We examined the mechanism of atrial natriuretic factor (ANF) transcription by isoproterenol (ISO), an agonist for the ␤-adrenergic receptor (␤AR), in cardiac myocytes. ISO only modestly activated members of the mitogen-activated protein kinase family. ISO-induced ANF transcription was not affected by inhibition of mitogen-activated protein kinases, whereas it was significantly inhibited by KN93, an inhibitor of Ca 2؉ /calmodulin-dependent kinase (CaM kinase II). Production of 3-phosphorylated phosphatidylinositides (3 phosphoinositides) was also required for ISO-induced ANF transcription. ISO caused phosphorylation (Ser-473) and activation of Akt through CaM kinase II-and 3 phosphoinositides-dependent mechanisms. Constitutively active Akt increased myocyte surface area, total protein content, and ANF expression, whereas dominant negative Akt blocked ISO-stimulated ANF transcription. ISO caused Ser-9 phosphorylation and decreased activities of GSK3␤. Overexpression of GSK3␤ inhibited ANF transcription, which was reversed by ISO. ISO failed to reverse the inhibitory effect of GSK3␤(S9A), an Akt-insensitive mutant. Kinase-inactive GSK3␤ increased ANF transcription. Cyclosporin A partially inhibited ISOstimulated ANF transcription, indicating that calcineurin only partially mediates ANF transcription. These results suggest that both CaM kinase II and 3 phosphoinositides mediate ␤AR-induced Akt activation and ANF transcription in cardiac myocytes. Furthermore, ␤AR-stimulated ANF transcription is predominantly mediated by activation of Akt and subsequent phosphorylation/inhibition of GSK3␤.The development of cardiac hypertrophy is a complex process mediated by mechanical forces, neurotransmitters, and hormonal factors (1, 2). In vivo and in vitro studies have shown that stimulation of myocardial ␤-adrenergic receptors (␤ARs) 1 results in cardiac hypertrophy characterized by increases in the cell size, reexpression of the "fetal gene" program (atrial natriuretic factor (ANF) and skeletal ␣-actin), and organization of actin cytoskeleton (3-8). 2 The phenotype of cardiac hypertrophy stimulated by Gs-coupled ␤AR is similar, if not identical, to that by agonists for Gq␣-coupled receptors, such as angiotensin II, phenylephrine (PE), and endothelin-1, 2 despite the fact that the intracellular signaling mechanism activated by Gs␣ and that by Gq␣ are substantially different. We have shown that increases in the protein content and transcription of ANF induced by ␤AR stimulation are predominantly mediated by the ␤1AR subtype and that both Gs␣ and G␤␥ in concert mediate ␤AR-stimulated ANF transcription.2 The intracellular signaling mechanism remains unclear, however, as to how stimulation of the ␤1AR causes cardiac hypertrophy.Many protein kinases and protein phosphatases are activated by hypertrophic stimuli in the heart, and a series of protein phosphorylation and de-phosphorylation events are responsible for induction of specific phenotypes in cardiac hypertrophy. Among them, growing lines of evidence suggest that members of t...

In contrast to mammals, zebrafish regenerate heart injuries via proliferation of cardiomyocytes located near the wound border. To identify regulators of cardiomyocyte proliferation, we used spatially resolved RNA sequencing (tomo-seq) and generated a high-resolution genome-wide atlas of gene expression in the regenerating zebrafish heart. Interestingly, we identified two wound border zones with distinct expression profiles, including the re-expression of embryonic cardiac genes and targets of bone morphogenetic protein (BMP) signaling. Endogenous BMP signaling has been reported to be detrimental to mammalian cardiac repair. In contrast, we find that genetic or chemical inhibition of BMP signaling in zebrafish reduces cardiomyocyte dedifferentiation and proliferation, ultimately compromising myocardial regeneration, while bmp2b overexpression is sufficient to enhance it. Our results provide a resource for further studies on the molecular regulation of cardiac regeneration and reveal intriguing differential cellular responses of cardiomyocytes to a conserved signaling pathway in regenerative versus non-regenerative hearts.

Mammalian cardiomyocytes become post-mitotic shortly after birth. Understanding how this occurs is highly relevant to cardiac regenerative therapy. Yet, how cardiomyocytes achieve and maintain a post-mitotic state is unknown. Here, we show that cardiomyocyte centrosome integrity is lost shortly after birth. This is coupled with relocalization of various centrosome proteins to the nuclear envelope. Consequently, postnatal cardiomyocytes are unable to undergo ciliogenesis and the nuclear envelope adopts the function as cellular microtubule organizing center. Loss of centrosome integrity is associated with, and can promote, cardiomyocyte G0/G1 cell cycle arrest suggesting that centrosome disassembly is developmentally utilized to achieve the post-mitotic state in mammalian cardiomyocytes. Adult cardiomyocytes of zebrafish and newt, which are able to proliferate, maintain centrosome integrity. Collectively, our data provide a novel mechanism underlying the post-mitotic state of mammalian cardiomyocytes as well as a potential explanation for why zebrafish and newts, but not mammals, can regenerate their heart.DOI: http://dx.doi.org/10.7554/eLife.05563.001

No abstract