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The activation of the receptor for advanced glycation end products (RAGE) is involved in the development of diabetic nephropathy. Analysis of protein phosphatase-1 indicated that advanced glycation end products did not affect its expression, but increased its phosphatase activity. Using differential display analysis we previously demonstrated that stimulation of RAGE in podocytes modulates the expression of numerous genes, among others nuclear inhibitor of protein phosphatase-1 (NIPP1). Here we found that silencing of NIPP1 induced podocyte hypertrophy, cell cycle arrest, and significantly increased protein phosphatase-1 activity. NIPP1 downregulation was associated with increased p27Kip1 protein expression. Reporter assays revealed a transcriptional activation of nuclear factor-κB in podocytes after suppression of NIPP1. The protein level of NIPP1 was also significantly reduced in podocytes of diabetic mice. Blocking the RAGE in vivo by a soluble analog elevated the NIPP1 protein in podocytes of diabetic mice. Thus, activation of the RAGE by advanced glycation end products or other ligands suppresses NIPP1 expression in diabetic nephropathy, contributes to podocyte hypertrophy, and glomerular inflammation.

Background: Advanced glycation end products (AGEs) play an important role in diabetic nephropathy. The receptor for AGEs, called RAGE, is present on podocytes. We investigated whether angiotensin II (ANG II) modulates RAGE expression on cultured differentiated podocytes. Results: Cultured podocytes expressed AT1 and AT2 receptors. Surprisingly, ANG II induced RAGE mRNA and protein expression through AT2 receptors. ANG II had no influence on proliferation or protein content of podocytes. The increase in RAGE expression depended on stimulated transcriptional activity. Using various mutant reporter constructs of the RAGE promoter region, it was shown that a NF-κB binding site at –1519 was essential for ANG II-induced transcriptional activity. Preincubation with ANG II increased the expression of tumor necrosis factor-α mRNA and protein expression induced by AGE, indicating that the ANG II-mediated upregulation of RAGE has functional consequences. AGE-BSA was incorporated into cells as measured by Western blots for Nε-carboxymethyllysine, but ANG II did not influence this process. ANG II in the absence or presence of AGE-BSA did not induce apoptosis of podocytes. Conclusion: Our study revealed aninteraction between the renin-angiotensin system and the AGE/RAGE axis in podocytes. Since intraglomerular ANG II levels are increased in diabetic nephropathy, this interaction may have pathophysiological consequences for podocyte injury and inflammation associated with the development of diabetic nephropathy.

Oxidative stress and inflammatory processes accelerate the formation of advanced glycation end products (AGE), e.g. of pentosidine. The aim of this study was to investigate the relationships between levels of pentosidine in serum and synovial fluid, proinflammatory cytokines, other markers of inflammatory activity, and the state of radiologically visible bone destruction in patients with rheumatoid arthritis (RA). One hundred thirty-three nondiabetic RA patients and 56 age-matched, healthy subjects were included. Serum and synovial fluid pentosidine, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and rheumatoid factor levels were determined. In 30 patients, the proinflammatory cytokines interleukin (IL)-1beta, IL-6, and TNF-alpha and the soluble receptors sIL-2R, sIL-6R, sTNF-alpha, and RI/RII were also measured. Serum levels of pentosidine were on average significantly higher in RA patients than in healthy subjects and correlated significantly to ESR, CRP, and serum levels of IL-6. Serum and synovial fluid pentosidine did not show any differences. Rheumatoid factor-positive RA patients had higher pentosidine levels in the synovial fluid than rheumatoid factor-negative patients. Correlations could not be found between pentosidine and the other cytokines or cytokine receptors measured. The binding of AGE on cell receptors induces activation of nuclear factor kappa B, resulting in enhanced synthesis of proinflammatory cytokines. Moreover, AGE generation may also lead to the formation of new, immunologically relevant epitopes at synovial proteins. Both mechanisms could contribute to initiation and perpetuation of the inflammatory and destructive processes in RA.

Advanced glycation end products (AGEs) have been linked to the pathogenesis of diabetic nephropathy. Here we tested the effect of AGE-modified bovine serum albumin (AGE-BSA) on differentiated mouse podocytes in culture. Differential display and real-time PCR analyses showed that in addition to neuropilin-1, the entire signaling receptor complex of neuropilin-2, semaphorin-3A, and plexin-A1, was significantly reduced by AGE-BSA as was neuropilin-1 protein. The effect was specific for podocytes compared to isolated mesangial and tubular epithelial cells. Further, AGE-BSA was not toxic to podocytes. Neutopilin-1 expression was decreased in glomeruli of diabetic db/db mice compared to their non-diabetic littermates. Transcripts of both neuropilins were found to be decreased in renal biopsies from patients with diabetic nephropathy compared to transplant donors. Podocyte migration was inhibited by AGE-BSA with similar results found in the absence of AGE-BSA when neuropilin-1 expression was down-regulated by siRNA. In contrast, podocyte migration was stimulated by overexpression of neuropilin-1 even in the presence of AGE-BSA. Our study shows that AGE-BSA inhibited podocyte migration by down-regulating neuropilin-1. The decreased migration could lead to adherence of uncovered areas of the glomerular basement membrane to Bowman's capsule contributing to focal glomerulosclerosis.

Potential cardiovascular risk factors in chronic kidney disease: AGEs, total homocysteine and metabolites, and the C-reactive protein. Total homocysteine (tHcy) and advanced glycation end-products (AGEs) are implicated in the pathogenesis of vascular damage. This study aimed to investigate whether elevated serum levels of the AGEs pentosidine, Nε-carboxymethyllysine (CML) and imidazolone; tHcy, cystathionine, methylmalonic acid (MMA), and 2-methylcitric acid (2-MCA), as well as C-reactive protein (CRP), are related to a higher risk for cardiovascular events. A total of 232 patients with chronic kidney diseases (mean age 57.6 ± 13.1 years, 82 female and 150 male); 99 with chronic renal failure (CRF), 84 maintenance hemodialysis patients and 49 renal transplant recipients were followed for 2 years. The relationship between the parameters of interest, conventional risk factors and elevated levels of CRP with cardiovascular events was tested in all subjects by the Cox proportional hazards model. Mean serum levels of AGEs, tHcy, and of the metabolites were found to be significantly increased in all three groups compared to the healthy subjects (P < 0.01, respectively). Fifty-three cardiovascular events occurred during follow-up; a total of 40 patients died. Final multivariate analysis showed diabetes (RR 2.06, 95% CI 1.17–3.60, P = 0.013), end-stage renal disease (ESRD) (RR 4.88, 95% CI 2.40–9.89, P < 0.001) and elevated CRP levels (RR 2.00, 95% CI 1.11–3.60, P = 0.021) as independent risk factors for cardiovascular events. Data from a group consisting of patients with CRF, patients undergoing maintenance hemodialysis treatment, and renal transplant recipients provide evidence that conventional risk factors such as the presence of diabetes, ESRD, as well as elevated levels of the considered risk factor CRP, seem to play a more important role for cardiovascular outcome in patients with chronic kidney disease than elevated levels of AGEs, tHcy, and related metabolites. The evidence suggests that routine CRP measurement can be recommended in cases of chronic renal insufficiency.

Immune system and bone are interacting in a complex way. Rheumatoid arthritis is characterized not only by joint destruction, but also by development of systemic osteopenia and osteoporosis. The CD20-depleting antibody Rituximab (Rtx) is a novel therapeutic option able significantly to slow the destructive joint process of rheumatoid arthritis. However, there are little data whether Rtx influences systemic bone remodeling. In the present prospective study, we evaluated the influence of Rtx on markers of bone metabolism with a follow-up of 3–15 months after Rtx therapy (2 dose of each 1,000 mg) in 13 patients with rheumatoid arthritis. There was no significant change of the bone formation markers bone alkaline phosphatase and c-terminal propeptide of collagen I. However, a non-significant tendency of decrease of RANKL (with no chance of osteoprotegerin) and a significant decrease of the bone degradation marker desoxypyridinolin crosslinked collagen I was observed 15 months after Rtx application. These initial results provide no evidence of a negative systemic influence of Rtx on bone remodeling. In contrast, it appears that Rtx lowered osteoclast activity often found increased in active rheumatoid arthritis contributing to osteoporosis in this disease.

Background: The mitogen-activated protein kinase organizer 1 (Morg1) belongs to the WD-40 repeat protein family and is a scaffold molecule for the extracellular regulated kinase signaling pathway. Morg1 also binds to prolyl-hydroxylase 3 (PHD3) and regulates the hypoxia-inducible factor-1α (HIF-1α) expression via PHD3 stabilization. Morg1 has been detected in the kidney as well as in other cell tissues but its expression in renal cells has not been well investigated. It has been widely shown that angiotensin II (ANG II) mediates renal damage. We have previously shown that ANG II downregulates the expression of PHD3 in PC12 cells. The aim of this study was to analyze whether ANG II regulates Morg1 expression in mouse mesangial cells (MMC), mouse proximal tubular cells (MTC) and in differentiated podocytes. The correlation between the expression of Morg1 and PHD3 activity was also addressed. Methods: Effect of ANG II on the Morg1 mRNA expression level was assessed by real-time PCR. Morg1 and HIF-1α cellular localization was analyzed by immunohistochemistry. HIF-1α promoter activity was investigated using a reporter gene system. PHD3 hydroxylase activity test was measured with a hydroxylation-coupled decarboxylation assay. Results: ANG II differentially regulates Morg1 expression in MMC, MTC and differentiated podocytes. We detected a biphasic effect of ANG II on Morg1 mRNA expression which was time dependent. While 9-hour ANG II treatment downregulated Morg1 expression in MMC, it induced Morg1 expression in MTC. Conversely, 24-hour ANG II stimulation upregulated the expression of Morg1 mRNA in MMC, but showed an opposite effect in MTC and differentiated podocytes. In addition, we found that ANG II signals mostly through the AT 1 receptor subtype in MMC and via the AT 2 subtype in MTC. PHD3 activity correlated to Morg1 expression patterns. Our data also demonstrate that HIF-1α transcriptional activity in MTC contrasted to PHD3 activity at 9 and 24 h, whereas in the MMC and in podocytes we did not find any correlation between PHD3 HIF-1α hydroxylation ability and HIF-1α transcriptional activation, suggesting a different mechanism of regulation in these cell types. Interestingly, the reduced expression of Morg1 in mesangial cells isolated from Morg1 (+/–) heterozygous mice correlated with a reduced PHD3 enzymatic activity and an increased HIF-1α transcriptional activity compared with mesangial cells originated from wild-type (Morg1 +/+) mice. Conclusions: We show for the first time in various renal cells that ANG II modulates Morg1 expression and HIF-1α transcriptional activity via cell type-specific mechanisms, demonstrating a novel mechanism by which ANG II may contribute to renal disease.

The aim of our study was to compare the significance of risk factors for osteoporosis according to gender and menopausal state in patients with rheumatoid arthritis (RA). Bone mineral density (dual X-ray absorptiometry), cumulative glucocorticoid dose, age, disease duration, body mass index (BMI) and parameters of disease activity and bone turnover were registered in 343 postmenopausal women, 100 premenopausal women and 108 men with RA. Osteoporosis was found in a significantly higher percentage in postmenopausal women (55.7%) and in men (50.5%) in comparison with premenopausal women (18%; P  < 0.001). The following risk factors for osteoporosis were found: older age, low BMI and high cumulative glucocorticoid dose in postmenopausal women, low BMI and high cumulative glucocorticoid dose in men and low BMI in premenopausal women. There is a very high prevalence of osteoporosis not only in postmenopausal women but also in men with RA. Osteoporosis risk factors are strongly dependent from gender and menopausal state.

Background: Podocyte damage and accumulation of advanced glycation end-products (AGEs) are implicated in the development and progression of diabetic nephropathy. We have previously shown that changes in podocyte pathophysiology, such as hypertrophy and reduced migration, are closely linked with the induction of the cell cycle inhibitor p27Kip1 and a decrease in neuropilin-1 (NRP1) expression. We investigated whether the erythropoietin receptor activators CERA and epoetin-β may prevent AGE-mediated changes in podocytes. Methods: Differentiated mouse podocytes in culture were challenged by AGE-modified bovine serum albumin (BSA) or control BSA in the presence or absence of CERA as well as epoetin-β. Cell cycle analysis and determination of apoptosis markers were performed. p27Kip1 and NRP1 expression was measured by RT-PCR and Western blots. Results: Differentiated mouse podocytes in culture expressed erythropoietin receptors which were phosphorylated after incubation with CERA or epoetin-β. CERA or epoetin-β prevented the p27Kip1-dependent cell cycle arrest and cellular hypertrophy induced by AGE-BSA incubation. Furthermore, the p27Kip1-dependent AGE-BSA-induced decrease in cell viability and decrease in cell proliferation was ameliorated in the presence of CERA or epoetin-β. Following erythropoietin treatment, AGE-BSA failed to further reduce NRP1 expression, resulting in improved podocyte migration. Conclusion: Treatment with the erythropoietin receptor activators epoetin-β or CERA protected podocytes from AGE-BSA-mediated damage via an effect on p27Kip1 and NRP1 expression. Consequently, early treatment with erythropoietin may help to prevent diabetic nephropathy. Copyright © 2010 S. Karger AG, Basel [PUBLICATION ABSTRACT]

The objective of this study is to investigate the relationship between soluble components of the interleukin 6 (IL-6) system mediating and modifying IL-6 trans-signaling and the RANKL–RANK–osteoprotegerin system in postmenopausal women with rheumatoid arthritis (RA). The following parameters were investigated in 126 postmenopausal women with RA: IL-6, soluble IL-6-receptor (sIL-6R), soluble glycoprotein 130 (sgp130), sRANKL, osteoprotegerin (OPG), osteocalcin, erythrocyte sedimentation rate and C-reactive protein in sera, pyridinolin and desoxypyridinolin crosslinks in the morning urine. Bone mineral density (BMD) was measured by dual X-ray absorptiometry at the lumbar spine (BMD-LS) and at the femoral neck (BMD-FN). Predictors of RANKL/OPG ratio and BMD were evaluated by multiple linear regression analysis. The following determinants of the RANKL/OPG ratio were identified: sIL-6R/sgp130 ratio and daily glucocorticoid (GC) dose as positive determinants in the whole group ( R 2  = 0.56; P  = 0.001), sIL-6R/sgp130 ratio as the exclusive positive determinant in patients with GC therapy ( R 2  = 0.48; P  = 0.001) and sgp130 as negative determinant in patients without GC ( R 2  = 0.42; P  = 0.031). Sgp130 was highly significantly positively correlated with OPG in the whole group ( P  < 0.001) as well as in patients with ( n  = 70; P  < 0.05) and without GC therapy ( n  = 56; P  < 0.01). sIL-6R was the main negative predictor of BMD-LS ( R 2  = 0.41; P  = 0.019). High sIL-6R/sgp130 ratio and/or low sgp130 are associated with a high sRANKL/OPG ratio in sera of postmenopausal women with RA indicating the critical significance of IL-6 trans-signaling for an increase in the RANKL/OPG ratio and of bone resorption. Inhibition of IL-6 trans-signaling may be an effective bone-protecting principle in postmenopausal women with RA.