Skeletal Muscle Fat Infiltration with Aging An Important Factor of Sarcopenia

Muscle deconditioning occurring with aging is characterized by a decrease in muscle mass, muscle strength, and physical performance and is now well known as a geriatric syndrome called sarcopenia. Recent findings pointed out in this chapter also highlight fatty infiltrations as a new important factor of sarcopenia. These fatty infiltrations, commonly called IMAT (intermuscular adipose tissue), represent adipocyte depots located between muscle fibers. Their development and accumulation have been linked to skeletal muscle function and performance deterioration and thus directly related to a decreased mobility in older adults. This chapter highlights that IMAT accumulation seems to be linked to inactivity more than aging per se , and that physical activity interventions appear to be of major relevance in older populations. Identification of cost-effective interventions to fight against sarcopenia is an important public health challenge, and it requires understanding of the cellular and molecular mechanisms involved. Subsequently, this chapter also discusses the cellular and molecular players involved in aging-induced IMAT development. The role of a specific mesenchymal stem cell population called FAPs (fibro-adipogenic progenitors) is also described as well as potential signaling pathways involved.