Serum C-terminal agrin fragment as a biomarker of age-related neuromuscular decline in men: influence of physical activity

Background

Aging is associated with progressive neuromuscular junction (NMJ) degeneration. The C-terminal agrin fragment (CAF), a circulating product of agrin cleavage, has been proposed as a minimally invasive biomarker of NMJ degradation, but its relationships with specific neuromuscular and functional characteristics, and the potential modulating role of physical activity, remain poorly defined.

Objective

To examine age- and physical activity-related differences in serum CAF and to test its associations with neuromuscular integrity and functional capacity across the adult male lifespan.

Methods

We studied 136 community-dwelling men aged 20-92 years (active, n=87; inactive, n=49). Serum CAF was measured by ELISA; NCAM-positive fiber proportion, a widely used marker of myofiber denervation, was assessed by immunolabeling of vastus lateralis biopsies (n=127). Neuromuscular assessments included maximal voluntary isometric contraction (MVIC), lower-limb muscle power, electromechanical delay (EMD), nerve conduction velocities, H/M ratio, central activation ratio, co-activation, and twitch characteristics. Functional capacity was assessed with the 6-minute walk test, alternating step test, Timed Up and Go, sit-to-stand tests, and fast gait speed.

Results

Serum CAF increased progressively with age (β= 21,51, p<0.001) and was positively associated with NCAM-positive fiber proportion (β= 119,5 p=0.01). Higher CAF was associated with lower MVIC (β=-0.01, p=0.026), reduced lower-limb power (β= -0.01, p=0.027), and poorer performance on the 6MWT, alternating step test, TUG, sit-to-stand, and gait speed (p<0.05). CAF was associated with longer EMD in the whole cohort (β= 0.003, p=0.017) and inactive men (β= 0.005, p=0.007), but not in active men, and with lower H/M ratio in inactive men only (β= -0.003, p=0.0217). No associations were found with nerve conduction velocities, central activation ratio, co-activation, or twitch amplitude. Active men showed lower CAF than inactive men, particularly after age 70 (p=0.023).

Conclusion

In community-dwelling men, serum CAF is associated with age-related declines in neuromuscular and functional capacity and shows tissue-level consistency with the proportion of NCAM-positive fibers, supporting its use as an accessible biomarker of NMJ remodeling. Its limited association with most electrophysiological measures indicates it captures a specific component of neuromuscular aging rather than a global index of neuromuscular function. Physical activity was associated with a more favorable CAF profile, particularly among older men, identifying physical activity as a potential modifiable factor in age-related NMJ decline.

Highlights

• Serum CAF rises progressively across the adult lifespan in men.

• CAF levels correlate with muscle fiber denervation markers.

• Elevated CAF is linked to poorer neuromuscular and physical function.

• Physical activity is associated with a more favorable CAF profile.