Involvement of MAPKs in ICAM-1 expression in glomerular endothelial cells in diabetic nephropathy.

Inflammatory processes are involved in the pathogenesis of diabetic nephropathy. The aim of this study was to clarify the role of mitogen-activated protein kinase (MAPK) pathways for induction of intercellular adhesion molecule-1 (ICAM-1) expression in glomerular endothelial cells under diabetic conditions. We examined the expression of ICAM-1 in the kidneys of experimental diabetic rats. Human glomerular endothelial cells (GE cells) were exposed to normal glucose concentration, high glucose concentration (HG), or high mannitol concentration (HM), and then the expression of the ICAM-1 protein and the phosphorylation of the 3 subfamilies of mitogen-activated protein kinase (MAPK) were determined using Western blot analysis. Next, to evaluate the involvement of MAPKs in HG- or HM-induced ICAM-1 expression, we preincubated GE cells with the inhibitors for ERK, p38 or JNK 1h prior to the application of glucose or mannitol. Expression of ICAM-1 was increased in the glomeruli of diabetic rats. Both HG and HM induced ICAM-1 expression and phosphorylation of ERK1/2, p38 and JNK in GE cells. Expression of ICAM-1 was significantly attenuated by inhibitors of ERK, p38 and JNK. We conclude that activation of ERK1/2, p38 and JNK cascades may be involved in ICAM-1 expression in glomerular endothelial cells under diabetic conditions.

Endothelial barrier protection by FTY720 under hyperglycemic condition: involvement of focal adhesion kinase, small GTPases, and adherens junction proteins.

Recently, sphingosine 1-phosphate (S1P) has been highlighted as an endothelial barrier-stabilizing mediator. FTY720 is a S1P analog originally developed as a novel immunosuppressant. The phosphorylated form of FTY720 binds to S1P receptors to exert S1P-like biological effects, suggesting endothelial barrier promotion by FTY720. To elucidate whether FTY720 induces signaling events related to endothelial barrier enhancement under hyperglycemic conditions, human microvascular endothelial cells (HMVECs) preincubated with hyperglycemic (30 mM) medium were treated with 100 nM FTY720 for 3 h. Immunofluorescent microscopy and coprecipitation study revealed FTY720-induced focal adhesion kinase (FAK)-associated adherens junction (AJ) assembly at cell-cell contacts coincident with formation of a prominent cortical actin ring. FTY720 also induced transmonolayer electrical resistance (TER) augmentation in HMVEC monolayers in both normoglycemic and hyperglycemic conditions, implying endothelial barrier enhancement. Similar to S1P, site-specific FAK tyrosine phosphorylation analysis revealed FTY720-induced FAK [Y576] phosphorylation without phosphorylation of FAK [Y397/Y925]. Furthermore, FTY720 conditioned the phosphorylation profile of FAK [Y397/Y576/Y925] in hyperglycemic medium to the same pattern observed in normoglycemic medium. FTY720 challenge resulted in small GTPase Rac activation under hyperglycemic conditions, whereas increased Rho activity in hyperglycemic medium was restored to the basal level. Rac protein depletion by small interfering RNA (siRNA) technique completely abolished FTY720-induced FAK [Y576] phosphorylation. These findings strongly suggest the barrier protective effect of FTY720 on HMVEC monolayers in hyperglycemic medium via S1P signaling, further implying the possibility of FTY720 as a therapeutic agent of diabetic vascular disorder.

Enhanced interaction between focal adhesion and adherens junction proteins: involvement in sphingosine 1-phosphate-induced endothelial barrier enhancement.

Sphingosine 1-phosphate (S1P) is an important vascular barrier regulatory agonist which enhances the junctional integrity of human lung endothelial cell monolayers. We have now demonstrated that S1P induced cortical actin ring formation and redistribution of focal adhesion kinase (FAK) and paxillin to the cell periphery suggesting the critical role of cell-cell adhesion in endothelial barrier enhancement. Co-immunoprecipitation studies revealed increased association of VE-cadherin with FAK and paxillin in S1P-challenged human pulmonary artery endothelial cell (HPAEC) monolayers. Furthermore, S1P-induced enhancement of VE-cadherin interaction with alpha-catenin and beta-catenin was associated with the increased formation of FAK-beta-catenin protein complexes. Depletion of beta-catenin (siRNA) resulted in loss of S1P-mediated VE-cadherin association with FAK and paxillin rearrangement. Furthermore, transendothelial electrical resistance (an index of barrier function) demonstrated that beta-catenin siRNA significantly attenuated S1P-induced barrier enhancement. These results demonstrate a mechanism of S1P-induced endothelial barrier enhancement via beta-catenin-linked adherens junction and focal adhesion interaction.

Edaravone mimics sphingosine-1-phosphate-induced endothelial barrier enhancement in human microvascular endothelial cells.

Edaravone is a potent scavenger of hydroxyl radicals and is quite successful in patients with acute cerebral ischemia, and several organ-protective effects have been reported. Treatment of human microvascular endothelial cells with edaravone (1.5 microM) resulted in the enhancement of transmonolayer electrical resistance coincident with cortical actin enhancement and redistribution of focal adhesion proteins and adherens junction proteins to the cell periphery. Edaravone also induced small GTPase Rac activation and focal adhesion kinase (FAK; Tyr(576)) phosphorylation associated with sphingosine-1-phosphate receptor type 1 (S1P(1)) transactivation. S1P(1) protein depletion by the short interfering RNA technique completely abolished edaravone-induced FAK (Tyr(576)) phosphorylation and Rac activation. This is the first report of edaravone-induced endothelial barrier enhancement coincident with focal adhesion remodeling and cytoskeletal rearrangement associated with Rac activation via S1P(1) transactivation. Considering the well-established endothelial barrier-protective effect of S1P, endothelial barrier enhancement as a consequence of S1P(1) transactivation may at least partly be the potent mechanisms for the organ-protective effect of edaravone and is suggestive of edaravone as a therapeutic agent against systemic vascular barrier disorder.

Changes of gene expression profiles in macrophages stimulated by angiotensin II--angiotensin II induces MCP-2 through AT1-receptor.

INTRODUCTION: Macrophages play critical roles in the development of atherosclerosis and diabetic nephropathy as well as many inflammatory diseases. Angiotensin II type 1 receptor antagonists (AIIA) are beneficial for the prevention of atherosclerosis and diabetic nephropathy suggesting that angiotensin II (Ang II) promotes the development of these diseases. It has recently been reported that Ang II exerts proinflammatory actions in vivo and in vitro. This study was aimed to clarify the direct effects of Ang II on monocytes/macrophages. MATERIALS AND METHODS: PMA-treated THP-1 cells, a human monocytic leukaemia cell line, were treated with Ang II (10-6 mol/L) for 24 hours with or without AIIA (CV11974). We evaluated gene expression profiles of these cells using DNA microarray system and quantified them by real-time RT-PCR. RESULTS: DNA microarray revealed that in total 19 genes, including monocyte chemoattractant protein (MCP)-2, were up-regulated by Ang II and down-regulated by AIIA. Real-time RT-PCR showed that up-regulation of MCP-2 with Ang II is blocked by the AIIA (CV11974) but not by an AT2-receptor antagonist. CONCLUSIONS: These results suggest that Ang II directly stimulates MCP-2 expression through AT1-receptors in activated macrophages. Ang II may contribute to the persistence or amplification of microinflammation in vessel walls, heart and kidney. Vasculoprotective or renoprotective effects of AIIA might partly depend on direct anti-inflammatory effects on macrophages.

Macrophage scavenger receptor-a-deficient mice are resistant against diabetic nephropathy through amelioration of microinflammation.

Microinflammation is a common major mechanism in the pathogenesis of diabetic vascular complications, including diabetic nephropathy. Macrophage scavenger receptor-A (SR-A) is a multifunctional receptor expressed on macrophages. This study aimed to determine the role of SR-A in diabetic nephropathy using SR-A-deficient (SR-A(-/-)) mice. Diabetes was induced in SR-A(-/-) and wild-type (SR-A(+/+)) mice by streptozotocin injection. Diabetic SR-A(+/+) mice presented characteristic features of diabetic nephropathy: albuminuria, glomerular hypertrophy, mesangial matrix expansion, and overexpression of transforming growth factor-beta at 6 months after induction of diabetes. These changes were markedly diminished in diabetic SR-A(-/-) mice, without differences in blood glucose and blood pressure levels. Interestingly, macrophage infiltration in the kidneys was dramatically decreased in diabetic SR-A(-/-) mice compared with diabetic SR-A(+/+) mice. DNA microarray revealed that proinflammatory genes were overexpressed in renal cortex of diabetic SR-A(+/+) mice and suppressed in diabetic SR-A(-/-) mice. Moreover, anti-SR-A antibody blocked the attachment of monocytes to type IV collagen substratum but not to endothelial cells. Our results suggest that SR-A promotes macrophage migration into diabetic kidneys by accelerating the attachment to renal extracellular matrices. SR-A may be a key molecule for the inflammatory process in pathogenesis of diabetic nephropathy and a novel therapeutic target for diabetic vascular complications.

Thiazolidinedione ameliorates renal injury in experimental diabetic rats through anti-inflammatory effects mediated by inhibition of NF-kappaB activation.

Thiazolidinedione (TZD), a ligand for peroxisome proliferator-activated receptor-gamma (PPAR-gamma), exerts anti-inflammatory effects independently of the insulin-sensitizing effect. In the present study, we tested the hypothesis that TZD prevents the progression of diabetic nephropathy by modulating the inflammatory process. Five-week-old Sprague-Dawley rats were divided into three groups: 1) nondiabetic control rats (non-DM), 2) diabetic rats (DM), and 3) diabetic rats treated with pioglitazone (DM+pio). Diabetes was induced by injection with streptozotocin (STZ). The DM+pio group received 0.0002% pioglitazone mixed in chow for 8 wk after induction of diabetes. Blood glucose and HbA1c were elevated in diabetic rats but did not change by treatment with pioglitazone. Pioglitazone reduced urinary albumin excretion and glomerular hypertrophy, suppressed the expression of transforming growth factor (TGF)-beta, type IV collagen, and ICAM-1, and infiltration of macrophages in the kidneys of diabetic rats. Furthermore, renal NF-kappaB activity was increased in diabetic rats and reduced by pioglitazone. PPAR-gamma was expressed in glomerular endothelial cells in the diabetic kidney and in cultured glomerular endothelial cells. High-glucose conditions increased the expression of ICAM-1 and the activation of NF-kappaB in cultured glomerular endothelial cells. These changes were reduced by pioglitazone, ciglitazone, and pyrrolidine dithiocarbamate, an inhibitor of NF-kappaB. However, pioglitazone did not show the changes in the presence of PPAR-gamma antagonist GW9662. Our results suggest that the preventive effects of pioglitazone may be mediated by its anti-inflammatory actions, including inhibition of NF-kappaB activation, ICAM-1 expression, and macrophage infiltration in the diabetic kidney.

Methotrexate prevents renal injury in experimental diabetic rats via anti-inflammatory actions.

Recent studies suggested the involvement of inflammatory processes in the pathogenesis of diabetic nephropathy. Methotrexate (MTX), a folic acid antagonist, is widely used for the treatment of inflammatory diseases. Recently, it has been shown that treatment with low-dose MTX reduces the cardiovascular mortality in patients with rheumatoid arthritis, suggesting that MTX has anti-atherosclerotic effects via its anti-inflammatory actions. This study was designed to determine the anti-inflammatory effects of this agent on diabetic nephropathy. Diabetes was induced in Sprague-Dawley rats with streptozotocin, and MTX (0.5 or 1.0 mg/kg) was administered once a week for 8 wk. Treatment with MTX reduced urinary albumin excretion, mesangial matrix expansion, macrophage infiltration, expression of TGF-beta and type IV collagen, and intercellular adhesion molecule-1 in glomeruli. MTX also reduced the high glucose-induced NF-kappaB activation in vitro and in vivo. The results indicate that intermittent administration of MTX prevented renal injuries without changes in blood glucose level and BP in experimental diabetic rats. The protective effects of MTX are suggested to be mediated by its anti-inflammatory actions through inhibition of NF-kappaB activation and consequent reduction of intercellular adhesion molecule-1 expression and macrophage infiltration. The results suggest that anti-inflammatory agents might be beneficial for the treatment of diabetic nephropathy.

Differential effects of shear stress and cyclic stretch on focal adhesion remodeling, site-specific FAK phosphorylation, and small GTPases in human lung endothelial cells.

Regulation of endothelial cell (EC) permeability by bioactive molecules is associated with specific patterns of cytoskeletal and cell contact remodeling. A role for mechanical factors such as shear stress (SS) and cyclic stretch (CS) in cytoskeletal rearrangements and regulation of EC permeability becomes increasingly recognized. This paper examined redistribution of focal adhesion (FA) proteins, site-specific focal adhesion kinase (FAK) phosphorylation, small GTPase activation and barrier regulation in human pulmonary EC exposed to laminar shear stress (15 dyn/cm2) or cyclic stretch (18% elongation) in vitro. SS caused peripheral accumulation of FAs, whereas CS induced randomly distributed FAs attached to the ends of newly formed stress fibers. SS activated small GTPase Rac without effects on Rho, whereas 18% CS activated without effect on Rac. SS increased transendothelial electrical resistance (TER) in EC monolayers, which was further elevated by barrier-protective phospholipid sphingosine 1-phosphate. Finally, SS induced FAK phosphorylation at Y576, whereas CS induced FAK phosphorylation at Y397 and Y576. These results demonstrate for the first time differential effects of SS and CS on Rho and Rac activation, FA redistribution, site-specific FAK phosphorylation, and link them with SS-mediated barrier enhancement. Thus, our results suggest common signaling and cytoskeletal mechanisms shared by mechanical and chemical factors involved in EC barrier regulation.

Sulfated hyaluronic acid, a potential selectin inhibitor, ameliorates experimentally induced crescentic glomerulonephritis.

BACKGROUND/AIMS: Sulfated polysaccharides are known to interfere with the binding of selectins and their ligands. Recently, we demonstrated that sulfated hyaluronic acid (SHA), a synthetic sulfated polysaccharide, showed preventive and therapeutic effects on experimental mesangial proliferative glomerulonephritis. Here we evaluated the protective potential of SHA on crescentic glomerulonephritis, using nephrotoxic serum (NTS) nephritis in Wistar-Kyoto (WKY) rats. METHODS: Crescentic glomerulonephritis was induced by injection of NTS in WKY rats. Rats subsequently received intraperitoneal administration of SHA (0.5 or 1.5 mg/kg/day) or non-sulfated hyaluronic acid (HA) (1.5 mg/kg/day) for 14 days. The urinary protein excretion was measured, and expression of selectins, intraglomerular leukocytes and crescent formation were examined by immunohistochemistry. In addition, we examined the urinary protein excretion of SHA (1.5 mg/kg/day) administered from day 7 after the induction of crescentic glomerulonephritis. RESULTS: The expression of P-selectin was increased in the glomerulus of crescentic glomerulonephritis. SHA reduced proteinuria, macrophage infiltration, and crescent formation in a dose-dependent manner. Furthermore, administration of SHA (1.5 mg/kg/day) from day 7 also reduced the urinary protein excretion on day 14 compared with that in saline and HA group. CONCLUSION: Our results suggest that SHA inhibits intraglomerular infiltration of macrophages, and prevents progression of experimental crescentic glomerulonephritis. Sulfated polysaccharides might be beneficial for the treatment of crescentic glomerulonephritis.

Involvement of site-specific FAK phosphorylation in sphingosine-1 phosphate- and thrombin-induced focal adhesion remodeling: role of Src and GIT.

Sphingosine-1 phosphate (S1P) and thrombin are agents with profound but divergent effects on vascular endothelial cell (EC) barrier properties. We have previously reported that S1P-induced focal adhesion (FA) remodeling involves interactions between focal adhesion kinase (FAK), paxillin, and G-protein-coupled receptor kinase-interacting proteins GIT1 and GIT2 and suggested a critical involvement of focal adhesions in the EC barrier regulation. In this study, we examined redistribution of FA proteins (FAK, paxillin, GIT1, and GIT2) and site-specific FAK tyrosine phosphorylation in human pulmonary artery endothelial cells stimulated with thrombin. In contrast to S1P, which we have shown to induce peripheral translocation of FA proteins associated with cortical actin ring formation, thrombin caused the redistribution of FA proteins to the ends of the newly formed massive stress fibers. S1P and thrombin induced distinct patterns of FAK site-specific phosphorylation with the FAK Y576 phosphorylation site targeted by SIP challenge and phosphorylation of three FAK sites (Y397, Y576, and Y925) in response to thrombin stimulation. Pharmacological inhibition of Src with Src-specific inhibitor PP2 abolished S1P-induced translocation of FA proteins, cortical actin ring formation, and FAK [Y576] phosphorylation. However, PP2 failed to alter thrombin-induced morphological changes and exhibited only partial inhibition of FAK site-specific tyrosine phosphorylation. These observations highlight the differential mechanisms of focal adhesion protein complex remodeling and FAK activation by S1P and thrombin and link differential FA remodeling to EC barrier regulation.

Intercellular adhesion molecule-1-deficient mice are resistant against renal injury after induction of diabetes.

Diabetic nephropathy is a leading cause of end-stage renal failure. Several mechanisms, including activation of protein kinase C, advanced glycation end products, and overexpression of transforming growth factor (TGF)-beta, are believed to be involved in the pathogenesis of diabetic nephropathy. However, the significance of inflammatory processes in the pathogenesis of diabetic microvascular complications is poorly understood. Accumulation of macrophages and overexpression of leukocyte adhesion molecules and chemokines are prominent in diabetic human kidney tissues. We previously demonstrated that intercellular adhesion molecule (ICAM)-1 mediates macrophage infiltration into the diabetic kidney. In the present study, to investigate the role of ICAM-1 in diabetic nephropathy, we induced diabetes in ICAM-1-deficient (ICAM-1(-/-)) mice and ICAM-1(+/+) mice with streptozotocin and examined the renal pathology over a period of 6 months. The infiltration of macrophages was markedly suppressed in diabetic ICAM-1(-/-) mice compared with that of ICAM-1(+/+) mice. Urinary albumin excretion, glomerular hypertrophy, and mesangial matrix expansion were significantly lower in diabetic ICAM-1(-/-) mice than in diabetic ICAM-1(+/+) mice. Moreover, expressions of TGF-beta and type IV collagen in glomeruli were also suppressed in diabetic ICAM-1(-/-) mice. These results suggest that ICAM-1 is critically involved in the pathogenesis of diabetic nephropathy.

S1P induces FA remodeling in human pulmonary endothelial cells: role of Rac, GIT1, FAK, and paxillin.

Sphingosine 1-phosphate (S1P) enhances human pulmonary endothelial monolayer integrity via Rac GTPase-dependent formation of a cortical actin ring (Garcia et al. J Clin Invest 108: 689-701, 2001). The mechanisms underlying this response are not well understood but may involve rapid redistribution of focal adhesions (FA) as attachment sites for actin filaments. We evaluate the effects of S1P on the redistribution of paxillin, FA kinase (FAK), and the G protein-coupled receptor kinase-interacting proteins (GITs). S1P induced Rac GTPase activation and cortical actin ring formation at physiological concentrations (0.5 microM), whereas 5 microM S1P caused prominent stress fiber formation and activation of Rho and Rac GTPases. S1P (0.5 microM) stimulated the tyrosine phosphorylation of FAK Y(576), and paxillin was linked to FA disruption and redistribution to the cell periphery. Furthermore, S1P induced a transient association of GIT1 with paxillin and redistribution of the GIT2-paxillin complex to the cell cortical area without affecting GIT2-paxillin association. These results suggest a role of FA rearrangement in S1P-mediated barrier enhancement via Rac- and GIT-mediated processes.

Therapeutic effect of sulphated hyaluronic acid, a potential selectin-blocking agent, on experimental progressive mesangial proliferative glomerulonephritis.

The initial event in the process of leukocyte infiltration is characterized by leukocyte rolling on the surface of the endothelium, which is mediated by selectins. P- and L-selectin bind to the sulphated sugar chains of their natural ligands, including sulphated glycolipids such as sulphatide. Recently, it has been demonstrated that sulphated glycolipids and sulphated oligosaccharides interfere with selectin binding pathways. This study synthesized sulphated hyaluronic acid (SHA), which is a potential selectin-blocking agent, and examined its therapeutic effect on the experimental progressive mesangial proliferative glomerulonephritis induced by anti-Thy-1 monoclonal antibody (1-22-3 MAb) after unilateral nephrectomy. The selectin-inhibitory effect of SHA in vitro was confirmed. SHA inhibited the binding of P- and L-selectin to sulphatide, which is a glycolipid ligand for P- and L-selectin, at a concentration of 1.5 micro g/ml and 100 micro g/ml. Immunohistochemical examination showed that P-selectin was up-regulated in the glomeruli in the 1-22-3 MAb nephritis model, while the ligands for L-selectin were not detected in the glomerular tufts. A single administration of SHA ameliorated proteinuria and glomerular leukocyte infiltration in 24 h after the injection of anti-Thy-1 MAb. Anti-P-selectin MAb, but not anti-L-selectin MAb, inhibited proteinuria and glomerular leukocyte infiltration. To examine further the therapeutic effect of SHA on chronic glomerulonephritis, SHA was administered daily from day 3 to day 14 in this model. Proteinuria and glomerular leukocyte infiltration were significantly diminished in SHA-treated rats on day 14. These results suggest that SHA ameliorated rat progressive mesangial proliferative glomerulonephritis by inhibiting P-selectin-dependent leukocyte infiltration in glomeruli. Sulphated oligosaccharides may be beneficial for the therapy of mesangial proliferative glomerulonephritis.