Mj. Spencer et al., CALPAINS ARE ACTIVATED IN NECROTIC FIBERS FROM MDX DYSTROPHIC MICE, The Journal of biological chemistry, 270(18), 1995, pp. 10909-10914
Death of dystrophin-deficient muscle purportedly re suits from increas
es in [Ca](in) that cause the activation of calpains. We have tested w
hether calpains play a role in this process by assaying for changes in
calpain concentration and activation in peak necrotic mdx mice (4 wee
ks of age) and in completely regenerated mdx mice (14 weeks of age). B
iochemical fractionation and immunoblotting with epitope-specific anti
sera allowed measurement of the concentrations of m- and mu-calpains a
nd the extent of autoproteolytic modification. Our findings show that
total calpain concentration is elevated in both 4-week and 14-week mdx
mice. This increase in concentration was shown to result primarily fr
om a significant increase in m-calpain concentration at 4 weeks. North
ern analysis demonstrated that neither m- nor mu-calpain mRNA concentr
ations differed between mdx and controls suggesting that the increased
calpain concentration results from post-translational regulation. Imm
unoblotting with antibodies directed against amino-terminal peptides r
evealed an increase in autoproteolysis of mu-calpain, indicative of in
creased activation. The extent of autoproteolysis of mu-calpain return
s to control levels during regeneration. This is not a consequence of
increased calpastatin mRNA or protein. The findings reported here supp
ort a role for calpains in both the degenerative and regenerative aspe
cts of mdx dystrophy.