Thyroid Hormone in the Pathogenesis of Congenital Intestinal Dysganglionosis.

Introduction: The objective of this study is to investigate the role of thyroid hormone (TH) in the pathogenesis of intestinal dysganglionosis (ID).
Methods: A zebrafish model of congenital hypothyroidism (CH) was created by exposing the larvae to the 6-propyl-2-thiouracil (PTU). The enteric neurons were labeled with anti-HuC/D antibodies. The number of enteric neurons was counted. The larval intestine was dissociated and stained with anti-p75 and anti-α4 integrin antibodies. Mitosis and apoptosis of the p75 ⁺ α4 integrin ⁺ enteric neural crest cells (ENCCs) were studied using flow cytometry. Intestinal motility was studied by analyzing the transit of fluorescent tracers.
Results: PTU (25 mg/L) significantly reduced TH production at 6- and 9-days post fertilization without changing the body length, body weight, and intestinal length of the larvae. Furthermore, PTU inhibited mitosis of ENCCs and reduced the number of enteric neurons throughout the larval zebrafish intestine. Importantly, PTU inhibited intestinal transit of fluorescent tracers. Finally, thyroxine supplementation restored ENCC mitosis, increased the number of enteric neurons, and recovered intestinal motility in the PTU-treated larvae.
Conclusions: PTU inhibited TH production, reduced the number of enteric neurons, impaired intestinal motility, and impeded ENCC mitosis in zebrafish, suggesting a possible role of CH in the pathogenesis of ID.