Altered monocyte expression and expansion of non-classical monocyte subset in IgA nephropathy patients

Abstract

The main defect of immunoglobulin A nephropathy (IgAN) lies within the immune system and in peripheral blood mononuclear cells rather than in the kidney. Previously, we found an altered gene expression in monocytes compared with B and T cells isolated from IgAN patients; thus, our aim here has been to study this subset at a genome-wide and functional level. A total of 39 IgAN patients and 37 healthy blood donors (HBDs) were included in this study, and microarray technology was used to evaluate global gene expression differences in monocytes isolated from IgAN patients and HBDs. Aberrantly expressed genes and pathways were then validated on an independent set of IgAN patients with RT-PCR western blot and flow cytometric analysis. Gene expression differences in monocytes from IgAN patients and HBDs primarily involved apoptosis signalling, mitochondrial dysfunction, tnfr2/1 and death receptor signalling. Both the extrinsic and intrinsic apoptotic pathways seem to be implicated; in particular, the protein levels of NDUFS3 and TNFRSF1A were upregulated thus confirming the altered mitochondrial and death receptor homeostasis. Furthermore, the basal intracellular protein levels of TNF in monocytes were lower in IgAN patients compared with HBDs. We validated at protein level an enhanced apoptotic phenotype and a different subset distribution in monocytes from IgAN patients. We found that the non-classical monocyte subset (CD14(+)CD16(+)) was significantly expanded in all IgAN patients tested even though the total monocyte count remained unchanged. Our findings demonstrate, for the first time, an aberrant modulation of the mitochondrial respiratory system in monocytes isolated from IgAN patients. Furthermore, the aberrant expansion of the (CD14(+)CD16(+)) subset could explain the enhanced apoptotic phenotype seen in these cells thus revealing their potential role in the pathogenesis of IgAN.