Do bad neighbors make bad neighborhoods? Senescent cells as mediators of disease development in murine models of colitis

• Applicant: Dr. Marina Kolesnichenko, Ph.D.
• Subject Area: Gastroenterology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456560492

Patients with inflammatory bowel disease (IBD) are at high risk of developing colorectal cancer (CRC) and complications associated with repeated cycles of inflammation and wound healing. In IBD activation of the transcription factor NF-κB directly correlates with inflammation severity. However, a mouse model that specifically examines the role of NF-κB in intestinal epithelial cells (IEC), instead of upstream kinases with additional NF-κB-independent roles, was missing. We have developed such a model using an IEC-specific knockout of the inhibitor of NF-κB, IκBα (Nfkbia). Key hallmarks of IBD were observed. In addition, constitutive NF-κB upregulated transcription of inflammatory factors, comprising the senescence-associated secretory phenotype (SASP). Cellular senescence is the archetypical wound-healing response that drives inflammation, mediates fibrosis, and promotes tumorigenesis. NF-κB plays a key role in senescence via regulation of SASP. Senescent cells have been detected in IBD patients, yet their characterization has been difficult due to scarcity, and to lack of unique markers. In this project we aim to enable the induction of full-blown senescence in the mouse gut with either constitutively active or repressed NF-κB, by introducing additional environmental stress stimuli, thereby simulating the in vivo situation in IBD patients. We propose that cells at various stages of senescence and pro-tumorigenic capabilities accumulate at sites of DNA damage and inflammation in murine models of colitis and contribute to disease progression. In Work Package 1(WP1) we will identify distinct transcriptional programs in cells at different stages of senescence, and determine the contribution of constitutive NF-κB signaling to senescence and colitis progression. In WP2, we will explore how senescent cells affect their microenvironment in a paracrine manner by using a modified organoid reconstitution assay. This will address the current gap in knowledge – whether proximity of stem cells to senescent cells contributes to pro-tumorigenic changes in the stem-cell compartment. In WP3 we will expand on our findings from the first two work packages and determine whether proximity to senescent cells in vivo precipitates changes reminiscent of those observed in IBD progression. We will likewise determine whether proximity to full-blown senescent cell clusters promotes pro-carcinogenic changes in the gut. Access to relevant mouse models, to data that clearly define gene signatures including that of the inflammatory NF-κB signaling in senescence, and collaborations with labs performing Drop-seq and facilities performing orthotopic organoid engraftments puts us in a unique position to address these questions. Elucidation of the role of senescent cells in the disease progression would have profound implications in the clinic. NFKBIA is a known risk locus for CRC, and recently emerged as a risk locus for IBD, making this proposed study timely and highly relevant.

• DFG Programme: Research Grants