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  • iniparib Suspecting that ACL might regulate the

    2024-07-10

    Suspecting that ACL might regulate the expression or activity of myogenic transcription factors, Das knocked down MyoD and found that such intervention abolished the effect of ACL on fast MyHC expression and that, conversely, MyoD overexpression partially rescued reduced fast MyHC expression caused by ACL inhibition. ACL knockdown resulted in a generalized reduction of histone H3 acetylation and prompted the authors to evaluate H3 acetylation at the MyoD regulatory regions. Chromatin immunoprecipitation with iniparib directed against acetyl-H3(K9/K14) revealed that reducing ACL decreased H3 acetylation at a MyoD enhancer (distal regulatory region; DRR) and promoter, and prevented MyoD expression. Acetyl-H3(K9/K14/K27) at a more distal MyoD enhancer (core enhancer) was not affected, indicating a role of ACL in the H3 acetylation of specific MyoD regulatory regions. Complementary experiments revealed that ACL overexpression increased H3 acetylation at the DRR and MyoD promoter, and upregulated MyoD expression. ACL-mediated increased H3 acetylation and MyoD expression were counteracted by treatment of differentiating myoblasts with an inhibitor of the p300 histone acetyltransferase, confirming that the effects of ACL on myogenesis are mediated by acetylation. Das previously reported that ACL activity is regulated by the IGF1/PI3K/AKT pathway . Therefore, it was satisfying to observe that ACL silencing blunted some of the well-known effects of IGF1 on skeletal muscle, including IGF1-induced histone acetylation enrichment at the promoter. Skeletal muscle regeneration relies on SCs and, thus, provides an excellent experimental perturbation with which to investigate SC activation, proliferation, and differentiation . Das tested the role of ACL in injured tibialis muscle by overexpressing it before injury. Notably, ACL overexpression increased muscle weight and average fiber cross-sectional area, and led to formation of an increased number of large myofibers during muscle regeneration. ACL overexpression significantly enhanced the expression of Pax7, MyoD, and Myf5, as well as of Myh3, Myh8, Myh1, Myh2, and Myh4. The increased MyoD expression correlated with augmented H3 acetylation at the DRR and promoter. These findings indicate that ACL, by influencing histone acetylation, critically regulates both SC activation and differentiation and, in doing so, mediates muscle repair after injury. ACL inhibition dramatically reduces the net amount of cellular acetyl-CoA in cancer cells . Whether this also occurs in normal mammalian cells has not yet been tested. However, since glucose acts as the major carbon source of acetyl-CoA, ACL knockdown or overexpression is likely to reduce or increase, respectively, the net abundance of acetyl-CoA also in normal muscle cells. The concomitant upregulation of ACL expression and increased acetyl-H3(K9/K14), but not acetyl-H3(K27), during differentiation is of interest and suggests that different histone acetyltransferases have distinct sensitivity for acetyl-CoA level alteration. Overall, these findings indicate that the ACL/acetyl-CoA/p300 pathway is a previously undescribed transduction arm for IGF1 function. Myogenesis is a process precisely controlled by gene networks. The work of Das provides an additional mechanistic explanation to how growth factors regulate myogenesis by providing evidence that IGF1 activates the ACL/acetyl-CoA/p300 pathway leading to SC differentiation through transcriptional regulation of master regulatory genes. Considering the important roles exerted by IGF1 in muscle physiology , manipulating ACL activity might provide new ways to treat muscle diseases and aging. Moreover, since acetyl-H3(K9/27) acetylation-mediated gene expression participates in the progress of hematological malignancies, such as leukemia , , the ACL/acetyl-CoA/H3 acetylation pathway may have key roles in hematological malignancies, and its manipulation could provide promising therapeutic targets for combatting these diseases.