Normal cardiac lymphatics and their mimics.

Area of Science:

• Cardiovascular Biology
• Lymphatic System Research
• Developmental Biology

Background:

• Lymphatic vessels (LyVs) are crucial for fluid homeostasis and immune surveillance.
• Dysfunction of cardiac LyVs is implicated in cardiovascular diseases.
• The normal anatomical distribution of LyVs within the heart remains poorly understood.

Purpose of the Study:

• To comprehensively map the distribution of LyVs in the adult mouse heart.
• To identify specific cardiac anatomical sites with LyV presence.
• To characterize the cellular heterogeneity of cardiac lymphatic endothelial cells.

Main Methods:

• Utilized Prox1-tdTomato lymphatic reporter mice for LyV visualization.
• Employed light sheet microscopy and cryo-/vibratome sectioning for anatomical mapping.
• Performed immunostaining for lymphatic markers (LYVE1, podoplanin, VEGFR3) and single-cell RNA sequencing (scRNA-Seq).

Main Results:

• Identified an extensive LyV network on the ventricular epicardium and subepicardial regions.
• Detected LyVs in the right ventricular septum endocardium, left atrium subepicardium, mitral valve, interatrial septum, and near the atrioventricular node.
• Revealed non-specific expression of lymphatic markers (LYVE1, PROX1) in non-lymphatic cells and identified six subtypes of cardiac lymphatic endothelial cells via scRNA-Seq.

Conclusions:

• Provides a detailed anatomical map of cardiac LyVs, serving as a foundational resource.
• Highlights the critical need for validated multi-marker strategies to accurately identify cardiac LyVs.
• Establishes a basis for investigating the role of cardiac LyVs in health and disease.