Platelet-derived growth factor receptor expression in hepatic stellate cells: how too much of a good thing can be bad.
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Adipocytes↗
Biomedical subjects
M Pinzani
Publications and source records attributed to M Pinzani.
Novel insights into the biology and physiology of the Ito cell.
Ito cells, perisinusoidal mesenchymal elements with possible pericytic functions within the liver, recently have been shown to play multiple physiological and pathophysiological roles. In particular, several in vivo and in vitro studies have clearly indicated that Ito cells play a relevant role in the progression of liver fibrogenesis. More recently, attention has been focussed on the mechanisms leading to Ito cell activation, proliferation and synthesis of extracellular matrix components. Among other soluble factors potentially involved in these processes, transforming growth factor-beta 1 and platelet-derived growth factor have been shown to act in a paracrine, and possibly autocrine, fashion on Ito cells, thus perpetuating their activated state. Finally, other studies have shown that Ito cells could play an active role in chronic liver tissue inflammation by promoting chemotaxis of infiltrating inflammatory cells.
Animals↗
Hepatic stellate (ITO) cells: expanding roles for a liver-specific pericyte.
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Animals↗
The mitogenic effect of platelet-derived growth factor in human hepatic stellate cells requires calcium influx.
Platelet-derived growth factor (PDGF) is a key mitogen for hepatic stellate cells (HSC) and has been shown to be implicated in liver tissue repair and fibrogenesis. In this study the relationship between PDGF-induced intracellular Ca2+ concentration ([Ca2+]i) increase and mitogenesis in cultured human HSC was evaluated. In high-density cell cultures (80-90% subconfluence), PDGF induced a significant increase in [Ca2+]i, characterized by a short-lasting peak phase, which was followed by a long-lasting plateau phase. The plateau phase was abolished in the absence of extracellular Ca2+. However, in low-density cell cultures (30-40% subconfluence), the plateau phase was absent or markedly less pronounced. In parallel sets of experiments, PDGF was significantly less effective in inducing mitogenesis in low-density cell cultures than in high-density cell cultures and was totally ineffective in the absence of extracellular Ca2+. These results suggest that 1) spatial and time dynamics of PDGF-induced [Ca2+]i increase are dependent on cell density and 2) PDGF-induced mitogenesis requires extracellular Ca2+ influx.
Becaplermin↗
Transforming growth factor-beta 1 regulates platelet-derived growth factor receptor beta subunit in human liver fat-storing cells.
Activated liver fat-storing cells (FSC) are known to play a key role in the development of liver fibrosis. An important element in FSC activation process is the increased expression of receptors for platelet-derived growth factor (PDGF), a potent mitogen for FSC. The aim of the present study was to evaluate the expression PDGF-receptor alpha and beta subunits in cultured human FSC and their regulation induced by transforming growth factor-beta 1 (TGF-beta), a cytokine potentially involved in an autocrine loop. TGF-beta induced a significant increase of the mitogenic effect of PDGF-BB and did not affect the mitogenicity of PDGF-AA and PDGF-AB, suggesting a selective action of the PDGF-receptor-beta subunit. This hypothesis was confirmed by regulation experiments showing selective and time-dependent upregulation of the messenger (m)RNA encoding for the PDGF-receptor-beta subunit and the relative protein induced by TGF-beta. In addition, binding studies showed a parallel increase of PDGF-BB binding sites after incubation of human FSC with TGF-beta. These studies provide evidence for an additional mechanism leading to the perpetuation of FSC activation and proliferation and contribute to a better understanding of the role of TGF-beta and PDGF in the development of liver fibrosis.
Becaplermin↗
Expression of platelet-derived growth factor in a model of acute liver injury.
Platelet-derived growth factor has been shown to play an important role in the repair process after acute tissue injury and in the pathogenesis of several fibrogenic disorders. The aim of this study was to evaluate whether increased expression of platelet-derived growth factor and its beta-receptor subunit occurs in a model of acute liver injury. Male Sprague-Dawley rats were given a single intragastric dose of carbon tetrachloride and killed at intervals of 24, 48 and 72 hr and 1 wk. Control animals were included in each group. Platelet-derived growth factor-B chain mRNA expression, analyzed by RNase protection assay, was not detectable in control samples or in samples obtained 24 hr or 1 wk after carbon tetrachloride. However, the presence of protected fragments of 130 kb was clearly detected after 48 hr and was still present, although less abundant, after 72 hr. The distribution of platelet-derived growth factor protein in liver tissue sections, evaluated by immunohistochemistry, was restricted to centrilobular veins and portal tracts in normal liver. In carbon tetrachloride-treated rats, prominent staining was observed in areas corresponding to hepatocellular necrosis and inflammatory infiltration. This feature, already present at 24 hr after carbon tetrachloride, became more marked at 48 hr with a gradual resolution after 72 hr. The expression of platelet-derived growth factor-receptor beta-subunit mRNA, evaluated by in situ hybridization, was markedly increased after carbon tetrachloride with a peak at 24 hr and was mainly localized over mesenchymal cells in the hepatic sinusoids.(ABSTRACT TRUNCATED AT 250 WORDS)
Acute Disease↗
Undulin RNA and protein expression in normal and fibrotic human liver.
We have analyzed the distribution, gene expression and cellular origin of undulin, a large extracellular matrix glycoprotein associated with mature collagen fibrils, in human liver by immunohistochemistry, Northern-blot analysis and in situ hybridization. In normal liver, undulin was distributed as densely packed fibers in portal tract stroma, and as fine fibers along sinusoids, and around central veins. Undulin ribonucleic acid expression was low in normal liver, and confined to mesenchymal cells of portal tract stroma, vessel walls and perisinusoidal space. In fibrotic liver, undulin deposition and gene expression were enhanced in fibrotic stroma and areas of fibrogenesis identified by the presence of active septa and inflammatory infiltrate. Undulin gene expression in fibrotic liver was exclusively localized in mesenchymal cells that could be identified by staining for vimentin, and partially for alpha-smooth muscle actin as (myo)fibroblasts, and possibly fat-storing cells. These data suggest that undulin is a constituent of the hepatic extracellular matrix of normal human liver, and that it participates in the rearrangement of connective tissue occurring in hepatic fibrosis.
Adolescent↗
Actions of platelet-derived growth factor isoforms in mesangial cells.
Platelet-derived growth factor (PDGF) occurs as homodimers or heterodimers of related polypeptide chains PDGF-BB, -AA, and -AB. There are two receptors that bind PDGF, termed alpha and beta. The beta receptor recognizes PDGF B chain and is dimerized in response to PDGF BB. The alpha receptor recognizes PDGF B as well as A chains and can be dimerized by the three dimeric forms of PDGF AA, AB, and BB. To characterize PDGF receptor signaling mechanisms and biologic activities in human mesangial cells (MC), we explored the effects of the three PDGF isoforms on DNA synthesis, phospholipase C activation, and PDGF protooncogene induction. PDGF-BB homodimer and AB heterodimer induced a marked increase in DNA synthesis, activation of phospholipase C, and autoinduction of PDGF A and B chain mRNAs, whereas PDGF-AA homodimer was without effect. The lack of response to PDGF AA could be accounted for by down-regulation of the PDGF-alpha receptor since preincubation of MC with suramin restored PDGF AA-induced DNA synthesis. Ligand binding studies demonstrate specific binding of labeled PDGF BB and AB and to a lower extent PDGF AA isoforms to mesangial cells. These results are consistent with predominant expression of PDGF beta receptor in MC, which is linked to phospholipase-C activation. The potent biologic effects of PDGF-AB heterodimer in cells that express very few alpha receptors and do not respond to PDGF AA are somewhat inconsistent with the currently accepted model of PDGF receptor interaction and suggest the presence of additional mechanisms for PDGF isoform binding and activation.
Biological Transport↗
Biosynthesis of platelet-activating factor and its 1O-acyl analogue by liver fat-storing cells.
BACKGROUND/AIMS: Platelet-activating factor (PAF) is an important mediator of proinflammatory cell-to-cell interactions with powerful vasoactive properties. We evaluated the biosynthesis of PAF by cultured human fat-storing cells (FSC), liver-specific pericytes involved in the inflammatory and fibrogenic process of liver tissue. METHODS: PAF synthesis was evaluated by measuring [3H]acetate incorporation under basal conditions and upon stimulation with A23187, thrombin, and lipopolysaccharide. Further analysis of PAF species synthesized by FSC was performed using gas chromatography/mass spectrometry. RESULTS: All stimuli induced a significant increase of basal PAF synthesis by FSC. Further analysis showed that > 50% of the newly synthesized PAF species was secreted whereas the remaining fraction was cell-associated. PAF species produced by FSC were able to induce aggregation of rabbit washed platelets with an effectiveness correspondent to 10(-9) mol/L authentic PAF. Gas chromatography/mass spectrometry analysis revealed that a large percentage (74%) of PAF-like lipids synthesized by FSC consisted of 1O-acyl PAF. Finally, stimulation of FSC with PAF caused an increase in cytosolic free calcium, thus suggesting a possible involvement of this pericyte in the well-known effects of PAF on portal pressure. CONCLUSIONS: These results expand the available knowledge concerning the role of PAF in conditions characterized by extensive activation and damage of the liver sinusoidal endothelium and decreased hepatic scavenger activity.
Acetates↗
Regulation of platelet-derived growth factor secretion and gene expression in human liver fat-storing cells.
BACKGROUND/AIMS: Liver fat-storing cells (FSCs) actively proliferate and secrete extracellular matrix during liver injury. Platelet-derived growth factor (PDGF) is a potent mitogen for cultured FSCs. In the present study, we investigated the regulation of PDGF gene expression and production in cultured human liver FSCs. METHODS: PDGF A-chain and B-chain expression was analyzed by Northern blotting and ribonuclease protection assay, respectively. Secretion of PDGF was evaluated by immunoprecipitation and immunoblotting of conditioned medium and metabolic labeling of FSC followed by immunoprecipitation. RESULTS: Three PDGF A-chain transcripts were detectable. Stimulation of FSC with phorbol myristate acetate (10(-7) mol/L) or PDGF BB (20 ng/mL) increased steady-state levels of PDGF A-chain and B-chain messenger RNA. PDGF AA had a small stimulatory effect on A-chain but not B-chain messenger RNA levels. FSCs secrete PDGF in the conditioned medium. The secreted protein is bioactive, because concentrated conditioned medium induced an increase in thymidine incorporation that was inhibited by anti-PDGF antibodies. CONCLUSIONS: This study shows that cultured FSCs express PDGF A- and B-chain genes and release bioactive PDGF in the culture medium. These data raise the possibility of an autocrine or short-loop paracrine effect of PDGF in FSCs as a mechanism contributing to the maintenance of the proliferative state during liver injury.
Cells, Cultured↗
Expression of platelet-derived growth factor receptors in normal and diseased human kidney. An immunohistochemistry and in situ hybridization study.
We studied the expression of PDGF-alpha and -beta receptors in 10 normal and 40 pathologic human kidneys (five minimal change disease, five membranous nephropathy, 25 IgA nephropathy, five lupus nephritis), by both immunohistochemistry and in situ hybridization techniques. In normal-appearing kidneys, both PDGF-alpha and -beta receptors were expressed at the glomerular and interstitial level, the latter receptor more intensely than the former. The distribution and degree of expression of both receptors in nonproliferative glomerulonephritides were comparable with those found in normal-appearing kidneys. PDGF-beta receptor gene and protein expression were upregulated in proliferative nephritides both at the glomerular and the interstitial level and strictly correlated with the grade of histologic lesions. Finally, PDGF beta receptor expression was observed at a low level in normal-appearing renal vessels, and strikingly increased in injured arteries. Diseased kidneys displayed only a slight increase of PDGF-alpha receptor expression, chiefly at the interstitial level. Noteworthy, a few cases of lupus nephritis showed a moderate increase of PDGF-alpha receptor also at the glomerular level. These data establish PDGF-beta receptor activation as a candidate for driving glomerular and interstitial proliferation and, probably, expansion of extracellular matrix in proliferative glomerulonephritis, while the role of PDGF-alpha receptor activation at the renal level remains to be elucidated.
Cells, Cultured↗
Differential expression of matrix-metalloproteinase-1 and -2 genes in normal and fibrotic human liver.
Altered degradation of extracellular matrix has been implicated in the pathogenesis of hepatic fibrosis. We investigated levels and cellular sites of gene expression of two major collagen-degrading enzymes, matrix-metalloproteinase (MMP)-1 (fibroblast type-interstitial collagenase) and MMP-2 (72-kd gelatinase, type IV collagenase) in five normal and 18 fibrotic human livers as well as in cultured human hepatic fat-storing cells by Northern blot analysis and in situ hybridization. Fat-storing cells expressed both MMP-1 and MMP-2 RNA in vitro. In vivo, MMP-1 was undetectable in mesenchymal and parenchymal cells of all liver specimens, whereas MMP-2 transcripts were expressed in all livers by vimentin-positive, CD68-negative mesenchymal cells. Mesenchymal cells of all fibrotic livers displayed high transcript levels of transforming growth factor-beta 1, which is known to modulate MMP expression. Along with de novo fibrogenesis and possibly influenced by transforming growth factor-beta 1, expression of MMP-2 in the absence of MMP-1 expression may be responsible for the quantitative and qualitative changes of extracellular matrix observed in chronic liver disease.
Autoradiography↗
Stimulation of lipid peroxidation or 4-hydroxynonenal treatment increases procollagen alpha 1 (I) gene expression in human liver fat-storing cells.
Hepatic fat-storing cells (FSC) play a key role in the development of fibrosis as a major source of collagen and other extracellular matrix (ECM) proteins in the injured liver. Both experimental and clinical studies have shown that lipid peroxidation is often associated with the development of liver fibrosis. Here we report that exposure of cultured human liver FSC to the pro-oxidant system ascorbate/iron results in an early induction of lipid peroxidation, as monitored in terms of MDA and fluorescent aldehyde/protein adducts production, and in a significant increase of the constitutive expression of procollagen type I mRNA paralleled by the accumulation of the protein in cell culture media. This fibrogenic effect is almost completely abolished by pretreatment of FSC cultures with the antioxidants alpha-tocopherol (Vitamin E) or diphenylphenylendiamine (DPPD). Moreover, treatment of FSC with 1.0 microM 4-hydroxynonenal (HNE), a highly reactive aldehydic end-product of lipid peroxidation, results in a significant stimulation of procollagen type I gene expression and synthesis, suggesting that this aldehyde also exerts profibrogenic activity. These findings indicate that oxidative reactions can directly influence procollagen I gene expression and synthesis in FSC, thus contributing to the development of liver fibrosis.
Adipose Tissue↗
Regulation of extracellular matrix synthesis by transforming growth factor beta 1 in human fat-storing cells.
BACKGROUND: Fat storing cells (FSC) are nonparenchymal liver cells generally considered the major source of the hepatic extracellular matrix (ECM). Transforming growth factor beta 1 (TGF-beta 1) is a potent regulator of ECM synthesis in various cell types. In this study, the effect of TGF-beta 1 on procollagen types I, III, IV, laminin (Lam), and fibronectin (FN) synthesis in cultured human FSCs was analyzed. METHODS: FSCs were isolated from wedge sections of normal human livers. Morphological studies were performed by immunofluorescence and electron microscopy. ECM components in human FSC cultures were measured by an enzyme-linked immunosorbent assay. The expression of messenger RNA (mRNA) was evaluated by Northern blot and in situ hybridization. RESULTS: Cultured human FSCs displayed numerous fat droplets in the perinuclear zone, and immunoreactivity for vimentin and alpha-smooth muscle actin. A weak nonfibrillar staining was observed by using a polyclonal antidesmin antibody. TGF-beta 1 induced a dose-dependent increase of procollagen I, III, and FN accumulation in human FSC cultures, whereas procollagen IV and Lam production was not affected. Furthermore, TGF-beta 1 increased the expression of alpha 1 (I), alpha 1 (III) procollagen, FN and TGF-beta 1 mRNA in human FSC cultures. CONCLUSIONS: These data indicate that TGF-beta 1 is able to increase the synthesis of procollagen I, III, and FN in cultured human FSCs. Moreover, TGF-beta 1 can induce its own mRNA in the same cells.
Adipose Tissue↗
Effects of low-dose captopril on renal hemodynamics and function in patients with cirrhosis of the liver.
BACKGROUND: In cirrhotic patients with ascites, captopril has deleterious effects on renal function, which have been referred to as captopril-induced arterial hypotension. The effects of this drug on renal function in cirrhosis were evaluated using low-dose captopril, thereby avoiding any change in arterial pressure. METHODS: In a randomized, double-blind, placebo controlled, cross-over trial, the effects of 12.5 mg captopril on renal plasma flow, glomerular filtration rate (measured by radioisotopic techniques), and sodium excretion in healthy controls and cirrhotic patients with and without ascites were determined. RESULTS: In healthy subjects, captopril only induced a significant, 18% increase in renal plasma flow. In contrast, glomerular filtration rate significantly decreased in patients with (from 108 +/- 7 to 78 +/- 9 mL/min) and without ascites (from 102 +/- 4 to 88 +/- 3 mL/min), whereas renal plasma flow did not change. Urinary sodium excretion also significantly decreased in ascitic patients (from 43.8 +/- 4.4 to 30.6 +/- 3.8 mumol/min). CONCLUSIONS: These data suggest that angiotensin II contributes to maintain renal hemodynamics in cirrhosis with and without ascites.
Aged↗
Modulation of hepatic fibrogenesis by antioxidants.
The oxidative damage of liver tissue appears to favour a fibrogenic process, through the stimulation of TGF beta 1 and procollagen gene expression. The latter effect has been also showed by a well defined end-product of lipid peroxidation, 4-hydroxy-2,3-nonenal in human Ito cell culture. "In vivo" and "in vitro" data give evidence of a strong down modulation of TGF beta 1 and collagen expression afforded by supplementation with different antioxidant molecules.
Animals↗
Cultured human liver fat-storing cells produce monocyte chemotactic protein-1. Regulation by proinflammatory cytokines.
Monocytes infiltrate the portal space during chronic liver inflammation. Monocyte chemotactic protein-1 (MCP-1) is a cytokine that induces monocyte chemotaxis and activation. We investigated if human liver fat-storing cells (FSC) secrete MCP-1, and the mechanisms that regulate MCP-1 production. Unstimulated FSC secrete MCP-1 as measured by radioimmunoassay as well as a chemotactic assay and express mRNA that encodes for this cytokine. A two- to threefold increase in MCP-1 secretion was observed when FSC were treated with either interleukin-1 alpha (IL-1 alpha) or interferon-gamma (IFN-gamma). Tumor necrosis factor-alpha (TNF alpha) also increased MCP-1 secretion, although to a lesser extent (1.6-fold). Northern blot analysis showed that IL-1 alpha and IFN-gamma strongly increase the levels of mRNA that encodes for MCP-1, whereas TNF alpha appears to be a weaker stimulus. Analysis of FSC-conditioned medium by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting revealed three bands of MCP-1 that most likely represent isoforms of different apparent molecular weights. Pretreatment of FSC with H-7, a protein kinase C inhibitor, blocked cytokine-induced increase in both MCP-1 gene expression and secretion. To determine the potential role of MCP-1 in vivo, we also analyzed normal and pathologic human liver tissue. Northern blot analysis showed that MCP-1 mRNA expression is more abundant in liver tissue obtained from patients with chronic active hepatitis compared with normal liver tissue. These studies indicate that MCP-1 secreted by FSC is stimulated by proinflammatory cytokines and that MCP-1 gene expression is upregulated in chronic inflammatory liver disease. MCP-1 released by FSC may participate in the recruitment and activation of monocytes at sites of liver injury.
1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
Circulating growth hormone and insulin-like growth factor-I in nonalcoholic liver cirrhosis with or without superimposed hepatocarcinoma: evidence of an altered circadian rhythm.
Adult liver is considered the major source of circulating insulin-like growth factor-I (IGF-I). Growth hormone (GH) exerts its effects by stimulating IGF-I release from the liver, which then mediates the somatogenic actions in target tissues. In turn, circulating IGF-I levels operate a negative feedback mechanism on GH release. In cirrhotic patients, single daily determinations, performed after an overnight fast, indicated that serum IGF-I are decreased, whereas GH levels are increased. To verify whether this phenomenon occurs through the 24-h period, we have studied the profiles of GH and IGF-I in cirrhotic patients with or without superimposed hepatocellular carcinoma (HCC) and in a group of control subjects. The results of the present studies suggest that in cirrhotic patients, the above changes are constantly present through the 24-h period, and are associated with a loss of circadian rhythm for both GH and IGF-I. These data are consistent with a failure of the liver to synthesize and release IGF-I in response to GH. In addition, the presence of constantly higher IGF-I levels in cirrhotic patients with superimposed HCC, compared with cirrhotic patients without HCC, raises the hypothesis of a causal relationship between IGF-I and the development of HCC.
Adult↗