We characterize a sonic hedgehog (Shh) signaling domain restricted to the adventitial layer of artery wall that supports resident Sca1-positive vascular progenitor cells (AdvSca1). Using patched-1 (Ptc1 lacZ ) and patched-2 (Ptc2 lacZ ) reporter mice, adventitial Shh signaling activity was first detected at embryonic day (E) 15.5, reached the highest levels between postnatal day 1 (P1) and P10, was diminished in adult vessels, and colocalized with a circumferential ring of Shh protein deposited between the media and adventitia. In Shh ؊/؊ mice, AdvSca1 cells normally found at the aortic root were either absent or greatly diminished in number. Using a Wnt1-cre lineage marker that identifies cells of neural crest origin, we found that neither the adventitia nor AdvSca1 cells were labeled in arteries composed of neural crest-derived smooth muscle cells (SMCs). Although AdvSca1 cells do not express SMC marker proteins in vivo, they do express transcription factors thought to be required for SMC differentiation, including serum response factor (SRF) and myocardin family members, and readily differentiate to SMC-like cells in vitro. However, AdvSca1 cells also express potent repressors of SRF-dependent transcription, including Klf4, Msx1, and FoxO4, which may be critical for maintenance of the SMC progenitor phenotype of AdvSca1 cells in vivo. We conclude that a restricted domain of Shh signaling is localized to the arterial adventitia and may play important roles in maintenance of resident vascular SMC progenitor cells in the artery wall.artery ͉ differentiation ͉ Klf4 ͉ self-renewal ͉ serum response factor

Background-Mutations in the ␥ 2 subunit (PRKAG2) of AMP-activated protein kinase produce an unusual human cardiomyopathy characterized by ventricular hypertrophy and electrophysiological abnormalities: Wolff-ParkinsonWhite syndrome (WPW) and progressive degenerative conduction system disease. Pathological examinations of affected human hearts reveal vacuoles containing amylopectin, a glycogen-related substance. Methods and Results-To elucidate the mechanism by which PRKAG2 mutations produce hypertrophy with electrophysiological abnormalities, we constructed transgenic mice overexpressing the PRKAG2 cDNA with or without a missense N488I human mutation. Transgenic mutant mice showed elevated AMP-activated protein kinase activity, accumulated large amounts of cardiac glycogen (30-fold above normal), developed dramatic left ventricular hypertrophy, and exhibited ventricular preexcitation and sinus node dysfunction. Electrophysiological testing demonstrated alternative atrioventricular conduction pathways consistent with WPW. Cardiac histopathology revealed that the annulus fibrosis, which normally insulates the ventricles from inappropriate excitation by the atria, was disrupted by glycogen-filled myocytes. These anomalous microscopic atrioventricular connections, rather than morphologically distinct bypass tracts, appeared to provide the anatomic substrate for ventricular preexcitation. Conclusions-Our data establish PRKAG2 mutations as a glycogen storage cardiomyopathy, provide an anatomic explanation for electrophysiological findings, and implicate disruption of the annulus fibrosis by glycogen-engorged myocytes as the cause of preexcitation in Pompe, Danon, and other glycogen storage diseases.

We developed a technology for heart rate (HR) variability (HRV) analysis in the mouse for characterization of HR dynamics, modulated by vagal and sympathetic activity. The mouse is the principal animal model for studying biological processes. Mouse strains are now available harboring gene mutations providing fundamental insights into molecular mechanisms underlying cardiac electrical diseases. Future progress depends on enhanced understanding of these fundamental mechanisms and the implementation of methods for the functional analysis of mouse cardiovascular physiology. By telemetric techniques, standard time and frequency-domain measures of HRV were computed with and without autonomic blockade, and baroreflex sensitivity testing was performed. HR modulation in the high-frequency component is predominantly mediated by the parasympathetic nervous system, whereas the low-frequency component is under the influence of both the parasympathetic and sympathetic systems. The presented technology and protocol allow for assessment of autonomic regulation of the murine HR. Phenotypic screening for HR regulation in mice will further enhance the value of the mouse as a model of heritable electrophysiological human disease.