Administration of dexamethasone protects mice against ischemia/reperfusion induced renal injury by suppressing PI3K/AKT signaling

Abstract

Dexamethasone (DEX), a ligand for glucocorticoid receptor (GR), has long been used in the clinical practice due to its anti-inflammatory and immunosuppressive properties. Given that ischemia/reperfusion (IR)-induced renal injury is featured by the excessive immune response; the current study is therefore designed to address the impact of dexamethasone on IR-induced renal injury, a common disorder in the clinical settings. Precondition of mice with 4 mg/kg of dexamethasone significantly attenuated IR-induced injury as manifested by the improved renal function along with ameliorated pathological changes and suppressed inflammatory infiltration. Mechanistic studies revealed that dexamethasone promotes GR activation, and by which it attenuates the signals for PI3K/AKT activation. Attenuated PI3K/AKT signaling thus suppresses inflammatory response which then protects kidneys from IR-induced injury. All together, our data support that dexamethasone could be a good alternative therapy for prevention and treatment of IR-induced renal injury in the clinical practice.

Keywords: Inflammatory response; PI3K/AKT signaling; dexamethasone; glucocorticoid receptor; ischemia/reperfusion injury.

Figure 1

Dexamethasone precondition ameliorates IR-induced renal injury. A. Serum levels for creatinine. B. Levels for blood urea nitrogen (BUN). C. Real-time PCR results for KIM-1 expression in renal tissues. Mice preconditioned with dexamethasone displayed significantly lower levels for BUN and Cr as well as KIM-1 expression. ***, P < 0.001 (IRI vs. Sham); ##, P < 0.01 (IRI vs. DEX).

Figure 2

Histological analysis of renal sections. Representative PAS staining results for renal sections originated from: A. Sham mice; B. IRI mice; and C. DEX mice. Representative MPO staining results of renal sections originated from: D. Sham mice; E. IRI mice; and F. DEX mice. G. Semi-quantitative analysis of PAS staining for all mice included. H. Semi-quantitative assessment of MPO staining of all mice studied. Three mice were analyzed in each group, and the images are presented at × 200/× 400 magnifications. **, P < 0.01 (IRI vs. Sham); ##, P < 0.05 (IRI vs. DEX).

Figure 3

Precondition of dexamethasone promotes GR activation. Western blot analysis was employed to assess GR expression and activation by evaluating the levels for total GR and activated GR (p-GR). A. A representative result for Western blot analysis. B. Semi-quantitative analysis of 6 animals studied in each group. The relative amount of GR and p-GR in each group of mice was normalized by β-actin and presented as a ratio between p-GR and GR. *, P < 0.05 (IRI vs. Sham); #, P < 0.01 (DEX vs. IRI).

Figure 4

Administration of dexamethasone attenuates PI3K/AKT signaling. The p85 regulatory subunit was used for assessing the activity of PI3K, while the phosphorylated AKT (p-AKT) was employed for evaluating AKT activation. A. A representative Western blot result for p85 and p-p85. B. Results for quantitative analysis of p-p85 in all animals. C. Representative results for AKT Western blot analysis. D. Quantitative analysis of AKT activity in all mice studied. Similar as above, the relative activity for PI3K and AKT was assessed by a ratio between the phosphorylated form and total form. Six mice were included in each study group. **, P < 0.001 (IRI vs. Sham); #, P < 0.01 (IRI vs. DEX).

Figure 5

Dexamethasone treatment suppresses IR-induced cytokine expressions in the kidney. Real-time PCR was employed to assess the expression of inflammatory cytokines in the kidney. We selectively analyzed the expression levels for TNF-α (A), IL-6 (B) and IFN-γ (C) after 24 h renal IR insult. ***, P < 0.001 (IRI vs. Sham); ##, P < 0.01 (IRI vs. DEX); #, P < 0.05 (IRI vs. DEX). Six mice were included in each study group.