Death receptor triggering can also induce cell death by caspase-independent, necrotic pathway

ethasone nor Ru486 had significant effects on the cell size of mononucleated or binucleated cardiomyocytes. 5-AZA inhibits dexamethasone-induced effects on heart development in neonatal rats Given that epigenetic modifications play an get LY341495 important role in the heart development and the activation of GR has been noted to alter the methylation pattern of multiple genes, we determined whether heightened methylation played a role in dexamethasone-induced effects on the heart development in neonatal rats. The effects of dexamethasone was evaluated in the absence or presence of a methylation inhibitor 5-AZA. Although 5-AZA treatment alone had no significant effects on either heart weight or body weight in P4 and P7 pups, it caused a significant but symmetric decrease in both heart and body weight in P14 pups. Interestingly, although it had no significant effects on either heart or body weight in P7 pups, it significantly increased the heart to body ratio in P7 pups. Of importance, in the presence of 5-AZA, effects of dexamethasone on heart weight, body weight and the heart to body weight ration were abrogated, suggesting DNA methylation as a critical mechanism of dexamethasone effects. 5-AZA blocks dexamethasone-mediated premature cardiomyocyte terminal differentiation The effects of 5-AZA on dexamethasone-induced premature cardiomyocyte binucleation and inhibition of proliferation were further studied. As shown in Fig 6A, the dexamethasone-induced decrease of Ki67-positive cardiomyocytes in P7 pups was blocked by 5-AZA. Similarly, dexamethasone-mediated suppression of BrdU incorporation was inhibited by 5-AZA, suggesting a methylation-dependent mechanism in dexamethasone-induced decease in 7 / 20 Dexamethasone and Heart Development Fig 3. Effect of dexamethasone on cardiomyocyte proliferation in neonatal rats. Newborn rats were treated with tapered dose of DEX in the absence PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19777101 or presence of Ru486 during the first three days of postnatal life. Ru486 was administered 30 minutes prior to the DEX treatment. Panel A: Cardiomyocytes isolated from day 4 and day 7 neonatal hearts were double stained with -actinin and Ki67, and nuclei were stained with Hoechst. Representative staining of -actinin and Ki67 co-localization was shown in the upper panel. Panel B: Cardiomyocytes isolated from P7 neonatal hearts were examined for BrdU incorporation. Data are mean SEM, PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19778700 n = 414. p<0.05, DEX vs. Saline. doi:10.1371/journal.pone.0125033.g003 8 / 20 Dexamethasone and Heart Development Fig 4. Effect of dexamethasone on cardiomyocyte number in neonatal rats. Newborn rats were treated with tapered dose of DEX in the absence or presence of Ru486 during the first three days of postnatal life. Ru486 was administered 30 minutes prior to the DEX treatment. Cardiomyocytes isolated from day 4, day 7 and day 14 neonatal hearts were counted and normalized to per gram of heart weight. Data are mean SEM, n = 620. p<0.05, DEX vs. Saline; p<0.05, P7 vs. P4. doi:10.1371/journal.pone.0125033.g004 cardiomyoctye proliferation. Of interest, 5-AZA alone significantly increased Ki67-positive cardiomyocytes, despite the effects of dexamethasone. Although 5-AZA alone had no significant effect on cardiomyocyte binucleation, it inhibited the dexamethasone-induced increase of percent binucleated cells in the hearts of P4 pups. 5-AZA abrogates the effects of dexamethasone on cardiomyocyte endowment As shown in Fig 7, in P4 pups, 5-AZA treatment did not influence cardiomyocyte numbers in either