Regulation of cardiomyocyte pathological hypertrophy by Stress-inducible phosphoprotein I (STIP1)

Increased protein misfolded can contribute to the development of cardiac dysfunction, pointing to chaperones as potential guardians of heart function. Stress inducible phosphoprotein I (STIP1) is a co-chaperone that bridges Hsp70 and Hsp90, but its function in the heart is unclear. Here, we assessed the role of STIP1 in the heart in both healthy and diseased conditions. First, we investigated STIP1 protein expression in human cardiac samples from healthy and heart failure (HF) patients obtained from the Duke Human Heart Repository by Western blot. STIP1 is expressed in the human heart, and its levels are reduced in HF patients. To determine whether reduced STIP1 contributes to changes in heart function, we used a STIP1 haploinsufficient mice (STIP1 +/- ) with 50% reduction in cardiac STIP1 protein levels. Echocardiography evaluation showed that STIP1 +/- mice developed normally with no evidence of major cardiac alterations. Next, we evaluated the ability of STIP1 +/- mice to cope with myocardial damage induced by 7 days of Isoproterenol (ISO) treatment. Both wild-type (WT) and STIP1 +/- mice treated with ISO showed an increase in heart weight/tibia length ratio, however STIP1 +/- /ISO mice exhibited more pronounced inflammation and fibrosis. Strikingly, cardiomyocytes (CMs) isolated from STIP1 +/- /ISO mice did not grow in area, indicating that the organ-level hypertrophy observed in this group is likely due to fibrosis and inflammation. To establish a causal relationship between STIP1 levels and the process of hypertrophy, we transfected neonatal rat cardiomyocytes (NRCMs) with an siRNA against STIP1 mRNA and treated the cells with ISO (20µM) for 48h. The NRCMs transfected with STIP1-siRNA showed a decrease in 80% of STIP1 mRNA, as shown by qPCR and immunofluorescence. Mock CMs treated with ISO exhibited an increase in area, while STIP1-siRNA CMs showed no hypertrophy in response to ISO. To determine if the participation of STIP1 in the hypertrophic response extends to other hypertrophic pathways, we treated NRCMs with angiotensin II (Ang II, 100nM for 48h). Decreased STIP1 levels blunted Ang II hypertrophy. CM hypertrophy is characterized by increased protein synthesis, therefore to investigate whether STIP1 deficiency impairs protein translation, we used puromycin labeling of nascent peptides. Confirming our findings, CMs transfected with STIP1-siRNA did not increase protein synthesis rate in response to ISO. To assess the mechanism through which diminished STIP1 levels impair protein synthesis in response to ISO, we performed proteomics of cardiac tissue from WT and STIP1 +/- mice subjected to the in vivo ISO treatment. The ingenuity pathway analysis confirmed that the differentially expressed proteins detected in the STIP1 +/- /ISO heart were mainly related to adverse remodeling, including cardiac hypertrophy and fibrosis. A finding which is in line with the cardiac phenotype described for the STIP1 +/- mice treated with ISO. Analysis using the Reactome database revealed several dysregulated pathways related to proteins synthesis, including a downregulation of ribosomal proteins, initiation factors and components of mTORC1 pathway in the STIP1 +/- /ISO heart compared to WT/ISO. Our data reveals, for the first time, a critical role for STIP1 as a regulator of protein synthesis during pathological hypertrophy in cardiomyocytes. CNPq, CAPES, FAPEMIG, PRPq This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.