Expression profiling reveals heightened apoptosis and supports fiber size economy in the murine muscles of mastication

摘要

Distinctions be-tween craniofacial and axial muscles exist from the onset of devel-opment and throughout adulthood. The masticatory muscles are aspecialized group of craniofacial muscles that retain embryonic fiberproperties in the adult, suggesting that the developmental origin ofthese muscles may govern a pattern of expression that differs fromlimb muscles. To determine the extent of these differences, expressionprofiling of total RNA isolated from the masseter and tibialis anterior(TA) muscles of adult female mice was performed, which identifiedtranscriptional changes in unanticipated functional classes of genes inaddition to those attributable to fiber type. In particular, the massetersdisplayed a reduction of transcripts associated with contractile andcytoskeletal load-sensing and anabolic processes, and heightenedexpression of genes associated with stress. Associated with theseobservations was a significantly smaller fiber cross-sectional area inmasseters, significantly elevated load-sensing signaling (phosphory-lated focal adhesion kinase), and increased apoptotic index in masse-ters compared with TA muscles. Based on these results, we hypoth-esize that masticatory muscles may have a fundamentally differentstrategy for muscle design, compared with axial muscles. Specificallythere are small diameter fibers that have an attenuated ability tohypertrophy, but an increased propensity to undergo apoptosis. Theseresults may provide insight into the molecular basis for specificmuscle-related pathologies associated with masticatory muscles.