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Yuan Zhu, Qun Wu, Jin-Fang Xu, Dorothea Miller, I. Erol Sandalcioglu, Jian-Min Zhang, and Ulrich Sure

Object

Loss-of-function mutations in CCM genes are frequently detected in familial cerebral cavernous malformations (CCMs). However, the current functional studies of the CCM genes in vitro have been performed mostly in commercially purchased normal cell lines and the results appeared discrepant. The fact that the cerebral vascular defects are rarely observed in CCM gene-deficient animals suggests the requirement of additional pathological background for the formation of vascular lesions. Consistent with these data, the authors assumed that silencing CCM genes in the endothelium derived from CCMs (CCM-ECs) serves as a unique and valuable model for investigating the function of the CCM genes in the pathogenesis of CCMs. To this end, the authors investigated the role and signaling of CCM2 and CCM3 in the key steps of angiogenesis using CCM-ECs.

Methods

Endothelial cells (ECs) derived from CCMs were isolated, purified, and cultured from the fresh operative specimens of sporadic CCMs (31 cases). The CCM2 and CCM3 genes were silenced by the specific short interfering RNAs in CCM-ECs and in control cultures (human brain microvascular ECs and human umbilical vein ECs). The efficiency of gene silencing was proven by real-time reverse transcriptase polymerase chain reaction. Cell proliferation and apoptosis, migration, tube formation, and the expression of phosphor-p38, phosphor-Akt, and phosphor-extracellular signal-regulated kinase–1 and 2 (ERK1/2) were analyzed under CCM2 and CCM3 silenced conditions in CCM-ECs.

Results

The CCM3 silencing significantly promoted proliferation and reduced apoptosis in all 3 types of endothelium, but accelerated cell migration exclusively in CCM-ECs. Interestingly, CCM2 siRNA influenced neither cell proliferation nor migration. Silencing of CCM3, and to a lesser extent CCM2, stimulated the growth and extension of sprouts selectively in CCM-ECs. Loss of CCM2 or CCM3 did not significantly influence the formation of the tubelike structure. However, the maintenance of tube stability was largely impaired by CCM2, but not CCM3, silencing. Western blot analysis revealed that CCM2 and CCM3 silencing commonly activated p38, Akt, and ERK1/2 in CCM-ECs.

Conclusions

The unique response of CCM-ECs to CCM2 or CCM3 siRNA indicates that silencing CCM genes in CCM-ECs is valuable for further studies on the pathogenesis of CCMs. Using this model system, the authors demonstrate a distinct role of CCM2 and CCM3 in modulating the different processes of angiogenesis. The stimulation of endothelial proliferation, migration, and massively growing and branching angiogenic sprouts after CCM3 silencing may potentially contribute to the formation of enriched capillary-like immature vessels in CCM lesions. The severe impairment of the tube integrity by CCM2, but not CCM3, silencing is associated with the different intracranial hemorrhage rate observed from CCM2 and CCM3 mutation carriers. The activation of p38, ERK1/2, and Akt signal proteins in CCM2- or CCM3-silenced CCM-ECs suggests a possible involvement of these common pathways in the pathogenesis of CCMs. However, the specific signaling mediating the distinct function of CCM genes in the pathogenesis of CCMs needs to be further elucidated.

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Yuan Zhu, Christian Peters, Monika Hallier-Neelsen, Dorothea Miller, Axel Pagenstecher, Helmut Bertalanffy, and Ulrich Sure

Object

Cerebral cavernous malformations (CCMs) are the most common vascular malformation of the central nervous system and involve dysregulated angiogenesis. However, the underlying mechanism of this disease is poorly understood. Phosphatase and tensin homolog (PTEN) plays a crucial role in regulating angiogenesis. The authors attempted to determine whether PTEN is involved in the pathological angiogenesis of CCM.

Methods

The authors used Western blot analysis and immunohistochemical methods to detect the expression of PTEN, PCNA, and P-Akt in the surgical specimens of CCMs and controls. The function of PTEN in cell proliferation was studied after PTEN silencing in endothelial cultures by using the short interfering RNA technique.

Results

Western blot analysis showed significant reduction of PTEN protein expression in CCMs compared with control brain tissue (p < 0.01). Immunohistochemical analysis confirmed PTEN insufficiency in 33% of vascular endothelia of CCMs, which was significantly higher than that of controls (2%, p < 0.01). Furthermore, PTEN insufficiency occurred more frequently in multiple CCMs (44%) and in small lesions (39%) than in single CCMs (28%, p < 0.05) and large lesions (30%, p < 0.05), respectively, suggesting a potential role of PTEN in the progression of the lesions. Of note, a negative correlation was observed between the expression of PTEN and PCNA in CCM endothelial cells. However, Akt was not constitutively activated in CCMs. Using cultured endothelial cells, the authors demonstrated that PTEN silencing by short interfering RNA increased Akt activation, PCNA expression, and cell proliferation (p < 0.001). Surprisingly, the PTEN silencing–mediated increase in endothelial proliferation was not reversed by the PI3K inhibitor wortmannin.

Conclusions

In this study, the authors report for the first time a significant PTEN insufficiency in CCM vessels associated with endothelial proliferation. The in vitro study provides direct evidence for a pivotal role of PTEN in regulating endothelial proliferation, most likely through a PI3K-independent pathway. The authors suggest that PTEN insufficiency is potentially involved in CCM by stimulating angiogenesis.