The recent discovery that hydrogen sulfide (H2S) is an endogenously produced gaseous second messenger capable of modulating many physiological processes, much like nitric oxide, prompted us to investigate the potential of H2S as a cardioprotective agent. In the current study, we demonstrate that the delivery of H2S at the time of reperfusion limits infarct size and preserves left ventricular (LV) function in an in vivo model of myocardial ischemiareperfusion (MI-R). This observed cytoprotection is associated with an inhibition of myocardial inflammation and a preservation of both mitochondrial structure and function after I-R injury. Additionally, we show that modulation of endogenously produced H2S by cardiac-specific overexpression of cystathionine ␥-lyase (␣-MHC-CGL-Tg mouse) significantly limits the extent of injury. These findings demonstrate that H2S may be of value in cytoprotection during the evolution of myocardial infarction and that either administration of H2S or the modulation of endogenous production may be of clinical benefit in ischemic disorders.

Virtually every mammalian cell, including cardiomyocytes, possesses an intrinsic circadian clock. The role of this transcriptionally based molecular mechanism in cardiovascular biology is poorly understood. We hypothesized that the circadian clock within the cardiomyocyte influences diurnal variations in myocardial biology. We, therefore, generated a cardiomyocyte-specific circadian clock mutant (CCM) mouse to test this hypothesis. At 12 wk of age, CCM mice exhibit normal myocardial contractile function in vivo, as assessed by echocardiography. Radiotelemetry studies reveal attenuation of heart rate diurnal variations and bradycardia in CCM mice (in the absence of conduction system abnormalities). Reduced heart rate persisted in CCM hearts perfused ex vivo in the working mode, highlighting the intrinsic nature of this phenotype. Wild-type, but not CCM, hearts exhibited a marked diurnal variation in responsiveness to an elevation in workload (80 mmHg plus 1 M epinephrine) ex vivo, with a greater increase in cardiac power and efficiency during the dark (active) phase vs. the light (inactive) phase. Moreover, myocardial oxygen consumption and fatty acid oxidation rates were increased, whereas cardiac efficiency was decreased, in CCM hearts. These observations were associated with no alterations in mitochondrial content or structure and modest mitochondrial dysfunction in CCM hearts. Gene expression microarray analysis identified 548 and 176 genes in atria and ventricles, respectively, whose normal diurnal expression patterns were altered in CCM mice. These studies suggest that the cardiomyocyte circadian clock influences myocardial contractile function, metabolism, and gene expression.

Gonadotropin-releasing hormone (GnRH) regulates the expression of all three gonadotropin genes, encoding the common ␣ subunit (␣GSU) and hormone-specific ␤ subunits, through the activation of several signal transduction pathways. We have shown that GnRH also upregulates calcineurin, and we hypothesized that calcineurin mediates the effects of GnRH on the transcription of the ␣GSU and follicle-stimulating hormone ␤ (FSH␤) genes through two of its targets: nuclear factor of activated T cells (NFAT) and CREB-regulated transcription coactivator (TORC). We show that calcineurin is essential for GnRH-induced expression of both genes but that NFAT and TORC1 play quite distinct roles in activating each gene. GnRH induces calcineurindependent nuclear import of NFAT3, which activates the ␣GSU promoter, while TORC1 also mediates GnRH activation of this promoter, but not through CREB. GnRH initially stimulates the degradation of TORC1 but protects the N terminus of the newly synthesized protein to enhance its activity. Calcineurin induces Nur77 expression, likely via NFAT3, and Nur77 interacts synergistically with TORC1 and CREB to increase FSH␤ promoter activity. Although TORC plays a role in the basal activity of the FSH␤ promoter, it does not interact with phosphorylated CREB and probably does not play a major role in direct GnRH signaling to this gene. TORC may be part of an alternatively regulated pathway, possibly involving cross talk with other stimulatory hormones.In the pituitary gonadotrope, the gonadotropin-releasing hormone (GnRH) plays a crucial role in activating the transcription of all three gonadotropin subunit genes: the common ␣ subunit (␣GSU) and the hormone-specific ␤ subunits encoding luteinizing hormone (LH␤) and follicle-stimulating hormone (FSH␤). Upon binding its G-protein-coupled receptor (GPCR), GnRH activates protein kinase C (PKC) and a number of well-characterized mitogen-activated protein kinase (MAPK) pathways, as well as elevating cyclic AMP (cAMP) levels to activate protein kinase A (PKA) (7,20,33,42,53). It also induces an increase in intracellular calcium levels by stimulating calcium release from intracellular stores as well as the influx of extracellular calcium through voltage-sensitive channels (7, 42). One of the effects of this increase in calcium levels is the activation of calmodulin and calmodulin-dependent kinases (CaMKs), which mediate various aspects of GnRH-induced signaling, including inhibition of histone deacetylases and regulation of extracellular signal-regulated kinase (ERK) activity (6,10,23,24,34,44,61). Calmodulin also activates the serine/threonine protein phosphatase calcineurin to regulate the expression of various genes (26). In the gonadotrope, calcineurin moderates the activity of the prolyl isomerase Pin1, facilitating its localization to the nucleus, where it plays an important role in GnRH signaling to several key transcription factors (36). Calcineurin also plays a role in the GnRH-induced derepression of FSH␤ gene expression in immature ␣T3-1 gonadotrope ...