Obesity-induced activation of JunD promotes myocardial lipid accumulation and metabolic cardiomyopathy
EUROPEAN HEART JOURNAL
Authors: Costantino, Sarah; Akhmedov, Alexander; Melina, Giovanni; Mohammed, Shafeeq A.; Othman, Alaa; Ambrosini, Samuele; Wijnen, Winandus J.; Sada, Lidia; Ciavarella, Giuseppino M.; Liberale, Luca; Tanner, Felix C.; Matter, Christian M.; Hornemann, Thorsten; Volpe, Massimo; Mechta-Grigoriou, Fatima; Camici, Giovanni G.; Sinatra, Riccardo; Luscher, Thomas F.; Paneni, Francesco
Abstract
Aims Metabolic cardiomyopathy (MC)characterized by intra-myocardial triglyceride (TG) accumulation and lipotoxic damageis an emerging cause of heart failure in obese patients. Yet, its mechanisms remain poorly understood. The Activator Protein 1 (AP-1) member JunD was recently identified as a key modulator of hepatic lipid metabolism in obese mice. The present study investigates the role of JunD in obesity-induced MC. Methods and results JunD transcriptional activity was increased in hearts from diet-induced obese (DIO) mice and was associated with myocardial TG accumulation and left ventricular (LV) dysfunction. Obese mice lacking JunD were protected against MC. In DIO hearts, JunD directly binds PPAR promoter thus enabling transcription of genes involved in TG synthesis, uptake, hydrolysis, and storage (i.e. Fas, Cd36, Lpl, Plin5). Cardiac-specific overexpression of JunD in lean mice led to PPAR activation, cardiac steatosis, and dysfunction, thereby mimicking the MC phenotype. In DIO hearts as well as in neonatal rat ventricular myocytes exposed to palmitic acid, Ago2 immunoprecipitation, and luciferase assays revealed JunD as a direct target of miR-494-3p. Indeed, miR-494-3p was down-regulated in hearts from obese mice, while its overexpression prevented lipotoxic damage by suppressing JunD/PPAR signalling. JunD and miR-494-3p were also dysregulated in myocardial specimens from obese patients as compared with non-obese controls, and correlated with myocardial TG content, expression of PPAR-dependent genes, and echocardiographic indices of LV dysfunction. Conclusion miR-494-3p/JunD is a novel molecular axis involved in obesity-related MC. These results pave the way for approaches to prevent or treat LV dysfunction in obese patients.
The miR-26b-5p/KPNA2 Axis Is an Important Regulator of Burkitt Lymphoma Cell Growth
CANCERS
Authors: Niu, Fubiao; Kazimierska, Marta; Nolte, Ilja M.; Terpstra, Miente Martijn; de Jong, Debora; Koerts, Jasper; van der Sluis, Tineke; Rutgers, Bea; O'Connell, Ryan M.; Kok, Klaas; van den Berg, Anke; Dzikiewicz-Krawczyk, Agnieszka; Kluiver, Joost
Abstract
The expression of several microRNAs (miRNAs) is known to be changed in Burkitt lymphoma (BL), compared to its normal counterparts. Although for some miRNAs, a role in BL was demonstrated, for most of them, their function is unclear. In this study, we aimed to identify miRNAs that control BL cell growth. Two BL cell lines were infected with lentiviral pools containing either 58 miRNA inhibitors or 44 miRNA overexpression constructs. Eighteen constructs showed significant changes in abundance over time, indicating that they affected BL growth. The screening results were validated by individual green fluorescent protein (GFP) growth competition assays for fifteen of the eighteen constructs. For functional follow-up studies, we focused on miR-26b-5p, whose overexpression inhibited BL cell growth. Argonaute 2 RNA immunoprecipitation (Ago2-IP) in two BL cell lines revealed 47 potential target genes of miR-26b-5p. Overlapping the list of putative targets with genes showing a growth repression phenotype in a genome-wide CRISPR/Cas9 knockout screen, revealed eight genes. The top-5 candidates included EZH2, COPS2, KPNA2, MRPL15, and NOL12. EZH2 is a known target of miR-26b-5p, with oncogenic properties in BL. The relevance of the latter four targets was confirmed using sgRNAs targeting these genes in individual GFP growth competition assays. Luciferase reporter assay confirmed binding of miR-26b-5p to the predicted target site for KPNA2, but not to the other genes. In summary, we identified 18 miRNAs that affected BL cell growth in a loss- or gain-of-function screening. A tumor suppressor role was confirmed for miR-26b-5p, and this effect could at least in part be attributed to KPNA2, a known regulator of OCT4, c-jun, and MYC.