Angiotensin II-induced podocyte apoptosis is mediated by endoplasmic reticulum stress/PKC-δ/p38 MAPK pathway activation and trough increased Na+/H+ exchanger isoform 1 activity

Abstract\ud \ud Background\ud Angiotensin II (Ang II) contributes to the progression of renal diseases associated with proteinuria and glomerulosclerosis mainly by inducing podocyte apoptosis. In the present study, we investigated whether the chronic effects of Ang II via AT1 receptor (AT1R) would result in endoplasmic reticulum (ER) stress/PKC-delta/p38 MAPK stimulation, and consequently podocyte apoptosis.\ud \ud \ud Methods\ud Wistar rats were treated with Ang II (200 ng·kg−1·min−1, 42 days) and or losartan (10 mg·kg−1·day−1, 14 days). Immortalized mouse podocyte were treated with 1 μM Ang II and/or losartan (1 μM) or SB203580 (0.1 μM) (AT1 receptor antagonist and p38 MAPK inhibitor) for 24 h. Kidney sections and cultured podocytes were used to evaluate protein expression by immunofluorescence and immunoblotting. Apoptosis was evaluated by flow cytometry and intracellular pH (pHi) was analyzed using microscopy combined with the fluorescent probe BCECF/AM.\ud \ud \ud Results\ud Compared with controls, Ang II via AT1R increased chaperone GRP 78/Bip protein expression in rat glomeruli (p < 0.001) as well as in podocyte culture (p < 0.01); increased phosphorylated eIf2-α (p < 0.05), PKC-delta (p < 0.01) and p38 MAPK (p < 0.001) protein expression. Furthermore, Ang II induced p38 MAPK-mediated late apoptosis and increased the Bax/Bcl-2 ratio (p < 0.001). Simultaneously, Ang II via AT1R induced p38 MAPK-NHE1-mediated increase of pHi recovery rate after acid loading.\ud \ud \ud Conclusion\ud Together, our results indicate that Ang II-induced podocyte apoptosis is associated with AT1R/ER stress/PKC-delta/p38 MAPK axis and enhanced NHE1-mediated pHi recovery rate.This work was supported by the Fundação de Amparo a Pesquisa do Estado\ud de São Paulo (FAPESP) to Maria Oliveira-Souza (13/19569–3; 17/02020–0),\ud Gerhard Malnic (13/23087–4), Vanessa Gerolde Cardoso (14/19154–0), Karina\ud Thieme (14/17251–9), Fernando Augusto Malavazzi Casare (11/14022–0); by\ud the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)\ud to Mariana Charleaux de Ponte (14/151575–2) and Bruna Bezerra Lins\ud (140141/2016–2); by Coordenação de Aperfeiçoamento de Pessoal de Nível\ud Superior to Guilherme Lopes Gonçalves