Regional activation of the immediate-early response gene c-fos in infarcted rat hearts

The effect of c-fos on acute myocardial infarction and the significance of metoprolol intervention in a rat model

Over-expression of c-fos may play a role in some diseases. Research pertaining to the expression of c-fos in acute myocardial ınfarction (AMI) is rare, and the detailed role of c-fos in AMI has not been reported. Therefore, the purpose of this project was to elucidate the detailed effect of c-fos on AMI rats and evaluate the effect of a metoprolol intervention. An AMI rat model was established for the purposes of this study. The expression of c-fos in AMI was evaluated via immunohistochemical analysis and in situ hybridization. Simultaneously, we investigated the effect of c-fos on AMI rats via medicinal treatment with c-fos monoclonal antibody, isoproterenol, and metoprolol. Positive c-Fos protein expression and c-fos mRNA expression in cardiomyocytes were increased at 1, 3, 7, and 10 days after ligation in AMI rats compared with a sham-operated group. Peak expression occurred at 3 days after ligation. The weight percentage fraction of infarct size was decreased in rats treated with c-fos monoclonal antibody compared with the control normal saline treatment group. The weight percentage fraction of infarction size was increased after c-fos was increased via the administration of isoproterenol. c-Fos protein expression and the infarct size in rats treated with metoprolol were also decreased compared with the control normal saline treatment group. The results showed that c-fos expression rapidly increased after coronary ligation; c-fos plays an important role in myocardial lesions and is likely to be involved in the pathogenesis of AMI as well. Metoprolol can inhibit the expression of c-fos and has a positive therapeutic effect on rats after AMI; the involvement effect of metoprolol on myocardial infarction might be correlated with its effect on the inhibition of c-fos.

A genome-wide screen reveals a role for microRNA-1 in modulating cardiac cell polarity

Many molecular pathways involved in heart disease have their roots in evolutionarily ancient developmental programs that depend critically on gene dosage and timing. MicroRNAs (miRNAs) modulate gene dosage posttranscriptionally, and among these, the muscle-specific miR-1 is particularly important for developing and maintaining somatic/skeletal and cardiac muscle. To identify pathways regulated by miR-1, we performed a forward genetic screen in Drosophila using wing-vein patterning as a biological assay. We identified several unexpected genes that genetically interacted with dmiR-1, one of which was kayak, encodes a developmentally regulated transcription factor. Additional studies directed at this genetic relationship revealed a previously unappreciated function of dmiR-1 in regulating the polarity of cardiac progenitor cells. The mammalian ortholog of kayak, c-Fos, was dysregulated in hearts of gain- or loss-of-function miR-1 mutant mice in a stress-dependent manner. These findings illustrate the power of Drosophila-based screens to find points of intersection between miRNAs and conserved pathways in mammals.

Myocardial hypertrophy is not a prerequisite for changes in early gene expression in left ventricular volume overload

Currently it is not certain whether hypertrophy or the underlying disease is the primary trigger of the alterations in early gene expression in the progression of cardiac disease to end-stage heart failure. In this study, we tested the notion that in left ventricular overload disorders, the changes in early gene expression in the progression to heart failure is independent of the manifestation of cardiac hypertrophy. We compared the expression of the early genes c-fos, c-myc, and c-jun in six dilated cardiomyopathic hearts (DCM) and 15 patients with left ventricular volume overload (VOL) resulting from mitral/aortic regurgitation and no significant stenosis or hypertrophic manifestations, using eight healthy donor hearts as controls. In VOL, c-myc was elevated by 88% (P < 0.01) in the left ventricle, 46% in the right ventricle, onefold (P < 0.01) in the left atrium, and 54% (P < 0.05) in the right atrium, while in DCM, it was increased by 71% (P < 0.02), 55%, 48% (P < 0.05) and 91% (P < 0.05), respectively. Similarly, c-jun was elevated by 41% (P < 0.01) in the left ventricle, 39% (P < 0.05) in the right ventricle, 83% (P < 0.02) in the left atrium and 21% in the right atrium in VOL, while in DCM it was elevated by 13% in the left ventricle, 29% in the left atrium, and 41% in the right atrium, but decreased by 13% in the right ventricle. In contrast, c-fos was slightly decreased in the left ventricle and atrium of both DCM and VOL, and in left atrium of the VOL group, but remained unchanged in the other myocardial chambers. These results show that, in the human myocardium, the three early genes are regulated differently, possibly in disease- and chamber-specific fashions, and manifestation of left ventricular hypertrophy is not a prerequisite for the elevation in their expression in left ventricular overload disorders.

Morphine withdrawal-induced c-fos expression in the heart: a peripheral mechanism

We previously demonstrated that hyperactivity of cardiac noradrenergic pathways observed during morphine withdrawal is mediated by peripheral mechanisms. In the present study, naloxone methiodide (quaternary derivative of naloxone that does not cross the blood-brain barrier) and naloxone were administered to morphine-dependent rats and Fos immunostaining was used as a reflection of neuronal activity. Dependence on morphine was induced by 7-day chronic subcutaneous (s.c.) implantation of six morphine pellets (75 mg). Morphine withdrawal was precipitated by administration of naloxone methiodide (5 mg/kg, s.c.) or naloxone (5 mg/kg, s.c.) on day 8. Using immunohistochemical staining of Fos, present results indicate that the administration of naloxone methiodide or naloxone to morphine-dependent rats induced marked Fos immunoreactivity within the cardiomyocyte nuclei. Moreover, Western blot analysis revealed a peak expression of c-fos in the right and left ventricles after naloxone methiodide- or naloxone-precipitated withdrawal. In addition, in the hypothalamic paraventricular nucleus (PVN), Fos expression was increased after naloxone-but not after naloxone methiodide-administration to morphine-dependent rats. These results suggest that the activation of c-fos expression observed during morphine withdrawal in the heart is due to intrinsic mechanisms outside the central nervous system (CNS).

Activation of c-fos expression in the heart after morphine but not U-50,488H withdrawal

1. In the present work we have studied in the heart the expression of Fos, the protein product of the c-fos proto-oncogene and the adaptive changes in noradrenergic neurons after naloxone or nor-binaltorphimine (nor-BNI) administration to morphine or U-50,488H pretreated rats. 2. Male rats were implanted with placebo (naïve) or morphine (tolerant/dependent) pellets for 7 days. On day 8 rats received saline s.c., naloxone (5 mg kg(-1) s.c.) or nor-BNI (5 mg kg(-1) i.p.). Other groups of rats were rendered tolerant/dependent on U-50,488H by injecting the drug twice daily (15 mg kg(-1) i.p.) for 4 days. Control animals received saline. On day 5 the animals were injected with vehicle i.p. or nor-BNI (5 mg kg(-1) i.p.). 3. Using immunohistochemical staining of Fos, present results indicate that morphine withdrawal induced marked Fos immunoreactivity (Fos-IR) within the cardiomyocyte nuclei. Moreover, Western blots analysis revealed a peak expression of c-fos in right and left ventricle after naloxone induced withdrawal in parallel with an increase in noradrenaline (NA) turnover. 4. However, after nor-BNI administration to rats chronically treated with U-50,488H, we found a decrease in the NA turnover. In addition, the administration of nor-BNI to rats chronically treated with U-50,488H or morphine did not induce modifications in the Fos-IR, in the heart. 5. These results demonstrated that morphine withdrawal induces the expression of Fos protein, as well as an enhancement of noradrenergic activity in the heart. In contrast to morphine U-50,488 withdrawal produces no changes in Fos-IR in parallel with a decrease in NA turnover, indicating that the kappa-opioid receptors are not involved in the molecular adaptive mechanisms responsible for the development of opioid dependence in the heart.