Predisposition to Arrhythmia and Autonomic Dysfunction in Nhlh1-Deficient Mice

Abstract

Nhlh1 is a basic helix-loop-helix transcription factor whose expression is restricted to the nervous system and which may play a role in neuronal differentiation. To directly study Nhlh1 function, we generated null mice. Homozygous mutant mice were predisposed to premature, adult-onset, unexpected death. Electrocardiograms revealed decreased total heart rate variability, stress-induced arrhythmia, and impaired baroreceptor sensitivity. This predisposition to arrhythmia is a likely cause of the observed death in the mutant mice. Heterozygosity for the closely related transcription factor Nhlh2 increased the severity of the Nhlh1-null phenotype. No signs of primary cardiac structural or conduction abnormalities could be detected upon necropsy of the null mice. The pattern of altered heart rhythm observed in basal and experimental conditions (stress and pharmacologically induced) suggests that a deficient parasympathetic tone may contribute to the arrhythmia in the Nhlh1-null mouse. The expression of Nhlh1 in the developing brain stem and in the vagal nuclei in the wild-type mouse further supports this hypothesis. The Nhlh1 mutant mouse may thus provide a model to investigate the contribution of the autonomic nervous system to arrhythmogenesis.

We thank F. D. Porter, S.-P. Huang, and H. Westphal for embryonic stem cells and help with generating the Nhlh1^−/− mouse; E. J. Lee for blastocyst injections; J. Czaja for excellent skills in performing surgical procedures; E. Mezey and M. Rusnák for assistance with the in situ hybridization; K. F. Shotwell for β-AR measurements; R. Molina for technical support in the mouse room; J. Quigley for statistical analysis; N. Montano and A. Rapacciuolo for fruitful discussions; and R. D. Berger, W. M. Kuehl, K. S. Kuehl, J. J. O'Shea, S. Wray, M. Nau, and C. Coyle for valuable comments on the manuscript. Special thanks go to S. Izraeli and G. Tonon for continuous support, ideas, and critical review of the manuscript.

T. Cogliati and D. J. Good contributed equally to this work.