Aging is a biological process characterized by the irreversible and time-dependent deterioration of cell functions, tissues, and organs. Accumulating studies in a wide range of species from yeast to human revealed changes associated with the aging process to be conserved throughout evolution. The main characteristics of aging are (i) genomic instability, (ii) loss of telomere function, (iii) epigenetic changes,(iv) increased cellular senescence, (v) depletion of the stem cell pool, (vi) altered intercellular communication and (vii) loss of protein homeostasis. Among the multiple molecular mechanisms underlying aging, alterations of the translation machinery affecting the rate and selectivity of protein biosynthesis seem to play a central role. At the very heart of translation is the ribosome, a multifaceted and universally conserved RNA-protein particle responsible for accurate polypeptide synthesis and co-translational protein folding. Here we summarize and discuss recent developments on the contribution of altered translation and age-dependent modifications on the ribosome structure to aging and cellular senescence.

Modifications of ribosomal RNA expand the nucleotide repertoire and thereby contribute to ribosome heterogeneity and translational regulation of gene expression. One particular m5C modification of 25S ribosomal RNA, which is introduced by Rcm1p, was previously shown to modulate stress responses and lifespan in yeast and other small organisms. Here, we report that NSUN5 is the functional orthologue of Rcm1p, introducing m5C3782 into human and m5C3438 into mouse 28S ribosomal RNA. Haploinsufficiency of the NSUN5 gene in fibroblasts from William Beuren syndrome patients causes partial loss of this modification. The N-terminal domain of NSUN5 is required for targeting to nucleoli, while two evolutionary highly conserved cysteines mediate catalysis. Phenotypic consequences of NSUN5 deficiency in mammalian cells include decreased proliferation and size, which can be attributed to a reduction in total protein synthesis by altered ribosomes. Strikingly, Nsun5 knockout in mice causes decreased body weight and lean mass without alterations in food intake, as well as a trend towards reduced protein synthesis in several tissues. Together, our findings emphasize the importance of single RNA modifications for ribosome function and normal cellular and organismal physiology.

Lactococcus lactis possesses a pronounced extracellular Cu 2+ -reduction activity which leads to the accumulation of Cu + in the medium. The kinetics of this reaction were not saturable by increasing copper concentrations, suggesting a non-enzymic reaction. A copper-reductasedeficient mutant, isolated by random transposon mutagenesis, had an insertion in the menE gene, which encodes O-succinylbenzoic acid CoA ligase. This is a key enzyme in menaquinone biosynthesis. The DmenE mutant was deficient in short-chain menaquinones, and exogenously added menaquinone complemented the copper-reductase-deficient phenotype. Haem-induced respiration of wild-type L. lactis efficiently suppressed copper reduction, presumably by competition by the bd-type quinol oxidase for menaquinone. As expected, the DmenE mutant was respiration-deficient, but could be made respiration-proficient by supplementation with menaquinone. Growth of wild-type cells was more copper-sensitive than that of the DmenE mutant, due to the production of Cu + ions by the wild-type. This growth inhibition of the wild-type was strongly attenuated if Cu + was scavenged with the Cu(I) chelator bicinchoninic acid. These findings support a model whereby copper is non-enzymically reduced at the membrane by menaquinones. Respiration effectively competes for reduced quinones, which suppresses copper reduction. These findings highlight novel links between copper reduction, respiration and Cu + toxicity in L. lactis.

Originally considered futile degradation products, tRNA-derived RNA fragments (tdRs) have been shown over the recent past to be crucial players in orchestrating various cellular functions. Unlike other small non-coding RNA (ncRNA) classes, tdRs possess a multifaceted functional repertoire ranging from regulating transcription, apoptosis, RNA interference, ribosome biogenesis to controlling translation efficiency. A subset of the latter tdRs has been shown to directly target the ribosome, the central molecular machine of protein biosynthesis. Here we describe the function of the mammalian tRNA Pro 5ʹ half, a 35 residue long ncRNA associated with ribosomes and polysomes in several mammalian cell lines. Addition of tRNA Pro halves to mammalian in vitro translation systems results in global translation inhibition and concomitantly causes the upregulation of a specific low molecular weight translational product. This tRNA Pro 5ʹ half-dependent translation product consists of both RNA and amino acids. Transfection of the tRNA Pro half into HeLa cells leads to the formation of the same product in vivo. The migration of this product in acidic gels, the insensitivity to copper sulphate treatment, the resistance to 3ʹ polyadenylation, and the association with 80S monosomes indicate that the accumulated product is peptidyl-tRNA. Our data thus suggest that binding of the tRNA Pro 5ʹ half to the ribosome leads to ribosome stalling and to the formation of peptidyl-tRNA. Our findings revealed a so far unknown functional role of a tdR thus further enlarging the functional heterogeneity of this emerging class of ribo-regulators.

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SummaryQuinones are ubiquitous in the environment. They occur naturally but are also in widespread use in human and industrial activities. Quinones alone are relatively benign to bacteria, but in combination with copper, they become toxic by a mechanism that leads to intracellular thiol depletion. Here, it was shown that the yahCD-yaiAB operon of Lactococcus lactis IL1403 provides resistance to combined copper/quinone stress. The operon is under the control of CopR, which also regulates expression of the copRZA copper resistance operon as well as other L. lactis genes. Expression of the yahCD-yaiAB operon is induced by copper but not by quinones. Two of the proteins encoded by the operon appear to play key roles in alleviating quinone/copper stress: YaiB is a flavoprotein that converts p-benzoquinones to less toxic hydroquinones, using reduced nicotinamide adenine dinucleotide phosphate (NADPH) as reductant; YaiA is a hydroquinone dioxygenase that converts hydroquinone putatively to 4-hydroxymuconic semialdehyde in an oxygen-consuming reaction. Hydroquinone and methylhydroquinone are both substrates of YaiA. Deletion of yaiB causes increased sensitivity of L. lactis to quinones and complete growth arrest under combined quinone and copper stress. Copper induction of the yahCD-yaiAB operon offers protection to copper/quinone toxicity and could provide a growth advantage to L. lactis in some environments.

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Psoriasis is generally thought to has the aspects of a genetic predisposition and environmental insults. Around one-third of patients report a family history and identical twin studies suggest a 70% chance of onset if the other twin has psoriasis. The prevalence rate in the Western countries is 2 to 3%, however, it's only 0.2 % in Japan. The aldo-keto reductase (AKR) 1C3, a NAD(P)H-dependent oxidoreductase, is reported to induce keratin 10 and reduce loricrin in the human skin. Down-regulation of AKR1C3 induces epidermal hyperplasia with abnormal terminal differentiation resembling pathophysiology of psoriasis lesions. In fact, according to GEO array database, AKR1C3 is down regulated in psoriasis lesion (GSE 13355). In this study, we focused on rs12529, a single nucleotide polymorphism (SNP) in human AKR1C3 gene and reported high probability in Caucasians (40-46%) but rare in Japanese (7-8%). DNA is isolated from whole blood obtained from 232 psoriasis patients. The cohort included 138 patients of psoriasis vulgaris, 75 patients of psoriatic arthritis, and 19 patients of generalized pustular psoriasis. Male to female sex ratio is approximately 2.8:1. As the results of TaqMan SNP genotyping assay, Genotype detail of our cohort was G/G:73%, G/C:25.2%