Background: miR1 is a muscle-specific microRNA, however, its role in muscle atrophy is unclear. Results: Excess dexamethasone and myostatin induced miR1 via glucocorticoid receptor, resulting in reduced HSP70 and development of muscle atrophy. Conclusion: miR1 mediates muscle atrophy by regulating the levels of HSP70. Significance: Given that miR1 has a role in muscle atrophy, its antagonism may be beneficial during atrophy.

In this study, we report that the integrin LFA-1 cross-linking with its ligand ICAM-1 in human PBMCs or CD4+ T cells promotes Th1 polarization by upregulating IFN-γ secretion and T-bet expression. LFA-1 stimulation in PBMCs, CD4+ T cells, or the T cell line HuT78 activates the Notch pathway by nuclear translocation of cleaved Notch1 intracellular domain (NICD) and upregulation of target molecules Hey1 and Hes1. Blocking LFA-1 by a neutralizing Ab or specific inhibition of Notch1 by a γ-secretase inhibitor substantially inhibits LFA-1/ICAM-1–mediated activation of Notch signaling. We further demonstrate that the Notch pathway activation is dependent on LFA-1/ICAM-1–induced inactivation of glycogen synthase kinase 3β (GSK3β), which is mediated via Akt and ERK. Furthermore, in silico analysis in combination with coimmunoprecipitation assays show an interaction between NICD and GSK3β. Thus, there exists a molecular cross-talk between LFA-1 and Notch1 through the Akt/ERK–GSK3β signaling axis that ultimately enhances T cell differentiation toward Th1. Although clinical use of LFA-1 antagonists is limited by toxicity related to immunosuppression, these findings support the concept that Notch inhibitors could be attractive for prevention or treatment of Th1-related immunologic disorders and have implications at the level of local inflammatory responses.

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Aging skeletal muscle shows perturbations in metabolic functions. MicroRNAs have been shown to play a critical role in aging and metabolic functions of skeletal muscle. MicroRNA-34a (miR-34a) is implicated in the brain and cardiac aging, however, its role in aging muscle is unclear. We analyzed levels of miR-34a, ceramide kinase (CERK) and other insulin signaling molecules in skeletal muscle from old mice. In addition to in vivo model, levels of these molecules were also analyzed in myoblast derived from insulin resistant (IR) humans and C2C12 myoblasts overexpressing mir-34a. Our results show that miR-34a is elevated in the muscles of 2-year-old mice and in the myoblasts of IR humans.Overexpression of miR-34a in C2C12 myoblasts leads to alterations in the insulin signaling pathway, which were rescued by its antagonism. Our analyses revealed that miR-34a targets CERK resulting in ceramide accumulation, activation of PP2A and the pJNK pathway in muscle and C2C12 myoblasts. Also, myostatin (Mstn) levels were increased in 2-year-old mouse muscle and Mstn treatment upregulated miR-34a in C2C12 myoblasts. In addition, miR-34a expression and ceramide levels did not increase during aging in Mstn −/− mice muscle. In summary, we, therefore, propose that Mstn levels increase in aging muscle and upregulate miR-34a, which inhibits CERK resulting in increased ceramide levels. This ceramide accumulation activates PP2A and pJNK causing hypophosphorylation of AKT and hyperphosphorylation of IRS1 (Ser307), respectively, impairing insulin signaling pathway and eventually inhibiting the sarcolemma localization of GLUT4. These changes would result in reduced glucose uptake and insulin resistance. This study is the first to explain the phenomenon of ceramide accrual and impairment of insulin signaling pathway in aging muscle through a miR-34a based mechanism. In conclusion, our results suggest that Mstn and miR-34a antagonism can help ameliorate ceramide accumulation and loss of insulin sensitivity in aging skeletal muscle. K E Y W O R D Saging muscle, CERK, insulin signaling pathway, miR-34aHow to cite this article: Kukreti H, Amuthavalli K. microRNA-34a causes ceramide accumulation and effects insulin signaling pathway by targeting Ceramide kinase (CERK) in aging skeletal muscle.

In the Western immunoblot panels in Fig. 4A and 4B, phospho-and total-Akt/ERK blot panels were inadvertently presented from CD4 1 T cells purified from different donors. In the published Fig. 4A, the top blot [pAkt(Thr308)] was taken from a different donor than the middle [pAkt(Ser473)] and lower [Akt] blots, and both the pERK1/2 and ERK1/2 blots in Fig. 4B were taken from two different donors. The time-point 6 h for cell incubation on rICAM-1 was missing in the originally published legend to Fig. 4. The corrected version of Fig. 4, with Fig. 4A and 4B showing phospho-and total-Akt/ERK immunoblots using T cells from the same donor (out of three different donors), is shown below. The corrected figure legend is also shown below. The data and conclusions in the article are not affected.