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

Illuminating mitochondrial translation through mouse models

Mitochondria are hubs of metabolic activity with a major role in ATP conversion by oxidative phosphorylation (OXPHOS). The mammalian mitochondrial genome encodes 11 mRNAs encoding 13 OXPHOS proteins along with 2 rRNAs and 22 tRNAs, that facilitate their translation on mitoribosomes. Maintaining the internal production of core OXPHOS subunits requires modulation of the mitochondrial capacity to match the cellular requirements and correct insertion of particularly hydrophobic proteins into the inner mitochondrial membrane. The mitochondrial translation system is essential for energy production and defects result in severe, phenotypically diverse diseases, including mitochondrial diseases that typically affect postmitotic tissues with high metabolic demands. Understanding the complex mechanisms that underlie the pathologies of diseases involving impaired mitochondrial translation is key to tailoring specific treatments and effectively targeting the affected organs. Disease mutations have provided a fundamental, yet limited, understanding of mitochondrial protein synthesis, since effective modification of the mitochondrial genome has proven challenging. However, advances in next generation sequencing, cryoelectron microscopy, and multi-omic technologies have revealed unexpected and unusual features of the mitochondrial protein synthesis machinery in the last decade. Genome editing tools have generated unique models that have accelerated our mechanistic understanding of mitochondrial translation and its physiological importance. Here we review the most recent mouse models of disease pathogenesis caused by defects in mitochondrial protein synthesis and discuss their value for preclinical research and therapeutic development.

The molecular machinery for maturation of primary mtDNA transcripts

Human mitochondria harbour a circular, polyploid genome (mtDNA) encoding 11 messenger RNAs (mRNAs), two ribosomal RNAs (rRNAs) and 22 transfer RNAs (tRNAs). Mitochondrial transcription produces long, polycistronic transcripts that span almost the entire length of the genome, and hence contain all three types of RNAs. The primary transcripts then undergo a number of processing and maturation steps, which constitute key regulatory points of mitochondrial gene expression. The first step of mitochondrial RNA processing consists of the separation of primary transcripts into individual, functional RNA molecules and can occur by two distinct pathways. Both are carried out by dedicated molecular machineries that substantially differ from RNA processing enzymes found elsewhere. As a result, the underlying molecular mechanisms remain poorly understood. Over the last years, genetic, biochemical and structural studies have identified key players involved in both RNA processing pathways and provided the first insights into the underlying mechanisms. Here, we review our current understanding of RNA processing in mammalian mitochondria and provide an outlook on open questions in the field.

Comprehensive functional interrogation of susceptibility loci in GWASs identified KIAA0391 as a novel oncogenic driver via regulating pyroptosis in NSCLC

Approximately 51 non-small-cell lung cancer (NSCLC) risk loci have been identified by genome-wide association studies (GWASs). We conducted a high throughput RNA-interference (RNAi) screening to identify the candidate causal genes in NSCLC risk loci. KIAA0391 at 14q13.1 had the highest score and could promote proliferation and metastasis of NSCLC in vitro and in vivo. We next prioritized rs3783313 as a causal variant at 14q13.1, by integrating a large-scale population study consisting of 27,120 lung cancer cases and 27,355 controls, functional annotation, and expression quantitative trait locus (eQTL) analysis. Then we found that rs3783313 could facilitate a promoter-enhancer interaction to upregulate KIAA0391 expression by affecting the affinity of transcription factor NFYA. Mechanistically, KIAA0391 knockdown dramatically influenced pyroptosis-related pathways and increased the expression of CASP1. And KIAA0391 transcriptionally repressed CASP1 by binding to SMAD2 and induced an anti-pyroptosis phenotype, promoting tumorigenesis of NSCLC, which provides new insights and potential target for NSCLC.

Multiple structural flavors of RNase P in precursor tRNA processing

The precursor transfer RNAs (pre-tRNAs) require extensive processing to generate mature tRNAs possessing proper fold, structural stability, and functionality required to sustain cellular viability. The road to tRNA maturation follows an ordered process: 5'-processing, 3'-processing, modifications at specific sites, if any, and 3'-CCA addition before aminoacylation and recruitment to the cellular protein synthesis machinery. Ribonuclease P (RNase P) is a universally conserved endonuclease in all domains of life, performing the hydrolysis of pre-tRNA sequences at the 5' end by the removal of phosphodiester linkages between nucleotides at position -1 and +1. Except for an archaeal species: Nanoarchaeum equitans where tRNAs are transcribed from leaderless-position +1, RNase P is indispensable for life and displays fundamental variations in terms of enzyme subunit composition, mechanism of substrate recognition and active site architecture, utilizing in all cases a two metal ion-mediated conserved catalytic reaction. While the canonical RNA-based ribonucleoprotein RNase P has been well-known to occur in bacteria, archaea, and eukaryotes, the occurrence of RNA-free protein-only RNase P in eukaryotes and RNA-free homologs of Aquifex RNase P in prokaryotes has been discovered more recently. This review aims to provide a comprehensive overview of structural diversity displayed by various RNA-based and RNA-free RNase P holoenzymes towards harnessing critical RNA-protein and protein-protein interactions in achieving conserved pre-tRNA processing functionality. Furthermore, alternate roles and functional interchangeability of RNase P are discussed in the context of its employability in several clinical and biotechnological applications. This article is categorized under: RNA Processing > tRNA Processing RNA Evolution and Genomics > RNA and Ribonucleoprotein Evolution RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Identification of genetic variants and individual genes associated with postpartum hypocalcemia in Holstein cows

Periparturient hypocalcemia is a complex metabolic disorder that occurs at the onset of lactation because of a sudden irreversible loss of Ca incorporated into colostrum and milk. Some cows are unable to quickly adapt to this demand and succumb to clinical hypocalcemia, commonly known as milk fever, whereas a larger proportion of cows develop subclinical hypocalcemia. The main goal of this study was to identify causative mutations and candidate genes affecting postpartum blood calcium concentration in Holstein cows. Data consisted of blood calcium concentration measured in 2513 Holstein cows on the first three days after parturition. All cows had genotypic information for 79 k SNP markers. Two consecutive rounds of imputation were performed: first, the 2513 Holstein cows were imputed from 79 k to 312 k SNP markers. This imputation was performed using a reference set of 17,131 proven Holstein bulls with 312 k SNP markers. Then, the 2513 Holstein cows were imputed from 312 k markers to whole-genome sequence data. This second round of imputation used 179 Holstein animals from the 1000 Bulls Genome Project as a reference set. Three alternative phenotypes were evaluated: (1) total calcium concentration in the first 24 h postpartum, (2) total calcium concentration in the first 72 h postpartum calculated as the area under the curve; and (3) the recovery of total calcium concentration calculated as the difference in total calcium concentration between 72 and 24 h. The identification of genetic variants associated with these traits was performed using a two-step mixed model-based approach implemented in the R package MixABEL. The most significant variants were located within or near genes involved in calcium homeostasis and vitamin D transport (GC), calcium and potassium channels (JPH3 and KCNK13), energy and lipid metabolism (CA5A, PRORP, and SREBP1), and immune response (IL12RB2 and CXCL8), among other functions. This work provides the foundation for the development of novel breeding and management tools for reducing the incidence of periparturient hypocalcemia in dairy cattle.

Blood-Glucose-Powered Metabolic Fuel Cell for Self-Sufficient Bioelectronics

Currently available bioelectronic devices consume too much power to be continuously operated on rechargeable batteries, and are often powered wirelessly, with attendant issues regarding reliability, convenience, and mobility. Thus, the availability of a robust, self-sufficient, implantable electrical power generator that works under physiological conditions would be transformative for many applications, from driving bioelectronic implants and prostheses to programing cellular behavior and patients' metabolism. Here, capitalizing on a new copper-containing, conductively tuned 3D carbon nanotube composite, an implantable blood-glucose-powered metabolic fuel cell is designed that continuously monitors blood-glucose levels, converts excess glucose into electrical power during hyperglycemia, and produces sufficient energy (0.7 mW cm^-2 , 0.9 V, 50 mm glucose) to drive opto- and electro-genetic regulation of vesicular insulin release from engineered beta cells. It is shown that this integration of blood-glucose monitoring with elimination of excessive blood glucose by combined electro-metabolic conversion and insulin-release-mediated cellular consumption enables the metabolic fuel cell to restore blood-glucose homeostasis in an automatic, self-sufficient, and closed-loop manner in an experimental model of type-1 diabetes.

Organization and expression of the mammalian mitochondrial genome

The mitochondrial genome encodes core subunits of the respiratory chain that drives oxidative phosphorylation and is, therefore, essential for energy conversion. Advances in high-throughput sequencing technologies and cryoelectron microscopy have shed light on the structure and organization of the mitochondrial genome and revealed unique mechanisms of mitochondrial gene regulation. New animal models of impaired mitochondrial protein synthesis have shown how the coordinated regulation of the cytoplasmic and mitochondrial translation machineries ensures the correct assembly of the respiratory chain complexes. These new technologies and disease models are providing a deeper understanding of mitochondrial genome organization and expression and of the diseases caused by impaired energy conversion, including mitochondrial, neurodegenerative, cardiovascular and metabolic diseases. They also provide avenues for the development of treatments for these conditions.