H19X‐encoded miR‐322(424)/miR‐503 regulates muscle mass by targeting translation initiation factors

Abstract

Background Skeletal muscle atrophy is a debilitating complication of many chronic diseases, disuse conditions, and ageing. Genome‐wide gene expression analyses have identified that elevated levels of microRNAs encoded by the H19X locus are among the most significant changes in skeletal muscles in a wide scope of human cachectic conditions. We have previously reported that the H19X locus is important for the establishment of striated muscle fate during embryogenesis. However, the role of H19X‐encoded microRNAs in regulating skeletal mass in adults is unknown. Methods We have created a transgenic mouse strain in which ectopic expression of miR‐322/miR‐503 is driven by the skeletal muscle‐specific muscle creatine kinase promoter. We also used an H19X mutant mouse strain in which transcription from the locus is interrupted by a gene trap. Animal phenotypes were analysed by standard histological methods. Underlying mechanisms were explored by using transcriptome profiling and validated in the two animal models and cultured myotubes. Results Our results demonstrate that the levels of H19X microRNAs are inversely related to postnatal skeletal muscle growth. Targeted overexpression of miR‐322/miR‐503 impeded skeletal muscle growth. The weight of gastrocnemius muscles of transgenic mice was only 54.5% of the counterparts of wild‐type littermates. By contrast, interruption of transcription from the H19X locus stimulates postnatal muscle growth by 14.4–14.9% and attenuates the loss of skeletal muscle mass in response to starvation by 12.8–21.0%. Impeded muscle growth was not caused by impaired IGF1/AKT/mTOR signalling or a hyperactive ubiquitin–proteasome system, instead accompanied by markedly dropped abundance of translation initiation factors in transgenic mice. miR‐322/miR‐503 directly targets eIF4E, eIF4G1, eIF4B, eIF2B5, and eIF3M. Conclusions Our study illustrates a novel pathway wherein H19X microRNAs regulate skeletal muscle growth and atrophy through regulating the abundance of translation initiation factors, thereby protein synthesis. The study highlights how translation initiation factors lie at the crux of multiple signalling pathways that control skeletal muscle mass.

The role of microRNAs in muscle wasting and recovery during critical illness: a systematic review

“…miR‐424‐5p has also been shown to target HSPA90AA 48 and inhibit myogenesis, and miR‐424‐5p levels were also altered in muscle of cachexic patients 49 . In addition, data from animal studies support the role of miR‐424 as a negative regulator of muscle growth; specifically, ectopic expression of miR‐322(494)/miR‐503, driven by muscle‐specific creatine kinase promoter, has been shown to inhibit muscle growth through decreased levels of translation initiation factors, but not the IGF1/AKT/mTOR signalling pathway 50 . Conversely, lower levels of these miRs have been shown to facilitate muscle growth: Supporting these data, Geng et al .…”

“…49 In addition, data from animal studies support the role of miR-424 as a negative regulator of muscle growth; specifically, ectopic expression of miR-322(494)/miR-503, driven by muscle-specific creatine kinase promoter, has been shown to inhibit muscle growth through decreased levels of translation initiation factors, but not the IGF1/AKT/mTOR signalling pathway. 50 Conversely, lower levels of these miRs have been shown to facilitate muscle growth: Supporting these data, Geng et al demonstrated that miR-322 (494) aggravated dexamethasone-induced atrophy of C2C12 myotubes and in vivo, through regulation of Igf1r and Insr expression. 51 Together, these data suggest that increases in miR-424-5p may be associated with suppression of anabolic processes in muscle during ICU admissions and its subsequent downregulation may be a part of the regenerative process.…”

Identification of Unique microRNA Profiles in Different Types of Idiopathic Inflammatory Myopathy

“…Many of the commonly deregulated miRNAs have already established associations with muscle physiology and muscle-related disorders [4,5,24,25]. Published research on muscle-related miRNAs in IIM has paid special attention to the miRNAs known as classical myomiRs.…”

miR-27b-3p Attenuates Muscle Atrophy by Targeting Cbl-b in Skeletal Muscles

“…miRNA can inhibit the expression of target genes in two ways by organizing mRNA translation or causing it to be explained by RISC [ 22 , 23 ]. In previous studies, it was found that miRNAs are involved in various regulatory pathways in skeletal muscle [ 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. For example, miR-696 has been confirmed to be a physical-activity-dependent miRNA.…”