Muscle undergoes atrophy in association with increase of lysosomal cathepsin activity in interleukin-6 transgenic mouse.

Interleukin(IL)-6 transgenic mice were produced by microinjection of human IL-6 cDNA fused with H-2Ld promoter into the pronucleus of fertilized eggs from C57BL/6J mice. At 16 weeks old, the gastrocnemius muscles of the IL-6 transgenic mice became atrophic as compared to those of the normal mice, while the body weights increased significantly. The activities and mRNA levels of lysosomal cathepsins B and L were increased in the muscles of the transgenic mice. Immunohistochemical study on the muscles showed increased staining of both cathepsins B and L in the transgenic mice. IL-6 is responsible for enhanced muscle catabolism by activating the lysosomal cathepsin (B and L) system.