Ewart Kuijk

Background: Pediatric Inflammatory Bowel Disease (IBD) is a chronic condition characterized by persistent intestinal inflammation in children. It often presents with distinct clinical phenotypes and is more frequently linked to rare monogenic variants affecting epithelial barrier function or mucosal immunity. Although over 100 genes are associated with monogenic IBD, their roles in the intestinal epithelium remain poorly defined. This study aimed to improve our understanding of epithelial dysfunction in early-onset IBD through molecular and cellular analyses to uncover patient-specific phenotypes and potential therapeutic targets. Methods: We generated intestinal epithelial organoids (IEOs) from 94 pediatric IBD patients, including those with monogenic variants (BTK, TTC7A, IL10RA, LRBA, STXBP2, TRNT1, SKIV2L), along with 46 non-IBD controls. RNA sequencing was performed on 38 patient and 20 control lines, under both baseline conditions and after immunological stimulation, yielding a valuable dataset for studying epithelial responses in IBD. Results: IEOs effectively initiated inflammation upon bacterial lysate stimulation, regardless of disease status, origin, or genotype. Inflammatory stimulation triggered upregulation of IBD-linked genes SERPINA1 and LIFR in IBD organoids, suggesting their role in epithelial innate immunity. However, network analysis showed no consistent transcriptional signatures across all IBD cases. Instead, specific genotypes (TTC7A, STXBP2, LRBA) revealed responses, with STXBP2 and LRBA showing shared upregulation of IL-1 and SLC30-mediated zinc trafficking pathways. Conclusions: These findings underscore the potential of IEOs as a valuable model for studying IBD and offer key insights that could guide the development of targeted therapies for both monogenic and non-monogenic forms of IBD.

Intestinal epithelial cells (IECs) are capable of mounting an adequate antimicrobial inflammatory response to pathogens while tolerating commensals. The underlying regulatory mechanisms of immune sensitivity remain incompletely understood, particularly in the context of human IECs. To enhance our understanding of the immune response of IECs to bacterial epithelial barrier breach, we investigated whether epithelial responsiveness is contingent on cell identity and cell polarization. We exposed human intestinal organoids to bacterial antigens to study their immune responses. Notable discrepancies were observed in the specific reactions exhibited by intestinal stem cells (ISCs) and enterocytes. It was determined that basolateral exposure of IECs to bacterial antigens resulted in a robust response, whereas apical exposure elicited a significantly more modest response. We identified ISCs as the principal responders, while the reaction of enterocytes was found to be attenuated. The regulation of bacterial responsiveness in enterocytes occurs at multiple levels, including the modulation of NFκB activation and post-transcriptional control of mRNA stability. Our findings demonstrate that differentiated non-responsive enterocytes can be sensitized to bacterial antigens through the activation of the WNT pathway. These findings extend the crucial role of WNT signaling for intestinal epithelial homeostasis and regulation of stem cell maintenance, proliferation, differentiation, and tissue architecture in the gut. Additionally, they reveal a new function of WNT signaling in regulating microbial responses within the intestinal environment.

Pediatric Inflammatory Bowel Disease (IBD) is a chronic condition characterized by per-sistent intestinal inflammation in children and adolescents. Despite a rising global incidence, the underlying causes and optimal management strategies for pediatric IBD are still not fully understood. Compared to adult IBD, pediatric IBD frequently presents with distinct disease phenotypes, and is more commonly linked to rare monogenic variants that cause intestinal epithelial barrier dysfunction or affect the function of mucosal immune cells. While more than 100 genes have been associated with early-onset IBD, the roles of many of these genes in the intestinal epithelium and the mechanisms by which genetic variants contribute to disease remain poorly defined. Here we aimed to improve our understanding of intestinal epithelium dysfunction in early-onset IBD by conducting extensive molecular and cellular characterization to gain insights into patient-specific epithelial phenotypes and identify therapeutic targets. We generated intestinal epithelial organoids (IEOs) from 94 pediatric IBD patients, representing diverse clinical characteristics and including those with monogenic variants ( BTK n=4, TTC7A n=3, IL10RA n=1, LRBA n=1, STXBP2 n=1, TTC37 n=1, TRNT1 n=1, PLCG2 n=1, DKC1 n=1, POLA1 n=1), and 46 non-IBD controls. This effort resulted in the largest RNA-seq dataset of pediatric IBD intestinal epithelial organoids to date, encompassing both baseline conditions and post-immunological stimulation, serving as a valuable resource for future research. We observed that IEOs effectively initiate inflammation upon stimulation with bacterial lysate, regardless of disease status, origin, or mutation status. Inflammatory stimulation triggered single-gene upregulation of IBD-linked SERPINA1 and LIFR across the IBD population compared to controls, suggesting their role in intestinal epithelial innate immune responses. However, co-expression network analysis showed no consistent transcriptional signatures across the entire IBD group at the systems level. Instead, differences emerged between controls and specific genotypes ( TTC7A , STXBP2 , LRBA ), with STXBP2 and LRBA sharing an upregulated transcriptional response of IL-1 and SLC30-mediated zinc trafficking pathways. These findings underscore the potential of IEOs as a valuable model for studying IBD and offer key insights that could guide the development of targeted therapies for both monogenic and non-monogenic forms of IBD. Abstract Figure:

Pathogenic mutations in Tetratricopeptide repeat domain 7A ( TTC7A ) result in gastrointestinal and immunological disorders of which the pathobiology is not fully understood. Previous case reports indicate that TTC7A plays an important role in preserving intestinal epithelial integrity, but thus far only few variants have been investigated and it is unclear if different variants exert the same effects. Here, we aim to study the effects of different variants on the intestinal epithelium. We present three instances of pediatric inflammatory bowel disease (IBD), displaying varying clinical symptoms and severity levels, and associated with different heterozygous missense mutations in TTC7A . Intestinal organoids derived from patients show dissimilar epithelial phenotypes and exhibit differences in growth, morphology, apicobasal polarity, responses to specific drugs, TTC7A expression, and transcriptional profiles. The findings of our study suggest differences in pathobiology between individuals with different TTC7A mutations. This investigation enhances our comprehension of TTC7A-related conditions and can have implications for developing targeted therapies for TTC7A-associated disorders.

Intestinal epithelial cells (IECs) are capable of mounting an adequate antimicrobial inflammatory response to pathogens while tolerating commensals. The underlying regulatory mechanisms of immune sensitivity remain incompletely understood, particularly in the context of human IECs. To enhance our understanding of the immune response of IECs to bacterial epithelial barrier breach, we investigated whether epithelial responsiveness is contingent on cell identity and cell polarization. We exposed human intestinal organoids to bacterial antigens to study their immune responses. Notable discrepancies were observed in the specific reactions exhibited by intestinal stem cells (ISCs) and enterocytes. It was determined that basolateral exposure of IECs to bacterial antigens resulted in a robust response, whereas apical exposure elicited a significantly more modest response. We identified ISCs as the responders, while the reaction of enterocytes was found to be attenuated. The regulation of bacterial responsiveness in enterocytes occurs at multiple levels, including the modulation of NFκB activation and post-transcriptional control of mRNA stability. Our findings demonstrate that differentiated non-responsive enterocytes can be sensitized to bacterial antigens through the activation of the WNT pathway. These findings extend the crucial role of WNT signaling for intestinal epithelial homeostasis and regulation of stem cell maintenance, proliferation, differentiation, and tissue architecture in the gut. Additionally, they reveal a new function of WNT signaling in regulating microbial responses within the intestinal environment.

Biallelic mutations in tetratricopeptide repeat domain 7A (TTC7A) give rise to intestinal and immune disorders. However, our understanding of the genotype–phenotype relationship is limited, because TTC7A variants are mostly compound heterozygous and the disease phenotypes are highly diverse. This study aims to clarify how different TTC7A variants impact the severity of intestinal epithelial disorders. We individually characterized the molecular and cellular consequences of 11 different TTC7A missense mutations in TTC7A knockout Caco-2 cells. We examined variant-specific RNA expression profiles, TTC7A protein abundance, and endoplasmic reticulum (ER) stress by using RNA sequencing and imaging flow cytometry. For six variants we detected no significant alterations on these assays, suggesting that protein function may not be severely compromised. However, for five variants we observed molecular phenotypes, with overlapping gene expression signatures between specific variants. Remarkably, the TTC7AE71K variant displayed a unique expression profile, along with reduced TTC7A RNA and protein expression, which set it apart from all other variants. The findings from this study offer a better understanding of the role of specific TTC7A variants in disease and provide a framework for the classification of the variants based on the severity of impact. We propose a classification system for TTC7A variants that could help diagnosis, guide future treatment decisions and may aid in developing effective molecular therapies for patients that carry specific TTC7A variants.

DNA methylation is important for establishing and maintaining cell identity and for genomic stability. This is achieved by regulating the accessibility of regulatory and transcriptional elements and the compaction of subtelomeric, centromeric, and other inactive genomic regions. Carcinogenesis is accompanied by a global loss in DNA methylation, which facilitates the transformation of cells. Cancer hypomethylation may also cause genomic instability, for example through interference with the protective function of telomeres and centromeres. However, understanding the role(s) of hypomethylation in tumor evolution is incomplete because the precise mutational consequences of global hypomethylation have thus far not been systematically assessed. Here we made genome-wide inventories of all possible genetic variation that accumulates in single cells upon the long-term global hypomethylation by CRISPR interference-mediated conditional knockdown of DNMT1. Depletion of DNMT1 resulted in a genomewide reduction in DNA methylation. The degree of DNA methylation loss was similar to that observed in many cancer types. Hypomethylated cells showed reduced proliferation rates, increased transcription of genes, reactivation of the inactive X-chromosome and abnormal nuclear morphologies. Prolonged hypomethylation was accompanied by increased chromosomal instability. However, there was no increase in mutational burden, enrichment for certain mutational signatures or accumulation of structural variation to the genome. In conclusion, the primary consequence of hypomethylation is genomic instability, which in cancer leads to increased tumor heterogeneity and thereby fuels cancer evolution.

Genome-wide mutation analyses have revealed that specific anti-cancer drugs are highly mutagenic to cancer cells, but the mutational impact of anti-cancer therapies on normal cells is not known. Here, we examine genome-wide somatic mutation patterns in 42 healthy adult stem cells (ASCs) of the colon or the liver from 14 cancer patients (mean of 3.2 ASC per donor) that received systemic chemotherapy and/or local radiotherapy. The platinum-based chemo-drug Oxaliplatin induces on average 535 ± 260 mutations in colon ASC, while 5-FU shows a complete mutagenic absence in most, but not all colon ASCs. In contrast with the colon, normal liver ASCs escape mutagenesis from systemic treatment with Oxaliplatin and 5-FU. Thus, while chemotherapies are highly effective at killing cancer cells, their systemic use also increases the mutational burden of long-lived normal stem cells responsible for tissue renewal thereby increasing the risk for developing second cancers.