Culture conditions influence satellite cell activation and survival of single myofibers

Translational mobility medicine and ugo carraro: a life of significant scientific contributions reviewed in celebration

Prof. Ugo Carraro reached 80 years of age on 23 February 2023, and we wish to celebrate him and his work by reviewing his lifetime of scientific achievements in Translational Myology. Currently, he is a Senior Scholar with the University of Padova, Italy, where, as a tenured faculty member, he founded the Interdepartmental Research Center of Myology. Prof. Carraro, a pioneer in skeletal muscle research, is a world-class expert in structural and molecular investigations of skeletal muscle biology, physiology, pathology, and care. An authority in bidimensional gel electrophoresis for myosin light chains, he was the first to separate mammalian muscle myosin heavy chain isoforms by SDS-gel electrophoresis. He has demonstrated that long-term denervated muscle can survive denervation by myofiber regeneration, and shown that an athletic lifestyle has beneficial impacts on muscle reinnervation. He has utilized his expertise in translational myology to develop and validate rehabilitative treatments for denervated and ageing skeletal muscle. He has authored more than 160 PubMed listed papers and numerous scholarly books, including his recent autobiography. Prof. Carraro founded and serves as Editor-in-Chief of the European Journal of Translational Myology and Mobility Medicine. He has organized more than 40 Padua Muscle Days Meetings and continues this, encouraging students and young scientists to participate. As he dreams endlessly, he is currently validating non-invasive analyses on saliva, a promising approach that will allow increased frequency sampling to analyze systemic factors during the transient effects of training and rehabilitation by his proposed Full-Body in- Bed Gym for bed-ridden elderly.

Improved culture procedure for bovine muscle satellite cells for cultured meat

Many researchers and companies around the world are reported to have developed cultured meat, but their specific techniques have rarely been disclosed. Thus, the purpose of this study is to provide an improved procedure for cultured meat. There are four major steps in this cultured meat production: muscle cell isolation, proliferation, differentiation, and validation. The improved isolation enabled the efficient removal of unnecessary cells and tissues compared to previous procedures. In addition, proper use of basal media can improve the proliferation efficiency by about 2-fold. During the differentiation process, improved procedure was performed by using 10 % horse serum-containing media after 3 days of initial differentiation for myotube induction. This method demonstrated significantly enhanced myotube formation, up to 2.6-fold increase in area and up to 1.9-fold increase in fusion index compared to the previous method. This study provides a simple, improved procedure to enable more effective cultured meat production compared to previous procedures and is expected to help produce inexpensive and safe cultured meat.

Estrogen Signaling Dictates Musculoskeletal Stem Cell Behavior: Sex Differences in Tissue Repair

Sexual dimorphisms in humans and other species exist in visually evident features such as body size and less apparent characteristics, including disease prevalence. Current research is adding to a growing understanding of sex differences in stem cell function and response to external stimuli, including sex hormones such as estrogens. These differences are proving significant and directly impact both the understanding of stem cell processes in tissue repair and the clinical implementation of stem cell therapies. Adult stem cells of the musculoskeletal system, including those used for development and repair of muscle, bone, cartilage, fibrocartilage, ligaments, and tendons, are no exception. Both in vitro and in vivo studies have found differences in stem cell number, proliferative and differentiation capabilities, and response to estrogen treatment between males and females of many species. Maintaining the stemness and reducing senescence of adult stem cells is an important topic with implications in regenerative therapy and aging. As such, this review discusses the effect of estrogens on musculoskeletal system stem cell response in multiple species and highlights the research gaps that still need to be addressed. The following evidence from investigations of sex-related phenotypes in adult progenitor and stem cells are pieces to the big puzzle of sex-related effects on aging and disease and critical information for both fundamental tissue repair and regeneration studies and safe and effective clinical use of stem cells. Impact Statement This review summarizes current knowledge of sex differences in and the effects of estrogen treatment on musculoskeletal stem cells in the context of tissue engineering. Specifically, it highlights the impact of sex on musculoskeletal stem cell function and ability to regenerate tissue. Furthermore, it discusses the varying effects of estrogen on stem cell properties, including proliferation and differentiation, important to tissue engineering. This review aims to highlight the potential impact of estrogens and the importance of performing sex comparative studies in the field of tissue engineering.

Cytoplasmic HDAC4 regulates the membrane repair mechanism in Duchenne muscular dystrophy

BACKGROUND

Histone deacetylase 4 (HDAC4) is a stress-responsive factor that mediates multiple cellular responses. As a member of class IIa HDACs, HDAC4 shuttles between the nucleus and the cytoplasm; however, HDAC4 cytoplasmic functions have never been fully investigated. Duchenne muscular dystrophy (DMD) is a genetic, progressive, incurable disorder, characterized by muscle wasting, which can be treated with the unspecific inhibition of HDACs, despite this approach being only partially effective. More efficient strategies may be proposed for DMD only after the different HDAC members will be characterized.

METHODS

To fully understand HDAC4 functions, we generated dystrophic mice carrying a skeletal muscle-specific deletion of HDAC4 (mdx;KO mice). The progression of muscular dystrophy was characterized in mdx and age-matched mdx;KO mice by means of histological, molecular, and functional analyses. Satellite cells (SCs) from these mice were differentiated in vitro, to identify HDAC4 intrinsic functions influencing the myogenic potential of dystrophic SCs. Gain-of-function experiments revealed the cytoplasmic functions of HDAC4 in mdx;KO muscles.

RESULTS

Histone deacetylase 4 increased in the skeletal muscles of mdx mice (~3-fold; P < 0.05) and of DMD patients (n = 3, males, mean age 13.3 ± 1.5 years), suggesting that HDAC4 has a role in DMD. Its deletion in skeletal muscles importantly worsens the pathological features of DMD, leading to greater muscle fragility and degeneration over time. Additionally, it impairs SC survival, myogenic potential, and muscle regeneration, ultimately compromising muscle function (P < 0.05-0.001). The impaired membrane repair mechanism in muscles and SCs accounts for the mdx;KO phenotype. Indeed, the ectopic expression of Trim72, a major player in the membrane repair mechanism, prevents SC death (~20%; P < 0.01) and increases myogenic fusion (~40%; P < 0.01) in vitro; in vivo it significantly reduces myofibre damage (~10%; P < 0.005) and improves mdx;KO muscle function (P < 0.05). The mdx;KO phenotype is also fully rescued by restoring cytoplasmic levels of HDAC4, both in vitro and in vivo. The protective role of HDAC4 in the cytoplasm of mdx;KO muscles is, in part, independent of its deacetylase activity. HDAC4 expression correlates with Trim72 mRNA levels; furthermore, Trim72 mRNA decays more rapidly (P < 0.01) in mdx;KO muscle cells, compared with mdx ones.

CONCLUSIONS

Histone deacetylase 4 performs crucial functions in the cytoplasm of dystrophic muscles, by mediating the muscle repair response to damage, an important role in ensuring muscle homeostasis, probably by stabilizing Trim72 mRNA. Consequently, the cytoplasmic functions of HDAC4 should be stimulated rather than inhibited in muscular dystrophy treatments, a fact to be considered in future therapeutic approaches.

A tribute to Professor Sergio Adamo, Full Professor of Histology and Embryology at Sapienza University, Rome

Sergio Adamo prematurely left us on January 7th 2022, just one year after his retirement, leaving his family, friends and colleagues deeply sad and grieving. Sergio was a full Professor of Histology and Embryology at the Sapienza University of Rome. Since the foundation of the Institute of Histology and Embryology more than 50 years ago, he dedicated himself to the institution, research, and teaching with integrity, generosity, and a great sense of teamwork. Sergio's main research interests have been the mechanisms of myogenesis, muscle homeostasis and regeneration under normal and pathological conditions. Most relevant results obtained by Sergio and his collaborators indicate novel functions for the neurohypophyseal hormones, vasopressin and oxytocin, upon striated muscle differentiation, trophism, and homeostasis. Here we like to give the proper tribute to a mentor, a colleague and a sincere friend. He left an indelible mark on the professional and personal lives of all of us and his absence provokes a profound sense of emptiness. “The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt.” Bertrand Russell

Available In Vitro Models for Human Satellite Cells from Skeletal Muscle

Skeletal muscle accounts for almost 40% of the total adult human body mass. This tissue is essential for structural and mechanical functions such as posture, locomotion, and breathing, and it is endowed with an extraordinary ability to adapt to physiological changes associated with growth and physical exercise, as well as tissue damage. Moreover, skeletal muscle is the most age-sensitive tissue in mammals. Due to aging, but also to several diseases, muscle wasting occurs with a loss of muscle mass and functionality, resulting from disuse atrophy and defective muscle regeneration, associated with dysfunction of satellite cells, which are the cells responsible for maintaining and repairing adult muscle. The most established cell lines commonly used to study muscle homeostasis come from rodents, but there is a need to study skeletal muscle using human models, which, due to ethical implications, consist primarily of in vitro culture, which is the only alternative way to vertebrate model organisms. This review will survey in vitro 2D/3D models of human satellite cells to assess skeletal muscle biology for pre-clinical investigations and future directions.

Tissue-Engineered Skeletal Muscle Models to Study Muscle Function, Plasticity, and Disease

Skeletal muscle possesses remarkable plasticity that permits functional adaptations to a wide range of signals such as motor input, exercise, and disease. Small animal models have been pivotal in elucidating the molecular mechanisms regulating skeletal muscle adaptation and plasticity. However, these small animal models fail to accurately model human muscle disease resulting in poor clinical success of therapies. Here, we review the potential of in vitro three-dimensional tissue-engineered skeletal muscle models to study muscle function, plasticity, and disease. First, we discuss the generation and function of in vitro skeletal muscle models. We then discuss the genetic, neural, and hormonal factors regulating skeletal muscle fiber-type in vivo and the ability of current in vitro models to study muscle fiber-type regulation. We also evaluate the potential of these systems to be utilized in a patient-specific manner to accurately model and gain novel insights into diseases such as Duchenne muscular dystrophy (DMD) and volumetric muscle loss. We conclude with a discussion on future developments required for tissue-engineered skeletal muscle models to become more mature, biomimetic, and widely utilized for studying muscle physiology, disease, and clinical use.

Targeting PKCθ Promotes Satellite Cell Self-Renewal

Skeletal muscle regeneration following injury depends on the ability of satellite cells (SCs) to proliferate, self-renew, and eventually differentiate. The factors that regulate the process of self-renewal are poorly understood. In this study we examined the role of PKCθ in SC self-renewal and differentiation. We show that PKCθ is expressed in SCs, and its active form is localized to the chromosomes, centrosomes, and midbody during mitosis. Lack of PKCθ promotes SC symmetric self-renewal division by regulating Pard3 polarity protein localization, without affecting the overall proliferation rate. Genetic ablation of PKCθ or its pharmacological inhibition in vivo did not affect SC number in healthy muscle. By contrast, after induction of muscle injury, lack or inhibition of PKCθ resulted in a significant expansion of the quiescent SC pool. Finally, we show that lack of PKCθ does not alter the inflammatory milieu after acute injury in muscle, suggesting that the enhanced self-renewal ability of SCs in PKCθ-/- mice is not due to an alteration in the inflammatory milieu. Together, these results suggest that PKCθ plays an important role in SC self-renewal by stimulating their expansion through symmetric division, and it may represent a promising target to manipulate satellite cell self-renewal in pathological conditions.

Review: Analysis of the process and drivers for cellular meat production

Cell-based meat, also called 'clean', lab, synthetic or in vitro meat, has attracted much media interest recently. Consumer demand for cellular meat production derives principally from concerns over environment and animal welfare, while secondary considerations include consumer and public health aspects of animal production, and food security. The present limitations to cellular meat production include the identification of immortal cell lines, availability of cost-effective, bovine-serum-free growth medium for cell proliferation and maturation, scaffold materials for cell growth, scaling up to an industrial level, regulatory and labelling issues and at what stage mixing of myo-, adipo- and even fibrocytes can potentially occur. Consumer perceptions that cell-based meat production will result in improvements to animal welfare and the environment have been challenged, with the outcome needing to wait until the processes used in cell-based meat are close to a commercial reality. Challenges for cell-based meat products include the simulation of nutritional attributes, texture, flavour and mouthfeel of animal-derived meat products. There is some question over whether consumers will accept the technology, but likely there will be acceptance of cell-based meat products, in particular market segments. Currently, the cost of growth media, industry scale-up of specific components of the cell culture process, intellectual property sharing issues and regulatory hurdles mean that it will likely require an extended period for cellular meat to be consistently available in high-end restaurants and even longer to be available for the mass market. The progress in plant-based meat analogues is already well achieved, with products such as the ImpossibleTM Burger and other products already available. These developments may make the development of cellular meat products obsolete. But the challenges remain of mimicking not only the nutritional attributes, flavour, shape and structure of real meat, but also the changes in regulation and labelling.

Report on Abstracts of the 15th Meeting of IIM, the Interuniversity Institute of Myology - Assisi (Italy), October 11-14, 2018

On October 11-14, 2018, the 15th Meeting of the Interuniversity Institute of Myology (IIM) took place in the city Assisi, Italy. Muscle researchers from Italy, and various European and North-American countries gathered to discuss recent results on the physiology and diseases of skeletal muscle. The program showcased keynote lectures from world-renowned international speakers presenting advances in muscle stem cells, circadian rhythm, organismal development and growth, muscle physiology, and bioengineering. Novel, unpublished results from young trainees were presented as oral communications or posters, based on selection from submitted abstracts. Young trainees where directly involved in several aspects of the meeting by being responsible of organizing a scientific session, arranging three round tables tailored to the interests of their peers and chairing all scientific sessions. The meeting offered a unique opportunity for young researchers to present their work, have feedback from more experienced colleagues and establish collaborations to further understanding of muscular diseases and develop therapeutic strategies. The open, informal and friendly atmosphere of the meeting stimulated lively discussions, instrumental to highlight key areas of muscle research and foster scientific cross-fertilization and new collaborations. The meeting was very successful. A sign that the IIM community will continue to deliver important contributions to the training of young students and fellows, promoting our understanding of muscle formation and activity, the mechanism of muscle diseases and the progress toward therapeutic approaches. The Myology field is strong and articulated in basic, translational and early clinical research, moving toward the development of treatments for several muscle diseases as documented by the abstracts of the IIM meeting.

EJTM3 is also covering Mobility and Medicine at large, an update

Since the first 2018 issue, the European Journal of Translational Myology expanded its authorship and readership from the strict topics of biology, physiology, diagnostic, management and rehabilitation of skeletal muscle to the more clinically relevant fields of human mobility to those of general medicine. This third issue opens with a review on Chronic Fatigue Syndrome, a very complex medical problem, as its other names testify (Myalgic Encephalomyelitis or Systemic Exertion Intolerance Disease). A more typical molecular myology original article follows (Increasing autophagy does not affect neurogenic muscle atrophy), but then several Rapid Reports cover different Medical Specialties fields, related or unrelated to neuromyology, mobility problems and their potential solutions. The Advisors of EJTM invite Authors to submit typescripts, taking into account that the journal is keen to publish high-level papers in the fields of Translational Myology, Mobility and Medicine at large.

Implementing EjtM3 (European Journal of Translational Myology, Mobility, Medicine) along the silk-road

Two main novelties will appear in the second 2018 Issue of the European Journal of Translational Myology demonstrating that the journal is vital and in expansion, one novelty is that the journal is implementing its authorship and readership to broader clinical fields from muscle myology and mobility to clinical medicine and surgery. Consequently, the Editorial Board is also expanding to allow a broader expert evaluation of Authors submitted typescripts. The expanded Editorial Board recently evaluated the option to change the name of the journal from Ejtm to EjtM3 (Myology, Mobility, Medicine), in order to expand the original journal title meaning. Another important novelty is the first BAM Seminal Paper by Damraurer et al. 18(5): 139-148, 2008. It is now reprinted (with Basic and Applied Myology permission) in this Ejtm 28(2), 2018. The topic (chemotherapy-induced muscle wasting) was up-dated by one of our Editors stressing the relevance of the BAM 2008 paper to focus attention not only of myologists, but also of oncologists. From 2008, BAM (renamed from 2010 European Journal of Translational Myology) went far beyond the limits of pure Myology. Al last, but hopefully not at least, a series of Rapid Reports from Iranian Authors are paving the pathway Venetia-extreme Orient, along the ancient silk-road. Ejtm will enthusiastically publish clinical activities from surrounding and extreme Orient. The Marco Polo tradition and his bravery seem successfully continuing.