Konstantin Gängel's research projects on vascular malformations and anomalies
Developing better models to study vascular anomalies
We are committed to developing better models that recapitulate the complexity of human vascular anomalies. We currently focus most of our efforts on a disease called Cerebral Cavernous Malformations (CCM). Patients with CCM suffer from vascular malformations that predominantly form in the brain and affect the capillary-venous vasculature.
CCM lesions can grow to several centimeters in size and impose a serious threat as the affected blood vessels are prone to leak and their rupture can result in life-threatening brain bleedings. In addition, blood clots can form in the malformed vessels and result in vessel occlusion and ischemia. Common symptoms include headaches, focal neurological deficits, epileptic seizures and paralysis. At present, there is no pharmacological treatment for CCM available and neurosurgical resection of the vascular lesions is the only available intervention.
CCM lesions can develop spontaneously but in about 20% of the cases there is a familiar history and mutations in three genes CCM1 (KRIT1), CCM2 and CCM3 (PCDC10) have been linked to the disease. The predisposition to develop the disease is given through heterozygous germline mutations in any of the CCM genes, but unless a second-hit somatic mutation occurs in the healthy allele the disease won’t develop. For a long time CCM1, CCM2 and CCM3 have been the only genes linked to the disease but recent studies have shown that about 70% of CCMs (both familial and sporadic) carry also somatic PIK3CA gain-of-function mutations. In addition, in a subset of CCMs, MAP3K3 gain-of-function mutations have been identified and polymorphisms that increase the expression of the innate immune receptor TLR4 or its co-receptor CD14 have been associated with increased CCM lesion burden.
In order to understand the role of the different pathways implicated in CCM disease, we are developing new mouse models based on human mutations. These mouse models will allow us to better investigate the cellular and molecular basis of the disease and to test promising drugs for intervention.
Characterization of the gene expression patterns underlying vascular malformations
In order to characterize the molecular changes that underlay the formation of vascular malformations, we are using single-cell RNA sequencing approaches. Using this technique, we hope to gain further insides into the interplay of the various pathways involved in lesion formation and growth. Our hope is to discover new biomarkers and to identify potential drug targets. Our long-term aim is to provide the scientific community with comprehensive searchable databases from animal models and human CCM lesions.
Defective endothelial cell migration can trigger the formation of vascular malformations
Several pathways have been implicated to contribute to the growth of CCM lesions, but what causes their initial formation is still poorly understood. Interestingly, one of the earliest cellular events that precede and subsequently trigger vascular malformations appears to be defects in endothelial cell migration. The Rho GTPase Cdc42 is a key regulator of cellular motility and migration and we are using genetic approaches to study its role in vascular malformations.
Endothelial-specific deletion of Cdc42 in neonatal mice results in the formation of multiple cavernous malformations in both the retinal and brain vasculature. Those lesions resemble human CCM lesions as well as lesions in existing CCM mouse models in location, morphology and molecular characteristics. Using mosaic analysis to specifically label and trace Cdc42 depleted endothelial cells in otherwise normal tissues, we could demonstrate that endothelial cell migration defects precede and subsequently trigger the formation of vascular malformations.
Interestingly, during vascular development, migration defects only seem to impose a problem in capillaries and veins, areas in which endothelial cells naturally proliferate at a higher rate than in arteries. The high proliferation rates in capillaries and veins lead to the local amplification and accumulation of migration defective endothelial cells which form initially small lesions that subsequently progress into the characteristic mulberry-shaped cavernous vascular malformations. This also might explain why CCM lesions are restricted to capillaries and veins and why arteries remain unaffected.
Intravital imaging of vascular anomalies
By using advanced intravital microscopy techniques we hope to gain a better understanding of the events that lead to the growth and progression of vascular malformations in CCM and to study defects of blood vessel function in other types of vascular anomalies. These techniques allow us to study blood flow, vascular leakage, blood clot formation and immune cell infiltration in CCM mouse models and the contraction of smooth muscle cells in other types of vascular anomalies. Longitudinal studies provide us with unique insights into the dynamics that underlay the growth of vascular malformations and allow us to characterize the sequence of events.
The role of mural cells in vascular malformations
We are also studying to what degree non-endothelial cells contribute to the formation of vascular malformations and are currently focusing on mural cells in this context. Mural cells are perivascular cells that are tightly associated with blood vessels. Depending on their location and molecular properties we distinguish two types of mural cells: vascular smooth muscle cells (vSMCs), which are associated with the bigger caliber vessels, arteries, arterioles, veins and venules and pericytes (PC), which cover capillaries, the smallest diameter blood vessels. Mural cells are essential for vascular integrity, and their loss has been associated with numerous diseases, yet little is known about their role in vascular malformations.
We have recently generated a mouse model that allows us to delete the Serum Response Transcription Factor (SRF) in mural cells and found that its deletion causes the formation of arterio-venous malformations in retinal blood vessels (Fig 2). SRF positively regulates the expression of smooth muscle genes and by deleting SRF, the smooth muscle cells lose their ability to contract and to maintain the vascular tone. This has severe consequences since the affected blood vessels cannot regulate blood flow any longer which results in reduced oxygenation and long-term tissue damage. In an attempt to normalize blood flow some branches remodel into arteriovenous shunts that funnel a proportion of the blood directly to the venous circulation.
We are currently also studying the role of mural cells in lymphatic malfunction. Inducible mural cell- specific deletion of the SRF transcription factor (SrfiMCKO) leads to the formation of arterio-venous malformations in retinas of mice at postnatal day 25.
Read more about the role of mural cells in vascular malformations in the article Mural Cell SRF Controls Pericyte Migration, Vessel Patterning and Blood Flow.