Cerebral Cavernous Malformations (CCM) is a neurovascular disease affecting up to 0.5% of the population. CCM are mulberry-like lesions found primarily in blood capillaries of the brain that are thought to be the result of junctional defects between endothelial cells lining the capillaries. This causes blood to leak into the brains of CCM patients and can cause symptoms that range from headaches and seizures to hemorrhagic stroke. Unfortunately, there are currently no pharmacological treatments for this disease, leaving invasive neurosurgery the sole treatment option.
Familial CCM follows an autosomal dominant inheritance pattern caused by loss-of-function mutations in one of three genes: CCM1/KRIT-1, CCM2/Malcavernin and CCM3/PDCD10. To study the biological functions of these genes, which encode three different scaffold proteins, we use the nematode worm Caenorhabditis elegans as an in vivo model system. Our work has revealed mechanistic insight into how the CCM1 and CCM3 proteins regulate cross-tissue signalling and vascular integrity.
This project has been highly collaborative involving many scientists in Toronto (Drs. Ian Scott, Anne-Claude Gingras and Peter Roy), Berlin (Dr. Salim Seyfried), and Paris (Dr. Elisabeth Tournier-Lasserve). Our team is also sequencing the genomes of CCM patients to help identify additional genes that modify the spectrum and severity of this disease.
Currently we are working on the following projects
After showing that ccm-3 is required for the integrity of unicellular and multicellular biological tubes we are exploiting this model to identify a comprehensive set of genes that cooperate with ccm-3. Using genetics and reverse genetics approaches we have identified several genes that cause similar phenotypes as ccm-3 mutants (excretory canal truncations and germline membrane defects).
Like multicellular mammalian tubes such as blood vessels, the C. elegans excretory canal has apical and basal surfaces and utilizes conserved biological
processes during its developmental. For example, work by Dr. Benjamin Lant showed that CCM-3 and its associated protein complex (STRIPAK) regulate
endocytic recycling to promote excretory canal extension and membrane integrity. We are currently interrogating the functions of genes that cooperate with
CCM-3 in this cell. In collaboration with Anne-Claude Gingras we have identified protein binding partners for CCM-3 and KRI-1.
More on this can be found here.
Unlike the unicellular excretory canal, the germline is a multicellular tube-like structure, which Dr. Swati Pal has shown to require CCM-3 for its development. Loss of ccm-3 dampens multiple signal transduction pathways that lead to collapse of a tubular germline structure called the rachis, which results in abnormally small oocytes that render the animal sterile.
CCM-3 localizes along the apical (luminal) membrane of the germline to regulate cytoskeletal proteins called anilins, as well as endocytic recycling proteins similar to what we observed in the excretory canal. In early embryos, CCM-3 localizes to the cytokinetic furrow to promote cytokinesis. Loss of CCM-3 in early embryos causes mislocalization of polarity proteins that lead to polarity defects and arrested development due to cytokinesis defects. We have developed tools to control CCM-3 protein levels at various stages of development to determine when it is required for polarity establishment, cytokinesis, and germline development.
We have completed a screen for genes that cooperate with CCM-3 but now want to suppress ccm-3 mutants, so PhD candidate Evelyn Popiel has been carrying out a mutagenesis screen to restore fertility in ccm-3 mutant worms. In addition, we are collaborating with Dr. Issam Awad at the University of Chicago to perform RNA sequencing of ccm-3 mutant worms, mice and CCM3 patient samples. We anticipate that this will uncover conserved genes that function downstream of CCM3 across phyla, and identify potential pharmacological targets.
Small molecule screen. In collaboration with an international team we obtained an E-RARE grant to screen small molecule libraries in C. elegans (Derry and Peter Roy), zebrafish (Salim Seyfried), endothelial cells (Corrine Abigles-Rizo and Eva Faurobert), and preclinical modeling of the top candidates in mouse CCM models (Elisabeth Tournier-Lasserve). From this screen we have identified several small molecules that suppress defects caused by loss of CCM proteins in worms, fish and human cells.
Dr. Ben Lant