Identification of the adhesion GPCR ADGRL4/ELTD1 as a novel potential prognostic biomarker for cerebral cavernous malformation disease

Background: Cerebral cavernous malformations (CCM) are angiographically occult vascular anomalies of the brain, characterized by dilated capillaries, increased vascular permeability, and loss of endothelial junctional protein complexes. Loss-of-function mutations in one of the three genes, namely KRIT1/CCM1, CCM2, and PDCD10/CCM3, have been associated with the disease pathogenesis, although the contribution of other genetic determinants besides CCM genes has been recently identified. Despite recent advances in understanding the molecular mechanism of the disease, the current lack of therapies and its unpredictable clinical behavior represent a significant challenge in the identification of diagnostic biomarkers. ADGRL4/ETLD1 (epidermal growth factor, latrophilin and seven transmembrane domain-containing protein 1), a G-protein coupled receptor (GPCR) protein is a known biomarker of angiogenesis and inflammation, and it has been suggested to be a key therapeutic target for stroke and high-grade gliomas. However, the relevance of ELTD1 in CCM pathogenesis remains unexplored. Methods: Through different analyses, including whole RNA transcriptome, immunohistochemistry, and real-time PCR, conducted in human CCM patients, cellular and animal models, herein we show the association between CCM disease and ELTD1. Results: The whole RNA transcriptome approaches demonstrated ELTD1 is differentially expressed, and gene expression analysis revealed it is significantly upregulated in surgically resected tissue and plasma samples from CCMs, and clinical correlation analysis showed that increased ELTD1 associates with the presence of Focal Neurological Deficits in patients. Immuno-expression showed a strong ELTD1 immunoreactivity in endothelial cells lining affected lesions. According to these elevated levels of ELTD1 in human patients, we also showed a robust increase in the expression level of ELTD1 in cellular and animal models of CCM disease. Conclusions: Taken together, our results demonstrate for the first time ELTD1 involvement in CCM pathogenesis, and its tight link with CCM genes. Thanks to this putative new prognostic biomarker, future clinical studies in larger patient cohorts will aim at improving the CCM disease management and risk stratification in patients, as well as placing the basis for targeted therapeutic strategies in CCM.