Extracellular vesicle-derived miRNAs improve stem cell-based therapeutic approaches in muscle wasting conditions.

Skeletal muscle holds an intrinsic capability of growth and regeneration both in physiological conditions and in case of injury. Chronic muscle illnesses, generally caused by genetic and acquired factors, lead to deconditioning of the skeletal muscle structure and function, and are associated with a significant loss in muscle mass. At the same time, progressive muscle wasting is a hallmark of aging. Given the paracrine properties of myogenic stem cells, extracellular vesicle-derived signals have been studied for their potential implication in both the pathogenesis of degenerative neuromuscular diseases and as a possible therapeutic target. In this study, we screened the content of extracellular vesicles from animal models of muscle hypertrophy and muscle wasting associated with chronic disease and aging. Analysis of the transcriptome, protein cargo, and microRNAs (miRNAs) allowed us to identify a hypertrophic miRNA signature amenable for targeting muscle wasting, consisting of miR-1 and miR-208a. We tested this signature among others in vitro on mesoangioblasts (MABs), vessel-associated adult stem cells, and we observed an increase in the efficiency of myogenic differentiation. Furthermore, injections of miRNA-treated MABs in aged mice resulted in an improvement in skeletal muscle features, such as muscle weight, strength, cross-sectional area, and fibrosis compared to controls. Overall, we provide evidence that the extracellular vesicle-derived miRNA signature we identified enhances the myogenic potential of myogenic stem cells.

Isolation of Mammalian Mesoangioblasts: A Subset of Pericytes with Myogenic Potential.

Mesoangioblasts (MABs) are vessel-associated stem cells that express pericyte markers and are originally isolated from the embryonic dorsal aorta. From postnatal small vessels of skeletal muscle and heart, it is possible to isolate cells with similar characteristics to embryonic MABs. Adult MABs have the capacity to self-renew and to differentiate into cell types of mesodermal lineages upon proper culture conditions. To date, the origin of MABs and the relationship with other muscle stem cells are still debated. Recently, in a phase I-II clinical trial, intra-arterial HLA-matched MABs were proved to be relatively safe. Novel information on MAB pure populations is desirable, and implementation of their therapeutic potential is mandatory to approach efficacy in MAB-based treatments. This chapter provides an overview of the current techniques for isolation and characterization of rodent, canine, human, and equine adult MABs.

Aging affects the in vivo regenerative potential of human mesoangioblasts.

Sarcopenia is the age-related loss of muscle mass, strength, and function. Although the role of human satellite cells (SCs) as adult skeletal muscle stem cells has been deeply investigated, little is known about the impact of aging on muscle interstitial stem cells. Here, we isolated the non-SC CD56- fraction from human muscle biopsies of young and elderly subjects. The elderly interstitial cell population contained a higher number of CD15+ and PDGFRα+ cells when compared to young samples. In addition, we found that the CD56- /ALP+ cells were well represented as a multipotent stem cell population inside the CD56- fraction. CD56- /ALP+ /CD15- cells were clonogenic, and since they were myogenic and expressed NG2, α-SMA and PDGFRß can be considered mesoangioblasts (MABs). Interestingly, elderly MABs displayed a dramatic impairment in the myogenic differentiation ability in vitro and when transplanted in dystrophic immunodeficient Sgcb-null Rag2-null γc-null mice. In addition, elderly MABs proliferated less, but yet retained other multilineage capabilities. Overall, our results indicate that aging negatively impacted on the regenerative potential of MABs and this should be carefully considered for potential therapeutic applications of MABs.

Interactions between microRNAs and long non-coding RNAs in cardiac development and repair.

Non-coding RNAs (ncRNAs) are emerging players in muscle regulation. Based on their length and differences in molecular structure, ncRNAs are subdivided into several categories including small interfering RNAs, stable non-coding RNAs, microRNAs (miRs), long non-coding RNAs (lncRNAs), and circular RNAs. miRs and lncRNAs are able to post-transcriptionally regulate many genes and bring into play several traits simultaneously due to a myriad of different targets. Recent studies have emphasized their importance in cardiac regeneration and repair. As their altered expression affects cardiac function, miRs and lncRNAs could be potential targets for therapeutic intervention. In this context, miR- and lncRNA-based gene therapies are an interesting field for harnessing the complexity of ncRNA-based therapeutic approaches in cardiac diseases. In this review we will focus on lncRNA- and miR-driven regulations of cardiac development and repair. Finally, we will summarize miRs and lncRNAs as promising candidates for the treatment of heart diseases.

Human dental pulp pluripotent-like stem cells promote wound healing and muscle regeneration.

BACKGROUND: Dental pulp represents an easily accessible autologous source of adult stem cells. A subset of these cells, named dental pulp pluripotent-like stem cells (DPPSC), shows high plasticity and can undergo multiple population doublings, making DPPSC an appealing tool for tissue repair or maintenance. METHODS: DPPSC were harvested from the dental pulp of third molars extracted from young patients. Growth factors released by DPPSC were analysed using antibody arrays. Cells were cultured in specific differentiation media and their endothelial, smooth and skeletal muscle differentiation potential was evaluated. The therapeutic potential of DPPSC was tested in a wound healing mouse model and in two genetic mouse models of muscular dystrophy (Scid/mdx and Sgcb-null Rag2-null γc-null). RESULTS: DPPSC secreted several growth factors involved in angiogenesis and extracellular matrix deposition and improved vascularisation in all three murine models. Moreover, DPPSC stimulated re-epithelialisation and ameliorated collagen deposition and organisation in healing wounds. In dystrophic mice, DPPSC engrafted in the skeletal muscle of both dystrophic murine models and showed integration in muscular fibres and vessels. In addition, DPPSC treatment resulted in reduced fibrosis and collagen content, larger cross-sectional area of type II fast-glycolytic fibres and infiltration of higher numbers of proangiogenic CD206+ macrophages. CONCLUSIONS: Overall, DPPSC represent a potential source of stem cells to enhance the wound healing process and slow down dystrophic muscle degeneration.

Denervation does not Induce Muscle Atrophy Through Oxidative Stress.

Denervation leads to the activation of the catabolic pathways, such as the ubiquitin-proteasome and autophagy, resulting in skeletal muscle atrophy and weakness. Furthermore, denervation induces oxidative stress in skeletal muscle, which is thought to contribute to the induction of skeletal muscle atrophy. Several muscle diseases are characterized by denervation, but the molecular pathways contributing to muscle atrophy have been only partially described. Our study delineates the kinetics of activation of oxidative stress response in skeletal muscle following denervation. Despite the denervation-dependent induction of oxidative stress in skeletal muscle, treatments with anti-oxidant drugs do not prevent the reduction of muscle mass. Our results indicate that, although oxidative stress may contribute to the activation of the response to denervation, it is not responsible by itself of oxidative damage or neurogenic muscle atrophy.

Low Intensity Exercise Training Improves Skeletal Muscle Regeneration Potential.

PURPOSE: The aim of this study was to determine whether 12 days of low-to-moderate exercise training at low altitude (598 m a.s.l.) improves skeletal muscle regeneration in sedentary adult women. METHODS: Satellite cells were obtained from the vastus lateralis skeletal muscle of seven women before and after this exercise training at low altitude. They were investigated for differentiation aspects, superoxide anion production, antioxidant enzymes, mitochondrial potential variation after a depolarizing insult, intracellular Ca(2+) concentrations, and micro (mi)RNA expression (miR-1, miR-133, miR-206). RESULTS: In these myogenic populations of adult stem cells, those obtained after exercise training, showed increased Fusion Index and intracellular Ca(2+) concentrations. This exercise training also generally reduced superoxide anion production in cells (by 12-67%), although not in two women, where there was an increase of ~15% along with a reduced superoxide dismutase activity. miRNA expression showed an exercise-induced epigenetic transcription profile that was specific according to the reduced or increased superoxide anion production of the cells. CONCLUSIONS: The present study shows that low-to-moderate exercise training at low altitude improves the regenerative capacity of skeletal muscle in adult women. The differentiation of cells was favored by increased intracellular calcium concentration and increased the fusion index. This low-to-moderate training at low altitude also depicted the epigenetic signature of cells.