ABSTRACT
OBJECTIVES: The aim of this study was to elucidate age-related changes from adult to middle age in the contractile properties of the masseter, genioglossus and geniohyoid muscles of the rat. MATERIALS AND METHODS: We analysed the expressions of myosin heavy chain (MyHC) mRNAs and proteins as indicators of the contractile properties in these muscles obtained from rats at 6, 12, 18 and 24 months of age using real-time PCR and SDS-PAGE. RESULTS: We found no marked age-related changes in the expressions of MyHC mRNAs and proteins in rat masseter and geniohyoid muscles, suggesting that the biological ageing process does not affect contractile properties in these muscles. However, we found a decrease in the expression of MyHC IIb mRNA with ageing in the rat genioglossus muscle, suggesting that biological ageing process induces at least some fast-to-slow myofibre phenotype transition. CONCLUSION: The biological ageing process from adult to middle age appears to differentially affect different types of craniofacial muscles.
Subject(s)
Aging/pathology , Masseter Muscle/pathology , Neck Muscles/pathology , Tongue/pathology , Aging/metabolism , Animals , Body Weight , Male , Masseter Muscle/chemistry , Muscle Contraction , Muscle Fibers, Fast-Twitch/chemistry , Muscle Fibers, Fast-Twitch/pathology , Muscle Fibers, Slow-Twitch/chemistry , Muscle Fibers, Slow-Twitch/pathology , Myosin Heavy Chains/analysis , Myosin Type II/analysis , Neck Muscles/chemistry , Phenotype , Rats , Rats, Wistar , Tongue/chemistryABSTRACT
Clenbuterol, a ß2-adrenergic agonist, increases the hypertrophy of skeletal muscle. Insulin-like growth factor (IGF) is reported to work as a potent positive regulator in the clenbuterol-induced hypertrophy of skeletal muscles. However, the precise regulatory mechanism for the hypertrophy of skeletal muscle induced by clenbuterol is unknown. Myostatin, a member of the TGFß super family, is a negative regulator of muscle growth. The aim of the present study is to elucidate the function of myostatin and IGF in the hypertrophy of rat masseter muscle induced by clenbuterol. To investigate the function of myostatin and IGF in regulatory mechanism for the clenbuterol-induced hypertrophy of skeletal muscles, we analysed the expression of myostatin and phosphorylation levels of myostatin and IGF signaling components in the masseter muscle of rat to which clenbuterol was orally administered for 21 days. Hypertrophy of the rat masseter muscle was induced between 3 and 14 days of oral administration of clenbuterol and was terminated at 21 days. The expression of myostatin and the phosphorylation of smad2/3 were elevated at 21 days. The phosphorylation of IGF receptor 1 (IGFR1) and akt1 was elevated at 3 and 7 days. These results suggest that myostatin functions as a negative regulator in the later stages in the hypertrophy of rat masseter muscle induced by clenbuterol, whereas IGF works as a positive regulator in the earlier stages.
Subject(s)
Clenbuterol/pharmacology , Muscle, Skeletal/drug effects , Myostatin/metabolism , Signal Transduction/drug effects , Somatomedins/metabolism , Administration, Oral , Adrenergic beta-Agonists/administration & dosage , Adrenergic beta-Agonists/pharmacology , Animals , Blotting, Western , Clenbuterol/administration & dosage , Hypertrophy , Male , Muscle, Skeletal/metabolism , Muscle, Skeletal/pathology , Phosphorylation/drug effects , Proto-Oncogene Proteins c-akt/metabolism , Rats , Rats, Wistar , Receptor, IGF Type 1/metabolism , Smad2 Protein/metabolism , Smad3 Protein/metabolism , Time FactorsABSTRACT
Little is known about the effects of obesity on skeletal muscle consisting of approximately 80% type I (slow) fibers, such as that in the soleus muscle, although type I fibers have an enhanced capacity for mitochondrial respiration and fatty acid oxidation. We investigated the effects of obesity on the soleus muscle in the rat. Rats were fed a high-fat diet (protein:fat:carbohydrate = 20:57:23; 508 kcal/100 g) or a control diet (protein:fat:carbohydrate = 20:10:70; 366 kcal/100 g) for 10 weeks. We analyzed the accumulation of intramyocellular triacylglycerol (IMTG), fiber type composition, and the biogenesis and function of the mitochondria in the soleus muscle of the rat during 10 weeks of feeding, using histochemical and real-time polymerase chain reaction analyses. Obesity increased body weight and markedly elevated IMTG levels in type I, but not in type II, fibers of the soleus muscle throughout the feeding period. Obesity also inhibited the biogenesis and function in the mitochondria and altered the fiber type composition in the soleus muscle. The suppression of biogenesis and function in the mitochondria, and the alteration in the fiber type composition may be attributable to the marked IMTG accumulation in the soleus muscle of the rat.
Subject(s)
Mitochondria, Muscle/metabolism , Muscle Fibers, Slow-Twitch/metabolism , Obesity/metabolism , Triglycerides/metabolism , Animals , Disease Models, Animal , Male , Mitochondria, Muscle/pathology , Mitochondrial Proteins/genetics , Mitochondrial Proteins/metabolism , Muscle Fibers, Fast-Twitch/metabolism , Muscle Fibers, Fast-Twitch/pathology , Muscle Fibers, Slow-Twitch/pathology , Muscle Proteins/genetics , Muscle Proteins/metabolism , Obesity/genetics , Obesity/pathology , Rats , Rats, Wistar , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Staining and Labeling , Time Factors , Weight GainABSTRACT
Klotho mutant (kl/kl) mice, a type of short-lived mouse models, display several aging-related phenotypes. To investigate whether the atrophy of skeletal muscles is induced in these mice via activation of the ubiquitin-proteasomal pathway and/or the autophagic-lysosomal pathway through an alteration of insulin/IGF-I signaling, we analyzed the activity of the two pathways for protein degradation and components of the insulin/IGF signaling pathway in their skeletal muscles. The masseter, tongue, and gastrocnemius muscles in kl/kl showed marked reductions in muscle weight and in myofiber diameter compared with +/+. The autophagic-lysosomal pathway in kl/kl was activated in the masseter and tongue, but not in the gastrocnemius, compared with that in +/+, whereas the ubiquitin-proteasomal pathway in these three muscles of kl/kl was not altered. No marked difference in the phosphorylation levels of insulin/IGF-I signaling components, such as insulin/IGF-I receptor, Akt, and FoxO in three muscles studied were found between kl/kl and +/+, but the phosphorylation levels of signaling component at the downstream of mTOR such as 4E-BP1 and p70 S6K were suppressed in the masseter and tongue of kl/kl compared with +/+. Deficiency of essential amino acids is reported to activate the autophagy-lysosomal pathway through the down-regulation of mTOR, not through IGF-Akt-FoxO. The masseter and tongue seem to be more actively moved than limb muscles in kl/kl, because they are essential for survival activities such as mastication, swallowing, and respiration. Thus, the deficiency of amino acid by the active movement of the masseter and tongue seems to stimulate the autophagic-lysosomal pathway via the down-regulation of mTOR signalling pathway.
Subject(s)
Aging/metabolism , Autophagy , Glucuronidase/genetics , Lysosomes/metabolism , Masseter Muscle/metabolism , Signal Transduction , Tongue/metabolism , Adaptor Proteins, Signal Transducing , Aging/genetics , Aging/pathology , Amino Acids, Essential/deficiency , Animals , Atrophy , Carrier Proteins/metabolism , Cell Cycle Proteins , Eukaryotic Initiation Factors , Forkhead Transcription Factors/metabolism , Genotype , Insulin/metabolism , Insulin-Like Growth Factor I/metabolism , Klotho Proteins , Masseter Muscle/pathology , Mice , Mice, Inbred BALB C , Mice, Mutant Strains , Mutation , Phenotype , Phosphoproteins/metabolism , Phosphorylation , Proteasome Endopeptidase Complex/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Ribosomal Protein S6 Kinases, 70-kDa/metabolism , TOR Serine-Threonine Kinases/metabolism , Tongue/pathology , Ubiquitin/metabolismABSTRACT
The aim of this study is to investigate whether BMP-2 regulates the oral sulcus formation of mouse embryonic tongue by modifying the expression of TIMP and MMP. The BMP-2 siRNA induced a 180% increase in the depth of oral sulcus cavity (P < 0.01) by stimulating the invagination of oral sulcus into the mesenchymal tissues consisting of tongue floor, whereas the recombinant BMP-2 suppressed the process in the organ culture system of mouse embryonic tongue. The BMP-2 siRNA induced a 60% decrease in the expression of TIMP-1 mRNA (P < 0.05) and a drastic decline in TIMP-1 protein was observed around the oral sulcus in the BMP-2 siRNA treated mandibles. The recombinant BMP-2 induced a 220% increases in the expression of TIMP-1 mRNA and the area of the immunostaining for TIMP-1 around the oral sulcus was larger in the mandibles treated with the recombinant BMP-2 than the vehicle. The BMP-2 siRNA induced a 60% increase in the expression of MMP-13 protein and a marked increase in the staining intensity for MMP-13 was observed in the epithelial region of the BMP-2 siRNA treated mandibles. The recombinant BMP-2 induced a 70% decrease in the expression of MMP-13 mRNA and the decrease was mainly observed in the tissues around oral sulcus. The expressions of BMP-2, TIMP-1, and MMP-13 were verified in the tissues around in vivo developing oral sulcus at E11, 12, and 13 by immunohistochemistry. These results suggest that BMP-2 regulates the formation of oral sulcus by altering the balance between TIMP-1 and MMP-13.
