VDL Groep (Netherlands)

Phenotypic plasticity is the ability of cells to switch from one identity to another without alterations in genotype. In the healthy intestine, plasticity occurs in response to stem cell loss and facilitates tissue regeneration, while in cancer it contributes to therapeutic resistance, metastasis, and immune evasion. Human organoid models have emerged as a powerful platform for studying phenotypic plasticity in vitro. To study plasticity in the human intestine, this thesis employed a combination of CRISPR/Cas9 genome editing and organoid models. In particular, we used in-trans paired nicking (ITPN) to seamlessly integrate fluorescent knock-in reporters while minimizing off-target effects. In normal human colon organoids, we developed a novel cell type-specific ablation tool based on the diphtheria toxin receptor (DTR), which had not previously been feasible in a human context. Following the selective elimination of LGR5⁺ stem cells, surviving colonocytes respond by reprogramming to the stem cell state. Transcriptomic profiling of this regenerative response revealed the upregulation of injury-induced gene programs and identified a role for retinoic acid (RA), a ligand secreted by stem cells, as a suppressor of plasticity during homeostasis. These findings indicate that stem cells actively repress regenerative plasticity in their progeny by producing RA. To study plasticity in early colorectal cancer (CRC), we established a biobank of early-stage CRC organoids and performed spatial transcriptomic analyses of patient tumor tissues. We identified high-relapse cells specifically at the invasive fronts, where they co-localize with trophocyte-like fibroblasts. These fibroblasts interact with tumor cells to drive the expression of metastatic transcription programs. We validated this interaction using organoid-fibroblast co-cultures and showed that it is mediated by TGF-β and prostaglandins. In conclusion, the human intestinal epithelium displays high levels of phenotypic plasticity in regeneration and cancer. In the healthy intestine, regenerative plasticity is normally suppressed by the stem cells, while in early-stage colorectal cancer, fibroblasts at the invasive front promote metastatic cellular programs in the tumor. These insights into the molecular mechanisms of cell fate plasticity will be instrumental to modulate regenerative processes in therapeutic interventions.

Chronic kidney disease and pregnancy are not a rare combination. In the Netherlands, approximately 4.5% of women aged 20 to 44 have a form of chronic kidney disease. Among a subset of these patients who develop kidney failure under the age of 50, around 20% have a hereditary kidney disease. Many of these women have questions about pregnancy: What does it mean for their own health? What are the risks for their baby? And what are the chances of passing on the disease? Pregnancy in women with kidney disease carries increased risks, such as high blood pressure, preeclampsia, and preterm birth. For a long time, the exact risks and long-term impact of pregnancy on maternal kidney function remained unclear. This thesis provides answers. It shows that pregnancy is often possible, even after a kidney transplant. The better the kidney function before pregnancy, the better the outcomes for both mother and child. Furthermore, this thesis highlights that understanding pregnancy outcomes for specific kidney diseases—even down to the precise hereditary type—helps in predicting risks more accurately and providing women with more tailored counseling. Both men and women with hereditary kidney disease should be well-informed about their reproductive options, including embryo selection to prevent passing on the disease, as well as the importance of follow-up care for children at risk. Providing this information in a timely and personalized manner by healthcare professionals with expertise in this field, such as clinical geneticists, gynecologists, and nephrologists, helps patients make informed reproductive decisions. Finally, this dissertation provides recommendations to improve access to genetic diagnostics across Europe, ensuring that individuals with hereditary kidney diseases receive the right care, regardless of where they live.

To standardize and assess the reliability of ultrasonographic assessment of inflammatory and structural lesions in patients with hand osteoarthritis (OA). The Outcome Measures in Rheumatology Ultrasound Working Group selected synovial hypertrophy (SH), joint effusion (JE), and power Doppler (PD) signals as the main inflammatory lesions in hand OA, and suggested osteophytes in the scapho-trapezio-trapezoid (STT) and cartilage defects in the proximal interphalangeal (PIP) joints as novel additions to previous structural scoring systems. A complementary imaging atlas provided detailed examples of the scores. A reliability exercise of static images was performed for the inflammatory features, followed by a patient-based exercise with 6 sonographers testing inflammatory and structural features in 12 hand OA patients. We used Cohen's kappa for intrareader and Light's kappa for interreader reliability for all features except PD, in which prevalence-adjusted bias-adjusted kappa (PABAK) was applied. Percentage agreement was also assessed. The web-based reliability exercise demonstrated substantial intra- and interreader reliability for all inflammatory features (κ > 0.64). In the patient-based exercise, intra- and interreader reliability, respectively, varied: SH κ=0.73 and 0.45; JE κ=0.70 and 0.55; PD PABAK=0.90 and 0.88; PIP joint cartilage κ=0.56 and 0.45; and STT osteophytes κ=0.62 and 0.36. Percentage close agreement was high for all features (>85%). With ultrasound, substantial to excellent intrareader reliability was found for inflammatory features of hand OA. Interreader reliability was moderate, but overall high close agreement between readers suggests that better reliability is achievable after further training. Assessment of osteophytes in the STT joint and cartilage in the PIP joints achieved less reliability and the latter is not endorsed.