Non-autonomous effects of CCM genes loss

Cerebral cavernous malformation (CCM) is a rare disease of proven genetic origin characterized by vascular lesions affecting capillaries and small vessels of the central nervous system. CCM lesions occur in a range of different phenotypes, including wide differences in lesion number, size, and susceptibility to intracerebral hemorrhage. CCM lesion genesis requires loss of function of any of three genes, namely KRIT1 (CCM1), MGC4607 (CCM2), and PDCD10 (CCM3). These genes exert pleiotropic effects regulating multiple mechanisms involved in angiogenesis, cellular response, cell-cell and cell-matrix adhesion, cytoskeleton dynamics, and oxidative damage protection. Familial CCM is an autosomal-dominantly inherited disease in which the loss of any of the three CCM genes follows a two-hit mechanism. The heterozygous loss-of-function germline variants in one of the involved genes seems to be associated with a second postzygotic mutation, according to Knudson’s two-hit model of tumor suppressor genes. This review is an overview of very recent literature on CCM onset and progression focused on the novel concept that the loss of a CCM gene in a single cell is sufficient to induce vascular lesions. Mutated cells undergo clonal expansion and become able to promote the recruitment of non-mutated cells and to induce their angiogenic switch through the increased production of angiogenic factors and downregulation of antiangiogenic factors. A deep understanding of this process and the knowledge of unbalanced secreted factors will be useful to design new pharmacological strategies for CCM patients.