Movement, breathing, metabolism, body posture, and body temperature maintenance all depend on skeletal muscle, and malfunctions in the skeletal muscle can, thus, cause debilitating pathologies (i.e., myopathies, muscular dystrophies, etc.)1. Given its essential functions and abundance, skeletal muscle has drawn the attention of research labs worldwide that strive to understand the key aspects that support normal muscle function and can serve as therapeutic targets. In addition, skeletal muscle is a widely used model to study regeneration and stem cell function, as healthy muscle can fully self-repair after complete injury and degeneration, mostly due to its resident stem cells2; these are also called satellite cells and are localized under the basal lamina in the periphery of the muscle fibers3.
The core cells of adult skeletal muscle are the myofibers (long syncytial multinuclear cells) and the satellite cells (stem cells with myogenic potential that are quiescent until an injury activates them). The latter cells are the central cells of muscle regeneration, and this process cannot occur in their absence4,5,6,7. In their immediate microenvironment, there are multiple cell types and molecular factors that signal to them. This niche is gradually established throughout development and until adulthood8. Adult muscle contains multiple cell types (endothelial cells, pericytes, macrophages, fibro-adipogenic progenitors-FAPs, regulatory T cells, etc.)9,10 and extracellular matrix components (laminins, collagens, fibronectin, fibrillins, periostin, etc.)11 that interact with each other and with the satellite cells in the context of health, disease, and regeneration.
Preserving this complex niche in experimental settings is fundamental but challenging. Equally difficult is to maintain or return to quiescence, a cell state that is critical for satellite cells9. Several methods have been introduced to partially tackle these challenges, each with its advantages and disadvantages (detailed in the discussion section). Here, a method is presented that can partially overcome these two barriers. Muscles are initially harvested and then broken down mechanically and enzymatically before the heterogenous cell mixture is put into culture. Over the course of the culture, many cell types of the niche are detected, and satellite cells that have returned to quiescence are observed. As a last step of the protocol, the immunofluorescence steps that allow for the detection of each cell type through the use of universally accepted markers, are presented.