Key result
Tbx1 mutation in mice reduces cardiac vagal innervation and accelerates heart rate recovery to carbachol.
Why the study?
Haploinsufficiency of TBX1 causes features of 22q11.2 deletion syndrome including neural crest and cranial ganglion defects, prompting investigation of vagal innervation in Tbx1 mutant hearts.
Tbx1 haploinsufficiency in mice leads to defective vagal innervation and decreased parasympathetic drive, suggesting a potential pro-arrhythmic substrate in 22q11.2 deletion syndrome patients.
Reduced vagal innervation in Tbx1 mutants may heighten arrhythmia susceptibility in 22q11.2DS; leaves open translation to human cardiac autonomic function.
Haploinsufficiency of the T-box transcription factor TBX1 is responsible for many features of 22q11.2 deletion syndrome. Tbx1 is expressed dynamically in the pharyngeal apparatus during mouse development and Tbx1 homozygous mutants display numerous severe defects including abnormal cranial ganglion formation and neural crest cell defects. These abnormalities prompted us to investigate whether parasympathetic (vagal) innervation of the heart was affected in Tbx1 mutant embryos. In this report, we used an allelic series of Tbx1 mouse mutants, embryo tissue explants and cardiac electrophysiology to characterise, in detail, the function of Tbx1 in vagal innervation of the heart. We found that total nerve branch length was significantly reduced in Tbx1+/− and Tbx1neo2/− mutant hearts expressing 50% and 15% levels of Tbx1. We also found that neural crest cells migrated normally to the heart of Tbx1+/−, but not in Tbx1neo2 mutant embryos. In addition, we showed that cranial ganglia IXth and Xth were fused in Tbx1neo2/− but neuronal differentiation appeared intact. Finally, we used telemetry to monitor heart response to carbachol, a cholinergic receptor agonist, and found that heart rate recovered more quickly in Tbx1+/− animals versus controls. We speculate that this condition of decreased parasympathetic drive could result in a pro-arrhythmic substrate in some 22q11.2DS patients.
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Calmont et al. (2018) studied Tbx1 mutation / 22q11.2 deletion syndrome model. Tbx1 mutation vs. controls was evaluated on vagal innervation of the heart, total nerve branch length, and heart rate recovery to carbachol. Tbx1 mutant mice exhibited significantly reduced total nerve branch length, abnormal neural crest cell migration, fused cranial ganglia, and faster heart rate recovery to carbachol compared to controls.
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