Specific Endothelin A (ETA) Receptor Blockade Results In Reduced Expression of Endoplasmic Reticulum (ER) Stress Proteins in Renal Medulla of Type‐1 Diabetic (T1D) Rats

Abstract

Renal levels of endothelin‐1 (ET‐1) are upregulated in diabetic kidney injury; however, the molecular mechanisms by which ET‐1 leads to renal damage are unclear. We hypothesized that ET‐1, through activation of ETA receptor, increases renal ER stress, thus, ETA blockade diminishes renal medullary ER stress. ER stress is caused by misfolded protein accumulation in the ER, leading to increased transcription of ER chaperones and proteins, eventually leading to cellular death. T1D was induced in Sprague‐Dawley rats by i.v. injection of streptozotocin (65mg/kg); control animals received an injection of saline. Initial immunohistochemical studies demonstrated elevated presence of ER stress markers 78KDa glucose regulated protein (GRP78) and C/EBP homologous protein (CHOP) in renal medulla 10 weeks post‐T1D induction. Immunoblotting analysis confirmed that CHOP expression in isolated medullary thick ascending limbs (mTAL) was 10 times greater in diabetic rats than in controls (0.018±0.004 R.D.U. vs. 0.002±0.002 R.D.U., respectively). T1D rats received either ABT‐627 (specific ETA receptor blocker; 5 mg/kg/day) in drinking water for 10 weeks or untreated water (n=8–10/group). ABT‐627 treatment resulted in reduced outer medullary expression of GRP78 and CHOP by immunohistochemistry. These results implicate the direct participation of ET‐1/ETA pathway in ER stress development in the diabetic kidney.