Renal Endoplasmic Reticulum Stress Research Articles

Shiga toxin 2-induced endoplasmic reticulum stress is minimized by activated protein C but does not correlate with lethal kidney injury.

Enterohemorrhagic Escherichia coli produce ribotoxic Shiga toxins (Stx), which are responsible for kidney injury and development of hemolytic uremic syndrome. The endoplasmic reticulum (ER) stress response is hypothesized to induce apoptosis contributing to organ injury; however, this process has been described only in vitro. ER stress marker transcripts of spliced XBP1 (1.78-fold), HSP40 (4.45-fold) and CHOP (7.69-fold) were up-regulated early in kidneys of Stx2 challenged mice compared to saline controls. Anti-apoptotic Bcl2 decreased (−2.41-fold vs. saline) and pro-apoptotic DR5 increased (6.38-fold vs. saline) at later time points. Cytoprotective activated protein C (APC) reduced early CHOP expression (−3.3-fold vs. untreated), increased later Bcl2 expression (5.8-fold vs. untreated), and had early effects on survival but did not alter DR5 expression. Changes in kidney ER stress and apoptotic marker transcripts were observed in Stx2-producing C. rodentium challenged mice compared to mice infected with a non-toxigenic control strain. CHOP (4.14-fold) and DR5 (2.81-fold) were increased and Bcl2 (−1.65-fold) was decreased. APC reduced CHOP expression and increased Bcl2 expression, but did not alter mortality. These data indicate that Stx2 induces renal ER stress and apoptosis in murine models of Stx2-induced kidney injury, but decreasing these processes alone was not sufficient to alter survival outcome.

Epidermal growth factor receptor signaling and the progression of diabetic nephropathy.

Epidermal growth factor receptor signaling and the progression of diabetic nephropathy.

Renal endoplasmic reticulum stress is induced via endothelin A receptor activation (857.7)

The endothelin (ET‐1) system has been recently implicated in renal endoplasmic reticulum (ER) stress development, a type of cellular stress caused by misfolded protein accumulation within this organelle. To clarify the role of the ETA receptor in renal ER stress, we hypothesized that pharmacological blockade of this receptor via ABT‐627 leads to reduced renal response to the ER stress inducer tunicamycin (TM). WT and ETB deficient (sl/sl) rats (n=3‐4/group) were pre‐treated with ABT‐627 (5mg/kg/day; drinking water) for 1 week and given a single injection of TM (2ug/g bwt; i.p.). Kidneys, plasma and urine were collected 24h later. ER stress markers in renal cortical and medullary regions were determined by qRT‐PCR. Treatment of WT animals with ABT‐627 significantly reduced the ER stress response to TM in cortex and outer medulla (fold change/WT+H2O; GRP78 (0.12±0.02 and 0.04± 0.01, respectively), ATF‐4 (0.20± 0.02 and 0.15± 0.02), ATF‐6 (0.28± 0.08 and 0.18± 0.04), spliced XBP‐1 (0.03+0.01 and 0.05± 0.01) and CHOP (0.02± 0.01 and 0.04± 0.01). On the contrary, ABT‐627 pre‐treatment failed to decrease cortical and medullary ER stress development in sl/sl rats. These results indicate that ETA receptor activation leads to induction of renal ER stress genes, while ETB receptor activation has protective effects. Modulation of the ET system may have therapeutic value in protecting against ER stress‐induced renal injury.Grant Funding Source: Supported by NIH and AHA

Endothelin B (ETB) receptor protects against endoplasmic reticulum (ER) stress‐induced renal damage

Tunicamycin (TM) blocks glycoprotein synthesis, leading to endoplasmic reticulum (ER) stress and tissue damage. Endothelin (ET1) via ETA and ETB receptors is implicated in renal injury. We hypothesized that ETB deficient rats (sl/sl) develop exaggerated renal ER stress and/or inflammation compared to wild type (wt) rats in response to acute TM treatment. Wt and sl/sl rats (n=3–5) were treated with TM (2μg/g bwt; i.p.) or vehicle; kidneys, plasma and urine were collected 24h later. ER stress markers and cytokines were determined by qRT‐PCR in renal cortex, outer and inner medulla. Plasma, urine ET1 and renal inflammatory cell infiltration were assessed by ELISA and histology. Sl/sl rats showed enhanced sensitivity to TM by increased expression of GRP78 in inner medulla (wt vs. sl/sl, fold change: 1.52±0.31 vs. 4.60±0.32) and outer medulla (153.6±57.3 vs. 3413±625.8), CHOP in inner medulla (1.46±0.63 vs. 25.50±2.6) and cortex (0.34±0.08 vs. 12.08±2.77), and spliced XBP‐1 in outer medulla (0.91±0.61 vs. 15.71±1.92) and cortex (0.28±0.03 vs. 7.96±1.84). TM did not increase plasma ET1 or urinary ET1 excretion in either rat genotype. Renal CCL2 and IL‐6 expression, as well as macrophage and T‐cell infiltration, were similar between both genotypes in response to TM. Induction of renal ER stress genes is significantly greater in sl/sl rats, thus ETB receptors may be protective against ER stress‐induced renal damage.

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

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.