Retinaldehyde dehydrogenase enzymes regulate colon enteric nervous system structure and function

Abstract

The enteric nervous system (ENS) forms from neural crest-derived precursors that colonize the bowel before differentiating into a network of neurons and glia that control intestinal function. Retinoids are essential for normal ENS development, but the role of retinoic acid (RA) metabolism in development remains incompletely understood. Because RA is produced locally in tissues where it acts by stimulating RAR and RXR receptors, RA signaling during development is absolutely dependent on the rate of RA synthesis and degradation. RA is produced by three different enzymes called retinaldehyde dehydrogenases (RALDH1, RALDH2 and RALDH3) that are all expressed in developing bowel. To determine the relative importance of these enzymes for ENS development, we analyzed whole mount preparations of adult (8–12 week old) myenteric and submucosal plexus stained with NADPH diaphorase (neurons and neurites), anti-TuJ1 (neurons and neurites), anti-HuC/HuD (neurons), and anti-S1003 (glia) in an allelic series of mice with mutations in Raldh1, Raldh2, and Raldh3. We found that Raldh1−/−, Raldh2+/−, Raldh3+/− (R1KOR2HetR3Het) mutant mice had a reduced colon myenteric neuron density, reduced colon myenteric neuron to glia ratio, reduced colon submucosal neuron density, and increased colon myenteric fibers per neuron when compared to wild type (WT; Raldh1WT, Raldh2WT, Raldh3WT) mice. These defects are unlikely to be due to defective ENS precursor migration since R1KOR2HetR3KO mice had increased enteric neuron progenitor migration into the distal colon compared to WT during development. RALDH mutant mice also have reduced contractility in the colon compared to WT mice. These data suggest that RALDH1, RALDH2 and RALDH3 each contribute to ENS development and function.

Male‐specific colon motility dysfunction in the TashT mouse line

“…C–D). Taken together with the data obtained with the other models mentioned above in which neuronal loss was ≥45%, this strongly suggests that a ~40% decrease of myenteric neuronal density might represent a threshold level above which impairment of distal colon motility is more likely to occur.…”

Mouse models of Hirschsprung disease and other developmental disorders of the enteric nervous system: Old and new players

“…Previous studies demonstrated that hedgehog signaling is required for the normal migration of enteric neural progenitors and glial cell generation through Sox10 regulation (Liu et al, 2015; Ngan et al, 2011). In Sufu mutants, the networks of enteric ganglia were disorganized and neuron:glial cell ratios were reduced, a defect reminiscent of that recently described in Sox10 and Raldh1, -2, and -3 mutants (Musser et al, 2015; Wright-Jin et al, 2013). Because mice lacking Sufu in neural crest cells die before the gut is completely colonized by ENCCs, the authors were however not able to determine whether loss of Sufu results in an absence of neurons in the distal bowel and thus a HSCR-like phenotype.…”

“…It was also found that Raldh mutants have altered colonic motility in response to mucosal stimulation. These findings indicate that each of the Raldh genes contribute to ENS development and function (Wright-Jin et al, 2013). Generation of conditional knock-outs are now needed to confirm the tissue specific requirement of retinoic acid during ENS development.…”

Retinoic Acid and the Development of the Endoderm

“…In mice lacking Aldh1a1, Aldh1a2, and Aldh1a3, there is reduced density of enteric neurons and this reduced innervation results in reduced motility of the colon [136,137]. Interestingly, different deletion combinations of the retinaldehyde dehydrogenases had varying effects on different subtypes of enteric neurons suggesting that understanding the exact roles for RA in gut innervation will be complex.…”