A Splicing Mutation in the Novel Mitochondrial Protein DNAJC11 Causes Motor Neuron Pathology Associated with Cristae Disorganization, and Lymphoid Abnormalities in Mice

Abstract

Mitochondrial structure and function is emerging as a major contributor to neuromuscular disease, highlighting the need for the complete elucidation of the underlying molecular and pathophysiological mechanisms. Following a forward genetics approach with N-ethyl-N-nitrosourea (ENU)-mediated random mutagenesis, we identified a novel mouse model of autosomal recessive neuromuscular disease caused by a splice-site hypomorphic mutation in a novel gene of unknown function, DnaJC11. Recent findings have demonstrated that DNAJC11 protein co-immunoprecipitates with proteins of the mitochondrial contact site (MICOS) complex involved in the formation of mitochondrial cristae and cristae junctions. Homozygous mutant mice developed locomotion defects, muscle weakness, spasticity, limb tremor, leucopenia, thymic and splenic hypoplasia, general wasting and early lethality. Neuropathological analysis showed severe vacuolation of the motor neurons in the spinal cord, originating from dilatations of the endoplasmic reticulum and notably from mitochondria that had lost their proper inner membrane organization. The causal role of the identified mutation in DnaJC11 was verified in rescue experiments by overexpressing the human ortholog. The full length 63 kDa isoform of human DNAJC11 was shown to localize in the periphery of the mitochondrial outer membrane whereas putative additional isoforms displayed differential submitochondrial localization. Moreover, we showed that DNAJC11 is assembled in a high molecular weight complex, similarly to mitofilin and that downregulation of mitofilin or SAM50 affected the levels of DNAJC11 in HeLa cells. Our findings provide the first mouse mutant for a putative MICOS protein and establish a link between DNAJC11 and neuromuscular diseases.

Novel insights into SLC25A46-related pathologies in a genetic mouse model

“…Following a forward genetics approach through N-ethyl-N-nitrosourea (ENU) random mutagenesis [17,18], we have recently identified a novel mouse model of autosomal recessive neurological phenotype characterized by ataxia, unsteady locomotion, tonic-clonic seizures, limb-clasping during tail suspension, reduced muscle strength, and growth retardation with premature lethality by the age of 3 months (Fig 1A–1D, S1 Video). Because of the prominent neurological symptoms, this phenotype was designated as ataxic ( atc ).…”

“…50 mg of mitochondria were freshly isolated from WT cerebellum and resuspended either in isotonic buffer (250 mM sucrose, 1 mM EDTA, 10 mM Tris/HCl pH 7.6) or hypotonic buffer (1 mM EDTA, 10 mM Tris/HCl pH 7.6) on ice, as previously described [18]. After 45 min incubation, mitochondria were pelleted by centrifugation (12.000 g, 5 min, 4°C).…”

“…A 202.693 bp fragment containing the human Slc25a46 gene was isolated upon electrophoresis in a 4% low melting agarose gel and digestion with β-agarase (New England Biolabs). This fragment was microinjected into fertilized (C57BL/6J x CBA/J) F2 oocytes as previously described [18,38,39]. Microinjections and embryo implantations were carried out by Transgenics & Gene Targeting Facility at B.S.R.C.…”

Shaping the mitochondrial inner membrane in health and disease

“…TMEM11 and its Drosophila ortholog PMI have been proposed to regulate cristae size . Mutation of the J‐protein DNAJC11, which is part of the MIB complex, results in severely aberrant cristae architecture and causes motor neuron pathology in mice (Table ) .…”

Shaping the multi-scale architecture of mitochondria

“…Interestingly, Cox17, a protein important for cytochrome c oxidase assembly, was also found to regulate MICOS complex stability in a copper ion dependent manner [29]. Other potential MICOS regulators include the previously uncharacterized protein DNACJ11 [30] and a novel set of MICOS-interacting proteins identified via proteomic analysis [28]. Further work is needed to understand how these different regulators modulate MICOS complex assembly, function, and IMM organization as well as how these interactions contribute to disease.…”