-dependent manner. With olmesartan [Ang II type 1 receptor (AT1R) antagonist] pretreatment, p-ERK plateau levels decreased in a dose-dependent manner (EC(50) = 1.3 x 10(-8) M, maximal inhibition 50.6 +/- 11.0% at 10(-5) M); a similar effect was observed with RNA interference against Ang II type 1A receptor (AT(1A)R) and Tempol, a superoxide dismutase mimetic. In addition to the inhibition of p-ERK levels, olmesartan blocked the increase in cell surface and phosphorylated p47(phox) induced by mechanical strain and also lowered the mRNA expression levels of NADPH oxidase subunits. These results demonstrate that mechanical strain stimulates AT1R to phosphorylate ERK in mesangial cells in the absence of Ang II. This mechanotransduction mechanism is involved in the oxidative stress caused by NADPH oxidase and is blocked by olmesartan. The inverse agonistic activity of this AT1R blocker may be useful for the prevention of mesangial proliferation and renal damage caused by mechanical strain/oxidative stress regardless of circulating or tissue Ang II levels.

Periostin is essential for the integrity and function of the periodontal ligament during occlusal loading in mice

BACKGROUND

The ability of the periodontal ligament (PDL) to absorb and distribute forces is necessary for periodontal homeostasis. This adaptive response may be determined, in part, by a key molecule, periostin, which maintains the integrity of the PDL during occlusal function and inflammation. Periostin is primarily expressed in the PDL and is highly homologous to betaig-H3 (transforming growth factor-beta [TGF-beta] inducible gene). Cementum, alveolar bone, and the PDL of periostin-null mice dramatically deteriorate following tooth eruption. The purpose of this study was to determine the role of periostin in maintaining the functional integrity of the periodontium.

METHODS

The periodontia from periostin-null mice were characterized followed by unloading the incisors. The effect of substrate stretching on periostin expression was evaluated using a murine PDL cell line. Real-time reverse transcription-polymerase chain reaction was used to quantify mRNA levels of periostin and TGF-beta. TGF-beta1 neutralizing antibodies were used to determine whether the effects of substrate stretching on periostin expression are mediated through TGF-beta.

RESULTS

Severe periodontal defects were observed in the periostin-null mice after tooth eruption. The removal of masticatory forces in periostin-null mice rescue the periodontal defects. Periostin expression was increased in strained PDL cells by 9.2-fold at 48 hours and was preceded by a transient increase in TGF-beta mRNA in vitro. Elevation of periostin in response to mechanical stress was blocked by the addition of 2.5 ng/ml neutralizing antibody to TGF-beta1, suggesting that mechanical strain activates TGF-beta to have potential autocrine effects and to increase periostin expression.

CONCLUSION

Mechanical loading maintains sufficient periostin expression to ensure the integrity of the periodontium in response to occlusal load.

Experimental Oligohydramnios Decreases Collagen in Hypoplastic Fetal Rat Lungs

Neonates with premature rupture of the membrane and oligohydramnios have an increased risk of acute respiratory morbidity. The aims of this study are to investigate the effects of experimental oligohydramnios on transforming growth factor (TGF)-β1 and connective tissue growth factor (CTGF) expressions and collagen level in fetal rat lungs. On day 16 of gestation, we anesthetized timed pregnant Sprague-Dawley dams, punctured the uterine wall and fetal membranes of each amniotic sac which resulted in oligohydramnios. Fetuses in the opposite uterine horn served as controls. On days 19 and 21 of gestation, fetuses were delivered by cesarean section. Rats exposed to oligohydramnios exhibited significantly lower lung weight/body weight ratios on days 19 and 21 of gestation than did the control rats. Lung type I collagen and TGF-β1 mRNA expressions and lung collagen levels were significantly decreased in rats exposed to oligohydramnios on days 19 and 21 of gestation. Type I collagen and inhibitors of metalloproteinase-1 (TIMP-1) proteins were decreased and matrix metalloproteinase-1 (MMP-1) was increased in oligohydramnios-exposed rats on days 19 and 21 of gestation. CTGF mRNA expressions were comparable between control and oligohydramnios-exposed rats on days 19 and 21 of gestation. These data suggest that downregulation of collagen might be involved in the pathogenesis of oligohydramnios-induced respiratory morbidity.

Integrins and the activation of latent transforming growth factor beta1 - an intimate relationship

Integrins are crucial for the ability of cells to sense mechanical perturbations and to transmit intracellular stress to their environment. We here review the more recently discovered role of integrins in activating the pleiotrophic cytokine transforming growth factor beta 1 (TGF-beta1). TGF-beta1 controls tissue homeostasis in embryonic and normal adult tissues and contributes to the development of fibrosis, cancer, autoimmune and vascular diseases when being mis-regulated. In most of these conditions, active TGF-beta1 is generated by dissociation from a large latent protein complex that sequesters latent TGF-beta1 in the extracellular matrix (ECM). Two main models are proposed how integrins contribute to latent TGF-beta1 activation: (1) In a protease-dependent mechanism, integrins alphavbeta8 and alphavbeta3 are suggested to simultaneously bind the latent TGF-beta1 complex and proteinases. This close vicinity at the cell surface improves enzymatic cleavage of the latent complex to release active TGF-beta1. (2) Integrins alphavbeta3, alphavbeta5, alphavbeta6, and alphavbeta8 appear to change the conformation of the latent TGF-beta1 complex by transmitting cell traction forces. This action requires association of the latent complex with a mechanically resistant ECM and is independent from proteolysis. Understanding that different integrins use different mechanisms to activate latent TGF-beta1 opens new possibilities to develop cell-specific therapeutic strategies for TGF-beta1-induced pathologies.

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

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

Adjuvant strategies for prevention of glomerulosclerosis

The glomerulosclerosis which frequently complicates diabetes and severe hypertension is mediated primarily by increased mesangial production and activation of transforming growth factor-beta (TGF-beta), which acts on mesangial cells to boost their production of matrix proteins while suppressing extracellular proteolytic activity. Hyperglycemia and glomerular hypertension work in various complementary ways to stimulate superoxide production via NADPH oxidase in mesangial cells; the resulting oxidant stress results in the induction and activation of TFG-beta. Nitric oxide, generated by glomerular capillaries and by mesangial cells themselves, functions physiologically to oppose mesangial TGF-beta overproduction; however, NO bioactivity is compromised by oxidant stress. In addition to low-protein diets and drugs that suppress angiotensin II activity, a variety of other agents and measures may have potential for impeding the process of glomerulosclerosis. These include vitamin E, which blunts the rise in mesangial diacylglycerol levels induced by hyperglycemia; statins and (possibly) policosanol, which down-regulate NADPH oxidase activity by diminishing isoprenylation of Rac1; lipoic acid, whose potent antioxidant activity antagonizes the impact of oxidant stress on TGF-beta expression; pyridoxamine, which inhibits production of advanced glycation endproducts; arginine, high-dose folate, vitamin C, and salt restriction, which may support glomerular production of nitric oxide; and estrogen and soy isoflavones, which may induce nitric oxide synthase in glomerular capillaries while also interfering with TGF-beta signaling. Further research along these lines may enable the development of complex nutraceuticals which have important clinical utility for controlling and preventing glomerulosclerosis and renal failure. Most of these measures may likewise reduce risk for left ventricular hypertrophy in hypertensives, inasmuch as the signaling mechanisms which mediate this disorder appear similar to those involved in glomerulosclerosis.

Induction and coexpression of latent transforming growth factor beta-binding protein-1 and fibrillin-1 in experimental glomerulonephritis

BACKGROUND

Latent transforming growth factor-beta-binding protein 1 (LTBP-1) and fibrillin-1 were shown to colocalize and interact in the extracellular matrix of the skin and vasculature. This interaction may regulate transforming growth factor-beta (TGF-beta) activity. TGF-beta is an important progression factor for glomerular diseases. We hypothesized that LTBP-1 and fibrillin-1 are coexpressed in the glomerulus and upregulated during glomerulonephritis.

METHODS

Acute anti-Thy1.1 glomerulonephritis was induced with a single intravenous injection (1 mg/kg body weight) of a monoclonal anti-Thy1.1 antibody in rats. Real-time RT-PCR and immunohistochemical analyses for LTBP-1 and fibrillin-1 were performed.

RESULTS

Induction of glomerular LTBP-1 mRNA was detected on day 2 of disease, while mRNA for fibrillin-1 was already upregulated 1 day after induction of disease. Both LTBP-1 and fibrillin-1 showed a mesangial distribution. An expansion of the LTBP-1 and fibrillin-1-positive mesangial area was seen on day 6 of disease, when transient matrix accumulation was most prominent. On day 12 of disease, glomerular LTBP-1 and fibrillin-1 immunoreactivities had returned to control levels. In serial sections, some colocalization of LTBP-1 and fibrillin-1 was detected in control as well as in nephritic glomeruli.

CONCLUSION

Mesangial expression of LTBP-1 and fibrillin-1 is induced early in experimental nephritis and LTBP-1 and fibrillin-1 are partially colocalized in the nephritic glomerulus. An interaction of these molecules could stabilize latent TGF-beta complexes and thus attenuate the activation of TGF-beta during this self-limited glomerular disease.

The cardiac fibroblast: therapeutic target in myocardial remodeling and failure

Cardiac fibroblasts play a central role in the maintenance of extracellular matrix in the normal heart and as mediators of inflammatory and fibrotic myocardial remodeling in the injured and failing heart. In this review, we evaluate the cardiac fibroblast as a therapeutic target in heart disease. Unique features of cardiac fibroblast cell biology are discussed in relation to normal and pathophysiological cardiac function. The contribution of cardiac fibrosis as an independent risk factor in the outcome of heart failure is considered. Candidate drug therapies that derive benefit from actions on cardiac fibroblasts are summarized, including inhibitors of angiotensin-aldosterone systems, endothelin receptor antagonists, statins, anticytokine therapies, matrix metalloproteinase inhibitors, and novel antifibrotic/anti-inflammatory agents. These findings point the way to future challenges in cardiac fibroblast biology and pharmacotherapy.

Cyclooxygenase-2 Inhibitor Decreases Extracellular Matrix Synthesis in Stretched Renal Fibroblasts

BACKGROUND/AIMS

Both TGF-beta and cyclooxygenase-2 have been implicated in the pathogenesis of interstitial fibrosis in unilateral ureteral obstruction (UUO). Cyclic tensile stretch has been used in vitro to mimic the changes in intrarenal pressure in UUO. We sought to determine the effect of meloxicam (a selective cyclooxygenase-2 inhibitor) on extracellular matrix and TGF-beta synthesis in stretched renal fibroblasts (NRK-49F).

METHODS

NRK-49F cells were subject to cyclic stretch (6 cycles/min, 15% elongation) using a Flexcell apparatus. Cells were stretched in the absence or presence of meloxicam for 48 h, and then cells and supernatants were isolated. Collagen was quantified by the Sircol assay; fibronectin and laminin were visualized using immunofluorescence. TGF-beta was quantified by ELISA, and protease activity determined by a colorimetric assay.

RESULTS

Both collagen and TGF-beta synthesis were increased following a 48-hour stretch of NRK-49F. Meloxicam significantly decreased the collagen and TGF-beta response to stretch. Stretch-induced fibronectin and laminin synthesis was also decreased by meloxicam. NRK-49F protease activity was decreased by stretch; this was unaffected by meloxicam.

CONCLUSIONS

Stretch of NRK-49F results in extracellular matrix synthesis, a process which may be activated in UUO and contribute to interstitial fibrosis. Inhibition of cyclooxygenase-2 may reduce fibrosis through a TGF-beta-dependent process.

Akt mediates mechanical strain-induced collagen production by mesangial cells

Increased glomerular hydrostatic pressure is an important determinant of glomerulosclerosis and can be modeled by in vitro exposure of mesangial cells to cyclic mechanical strain. Stretched mesangial cells increase extracellular matrix protein production, the hallmark of glomerulosclerosis. Recent data indicate that the serine/threonine kinase Akt may be involved in matrix modulation. Thus, Akt activation and matrix synthesis in stretched mesangial cells were studied. Exposure of mesangial cells to 1 Hz cyclic strain led to prompt Akt activation, which was biphasic to 24 h. Activation was dependent on signaling through phosphatidylinositol-3-kinase and required EGF receptor transactivation. Inhibition of signaling through the PDGF receptor, Src kinase, or cytoskeletal disruption failed to prevent strain-induced Akt activation. Collagen type 1A1 transcript expression, promoter activation, and protein secretion were increased by stretch at 24 h and were dependent on phosphatidylinositol-3 kinase. Overexpression of dominant-negative Akt inhibited strain-induced collagen 1A1 production. Conversely, overexpression of constitutively active Akt led to increased collagen 1A1 upregulation and secretion. Finally, Akt activation was observed in the glomeruli of remnant rat kidneys, a model marked by increased intraglomerular pressure. The authors conclude that mechanical strain induces Akt activation in mesangial cells through a mechanism requiring phosphatidylinositol-3-kinase and EGF receptor transactivation. Type 1 collagen production is dependent on Akt and can be induced by Akt overexpression. Akt activation is observed in remnant kidneys in vivo. Thus, the role of Akt in progression of chronic hemodynamic glomerular disease is worthy of further exploration.

Mechanical stretch induces TGF-beta synthesis in hepatic stellate cells

BACKGROUND

It is known that mechanical stress induces extracellular matrix via transforming growth factor-beta (TGF-beta) synthesis in vascular smooth muscle cells. Activated hepatic stellate cells (HSCs) are an important source of TGF-beta in the liver. However, it remains unclear whether mechanical stress induces TGF-beta in HSCs. The Rho small GTP-binding protein (Rho) has recently emerged as an important regulator of actin and cytoskeleton. We examined whether TGF-beta is expressed in stretched HSCs and whether Rho is involved in stretch-induced TGF-beta synthesis.

MATERIALS AND METHODS

A cultured human HSC cell line, LI90, was used for this study. Hepatic stellate cells were cyclically stretched using the Flexercell(R) strain unit. Concentration of TGF-beta in the conditioned medium was estimated by a bioassay using mink lung epithelial cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct. Transforming growth factor-beta mRNA expression of HSCs was estimated by a reverse-transcription polymerase chain reaction. Replication-defective adenoviral vectors expressing a dominant negative type of Rho was utilized to suppress its effect on HSCs.

RESULTS

Transforming growth factor-beta concentration of the conditioned media of stretched HSCs showed time-dependent increases as compared to nonstretched HSCs from 2 h to 24 h. Transforming growth factor-beta mRNA expression in stretched HSCs was increased compared with that in nonstretched HSCs. Transfection of dominant negative Rho inhibited the stretch-induced TGF-beta synthesis.

CONCLUSIONS

Mechanical stretch enhanced TGF-beta expression on mRNA and protein level in HSCs. Rho was closely related to stretch-induced TGF-beta synthesis in HSCs.

PDGF-BB induces expression of LTBP-1 but not TGF-beta1 in a rat cirrhotic fat storing cell line

TGF-beta, a profibrogenic cytokine is predominantly secreted as a latent molecule complexed with one of the latent TGF-beta binding proteins (LTBP). Due to the proposed functions of LTBP-1 and -3 in regulating TGF-beta-bioavailability and -activity, we investigated the effects of PDGF-BB and TGF-beta1 on their expression levels in Cirrhotic fat storing cells (CFSC). CFSC basally express LTBP-1 and -3 and TGF-beta1. LTBP-1 colocalizes with LAP and the cells secrete some active TGF-beta1. Promoter studies showed no strong induction of the LTBP-1 promoters after stimulation, although mRNA and protein levels were increased by PDGF-BB treatment without affecting TGF-beta1 expression. Vice versa, TGF-beta1 treatment did not alter LTBP-1 expression while an autocrine induction was found. Our data indicate that LTBP-1 but not TGF-beta1 is induced by PDGF-BB and that TGF-beta1 autoinduction does not affect the expression of LTBP-beta1. This divergent regulation may represent an important mechanism for modulation of TGF-beta bioavailability.

Activation of fibroblast procollagen alpha 1(I) transcription by mechanical strain is transforming growth factor-beta-dependent and involves increased binding of CCAAT-binding factor (CBF/NF-Y) at the proximal promoter

During normal developmental tissue growth and in a number of diseases of the cardiopulmonary system, adventitial and interstitial fibroblasts are subjected to increased mechanical strain. This leads to fibroblast activation and enhanced collagen synthesis, but the underlying mechanisms involved remain poorly understood. In this study, we have begun to identify and characterize mechanical strain-responsive elements in the rat procollagen alpha 1(I) (COL1A1) gene and show that the activity of COL1A1 promoter constructs, transiently transfected into cardiac fibroblasts, was increased between 2- and 4-fold by continuous cyclic mechanical strain. This was accompanied by an approximately 3-fold increase in the levels of total active transforming growth factor-beta (TGF-beta) released into the medium. Inclusion of a pan-specific TGF-beta neutralizing antibody inhibited strain-induced COL1A1 promoter activation. Deletion analysis revealed the presence of two potential strain response regions within the proximal promoter, one of which contains an inverted CCAAT-box overlapping a GC-rich element. Both mechanical strain and exogenously added TGF-beta1 enhanced the binding activity of CCAAT-binding factor, CBF/NF-Y, at this site. Moreover, this element was sufficient to confer strain-responsiveness to an otherwise unresponsive SV40 promoter. In summary, this study demonstrates that strain-induced COL1A1 promoter activation in cardiac fibroblasts is TGF-beta-dependent and involves increased binding of CCAAT-binding factor at the proximal promoter. Furthermore, these findings suggest a novel and potentially important TGF-beta response element in the rat COL1A1 gene.

Role of transforming growth factor-beta1 and its latent form binding protein in pseudoexfoliation syndrome

Pseudoexfoliation (PEX) syndrome is a common and clinically important systemic condition characterized by the pathologic production and accumulation of an abnormal fibrillar extracellular material in many intra- and extraocular tissues. Recent evidence suggests that it is a type of elastosis associated with the excess synthesis of elastic microfibrillar components such as fibrillin-1. Since transforming growth factor (TGF)-beta is a major modulator of extracellular matrix formation, the potential involvement of TGF-beta and its latent form binding protein (LTBP) in this aberrant matrix process was investigated. The expression of various isoforms of TGF-beta and LTBP was investigated in the anterior segment tissues of PEX and control eyes on the protein and mRNA level by light and electron microscopic immunohistochemistry, in situ hybridization, and semiquantitative RT-PCR. TGF-beta1 and TGF-beta2 levels were measured in aqueous humor and serum of PEX and control patients by ELISA. Cultures of Tenon's capsule fibroblasts were established to study the effect of TGF-beta1 on fibrillin-1 mRNA expression by Northern blot analysis. Significantly increased concentrations of both total and active TGF-beta1 were measured in the aqueous humor of PEX eyes without and with glaucoma as compared to control eyes, whereas levels of TGF-beta2 were not significantly different. The expression of TGF-beta1, LTBP-1, and LTBP-2, but not TGF-beta2, was markedly increased in anterior segment tissues of PEX eyes, particularly in the non-pigmented epithelium of the ciliary body, on both the mRNA and the protein level. Latent TGF-beta1 staining was consistently associated with PEX material deposits and could be released by proteolytic processing. Double immunolabeling revealed clear co-localization of LTBP-1 and -2 with latent TGF-beta1 and with fibrillin-1 on PEX fibrils. The expression of mRNA coding for fibrillin-1 was up-regulated in vitro by TGF-beta1. This study provides evidence for a significant role of TGF-beta1 and the LTBPs 1 and 2 in PEX syndrome. The results suggest that increased levels of latent and active TGF-beta1 in the aqueous humor of PEX patients, derived from enhanced local synthesis and activation, promote the buildup of the abnormal extracellular elastic material characteristic of PEX syndrome. They further support a dual role for LTBPs, both as integral structural components of PEX fibers and as a means of matrix anchorage of latent TGF-beta1, representing one possible mechanism for the regulation of TGF-beta1 activity in PEX eyes. Future therapeutic strategies might focus on TGF-beta1 antagonistic approaches.

Specific inhibition of transforming growth factor-beta2 expression in human osteoblast cells by antisense phosphorothioate oligonucleotides

To elucidate the role of endogenous transforming growth factor (TGF)-beta2 on human osteoblast cell, antisense phosphorothioate oligonucleotides (S-ODNs) complementary to regions in mRNA of TGF-beta2 were synthesized and examined their effects on TGF-beta2 production and cell proliferation in a human osteoblast cell line ROS 17/2. Antisense S-ODNs were designated for three different target regions in the mRNA of TGF-beta2. Among several antisense S-ODN analyzed, an oligonucleotide (AS-11) complementary to the translation initiation site of mRNA of TGF-beta2 demonstrated a selective and strong inhibitory effect on TGF-beta2 production in osteoblast cells. Other antisense S-ODNs which were designated for other regions in mRNA of TGF-beta2 and one- or three-base mismatched analogs of AS-11 showed little or much less antisense activities than AS-11. Therefore, the most effective target site in mRNA of TGF-beta2 is at the initiation codon region. The antisense effects of AS-11 were observed without reduction of levels of mRNA of TGF-beta2. Furthermore, the inhibition of TGF-beta2 expression by antisense S-ODN appeared to enhance cell proliferation, demonstrating the growth inhibitory effect of autocrine TGF-beta2 in osteoblast cells.

Thrombospondin-1 is the key activator of TGF-beta1 in human mesangial cells exposed to high glucose

Elevated levels of transforming growth factor-beta1 (TGF-beta1) are synthesized by human mesangial cells that are cultured in medium that contains high concentrations of glucose and mediate increased synthesis of fibronectin (FN), plasminogen activator inhibitor-1 (PAI-1), and changes in the expression of other genes. TGF-beta1 is synthesized as a latent complex. Previous work indicated that high-glucose conditions also upregulate expression of thrombospondin-1 (TSP-1), a potential activator of latent TGF-beta1. With the use of the synthetic peptide GGWSHW, an inhibitor of the TSP-1 activation mechanism, endogenous TSP-1 is shown to be responsible for converting high levels of latent TGF-beta1 to bioactive growth factor over 3 wk of exposure of mesangial cells to 30 mM D-glucose. Peptide inhibition of TGF-beta1 activation by TSP-1 in high-glucose conditions completely suppressed increases in FN and PAI-1 expression. Treating mesangial cells maintained in high glucose with a TSP-1 antisense oligonucleotide reduced TSP-1 expression to levels found in 4 mM D-glucose cultures, prevented TGF-beta1 activation, and normalized expression of FN.

Glycosaminoglycan therapy prevents TGF-beta1 overexpression and pathologic changes in renal tissue of long-term diabetic rats

Chronic induction of the prosclerotic cytokine transforming growth factor beta (TGF-beta) has been implicated in the pathogenesis of diabetic nephropathy. In a rat model of diabetes mellitus-induced glomerulosclerosis, daily administration of a modified heparin (mH) glycosaminoglycan (GAG) preparation with low anticoagulant activity prevented glomerular and tubular matrix accumulation, as well as overexpression of TGF-beta1 mRNA and albuminuria, without obvious side effects. To elucidate the molecular mechanisms of GAG/mH inhibitory actions on TGF-beta1, studies using cultured mesangial cells were also performed. In these cells, high glucose-induced, dose-dependent increases in TGF-beta1 mRNA and bioactive TGF-beta protein expression were inhibited by GAG/mH treatment, whereas basal TGF-beta1 expression was not affected. Both the heparin-derived GAG and dermatan sulfate were effective, indicating that the heparin chemical structure is not necessary for inhibitory activity. Coincubation of GAG with active TGF-beta1 demonstrated no inhibitory effect on TGF-beta1 bioactivity, excluding a neutralizing effect of GAG on TGF-beta1 a the protein level. Furthermore, it was demonstrated that GAG inhibited phorbol myristate acetate-induced translocation of protein kinase C-alpha (PKC-alpha) and -beta1 and activation of PKC-alpha, as well as high glucose-induced activation of PKC-alpha. These results suggest that GAG inhibit TGF-beta1 overexpression at the transcriptional level, possibly via inhibition of high glucose-activated PKC. The findings indicate the potential of GAG therapy for the prevention of diabetic glomerulosclerosis by the inhibition of chronic disease-induced TGF-beta1 mRNA overexpression.

Elastic fiber proteins in the glomerular mesangium in vivo and in cell culture

BACKGROUND

Glomerular capillaries of the mammalian kidney are exposed to high intraluminal hydrostatic pressures and require elastic constraint to maintain size, shape, and integrity. Previous morphological and functional studies indicated that the extracellular matrices of glomeruli, that is, basement membrane and mesangial matrix, contribute to glomerular resilience and mechanical stability. Immunofluorescence microscopy findings demonstrated elastic fiber components to be located in the renal vasculature, including glomeruli. The aim of this study was to clarify the exact glomerular localization, composition, and cellular production of these proteins.

METHODS

We examined the renal distribution of the elastic fiber proteins fibrillin-1, emilin, microfibril-associated glycoproteins (MAGPs) 1 and 2, latent transforming growth factor-binding protein-1 (LTBP-1), and elastin using immunohistology and immunoelectron microscopy of human, rat, and mouse kidneys. In mesangial cell cultures, we also studied the expression and extracellular deposition of such proteins by use of Northern blotting and immunocytochemistry.

RESULTS

Fibrillin-1, emilin, MAGPs 1 and 2, and LTBP-1 were present in glomeruli of mouse, rat, and human kidney, where they were located predominantly in the mesangial extracellular matrix underlying glomerular endothelium and basement membrane. Several of these proteins, as well as elastin, were also expressed in the renal vasculature. While elastin localized to the glomerular vascular pole in afferent and efferent arterioles extending to Bowman's capsule, it was not found in the glomerular capillary tuft. Cultured mesangial cells of rat, mouse, and human kidneys expressed mRNAs of fibrillin-1, emilin, MAGP-2, and elastin, and the respective proteins localized within and outside of mesangial cells, as shown by immunocytochemistry. mRNA expression of fibrillin-1, emilin, and elastin was strong in quiescent mesangial cells; their gene expression was further up-regulated by transforming growth factor-beta1, while it was transiently reduced when cells were exposed to mitogenic 10% fetal calf serum and platelet-derived growth factor.

CONCLUSIONS

These findings demonstrate that specific elastic fiber proteins are produced and secreted by mesangial cells. This process is regulated by growth factors. Their abundance in the extracellular matrix of the mesangium is in keeping with the concept that elastic fiber proteins contribute to the mechanical stability and elastic strength of the glomerular capillary tuft.

Mechanical strain-induced extracellular matrix production by human vascular smooth muscle cells: role of TGF-beta(1)

Elevated blood pressure imposes increased mechanical stress on the vascular wall, and mechanical strain is a mitogenic stimulus for vascular smooth muscle (VSM) cells. The role of mechanical forces in regulating the production of noncellular material by VSM cells for VSM cells of human origin remains undefined. We thus investigated the effects of chronic cyclical mechanical strain on extracellular matrix (ECM) protein production by cultured human VSM cells. To simulate a blood pressure of 120/80 mm Hg, human VSM cells were repetitively stretched and relaxed by 10% to 16% of their original length with the Flexercell apparatus. Fibronectin and collagen protein concentrations, matrix metalloproteinase (MMP) activity, and transforming growth factor-beta(1) (TGF-beta(1)) mRNA expression by human VSM cells were measured in response to mechanical strain. Exposing human VSM cells to 5 days of chronic cyclical mechanical strain increased fibronectin (+48%, P:<0.01) and collagen (+50%, P:<0.001) concentrations when compared with cells grown in static conditions. Mechanical strain also increased MMP-2 activity, the predominant matrix-degrading isoform (+11%, P:<0.05) in human VSM cells, thus strain-induced ECM accumulation was not due to inhibition of ECM protein degradation. Strain also increased TGF-beta(1) mRNA expression and the production of a soluble factor that increased ECM protein production. Moreover, a TGF-beta-blocking antibody inhibited the effect of strain-conditioned media on matrix production by human VSM cells. These results suggest that chronic cyclical mechanical strain can directly modulate the fibrogenic activity of human VSM cells by inducing ECM protein synthesis and MMP activity. This occurs, at least in part, through mechanical strain-induced TGF-beta(1) production, a mechanism that could explain the increased vascular ECM deposition in hypertension.

Generation of recombinant human large latent transforming growth factor-beta 1 and monoclonal antibodies to it

Transforming growth factor beta 1 (TGF-beta 1) is a regulator of cell growth and differentiation. It is produced in various of cells and tissues as a biologically latent complex, whose significance is still unknown. We established a Chinese hamster ovary cells that produced recombinant human large latent TGF-beta 1. The growth factor was purified from serum-free conditioned medium of the cell line was purified to apparent homogeneity by four steps of column chromatography. The purified protein gave a single band with the apparent molecular weight of 210,000 on SDS-PAGE, and had four subunits, of 12.5, 40, 53, and 150-190 kDa. These components were identical to TGF-beta 1, the N-terminal remnant of pro-TGF-beta 1, pro-TGF-beta 1, and latent TGF-beta 1 binding protein, respectively. The purified growth factor had biological activity similar to that of the growth factor purified from human platelets. We prepared four monoclonal antibodies by immunization of mice with the recombinant protein. In western blotting, two of the antibodies bound to latent TGF-beta 1 binding protein. The two other antibodies reacted with the N-terminal remnant of pro-TGF-beta 1. Recombinant large latent TGF-beta 1 and its monoclonal antibodies could be used for detailed structural and functional studies of the large latent TGF-beta 1 complex.

The molecular genetics of Marfan syndrome and related microfibrillopathies

Mutations in the gene for fibrillin-1 (FBN1) have been shown to cause Marfan syndrome, an autosomal dominant disorder of connective tissue characterised by pleiotropic manifestations involving primarily the ocular, skeletal, and cardiovascular systems. Fibrillin-1 is a major component of the 10-12 nm microfibrils, which are thought to play a role in tropoelastin deposition and elastic fibre formation in addition to possessing an anchoring function in some tissues. Fibrillin-1 mutations have also been found in patients who do not fulfil clinical criteria for the diagnosis of Marfan syndrome, but have related disorders of connective tissue, such as isolated ectopia lentis, familial aortic aneurysm, and Marfan-like skeletal abnormalities, so that Marfan syndrome may be regarded as one of a range of type 1 fibrillinopathies. There appear to be no particular hot spots since mutations are found throughout the entire fibrillin-1 gene. However, a clustering of mutations associated with the most severe form of Marfan syndrome, neonatal Marfan syndrome, has been noted in a region encompassing exons 24 to 32. The gene for fibrillin-2 (FBN2) is highly homologous to FBN1, and mutations in FBN2 have been shown to cause a phenotypically related disorder termed congenital contractural arachnodactyly. Since mutations in the fibrillin genes are likely to affect the global function of the microfibrils, the term microfibrillopathy may be the most appropriate to designate the spectrum of disease associated with dysfunction of these molecules. The understanding of the global and the molecular functions of the fibrillin containing microfibrils is still incomplete and, correspondingly, no comprehensive theory of the pathogenesis of Marfan syndrome has emerged to date. Many, but not all, fibrillin-1 gene mutations are expected to exert a dominant negative effect, whereby mutant fibrillin monomers impair the global function of the microfibrils. In this paper we review the molecular physiology and pathophysiology of Marfan syndrome and related microfibrillopathies.

Modelling the effects of vascular stress in mesangial cells

It has recently been shown that mesangial cells are subjected to multiple forms of mechanical strain (fluid shear, hydrostatic pressure, and triaxial stretch) as a result of forces exerted by the vasculature. Nevertheless, the exact nature and the relative response to these stimuli have not been clarified. Although it is now well established that cyclic stretching of mesangial cells in culture results in the overproduction of extracellular matrix, indicating how intraglomerular hypertension may lead to glomerular scar formation, the contribution of different intracellular signalling mechanisms and extracellular mediators of the response are only now being identified. Recent studies point to a role for high glucose concentrations, transforming growth factor beta and its receptors, vascular endothelial growth factor, and connective tissue growth factor as important mediators, or modifiers of the response to mechanical strain. Although evidence exists for a role for protein kinase C, recent studies also implicate the mitogen-activated protein kinases along with enhanced DNA-binding activity of AP-1 as part of the signalling cascade altering matrix synthesis and cell proliferation in response to stretch. Finally, recent studies examining the effects of oscillating hyperbaric pressure demonstrate similarities, as well as differences, in comparison to those of cyclic stretch.

Regulation of cell surface tissue transglutaminase: effects on matrix storage of latent transforming growth factor-beta binding protein-1

Using a cytochemical approach, we examined the role of tissue transglutaminase (tTgase, Type II) in the incorporation of latent TGF-beta binding protein-1 (LTBP-1) in the extracellular matrix of Swiss 3T3 fibroblasts in which tTgase expression can be modulated through a tetracycline-controlled promoter. Increased tTgase expression led to an increased rate of LTBP-1 deposition in the matrix, which was accompanied by an increased pool of deoxycholate-insoluble fibronectin. Matrix deposition of LTBP-1 could also be reduced by the competitive amine substrate putrescine. Immunolocalization at the fluorescence and electron microscopic level showed that extracellular tTgase is located at the basal and apical surfaces of cells and at cell-cell contacts, and that LTBP-1 is co-distributed with cell surface tTgase, suggesting an early contribution of tTgase to the binding of LTBP-1 to matrix proteins. LTPB-1 was also found to co-localize with both intracellular and extracellular fibronectin, and increased immunoreactivity for LTBP-1 and fibronectin was found in large molecular weight polymers in the deoxycholate-insoluble matrix of fibroblasts overexpressing tTgase. We conclude that regulation of tTgase expression is important for controlling matrix storage of latent TGF-beta1 complexes and that fibronectin may be one extracellular component to which LTBP-1 is crosslinked when LTBP-1 and tTgase interact at the cell surface. (J Histochem Cytochem 47:1417-1432, 1999)

Expression of alternatively spliced human latent transforming growth factor beta binding protein-1

Latent transforming growth factor beta binding protein-1 (LTBP1) is important in regulating the localisation and activation of transforming growth factor beta(TGFbeta). Three forms of LTBP1 mRNA have previously been described, LTBP1L, LTBP1S and LTBPdelta53. Here, we have analysed the LTBP1 coding sequence and identified two other spliced forms, LTBP1delta55 and LTBP1delta41. LTBP1delta55 is a short form of LTBPIL which lacks 55 amino acids including two consensus N-glycosylation sites and LTBP1delta41 is a form of LTBP1 which lacks the 12th EGF-like repeat. Furthermore, sequencing of genomic clones showed that splicing to generate LTBP1L occurs using an intra-exonic 3' splice acceptor site in the first coding exon of LTBP1S and that LTBP1delta55 arises from the alternative use of an exonic 3' splice acceptor site at the end of the following intron. LTBP1delta41 arises from skipping the exon which encodes the 12th EGF-like repeat. LTBP1delta55 and LTBP1delta41 mRNA are expressed in a wide variety of human tissues but the proportions of each splice form vary in the tissues.