O braço molecular induzido pela Fosfoproteína induzida por estresse 1 (STIP1) e Proteína Priônica Celular (PRPC) atua na adaptação e resiliência de Cardiomiócitos a Hiperatividade Adrenérgica e a Hipóxia

Abstract

Stress-induced phosphoprotein 1 (STIP1) is a co-chaperone involved in neuronal proteostasis and stress resilience. Although expressed in the heart, its function remains undefined. In previous studies by our group, we identified reduced STIP1 expression in cardiac tissue from patients with heart failure. Using haploinsufficient mice for STIP1 (STIP1+/-), we demonstrated that these animals were more susceptible to cardiac stress generated by the β-adrenergic agonist isoproterenol (ISO), and their cardiomyocytes did not hypertrophy in response to the stimulus. In a proteomic assay, we identified several negatively regulated proteins related to the protein synthesis process in STIP1+/-/ISO animals when compared to WT/ISO. We also identified several altered cellular pathways related to the oxidative stress process, as well as an inhibition of the NRF2 transcription factor pathway. Thus, the aim of this study was to investigate the importance of STIP1 for protein synthesis preceding cardiomyocyte hypertrophy, as well as the relevance of STIP1 in the context of hypoxia in cardiomyocytes and its relationship with NRF2 in this process. Initially, we transfected neonatal rat cardiomyocytes (NRCMs) with siRNA that was able to reduce the expression of STIP1 mRNA and protein. Subsequently, we identified that STIP1 is important for NRCM hypertrophy in response to ISO, but does not appear to be necessary for IGF-1-mediated cell enlargement. We also validated the findings of the proteomic experiment by showing that STIP1 is relevant for increased protein synthesis in response to ISO as well as for eIF4E expression. The pathway by which STIP1 modulates cardiomyocyte hypertrophy appears to be PrPc-dependent, since silencing the protein prevents NRCM hypertrophy in response to ISO, phenocopying STIP1 silencing. We also identified the ability of NRCMs to secrete STIP1 as well as its binding to PrPc in these cells. Next, we demonstrated that the expression and nuclear localization of STIP1 is positively modulated in cardiomyocytes subjected to CoCl2-induced hypoxia. This same context induces STIP1 secretion by NRCMs. STIP1 silencing led to increased production of reactive oxygen species (ROS), as well as exacerbated cardiomyocyte death in response to hypoxia. Finally, we identified that the presence of STIP1 is relevant to ensure the expression and nuclear localization of NRF2 in the context of CoCl2-mediated oxidative stress. In conclusion, STIP1 proves to be a fundamental molecule in the adaptation of cardiomyocytes to oxidative stress as well as in adrenergic hyperactivity. Thus, this study positions the STIP1-PrPc molecular arm as an important therapeutic target to be investigated in the context of cardiac diseases.