Photobiomodulation as an Approach to Restore Lost Function in Neuromuscular Junctions
Evidence suggests that one of the major components of muscle aging is degeneration of neuromuscular junctions, the structures linking the nervous system to muscle fibers. Absent the signaling from nervous system to muscle, muscles will degenerate. That signaling is necessary for muscle tissue maintenance and growth. Thus a loss of function in neuromuscular junctions will contribute to the characteristic age-related loss of muscle mass and strength that leads inexorably to the line in the sand that marks the conditions known as sarcopenia and dynapenia. Can the degeneration of neuromuscular junctions be reversed to any great degree? Today's open access paper provides animal study evidence for photobiomodulation to achieve this goal, though it must be said that the broader context surrounding the widespread clinical use of photobiomodulation suggests caution in taking this data at face value.
Photobiomodulation as practiced by clinicians largely means low-level red laser light therapy. There is some debate over the degree to which red wavelengths penetrate tissues and may thus still be as beneficial in larger animals as it is assessed to be in smaller animals. This form of treatment is thought to improve mitochondrial function, though it is still a mystery as to how exactly this works. Sadly, while researchers can and do publish interesting mechanistic papers on what might be going on under the hood, we largely know the bounds of the possible for photobiomodulation. People undergo this sort of therapy in large numbers, and have done so for a long time. It simply isn't possible in this sort of an environment to hide very large effect sizes on, say, muscle function. One has to assume that effects on health and tissue function in humans, while quite interesting, are small to vanishing in the practical sense.
Aging is characterized by progressive degeneration of neuromuscular junctions (NMJs), which significantly contributes to muscle weakness and the development of sarcopenia. Photobiomodulation (PBM), a non-invasive therapeutic method based on the use of low-intensity light, has shown promising results in mitigating muscle degeneration in both experimental and clinical studies. The aim of this study was to evaluate the ultrastructural effects of photobiomodulation on neuromuscular junctions and skeletal muscle fibers in the vastus lateralis muscle of aged rats using light and transmission electron microscopy. Male Wistar rats (18 months old, body weight 650-800 grams, n = 10) were subjected to photobiomodulation of the right vastus lateralis muscle (650 nm wavelength, 6 J/cm^2, four consecutive daily sessions of 3 min each). The contralateral left limb served as an untreated control.
Muscle samples were analyzed by light and transmission electron microscopy. Histological examination revealed typical age-related changes in control muscles, including variability in muscle fiber diameter, centrally located nuclei, and an increased volume of connective tissue. Ultrastructural analysis confirmed signs of skeletal muscle aging, such as myofibril fragmentation, sarcomere disorganization, lipofuscin accumulation, and tubular aggregate formation. Morphometric analysis of neuromuscular junctions after photobiomodulation showed an increase in the number of active zones on the presynaptic membrane, elongation of the postsynaptic membrane, and a reduction in the width of the synaptic cleft. In addition, mitochondrial hyperplasia was observed in presynaptic terminals, while the total number of synaptic vesicles decreased.
These findings indicate a compensatory reorganization of neuromuscular junctions and suggest that photobiomodulation can enhance their functional activity in aged skeletal muscle.