Sarcopenia refers to a condition of progressive loss of skeletal muscle mass and function associated with a higher risk of falls and fractures in older adults. Musculoskeletal aging leads to reduced muscle mass and strength, affecting the quality of life in elderly people. In recent years, several studies contributed to improve the knowledge of the pathophysiological alterations that lead to skeletal muscle dysfunction; however, the molecular mechanisms underlying sarcopenia are still not fully understood. Muscle development and homeostasis require a fine gene expression modulation by mechanisms in which microRNAs (miRNAs) play a crucial role. miRNAs modulate key steps of skeletal myogenesis including satellite cells renewal, skeletal muscle plasticity, and regeneration. Here, we provide an overview of the general aspects of muscle regeneration and miRNAs role in skeletal mass homeostasis and plasticity with a special interest in their expression in sarcopenia and skeletal muscle adaptation to exercise in the elderly.

Background/Objectives: ETV6-related thrombocytopenia (ETV6-RT) is a rare autosomal dominant disorder characterized by mild thrombocytopenia since birth and an increased predisposition to hematologic malignancies. ETV6 functions as a transcriptional repressor, and its pathogenic variants, predominantly within the ETS domain, disrupt nuclear localization and transcriptional activity. In individuals with congenital thrombocytopenia, we identified two missense variants: c.1110A>G, p.Ile370Met, a novel variant, and c.1133G>A, p.Arg378Gln, a known variant with conflicting pathogenicity interpretations, for which functional characterization is necessary to provide an accurate molecular diagnosis. Methods: In silico bioinformatic tools and structural modeling were used to predict the impact of the variants. Functional assays included a dual-luciferase reporter assay to measure transcriptional activity and immunofluorescence/immunoblotting to assess intracellular localization in transfected HEK293T and HeLa cells. Results: Bioinformatic predictions and structural analyses suggested that the two variants might play a role in altering the folding or function of the ETS domain. Functional analysis revealed that p.Ile370Met abolished the ETV6 transcriptional repression activity, confirming its pathogenicity. p.Arg378Gln had no effect on the reporter gene levels, and, as expected, it localized in the nucleus. Interestingly, unlike the known mutations, which fail to enter the nucleus, p.Ile370Met retained partial nuclear localization. Conclusions: Since we described the first ETV6 mutation localized in the ETS domain that causes a loss of transcriptional activity, although it maintains the ability to enter the nucleus, we suggest that both transcriptional activity and intracellular localization assays are important for the accurate classification of ETV6 variants by functional studies.

Background/Objectives: Non-coding microRNA-34a (miR-34a) regulates the expression of key factors involved in several cellular processes, such as differentiation, apoptosis, proliferation, cell cycle, and senescence. Deregulation of the expression of these factors is implicated in the onset and progression of several human diseases, including cancer, neurodegenerative disorders, and pathologies associated with viral infections and inflammation. Despite numerous studies, the molecular mechanisms regulated by miR-34a remain to be fully understood. The present study aimed to generate miR-34a knockout cell lines to identify novel genes potentially regulated by its expression. Methods: We employed the CRISPR-Cas9 gene editing system to knock out the hsa-miR-34a gene in HeLa and 293T cell lines, two widely used models for studying molecular and cellular mechanisms. We compared proliferation rates and gene expression profiles via RNA-seq and qPCR analyses between the wild-type and miR-34a KO cell lines. Results: Knockout of miR-34a resulted in a decreased proliferation rate in both cell lines. Noteworthy, the ablation of miR-34a resulted in increased expression of the long non-coding RNA MALAT1. Additionally, miR-34a-5p silencing in the A375 melanoma cell line led to MALAT1 overexpression. Conclusions: Our findings support the role of the miR-34a/MALAT1 axis in regulating proliferation processes.