Role of the alarmin S100A9 in the pathogenesis of heart failure with preserved ejection fraction
Authors: Voss I , Pappritz K , El-Shafeey M , Matz I , Vogl T , Tschoepe C , Van Linthout S 
Published: October 2024

Abstract

Background
A systemic low-grade inflammation induced by comorbidities is recognized to underlie heart failure (HF) with preserved ejection fraction (HFpEF)-specific remodelling. Recent evidence states that the innate immunity member S100A9, which is mainly present as the heterodimer S100A8/9, is an important contributor of sterile inflammation in the comorbidities of HFpEF, with adipose tissue being an important source. Though, its specific involvement in HFpEF has not been explored so far.

Purpose
The present study aimed to unravel the role of S100A9 in the pathogenesis of HFpEF via the two-hit HFpEF mouse model, S100A8/9 stimulation on murine left ventricle (LV) and C4 fibroblasts (Fb) and gene expression analysis of endomyocardial biopsy (EMB)-derived Fb from HFpEF and HF with reduced ejection fraction (HFrEF) patients.

Methods
Wild type (WT) C57BL/6JN or S100A9 knock-out (ko) mice were exposed to a high-fat diet (HFD) and L-NAME (1 g/L in drinking water) over 15 weeks. Controls received standard diet. LV function was characterized via conductance catheter measurements. At the day of sacrifice, the LV, spleen, blood, and adipose tissue were collected for subsequent analyses. In vitro, murine LV-derived Fb and C4 Fb were stimulated with the heterodimer S100A8/9. EMB-Fb from HFpEF and HFrEF patients were screened for S100A9 and downstream components of the NLRP3 inflammasome.

Results
WT HFD+L-NAME mice exhibited a preserved EF, combined with a reduced LV relaxation (dP/dtmin; p&lt;0.01), elevated LV relaxation time (Tau; p&lt;0.05), and impaired LV contractility (dP/dtmax; p&lt;0.05), in parallel to a low-grade systemic inflammation evident by increased C-reactive protein levels. S100A9+, CD68+ and Ly6G+ cells, and CD68+ and Ly6G+ cells expressing S100A9 were increased in the LV, spleen and adipose tissue of WT HFD+L-NAME mice compared to WT mice on chow diet. Changes in LV function were less pronounced in S100A9ko HFD+L-NAME mice, which were characterized by lower systemic C-reactive protein levels, and lower presence of CD68+ and Ly6G+ cells in the LV, spleen and adipose tissue versus WT HFD+L-NAME mice, in the absence of S100A9. Moreover, S100A9ko HFD+L-NAME exhibited lower expression of pro-inflammatory and fibrosis-related genes versus WT HFD+L-NAME mice. Stimulation of murine LV-Fb and C4 Fb with S100A8/A9 increased the mRNA expression of the pro-inflammatory chemokines chemokine (C-C motif) ligand (CCL) 2 and CCL7, and the % of NLRP3-, ASC-, caspase 1-, and IL-1ß-expressing cells, respectively. Finally, mRNA expression of S100A9 and components of the NLRP3 inflammasome was higher in EMB-Fb of HFpEF versus HFrEF patients.

Conclusion
These data support that adipose tissue is an extra-cardiac source of S100A9 contributing to systemic low-grade inflammation. S100A8/9 in the heart can boost the inflammatory potential of cardiac fibroblasts, further supporting the pro-inflammatory role of S100A9 in the pathogenesis of HFpEF development.