Expression of muscle-specific integrins in masseter muscle fibers during malocclusion disease

Integrins are heterodimeric cell surface membrane proteins linking the extracellular matrix to actin. alpha 7B integrin is detected in proliferating and adult myofibers, whereas alpha 7A plays a role in regenerating muscle fibers with a minor function in mature muscle fibers. The expression levels of beta 1A appear to be very low, whereas beta 1D appears to be the predominant integrin form in mature muscle. Considering the important features of masseter muscle we have studied integrin expression in masseter muscle specimens of surgical patients with posterior right crossbite and comparing them to left side masseter muscle specimens. Our results showed that the expression of integrins was significantly lower in the crossbite side muscle. Furthermore, the most important finding is that beta 1A is clearly detectable in adult masseter muscle. This behavior could be due to the particular composition of masseter, since it contains hybrid fibers showing the capacity to modify the contractile properties to optimize the energy efficiency or the action of the muscle during contraction. Moreover, masseter is characterized by a high turnover of muscle fibers producing a regeneration process. This may indicate a longer time to heal, justifying the loss of beta 1D and the consequential increase of beta 1A. Thus, our data provide the first suggestion that integrins in masseter muscle play a key role regulating the functional activity of muscle and allowing the optimization of contractile forces.