Fibrin, Bone Marrow Cells And Macrophages Interactively Modulate Cardiomyoblast Fate: An In Vitro Study
Authors: Borrego I , Frobert A , Cook S , Dengjel J , Giraud MN 
Published: June 2022

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): The study was supported by the Swiss National Science Foundation (SNF 310030_149986) attributed to MNG, the University of Fribourg and the Fonds Scientifique Cardiovasculaire FSC, Fribourg Hospital attributed to SC
The spatiotemporal interaction of macrophages with the cardiac extracellular matrix, cardiomyocytes and non-cardiomyocytes has shown increasing interest in cardiac repair and regeneration. Due to their immunomodulatory capacities, cell-based therapies for myocardial infarction (MI) may influence macrophages fate. In addition, the use of biomaterials combined with cells is nowadays a recommended approach for cell-based therapies to fosters cell retention and survival. Depending on their composition and structure, scaffolds may modulate macrophage phenotypes. We interrogated the influence of fibrin, a biologically active scaffold, on the fate of cells including bone marrow cells (BMC), macrophages and cardiomyoblasts.

Methods
In vivo, two weeks post-MI induction, animals with an ejection fraction between 35-60% were either sham-operated animals or treated with an epicardial implantation of a BMC and fibrin. In vivo, two weeks post-MI induction, animals with an ejection fraction between 35-60% were either sham-operated animals or treated with an epicardial implantation of a BMC and fibrin. In vitro, non-polarized macrophages were differentiated toward either pro-inflammatory or anti-inflammatory phenotypes and stimulated with the conditioned medium of fibrin-primed BMC (F-BMC). Proteomic, cytokine levels quantification, and qPCR were performed. EdU incorporation and real time cell analysis assessed the effect of F-BMC on macrophages and cardiomyoblasts H9C2 proliferation.

Results
In vivo, epicardial implantation of Fibrin and BMC reduced the loss of cardiac function induced by MI and prevented the fibrotic scar expansion. After 4 and 12 weeks, the infarct content of CD68+ and CD206+ macrophages were similar in control and treated animals. To investigate acute effect, we performed in vitro assays. We showed that fibrin profoundly influenced gene expression and the secreted proteome of BMC, simultaneously upregulating both pro- and anti-inflammatory mediators. Furthermore, the conditioned medium from F-BMC significantly increased the proliferation of anti-inflammatory macrophages and modulated their gene expression and cytokines secretion. For example, F-BMC downregulated the expression of pro-inflammatory genes, in particular Nos2, Il6 and Ccl2/Mcp1. Anti-inflammatory genes such as Arg1, Tgfb and IL10 were significantly upregulated. Interestingly, anti-inflammatory macrophages educated by F-BMC stimulated EdU incorporation in H9C2 cardiomyoblasts.
In conclusion, our study provides evidence that F-BMC secretome promoted the growth of anti-inflammatory macrophages, stimulated macrophage plasticity and altered the balance between the pro and anti-inflammatory macrophage subsets. F-BMC secretome favoured the mitogenic properties of anti-inflammatory macrophages promoting cardiac cell growth. In vivo, F-BMC treatment lowered the infarct extent and increased wall thickness and improved cardiac function.