Cerebral cavernous malformations arise from endothelial gain of MEKK3–KLF2/4 signalling

Abstract

Cerebral cavernous malformations (CCMs) are common inherited and sporadic vascular malformations that cause stroke and seizures in younger individuals1. CCMs arise from endothelial cell loss of KRIT1, CCM2, or PDCD10, non-homologous proteins that form an adaptor complex2. How disruption of the CCM complex results in disease remains controversial, with numerous signaling pathways (including Rho3,4, SMAD5 and Wnt/β-catenin6) and processes such as endothelial-mesenchymal transition (EndMT)5 proposed to play causal roles. CCM2 binds MEKK37–11, and we have recently demonstrated that CCM complex regulation of MEKK3 is essential during vertebrate heart development12. Here, we investigate this mechanism in CCM disease pathogenesis. Using a neonatal mouse model of CCM disease, we find that expression of the MEKK3 target genes KLF2 and KLF4, as well as Rho and ADAMTS protease activity, are increased in the endothelial cells of early CCM lesions. In contrast, we find no evidence of EndMT or increased SMAD or Wnt signaling during early CCM formation. Endothelial-specific loss of Mekk3, Klf2, or Klf4 dramatically prevents lesion formation, reverses the increase in Rho activity, and rescues lethality. Consistent with these findings in mice, we demonstrate that endothelial expression of KLF2 and KLF4 is elevated in human familial and sporadic CCM lesions, and that a disease-causing human CCM2 mutation abrogates MEKK3 interaction without affecting CCM complex formation. These studies identify gain of MEKK3 signaling and KLF2/4 function as causal mechanisms for CCM pathogenesis that may be targeted to develop new CCM therapeutics.

Oxidative stress and inflammation in cerebral cavernous malformation disease pathogenesis: Two sides of the same coin

“…Accordingly, it has been reported that CCM3 mouse mutants only develop lesions in conjunction with severe astrocytosis at the lesion site, suggesting that injury of astrocytes may play a role in lesion formation (Louvi et al, 2011), a notion consistent with clinical reports of CCM developing or expanding after physical trauma, injury, or radiation (Cutsforth-Gregory et al, 2015, Louvi et al, 2011). Furthermore and importantly, the development of CCM lesions induced by endothelial-specific conditional knockout of CCM genes in neonatal mice is highly restricted, both spatially and temporally, despite the pan-endothelial deletion of CCM genes (Boulday et al, 2011, Chan et al, 2011, Gibson et al, 2015, Zhou et al, 2016). This clearly demonstrates that the homozygous loss of CCM genes is not fully sufficient to cause CCM lesion formation and disease progression, and suggests the necessary contribution of additional triggers occurring locally, which may include micro-environmental stress factors or brain injuries.…”

Combined HMG-COA reductase and prenylation inhibition in treatment of CCM

“…5 A′′-F′′ and U). Previous work showed that KLF2/4 are up-regulated following CCM loss in endothelial cells (29)(30)(31)(32)(33). KLF2/4 signals were increased in the cerebellum of cKO mice, but the drugs did not reverse this effect (Fig.…”

“…Combined treatment with fluvastatin and zoledronate appears to have effects comparable to sulindac sulfide on survival; both approaches also reduced lesion burden, although slight differences in analyses preclude direct comparisons. Because endothelial gain of MEKK3 was suggested in CCM1 disease (33), future studies will likely test inhibitors of this cascade. In conclusion, fluvastatin/zoledronate combination therapy, which effectively inhibits the mevalonate pathway, warrants further evaluation as a pharmacological intervention in familial and potentially in sporadic CCM disease.…”

The Vascular Wall: a Plastic Hub of Activity in Cardiovascular Homeostasis and Disease

“…KLF4 activation has been recently identified as the major inducer of EndMT in cerebral cavernous malformations, suggesting that KLF4 might be a key trigger of pathological EndMT [80,81]. Additional regulators of EndMT include Notch signaling, several miRs, endothelin 1, Tie1 tyrosine kinase receptors, and sonic hedgehog signaling, providing a wide range of potential targets to regulate EndMT in pathological conditions [29,37,[82][83][84][85][86][87].…”