Endothelial Cell–Specific Signaling Pathway Implicated in Cardiac Fibrosis Progression

Cardiac fibrosis remains a central driver of heart failure, yet its cellular origins and regulatory mechanisms continue to be refined. A new study published in Circulationbrings endothelial cells into sharper focus, identifying a previously underappreciated signaling pathway that appears to actively promote fibrotic remodeling in the myocardium.

Using a combination of single-cell RNA sequencing, lineage tracing, and murine models of cardiac injury, investigators mapped transcriptional changes across cardiac cell populations during fibrosis progression. While fibroblasts have traditionally been viewed as the principal mediators of extracellular matrix deposition, the study reveals that endothelial cells adopt a distinctly pro-fibrotic phenotype under stress conditions.

At the center of this transition is the activation of the Notch signaling pathway. The authors demonstrate that endothelial-specific upregulation of Notch ligands—particularly Jagged1—triggers downstream signaling cascades that influence neighboring fibroblasts. This paracrine communication appears to enhance fibroblast activation and collagen production, effectively amplifying fibrotic remodeling beyond what would be expected from fibroblast-autonomous signaling alone.

The spatial relationship between these cell types is critical. As illustrated in the immunofluorescence images on page 6, endothelial cells expressing high levels of Jagged1 are localized adjacent to activated fibroblasts within fibrotic regions. This proximity supports a model in which endothelial cells serve not merely as passive bystanders, but as active coordinators of tissue remodeling.

Mechanistically, the study also links endothelial Notch activation to endothelial-to-mesenchymal transition (EndMT), a process by which endothelial cells acquire mesenchymal characteristics. Evidence from lineage tracing experiments, detailed in the schematic on page 8, shows that a subset of fibroblast-like cells in fibrotic tissue originates from endothelial precursors. While EndMT has been described previously, these findings suggest it may contribute more substantially to the fibroblast pool than once thought.

Importantly, therapeutic modulation of this pathway produced measurable effects. In mouse models, genetic or pharmacologic inhibition of endothelial Notch signaling attenuated fibrosis, reducing collagen deposition and improving ventricular compliance. These functional improvements, summarized in the echocardiographic data on page 10, translated into better overall cardiac performance following injury.

The implications extend beyond mechanistic insight. By identifying endothelial cells as upstream regulators of fibrosis, the study opens new avenues for targeted intervention. Therapies aimed at modulating endothelial signaling—rather than directly suppressing fibroblast activity—could offer a more precise means of interrupting disease progression while preserving essential repair processes.

Still, several questions remain. The extent to which these findings translate to human disease will require further validation, particularly given the heterogeneity of heart failure etiologies. Additionally, Notch signaling plays diverse roles in vascular biology, raising important considerations about potential off-target effects of systemic inhibition.

Nevertheless, this work reframes the cellular hierarchy of cardiac fibrosis. Rather than acting solely as structural components of the vasculature, endothelial cells emerge as dynamic regulators of myocardial remodeling—positioned at a critical intersection between injury response and chronic disease progression.