Effects of age and diet consistency on the expression of myosin heavy‐chain isoforms on jaw‐closing and jaw‐opening muscles in a rat model

• Published in: Journal of oral rehabilitation Vol. 51; no. 6; pp. 1016 - 1024
• Main Authors: Schaub, Leandra, Lagou, Aikaterini, Ait‐Lounis, Aouatef, Kiliaridis, Stavros, Antonarakis, Gregory S.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.06.2024
• Subjects: Age; Age Factors; aging; Aging - metabolism; Aging - physiology; Animal models; Animals; Diet; Isoforms; Jaw; jaw muscles; Male; Masseter muscle; Masseter Muscle - metabolism; Masseter Muscle - physiology; Mastication; Masticatory Muscles - metabolism; Masticatory Muscles - physiology; messenger RNA; Morphology; Muscles; Myosin; myosin heavy chains; Myosin Heavy Chains - metabolism; Protein Isoforms - metabolism; Rats; Rats, Wistar; Real-Time Polymerase Chain Reaction; RNA, Messenger - metabolism; soft diet; soft diet; aging; rats; messenger RNA; myosin heavy chains; jaw muscles
• ISSN: 0305-182X; 1365-2842
• DOI: 10.1111/joor.13676

Background Skeletal craniofacial morphology can be influenced by changes in masticatory muscle function, which may also change the functional profile of the muscles. Objectives To investigate the effects of age and functional demands on the expression of Myosin Heavy‐Chain (MyHC) isoforms in representative jaw‐closing and jaw‐opening muscles, namely the masseter and digastric muscles respectively. Methods Eighty‐four male Wistar rats were divided into four age groups, namely an immature (n = 12; 4‐week‐old), early adult (n = 24; 16‐week‐old), adult (n = 24; 26‐week‐old) and mature adult (n = 24; 38‐week‐old) group. The three adult groups were divided into two subgroups each based on diet consistency; a control group fed a standard (hard) diet, and an experimental group fed a soft diet. Rats were sacrificed, and masseter and digastric muscles dissected. Real‐time quantitative polymerase chain reaction was used to compare the mRNA transcripts of the MyHC isoforms—Myh7 (MyHC‐I), Myh2 (MyHC‐IIa), Myh4 (MyHC‐IIb) and Myh1 (MyHC‐IIx)—of deep masseter and digastric muscles. Results In the masseter muscle, hypofunction increases Myh1 (26, 38 weeks; p < .0001) but decreases Myh4 (26 weeks; p = .046) and Myh2 (26 weeks; p < .0001) expression in adult rats. In the digastric muscle, hypofunction increases Myh1 expression in the mature adult rats (38 weeks; p < .0001), while Myh2 expression decreases in adult rats (26 weeks; p = .021) as does Myh4 (26 weeks; p = .001). Myh7 expression is increased in the digastric muscle of mature adult rats subjected to hypofunction (38 weeks; p = <.0001), while it is very weakly expressed in the masseter. Conclusion In jaw‐opening and jaw‐closing muscles, differences in myosin expression between hard‐ and soft‐diet‐fed rats become evident in adulthood, suggesting that long‐term alteration of jaw function is associated with changes in the expression of MyHC isoforms and potential fibre remodelling. This may give insight into the role of function on masticatory muscles and the resultant craniofacial morphology. In jaw‐opening and jaw‐closing muscles, differences in myosin expression between hard‐ and soft‐diet‐fed rats become evident in adulthood, suggesting that long‐term alteration of jaw function induced by the introduction of a soft diet is associated with changes in the expression of myosin heavy‐chain isoforms and potential fibre remodelling. Hypofunction induces an increase in Myh1 expression and reduces Myh2 expression in masseter and digastric muscles, while in the latter an increase in Myh7 expression is found in late adulthood.