IntroductionCardiac tissues are extensively innervated by autonomic nerves. The cardiac sympathetic nerve plays an important role in modulating heart rate, conduction velocity, myocardial contraction, and relaxation. Although several molecules that regulate the development of the heart have been well characterized, little is known about the mechanism that regulates sympathetic innervation of the heart. The cardiac sympathetic nerve extends from the sympathetic neuron in stellate ganglia (SG), which is derived from the neural crest (1). Nerve growth factor (NGF) is a prototypic member of the neurotrophin family, members of which are critical for the differentiation, survival, and synaptic activity of the peripheral sympathetic and sensory nervous systems (2, 3). Levels of NGF expression within innervated tissues roughly correspond to innervation density (4). The volume of sympathetic ganglion is reduced by at least 80% at postnatal day 3 in mice with a disruption of the NGF gene. In mice that lack the NGF receptor TrkA, no neurons remain at postnatal day 9 (2). Deletion of a single copy of the NGF gene results in a 50% reduction in sympathetic neurons (5), while overexpression of NGF in the heart results in cardiac hyperinnervation and hyperplasia in SG neurons (6). These results demonstrate the importance of NGF in the regulation of sympathetic neuron development and innervation.In pathological states, NGF production in the heart is variable. In ischemic hearts, an increase in cardiac NGF leads to regeneration of sympathetic nerves (7,8). In a previous experiment, we found that NGF was upregulated in streptozotocin-induced diabetic murine hearts (9). In contrast, it was reported that NGF and sympathetic innervation were reduced in congestive heart failure (10). Despite their importance, the molecular mechanisms that regulate NGF expression and sympathetic innervation in the heart remain poorly understood.Endothelin-1 (ET-1) is believed to play a critical role in the pathogenesis of cardiac hypertrophy, hypertension, and atherosclerosis. Gene targeting of ET-1 and its receptor endothelin-A (ET A ) resulted in unexpected craniofacial and cardiovascular abnormalities. These phenotypes are consistent with interference of neural crest differentiation. The influence of ET-1 on neural crest development remains undetermined (11-13).We hypothesized that ET-1 could affect the induction of neurotrophic factors, and that its disruption might contribute to the immature development of neural crest-derived cells. In this study, we found ET-1-specific induction of NGF in cardiomyocytes, idenEndothelin-1 regulates cardiac sympathetic innervation in the rodent heart by controlling nerve growth factor expression The cardiac sympathetic nerve plays an important role in regulating cardiac function, and nerve growth factor (NGF) contributes to its development and maintenance. However, little is known about the molecular mechanisms that regulate NGF expression and sympathetic innervation of the heart. In an effort to identify regulato...

The cardiac sympathetic nerve plays an important role in regulating cardiac function, and nerve growth factor (NGF) contributes to its development and maintenance. However, little is known about the molecular mechanisms that regulate NGF expression and sympathetic innervation of the heart. In an effort to identify regulators of NGF in cardiomyocytes, we found that endothelin-1 specifically upregulated NGF expression in primary cultured cardiomyocytes. Endothelin-1-induced NGF augmentation was mediated by the endothelin-A receptor, Gibetagamma, PKC, the Src family, EGFR, extracellular signal-regulated kinase, p38MAPK, activator protein-1, and the CCAAT/enhancer-binding protein delta element. Either conditioned medium or coculture with endothelin-1-stimulated cardiomyocytes caused NGF-mediated PC12 cell differentiation. NGF expression, cardiac sympathetic innervation, and norepinephrine concentration were specifically reduced in endothelin-1-deficient mouse hearts, but not in angiotensinogen-deficient mice. In endothelin-1-deficient mice the sympathetic stellate ganglia exhibited excess apoptosis and displayed loss of neurons at the late embryonic stage. Furthermore, cardiac-specific overexpression of NGF in endothelin-1-deficient mice overcame the reduced sympathetic innervation and loss of stellate ganglia neurons. These findings indicate that endothelin-1 regulates NGF expression in cardiomyocytes and plays a critical role in sympathetic innervation of the heart.

Gene-modified cell transplantation therapy induced strong angiogenesis and collateral vessel formation that could be controlled externally with ganciclovir.

Dividing cardiomyocytes are observed in autopsied human hearts following recent myocardial infarction, however there is a lack of information in the literature on the division of these cells. In this study we used a rat model to investigate how and when adult mammalian cardiomyocytes proliferate by cell division after myocardial infarction. Myocardial infarction was induced in Wistar rats by ligation of the left coronary artery. The rats were sacrificed periodically up to 28 days following induced myocardial infarction, and the hearts subjected to microscopic investigation. Cardiomyocytes entering the cell cycle were assayed by observation of nuclear morphology and measuring expression of Ki-67, a proliferating cell marker. Ki-67 positive cardiomyocytes and dividing nuclei were observed initially after 1 day. After 2 days dividing cells gradually increased in number at the ischemic border zone, reaching a peak increase of 1.12% after 3 days, then gradually decreasing in number. Dividing nuclei increased at the ischemic border zone after 3 days, peaked by 0.14% at day 5, and then decreased. In contrast, Ki-67 positive cells and dividing nuclei were limited in number in the non-ischemic area throughout all experiments. In conclusion, mitogenic cardiomyocytes are present in the adult rat heart following myocardial infarction, but were spatially and temporally restricted.

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