Mechamism of VEGF expression by high glucose in proximal tubule epithelial cells

Summary In mouse proximal tubular epithelial cells, high glucose (HG) for 24 h increases VEGF expression at the protein and the mRNA level, suggesting a transcriptional mechanism. HG-induced VEGF synthesis is prevented by captopril, an inhibitor of angiotensin-converting enzyme, and, by losartan, a specific antagonist of angiotensin type 1 receptor (AT1), suggesting that VEGF synthesis is mediated by Ang II. Synthesis of angiotensinogen (AGT), a precursor of Ang II, is induced by HG. Although renin and ACE expression is not affected, their activity is increased by HG. Ang I and Ang II synthesis is also increased by HG, and captopril prevents increased Ang II, but not Ang I, synthesis. AT1 activation is increased by with HG, and its activation is prevented by captopril and losartan. The ERK pathway is activated by HG within minutes of stimulation and lasting for up to 24h. The initial phase of ERK activation is due to HG itself and leads to AGT upregulation and the sustained phase is mediated for the most part by Ang II-activated AT1 receptor and leads to increased VEGF synthesis. In conclusion, our study shows that MCTs express an endogenous renin-angiotensin system that is activated by HG to stimulate VEGF synthesis, through activation of the ERK pathway. Angiotensin II (Ang II) and vascular endothelial growth factor (VEGF) are important mediators of kidney injury in diabetes. VEGF expression is increased in proximal tubules of mice with type 1 diabetes. In mouse proximal tubular epithelial cells (MCT) cultured with 30 mM glucose (HG) for 24 h, VEGF expression is increased at the protein and the mRNA level, suggesting a transcriptional mechanism. HG stimulation of VEGF synthesis is prevented by captopril, an inhibitor of angiotensin-converting enzyme, and, by losartan, a specific antagonist of angiotensin type 1 receptor (AT1), suggesting that VEGF synthesis is mediated by Ang II. Synthesis of angiotensinogen (AGT), a precursor of angiotensin II, is increased in MCTs cultured in HG. Although synthesis of renin and ACE is not affected by HG, their activity is increased in the conditioned medium. Concentrations of Ang I and Ang II are also increased in conditioned medium from HG-treated MCTs and captopril prevents increased Ang II, but not Ang I, synthesis. Finally, AT1 is activated in MCTs treated with HG, and its activation is prevented by captopril and losartan. The ERK pathway is activated by HG within minutes of stimulation and lasting for up to 24h. The initial phase of ERK activation is due to HG itself and leads to AGT upregulation and the sustained phase is mediated for the most part by Ang II-activated AT1 receptor and leads to increased VEGF synthesis. These data show that: 1) HG increases AGT synthesis and activation of renin and ACE by MCTs, leading to local production of Ang I and Ang II. 2) Ang II activates endogenous AT1 and stimulates synthesis of VEGF. 3) HG activation of ERK starts within minutes and lasts for up to 24h. Early ERK activation is involved in AGT upregulation and sustained ERK activation, mediated via AT1, is responsible for VEGF synthesis. In conclusion, our study shows that MCTs express an endogenous renin-angiotensin system that is activated by high glucose to stimulate the synthesis of VEGF, through activation of the ERK pathway.