Abstract
Gastrointestinal (GI) dysmotility is a highly prevalent and clinically significant feature of Rett syndrome (RTT), yet its underlying mechanisms remain poorly defined. Here, we investigated these mechanisms of GI dysmotility in a Mecp2-null mouse model of RTT. First, we observed that MeCP2 was expressed in murine myenteric ganglia, including in enteric neurons and that Mecp2-null males developed maturation-associated functional regression in their GI motility. In dysmotile mice, longitudinal muscle-myenteric plexus tissue showed marked reductions in enteric Bdnf i soforms IV, VI, and II , whereas expression of the BDNF receptor isoforms TrkB.FL and TrkB.T1 was not significantly altered, consistent with reduced enteric BDNF-TrkB signaling. Despite impaired GI motility, Mecp2-null mice showed no significant changes in total enteric neuronal density, nitrergic neuronal abundance, or expression of Nos1, Chat , and Uchl1. In contrast, Vip expression was significantly reduced, while expression of VIP receptor genes: Vipr1 and Vipr2 was increased, indicating disrupted VIPergic signaling. Integration with publicly available enteric single-cell/nucleus datasets and targeted qRT-PCR further suggested altered inhibitory neuronal subtype composition, with reduced Vip (+) Cartpt (+) signatures and increased Nfia expression, suggesting that MeCP2 loss differentially affects distinct inhibitory neuronal subpopulations. Finally, conditional loss of TrkB.FL in neural crest-derived cells reduced Vip expression without recapitulating the full Mecp2-null VIPergic phenotype, indicating that impaired BDNF-TrkB signaling contributes to, but does not completely explain, the GI dysmotility in this model of RTT. Together, these findings identify enteric BDNF-TrkB and VIPergic dysfunction as key mechanisms underlying GI dysmotility in RTT.