A common genetic variant of a mitochondrial RNA processing enzyme predisposes to insulin resistance.

Mitochondrial energy metabolism plays an important role in the pathophysiology of insulin resistance. Recently, a missense N437S variant was identified in the gene, which encodes a mitochondrial RNA processing enzyme within the RNase P complex, with predicted impact on metabolism. We used CRISPR-Cas9 genome editing to introduce this variant into the mouse gene and show that the variant causes insulin resistance on a high-fat diet.

Reduced mitochondrial translation prevents diet-induced metabolic dysfunction but not inflammation.

The contribution of dysregulated mitochondrial gene expression and consequent imbalance in biogenesis is not well understood in metabolic disorders such as insulin resistance and obesity. The ribosomal RNA maturation protein PTCD1 is essential for mitochondrial protein synthesis and its reduction causes adult-onset obesity and liver steatosis. We used haploinsufficient mice fed normal or high fat diets to understand how changes in mitochondrial biogenesis can lead to metabolic dysfunction.

Fidelity of translation initiation is required for coordinated respiratory complex assembly.

Mammalian mitochondrial ribosomes are unique molecular machines that translate 11 leaderless mRNAs; however, it is not clear how mitoribosomes initiate translation, since mitochondrial mRNAs lack untranslated regions. Mitochondrial translation initiation shares similarities with prokaryotes, such as the formation of a ternary complex of fMet-tRNA, mRNA and the 28 subunit, but differs in the requirements for initiation factors. Mitochondria have two initiation factors: MTIF2, which closes the decoding center and stabilizes the binding of the fMet-tRNA to the leaderless mRNAs, and MTIF3, whose role is not clear.

Stress signaling and cellular proliferation reverse the effects of mitochondrial mistranslation.

Translation fidelity is crucial for prokaryotes and eukaryotic nuclear-encoded proteins; however, little is known about the role of mistranslation in mitochondria and its potential effects on metabolism. We generated yeast and mouse models with error-prone and hyper-accurate mitochondrial translation, and found that translation rate is more important than translational accuracy for cell function in mammals. Specifically, we found that mitochondrial mistranslation causes reduced overall mitochondrial translation and respiratory complex assembly rates.

Concerted regulation of mitochondrial and nuclear non-coding RNAs by a dual-targeted RNase Z.

The molecular roles of the dually targeted ElaC domain protein 2 (ELAC2) during nuclear and mitochondrial RNA processing have not been distinguished. We generated conditional knockout mice of ELAC2 to identify that it is essential for life and its activity is non-redundant. Heart and skeletal muscle-specific loss of ELAC2 causes dilated cardiomyopathy and premature death at 4 weeks.

Tighter Ligand Binding Can Compensate for Impaired Stability of an RNA-Binding Protein.

It has been widely shown that ligand-binding residues, by virtue of their orientation, charge, and solvent exposure, often have a net destabilizing effect on proteins that is offset by stability conferring residues elsewhere in the protein. This structure-function trade-off can constrain possible adaptive evolutionary changes of function and may hamper protein engineering efforts to design proteins with new functions. Here, we present evidence from a large randomized mutant library screen that, in the case of PUF RNA-binding proteins, this structural relationship may be inverted and that active-site mutations that increase protein activity are also able to compensate for impaired stability.

Adult-onset obesity is triggered by impaired mitochondrial gene expression.

Mitochondrial gene expression is essential for energy production; however, an understanding of how it can influence physiology and metabolism is lacking. Several proteins from the pentatricopeptide repeat (PPR) family are essential for the regulation of mitochondrial gene expression, but the functions of the remaining members of this family are poorly understood. We created knockout mice to investigate the role of the PPR domain 1 (PTCD1) protein and show that loss of PTCD1 is embryonic lethal, whereas haploinsufficient, heterozygous mice develop age-induced obesity.

Hierarchical RNA Processing Is Required for Mitochondrial Ribosome Assembly.

The regulation of mitochondrial RNA processing and its importance for ribosome biogenesis and energy metabolism are not clear. We generated conditional knockout mice of the endoribonuclease component of the RNase P complex, MRPP3, and report that it is essential for life and that heart and skeletal-muscle-specific knockout leads to severe cardiomyopathy, indicating that its activity is non-redundant. Transcriptome-wide parallel analyses of RNA ends (PARE) and RNA-seq enabled us to identify that in vivo 5' tRNA cleavage precedes 3' tRNA processing, and this is required for the correct biogenesis of the mitochondrial ribosomal subunits.

Loss of the RNA-binding protein TACO1 causes late-onset mitochondrial dysfunction in mice.

The recognition and translation of mammalian mitochondrial mRNAs are poorly understood. To gain further insights into these processes in vivo, we characterized mice with a missense mutation that causes loss of the translational activator of cytochrome oxidase subunit I (TACO1). We report that TACO1 is not required for embryonic survival, although the mutant mice have substantially reduced COXI protein, causing an isolated complex IV deficiency.

The L-type Ca(2+) channel facilitates abnormal metabolic activity in the cTnI-G203S mouse model of hypertrophic cardiomyopathy.

Key Points: Genetic mutations in cardiac troponin I (cTnI) are associated with development of hypertrophic cardiomyopathy characterized by myocyte remodelling, disorganization of cytoskeletal proteins and altered energy metabolism. The L-type Ca(2+) channel is the main route for calcium influx and is crucial to cardiac excitation and contraction. The channel also regulates mitochondrial function in the heart by a functional communication between the channel and mitochondria via the cytoskeletal network.

The Role of the L-Type Ca Channel in Altered Metabolic Activity in a Murine Model of Hypertrophic Cardiomyopathy.

Heterozygous mice ( ) expressing the human disease-causing mutation exhibit cardinal features of hypertrophic cardiomyopathy (HCM) including hypertrophy, myocyte disarray, and increased myocardial fibrosis. Treatment of mice with the L-type calcium channel (I) antagonist diltiazem has been shown to decrease left ventricular anterior wall thickness, cardiac myocyte hypertrophy, disarray, and fibrosis. However, the role of the I in the development of HCM is not known.

A mutation in MT-TW causes a tRNA processing defect and reduced mitochondrial function in a family with Leigh syndrome.

Leigh syndrome (LS) is a progressive mitochondrial neurodegenerative disorder, whose symptoms most commonly include psychomotor delay with regression, lactic acidosis and a failure to thrive. Here we describe three siblings with LS, but with additional manifestations including hypertrophic cardiomyopathy, hepatosplenomegaly, cholestatic hepatitis, and seizures. All three affected siblings were found to be homoplasmic for an m.

Mutation in MRPS34 compromises protein synthesis and causes mitochondrial dysfunction.

The evolutionary divergence of mitochondrial ribosomes from their bacterial and cytoplasmic ancestors has resulted in reduced RNA content and the acquisition of mitochondria-specific proteins. The mitochondrial ribosomal protein of the small subunit 34 (MRPS34) is a mitochondria-specific ribosomal protein found only in chordates, whose function we investigated in mice carrying a homozygous mutation in the nuclear gene encoding this protein. The Mrps34 mutation causes a significant decrease of this protein, which we show is required for the stability of the 12S rRNA, the small ribosomal subunit and actively translating ribosomes.

Mitochondria: Unusual features of the mammalian mitoribosome.

Mitochondria are responsible for generating most of the energy required by the cell. The oxidative phosphorylation (OXPHOS) system that produces the energy is composed of nuclear and mitochondrial encoded polypeptides. The 13 polypeptides encoded by the mitochondrial genome are synthesized by mitochondrial ribosomes (mitoribosomes).

A bifunctional protein regulates mitochondrial protein synthesis.

Mitochondrial gene expression is predominantly regulated at the post-transcriptional level and mitochondrial ribonucleic acid (RNA)-binding proteins play a key role in RNA metabolism and protein synthesis. The AU-binding homolog of enoyl-coenzyme A (CoA) hydratase (AUH) is a bifunctional protein with RNA-binding activity and a role in leucine catabolism. AUH has a mitochondrial targeting sequence, however, its role in mitochondrial function has not been investigated.

RNA processing in human mitochondria.

Mammalian mitochondrial DNA is transcribed as precursor polycistronic transcripts containing 13 mRNAs, 2 rRNAs, punctuated by 22 tRNAs. The mechanisms involved in the excision of mitochondrial tRNAs from these polycistronic transcripts have remained largely unknown. We have investigated the roles of ELAC2, mitochondrial RNase P proteins 1 and 3, and pentatricopeptide repeat domain protein 1 in the processing of mitochondrial polycistronic transcripts.

Evidence for age-related and individual-specific changes in DNA methylation profile of mononuclear cells during early immune development in humans.

Environment induced epigenetic effects on gene expression in early life are likely to play important roles in mediating the risk of several immune-related diseases. In order to investigate this fully, it is essential to first document temporal changes in epigenetic profile in disease-free individuals as a prelude to defining environmentally mediated changes. Mononuclear cells (MC) were collected longitudinally from a small number of females at birth, 1 year, 2.

Differences in innate immune function between allergic and nonallergic children: new insights into immune ontogeny.

Background: Microbial products are of central interest in the modulation of allergic propensity.

Objective: We sought to explore whether allergic children show differences in microbial Toll-like receptor (TLR)-mediated responses over their first 5 years of life.

Methods: Mononuclear cells isolated from 35 allergic and 35 nonallergic children at birth and 1, 2.

Progress in understanding postnatal immune dysregulation in allergic disease.

It is increasingly unlikely that allergic disease is the result of isolated immune defects, but rather the result of altered gene activation patterns in intricate immune networks. This appears to be driven by complex environmental changes, including microbial exposure, diet, and pollutants, which are known to modify immune development in early life, beginning in pregnancy. The first models showing possible epigenetic mechanisms for these effects are beginning to emerge.