Fine-tuning the tRNA anticodon arm for multiple/consecutive incorporations of β-amino acids and analogs

Ribosomal incorporation of β-amino acids into nascent peptides is much less efficient than that of the canonical α-amino acids. To overcome this, we have engineered a tRNA chimera bearing T-stem of tRNAGlu and D-arm of tRNAPro1, referred to as tRNAPro1E2, which efficiently recruits EF-Tu and EF-P. Using tRNAPro1E2 indeed improved β-amino acid incorporation. However, multiple/consecutive incorporations of β-amino acids are still detrimentally poor. Here, we attempted fine-tuning of the anticodon arm of tRNAPro1E2 aiming at further enhancement of β-amino acid incorporation. By screening various mutations introduced into tRNAPro1E2, C31G39/C28G42 mutation showed an approximately 3-fold enhancement of two consecutive incorporation of β-homophenylglycine (βPhg) at CCG codons. The use of this tRNA made it possible for the first time to elongate up to ten consecutive βPhg's. Since the enhancement effect of anticodon arm mutations differs depending on the codon used for β-amino acid incorporation, we optimized anticodon arm sequences for five codons (CCG, CAU, CAG, ACU and UGG). Combination of the five optimal tRNAs for these codons made it possible to introduce five different kinds of β-amino acids and analogs simultaneously into model peptides, including a macrocyclic scaffold. This strategy would enable ribosomal synthesis of libraries of macrocyclic peptides containing multiple β-amino acids.

A thioacetamide-induced liver fibrosis model for pre-clinical studies in microminipig

Drug-induced liver fibrosis models are used in normal and immunosuppressed small animals for transplantation and regenerative medicine to improve liver fibrosis. Although large animal models are needed for pre-clinical studies, they are yet to be established owing to drug sensitivity in animal species and difficulty in setting doses. In this study, we evaluated liver fibrosis by administering thioacetamide (TA) to normal microminipig and thymectomized microminipig; 3 times for 1 week (total duration: 8 weeks). The pigs treated with TA showed elevated blood cytokine levels and a continuous liver injury at 8 weeks. RNA-seq of the liver showed increased expression of fibrosis-related genes after TA treatment. Histopathological examination showed degenerative necrosis of hepatocytes around the central vein, and revealed fibrogenesis and hepatocyte proliferation. TA treatment caused CD3-positive T cells and macrophages scattered within the hepatic lobule to congregate near the center of the lobule and increased αSMA-positive cells. Thymectomized pigs showed liver fibrosis similar to that of normal pigs, although the clinical signs tended to be milder. This model is similar to pathogenesis of liver fibrosis reported in other animal models. Therefore, it is expected to contribute to research as a drug discovery and pre-clinical transplantation models.