Research Josephina Meester

Abstract

Progressive dilatation of the thoracic aorta leads to the development of thoracic aortic aneurysms (TAAs), which are often asymptomatic but predispose to dissection and rupture. The latter are associated with high mortality rates. Even though over 40 TAA genes have been identified in the past, the cause remains elusive for the majority of patients (70% of familial and 85-90% of sporadic patients), despite exhaustive Mendelian whole exome sequencing efforts for both single nucleotide variants and copy number variant detection of the coding exons of these TAA genes. Moreover, all recently identified genes each only explain very small proportions (<1%) of previously genetically elusive TAA patients. Hence, there is a need to explore novel avenues that move beyond these traditional approaches. Various types of previously un(der)explored genetic variants may explain the missing TAA heritability. In this project, I will therefore determine (1) which proportion of sporadic TAA patients can genetically be explained by the presence of somatic mutation in affected aortic tissue using deep whole exome sequencing and (2) what is the role of (non-coding) structural variants in the development of TAA using short- and long-read whole genome sequencing.

Researcher(s)

• Promoter: Loeys Bart
• Fellow: Meester Josephina

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

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.

Researcher(s)

• Promoter: Loeys Bart
• Co-promoter: Meester Josephina
• Co-promoter: Verstraeten Aline
• Fellow: Hebert Anne

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

Chondrodysplasias refer to a large and heterogeneous group of skeletal disorders caused by primary defects in hyaline cartilage. They have a combined prevalence of about 1/4000 births and differ considerably with respect to disease severity; with some only inflicting mild joint symptoms, and others coming with severe dwarfism or even perinatal lethality. Especially the complications that arise from major growth problems (e.g. respiratory difficulties, spinal cord compression, hydrocephaly) impact significantly on the patient's quality of life. For many chondrodysplasias no therapies are on the market yet. Over the past years, endoplasmatic reticulum (ER) stress and the resulting excess of apoptosis have emerged as convincing converging chondrodysplasia pathomechanisms. This project builds further on these findings and aims to significantly improve future chondrodysplasia patient management by 1) establishing the protocols to create and study iPSC-chondrocytes as well as to use them for high-throughput drug screening approaches, with a primary focus on COL2A1 and BGN-related dysplasias, 2) investigating whether ER stress and UPR activation play a role in the etiology of BGN-related chondrodysplasia (i.e. a pathomechanistically unexplored severe form of dwarfism), and 3) developing and applying a novel iPSC-chondrocyte-based high-throughput high content assay to discover putative drug candidates that promote protein folding in ER stress-related chondrodysplasias.

Researcher(s)

• Promoter: Verstraeten Aline
• Co-promoter: Meester Josephina
• Fellow: De Kinderen Pauline

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

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 bi-allelic 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.

Researcher(s)

• Promoter: Verstraeten Aline
• Co-promoter: Loeys Bart
• Co-promoter: Meester Josephina
• Fellow: Valdivia Callejon Irene

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

Thoracic aortic aneurysm (TAA) is an abnormal widening of the thoracic aorta caused by blood vessel wall weakness. TAAs entail a high risk for aortic rupture or dissection, commonly leading to sudden death. To date, genetic defects in >35 genes have been linked with TAA, providing a molecular cause for about 30% of patients. Their identification and functional characterization have been key in acquiring our current pathomechanistic aortopathy knowledge. Yet, the genetic and mechanistic picture for TAA is far from complete, hampering identification of predictive markers for aneurysm formation and development of therapies capable of stopping or reversing aneurysm formation. In search for novel TAA genes, our research group most recently identified recessive truncating IPO8 mutations as a novel cause of syndromic TAA. This project builds on this exciting finding, remarkable Ipo8-/- mouse background differences and the availability of IPO8 mutant iPSCs and isogenic controls. More specifically, we aim to significantly improve our current pathomechanistic insight in TAA caused by IPO8 deficiency based on 1) transcriptomics to unravel the involved biological pathways; and 2) identification of proteins and miRNAs with an abnormal cytosol/nucleus distribution upon IPO8 depletion. In the long term, this project's anticipated results will identify new targets for drug therapies, improving TAA patient management.

Researcher(s)

• Promoter: Loeys Bart
• Co-promoter: Meester Josephina
• Co-promoter: Verstraeten Aline
• Fellow: Buccioli Lucia

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

The aorta is the body's main artery and supplies oxygenated blood to all parts of the body. Progressive dilatation of the aorta leads to the development of thoracic aortic aneurysms and dissections (TAADs), which are often asymptomatic but predispose to aortic dissection and rupture. The latter are associated with high mortality rates. In 2017, I identified mutations in BGN (Biglycan), an X-linked gene, as a novel cause of a severe syndromic form of TAAD, which shows clear clinical overlap with Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS), and is now designated as Meester-Loeys syndrome (MRLS). Based on the current knowledge, it remains unknown which molecular mechanisms explains how loss-of-function mutations in BGN lead to syndromic TAAD (MRLS). Within this project, I aim to further unravel the pathomechanism underlying MRLS using (single cell) transcriptomic approaches in an in vivo BALB/cA Bgn KO mouse model and validate these findings in an in vitro human iPSC-VSMC model. The expected results will be beneficial for genetic counselling and clinical follow-up of the families. Furthermore, they can lead to the development of more personalized preventive therapeutic strategies. In the long run, I anticipate that our research group will also use these mouse and cell models for drug compound screenings for syndromic TAAD.

Researcher(s)

• Promoter: Meester Josephina
• Co-promoter: Loeys Bart

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder with pleiotropic ocular, skeletal and cardiovascular manifestations. Morbidity and mortality are mostly determined by aortic root aneurysm, dissection and rupture. Although mutations in FBN1, coding for fibrillin-1, are the sole genetic MFS cause, there is a poor correlation between the MFS phenotype and the nature or location of the FBN1 variant. Wide intra- and interfamilial phenotypic variability, ranging from completely asymptomatic to sudden death at young age, is observed. The precise mechanisms underlying this variability remain elusive. In this project, we have selected an innovative strategy to fully understand the functional effects of the FBN1 mutation and discover genetic modifiers of MFS aortopathy with the following objectives: (1) CRISPR/Cas9 correction of the recurrent FBN1 p.Ile2585Thr in patient-derived iPSC-VSMCs and functional comparison to FBN1 mutant and control iPSC-VSMCs. (2) Whole genome and RNA-sequencing of patient iPSC-VSMCs at the extreme ends of the phenotypical spectrum for genetic modifier identification. (3) CRISPR-modification for validation of their modifying capacities. The understanding of the functional effects of the FBN1 mutation and the identification of genetic modifiers will advance the knowledge on aortopathy-mechanisms beyond current understanding, it will allow to individualize treatment protocols and will offer new leads to novel therapeutic targets.

Researcher(s)

• Promoter: Loeys Bart
• Co-promoter: Meester Josephina

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

Progressive dilatation of the aorta leads to the development of thoracic aortic aneurysms, which are often asymptomatic but predispose to aortic dissection and rupture. The latter are associated with high mortality rates. In 2017, I identified loss-of-function (LOF) mutations in BGN, an X-linked gene, as a novel cause of a severe syndromic form of thoracic aortic aneurysms and dissections (TAAD) and is now designated as Meester-Loeys syndrome (MRLS). The general aim of this proposal is to identify which cell type is the main driver of the development of syndromic TAAD in patients with a BGN mutation. This key question will be addressed by taking advantage of the innovative single cell RNA-sequencing approach in a BGN knock-out mouse model.

Researcher(s)

• Promoter: Meester Josephina

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

The aorta is the body's main artery and supplies oxygenated blood to all parts of the body. A dilatation of the thoracic aorta leads to the development of thoracic aortic aneurysms (TAA). These weakened regions are vulnerable to tearing and this often results in sudden death. In 2016, we identified BGN (Biglycan) as a novel cause of a severe form of TAA, which is now called Meester-Loeys syndrome (MLS). In parallel with our observations, different mutations in BGN were described as the cause of X-linked spondylo-epi-metaphyseal dysplasia (X-SEMD), which is characterized by short stature. Based on the current knowledge, it remains unknown which mechanisms explain why some mutations in BGN lead to X-SEMD and others lead to MLS and why only MLS patients with BGN deletions also develop skeletal symptoms. This project aims to answer these questions by addressing the following objectives: (1) characterization of the disease phenotypes and pathomechanisms in dedicated mouse models of TAA and X-SEMD, (2) the verification of the functional differences between BGN mutations causing MLS versus X-SEMD in a human cell model and (3) the identification of the role of an alternative splice form of the biglycan protein in the development of skeletal features in MLS.

Researcher(s)

• Promoter: Loeys Bart
• Co-promoter: Meester Josephina
• Co-promoter: Mortier Geert

Research team(s)

• Medical Genetics (MEDGEN)

Project type(s)

• Research Project

Abstract

The aorta is the body's main artery and supplies oxygenated blood to all parts of the body. A dilatation of the thoracic aorta leads to the development of thoracic aortic aneurysms (TAA). These weakened regions are vulnerable to tearing and this often results in sudden death. In 2016, I identified BGN (Biglycan) as a novel cause of a severe form of TAA, which is now called Meester-Loeys syndrome (MLS). In parallel with my observations, different mutations in BGN were described as the cause of X-linked spondylo-epi-metaphyseal dysplasia (X-SEMD), which is characterized by short stature. Based on the current knowledge, it remains unknown which mechanisms explain why some mutations in BGN lead to X-SEMD and others lead to MLS and why only MLS patients with BGN deletions also develop skeletal symptoms. This project aims to answer these questions by addressing the following objectives: (1) characterization of the disease phenotypes and pathomechanisms in dedicated mouse models of TAA and X-SEMD, (2) the verification of the functional differences between BGN mutations causing MLS versus X-SEMD in a human cell model and (3) the identification of the role of an alternative splice form of the biglycan protein in the development of skeletal features in MLS.

Researcher(s)

• Promoter: Meester Josephina

Research team(s)

Project type(s)

• Research Project

Abstract

The aorta is the body's main artery and supplies oxygenated blood to all parts of the body. A dilatation of the thoracic aorta leads to the development of thoracic aortic aneurysms (TAA). These weakened regions are vulnerable to tearing and this often results in sudden death. In 2016, I identified BGN (Biglycan) as a novel cause of a severe form of TAA, which is now called Meester-Loeys syndrome (MLS). In parallel with my observations, different mutations in BGN were described as the cause of X-linked spondylo-epi-metaphyseal dysplasia (X-SEMD), which is characterized by short stature. Based on the current knowledge, it remains unknown which mechanisms explain why some mutations in BGN lead to X-SEMD and others lead to MLS and why only MLS patients with BGN deletions also develop skeletal symptoms. This project aims to answer these questions by addressing the following objectives: (1) characterization of the disease phenotypes and pathomechanisms in dedicated mouse models of TAA and X-SEMD, (2) the verification of the functional differences between BGN mutations causing MLS versus X-SEMD in a human cell model and (3) the identification of the role of an alternative splice form of the biglycan protein in the development of skeletal features in MLS.

Researcher(s)

• Promoter: Loeys Bart
• Fellow: Meester Josephina

Research team(s)

Project type(s)

• Research Project

Abstract

Progressive dilatation of the aorta leads to the development of thoracic aortic aneurysms, which are often asymptomatic but predispose to aortic dissection and rupture. The latter are associated with high mortality rates. In 2016, I identified loss-of-function (LOF) mutations in BGN, an X-linked gene, as a novel cause of a severe syndromic form of thoracic aortic aneurysms and dissections (TAAD) and is now designated as Meester-Loeys syndrome (MLS). In parallel with my observations in aneurysmal phenotypes, missense mutations in BGN were described as the cause of an X-linked spondylo-epi-metaphyseal dysplasia (X-SEMD). The general aim of this proposal is to unravel the underlying mechanisms of different BGN mutations in the development of two very distinctive phenotypes: syndromic TAAD (MLS) and X-SEMD. We aim to further unravel these pathomechanisms using detailed phenotypical characterisation and transcriptomics in BALB/cA Bgn male knock-out (LOF) and knock-in (gain-of-function?) mouse models, respectively.

Researcher(s)

• Promoter: Meester Josephina

Research team(s)

Project type(s)

• Research Project

Abstract

The aorta is the body's main artery and supplies oxygenated blood to all parts of the body. A dilatation of the thoracic aorta leads to the development of thoracic aortic aneurysms (TAA). These weakened regions are vulnerable to tearing and this often results in sudden death. In 2016, I identified BGN (Biglycan) as a novel cause of a severe form of TAA, which is now called Meester- Loeys syndrome (MLS). In parallel with my observations, different mutations in BGN were described as the cause of spondylo-epi-metaphyseal dysplasia (SEMD), which is characterized by short stature. Based on the current knowledge, it remains unknown which mechanisms explain why some mutations in BGN lead to X-SEMD and others lead to MLS and why only MLS patients with a BGN deletion also develop skeletal symptoms. This project aims to answer these questions by addressing the following objectives: (1) characterization of the disease phenotypes and pathomechanisms in dedicated mouse models of TAA and SEMD, (2) the verification of the functional differences between BGN mutations causing MLS versus SEMD in a human cell model and (3) the identification of the role of an alternative splice form of the biglycan protein in the development of skeletal features in MLS.

Researcher(s)

• Promoter: Loeys Bart
• Fellow: Meester Josephina

Research team(s)

Project type(s)

• Research Project