Glucocorticoid-induced leucine zipper: A key protein in the sensitization of monocytes to lipopolysaccharide in alcoholic hepatitis

Abstract

Glucocorticoid-induced leucine zipper (GILZ), a recently identified protein induced by glucocorticoids (GCs), inhibits the nuclear factor kappaB pathway and the activation of monocytes/macrophages by lipopolysaccharides (LPS). This study aimed to elucidate the contribution of GILZ to the pathogenesis of alcoholic hepatitis (AH): we (1) assessed GILZ expression in the livers of patients with AH and (2) treated patients with severe AH with GCs (prednisolone 40 mg/day) and studied the effect of GILZ modulation on circulating monocyte function. We quantified GILZ expression in the livers of 42 consecutive alcoholic patients (21 with and 21 without AH). GILZ messenger RNA (mRNA) levels were lower in the livers of patients with AH versus those without AH (P < 0.05). We collected circulating monocytes from patients with severe AH before and 48 hours after GC treatment to quantify GILZ expression and cytokine secretion. GC treatment induced significantly higher levels of GILZ mRNA than that observed before treatment and impaired LPS-induced tumor necrosis factor-alpha (TNF-alpha) and regulated upon activation, normal T cell-expressed secretion (RANTES) by these monocytes. We transfected circulating monocytes with GILZ small interfering RNA (siRNA), specifically blocking GILZ expression, to demonstrate the role of GILZ in mediating GC effect. GILZ siRNA abrogated the effect of GC treatment on LPS-induced TNF-alpha and RANTES secretion. Low expression of GILZ may contribute to liver inflammation in AH. GCs enhance GILZ expression, abrogating macrophage sensitivity to LPS and proinflammatory cytokine secretion. These findings may explain the beneficial effect of GC treatment in patients with severe AH.