Exercise-induced myokines are cytokines and peptides secreted by skeletal muscle during physical activity that exert systemic effects, including neuroprotection. These muscle-derived factors represent a key mechanism by which exercise benefits brain health across multiple neurodegenerative diseases. This page focuses on three major exercise-induced myokines—irisin, fibroblast growth factor 21 (FGF21), and growth differentiation factor 15 (GDF15)—and their therapeutic potential for Alzheimer's disease (AD), Parkinson's disease (PD), corticobasal syndrome (CBS), progressive supranuclear palsy (PSP), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Huntington's disease (HD).
Physical exercise triggers skeletal muscle to release a diverse array of bioactive molecules into the circulation[1]. These myokines can cross the blood-brain barrier and exert direct effects on brain cells, including neurons, astrocytes, and microglia. The neuroprotective effects of exercise-induced myokines include:
Irisin is a cleavage product of the transmembrane protein fibronectin type III domain-containing protein 5 (FNDC5), which is expressed in skeletal muscle, heart, and brain[2]. During exercise, FNDC5 is proteolytically cleaved by undefined proteases to release irisin into the circulation. Irisin acts primarily through integrin receptors and potentially through the FGF receptor family.
In Alzheimer's disease models, irisin has shown promising neuroprotective effects:
In PD models, irisin demonstrates protection against dopaminergic neuron loss:
Several challenges remain for irisin-based therapy:
FGF21 is a member of the fibroblast growth factor family that functions as a metabolic regulator[12]. Originally characterized as a hepatic hormone that promotes glucose uptake and lipid metabolism, FGF21 is also expressed in skeletal muscle and is induced by exercise. FGF21 signals through FGF receptors (FGFRs) in complex with the co-receptor beta-Klotho (KLB).
FGF21 shows potential for AD therapy through multiple mechanisms:
In PD, FGF21 demonstrates neuroprotective properties:
FGF21 has been investigated in ALS models:
GDF15 is a stress-responsive cytokine belonging to the TGF-beta superfamily[21]. While expressed in multiple tissues including muscle, liver, and kidney, GDF15 is strongly induced in response to cellular stress, mitochondrial dysfunction, and inflammation. GDF15 signals through the GDNF family receptor alpha-like (GFRAL) in the brainstem, which mediates its appetite-suppressing effects.
GDF15's role in neurodegeneration is emerging but shows promise:
| Myokine | AD | PD | CBS/PSP | ALS | FTD | HD |
|---|---|---|---|---|---|---|
| Irisin | Strong | Strong | Emerging | Moderate | Emerging | Moderate |
| FGF21 | Strong | Strong | Limited | Moderate | Limited | Limited |
| GDF15 | Emerging | Emerging | Preclinical | Preclinical | Preclinical | Preclinical |
Exercise remains the most effective way to naturally increase circulating myokine levels:
Several trials are investigating myokine-based interventions (NCT IDs TBD):
Exercise-induced myokines represent a promising therapeutic avenue for neurodegenerative diseases. Irisin, FGF21, and GDF15 each offer unique mechanisms of neuroprotection while sharing common pathways related to metabolism, inflammation, and autophagy. While exercise remains the most accessible intervention, pharmacological targeting of these myokines may provide new treatment options for patients unable to exercise adequately. Further clinical research is needed to translate these preclinical findings into effective therapies.
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