Mutations in human mitochondrial tRNA genes are responsible for a variety of human inherited diseases. Investigations of the molecular mechanisms of these diseases are of great interest for nowadays scientists. According to the study of post-transcriptional modification patterns of human mitochondrial tRNAs, novel taurine-containing modifications were identified at the anticodon wobble nucleotides of mitochondrial tRNALeu(UUR) and tRNALys. Recently, it was reported that mitochondrial tRNAs harboring one of those encephalomyopathies related mutations, such as A8344G, A3243G, T3271C etc., lacked the normal taurine-containing modification at their anticodon wobble positions. Wobble modification deficiencies of mutant mitochondrial tRNAs were found from cybrid cells, as well as from patient tissues. Molecular surgery experiments showed that the wobble modification is essential for the interaction between the anticodon in tRNA and the codon in mRNA. Furthermore, the enzyme that is responsible for the formation of the modification was identified and characterized. These studies strongly suggested a key molecular factor responsible for the inherited mitochondrial encephalomyopathies and could potentially lead to the development of a gene therapy for these diseases.

Aminoacyl-tRNA synthetases (AARSs) catalyze aminoacylation of their tRNAs for protein biosynthesis. As belong to one of the most ancient and conserved enzyme family their additional functions in mammalian cells were focused recently. Mutations in tyrosyl-tRNA synthetase, glycyl-tRNA synthetase and alanyl-tRNA synthetase from patients and mice models were identified to cause two subtypes of Charcot-Marie-Tooth disease and cerebellar Purkinje cell loss, respectively. These mutations affect different functions of the three enzymes including aminoacylation, editing and unknown functions. These results combined AARSs with neurodegeneration and gave new sights into neuropathy.

Aminoacyl-tRNA synthetase is a class of ancient proteins, catalyzing the first reaction of protein biosynthesis. It has been found that they also participate in a lot of other cellular processes such as editing, tRNA maturation and transfer, RNA cleavage and function as cellular factors. Recent studies showed that some mitochondrial aminoacyl-tRNA synthetases are closely related with human diseases. A single point mutation in intervening sequence 2 (IVS2) of human mitochondrial arginyl-tRNA synthetase gene causes abnormal cleavage of its transcript, resulting in pontocerebellar hypoplasia. A series of mutations in human mitochondrial aspartyl-tRNA synthetase gene cause rapid decay of its mRNA or alteration in protein primary sequence, leading to leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation. A single nucleotide polymorphism in human mitochondrial leucyl-tRNA synthetase is significantly associated with type 2 diabetes. These results further enhance our understanding about the cellular function of aminoacyl-tRNA synthetase and promote studies toward the mechanism and therapy of aminoacyl-tRNA synthetase-causing mitochondrial diseases.

Aminoacyl-tRNA synthetase catalyzing the first reaction of protein biosynthesis. In mammalian cells, eight aminoacyl-tRNA synthetases (aaRSs) and three auxiliary protein factors form a macromolecular aminoacyl-tRNA synthetases complex (aaRS complex). The three nonsynthetase protein factors, namely, p43, p38, and p18 were found to be involved in many other important life activities besides their roles in the complex. The auxiliary factor p43 was the precursor of endothelial monocyte activating polypeptideⅡ (EMAPⅡ), which involved in angiogenesis and apoptosis. The auxiliary factor p38 was crucial for the development of lung, and its abnormal accumulation in neuron would be related to the Parkinson’s disease. The auxiliary factor p38 and p18 could promote the repair of DNA damage via different pathways in a highly organized way. All these breakthroughs enhance our understanding about the interaction between the aaRS complex and the macromolecular signaling network and promote the studies on this field.

Objective:To study the cytocompatibility of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation.Methods:Components of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation in three different voltages of 300 V,350 V and 400 V,Zr-Cu-Al-Ag alloy as cast condition and TI6Al4V alloy were made for the test.The water extracted from the components were obtained according to national standard.The L929 cells were cultivated in vitro in the extracts of these components separately.The L929 cells,cultured in Dulbecco's modified Eagle medium supplemented with 10 ％ fetal calf serum,served as the negative control group.And cells,cultured in Dulbecco's modified Eagle medium supplemented with 10 ％ fetal calf serum and 64 g/L phenol,served as the positive control group.The cytocompatibility of these components were evaluated by MTT colorimetric.Results:The cytotoxicity of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation is 0 grade.Microscopy showed that the morphology of L929 cells,cultured in the extracts of Zr-Cu-Al-Ag alloy coated by micro-arc oxidation were normal.There were no significant differences between micro-arc oxidationt and negative control groups.The cell multiplication curves of micro-arc oxidation and negative control groups were nearly overlapping and in the linearity increasing trend.The OD in micro-arc oxidation groups had no significant differences with negative control group (P＞0.05),but were higher than that of Zr-Cu-Al-Ag alloy as cast condition,TI6Al4V alloy and positive control groups (P＜0.05).Conclusions:The cytocompatibility of Zr-Cu-Al-Ag alloy has been improved by micro-arc oxidation technique.

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