Thoracic aortic aneurysm

Using human iPSC-derived models to investigate the divergent pathomechanisms underlying biglycan-related Meester-Loeys syndrome and X-linked spondyloepimetaphyseal dysplasia.

Pathogenic variants in biglycan cause two divergent phenotypes: Meester-Loeys syndrome (MRLS) and X-linked spondyloepimetaphyseal dysplasia (SEMDX). The latter is characterized by a disproportionate short stature and caused by missense variants. MRLS, on the other hand, is a syndromic form of thoracic aortic aneurysm that is caused by loss-of-function variants. Intriguingly, MRLS patients with partial biglycan deletions present with a more severe skeletal phenotype. To date, discriminative pathomechanisms explaining why certain biglycan mutations cause MRLS and others SEMDX remain elusive. This PhD project aims to answer this research question using induced pluripotent stem cells (iPSCs) of both patient groups and their respective (isogenic) controls. IPSC-based disease modeling provides a unique opportunity for pathomechanistic investigation in a patient-, variant- and cell type-specific manner. After the creation of disease-relevant patient-derived iPSC-vascular smooth muscle cells and -chondrocytes, I will identify cell type-specific differences between MRLS and SEMDX using (1) functional assays tailored to existing pathomechanistic insights, and (2) hypothesis-free transcriptomic and proteomic approaches. Finally, I will investigate the mutational effect of partial biglycan deletions to establish a specific MRLS genotype-phenotype association.

PhD student: Anne Hebert
Promotors: Bart Loeys, Aline Verstraeten & Josephina Meester

Investigating thoracic aortic aneurysm pathogenesis at single-cell resolution.

Thoracic aortic aneurysm (TAA) is an abnormal widening of the aorta in the chest, caused by the weakening of the aortic wall. TAAs can lead to rupture or dissection, a devastating complication with a mortality rate of 50%. Despite considerable efforts to gain insights on the molecular mechanisms underlying TAAs, there is currently no therapy that effectively stops or reverses TAA development. Single-cell RNA sequencing (scRNA-seq) is emerging as a ground-breaking technology to investigate gene expression at single-cell level and is opening new avenues to discover yet unexplored disease pathways. In my project, I will apply this technique to investigate a novel TAA disorder caused by biallelic pathogenic variants in the IPO8 gene, recently discovered in our Cardiogenomics research group. I will search for differentially expressed genes (DEGs) within the different aortic cell populations from an Ipo8^-/- mouse model that recapitulates the human aortic aneurysmal phenotype. I will also investigate shared DEGs between Ipo8^-/- mice and additional TAAs mouse models to find convergent disease pathways in clinically related TAA disorders. Subsequently, I will validate the role of the identified candidate culprits in mouse TAA development in a human setting, by using CRISPR-inhibition or -activation in iPSCs derived vascular smooth muscle cells or endothelial cells. The predicted outcomes will potentially pinpoint novel TAA drivers and hence, unveil potential new therapeutic targets.

PhD student: Irene Valdivia Callejon
Promotors: Aline Verstraeten, Bart Loeys & Josephina Meester

Thoracic aortic aneurysm (TAA) refers to progressive enlargement of the thoracic aorta. It often remains unnoticed until aortic dissection or rupture occur, which are associated with high mortality rates. Available drug therapies slow down TAA progression but fail to prevent the associated lethal complications. TAA is a hallmark of Loeys-Dietz syndrome (LDS), a rare connective tissue disorder characterized by an early onset and aggressive TAA course.

Leveraging the in-house expertise in induced pluripotent stem cell (iPSC)-based disease modeling and both clinical and pathophysiological LDS research, I aim to be the first to develop an LDS iPSC-derived aorta-on-a-chip (AoC) model, which comprises both endothelial cells and vascular smooth muscle cells, and mimics the concentric-layered structure of the native aorta. Following establishing and validating a control proof-of-concept model, I will demonstrate exhibition of the known LDS pathomechanisms and drug responses in SMAD3 patient AoCs. Moreover, I will investigate if the LDS-AoCs can accurately recapitulate between-patient variability in TAA severity. This novel pre-clinical tool will enable the exploration and therapeutic targeting of LDS mechanisms in a human setting that mimics the native aorta better than ever before. Additionally, the expected outcomes will hold a broader significance for aortic diseases, as the AoC expertise developed within this project can be extended to other TAA conditions and/or aortopathies.

Towards patient-specific aorta-on-a-chip models for thoracic aortic aneurysm and dissection.

Thoracic aortic aneurysm (TAA) denotes a progressive enlargement of the thoracic aorta, entailing a significant risk for life-threatening aortic dissection and/or rupture. At present, mouse models are often used to investigate and therapeutically target the molecular defects underlying TAA, as native aortic samples of patients and, especially, control individuals are hard to collect. Yet, murine in vivo studies are often lengthy and drug testing results did previously not always recapitulate in patients. With the advent of induced pluripotent stem cells (iPSCs), the field is closing in on apt solutions to faithfully model patient and control aortas in a dish. The currently available vascular smooth muscle cell (VSMC) or endothelial cell (EC) monocultures are still overly simplified, as they fail to adequately replicate the complex multilayered and multicellular structure of the aorta. Taking advantage of available iPSCs from syndromic TAA patients (FBN1 & IPO8), my project aims to 1) develop and consolidate the validity of the first iPSC-derived TAA aorta-on-a-chip models, comprising the two VSMC subtypes populating the native ascending aorta along with a layer of arterial ECs, and 2) use the established model to further investigate the disease mechanisms underlying the relatively unexplored IPO8 syndrome. The anticipated outcomes will contribute to the replacement of mouse models (3R principle) and expedite pathophysiological TAA research and drug discovery.

PhD student: Ivanna Fedoryshchenko
Promotors: Aline Verstraeten, Bart Loeys, Ilse Luyck