Skeletal muscle as an endocrine organ: PGC-1α, myokines and exercise

• Besides its traditional functions, skeletal muscle has recently been discovered to be an endocrine organ.
• Myokines are signaling molecules with auto-, para- and/or endocrine functions that are secreted from skeletal muscle cells.
• Myokines affect most organs and thereby provide a molecular explanation for the cross-talk between skeletal muscle and other tissues.

An active lifestyle is crucial to maintain health into old age; inversely, sedentariness has been linked to an elevated risk for many chronic diseases. The discovery of myokines, hormones produced by skeletal muscle tissue, suggests the possibility that these might be molecular mediators of the whole body effects of exercise originating from contracting muscle fibers. Even though less is known about the sedentary state, the lack of contraction-induced myokines or the production of a distinct set of hormones in the inactive muscle could likewise contribute to pathological consequences in this context. In this review, we try to summarize the most recent developments in the study of muscle as an endocrine organ and speculate about the potential impact on our understanding of exercise and sedentary physiology, respectively.This article is part of a Special Issue entitled "Muscle Bone Interactions".