Academic Background

The formation and maintenance of vascular networks are critical processes in embryonic development and tissue regeneration, involving the regulation of various biophysical forces. Endothelial cells (ECs) play a central role in angiogenesis and vasculogenesis, with the contractile forces of the cytoskeleton (actomyosin contractility) being particularly important in these processes. However, the mechanisms by which the cytoskeleton is organized and regulated in different cellular compartments, especially during vascular network formation, remain poorly understood.

Cerebral cavernous malformations (CCMs) are a common vascular abnormality typically caused by mutations in the KRIT1, CCM2, and PDCD10 genes. These mutations lead to thinning of vessel walls, vascular dilation, and symptoms such as headaches, seizures, and strokes. Although the pathological mechanisms of CCMs have been studied to some extent, the specific molecular mechanisms, particularly in endothelial cell interactions and lumen formation, remain unclear.

This study used zebrafish as a model to explore the roles of the CCM-related genes HEG1 and KRIT1 in angiogenesis, particularly their mechanisms in regulating endothelial cell interactions and lumen formation. By combining live imaging, genetic analysis, and optogenetic tools, the study revealed the critical roles of HEG1 and KRIT1 in maintaining endothelial cell interfaces and continuous lumen formation.

Source of the Paper

The paper was co-authored by Jianmin Yin, Ludovico Maggi, Cora Wiesner, Markus Affolter, and Heinz-Georg Belting, all from the Department of Cell Biology at the University of Basel, Switzerland. The paper was published online on September 9, 2024, in the journal Angiogenesis, with the DOI 10.1007/s10456-024-09945-5.

Research Process and Results

Research Process

1. Zebrafish Model and Mutant Construction
   The study used zebrafish as an experimental model and constructed HEG1 and KRIT1 mutants. Through transgenic technology, researchers expressed various fluorescently labeled proteins, such as HEG1-GFP and KRIT1-GFP, in zebrafish embryos to enable live imaging and dynamic observation of cell interactions.

2. Live Imaging and Optogenetic Experiments
   Researchers performed live imaging on zebrafish embryos to observe endothelial cell interactions and lumen formation during angiogenesis. Using optogenetic tools, they activated the RhoA signaling pathway in specific regions to study its effects on cell interfaces and lumen formation.

3. Image Analysis and Data Processing
   Live imaging data were analyzed using ImageJ and MATLAB to quantify changes in cell interface shape, myosin distribution, and the dynamics of lumen expansion and contraction.

Key Results

1. Roles of HEG1 and KRIT1 in Cell Interface Formation
   The study found that endothelial cell interfaces in HEG1 and KRIT1 mutants exhibited twisted and fragmented features, indicating that these genes play a key role in maintaining interface stability. Live imaging revealed that the mutants lacked actomyosin contractility at cell interfaces, leading to interface distortion and impaired lumen formation.

2. Role of Oscillatory Contractility in Lumen Formation
   In wild-type zebrafish embryos, researchers observed oscillatory contractions at endothelial cell interfaces, which helped straighten the interfaces and eliminate excess connections. In HEG1 and KRIT1 mutants, this oscillatory contractility was absent, resulting in twisted interfaces and discontinuous lumens.

3. Optogenetic Activation of the RhoA Signaling Pathway
   Using optogenetic tools, researchers activated the RhoA signaling pathway in KRIT1 mutants, successfully restoring contractility at cell interfaces and straightening the twisted interfaces. This result demonstrated the importance of the RhoA signaling pathway in maintaining cell interfaces and lumen formation.

Conclusions and Significance

The study found that HEG1 and KRIT1 regulate oscillatory contractility at endothelial cell interfaces, maintaining interface stability and promoting continuous lumen formation. This discovery not only reveals the molecular mechanisms of CCM-related genes in angiogenesis but also provides new insights for the treatment of CCMs. Restoring contractility at cell interfaces may help improve vascular abnormalities in CCM patients.

Research Highlights

1. Revealed the Key Roles of HEG1 and KRIT1 in Angiogenesis: The study found that HEG1 and KRIT1 regulate oscillatory contractility at endothelial cell interfaces, maintaining interface stability and promoting continuous lumen formation.

2. Innovative Combination of Live Imaging and Optogenetic Tools: Through live imaging and optogenetic tools, researchers dynamically observed endothelial cell interactions and successfully restored contractility at cell interfaces in mutants.

3. Provided New Insights for CCM Treatment: Restoring contractility at cell interfaces may help improve vascular abnormalities in CCM patients, offering a theoretical basis for future treatment strategies.

Other Valuable Information

The study also found that hemodynamic forces play a complementary role in lumen formation, particularly in mutants, where blood flow can promote the straightening of twisted interfaces and the formation of continuous lumens. This finding further emphasizes the importance of biophysical forces in angiogenesis.