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

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.

Circulatory miR-221 & miR-542 expression profiles as potential molecular biomarkers in Hepatitis C Virus mediated liver cirrhosis and hepatocellular carcinoma

Chronic hepatitis C virus (cHCV) is a leading cause for liver cirrhosis (LC) and hepatocellular carcinoma (HCC) globally. So far, there is no optimal non-invasive biomarker for diagnosing HCV associated hepatic disorders. Circulatory miRNAs have drawn great attention as potential non-invasive biomarkers in various diseases. We quantified miR-221 and miR-542 levels in the plasma of 153 Egyptian patients (38 healthy controls (HC), 36 cHCV, 39 HCV-LC and 40 HCV mediated HCC groups) using qRT-PCR. All diseased groups exhibited significant upregulation in miR-221 expression (P < 0.001) with an increasing trend towards late stages (HCV-LC+HCV-HCC) as compared to early stages (cHCV). MiR-221 could significantly discriminate HCC patients from cHCV and HCV-LC with (AUC=0.698; P = 0.002) and (AUC=0.644; P = 0.032) respectively. Furthermore, miR-221 could significantly discriminate between HCC and non-HCC groups (AUC=0.670, P<0.001). HCV-LC & cHCV groups showed significant upregulation in miR-542 with remarkable downregulation in HCC group (P = 0.004). MiR-542 exhibited diagnostic power of (AUC=0.640; P = 0.044) and (AUC= 0.644; P = 0.040) for discriminating HCV-LC from HCC and cHCV groups respectively. Both miR-221 and miR-542 were significantly upregulated in cirrhotic group (HCV-LC) (P = 0.046 and P = 0.002 respectively) as compared to non-cirrhotic group (cHCV+HC). Combining both miRNAs in a panel significantly improved diagnostic performance as follows; HC and HCC (AUC=0.714, P < 0.001); HCC and LC (AUC=0.714, P = 0.001); HC and LC (AUC=0.710, P = 0.002) and also cHCV and HCC (AUC=0.672, P = 0.006). In conclusion, both miR-221 & miR-542 could stand as a standalone biomarker for staging various HCV associated disorders. Combining them would greatly enhance their diagnostic potential.