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Expression of functional CCR and CXCR chemokine receptors in podocytes
Tobias Bruno Huber1, Hans Christian Reinhardt, Markus Exner
1Department of Medicine, Division of Nephrology, University of Freiburg, Freiburg, Germany.
Abstract:
Chemokines and their receptors play an important role in the pathogenesis of acute and chronic glomerular inflammation. However, their expression pattern and function in glomerular podocytes, the primary target cells in a variety of glomerulopathies, have not been investigated as of yet. Using RT-PCR, we now demonstrate the expression of CCR4, CCR8, CCR9, CCR10, CXCR1, CXCR3, CXCR4, and CXCR5 in cultured human podocytes. Stimulation of these receptors induced a concentration-dependent biphasic increase of the free cytosolic calcium concentration in podocytes in culture. In addition, we demonstrate that podocytes release IL-8 in the presence of FCS and that IL-8 down-regulates cell surface CXCR1. Chemokine stimulation of the detected CCRs and CXCRs increased activity of NADPH-oxidase, the primary source of superoxide anions in podocytes. Immunohistochemistry studies revealed only diffuse and weak CXCR expression in healthy human glomerula. In contrast, in membranous nephropathy, a characteristic podocyte disorder, the expression of CXCR1, CXCR3, and CXCR5 is up-regulated in podocytes. In conclusion, podocytes in culture and podocytes in human kidney sections express a set of chemokine receptors. The release of oxygen radicals that accompanies the activation of CCRs and CXCRs may contribute to podocyte injury and the development of proteinuria during membranous nephropathy.
Insights
Podocytes express chemokine receptors (CCRs and CXCRs) that activate NADPH-oxidase, releasing oxygen radicals. This may contribute to podocyte injury and proteinuria in membranous nephropathy.
Area of Science:
- Nephrology
- Immunology
- Cell Biology
Background:
- Chemokines and receptors are implicated in glomerular inflammation.
- Podocyte expression and function of these molecules remain largely uncharacterized.
Purpose of the Study:
- To investigate the expression and function of chemokine receptors in human podocytes.
- To explore the role of these receptors in podocyte injury and membranous nephropathy.
Main Methods:
- Reverse transcription-polymerase chain reaction (RT-PCR) for gene expression.
- Calcium imaging and NADPH-oxidase activity assays in cultured podocytes.
- Immunohistochemistry on human kidney tissue.
Main Results:
- Cultured human podocytes express CCR4, CCR8, CCR9, CCR10, CXCR1, CXCR3, CXCR4, and CXCR5.
- Chemokine receptor stimulation increased intracellular calcium and NADPH-oxidase activity.
- Increased CXCR1, CXCR3, and CXCR5 expression observed in podocytes in membranous nephropathy.
Conclusions:
- Human podocytes express a range of chemokine receptors.
- Activation of these receptors leads to oxygen radical release, potentially causing podocyte injury.
- Upregulated CXCR expression in membranous nephropathy suggests a role in disease pathogenesis.