The role of PDCD10 in cerebral cavernous malformation

Cerebral cavernous malformation (CCM) is one of the vascular malformations observed in the central nervous system consisting of endothelium-lined vascular channels without intervening normal brain parenchyma. So far, three CCM loci have been mapped as Ccm1, Ccm2, Ccm3 genes in CCM. Mutations in the programmed cell death 10 gene, PDCD10, cause the autosomal-dominant familial cerebral cavernous malformation 3 (CCM3). Little is known about the function of this gene in disease pathogenesis. The recent identification of PDCD10 as the gene mutated in CCM3 led us to hypothesize that CCM3 lesions might be due to derailed apoptosis which is important in CNS vascular remodelling. To test this hypothesis, first, we generated and characterized CCM3-specific polyclonal antibodies and analyzed CCM3 protein expression in human cerebral and solid organ (extra-cerebral) tissues using immunohistochemistry. Moreover, we reported CCM3 expression in mice by using immunoflourescence staining. Afterwards, we analyzed the messenger ribonucleic acid (mRNA) expression of CCM3 in the prenatal and postnatal mouse brain by in situ hybridization.This study shows the expression of CCM3 in arterial vascular endothelium in various human organs and nervous system. CCM3/PDCD10 protein is strongly expressed in arterial endothelium but not or barely detectable in venous endothelium of extra-cerebral tissues. The expression pattern of CCM3/PDCD10 in multiple organ systems displays similarities to CCM1 and CCM2. As a result of this, PDCD10/CCM3 is highly expressed in the neurovascular unit and in the arterial endothelium of multiple organ systems, including the brain.In embryonic mouse brain, Ccm3 mRNA was observed in the ventricular, subventricular, intermediate zones, the cortical plate, the developing septum, striatum, midbrain, pons, cerebellum, and medulla. In the postnatal mouse brain, we detected Ccm3/PDCD10 expression in the olfactory bulb, neocortex, striatum, septal nuclei, hippocampus, dentate gyrus, thalamic and hypothalamic nuclei, inferior colliculus, Purkinje, granule cell layers , deep nuclei of the cerebellum, in many cells and nuclei of the medulla.In order to investigate the apoptotic effects of the gene we used a cloning protocol and also, investigated the expression of CCM3. After cloning of the PDCD10 in cell lines we showed that it increases levels of TUNEL expression and also confirmed by DAPI labelling in the nuclei of the cell lines.These results demonstrate that Ccm3 plays an active role in neurovascular angiogenesis by inducing endothelial cell migration throughout postnatal life and also induces the apoptotic process. In conclusion, we suggest that CCM lesions may occur as a consequence of aberrant apoptosis, potentially altering the balance between the endothelium and neural cells within the neurovascular unit.Keywords: PDCD10, cerebral cavernous malformation, CCM, apoptosis, neurovascular unit