CTGF/CCN2 activates canonical Wnt signalling in mesangial cells through LRP6: implications for the pathogenesis of diabetic nephropathy

We describe the activation of Wnt signalling in mesangial cells by CCN2. CCN2 stimulates phosphorylation of LRP6 and GSK-3β resulting in accumulation and nuclear localisation of β-catenin, TCF/LEF activity and expression of Wnt targets. This is coincident with decreased phosphorylation of β-catenin on Ser 33/37 and increased phosphorylation on Tyr142. DKK-1 and LRP6 siRNA reversed CCN2’s effects. Microarray analyses of diabetic patients identified differentially expressed Wnt components. β-Catenin is increased in type 1 diabetic and UUO mice and in in vitro models of hyperglycaemia and hypertension. These findings suggest that Wnt/CCN2 signalling plays a role in the pathogenesis of diabetic nephropathy.     

Megalin is downregulated via LPS-TNF-α-ERK1/2 signaling pathway in proximal tubule cells

Expression and function of megalin, an endocytic receptor in proximal tubule cells (PTCs), are reduced in diabetic nephropathy, involved in the development of proteinuria/albuminuria. Lipopolysaccharide (LPS) is chronically increased in diabetic sera, by the mechanism called metabolic endotoxemia. We investigated low-level LPS-mediated signaling that regulates megalin expression in immortalized rat PTCs (IRPTCs). Incubation of the cells with LPS (10 ng/ml) for 48 h suppressed megalin protein expression and its endocytic function. TNF-α mRNA expression was increased by LPS treatment, and knockdown of the mRNA with siRNA inhibited LPS-mediated downregulation of megalin mRNA expression at the 24-h time point. Incubation of IRPTCs with exogenous TNF-α also suppressed megalin mRNA and protein expression at the 24- and 48-h time points, respectively. MEK1 inhibitor PD98059 competed partially but significantly TNF-α-mediated downregulation of megalin mRNA expression. Collectively, low-level LPS-mediated TNF-α-ERK1/2 signaling pathway is involved in downregulation of megalin expression in IRPTCs.     

Inhibition of renin angiotensin system decreases renal protein oxidative damage in diabetic rats

Renin angiotensin system (RAS) worsens diabetic nephropathy (DN) by increasing oxidative stress. We compared the effect of three different RAS inhibitors: the angiotensin converting enzyme inhibitor Ramipril, the vasopeptidase inhibitor AVE7688 and the angiotensin receptor (AT1) antagonist Losartan on the formation of oxidative and carbonyl stress derived protein modifications in kidney from Zucker obese hyperglycemic rats (ZDFn Gm-fa/fa). Gas chromatography-mass spectrometry was used to measure representative markers of several protein oxidative pathways: direct oxidation [dinitrophenylhydrazine reactive carbonyls (DNP), glutamic (GSA), and aminoadipic (AASA) semialdehydes], mixed glyco- and lipoxidation [N^ε-carboxyethyl-lysine (CEL) and N^ε-(carboxymethyl)-lysine (CML)] and lipoxidation-[N^ε-(malondialdehyde)-lysine-(MDAL)], as well as renal fatty acid composition. Urinary albumin (a marker of DN), DNP, GSA, and MDAL levels, were increased in all obese rats and were dose dependently decreased by AVE7688 whereas Ramipril and Losartan were less efficient. These results show that RAS inhibition improves DN at several levels, independently of its effects on blood pressure and glycemic control, via mechanisms depending of renal oxidative stress.     

Differential ConA-enriched urinary proteome in rat experimental glomerular diseases

Glomerular diseases are leading causes of end-stage renal diseases worldwide. They are considered to be consequences of injury primarily to the three types of glomerular cells. Differential diagnosis typically relies on invasive biopsy findings. We expected that injuries of different glomerular cells would cause different changes in urinary proteome. The goal of this study was to identify differential urinary proteins distinguishing between injuries of different glomerular cells before significant histopathologic changes. Adriamycin nephropathy and Thy1.1 glomerulonephritis were employed as models with different primary impaired cells. ConA-enriched urinary glycoproteome on day3 were profiled by gel-free shotgun tandem mass spectrometry, and compared with self-healthy controls to identify differential urinary proteins for each model. By comparing the changes of the differential proteins between these two models, we identified 39 proteins with different directions of changes, which may potentially be useful in differentiation; and 7 proteins with the same direction of changes, which may be potential indicators of early renal damage. These differential proteins were of several origins: plasma proteins, proteins with urine or kidney specificity, proteins without tissue-specificity (mainly inflammatory mediators) etc. Our results may help better understand the effects of injuries of different glomerular cells at the initial stage, and lead to the discovery of novel early diagnostic markers for human focal segmental glomerulosclerosis (FSGS) and mesangioproliferative glomerulonephritis (MsPGN) which have the same primary impaired cells with adriamycin nephropathy and Thy1.1 glomerulonephritis, respectively.     

Microarray analysis of tonsils in immunoglobulin A nephropathy patients

Background

Recently, combination of tonsillectomy and steroid pulse therapy was reported to be effective as the treatment of the immunoglobulin A nephropathy (IgAN). However, the gene expression difference between the tonsils in patients with IgAN and those in control patients is not established.

Methods

We performed tonsillectomy combined with steroid pulse as a treatment to IgAN, analyzed the gene expression in the tonsils (N = 23) using microarray, compared with those with patients suffering from chronic tonsillitis (N = 22). From some candidate genes related with IgAN, we confirmed the apolipoprotein B messenger RNA-editing enzyme catalytic polypeptides 2 (APOBEC2) gene expression in the tonsil and we also analyzed its expression levels and clinical features.

Results

Up-regulated genes seem to be categorized into two groups. One group belongs to the muscle related genes which might be caused by structural differences. The other group includes the immune system-related genes, such as APOBEC2, CALB2, DUSP27, and CXCL11. APOBEC2 was positively stained in the epithelium and the peripheral region of the germinal center in both tonsils. APOBEC2 expression level was negatively related with serum igg level, but did not correlate with clinical course after tonsillectomy.

Conclusion

We confirmed gene expression differences related with immune system and muscle structure. The APOBEC2 was confirmed to be elevated in the tonsils with IgAN patients, and the gene expression level was negatively related with serum igg level in overall patients. These results might be helpful to reveal the mechanism of IgAN.     

CCN-2 is up-regulated by and mediates effects of matrix bound advanced glycated end-products in human renal mesangial cells

CCN-2, also known as connective tissue growth factor (CCN-2/CTGF) is a cysteine rich, extracellular matrix protein that acts as a pro-fibrotic cytokine in tissues in many diseases, including in diabetic nephropathy. We have published that soluble advanced glycation end products (AGEs), that are present in increased amounts in diabetes, induce CCN-2. However in vivo AGEs are known to be heavily tissue bound and whether matrix bound AGEs regulate CCN-2 has not been investigated. In this study we determined in human renal mesangial cells if CCN-2 is induced by matrix associated AGEs and if CCN-2 may then secondarily mediate effects of matrix AGEs on extracellular matrix expansion. Data generated show that CCN-2 mRNA and protein expression are induced by matrix bound AGEs, and in contrast, this was not the case for TGF-β1 mRNA regulation. Using CCN-2 adenoviral anti-sense it was found that CCN-2 mediated the up-regulation of fibronectin and the tissue inhibitor of matrix metalloproteinase, TIMP-1, that was caused by matrix bound AGEs. In conclusion, CCN-2 is induced by non-enzymatically glycated matrix and it mediates downstream fibronectin and TIMP-1 increases, thus through this mechanism potentially contributing to ECM accumulation in the renal glomerulus in diabetes.