Restoration of mitochondrial function through activation of hypomodified tRNAs with pathogenic mutations associated with mitochondrial diseases.

Mutations in mitochondrial (mt-)tRNAs frequently cause mitochondrial dysfunction. Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), and myoclonus epilepsy associated with ragged red fibers (MERRF) are major clinical subgroups of mitochondrial diseases caused by pathogenic point mutations in tRNA genes encoded in mtDNA. We previously reported a severe reduction in the frequency of 5-taurinomethyluridine (τm5U) and its 2-thiouridine derivative (τm5s2U) in the anticodons of mutant mt-tRNAs isolated from the cells of patients with MELAS and MERRF, respectively. The hypomodified tRNAs fail to decode cognate codons efficiently, resulting in defective translation of respiratory chain proteins in mitochondria. To restore the mitochondrial activity of MELAS patient cells, we overexpressed MTO1, a τm5U-modifying enzyme, in patient-derived myoblasts. We used a newly developed primer extension method and showed that MTO1 overexpression almost completely restored the τm5U modification of the MELAS mutant mt-tRNALeu(UUR). An increase in mitochondrial protein synthesis and oxygen consumption rate suggested that the mitochondrial function of MELAS patient cells can be activated by restoring the τm5U of the mutant tRNA. In addition, we confirmed that MTO1 expression restored the τm5s2U of the mutant mt-tRNALys in MERRF patient cells. These findings pave the way for epitranscriptomic therapies for mitochondrial diseases.

Targeted delivery to macrophages and dendritic cells by chemically modified mannose ligand-conjugated siRNA.

Extrahepatic delivery of small interfering RNAs (siRNAs) may have applications in the development of novel therapeutic approaches. However, reports on such approaches are limited, and the scarcity of reports concerning the systemically targeted delivery of siRNAs with effective gene silencing activity presents a challenge. We herein report for the first time the targeted delivery of CD206-targetable chemically modified mannose-siRNA (CMM-siRNA) conjugates to macrophages and dendritic cells (DCs). CMM-siRNA exhibited a strong binding ability to CD206 and selectively delivered contents to CD206-expressing macrophages and DCs. Furthermore, the conjugates demonstrated strong gene silencing ability with long-lasting effects and protein downregulation in CD206-expressing cells in vivo. These findings could broaden the use of siRNA technology, provide additional therapeutic opportunities, and establish a basis for further innovative approaches for the targeted delivery of siRNAs to not only macrophages and DCs but also other cell types.

Complete chemical structures of human mitochondrial tRNAs.

Mitochondria generate most cellular energy via oxidative phosphorylation. Twenty-two species of mitochondrial (mt-)tRNAs encoded in mtDNA translate essential subunits of the respiratory chain complexes. mt-tRNAs contain post-transcriptional modifications introduced by nuclear-encoded tRNA-modifying enzymes. They are required for deciphering genetic code accurately, as well as stabilizing tRNA. Loss of tRNA modifications frequently results in severe pathological consequences. Here, we perform a comprehensive analysis of post-transcriptional modifications of all human mt-tRNAs, including 14 previously-uncharacterized species. In total, we find 18 kinds of RNA modifications at 137 positions (8.7% in 1575 nucleobases) in 22 species of human mt-tRNAs. An up-to-date list of 34 genes responsible for mt-tRNA modifications are provided. We identify two genes required for queuosine (Q) formation in mt-tRNAs. Our results provide insight into the molecular mechanisms underlying the decoding system and could help to elucidate the molecular pathogenesis of human mitochondrial diseases caused by aberrant tRNA modifications.

Current status of education and research on public health nutrition in Japan: comparison with South Korea, Taiwan, and mainland China.

BACKGROUND: Although the importance of capacity building for public health nutrition (PHN) has been increasing globally, reports on the current status of training programs for PHN in East-Asia including Japan are limited. The aim of this study was to compare the current status of education and research activities in the field of PHN in Japan with those in South Korea, Taiwan, and mainland China. METHODS: Necessary information was collected by internet search and telephone inquiry. Collection focused on the number of departments in colleges and universities with PHN as a compulsory subject in the 2016 academic year, and the number of articles and information related to these articles published in the journal Public Health Nutrition between 2007 and 2016. RESULTS: The number of departments with PHN as a compulsory subject was the highest in Japan (n = 137), followed by mainland China (n = 32), Taiwan (n = 18) and South Korea (n = 7). Using the classification list of education in each country and region, the majority of these departments were classified as home economics, natural science, health and welfare, and medical science in Japan, South Korea, Taiwan, and mainland China, respectively. Regarding publications, most of the articles were written in colleges and universities not having PHN as a compulsory subject in Japan, South Korea, and Taiwan. The number of articles per department among departments with compulsory PHN education was lowest in Japan (n = 0.3) compared to Taiwan, mainland China, and South Korea (n = 1.2, 2.7, and 3.7, respectively). CONCLUSIONS: Japan has a much higher number of departments with PHN as a compulsory subject than neighboring East Asian states and relatively low research activities in the field of PHN. This suggests that current university education may not lead to active PHN research in Japan. Further studies are warranted to explore the reasons for this.

Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease.

Modified uridine containing taurine, 5-taurinomethyluridine (τm5U), is found at the anticodon first position of mitochondrial (mt-)transfer RNAs (tRNAs). Previously, we reported that τm5U is absent in mt-tRNAs with pathogenic mutations associated with mitochondrial diseases. However, biogenesis and physiological role of τm5U remained elusive. Here, we elucidated τm5U biogenesis by confirming that 5,10-methylene-tetrahydrofolate and taurine are metabolic substrates for τm5U formation catalyzed by MTO1 and GTPBP3. GTPBP3-knockout cells exhibited respiratory defects and reduced mitochondrial translation. Very little τm5U34 was detected in patient's cells with the GTPBP3 mutation, demonstrating that lack of τm5U results in pathological consequences. Taurine starvation resulted in downregulation of τm5U frequency in cultured cells and animal tissues (cat liver and flatfish). Strikingly, 5-carboxymethylaminomethyluridine (cmnm5U), in which the taurine moiety of τm5U is replaced with glycine, was detected in mt-tRNAs from taurine-depleted cells. These results indicate that tRNA modifications are dynamically regulated via sensing of intracellular metabolites under physiological condition.

Defective Mitochondrial tRNA Taurine Modification Activates Global Proteostress and Leads to Mitochondrial Disease.

A subset of mitochondrial tRNAs (mt-tRNAs) contains taurine-derived modifications at 34U of the anticodon. Loss of taurine modification has been linked to the development of mitochondrial diseases, but the molecular mechanism is still unclear. Here, we showed that taurine modification is catalyzed by mitochondrial optimization 1 (Mto1) in mammals. Mto1 deficiency severely impaired mitochondrial translation and respiratory activity. Moreover, Mto1-deficient cells exhibited abnormal mitochondrial morphology owing to aberrant trafficking of nuclear DNA-encoded mitochondrial proteins, including Opa1. The mistargeted proteins were aggregated and misfolded in the cytoplasm, which induced cytotoxic unfolded protein response. Importantly, application of chemical chaperones successfully suppressed cytotoxicity by reducing protein misfolding and increasing functional mitochondrial proteins in Mto1-deficient cells and mice. Thus, our results demonstrate the essential role of taurine modification in mitochondrial translation and reveal an intrinsic protein homeostasis network between the mitochondria and cytosol, which has therapeutic potential for mitochondrial diseases.

Dietary intakes of adolescents from food insecure households: analysis of data from the 6th (2013-2015) Korea National Health and Nutrition Examination Survey.

BACKGROUND/OBJECTIVES: This study aimed at evaluating the dietary intakes of Korean adolescents affected by food insecurity, in comparison with those who were food secure. SUBJECTS/METHODS: The study used one day 24-hour dietary recall data from the 6th Korea National Health and Nutrition Examination Survey. The study subjects consisted of 1,453 adolescents of whom 695 were middle school-aged and 758 were high school-aged. Food security status was assessed using the 18-item questionnaire. Nutrient intake was evaluated in terms of nutrient density, insufficient intake, and excessive intake for selected nutrients, in addition to meeting the appropriate range for total energy intake and energy intakes from carbohydrate, sugar, protein, fat, and saturated fatty acids. Food intake was evaluated in terms of food group servings and dietary diversity score (DDS). RESULTS: The percentages of food insecurity were 11.1% for middle school-aged adolescents and 16.8% for high school-aged adolescents. Food insecure middle school-aged adolescents had higher intake of carbohydrate (P = 0.006) but lower intake of fat (P = 0.010) and saturated fatty acids (P = 0.005) than their food secure counterparts although the intake of both groups was in the recommended ranges. Nutrient intake among high school-aged adolescents was generally similar regardless of food security status. Both food secure and insecure adolescents showed insufficient intake of vitamin A, vitamin C, and calcium, and excessive sodium intake. They additionally had low prevalence of meeting appropriate intake ranges for energy, carbohydrate, and sugar. Food intake in terms of food group servings and DDS was also similar regardless of food security status among both age groups, with low intakes of foods from fruit and dairy groups. CONCLUSIONS: Except for a few nutrients among the middle school-aged adolescents, dietary intakes among Korean adolescents did not differ by food security status in this study.

Factors Related to Positive Changes in Perceived Health Status of Married Han Chinese and Korean-Chinese Women After Immigration to Korea.

This study aimed to compare factors related to changes in perceived health status of Han Chinese (traditional Chinese) and Korean-Chinese (Chinese nationals of Korean descent) women after immigration to Korea. During summer 2013, a survey was conducted with 151 Han and 158 Korean-Chinese women married to Korean men. Most of the respondents reported either no changes (82%) or positive changes (18%) in their perceived health status after immigration. The results of the multiple logistic regression analyses indicated healthy dietary behavior was related to positive changes in the perceived health status of both groups (odds ratio [OR] = 7.4 for Han Chinese; OR = 14.6 for Korean-Chinese). Among Han Chinese women, the length of residence in Korea and the change in perceived health status showed a negative relation (OR = 0.2). In contrast, their level of acculturation and health perception were positive (OR = 7.5). However, these results did not apply to the Korean-Chinese women. In conclusion, factors related to changes in perceived health status differed between the 2 groups although they shared healthy dietary behaviors as a common factor. Therefore, policies and programs aimed at promoting immigrant women's health should consider the differences between Han Chinese and Korean-Chinese.

NSUN3 methylase initiates 5-formylcytidine biogenesis in human mitochondrial tRNA(Met).

In human mitochondria, the AUA codon encodes methionine via a mitochondrial transfer RNA for methionine (mt-tRNA(Met)) that contains 5-formylcytidine (f(5)C) at the first position of the anticodon (position 34). f(5)C34 is required for deciphering the AUA codon during protein synthesis. Until now, the biogenesis and physiological role of f(5)C34 were unknown. We demonstrate that biogenesis of f(5)C34 is initiated by S-adenosylmethionine (AdoMet)-dependent methylation catalyzed by NSUN3, a putative methyltransferase in mitochondria. NSUN3-knockout cells showed strong reduction in mitochondrial protein synthesis and reduced oxygen consumption, leading to deficient mitochondrial activity. We reconstituted formation of 5-methylcytidine (m(5)C) at position 34 (m(5)C34) on mt-tRNA(Met) with recombinant NSUN3 in the presence of AdoMet, demonstrating that NSUN3-mediated m(5)C34 formation initiates f(5)C34 biogenesis. We also found two disease-associated point mutations in mt-tRNA(Met) that impaired m(5)C34 formation by NSUN3, indicating that a lack of f(5)C34 has pathological consequences.