Title DENERVATION IN MURINE FAST-TWITCH MUSCLE: SHORT TERM PHYSIOLOGICAL CHANGES AND TEMPORAL EXPRESSION PROFILING Authors

Denervation deeply affects muscle structure and function, the alterations being different in slow and fast muscles. Since the effects of denervation on fast muscles are still controversial and high throughput studies on gene expression in denervated muscles are lacking, we studied gene expression during atrophy progression following denervation in mouse tibialis anterior (TA). The sciatic nerve was cut close to trochanter in adult CD1 mice. 1, 3, 7 and 14 days after denervation animals were sacrificed and TA muscles were dissected out and utilized for physiological experiments and gene expression studies. Target cDNAs from TA muscles were hybridized on a dedicated cDNA microarray of muscle genes. Seventy-one genes were found differentially expressed. Microarray results were validated and the expression of relevant genes not probed on our array was monitored by RQ-PCR. Nuclearand mitochondrialencoded genes implicated in energy metabolism were consistently down-regulated. Among genes implicated in muscle contraction (myofibrillar and sarcoplasmic reticulum) genes typical of fast fibers were down-regulated, whereas those typical of slow fibers were up-regulated. Electrophoresis and Western blot showed less pronounced changes in myofibrillar protein expression, partially confirming changes in gene expression. Isometric tension of skinned fibers was little affected by denervation, whereas calcium sensitivity decreased. Functional studies in mouse EDL muscle showed prolongation in twitch time parameters and shift to the left in force-frequency curves after denervation. We conclude that, if studied at mRNA level, fast muscles appear not less responsive than slow muscles to the interruption of neural stimulation.