Apocynin treatment prevents loss of skeletal muscle function
caused by CS exposure
Eight weeks of CS exposure resulted in a loss of skeletal muscle mass in
mice similar to that observed in human smokers, as evidenced by a 10%
reduction in gross weight of the tibialis anterior (TA) muscle (Figure
2A) which is a prime mover of the hind limb, predominated by fast-twitch
myofibers. CS exposure also caused an ~8% reduction in
the weight of soleus (Table 2) which is a slow-twitch fibers
predominated muscle of the hind limbs (Timson, Bowlin, Dudenhoeffer &
George, 1985), suggesting the muscle wasting effect of CS exposure is
unbiased by fiber composition in our model. In addition to the loss of
muscle mass, CS exposure also resulted in a significant reduction in
contractile force (Figure 2B) and maximum contraction rate (Figure 2D)
of the TA muscles which translated to a 54% decrease in specific force
generated (Figure 2C), suggesting CS exposure caused muscle weakness. In
addition to preventing the loss of TA mass, apocynin treatment
attenuated the CS-induced skeletal muscle weakness as evidenced by the
improved contractile force, maximum contraction rate and specific force
(Figure 2A-D).
We next conducted qPCR analyses to examine the molecular changes within
the TA muscles. In line with the loss of mass and function, CS exposure
resulted in a 50% reduction in Igf1-eb (a precursor isoform of
muscle-derived IGF-1; Figure 2E) and a 2-fold increase in Mstn(myostatin; Figure 2F) expression which were completely prevented by
apocynin treatment. Tnfα expression remained unaltered regardless
of CS exposure or apocynin treatment, suggesting the CS-induced
phenotypical and molecular changes are unlikely to involve myocellular
inflammation. Lastly, our oxyblot analysis revealed a 2.3-fold increase
in protein carbonylation of TA muscles following CS exposure which was
completely prevented by apocynin treatment (Figure 2 H-I), suggesting
the protective effects of apocynin in vivo may be related to its
ability to antagonize the oxidative burden evoked by CS exposure.