# A59 EXPLORING THE ROLE OF ARID1A IN COLONIC HOMEOSTASIS AND REGENERATION

## TL;DR

This study investigates how the Arid1a gene affects colon health and recovery from injury, finding that its loss impairs regeneration and increases cancer risk.

## Contribution

The study reveals that Arid1a is essential for colonic regeneration and tumor suppression after injury, even though its deletion alone doesn't cause immediate morphological changes.

## Key findings

- Arid1a loss alone does not cause morphological changes in the colon.
- Arid1a loss after injury leads to impaired regeneration and prolonged loss of goblet cells.
- Long-term Arid1a loss increases tumor formation in the colon.

## Abstract

Recent advances in cancer genome analysis have revealed frequently mutated epigenetic regulators as a novel feature in cancer development. Within this context, the Arid1a (AT-rich interactive domain-containing protein 1A) gene, a subunit of the BAF chromatin remodeling complex, has emerged as a frequently mutated gene in many cancers. Additionally, repeated colonic injury caused by diseases such as inflammatory bowel disease (IBD), is also a major risk factor leading to colorectal cancer. Therefore, understanding the connection between colonic epigenetic regulation and its role in response to injury is particularly important for understanding the pathobiology of colorectal cancer.

Aim 1: Exploring the role of Arid1a during colonic homeostasis.

Mouse model with Arid1a conditionally knocked out in the colon will be analysed at different time points to test whether Arid1a is required during colonic homeostasis.

Aim 2: Determining the role of Arid1a during colonic injury and regeneration.

Mice will be exposed to a known colitis model to induce colonic injury. Arid1a will be deleted after injury to find out its role during regeneration and recovery from the injury.

To examine the effect of Arid1a loss on colonic homeostasis, mice between 6-10 weeks old were injected with 2mg/20g tamoxifen for three days to induce Arid1a knockout using the VilCreERT2; Arid1afl/fl mousseline. Mice were then euthanised using CO2 chamber and analysed 10 days, 3 weeks, and 8 weeks post Arid1a deletion. Histological analysis was performed to examine morphological changes in the colon. To examine the effect of Arid1a on injury caused by colitis, mice were treated with dextran sulfate sodium (DSS) to cause colitis-like injury. Then,

Arid1a is deleted by injecting 2mg/20g tamoxifen. Changes in histology and specific cell types will be examined both in the short- and long-term.

To test whether Arid1a loss alone causes morphological changes in the colon, I compared the crypt lengths between VilCreERT2; Arid1afl/fl mutant mice with their littermate controls and saw that there was no difference in both morphology and length of the crypts. My results show that

Arid1a loss in the colon after injury resulted in impaired regeneration characterized by the prolonged loss of goblet cells and cryptal structure in the distal colon. In the long term, Arid1a loss before or after DSS treatment both lead to tumor formation, suggesting that Arid1a is required for colonic regeneration and repair while suppressing tumorigenesis.

Based on my results, I conclude that Arid1a deletion alone does not cause significant morphological changes in the colon, but this loss affects colonic regeneration and recovery compared to colons with Arid1a intact. In the long term, the dysregulated colonic regeneration may lead to tumorigenesis.

University of Toronto Department of Molecular Genetics