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.

Novel Components of an Active Mitochondrial K+/H+ Exchange

“…A (4,5,37), and the present study demonstrated that LETM1 fully restores mitochondrial KHE activity of the yeast triple mutant mdm38⌬ mrs7⌬ ydl183c like the exogenous bona fide KHE nigericin. We believe that further studies will 2) and mdm38⌬ (lanes 3-5).…”

Deletions involving genes WHSC1 and LETM1 may be necessary, but are not sufficient to cause Wolf–Hirschhorn Syndrome

“…38 Its cellular function as an ion exchanger [37][38][39][40][41] suggests potential roles in cell signaling and energy production. In flies and worms, LETM1 loss-of-function causes severe growth restriction and decreased viability.…”

Functional Complementation in Yeast Allows Molecular Characterization of Missense Argininosuccinate Lyase Mutations

“…cerevisiae genomic DNA was extracted from the wild type strain BY4741 using standard rapid glass bead lysis and phenolchloroform extraction as previously described (8). The coding region of the yeast homolog of argininosuccinate lyase (ARG4) was amplified from genomic DNA using primers Ϫ5F (5Ј-CAAA-CATGTCAGACGGCACT-3Ј) and 1422R (5Ј-TGAAATTCTT-GCGCATAACG-3Ј), and PCR conditions were as above.…”