title: LETM1, deleted in Wolf-Hirschhorn syndrome is required for normal mitochondrial morphology and cellular viability.
abstract: Wolf-Hirschhorn syndrome (WHS) is a complex congenital syndrome caused by a monoallelic deletion of the short arm of chromosome 4. Seizures in WHS have been associated with deletion of LETM1 gene. LETM1 encodes for the human homologue of yeast Mdm38p, a mitochondria-shaping protein of unclear function. Here we show that human LETM1 is located in the inner membrane, exposed to the matrix and oligomerized in higher molecular weight complexes of unknown composition. Down-regulation of LETM1 did not disrupt these complexes, but led to DRP1-independent fragmentation of the mitochondrial network. Fragmentation was not associated with changes in the levels of respiratory chain complexes, or with obvious or latent mitochondrial dysfunction, but was recovered by nigericin, which catalyzes the electroneutral exchange of K+ against H+. Down-regulation of LETM1 caused 'necrosis-like' death, without activation of caspases and not inhibited by overexpression of Bcl-2. Primary fibroblasts from a WHS patient displayed reduced LETM1 mRNA and protein, but mitochondrial morphology was surprisingly unaffected, raising the question of whether and how WHS patients counteract the consequences of monoallelic deletion of LETM1. LETM1 highlights the relationship between mitochondrial ion homeostasis, integrity of the mitochondrial network and cell viability.
authors.affiliation: Venetian Institute of Molecular Medicine, 35129 Padova, Italy.
authors.forename: Kai Stefan
authors.initials: KS
authors.lastname: Dimmer
authors.forename: Francesca
authors.initials: F
authors.lastname: Navoni
authors.forename: Alberto
authors.initials: A
authors.lastname: Casarin
authors.forename: Eva
authors.initials: E
authors.lastname: Trevisson
authors.forename: Sabine
authors.initials: S
authors.lastname: Endele
authors.forename: Andreas
authors.initials: A
authors.lastname: Winterpacht
authors.forename: Leonardo
authors.initials: L
authors.lastname: Salviati
authors.forename: Luca
authors.initials: L
authors.lastname: Scorrano
mesh_terms: D002135:Calcium-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D002470:Cell Survival; D005347:Fibroblasts / Q000166:cytology; D017353:Gene Deletion; D006801:Humans; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000737:chemistry; D009336:Necrosis; D053140:Organelle Shape; D054877:Wolf-Hirschhorn Syndrome / Q000235:genetics* / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; C488528:LETM1 protein, human; D008565:Membrane Proteins