NOVEL MOLECULAR MECHANISMS IN CHRONIC INTESTINAL PSEUDO-OBSTRUCTION

Enteric neuropathies are challenging conditions characterized by a severe impairment of gut physiology, including motility. The clinical phenotype most commonly related to an underlying neuropathy is Chronic Intestinal Pseudo-Obstruction (CIPO), a very severe dysmotility disorder which manifests with recurrent sub-obstructive episodes, in the absence of mechanical causes of gut occlusion. Several genetic causes of CIPO have been identified in recent years. The discovery of new genes is of paramount importance for a better understanding of enteric neuropathies and related severe gut dysmotility. Also, these studies are expected to develop novel therapeutic targets for affected patients who typically represent a challenge for their complex clinical picture. Our group identified a novel homozygous mutation in a recessive form of CIPO, the damaging missense variant p.Ala622Thr of RAD21. RAD21 regulates different cell mechanisms as part of the cohesin, a multiprotein complex crucial for chromatin folding and transcriptional regulation. Rad21 functional ablation in zebrafish generated a severe impairment of gut motility, with a significant depletion of enteric neurons, reminiscent of the CIPO phenotype observed in the patients with the RAD21 mutation. In order to study how the RAD21 mutation affects ENS functionality we developed a Rad21 conditional knock-in mouse carrying the p.Ala626Thr mutation (position homologous to the p.Ala622Thr found in patients). This model is expected to recapitulate the main clinical and pathological features observed in patients. Preliminary results showed that cholinergic myenteric neurons were significantly reduced in Rad21A626T vs. WT mice. This initial finding provides a basis to further investigate the full spectrum of abnormalities in this mouse model as a paradigm to CIPO in humans. Therefore, the main goals of this project will be: (1) to recapitulate the functional impairment caused by the RAD21missense mutation in humans through the characterization of the Rad21A626T mouse model; (2) to identify RAD21-dependent dysregulation of target genes in the mouse GI system and correlate them to the CIPO phenotype. To our knowledge, this is the only available model for this condition and therefore will represent a valuable tool for further investigation of a still orphan disorder. Our study will provide a novel in depth analysis of the gut phenotype due to mutant Rad21 and will characterize not only the enteric neurons affected by the RAD21 mutation, but also the target genes regulated by RAD21 in the ENS. These data will improve the knowledge of the molecular impairment in patients with CIPO and is expected to pave the way to ad hoc therapeutic interventions.