Static pressure regulates connective tissue growth factor expression in human mesangial cells

Connective tissue growth factor (CTGF) is overexpressed in a variety of fibrotic disorders such as renal fibrosis and atherosclerosis. Fibrosis is a common final pathway of renal diseases of diverse etiology, including inflammation, hemodynamics, and metabolic injury. Mechanical strains such as stretch, shear stress, and static pressure are possible regulatory elements in CTGF expression. In this study, we examined the ability of static pressure to modulate CTGF gene expression in cultured human mesangial cells. Low static pressure (40-80 mm Hg) stimulated cell proliferation via a protein kinase C-dependent pathway. In contrast, high static pressure (100-180 mm Hg) induced apoptosis in human mesangial cells. This effect was reversed by treatment with CTGF antisense oligonucleotide but not with transforming growth factor beta1-neutralizing antibody or protein kinase C inhibitor. High static pressure not only up-regulated the expression of CTGF, but also the expression of extracellular matrix proteins (collagen I and IV, laminin). This up-regulation of extracellular matrix proteins was also reversed by treatment with CTGF antisense oligonucleotide. As judged by mRNA expression of a total of 1100 genes, including apoptosis-associated genes using DNA microarray techniques, recombinant CTGF protein induced apoptosis by down-regulation of a number of anti-apoptotic genes. Overexpression of CTGF in mesangial cells by transient transfection had similar effects. Taken together, these results suggest that high blood pressure up-regulates CTGF expression in mesangial cells. High levels of CTGF in turn enhance extracellular matrix production and induce apoptosis in mesangial cells, and may contribute to remodeling of mesangium and ultimately glomerulosclerosis.

Connective tissue growth factor induces apoptosis in human breast cancer cell line MCF-7

Connective tissue growth factor (CTGF) is a member of an emerging CCN gene family that is implicated in various diseases associated with fibro-proliferative disorder including scleroderma and atherosclerosis. The function of CTGF in human cancer is largely unknown. We now show that CTGF induces apoptosis in the human breast cancer cell line MCF-7. CTGF mRNA was completely absent in MCF-7 but strongly induced by treatment with transforming growth factor beta (TGF-beta). TGF-beta by itself induced apoptosis in MCF-7, and this effect was reversed by co-treatment with CTGF antisense oligonucleotide. Overexpression of CTGF gene in transiently transfected MCF-7 cells significantly augmented apoptosis. Moreover, recombinant CTGF protein significantly enhanced apoptosis in MCF-7 cells as evaluated by DNA fragmentation, Tdt-mediated dUTP biotin nick end-labeling staining, flow cytometry analysis, and nuclear staining using Hoechst 33258. Finally, recombinant CTGF showed no effect on Bax protein expression but significantly reduced Bcl2 protein expression. Taken together, these results suggest that CTGF is a major inducer of apoptosis in the human breast cancer cell line MCF-7 and that TGF-beta-induced apoptosis in MCF-7 cells is mediated, in part, by CTGF.

Overexpression of connective tissue growth factor gene induces apoptosis in human aortic smooth muscle cells

BACKGROUND

Connective tissue growth factor (CTGF) is expressed at very high levels particularly in the shoulder of human atherosclerotic lesions but not in normal blood vessels. Thus, CTGF may be important in the regulation of vascular smooth muscle cell function in atherosclerosis, but its precise role remains elusive.

METHODS AND RESULTS

Full-length CTGF cDNA driven by a cytomegalovirus promoter was transiently transfected into cultured human aortic smooth muscle cells (HASCs). Northern and Western analysis demonstrated that CTGF was overexpressed in these cells 48 hours after transfection. The effects of CTGF overexpression on cell proliferation were evaluated by [(3)H]thymidine uptake and cell count in quiescent HASCs or those stimulated with platelet-derived growth factor (PDGF). Although mock transfection showed no effect, CTGF overexpression significantly inhibited cell proliferation in cells stimulated by PDGF. Moreover, CTGF overexpression, but not mock transfection, significantly increased apoptosis as assessed by DNA fragmentation associated with histone, TdT-mediated dUTP biotin nick end-labeling, and appearance of hypodiploid cells by flow cytometry.

CONCLUSIONS

Our results for the first time demonstrate that CTGF can also act as a growth inhibitor in human aortic smooth muscle cells at least in part by inducing apoptosis. This may be important for the formation and composition of lesions and plaque stability in atherosclerosis.

Platelet-derived growth factor-induced vasodilatation in mesenteric resistance arteries by nitric oxide: blunted response in spontaneous hypertension

Platelet-derived growth factor (PDGF) is a potent mitogen for vascular smooth-muscle cells, but its effects on vasomotion remain controversial. Both vasoconstriction and vasodilatation of isolated rat aortic rings have been reported. The effects of PDGF on responses of perfused mesenteric resistance arteries from normotensive Wistar-Kyoto and spontaneously hypertensive rats were studied by using a video dimension analyzer. PDGF receptor messenger RNA (mRNA) expression in endothelial cells isolated from mesenteric arteries of both normotensive and hypertensive rats was studied by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. In both normotensive and hypertensive rats, PDGF-BB concentration-dependently induced vasodilatation (maximal response, 25 +/- 4% and 13 +/- 4% at 10(-8) M, respectively; p < 0.05, normotensive vs. hypertensive rats). Endothelium removal or preincubation with N(omega)-nitro-L-arginine methyl ester, but not indomethacin, inhibited these relaxations, indicating that these vasodilatations are endothelium dependent and mediated by nitric oxide. RT-PCR analysis showed that both PDGF-alpha and -beta receptor mRNAs were present in endothelial cells of the mesenteric arteries of normotensive as well as hypertensive rats. In addition, relaxations induced by both PDGF-AA and -AB were significantly less than those induced by PDGF-BB in both strains, suggesting that vasodilatation is mediated mainly by the PDGF-beta receptor subtype. No vasoconstriction was observed after application of PDGF-BB to both normotensive and hypertensive mesenteric arteries with or without endothelium. In rat mesenteric resistance arteries, PDGF induces endothelium-dependent vasodilatation mediated by nitric oxide. At sites where PDGF is released or locally produced, therefore, the growth factor may participate in regulating vascular tone, and this endothelium-dependent regulation is attenuated in spontaneous hypertension.

Reduced endothelial nitric oxide synthase expression and production in human atherosclerosis

BACKGROUND

NO regulates vascular tone and structure, platelets, and monocytes. NO is synthesized by endothelial NO synthase (eNOS). Endothelial dysfunction occurs in atherosclerosis.

METHODS AND RESULTS

With a porphyrinic microsensor, NO release was measured in atherosclerotic human carotid arteries and normal mammary arteries obtained during surgery. eNOS protein expression was analyzed by immunohistochemistry. In normal arteries, the initial rate of NO release after stimulation with calcium ionophore A23187 (10 micromol/L) was 0.42+/-0.05 (micromol/L)/s (n=10). In contrast, the initial rate of NO release was markedly reduced in atherosclerotic segments, to 0.08+/-0.04 (micromol/L)/s (n=10, P<0.0001). NO peak concentration in normal arteries was 0.9+/-0.09 micromol/L (n=10) and in atherosclerotic segments, 0.1+/-0.03 micromol/L (n=10, P<0.0001). Reduced NO release in atherosclerotic segments was accompanied by marked reduction of immunoreactive eNOS in luminal endothelial cells, although specific endothelial cell markers (CD31) were present (n=13). Endothelial cells of vasa vasorum of atherosclerotic segments, however, remained positive for eNOS, as was the endothelium of normal arteries.

CONCLUSIONS

In clinically relevant human atherosclerosis, eNOS protein expression and NO release are markedly reduced. This may be involved in the progression of atherosclerosis.

Expression of connective tissue growth factor in human renal fibrosis

Chronic renal failure may occur in etiologically diverse renal diseases and can be caused by hemodynamic, immunologic and metabolic factors. Initial damage may evoke irreversible scarring, which involves production of a number of proinflammatory and fibrogenic cytokines, including platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-beta). Connective tissue growth factor (CTGF), a cytokine of the family of growth regulators comprising sef10, cyr61, CTGF and nov, has recently been described in association with scleroderma and other scarring conditions. We investigated CTGF mRNA expression in 65 human renal biopsy specimens of various renal diseases by in situ hybridization. In control human kidney CTFG mRNA was mainly expressed in visceral epithelial cells, parietal epithelial cells, and some interstitial cells. Connective tissue growth factor was strongly up-regulated in the extracapillary and severe mesangial proliferative lesions of crescentic glomerulonephritis, IgA nephropathy, focal and segmental glomerulosclerosis and diabetic nephropathy. An increase in the number of cells expressing CTGF mRNA was observed at sites of chronic tubulointerstitial damage, which correlated with the degree of damage. in the tubulointerstitial area the majority of the CTGF mRNA positive cells coexpressed alpha-smooth muscle actin, and were negative for macrophage markers. Our results indicate that CTGF may be a common growth factor involved in renal fibrosis.

Different proliferative properties of smooth muscle cells of human arterial and venous bypass vessels: role of PDGF receptors, mitogen-activated protein kinase, and cyclin-dependent kinase inhibitors

BACKGROUND

Internal mammary artery (IMA) bypass grafts have a higher patency than saphenous vein (SV) grafts. Intimal hyperplasia of SV grafts is due to smooth muscle cell (SMC) proliferation and migration. We hypothesized that different SMC growth activity exists in IMA and SV, which may explain the different patencies of arterial and venous grafts.

METHODS AND RESULTS

SMCs were isolated from IMA and SV by explant culture and stimulated with serum or platelet-derived growth factor-BB (PDGF-BB). Cell growth was analyzed by explant outgrowth rate, 3H-thymidine incorporation, or cell counting. PDGF receptor expression and autophosphorylation, regulation of mitogen-activated protein kinases (MAPKs), and cyclin-dependent kinase inhibitors (p27Kip1 and p21Cip1) were analyzed by molecular techniques. SMC outgrowth from explants by serum (20%) over a 20-day period was more pronounced in SV (37+/-5%) than in IMA (4+/-3%; P<.001) of the same patients. Serum (10%) increased cell number more rapidly in SV (2 x 10(4)/well to 18+/-4 x 10(4)/well; P<.05) than in IMA (2 x 10(4)/well to 9+/-4 x 10(4)/well; P<.05) over an 8-day period. PDGF-BB (0.01 to 10 ng/mL) stimulated 3H-thymidine incorporation (1347+/-470% above control levels) and increased cell number in SV (2 x 10(4)/well to 5+/-1 x 10(4)/well; P<.05) but not in IMA. PDGF alpha- and beta-receptors were similarly expressed and were activated in both SV and IMA. PDGF-BB induced a similar MAPK activation (kinetics and maximal activity) in both SV and IMA cells but increased MAPK protein level only in SV. Furthermore, PDGF-BB markedly downregulated the cell cycle inhibitor p27Kip1 in SV, but this was much less pronounced in IMA.

CONCLUSIONS

SMCs from SVs exhibit enhanced proliferation compared with IMA in spite of functional growth factor receptor expression and MAPK activation. However, PDGF increased MAPK protein level only in SV and downregulated cell cycle inhibitor (p27Kip1) more potently in SV than in IMA. This may explain the resistance to growth stimuli of IMA SMCs and may contribute to the longer patency of arterial versus venous grafts.

Pulsatile stretch stimulates superoxide production and activates nuclear factor-kappa B in human coronary smooth muscle

There is increasing evidence that oxidative stress is of pathophysiological importance in cardiovascular disease. Mechanical forces such as pulsatility may also contribute. Using human coronary artery smooth muscle cells (HCAS), we tested the hypothesis that stretch-induced cell proliferation is associated with oxidative stress. Stretch induced DNA synthesis in HCAS, and this was prevented by the antioxidants N-acetylcysteine and pyrrolidinedithiocarbamate (PDTC). Pulsatile stretch also increased superoxide production from HCAS in a time- and stretch dependent manner. Stretch-induced superoxide production was inhibited by diphenyleneiodoniumchloride, an NADPH oxidase inhibitor, and p-chloromercuriphenylsulfonic acid, an NADH oxidase inhibitor, but not by the xanthine oxidase inhibitor oxypurinol or the cyclooxygenase inhibitor indomethacin. In electrophoretic mobility shift assays, tumor necrosis factor-alpha activated nuclear factor-kappa B (NF-kappa B) with a peak at approximately 3 hours, whereas pulsatile stretch showed sustained activation during stimulation for up to 24 hours. The sustained activation of NF-kappa B was abolished by cotreatment with N-acetylcysteine or PDTC. Furthermore, treatment of HCAS with antisense p65 and p50 oligodeoxynucleotides of NF-kappa B inhibited stretch-induced DNA synthesis. We propose that pulsatile stretch increases oxidative stress and, in turn, promotes DNA synthesis via NF-kappa B in cultured human coronary artery smooth muscle cells.

Connective tissue growth factor. Friend or foe?

Connective tissue growth factor (CTGF) is a novel cysteine-rich, secreted peptide, which is implicated in human atherosclerosis and fibrotic disorders such as systemic scleroderma. CTGF is a member of the peptide family that includes serum-induced immediate early gene products, a v-src-induced peptide, and a putative proto-oncogene. The CTGF gene family is a modular protein and is conserved throughout evolution. CTGF mRNA has been found in the human, mouse, chicken, frog, and fly. The functions of the CTGF gene family include embryogenesis, wound healing, and regulation of extracellular matrix production. Human CTGF is undetectable in normal blood vessels but overexpressed in atherosclerotic lesions, suggesting an important role in atherogenesis.

Bimodal effects of angiotensin II on migration of human and rat smooth muscle cells. Direct stimulation and indirect inhibition via transforming growth factor-beta 1

Angiotensin II may be an important mediator of neointima formation in vascular disease. This study was designed to examine the mechanisms involved in angiotensin II-stimulated migration of human and rat aortic vascular smooth muscle cells (VSMCs). VSMCs were seeded in one corner of Nunc four-well culture chambers; angiotensin II within filter paper was glued onto the wall of the opposite side. After 48 hours of incubation in serum-free medium containing growth-arresting factor, migrated cells were counted using a light microscope. Angiotensin II (2 x 10(-11) to 2 x 10(-8) mol/L) increased migration of VSMCs in a concentration-dependent manner. Interestingly, at higher concentrations of angiotensin II (up to 2 x 10(-6) mol/L), migration was reduced to levels comparable with control levels. Losartan, an AT1 receptor antagonist, prevented migration, while PD123319, an AT2 receptor antagonist, had no significant inhibitory effect. Transforming growth factor-beta 1 (TGF-beta 1; 0.01 to 10.0 pg/mL) inhibited migration induced by angiotensin II (2 x 10(-8) mol/L) in a concentration-dependent manner. A neutralizing TGF-beta antibody unmasked migratory effects of high concentrations of angiotensin II. Furthermore, angiotensin II (10(-6) mol/L) upregulated TGF-beta 1 mRNA levels fivefold in rat and fourfold in human VSMCs; this effect was prevented by losartan but not by PD123319. Thus, the effects of angiotensin II on migration of VSMCs are bimodal, ie, both migratory and antimigratory pathways are activated. Autocrine release of TGF-beta 1 induced by angiotensin II exerts an antimigratory effect in rat and human VSMCs. The AT1 receptor is involved in regulation of both pathways.

Human connective tissue growth factor is expressed in advanced atherosclerotic lesions

BACKGROUND

Atherosclerosis affects certain but not all vascular beds of the human circulation. Its molecular mechanisms are only partially understood. Human connective tissue growth factor (hCTGF) is a novel cysteine-rich, secreted polypeptide. hCTGF is implicated in connective tissue formation, which may play an important role in atherosclerosis.

METHODS AND RESULTS

By using a differential cloning technique, we isolated a cDNA clone from a human aorta cDNA library, which is identical to hCTGF. Northern analysis shows that hCTGF mRNA was expressed at 50- to 100-fold higher levels in atherosclerotic blood vessels compared with normal arteries. In vascular smooth muscle cells, high-level expression of hCTGF mRNA was induced by transforming growth factor-beta 1. Using in situ hybridization and immunohistochemistry, we found that all advanced atherosclerotic lesions of human carotid arteries (eight patients; mean age, 69; age range, 57 to 85 years) and femoral arteries (two patients; mean age, 71.5 years) that we tested expressed high levels of both hCTGF mRNA and protein. hCTGF expression was localized mainly to smooth muscle cells in the plaque lesions that are negative for proliferating cell nuclear antigen staining. In addition, some CD-31-positive endothelial cells of plaque vessels expressed high levels of hCTGF mRNA and protein. hCTGF-positive cells were found predominantly in areas with extracellular matrix accumulation and fibrosis. In contrast, in normal arteries, we were unable to detect either hCTGF mRNA or immunoreactive hCTGF protein.

CONCLUSIONS

In the present study, we have shown for the first time that both hCTGF mRNA and protein are expressed in human arteries in vivo and that hCTGF may represent a novel factor expressed at high levels specifically in advanced lesions and may play a role in the development and progression of atherosclerosis.

[Molecular and cellular mechanisms of arteriosclerosis and restenosis: possibilities of gene therapy]

Atherosclerosis and its consequences account for most of morbidity and mortality in Western countries. Atherosclerosis develops over a period of decades and has a complex pathogenesis. It is a disease of the intima and primarily involves four cell types, i.e., endothelial and vascular smooth muscle cells, monocytes and platelets. In recent years, knowledge on the cellular and molecular mechanisms of these cells and their alterations by cardiovascular risk factors and in atherosclerosis has greatly expanded. In particular, it became clear that endothelial cells play a crucial role in the regulation of platelet function, coagulation as well as vascular tone and structure. Interestingly, endothelial dysfunction occurs early, particularly if cardiovascular risk factors such as hyperlipidemia, hypertension and diabetes are present. This could lead to adhesion of circulating platelets and monocytes and increased accumulation of lipids in the subintima as well as increased contraction, migration and proliferation of vascular smooth muscle cells. The fact that atherosclerosis develops only in certain, but not in other parts of the circulation, however, has rarely been considered. With the development of molecular biology techniques it became possible to clone differentially expressed genes in vessels with or without atherosclerosis; this in turn allows to better characterize the molecular and cellular mechanisms of the disease. The search for such candidate genes could set the basis for future genetic interventions. This therapeutic approach is likely to reach clinical importance particularly in monogenetic diseases (i.e., familial hypercholesterinemia), while its use in complex polygenetic diseases such as atherosclerosis is more difficult. Restenosis, however, may be accessible to gene therapy earlier on as it is amenable to local gene transfection.

17 beta-Estradiol and smooth muscle cell proliferation in aortic cells of male and female rats

The low incidence of cardiovascular disease in women before menopause or during hormone replacement therapy suggests a protective effect of estrogens. The mechanism(s) are uncertain but may involve effects on lipids, coagulation and the endothelium. Vascular smooth muscle cell (VSMC) proliferation also contributes to atherosclerosis. Hence, we investigated whether 17 beta-estradiol (E2) inhibits VSMC proliferation. VSMC of 6 female and 6 male Wistar Kyoto rats (WKY; age 10-12 weeks) were incubated for 24 h with E2 and/or fetal calf serum (FCS). E2 (10(-9)-10(-5) M) alone reduced [3H]thymidine uptake at 10(-5) (n=8, p<0.05 vs control) in female cells only. In female and male VSMC, FCS (1%) increased [3H]thymidine uptake (4.5-fold, p<0.05 vs. control). When given simultaneously, E2 did not prevent this effect of FCS (1%). However, when cells were preincubated for 24 h with E2 and then stimulated with FCS, [3H]thymidine uptake was reduced by E2 at 10(-5) M in female VSMC (n=7, p<0.05 vs FCS alone), while in male VSMC this effect was minimal (n.s.): Both female and male VSMC expressed estrogen receptors as demonstrated by RT-PCR. Pretreatment of female VSMC cells with the E2 receptor antagonist tamoxifen prevented the antiproliferative effects exerted by E2. In aortic VSMC of female rats, E2 moderately inhibited proliferation on its own and during stimulation with FCS, while this effect was small in VSM of male rats. The expression of the E2 receptor in female and male VSMC and the effects of tamoxifen suggest that this effect is mediated by E2 receptors.

[Molecular medicine and gene therapy as exemplified with arteriosclerosis and restenosis]

Atherosclerosis and its consequences account for most morbidity and mortality in Western countries. Atherosclerosis develops over a period of decades and has a complex pathogenesis. It is a disease of the intima and primarily involves four cell types, i.e. endothelial and vascular smooth muscle cells, monocytes and platelets. In recent years, elucidation of the cellular and molecular mechanisms of these cells, and their alterations by cardiovascular risk factors and in atherosclerosis, has markedly expanded knowledge of this disease. In particular, it became clear that endothelial cells play a crucial role in the regulation of platelet function and coagulation, as well as vascular tone and structure. Interestingly, endothelial dysfunction occurs early on in the presence of cardiovascular risk factors such as hyperlipidemia, hypertension and diabetes. This could lead to adhesion of circulating platelets and monocytes, increased accumulation of lipids in the subintima, increased contraction, migration and proliferation of vascular smooth muscle cells. The fact that atherosclerosis develops only in some but not in other parts of the circulation, however, has rarely been considered. With the development of molecular biology it has now become possible to clone differentially expressed genes in vessels with or without atherosclerosis; this in turn makes it possible to characterize better the molecular and cellular mechanisms of the disease. The search for such candidate genes could form the basis for future genetic interventions. This therapeutic approach is likely to assume clinical importance, particularly in monogenetic diseases (i.e. familial hypercholesteremia), while its use in complex polygenetic diseases such as atherosclerosis is more difficult. Restenosis, however, may be accessible to gene therapy earlier on as it is accessible to local gene transfection.

Molecular and cellular mechanisms of atherosclerosis

At least three distinct cellular mechanisms are currently thought to be responsible for the initiation of atherosclerotic lesions in humans: (1) accumulation of lipids and plasma-derived lipoproteins in the arterial intima; (2) smooth muscle cell migration from the media into the intima, and smooth muscle cell proliferation or accumulation, or both, within the intima; and (3) accumulation of platelet and/or fibrin deposits in the intima. Independent of the triggering factor, it appears that the first step in atherogenesis involves activation of repair mechanisms in the blood vessel in an attempt to restore vascular homeostasis, which involves a delicate balance of growth promoting and growth inhibitory activities of the vascular wall cells. The healing process involves a series of specific and temporally coordinated events, such as platelet aggregation, monocyte adhesion and migration across endothelial cells, and migration and proliferation of vascular smooth muscle cells, which are normally orchestrated by a variety of growth factors, cytokines, adhesion molecules, and extracellular matrix proteins in a controlled, although not yet fully understood, manner. Alteration in any of these steps during the healing process can lead to changes in the patterns of protein synthesis, processing, and secretion in these cells. These in turn result in connective tissue deposition, lipid accumulation, cell death, mineralization, and finally the development of advanced, occluding atherosclerotic plaques.

Both ETA and ETB receptors mediate contraction to endothelin-1 in human blood vessels

BACKGROUND

Endothelin (ET)-1 has potent vascular effects. Two endothelin receptors have been cloned, namely, the ETA receptor, which preferentially binds ET-1, and the ETB receptor, which equally binds ET-1 and ET-3 and preferentially sarafotoxin S6c. We characterized endothelin receptor subtypes on vascular smooth muscle and endothelium of isolated human internal mammary artery (IMA) and vein (IMV) and porcine coronary artery (PCA) using the ETA antagonists FR139317 and BQ-123, the ETB ligand sarafotoxin S6c, and the ETA/ETB antagonist Ro 47-0203 (bosentan).

METHODS AND RESULTS

In endothelium-denuded IMA and PCA and less so in IMV, FR139317 and BQ-123 (in PCA only) shifted the concentration-contraction curves to ET-1 parallel to the right. However, even at 10(-5) mol/L, FR139317 did not inhibit a high-sensitivity portion of the concentration-contraction curve. Moreover, the ETB receptor agonist sarafotoxin S6c induced contraction in vessels preincubated with FR139317. IMV was significantly more sensitive to the contractile effect of ET-1 and sarafotoxin S6c than was IMA (P < .05). Prolonged incubation with sarafotoxin S6c (to downregulate ETB receptors) and FR139317 eliminated the contraction resistant to FR139317. The ETA/ETB receptor antagonist bosentan caused a parallel shift of the concentration-contraction curve to the right at all concentrations of endothelin. ETB receptor mRNA was detected by Northern blot analysis in IMA and aortic smooth muscle cells. In precontracted IMA and PCA with endothelium, sarafotoxin S6c did not cause endothelium-dependent relaxations, whereas transient responses occurred in IMV.

CONCLUSIONS

Vascular smooth muscle cells of human IMA, IMV, and PCA contain both ETA and ETB receptors, whereas the endothelium of IMA and PCA does not express functional ETB receptors linked to nitric oxide and/or prostacyclin production. Hence, inhibition of endothelin-induced contraction in patients requires the use of combined ETA/ETB antagonists.

Insulin like growth factor 1 receptor signal transduction to the nucleus

The mechanism by which IGF-1Rs regulate the growth and maintenance of cells in normal and disease states provides an important setting for studies addressing signal transduction events at the nuclear level. With the identification of c-Jun/AP-1 as a nuclear target of IGF-1 action we are provided with a model system for pursuing the molecular mechanisms triggered by IGF-1 action.

Insulin-like growth factor-1 induces tyrosyl phosphorylation of nuclear proteins

Stimulation of mesangial cells with insulin-like growth factor-1 (IGF-1) resulted in the rapid tyrosyl phosphorylation of nuclear proteins as indicated by fluorescence microscopy of cells stained with anti-phosphotyrosine antibodies. Immunoprecipitation of nuclear extracts with anti-phosphotyrosine antibodies revealed that IGF-1 induced a transient increase in immunoreactive phosphotyrosine in nuclear proteins of 43, 95, and 160 kDa. Using a double immunoprecipitation protocol, the transcription factor c-Jun was also found to increase in immunoreactive phosphotyrosine in response to IGF-1. A similar pattern of tyrosyl phosphorylation of nuclear proteins was observed in the epidermoid carcinoma cell line CaSki. These data suggest that tyrosyl phosphorylation of nuclear proteins may be a step in the transduction of mitogenic signals.

Regulation of insulin-like growth factor I receptors in diabetic mesangial cells

Mesangial cells are thought to play a central role in the renal complications of diabetes mellitus. Insulin-like growth factor I (IGF-I) has been found to promote mesangial cell proliferation and regulate normal mesangial cell function in an autocrine and/or paracrine fashion. To gain further insight into the potential regulatory role IGF-I may play in mesangial cell function in diabetes, IGF-I receptors were analyzed in mesangial cells isolated from diabetic mice (db/db) and their control littermates (db/m). Mesangial cells isolated from db/db mice exhibited higher levels of IGF-I receptors compared to cells from db/m mice. Insulin receptors were not detectable in either cell type by binding analyses; however, immunoblot analysis revealed insulin receptor alpha-subunits in wheat germ agglutinin-Sepharose-purified membranes from db/db cells. Northern blot analysis further indicated a lack of detectable insulin receptor mRNA in db/m cells, whereas db/db cells expressed multiple insulin receptor mRNA transcripts. Both IGF-I and insulin receptor mRNA levels were increased in db/db cells grown in the presence of high glucose (28 mM), whereas the receptor protein levels remained relatively constant or increased, respectively. This increased expression of IGF-I and insulin receptors in diabetic mesangial cells may have an important role in the development of diabetic nephropathy.

[What is the role of autoimmune processes in nephropathies?]

Classical autoimmune nephropathies rarely occur during childhood. They include the glomerulonephritis and tubulointerstitial nephritis caused by antibasement membrane antibodies and the systemic lupus erythematosus. The autoimmune pathogenesis of glomerulopathies such as minimal change disease and different forms of tubulointerstitial nephritis which are more frequent in children is not proven yet. The possible mechanisms of autoimmune disorders affecting the kidneys are 1. the genetic predisposition, 2. a defect in the immune system, 3. exogenous agents leading to cross-reactivity or polyclonal B cell stimulation, and 4. endogenous agents leading to immunogenic autoantigens. This review summarizes the current knowledge on the autoimmune pathogenesis of nephropathies derived from investigations in humans and animal experiments.

Four years' experience with cyclosporin A in pediatric kidney transplantation

From 1982 to 1987 sixty-three children were treated with cyclosporin A and low dose prednisolone after kidney transplantation. Patient survival rate at 4 years after transplantation was 98.3%, survival rate of living related grafts 100% (n = 10), and survival rate of cadaveric grafts 73% (n = 53). Adequate cyclosporin blood levels were achieved in all children with a dosage regimen related to body surface area. Major concerns during the observation period were the loss of glomerular filtration rate from 51.8 to 40.5 ml/min/1.73 m2, a hypertension rate of 77.8%, and hyperuricemia. Cyclosporin A-side effects were mild. Infections occurred in 11.1%. Growth retardation in prepubertal children improved by 0.74 standard deviations of normal height, and in pubertal children by 0.51. We conclude that cyclosporin A treatment in children enables excellent long term graft survival rates with improved growth rehabilitation, however, the prevention of the cyclosporin associated nephrotoxicity and hypertension remains the major problem.

[Cystic kidneys in children]

From 1976-1987 a total of 26 infants and children with polycystic kidney disease were treated at the Children's Hospital of the Medical School Hannover. 13 of them suffered from infantile recessive polycystic kidney disease (IRPKD), and 13 from adult dominant polycystic kidney disease (ADPKD). IRPKD was diagnosed at a median age of 0.33 years (range 1 day-13 years), ADPKD at 6.0 years (3 days-14 years). Of those with IRPKD two infants died from bacterial infection and two others developed terminal renal insufficiency at the age of 8 years, while the others are living and 1-20 years old. All those suffer from severe arterial hypertension and have reduced renal function, but only 5 developed signs of liver fibrosis. Of those with ADPKD one infant died from sepsis and renal insufficiency, while the others are well and now 2-17 years old. Only one child needs an antihypertensive treatment. The most important criteria to differentiate IRKPD and ADKPD in children are the genetic transmission, age of first manifestation, hypertension and renal function. The prognosis is much more severe in IRPKD than in ADPKD, but is not as infaust in IRPKD as often assumed.

Effect of cyclosporine on the renal tubular amino acid handling after kidney transplantation

The renal tubular handling of free amino acids was studied 5-6 weeks after successful renal transplantation (tx) in 20 children treated with CsA and in 10 children treated with azathioprine (Aza). The results were compared with those of 34 control children. The amino-acid clearance studies were performed in combination with short-term inulin clearance. The CsA group revealed a mean inulin clearance of 49 +/- 16.8 ml/min/1.73 m2, the Aza group of 76.9 +/- 18.2, and the controls of 114 +/- 15.6. The plasma amino-acid concentrations were not different between CsA- and Aza-treated groups; however, most of the essential amino acids were lower in transplanted children than in controls. The decrease was correlated with the GFR. The amino-acid-clearance rates were statistically not different between both transplanted groups, but lower values than in controls were found for alanine, glycine, histidine, lysine, and phenylalanine, and significantly higher values for methionine. The fractional clearance rates of most amino acids were significantly elevated in transplanted children compared to controls. In CsA-treated patients, the fractional clearance rates of arginine, glycine, and serine were higher than in Aza-treated patients. No influence of CsA blood levels or rejection episodes on the amino-acid handling were detectable. We conclude that CsA has no specific influence on the renal handling of amino acids. Most disturbances observed depend on the graft function or may be caused by injuries to the graft following the tx procedure.

Renal handling of uric acid under cyclosporin A treatment

The renal handling of uric acid during cyclosporin A (CyA) treatment was investigated by clearance studies using 24-h urine collections in 28 paediatric renal transplant recipients (CyA group), and the results were compared with those of 19 renal transplanted children treated with azathioprine and prednisolone (AZA group), 35 children with chronic renal failure (CRF) and 10 children with normal renal function (N group). Serum uric acid levels were significantly higher in the CyA group (567 +/- 156 mumol/l) compared with the AZA group (378 +/- 98), the CRF group (415 +/- 119) and the N group (290 +/- 68). Mean uric acid clearances in each group measured 3.9 +/- 2.8 ml/min per 1.73 m2 (CyA), 5.6 +/- 3.4 (AZA), 4.0 +/- 2.2 (CRF) and 8.4 +/- 3.7 (N). Calculation of the net tubular uric acid reabsorption per millilitre glomerular filtration rate revealed a significantly increased value of 0.53 +/- 0.15 mumol/ml in the CyA group (P less than 0.01) compared with 0.34 +/- 0.08, 0.29 +/- 0.15 and 0.27 +/- 0.07 mumol/l for the AZA, CRF and N groups respectively. We therefore conclude that CyA treatment is associated with an increased net tubular reabsorption of uric acid, which may lead to hyperuricaemia.

Anti-basement membrane glomerulopathy in experimental trypanosomiasis

The nature of kidney lesions in BD IX rats infected with Trypanosoma brucei was investigated. Proteinuria developed and increased up to 236 +/- 35 mg/24 hr at 7 wk after the infection. Antibodies were found to be deposited along the glomerular basement membrane (GBM) predominantly in a linear fashion, which changed to a more granular pattern 7 wk after the infection. At this stage of the disease, electron-dense deposits were found subendothelially along the GBM. In the sera and kidney eluates of diseased rats, anti-GBM antibodies were present. Enzyme-linked immunosorbent assay (ELISA) studies showed antibodies which reacted with GBM components laminin and type IV collagen and not with fibronectin. The antibody specificity was confirmed by using competitive and cross-absorption ELISA techniques, as well as immunoblotting. With the use of indirect immunofluorescence, no common antigenic sites were found on trypanosomes and GBM components. The observed linear immunofluorescence pattern seems to be caused by glomerular binding of antibodies directed against laminin and type IV collagen, which are known to be able to induce renal disease. Subendothelial complex formation in later stages of the disease might result from a molecular rearrangement of GBM components after in situ binding of the antibodies. The formation of auto-antibodies directed against laminin and type IV collagen is probably caused by restricted polyclonal B cell stimulation, a well known feature of trypanosomiasis.

Anti-basement membrane glomerulopathy in experimental trypanosomiasis

The nature of kidney lesions in BD IX rats infected with Trypanosoma brucei was investigated. Proteinuria developed and increased up to 236 +/- 35 mg/24 hr at 7 wk after the infection. Antibodies were found to be deposited along the glomerular basement membrane (GBM) predominantly in a linear fashion, which changed to a more granular pattern 7 wk after the infection. At this stage of the disease, electron-dense deposits were found subendothelially along the GBM. In the sera and kidney eluates of diseased rats, anti-GBM antibodies were present. Enzyme-linked immunosorbent assay (ELISA) studies showed antibodies which reacted with GBM components laminin and type IV collagen and not with fibronectin. The antibody specificity was confirmed by using competitive and cross-absorption ELISA techniques, as well as immunoblotting. With the use of indirect immunofluorescence, no common antigenic sites were found on trypanosomes and GBM components. The observed linear immunofluorescence pattern seems to be caused by glomerular binding of antibodies directed against laminin and type IV collagen, which are known to be able to induce renal disease. Subendothelial complex formation in later stages of the disease might result from a molecular rearrangement of GBM components after in situ binding of the antibodies. The formation of auto-antibodies directed against laminin and type IV collagen is probably caused by restricted polyclonal B cell stimulation, a well known feature of trypanosomiasis.

Renal glucosuria

Normal urine contains small amounts of glucose, called basal glucosuria, and other carbohydrates. Increased amounts of glucose beyond the basal excretion rates i.e. frank glucosuria, reflect reduced activity of tubular glucose reabsorption. Clinically, there are two conditions which are known to appear with a primary disturbance of epithelial glucose transport: intestinal glucose-galactose malabsorption and benign familial renal glucosuria. In the latter, both the renal threshold for glucose and maximal tubular glucose reabsorption are diminished. The degree of glucosuria is variable; the most severe defect demonstrates minimal glucose threshold values and extremely low levels of maximal glucose reabsorption (type 0). The moderate and mild types show variable reductions of both functional parameters. It is questionable whether these should be subdivided into type A and type B glucosurias. Data in the literature reveal that two distinct entities do not exist, but that there is instead a continuous transition from low to normal values. The defect is transmitted genetically, either in an autosomal dominant or autosomal recessive manner. It seems plausible that the different defects might be produced either by mutations on different gene loci, or by multiple alleles of the same gene locus that determines the synthesis of the glucose carrier.

Complete absence of tubular glucose reabsorption: a new type of renal glucosuria (type 0)

Primary renal glucosuria is an inherited defect of tubular glucose reabsorption and usually classified in type A and type B. We now observed a new type in a 15-year-old boy who had a complete absence of tubular glucose reabsorption. His father had a daily glucosuria of 1.1 g/1.73 m2 and his mother of 2.7 g/1.73 m2. Two siblings excreted 0.4 g/1.73 m2 and 0.3 g/1.73 m2 glucose and one sister had no glucosuria. The proband excreted daily 136 to 160 g/1.73 m2 glucose accompanied by normal blood glucose levels between 75-105 mg/dl. The glomerular filtration rate (inulin clearance) was 148-153 ml/min/1.73 m2 and the endogenous glucose clearance was 112-160 ml/min/1.73 m2 when blood glucose levels were 72-82 mg/dl. Thus, glucose clearance was nearly identical to inulin-clearance. After intravenous glucose loading with a blood glucose concentration of 261-342 mg/dl, glucose clearance remained in the same range and tubular glucose reabsorption was virtually absent. There were no disturbances in tubular reabsorption of other substrates. This new type of primary renal glucosuria was not recognized thus far, and we propose to call it type O glucosuria. The family tree revealed consanguinity and most probably the proband is homozygous and both his parents are heterozygous for type O renal glucosuria.

Influence of the lectins and polycation on the configuration of renal podocytes: a scanning electron microscopic study of renal podocytes after micropuncture of the glomerulus in vivo

The lectins concanavalin A (Con A), wheat germ agglutinin (WGA), Ricinus communis agglutinin (RCA) I+II and the polycation protamine sulfate were applied directly to renal glomerular podocytes by micropuncture techniques in vivo; others received a control solution. To make visible the distribution of lectins, some rats were given fluorescein isothiocyanate-conjugated Con A. The glomeruli undergoing the micropuncture experiments were labeled and then prepared for SEM and TEM observation, in some cases also for histochemical analysis. Comparatively, the effect of application of the Con A and protamine sulfate solution by intraarterial infusion was studied. The glomeruli of a total of 100 Munich-Wistar rats were studied. Con A and WGA cause varying degrees of 'retraction' of the foot processes of the podocytes when applied using the techniques of micropuncture. Intraarterial infusion of a Con A solution, on the other hand, causes no changes in the podocytes. RCA II, applied for 10 min using micropuncture techniques, causes thickening and swelling of the foot processes as well as the formation of intercellular junctions ('agglutination'). RCA I, on the other hand, causes no changes in the podocytes of the rat glomerulus. Glomeruli treated with the micropuncture application of the polycation protamine sulfate demonstrate largely 'agglutination' and only sometimes localized minimal retraction of the foot processes of the podocytes. The intraarterial infusion of protamine sulfate causes almost exclusively 'agglutination' of the podocyte foot processes. Retraction of the podocyte foot processes is probably a result of the active movement of the podocytes, which in turn induced by attachment of lectines to the lectin receptors in glycocalyx of the podocyte cell membrane. Simple reduction of the polyanions in the podocyte cell membrane by protamine sulfate appears to cause only simple electrostatic interaction which then results in 'agglutination' of the podocyte foot processes.