In a recent review, Drs. A. Pratesi, F. Tarantini and M. Di Bari discuss major hormonal and immune mechanisms that drive the age-related decline in muscle quantity and quality. Besides the hormonal factors, the authors outline the role of some skeletal muscles mediators, termed ‘myokines’ that act in an autocrine, paracrine, or ‘hormone-like’ fashion. This includes interleukin (IL)-6, IL-8, IL-15, Brain-Derived Neurotrophic Factor (BDNF), and Leukemia Inhibitory Factor (LIF).
The decrease in skeletal muscle mass, by 3-8 % per decade after the age of 30 years, is recently referred to as sarcopenia. This condition typically accelerates around age 75, and is a factor in the occurrence of frailty and the likelihood of falls and fractures, functional disability, decreased bone density, glucose intolerance, and decreased heat and cold tolerance in older adults.
Interleukin-6, a cytokine quite often considered a pro-inflammatory mediator or ‘hormone’ was the first cytokine to be proposed as a myokine by Pedersen et al. in 2003. Interestingly, it seems that contraction-induced production of IL-6 by skeletal muscles might display anti-inflammatory effects. Recent research suggests that this myokine is able to suppress IL-1 and TNF-alpha synthesis and stimulate production of IL-1ra and IL-10. Also of note, evidence, as discussed in this review, indicates that muscle activity might improve lipid metabolism and reduce visceral fat. This, in turn, may reduce the risk of cardiovascular diseases, diabetes mellitus, dementia, and some types of cancer, due at least in part by stimulating the production of BDNF and IL-15.
Why might this research have important clinical implications? Systemic low-grade inflammation has been implicated in the pathogenesis of atherosclerosis, insulin resistance, tumor growth, and neurodegeneration. Thus, according to the authors Drs. A. Pratesi, F. Tarantini and M. Di Bari it has been hypothesized that inflammation plays a causal role in the functional decline associated with aging, at least in part, through sarcopenia. Of note, low-grade inflammation has also been associated with frailty, defined as a multi-system impairment with increased vulnerability to stress in old age, distinct from, although inter-related with, comorbidity and disability.
Source: Clin Cases Miner Bone Metab, 2013; 10:11-4. doi: 10.11138/ccmbm/2013.10.1.011