# A Novel tRF-Lys-TTT-012 in Qingyu Pigs Mediates the Conversion of Muscle Fibers from Fast-Twitch to Slow-Twitch Type

## TL;DR

This study identifies a new RNA, tRF-Lys-TTT-012, that helps convert fast-twitch muscle fibers to slow-twitch in pigs, which could improve meat quality.

## Contribution

The study discovers tRF-Lys-TTT-012 as a novel tsRNA involved in muscle fiber type conversion in pigs.

## Key findings

- tRF-Lys-TTT-012 is upregulated in psoas major muscle and promotes myogenic differentiation.
- tRF-Lys-TTT-012 increases the proportion of slow muscle fibers and enhances mitochondrial function.
- tRF-Lys-TTT-012 may serve as a marker for slow muscle fibers and a target for fiber type transition.

## Abstract

Skeletal muscle is composed of various types of muscle fibers, and the composition of these fibers plays a significant role in muscle health, meat quality, and flavor. However, the mechanisms underlying tsRNA regulation of muscle fiber type conversion remain unclear. In this study, we used the psoas major muscle and latissimus dorsi muscle of pigs as models to reveal the expression profiles of tsRNAs in muscles with different fiber compositions. The results indicate that tsRNAs play a crucial regulatory role in muscle fiber type conversion. This study provides new insights into the molecular regulatory mechanisms of muscle fiber type conversion and offers references for the treatment and improvement of meat quality.

Skeletal muscle, the largest organ within the animal body, consists of multiple muscle fiber types. The distribution of these fiber types significantly impacts both athletic performance and the quality of meat. Growing evidence has demonstrated that transfer RNA (tRNA)-derived small RNAs (tsRNAs) are not merely byproducts of tRNA metabolism but also participate in multiple cellular metabolic processes. However, the role of tsRNAs in skeletal muscle fiber type transition remains elusive. In this study, a total of 403 differentially expressed tsRNAs were identified through small RNA sequencing in psoas major muscle (PM) and latissimus dorsi muscle (LD), among which 220 tsRNAs including tRF-Lys-TTT-012 were upregulated in psoas major muscle. Functional studies in C2C12 and PK15 cells demonstrated that it inhibited the proliferative capacity of C2C12 cells while promoting myogenic differentiation, increased the proportion of slow muscle fibers after differentiation, and drove muscle fiber type transition toward slow fibers. Additionally, tRF-Lys-TTT-012 enhanced mitochondrial number and function, potentially linking to the promotion of slow fiber characteristics. Collectively, tRF-Lys-TTT-012 may serve as a promising marker for slow muscle fibers and uncover a novel potential target for skeletal muscle fiber type transition toward the slow fiber phenotype.