Divergence of renal vascular endothelial growth factor mRNA expression and protein level in post-ischaemic rat kidneys

Abstract

Vascular endothelial growth factor (VEGF) is a potent regulator of angiogenesis and vascular protection. Synthesis of VEGF is induced by hypoxia and different cytokines including interleukin-6 (IL-6) and interleukin-1beta (IL-1beta). However, post-ischaemic alterations of this growth factor in the kidney are incompletely known. To determine VEGF synthesis in renal ischaemia/reperfusion (I/R) injury unilateral warm ischaemia was induced by cross-clamping the left renal pedicle for 55 min followed by 2 and 24 h of reperfusion (T-2 and T-24 kidneys; n = 6 in each group). Sham-operated, non-clamped animals served as controls (n = 6). Renal VEGF, IL-6 and 1L-1beta mRNA expression were determined by reverse transcription-polymerase chain reaction (RT-PCR). VEGF protein level and distribution were determined by Western blot and immunohistochemical analysis. Immunohistochemistry revealed prominent VEGF staining in the outer medulla of control, T-2 and T-24 kidneys. VEGF immunoreactivity accumulated at the basolateral area of tubular epithelial cells in T-2 kidneys, while it was diffuse in control and T-24 kidneys. VEGF protein levels were increased 2- to 3-fold in T-2 and T-24 kidneys (both P < 0.01 versus controls), while VEGF mRNA expression remained unchanged. IL-6 mRNA expression was increased (P < 0.01 versus controls) in T-2 kidneys, while IL-1beta mRNA expression remained unchanged. Increased VEGF protein levels but not mRNA expression suggests that during renal I/R injury VEGF synthesis in kidneys - unlike in other organs - is primarily regulated at a post-transcriptional level. As IL-6 mRNA expression increased simultaneously with VEGF protein levels, the post-ischaemic regulation of IL-6 and VEGF synthesis might be interrelated in rat kidney.