Constitutive Activation of Nrf2 in Mice Expands Enterogenesis in Small Intestine Through Negative Regulation of Math1

Abstract

Activation of Nrf2 signaling in the intestinal epithelium leads to lengthened intestines and expansion of enterogenesis, which is mediated through suppression of Notch downstream effector Math1 in enterocyte progenitor cells. This study indicates the facilitation of intestinal homeostasis by Nrf2. BACKGROUND & AIMS: Notch signaling coordinates cell differentiation processes in the intestinal epithelium. The transcription factor Nrf2 orchestrates defense mechanisms by regulating cellular redox homeostasis, which, as shown previously in murine liver, can be amplified through signaling crosstalk with the Notch pathway. However, interplay between these 2 signaling pathways in the gut is unknown. METHODS: Mice modified genetically to amplify Nrf2 in the intestinal epithelium (Keap1 f/f ::VilCre) were generated as well as pharmacological activation of Nrf2 and subjected to phenotypic and cell lineage analyses. Cell lines were used for reporter gene assays together with Nrf2 overexpression to study transcriptional regulation of the Notch downstream effector. RESULTS: Constitutive activation of Nrf2 signaling caused increased intestinal length along with expanded cell number and thickness of enterocytes without any alterations of secretory lineage, outcomes abrogated by concomitant disruption of Nrf2. The Nrf2 and Notch pathways in epithelium showed inverse spatial profiles, where Nrf2 activity in crypts was lower than villi. In progenitor cells of Keap1 f/f ::VilCre mice, Notch downstream effector Math1, which regulates a differentiation balance of cell lineage through lateral inhibition, showed suppressed expression. In vitro results demonstrated Nrf2 negatively regulated Math1, where 6 antioxidant response elements located in the regulatory regions contributed to this repression. CONCLUSIONS: Activation of Nrf2 perturbed the dialog of the Notch cascade though negative regulation of Math1 in progenitor cells, leading to enhanced enterogenesis. The crosstalk between the Nrf2 and Notch pathways could be critical for finetuning intestinal homeostasis and point to new approaches for the pharmacological management of absorptive deficiencies.

Nrf2 Transcriptional Activity Governs Intestine Development

“…In particular, it should be kept in mind that the phenotype of Nrf2 tKO mice is largely dependent on the balance between Nrf2 and Keap1 (summarized in [ 8 ]). Supportively, the Keap1 deficiency in mice is lethal at the weaning age due to the abnormal formation of the gastrointestinal tract [ 19 ] and a significant deregulation in enterocyte proliferation [ 15 ]. Therefore, the Keap1-related mechanisms governing hindgut formation cannot be excluded.…”

“…Given this striking increase in the Nrf2 level between E14.5 and E15.5 in the whole embryo, it would be worthy verifying whether this rise accounts for enhanced proliferation only at the intestinal level or at the organismal level. For instance, Nrf2 regulates the proliferation of enterocytes [ 15 ], hepatocytes [ 26 , 27 ], satellite cells [ 28 ], neuronal progenitor cells [ 29 ], and endothelial cells [ 16 ]. Thus, it is plausible that the regulation occurs at the organismal level and is not tissue specific.…”

“…Given the pronounced Nrf2 mRNA level in the hindgut during gestation [ 13 ] as well as the significant association of Nrf2 with the master regulator of intestinal differentiation Notch1 [ 14 , 15 ] and with the regulation of cellular proliferation [ 16 ], we speculated that the Nrf2-related intestinal abnormalities would appear in the early gestation or early weaning period. To address this issue, we decided to assess the colon morphology at postnatal day 4 and, if rationale, at the earlier timepoints during embryonic development.…”

Personalized redox medicine in inflammatory bowel diseases: an emerging role for HIF-1α and NRF2 as therapeutic targets

“…NRF2 is crucial for gut formation. It influences the NOTCH and WNT signaling pathways, which drive epithelial cell differentiation during intestinal development [ 131 , 132 ]. Constitutive activation of NRF2 signaling in the intestinal epithelium results in extended intestines and increased enterogenesis.…”

“…Constitutive activation of NRF2 signaling in the intestinal epithelium results in extended intestines and increased enterogenesis. This is achieved by suppressing the NOTCH downstream effector MATH1 in enterocyte progenitor cells [ 132 ]. On the other hand, Nrf2 deficiency results in the formation of a longer colon, a different distribution of crypts, and the enlargement of goblet cells with a noticeably higher level of mucin 2 [ 131 ].…”