Skeletal muscle hypertrophy is a result of increased load, such as functional and stretch-overload. Activation of satellite cells and proliferation, differentiation and fusion are required for hypertrophy of overloaded skeletal muscles. On the contrary, a dramatic loss of skeletal muscle mass determines atrophy settings. The epigenetic changes involved in gene regulation at DNA and chromatin level are critical for the opposing phenomena, muscle growth and atrophy. Physiological properties of skeletal muscle tissue play a fundamental role in health and disease since it is the most abundant tissue in mammals. In fact, protein synthesis and degradation are finely modulated to maintain an appropriate muscle mass. When the molecular signaling is altered muscle wasting and weakness occurred, and this happened in most common inherited and acquired disorders such as muscular dystrophies, cachexia, and age-related wasting. To date, there is no accepted treatment to improve muscle size and strength, and these conditions pose a considerable anxiety to patients as well as to public health. Several molecules, including Magic-F1, myostatin inhibitor, IGF, glucocorticoids and microRNAs are currently investigated to interfere positively in the blueprint of skeletal muscle growth and regeneration.

Mesoangioblasts (MABs) are mesoderm-derived stem cells, associated with small vessels and originally described in the mouse embryonic dorsal aorta. Similar though not identical cells have been later identified and characterized from postnatal small vessels of skeletal muscle and heart. They have in common the expression of pericyte markers, the anatomical location, the ability to self-renew in culture, and to differentiate into various types of mesodermal lineages upon proper culture conditions. Currently, the developmental origin of MABs and the relationship with other muscle stem cells are not understood in detail and are the subject of active research. This chapter provides an outline of the latest techniques for isolation and characterization of adult MABs from human and mouse skeletal muscles.

The efficiency of the repair process following ischemic cardiac injury is a crucial determinant for the progression into heart failure and is controlled by both intra- and intercellular signaling within the heart. An enhanced understanding of this complex interplay will enable better exploitation of these mechanisms for therapeutic use. We used single-cell transcriptomics to collect gene expression data of all main cardiac cell types at different time-points after ischemic injury. These data unveiled cellular and transcriptional heterogeneity and changes in cellular function during cardiac remodeling. Furthermore, we established potential intercellular communication networks after ischemic injury. Follow up experiments confirmed that cardiomyocytes express and secrete elevated levels of beta-2 microglobulin in response to ischemic damage, which can activate fibroblasts in a paracrine manner. Collectively, our data indicate phase-specific changes in cellular heterogeneity during different stages of cardiac remodeling and allow for the identification of therapeutic targets relevant for cardiac repair.

SummaryIn early mouse pre-implantation development, primitive endoderm (PrE) precursors are platelet-derived growth factor receptor alpha (PDGFRα) positive. Here, we demonstrated that cultured mouse embryonic stem cells (mESCs) express PDGFRα heterogeneously, fluctuating between a PDGFRα+ (PrE-primed) and a platelet endothelial cell adhesion molecule 1 (PECAM1)-positive state (epiblast-primed). The two surface markers can be co-detected on a third subpopulation, expressing epiblast and PrE determinants (double-positive). In vitro, these subpopulations differ in their self-renewal and differentiation capability, transcriptional and epigenetic states. In vivo, double-positive cells contributed to epiblast and PrE, while PrE-primed cells exclusively contributed to PrE derivatives. The transcriptome of PDGFRα+ subpopulations differs from previously described subpopulations and shows similarities with early/mid blastocyst cells. The heterogeneity did not depend on PDGFRα but on leukemia inhibitory factor and fibroblast growth factor signaling and DNA methylation. Thus, PDGFRα+ cells represent the in vitro counterpart of in vivo PrE precursors, and their selection from cultured mESCs yields pure PrE precursors.

Understanding stem cell commitment and differentiation is a critical step towards clinical translation of cell therapies. In past few years, several cell types have been characterized and transplanted in animal models for different diseased tissues, eligible for a cell-mediated regeneration. Skeletal muscle damage is a challenge for cell-and gene-based therapeutical approaches, given the unique architecture of the tissue and the clinical relevance of acute damages or dystrophies. In this review, we will consider the regenerative potential of embryonic and somatic stem cells and the outcomes achieved on their transplantation into animal models for muscular dystrophy or acute muscle impairment.

Aims Pathological cardiac remodeling is characterized by cardiomyocyte hypertrophy and fibroblast activation, which can ultimately lead to maladaptive hypertrophy and heart failure (HF). Genome-wide expression analysis on heart tissue has been instrumental for the identification of molecular mechanisms at play. However, these data were based on signals derived from all cardiac cell types. Here we aimed for a more detailed view on molecular changes driving maladaptive cardiomyocyte hypertrophy to aid in the development of therapies to reverse pathological remodeling. Methods and Results Utilizing cardiomyocyte-specific reporter mice exposed to pressure overload by transverse aortic banding and cardiomyocyte isolation by flow cytometry, we obtained gene expression profiles of hypertrophic cardiomyocytes in the more immediate phase after stress, and cardiomyocytes showing pathological hypertrophy. We identified subsets of genes differentially regulated and specific for either stage. Among the genes specifically upregulated in the cardiomyocytes during the maladaptive phase we found known stress markers, such as Nppb and Myh7, but additionally identified a set of genes with unknown roles in pathological hypertrophy, including the platelet isoform of phosphofructokinase (PFKP). Norepinephrine-angiotensin II treatment of cultured human cardiomyocytes induced secretion of NT pro-BNP and recapitulated the upregulation of these genes, indicating conservation of the upregulation in failing cardiomyocytes. Moreover, several genes induced during pathological hypertrophy were also found to be increased in human heart failure, with their expression positively correlating to the known stress markers NPPB and MYH7. Mechanistically, suppression of Pfkp in primary cardiomyocytes attenuated stress-induced gene expression and hypertrophy, indicating that Pfkp is an important novel player in pathological remodeling of cardiomyocytes. Conclusions Using cardiomyocyte-specific transcriptomic analysis we identified novel genes induced during pathological hypertrophy that are relevant for human HF, and we show that PFKP is a conserved failure-induced gene that can modulate the cardiomyocyte stress response. Translational perspective Maladaptive cardiac remodeling is a consequence of pathological hypertrophy which includes cardiomyocytes changes and a decline in contractility. Our cardiomyocyte-specific gene expression studies revealed a gene program specific for pathological hypertrophy that is conserved in diseased mouse and human cardiomyocytes. We identified PFKP as a novel gene actively involved in cardiomyocyte remodeling, indicating PFKP as a potential therapeutic target to block the progression of heart failure.

Duchenne muscular dystrophy (DMD) is a genetic neuromuscular disorder caused by the absence of dystrophin. We developed a novel gene therapy approach based on the use of the piggyBac (PB) transposon system to deliver the coding DNA sequence (CDS) of either full-length human dystrophin (DYS: 11.1 kb) or truncated microdystrophins (MD1: 3.6 kb; MD2: 4 kb). PB transposons encoding microdystrophins were transfected in C2C12 myoblasts, yielding 65±2% MD1 and 66±2% MD2 expression in differentiated multinucleated myotubes. A hyperactive PB (hyPB) transposase was then deployed to enable transposition of the large-size PB transposon (17 kb) encoding the full-length DYS and green fluorescence protein (GFP). Stable GFP expression attaining 78±3% could be achieved in the C2C12 myoblasts that had undergone transposition. Western blot analysis demonstrated expression of the full-length human DYS protein in myotubes. Subsequently, dystrophic mesoangioblasts from a Golden Retriever muscular dystrophy dog were transfected with the large-size PB transposon resulting in 50±5% GFP-expressing cells after stable transposition. This was consistent with correction of the differentiated dystrophic mesoangioblasts following expression of full-length human DYS. These results pave the way toward a novel non-viral gene therapy approach for DMD using PB transposons underscoring their potential to deliver large therapeutic genes.

Caveolin-1 (Cav-1) can ambiguously behave as either tumor suppressor or oncogene depending on its phosphorylation state and the type of cancer. In this study we show that Cav-1 was phosphorylated on tyrosine 14 (pCav-1) by Src-kinase family members in various human cell lines and primary mouse cultures of rhabdomyosarcoma (RMS), the most frequent soft-tissue sarcoma affecting childhood. Cav-1 overexpression in the human embryonal RD or alveolar RH30 cells yielded increased pCav-1 levels and reinforced the phosphorylation state of either ERK or AKT kinase, respectively, in turn enhancing in vitro cell proliferation, migration, invasiveness and chemoresistance. In contrast, reducing the pCav-1 levels by administration of a Src-kinase inhibitor or through targeted Cav-1 silencing counteracted the malignant in vitro phenotype of RMS cells. Consistent with these results, xenotransplantation of Cav-1 overexpressing RD cells into nude mice resulted in substantial tumor growth in comparison to control cells. Taken together, these data point to pCav-1 as an important and therapeutically valuable target for overcoming the progression and multidrug resistance of RMS.