Gianni’, MaurizioMaurizioGianni’Goracci, LauraLauraGoracciSchlaefli, AnnaAnnaSchlaefliDi Veroli, AlessandraAlessandraDi VeroliKurosaki, MamiMamiKurosakiGuarrera, LucaLucaGuarreraBolis, MarcoMarcoBolisFoglia, MarikaMarikaFogliaLupi, MonicaMonicaLupiTschan, MarioMarioTschan0000-0001-5897-3647Cruciani, GabrieleGabrieleCrucianiTerao, MinekoMinekoTeraoGarattini, EnricoEnricoGarattini2024-10-092024-10-092022https://boris-portal.unibe.ch/handle/20.500.12422/66670The role played by lipids in the process of granulocytic differentiation activated by all-trans retinoic acid (ATRA) in Acute-Promyelocytic-Leukemia (APL) blasts is unknown. The process of granulocytic differentiation activated by ATRA in APL blasts is recapitulated in the NB4 cell-line, which is characterized by expression of the pathogenic PML-RARα fusion protein. In the present study, we used the NB4 model to define the effects exerted by ATRA on lipid homeostasis. Using a high-throughput lipidomic approach, we demonstrate that exposure of the APL-derived NB4 cell-line to ATRA causes an early reduction in the amounts of cardiolipins, a major lipid component of the mitochondrial membranes. The decrease in the levels of cardiolipins results in a concomitant inhibition of mitochondrial activity. These ATRA-dependent effects are causally involved in the granulocytic maturation process. In fact, the ATRA-induced decrease of cardiolipins and the concomitant dysfunction of mitochondria precede the differentiation of retinoid-sensitive NB4 cells and the two phenomena are not observed in the retinoid-resistant NB4.306 counterparts. In addition, ethanolamine induced rescue of the mitochondrial dysfunction activated by cardiolipin deficiency inhibits ATRA-dependent granulocytic differentiation and induction of the associated autophagic process. The RNA-seq studies performed in parental NB4 cells and a NB4-derived cell population, characterized by silencing of the autophagy mediator, ATG5, provide insights into the mechanisms underlying the differentiating action of ATRA. The results indicate that ATRA causes a significant down-regulation of CRLS1 (Cardiolipin-synthase-1) and LPCAT1 (Lysophosphatidylcholine-Acyltransferase-1) mRNAs which code for two enzymes catalyzing the last steps of cardiolipin synthesis. ATRA-dependent down-regulation of CRLS1 and LPCAT1 mRNAs is functionally relevant, as it is accompanied by a significant decrease in the amounts of the corresponding proteins. Furthermore, the decrease in CRLS1 and LPCAT1 levels requires activation of the autophagic process, as down-regulation of the two proteins is blocked in ATG5-silenced NB4-shATG5 cells.en500 - Science::570 - Life sciences; biology600 - Technology::610 - Medicine & healtharticle10.48350/1643903501314210.1038/s41419-021-04476-z