Mural Cells Initiate Endothelial-to-Mesenchymal Transition in Adjacent Endothelial Cells in Extracranial AVMs

Area of Science:

• Vascular Biology
• Cellular Biology
• Pathology

Background:

• Extracranial arteriovenous malformations (eAVMs) are complex vascular lesions characterized by abnormal connections and instability.
• Disruptions in endothelial cell (EC)-to-mural cell (MC) interactions are a hallmark of eAVMs.
• The role of EC-to-mural cell interactions in eAVM pathogenesis, specifically EndMT, remains unclear.

Purpose of the Study:

• To investigate whether eAVM-MCs can induce endothelial-to-mesenchymal transition (EndMT) in the eAVM microenvironment.
• To analyze the expression of EC and EndMT markers in eAVM tissues and paired controls.
• To assess the capacity of isolated eAVM-MCs to induce EndMT in normal endothelial cells.

Main Methods:

• RT-PCR and immunohistochemistry (IHC) were used to analyze EC and EndMT markers in eAVM and control tissues.
• Flow cytometry was employed to isolate eAVM-MCs and normal MCs (NMCs) from human surgical samples.
• Co-culture experiments with HUVECs were performed to evaluate the effect of isolated MCs on endothelial cells.

Main Results:

• RT-PCR revealed upregulated EndMT markers in eAVM tissues compared to controls, with no significant difference in EC markers.
• IHC showed expanded eAVM-MCs surrounding abnormal vessels, with endothelium exhibiting markers of EndMT (loss of CD31, CD34, CDH5; upregulation of CDH2, SNAI1).
• Co-culture experiments demonstrated that isolated eAVM-MCs induced loss of CD31 in HUVECs, while NMCs did not.

Conclusions:

• The endothelium in eAVMs, particularly when surrounded by expanded eAVM-MCs, undergoes EndMT.
• eAVM-MCs are implicated in initiating EndMT, contributing to the formation of dilated and fragile vessels characteristic of eAVMs.
• These findings highlight a potential mechanism driving eAVM pathology and suggest eAVM-MCs as key players in EndMT induction.