Abstract
MicroRNAs (miRNAs) are small non-coding RNAs that can regulate their target genes at the post-transcriptional level. Skeletal muscle comprises different fiber types that can be broadly classified as red, intermediate, and white. Recently, a set of miRNAs was found expressed in a fiber type-specific manner in red and white fiber types. However, an in-depth analysis of the miRNA transcriptome differences between all three fiber types has not been undertaken. Herein, we collected 15 porcine skeletal muscles from different anatomical locations, which were then clearly divided into red, white, and intermediate fiber type based on the ratios of myosin heavy chain isoforms. We further illustrated that three muscles, which typically represented each muscle fiber type (i.e., red: peroneal longus (PL), intermediate: psoas major muscle (PMM), white: longissimus dorsi muscle (LDM)), have distinct metabolic patterns of mitochondrial and glycolytic enzyme levels. Furthermore, we constructed small RNA libraries for PL, PMM, and LDM using a deep sequencing approach. Results showed that the differentially expressed miRNAs were mainly enriched in PL and played a vital role in myogenesis and energy metabolism. Overall, this comprehensive analysis will contribute to a better understanding of the miRNA regulatory mechanism that achieves the phenotypic diversity of skeletal muscles.
Highlights
Skeletal muscle is the major organ, by weight, in the body, accounting for approximately 40% of the body’s mass
Results showed that red fibers have the highest mtDNA copy number (Figure 1b), while white fibers have the highest lactate dehydrogenase A (LDHA) expression levels (Figure 1c)
These 15 porcine skeletal muscles were collected in different anatomic locations: longissimus dorsi muscle (LDM), psoas major muscle (PMM), gluteus medius (GMED), latissimus dorsi (LD), gastrocnemius (GC), peroneal longus (PL), soleus (S), semitendinosus (ST), masseter (M), triceps brachii (TB), obliquus externus abdominis (OEA), trapezius (T), semimembranosus (SM), biceps femoris (BF), semispinalis capitis (SC)
Summary
Skeletal muscle is the major organ, by weight, in the body, accounting for approximately 40% of the body’s mass It plays an important role in exercise and energy metabolism [1], and is a heterogeneous tissue comprising fibers that can be broadly classified as red (oxidative), intermediate (oxidative-glycolytic), and white (glycolytic) fiber types. Several studies have found that, because of the metabolic needs of oxidative and glycolytic skeletal muscles, they shared most muscle-specific miRNAs that expressed at distinct levels [9,10]. To better understand and elucidate the major determinants for phenotypic properties of various muscle types at the miRNA level, we screened and selected three muscles that typically represented each muscle fiber type (i.e., red, intermediate, and white) from 15 candidates, based on differences in their muscle fiber composition and metabolic capacity, and investigated. Illuminating the miRNA-based post-transcriptional regulatory mechanism in different fiber types will enrich our knowledge of the roles of miRNA in muscle biology, and help us to further understand the characteristics of distinct muscle fiber types
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