Proteomic and phosphoproteomic profiles of human heart failure with preserved and reduced ejection fraction: insights into cardiac remodelling

Abstract Background Despite the high public-health importance, evidence-based therapeutic interventions for heart failure with preserved ejection fraction (HFpEF) are limited, and the underlying pathomechanisms remain poorly understood, although low-grade systemic inflammation and endothelial dysfunction may be involved. Purpose We aimed to elucidate differences in protein expression and phosphorylation in human HFpEF and heart failure with reduced ejection fraction (HFrEF) as compared to nonfailing patient hearts. Methods Left ventricular myocardial tissues from explanted or donor human hearts (Medical University Graz) were retrospectively categorised into three groups: nonfailing Control, HFpEF or HFrEF (mean EF (%): 63 (Control), 62 (HFpEF), 24 (HFrEF); mean age 58.1±9.5; mean BMI 26.6±2.7), and analysed by label-free quantitative mass spectrometry (N=6-7/group). Results Cardiac proteome analysis identified 49 significantly regulated proteins (fold-change 1.5, p0.05) in HFpEF and 161 in HFrEF compared to Control hearts, out of 1813 detected cardiac proteins. Low-grade systemic inflammation emerged as a contributing factor in both HFpEF and HFrEF hearts. This was supported by GO enrichment analysis of significantly regulated proteins in HFpEF and HFrEF versus Control hearts, demonstrating altered protein expression associated with "complement activation" (e.g., C6, C4B) and "innate immune response" (e.g., S100A8, STING1). Notably, the inflammatory state seems to be lower in HFpEF, as inflammation-associated proteins were downregulated in HFpEF compared to HFrEF hearts. The presence of low-grade systemic inflammation in both heart failure syndromes was validated by immunoblot analyses and immunohistochemistry due to substantially elevated expression of ICAM1 and S100A8 in failing hearts versus Control hearts. Phosphoproteome analysis identified 83 phosphosites in cardiac proteins that were differentially expressed (fold-change 1.5, p0.05) in HFpEF and 181 in HFrEF compared to Control hearts, out of 1045 distinct phosphosites mapped in cardiac proteins. Phosphoproteomic alterations in HFpEF and HFrEF primarily involved sarcomeric proteins (e.g., titin, desmin, troponin I), which were predominantly hyper-phosphorylated. GO enrichment analysis revealed that proteins associated with "protein kinase binding" (e.g., protein phosphatase 1 regulatory subunits 12A, 12B and 12C) were hyper-phosphorylated in HFpEF versus Control hearts. Conclusion Low-grade systemic inflammation is a common feature in the hearts of patients with both HFpEF and HFrEF. There is no distinct HFpEF inflammatory phenotype in this cohort that could be used for diagnostics or HFpEF-specific therapy development. However, our data suggest a link between systemic inflammation and sarcomeric protein phosphorylation, a relationship that will be investigated in greater detail in future research.