Mesangial autoantigens in IgA nephropathy: matrix synthesis and localization

Why, when and how should immunosuppressive therapy considered in patients with immunoglobulin A nephropathy?

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Lifelong mesangial deposition of IgA1 complexes subsist inflammation and nephron loss, but the complex pathogenesis in detail remains unclear. In regard to the heterogeneous course, classical immunosuppressive and specific therapeutic regimens adapted to the loss of renal function will here be discussed in addition to the essential common renal supportive therapy. Renal supportive therapy alleviates secondary, surrogate effects or sequelae on renal function and proteinuria of high intraglomerular pressure and subsequent nephrosclerosis by inhibition of the renin angiotensin system (RAASB). In patients with physiological (ΔGFR < 1·5 ml/min/year) or mild (ΔGFR 1·5-5 ml/min/year) decrease of renal function and proteinuric forms (> 1 g/day after RAASB), corticosteroids have shown a reduction of proteinuria and might protect further loss of renal function. In patients with progressive loss of renal function (ΔGFR > 3 ml/min within 3 months) or a rapidly progressive course with or without crescents in renal biopsy, cyclophosphamide with high-dose corticosteroids as induction therapy and azathioprine maintenance has proved effective in one randomized controlled study of a homogeneous cohort in loss of renal function (ΔGFR). Mycophenolic acid provided further maintenance in non-randomized trials. Differentiated, precise, larger, randomized, placebo-controlled studies focused on the loss of renal function in the heterogeneous forms of IgAN are still lacking. Prospectively, fewer toxic agents will be necessary in the treatment of IgAN.

Sublytic C5b-9 induces IL-6 and TGF-β1 production by glomerular mesangial cells in rat Thy-1 nephritis through p300-mediated C/EBPβ acetylation

CCAAT/enhancer-binding protein (C/EBPβ)-enhanced IL-6 and TGF-β1 promoter activity and p300-mediated C/EBPβ acetylation were involved in up-regulation of IL-6 and TGF-β1 expression in GMCs attacked by sublytic C5b-9. In detail, the elements of C/EBPβ binding to rat IL-6 and TGF-β1 promoter and 3 acetylated sites of rat C/EBPβ protein were first revealed. Furthermore, silencing the p300 or C/EBPβ gene in rat kidney significantly reduced the production of IL-6 and TGF-β1 and renal lesions in Thy-1N rats. Together, these data indicate that the mechanism of IL-6 and TGF-β1 production in renal tissue of Thy-1N rats is associated with sublytic C5b-9 up-regulated p300 and p300-mediated C/EBPβ acetylation as well as C/EBPβ-activated IL-6 and TGF-β1 genes.

TSP-1 promotes glomerular mesangial cell proliferation and extracellular matrix secretion in Thy-1 nephritis rats

The proliferation of glomerular mesangial cells (GMC) and secretion of the extracellular matrix (ECM) in rat with Thy-1 nephritis (Thy-1N) resembling human mesangioproliferative glomerulonephritis have been explored for many years; however, the molecular mechanisms of GMC proliferation and ECM production remain unclear. Our previous studies have demonstrated that the thrombospondin-1 (TSP-1) gene was involved in mediating rat GMC proliferation and ECM synthesis induced by sublytic C5b-9 in vitro. In the present study, the roles of the TSP-1 gene in GMC proliferation, ECM production, and urinary protein secretion in Thy-1N rats were determined by using TSP-1 small hairpin RNA, and the results revealed that silencing of the TSP-1 gene in rat renal tissues could diminish GMC proliferation (P < 0.01) and ECM secretion (P < 0.01) as well as urinary protein secretion (P < 0.05) in Thy-1N rats. Together, the current findings suggested that TSP-1 gene expression was required for GMC proliferation and ECM production in Thy-1N rats.

Clinicopathological and immunohistological features in childhood IgA nephropathy: a single-centre experience

Background

IgA nephropathy is a glomerular disease diagnosed by renal biopsy and is characterized by a highly variable course ranging from a completely benign condition to rapidly progressive renal failure. We aimed to evaluate the clinical, histopathological and inflammatory characteristics of children with IgA nephropathy.

Methods

Data of 37 patients with IgA nephropathy diagnosed between the years 1980 and 2008 were retrospectively reviewed. Immunohistochemistry was performed in 24 patients. Expression of CD3, CD4, CD8, CD20, CD68, IL-1β, IL-10, IL-17, TGF-β, TNF-α and the newly proposed tubulointerstitial fibrosis marker nestin were evaluated.

Results

The median age at diagnosis was 10 years. Recurrent macroscopic haematuria (66%) was the most common clinical manifestation, and 35% of the patients had synpharyngitic presentation. A significant correlation was found between proteinuria and increase in mesangial matrix (r = 0.406, P = 0.013). The presence of CD4+ T lymphocytes and CD68+ macrophages were also significantly associated with proteinuria >1 g/day. While cytokines IL-1β, IL-10 and TNF-α were mainly expressed in tubular epithelial cells, TGF-β was evident in glomeruli but they had no correlation to clinical features and severity of the disease. Nestin was detected at the tubules in almost half of the patients with no correlation to proteinuria and tubulointersititial fibrosis.

Conclusions

We found a correlation between proteinuria and mesangial matrix expansion. The presence of CD4+ T-lymphocytes and CD68+ macrophages were also significantly associated with proteinuria >1 g/day. Although there are many evidences, for immunological basis of IgA nephropathy, the immunological markers were not fully expressed in children to evaluate glomerular and tubulointerstitial inflammation, and progression of the disease. Further studies with the extended number of children are needed to shed light on the immunological basis of the disease.

Sublytic C5b-9 complexes induce apoptosis of glomerular mesangial cells in rats with Thy-1 nephritis through role of interferon regulatory factor-1-dependent caspase 8 activation

The apoptosis of glomerular mesangial cells (GMC) in rat Thy-1 nephritis (Thy-1N), a model of human mesangioproliferative glomerulonephritis, is accompanied by sublytic C5b-9 deposition, but the mechanism of sublytic C5b-9-mediated GMC apoptosis has not been elucidated. In the present study, the gene expression profiles both in the GMC stimulated by sublytic C5b-9 and the rat renal tissue of Thy-1N were detected using microarrays. Among the co-up-regulated genes, the up-regulation of interferon regulatory factor-1 (IRF-1) was further confirmed. Increased caspase 8 and caspase 3 expression and caspase 8 promoter activity in the GMC were also identified. Meanwhile, overexpression or knockdown of IRF-1 not only enhanced or inhibited GMC apoptosis and caspase 8 and 3 induction but also increased or decreased caspase 8 promoter activity, respectively. The element of IRF-1 binding to the caspase 8 promoter was first revealed. Furthermore, silencing IRF-1 or repressing the activation of caspases 8 and 3 significantly reduced GMC apoptosis, including other pathologic changes of Thy-1N. These novel findings indicate that GMC apoptosis of Thy-1N is associated with the IRF-1-activated caspase 8 pathway.

Sublytic C5b-9 complexes induce proliferative changes of glomerular mesangial cells in rat Thy-1 nephritis through TRAF6-mediated PI3K-dependent Akt1 activation

The proliferation of glomerular mesangial cells (GMCs) and secretion of extracellular matrix (ECM) in rat Thy-1 nephritis (Thy-1N), resembling human mesangioproliferative glomerulonephritis (MsPGN), have been studied for many years, but the mechanisms, especially the role of signalling pathway activation and its regulation in GMCs triggered by sublytic C5b-9 complexes in Thy-1N rats remain largely unclear. In the study, the proliferation of GMCs and production of ECM as well as the role of PI3K/Akt and its regulation, both in GMCs induced by sublytic C5b-9 (in vitro) and in the renal tissues of rats with Thy-1N (in vivo), were determined and the results revealed that GMCs proliferation and ECM secretion, both in vitro and in vivo, were notably increased, and that PI3K/Akt1 activation and its regulation, such as TNF receptor-associated factor 6 (TRAF6)-mediated Akt1 ubiquitination and PI3K-dependent Akt1 phosphorylation, were involved in the process of Thy-1N induction. On the other hand, silence of the TRAF6, PI3K or Akt1 genes could obviously diminish the proliferative damages and urinary protein secretion of Thy-1N rats. Together, these data implicated that sublytic C5b-9 complexes in Thy-1N rats could promote GMCs proliferation and ECM production through TRAF6-mediated PI3K-dependent Akt1 activation, in which the ubiquitination and phosphorylation of the Akt1 signal molecule played an important role in the initiation and development of the proliferative changes in the rats with Thy-1N.

Role of activating transcription factor 3 (ATF3) in sublytic C5b-9-induced glomerular mesangial cell apoptosis

Sublytic complement C5b-9 complexes can cause cell apoptosis, but the mechanism of glomerular mesangial cell (GMC) apoptosis mediated by these complexes has not been well defined. The activating transcription factor 3 (ATF3) gene is an immediate early gene for the cell to cope with a variety of stress signals and can promote apoptosis of some cells. In this study, ATF3 expression and cell apoptosis in GMCs induced by sublytic C5b-9 were measured, and then the effects of ATF3 gene over-expression or knockdown on GMC apoptosis induced by sublytic C5b-9 were examined at a fixed time. The results showed that both ATF3 expression and GMC apoptosis were markedly increased and ATF3 over-expression obviously increased sublytic C5b-9-induced GMC apoptosis, whereas ATF3 gene silencing had a significant opposite effect. Collectively, these findings indicate that upregulation of ATF3 gene expression is involved in regulating GMC apoptosis induced by sublytic C5b-9 complexes.

Expression of P311, a transforming growth factor beta latency-associated protein-binding protein, in human kidneys with IgA nephropathy

Background

In cultured NIH3T3 cells, P311 binds to the transforming growth factor-beta (TGF-β)-1 latency-associated protein (LAP) and induces the myofibroblast phenotype. In this study, we determined the levels of P311 and TGF-β1 proteins in tubulointerstitial tissue of patients with different severities of immunoglobulin-A nephropathy (IgAN), and analyzed the relationships between P311 protein expression and clinical data.

Methods

A total of 57 patients with IgAN and 5 controls (from partial nephrectomy) were included. P311 and TGF-β1 protein expression were measured by immunohistochemistry and clinical data (proteinuria, serum creatinine (Scr), eGFR and biopsy index) were recorded. The relationship between P311, TGF-β1, and clinical data was analyzed.

Results

P311 expression was significantly higher in the kidneys of IgAN patients than in controls and was higher in patients with advanced pathological grades of IgAN. P311 protein expression in tubulointerstitial tissue correlated with TGF-β1 and proteinuria. P311 expression was higher in patients with Scr > 133 μmol/L than in patients with Scr < 133 μmol/L.

Conclusion

P311 protein expression in the kidneys of IgAN patients correlates with TGF-β1 expression and with proteinuria. P311 might be a key cytokine in renal fibrosis and be involved in the progression of IgAN.

Apoptosis of glomerular mesangial cells induced by sublytic C5b-9 complexes in rats with Thy-1 nephritis is dependent on Gadd45 gamma upregulation

The complement C5b-9 complexes can result in cell apoptosis, but the mechanism of sublytic C5b-9-mediated glomerular mesangial cell (GMC) apoptosis in Thy-1 nephritis (Thy-1N) remains largely unclear. The Gadd45 gene is involved in the cellular response to DNA damage and can promote cell apoptosis. In this study, both Gadd45 gamma expression patterns and pathologic changes of renal tissue were examined in rat Thy-1N. Both Gadd45 gamma expression and GMC apoptosis were significantly decreased in Thy-1N rats upon the depletion of complement with cobra venom factor. Our in vitro studies showed that Gadd45 gamma over-expression increased sublytic C5b-9-induced GMC apoptosis, while Gadd45 gamma gene knockdown by siRNA greatly reduced GMC apoptosis. Moreover, Gadd45 gamma gene silencing in vivo markedly inhibited the pathologic changes in the renal tissue of Thy-1N rats. These data suggest that Gadd45 gamma gene expression is involved in regulating GMC apoptosis mediated by sublytic C5b-9 in Thy-1N.