The I-BET-762Thiamet G -Program

n.In the present study,we evaluated the mechanism by means of which agonist induced PPARd activation could exert protective effects against doxorubicin induced senescence.We found that pre treatment with specifiinhibitors of p38,JNK,and I-BET-762 Akt prevents the effect of L 165041 on Bcl6 levels and on doxorubicin induced SA gal,and that pre treatment using the Akt inhibitor also prevents the effect of L 165041 on the up regulation of PPARd.We demonstrated that not only Akt,but additionally p38 and JNactivation are necessary in order for PPARd activation to exert a protective effect.This is in agreement with both the study by Liang et al.who demonstrated that L 165041 inhibits reactive protein induced inflammation in cardiomyocytes and inh9c2 by means of p38 and JNand using the study by Yue et al who found that PPARd activation enhances Akt signaling and protects theheart from ischemia reperfusion injury in Zucker fatty rats.
We also found that pre treatment with L 165041 prevents the doxorubicin induced increase in pJNand pAkt but not the doxorubicin induced increase in pp38.It's achievable that the protection provided by L 165041 by means of Akt and JNsignaling is able to prevent doxorubicin I-BET-762 induced pressure so that doxorubicin does not lead to any further activation of these survival pathways.Protection by means of the activation of p38 occurs with an initial increase in phosphorylation because of pre treatment with L 165041,followed by a further increase in phosphorylation because of treatment with doxorubicin.
Collectively,our data show that Bcl6 plays a principal function in the protective effect exerted by L 165041 against doxorubicin induced senescence,L 165041 increases Bc16 expression levels by means of Thiamet G  p38,JNand Akt mediated pathways and induces its release from PPARd thus allowing Bcl6 binding to its target genes to exert its antsenescent actions.Although apoptosis was not the main problem of our study we repeated several experiments working with doxorubicin 1 mM,a pro apoptotidose,to compare the function played by the PPARd agonist in senescence and apoptosis.We found that pre treatment using the PPARd agonist L165041 is effective in preventing apoptosis induced by doxorubicin 1 mM.Although Bcl6 was down regulated by doxorubicin,RNA interference experiments docu mented that it really is neither implicated in the execution of doxorubicin induced apoptosis nor in the antapoptotieffects exerted by pre incubation using the PPARd agonist.
Studies investigating the function of Bcl6 in apoptosis created inconsistent outcomes.Given that doxorubicin induced apoptosis is largely reactive oxygen species mediated,we speculate that upon ligand binding,PPARd is enabled to induce transcription of genes encoding the antioxidant enzymes.Thishypothesis is in agreement with earlier studies by Pesant et al,who found that the PPARd agonist Ribonucleotide GW501516 protectsh9c2 Thiamet G  fromh2O2 induced cell apoptosis.They also found that this protection is totally dependent on PPARd and is carried out by means of catalase up regulation.Furthermore,considering that ithas been shown that PPARd agonists also enhance the physical interaction in between PPARd and also the p65 subunit of NF kB,thus preventing its capability to induce gene transcription,it may behypothesized that even this mechanism may contribute to safeguard cardiomyocytes from the pro apoptotieffects of doxorubicin.
It is also worthy of note that silencing Bcl6 in cells treated with doxorubicin 0.1 mM potentiated I-BET-762 the cardiotoxieffects of doxo rubicin by escalating its pro senescent effects with out inducing a switch to apoptosis.The fact that Bcl6 is critical for senescence induced by doxorubicin 0.1 mM,but not for apoptosis induced by doxorubicin Thiamet G  1 mM confirms that senescence and apoptosis are two very distinct pressure response cellular programs.Since the most functionally considerable cell variety in theheart is represented by post mitotic,terminally differentiated cardiomyo cytes,the idea of investigating both anthracycline cardiotoxicity and PPARd activation cardioprotection by studying mechanisms of cellular senescence in dividing neonatal rat cardiomyocytes andh9c2 may appear,at first glance,odd.
It should be saidhowever that this modelhas been extensively utilized in the past and ithas been considered I-BET-762 a convenient method for preliminary investigations.Furthermore,in very recent years,convincing evidencehas shown that the normalheart is not a post mitotiorgan considering that it consists of a pool of progenitor cells and also a population of immature,dividing myocytes that permit to get a turnover of cardiomyocytes involving the generation of new Thiamet G  cardiomyocytes in substitution in the damaged ones.A new view on anthracycline cardiotoicity was recently introduced using the demonstration that in comparison to differentiated cardiomyocytes,dividing cardiomy ocytes are a lot more sensitive to anthracyclines and that low doses of doxorubicin causes senescence like changes in these cells.These effects could inhibit the regenerative capacity of theheart and,by means of this mechanism,impair the self repairing potential of theheart,in the end l