Beyond mice: Emerging and transdisciplinary models for the study of early-onset myopathies.

The use of the adapted models to decipher patho-physiological mechanisms of human diseases is always a great challenge. This is of particular importance for early-onset myopathies, in which pathological mutations often impact not only on muscle structure and function but also on developmental processes. Mice are currently the main animal model used to study neuromuscular disorders including the early-onset myopathies. However strategies based on simple animal models and on transdisciplinary approaches exploring mechanical muscle cell properties emerge as attractive, non-exclusive alternatives. These new ways provide valuable opportunities to improve our knowledge on how mechanical, biochemical, and genetic/epigenetic cues modulate the formation, organization and function of muscle tissues. Here we provide an overview of how single cell and micro-tissue engineering in parallel to non-mammalian, Drosophila and zebrafish models could contribute to filling gaps in our understanding of pathogenic mechanisms underlying early-onset myopathies. We also discuss their potential impact on designing new diagnostic and therapeutic strategies.

Quick and easy microfabrication of T-shaped cantilevers to generate arrays of microtissues.

Over the past decade, a major effort was made to miniaturize engineered tissues, as to further improve the throughput of such approach. Most existing methods for generating microtissues thus rely on T-shaped cantilevers made by soft lithography and based on the use of negative SU-8 photoresist. However, photopatterning T-shaped microstructures with these negative photoresists is fastidious and time-consuming. Here we introduce a novel method to quickly generate T-shaped cantilevers dedicated to generation of cellular microtissues, based on the use of positive photoresist. With only two layers of photoresist and one photomask, we were able to fabricate arrays of microwells in less than 3 h, each containing two T-shaped cantilevers presenting either a rectangular or a circular geometry. As a proof of concept, these arrays were then replicated in poly(dimethylsiloxane) and microtissues composed of NIH 3T3 fibroblasts encapsulated in collagen I were generated, while the two cantilevers simultaneously constrain and report forces generated by the microtissues. Immunostainings showed longitudinally aligned and elongated fibroblasts over the whole microtissue after 8 days of culture. The method described here opens the potential to quick prototyping platforms for high-throughput, low-volume screening applications.

Quiescence of human muscle stem cells is favored by culture on natural biopolymeric films.

BACKGROUND: Satellite cells are quiescent resident muscle stem cells that present an important potential to regenerate damaged tissue. However, this potential is diminished once they are removed from their niche environment in vivo, prohibiting the long-term study and genetic investigation of these cells. This study therefore aimed to provide a novel biomaterial platform for the in-vitro culture of human satellite cells that maintains their stem-like quiescent state, an important step for cell therapeutic studies. METHODS: Human muscle satellite cells were isolated from two donors and cultured on soft biopolymeric films of controlled stiffness. Cell adhesive phenotype, maintenance of satellite cell quiescence and capacity for gene manipulation were investigated using FACS, western blotting, fluorescence microscopy and electron microscopy. RESULTS: About 85% of satellite cells cultured in vitro on soft biopolymer films for 3 days maintained expression of the quiescence marker Pax7, as compared with 60% on stiffer films and 50% on tissue culture plastic. The soft biopolymeric films allowed satellite cell culture for up to 6 days without renewing the media. These cells retained their stem-like properties, as evidenced by the expression of stem cell markers and reduced expression of differentiated markers. In addition, 95% of cells grown on these soft biopolymeric films were in the G0/G1 stage of the cell cycle, as opposed to those grown on plastic that became activated and began to proliferate and differentiate. CONCLUSIONS: Our study identifies a new biomaterial made of a biopolymer thin film for the maintenance of the quiescence state of muscle satellite cells. These cells could be activated at any point simply by replating them onto a plastic culture dish. Furthermore, these cells could be genetically manipulated by viral transduction, showing that this biomaterial may be further used for therapeutic strategies.