Severe Hyperosmotic Stress Issues an ER Stress-Mediated Death Sentence in H9c2 Cells, with p38-MAPK and Autophagy Coming to the Rescue

With several cardiovascular pathologies associated with osmotic perturbations, researchers are in pursuit of identifying the signaling sensors, mediators and effectors involved, aiming at formulating novel diagnostic and therapeutic strategies. In the present study, H9c2 cells were treated with 0.5 M sorbitol to elicit hyperosmotic stress. Immunoblotting as well as cell viability analyses revealed the simultaneous but independent triggering of multiple signaling pathways. In particular, our findings demonstrated the phosphorylation of eukaryotic translation initiation factor 2 (eIF2 alpha) and upregulation of the immunoglobulin heavy-chain-binding protein (BiP) expression, indicating the onset of the Integrated Stress Response (IRS) and endoplasmic reticulum stress (ERS), respectively. In addition, autophagy was also induced, evidenced by the enhancement of Beclin-1 protein expression and of AMP-dependent kinase (AMPK) and Raptor phosphorylation levels. The involvement of a Na+/H+ exchanger-1 (NHE-1) as well as NADPH oxidase (Nox) in 0.5 M sorbitol-induced eIF2 alpha phosphorylation was also indicated. Of note, while inhibition of ERS partially alleviated the detrimental effect of 0.5 M sorbitol on H9c2 cellular viability, attenuation of p38-MAPK activity and late phase autophagy further mitigated it. Deciphering the mode of these pathways' potential interactions and of their complications may contribute to the quest for effective clinical interventions against associated cardiovascular diseases.

Automated summary

This study found that hyperosmotic stress triggered multiple signaling pathways in H9c2 cells, including the Integrated Stress Response (IRS), endoplasmic reticulum stress (ERS), and autophagy. The phosphorylation of eukaryotic translation initiation factor 2 (eIF2 alpha) and upregulation of immunoglobulin heavy-chain-binding protein (BiP) expression indicated the activation of IRS and ERS, respectively. In addition, the involvement of a Na+/H+ exchanger-1 (NHE-1) and NADPH oxidase (Nox) in eIF2 alpha phosphorylation was also demonstrated. Attenuation of p38-MAPK activity and late phase autophagy mitigated the detrimental effect of hyperosmotic stress on cell viability.