Overexpression of acetyl-coenzyme A carboxylase beta increases proinflammatory cytokines in cultured human renal proximal tubular epithelial cells

Abstract

We have identified the acetyl-coenzyme A carboxylase beta gene (ACACB) as a strong susceptibility gene to diabetic nephropathy in individuals with type 2 diabetes. To elucidate the mechanism by which ACACB contributes to conferring susceptibility to diabetic nephropathy, we examined the role of ACACB in human renal proximal tubular epithelial cells (RPTECs). RPTECs were infected with adenovirus vectors encoding ACACB or LacZ (control), and messenger RNA (mRNA) expression profiles were evaluated with a microarray analysis. We determined the mRNA expressions of proinflammatory cytokines by real-time quantitative reverse transcription (RT) polymerase chain reaction (PCR) and secretion of these cytokines from cells by enzyme-linked immunosorbent assay (ELISA). Among 54,613 transcripts analyzed in the microarray analysis, genes encoding proinflammatory cytokines, including interleukin (IL)-6, chemokine (C-X-C motif) ligands (CXCL) 1, 2, 5, and 6, were remarkably up-regulated (>20-fold) in the ACACB-overexpressing cells. The increased expression of these inflammatory cytokines was reversed by the addition of a synthetic inhibitor of acetyl-coenzyme A carboxylase beta. Overexpression of ACACB could increase IL-6 mRNA expression and IL-6 protein secretion in a time-dependent manner. We further found that IL-6 mRNA stability and expression had significantly increased in ACACB-overexpressing RPTECs, and a treatment of the cells with p38 mitogen-activated protein kinase (MAPK) inhibitor partially but significantly reversed these effects. An excess of ACACB results in increased proinflammatory cytokine expression, such as IL-6, at least partly by increasing mRNA stability through a p38 MAPK-dependent pathway.