Chemokine receptor CCR5 and CXCR4 expression in HIV-associated kidney disease

Expression of functional CCR and CXCR chemokine receptors in podocytes

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.

Replication and compartmentalization of HIV-1 in kidney epithelium of patients with HIV-associated nephropathy

HIV-associated nephropathy is a clinicopathologic entity that includes proteinuria, focal segmental glomerulosclerosis often of the collapsing variant, and microcystic tubulointerstitial disease. Increasing evidence supports a role for HIV-1 infection of renal epithelium in the pathogenesis of HIV-associated nephropathy. Using in situ hybridization, we previously demonstrated HIV-1 gag and nef mRNA in renal epithelial cells of patients with HIV-associated nephropathy. Here, to investigate whether renal epithelial cells were productively infected by HIV-1, we examined renal tissue for the presence of HIV-1 DNA and mRNA by in situ hybridization and PCR, and we molecularly characterized the HIV-1 quasispecies in the renal compartment. Infected renal epithelial cells were removed by laser-capture microdissection from biopsies of two patients, DNA was extracted, and HIV-1 V3-loop or gp120-envelope sequences were amplified from individually dissected cells by nested PCR. Phylogenetic analysis of kidney-derived sequences as well as corresponding sequences from peripheral blood mononuclear cells of the same patients revealed evidence of tissue-specific viral evolution. In phylogenetic trees constructed from V3 and gp120 sequences, kidney-derived sequences formed tissue-specific subclusters within the radiation of blood mononuclear cell-derived viral sequences from both patients. These data, along with the detection of HIV-1-specific proviral DNA and mRNA in tubular epithelium cells, argue strongly for localized replication of HIV-1 in the kidney and the existence of a renal viral reservoir.