ROLE OF STARD7 IN MITOCHONDRIAL DYNAMICS

ROJAS, MARÍA L.; CRUZ DEL PUERTO, MARIANO; FLORES MARTIN, JESICA B.; MIRANDA ANDREA; KOURDOVA LUCILLE; PANZETTA-DUTARI, GRACIELA M.; GENTI-RAIMONDI, SUSANA

Salta

Congreso; Reunión Conjunta por el XIV Congreso de la Pan-American Association for Biochemistry and Molecular Biology y LV Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular; 2019

SAIB

Mitochondria are dynamic organelles crucial for cell function and survival implicated inoxidative energy production. Mitochondrial lipids affect several important functions such asrespiratory metabolism, membrane architecture, protein import, mitophagy and mitochondrialdynamics. StarD7.I is a lipid transport protein isoform that has a mitochondrial targeting signalinvolved in phosphatidylcholine (PC) delivery to the mitochondria. Previous studies haveshown that StarD7 knockdown induces alterations in mitochondria and endoplasmic reticulummorphology with a reduction in mitochondrial PC content, however how different StarD7levels affect the mitochondrial dynamics was not explored yet. Here, we generatedHTR8/SVneo stable cell lines expressing the mitochondrial StarD7.I and the cytosolic StarD7.IIisoforms, respectively. We demonstrated that StarD7.I overexpression promotes alteredmitochondrial morphology whereas no changes were observed in stable StarD7.II cellsregarding control cells. These data were confirmed by immunofluorescent analysis in HTR-8/SVneo wild type cells transiently transfected with the bicistronic p-Lenti-StarD7.I-IRES-EGFPand p-Lenti-StarD7.II-IRES-EGFP plasmids. Mitochondrial targeting photoactivatable (PA-GFP)protein assays indicate that mitochondria from StarD7.I-overexpressing cells are able to yieldfusions with higher motility than control cells. Stable StarD7.I cells maintain the mitochondrialmembrane potential and produce lower ROS generation than control cells. Additionally, anincrease in the expression of Drp-1 and Mfn2 proteins was established in StarD7.I cells. Incontrast the levels of Mfn1 were decreased and no changes were observed in PGC1α proteinlevels. Moreover, the overexpression of Drp1-K38A promotes mitochondrial networkinvariably to collapse into large perinuclear aggregates, inhibiting StarD7 overexpression-induced mitochondrial fragmentation. These results indicate that StarD7 overexpression-mediated mitochondrial fragmentation occurs in a fission-dependent manner via Drp1.Nocodazole treatment separates the aggregates showing how mutant Drp1 affects themitochondrial morphology. Finally, the StarD7 silenced cells lead to mitochondrialfragmentation with a donuts phenotype, without motility associated to a decreased level ofDrp1 and Mfn2 and increase in ROS generation. Altogether these findings indicate thatalterations in StarD7.I expression produce significant changes in the proteins that control themitochondrial morphology impacting in mitochondrial dynamics. Granted by FONCyT, SECyT-UNC.