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.

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.

Gene expression profiling of the masticatory muscle tendons and Achilles tendons under tensile strain in the Japanese macaque Macaca fuscata.

Both Achilles and masticatory muscle tendons are large load-bearing structures, and excessive mechanical loading leads to hypertrophic changes in these tendons. In the maxillofacial region, hyperplasia of the masticatory muscle tendons and aponeurosis affect muscle extensibility resulting in limited mouth opening. Although gene expression profiles of Achilles and patellar tendons under mechanical strain are well investigated in rodents, the gene expression profile of the masticatory muscle tendons remains unexplored. Herein, we examined the gene expression pattern of masticatory muscle tendons and compared it with that of Achilles tendons under tensile strain conditions in the Japanese macaque Macaca fuscata. Primary tenocytes isolated from the masticatory muscle tendons (temporal tendon and masseter aponeurosis) and Achilles tendons were mechanically loaded using the tensile force and gene expression was analyzed using the next-generation sequencing. In tendons exposed to tensile strain, we identified 1076 differentially expressed genes with a false discovery rate (FDR) < 10-10. To identify genes that are differentially expressed in temporal tendon and masseter aponeurosis, an FDR of < 10-10 was used, whereas the FDR for Achilles tendons was set at > 0.05. Results showed that 147 genes are differentially expressed between temporal tendons and masseter aponeurosis, out of which, 125 human orthologs were identified using the Ensemble database. Eight of these orthologs were related to tendons and among them the expression of the glycoprotein nmb and sphingosine kinase 1 was increased in temporal tendons and masseter aponeurosis following exposure to tensile strain. Moreover, the expression of tubulin beta 3 class III, which promotes cell cycle progression, and septin 9, which promotes cytoskeletal rearrangements, were decreased in stretched Achilles tendon cells and their expression was increased in stretched masseter aponeurosis and temporal tendon cells. In conclusion, cyclic strain differentially affects gene expression in Achilles tendons and tendons of the masticatory muscles.

Intense Increased 18F-FDG Uptake of Masticator Muscles After Cocaine Use.

F-FDG is the most widely used PET tracer worldwide. Before the examination, recommendations are given to patients to avoid muscular activities, with the goal to limit F-FDG uptake in muscles. Here, we report the case of a 36-year-old man with Hodgkin disease referred to our department to perform an F-FDG PET/CT for immunotherapy assessment. The PET images showed a homogeneous, symmetric, and very intense uptake of the masticatory muscles. The medical examination exhibited a trismus, and the patient revealed to have been using cocaine 15 minutes before injection of F-FDG.

Cytokines, Masticatory Muscle Inflammation, and Pain: an Update.

Cytokines are proteins secreted by diverse types of immune and non-immune cells and play a role in the communication between the immune and nervous systems. Cytokines include lymphokines, monokines, chemokines, interleukins, interferons, colony stimulating factors, and growth factors. They can be both pro- and anti-inflammatory and have autocrine, paracrine, and endocrine activities. These proteins are involved in initiation and persistence of pain, and the progress of hyperalgesia and allodynia, upon stimulating nociceptive sensory neurons, and inducing central sensitization. The objective of this review is to discuss several types of pro- and anti-inflammatory mediators and their relation with inflammatory pain in masticatory muscles.

A study of chewing muscles: Age-related changes in type I collagen and matrix metalloproteinase-2 expression.

OBJECTIVE: In this study, the aim was to investigate the biochemical, physiological and histological changes that occur in masticatory muscles of the masticatory system with aging. DESIGN: In this study, 14 BALB/c mice were used. Animals were divided into two equal groups of seven. Group I was organized as the group of young animals (n = 7) and Group II as the group of adult animals (n = 7). After routine histological follow-up was performed, the tissues were embedded in paraffin. 4-5 µm thick cross-sections were taken from paraffin-embedded tissues and they were stained with Haemotoxylin and Eosin Type I collagen and Matrix metalloproteinase-2 (MMP-2) immunohistochemically. RESULTS: It was observed that there was a decrease and shrinking in blood vessels due to aging. In young mice, Type I collagen and MMP-2 immunoreactivity in the masseter muscle tissue showed low staining, while Type I collagen and MMP-2 immunoreactivity in the temporal muscle tissue showed moderate staining. Type I collagen and MMP-2 immunoreactivity were significantly higher in the masseter and temporal muscles of elderly mice (p = 0.001). In the H-score evaluation, MMP-2 immune reactivity was significantly lower in young mice than in older mice (p = 0.001). CONCLUSION: It was determined that severe pain complications and functional losses are likely to occur with the increase of degeneration due to aging of masticator muscles.

Influence of age and gender on sex steroid receptors in rat masticatory muscles.

The temporomandibular muscle dysfunction is characterized by myofascial pain and is more prevalent in women of reproductive age. Sex steroid hormones are hypothetically involved in the dysfunction, but few are the studies of steroid receptors in masticatory and mastication-related muscles. Our aim was to determine estrogen and testosterone receptor expression in rat masticatory and mastication-related muscles within the context of age and gender. Twelve rats were equally divided into four groups: (a) 10-month-old females; (b) 10-month-old males; (c) 24-month-old females; and (d) 24-month-old males. Euthanasia of the females was performed in the proestrous phase (vaginal smears) and the masticatory and accessory muscles were removed for immunohistochemical analysis. Statistical analysis was performed with ANOVA and the Tukey test. Estrogen receptor expression was similarly low in all muscles and groups. Testosterone receptor expression in the Masseter muscle of the 24-month-old male rats was higher than that in the other groups and significantly superior to its expression in the Posterior Digastric muscle. In short, testosterone receptor expression was highest in old male rats. If we generalize to humans, this fact could indicate age- and sex-related hormonal influence on temporomandibular muscle dysfunction. Further studies, however, are necessary to strengthen this hypothesis.

Specialist and Generalist Fungal Parasites Induce Distinct Biochemical Changes in the Mandible Muscles of Their Host.

Some parasites have evolved the ability to adaptively manipulate host behavior. One notable example is the fungus Ophiocordyceps unilateralis sensu lato, which has evolved the ability to alter the behavior of ants in ways that enable fungal transmission and lifecycle completion. Because host mandibles are affected by the fungi, we focused on understanding changes in the metabolites of muscles during behavioral modification. We used High-Performance Liquid Chromatography-Mass/Mass (HPLC-MS/MS) to detect the metabolite difference between controls and O. unilateralis-infected ants. There was a significant difference between the global metabolome of O. unilateralis-infected ants and healthy ants, while there was no significant difference between the Beauveria bassiana treatment ants group compared to the healthy ants. A total of 31 and 16 of metabolites were putatively identified from comparisons of healthy ants with O. unilateralis-infected ants and comparisons of B. bassiana with O. unilateralis-infected samples, respectively. This result indicates that the concentrations of sugars, purines, ergothioneine, and hypoxanthine were significantly increased in O. unilateralis-infected ants in comparison to healthy ants and B. bassiana-infected ants. This study provides a comprehensive metabolic approach for understanding the interactions, at the level of host muscles, between healthy ants and fungal parasites.

Tooth extraction and subsequent dental implant placement in Sprague-Dawley rats induce differential changes in anterior digastric myofibre size and myosin heavy chain isoform expression.

OBJECTIVE: to determine if tooth loss and dental implant placement in rats induce changes in the morphological and histochemical features of the Anterior Digastric muscle. DESIGN: Adult male Sprague-Dawley rats had their right maxillary molar teeth extracted. 'Extraction-1' and 'Extraction-2 groups were sacrificed, respectively, 4 or 8 weeks later, and an Implant group had an implant placement 2 weeks after the molar extraction, and rats were sacrificed 3 weeks later (n = 4/group). Naive rats (n = 3) had no treatment. Morphometric and immunohistochemical techniques quantified Anterior Digastric muscle myofibres' cross-sectional area (CSA) and myosin heavy chain (MyHC) isoform proportions. Significant ANOVAs were followed by post-hoc tests; p < 0.05 and 0.1 were considered to reflect levels of statistical significance. RESULTS: In naïve rats, the peripheral regions of the Anterior Digastric muscle was dominated by MyHC-IIx/b isoform and there were no MyHC-I isoforms; the central regions dominated by MyHC-IIx/b and MyHC-IIa isoforms. Compared with naive rats, tooth extraction produced, 8 (but not 4) weeks later, a decreased proportion of fast-contracting fatigue-resistant MyHC-IIa isoform (p = 0.08), and increased proportion of fast and intermediate fatigue-resistance MyHC-IIa/x/b isoform (p = 0.03). Dental implant placement following tooth extraction attenuated the extraction effects but produced a decreased proportion of fast-contracting fatiguable MyHC-llx/b isoform (p = 0.03) in the peripheral region, and increased inter-animal variability in myofibre-CSAs. CONCLUSIONS: Given the crucial role that the Anterior Digastric muscle plays in many vital oral functions (e.g., chewing, swallowing), these changes may contribute to the changes in oral sensorimotor functions that occur in humans following such treatments.

Sleep deprivation induces pathological changes in rat masticatory muscles: Role of Toll like signaling pathway and atrophy.

The aim of this study was to evaluate the Toll like signaling pathway and atrophy after sleep deprivation (SD) in rat masticatory muscles: masseter and temporal. A total of 24 animals was distributed into three groups: Control group (CTL, n = 8), subjected to SD for 96 h (SD96, n = 8) and subjected to SD for 96 h more 96 h of sleep recovery (SD96 + R, n = 8). Histopathological analysis revealed the presence of acute inflammatory cells, congested vessels, fibrosis, and high cellularity in the skeletal muscle fibers from masseter and temporal submitted to SD. These morphological alterations were not observed in the control group since neither inflammatory cells nor congested vessels were observed to this group. In the group SD96 + R, the absence of inflammation was noticed to the masseter only. In this group, COX-2 and TNF-alpha downregulation were detected when comparing to control group. MyD88 and pIKK decreased in SD96 and SD96 + R groups being pNFKBp50 downregulatated in SD96 + R. MyD88 expression increased in rats submitted to SD96 and SD96 + R in temporal when compared to control group. On the other hand, pIKK decreased the protein expression in groups SD96 and SD96 + R while pNFKBp50 showed a decreased protein expression in group SD96 only. The activation of atrophy by means of MAFbx upregulation was detected in temporal muscle in SD96 and SD96 + R when compared to control. In summary, our results show that SD is able to induce morphological alterations in rat masticatory muscles. Toll like signaling pathway and atrophy play important roles in ethiopathogenesis induced by SD, being dependent of skeletal muscle type.

Functional and molecular outcomes of the human masticatory muscles.

The masticatory muscles achieve a broad range of different activities such as chewing, sucking, swallowing, and speech. In order to accomplish these duties, masticatory muscles have a unique and heterogeneous structure and fiber composition, enabling them to produce their strength and contraction speed largely dependent on their motor units and myosin proteins that can change in response to genetic and environmental factors. Human masticatory muscles express unique myosin isoforms, including a combination of thick fibers, expressing myosin light chains (MyLC) and myosin class I and II heavy chains (MyHC) -IIA, -IIX, α-cardiac, embryonic and neonatal and thin fibers, respectively. In this review, we discuss the current knowledge regarding the importance of fiber-type diversity in masticatory muscles versus supra- and infrahyoid muscles, and versus limb and trunk muscles. We also highlight new information regarding the adaptive response and specific genetic variations of muscle fibers on the functional significance of the masticatory muscles, which influences craniofacial characteristics, malocclusions, or asymmetry. These findings may offer future possibilities for the prevention of craniofacial growth disturbances.

[Measurement of the metabolites in the cortical masticatory area of patients with sleep bruxism: a magnetic resonance spectroscopy study].

OBJECTIVE: To determine whether there are in vivo differences of metabolites levels in bilateral cortical masticatory area(CMA) of patients with sleep bruxism, compared with healthy controls using proton magnetic resonance spectroscopy(1H-MRS). Accordingly to explore if cortical control of the central jaw motor system is abnormal in sleep bruxism patients. METHODS: Fifteen sleep bruxism patients and fifteen age- and gender-matched healthy controls underwent 1H-MRS of bilateral CMA using J-difference edited point-resolved spectroscopy sequence(MEGA-PRESS) technique. Levels of metabolites were quantified from the ratio of the metabolite integral to the unsuppressed water signal. Differences of levels of γ-aminobutyric acid(GABA), glutmate(Glu) and N-acetyl aspartate(NAA) in bilateral CMA between sleep bruxism patients and healthy controls were tested using two-way ANOVA. RESULTS: Edited spectra were successfully obtained from the bilateral CMA in all of the participants. Levels of GABA+, glutmate and NAA in right and left CMA in sleep bruxism patients were (2.45±0.48)×10(-3), (2.35±0.62)×10(-3), (10.65±1.84)×10(-3), (10.49±2.37)×10(-3), (10.70±3.61)×10(-3), and (11.26±4.01)×10(-3) respectively. In contrast, levels of GABA+, glutmate and NAA in right and left CMA in healthy controls were (2.63±0.68)×10(-3), (2.65±0.97)×10(-3), (11.19± 1.34)×10(-3), (10.58±3.14)×10(-3), (11.82±1.80)×10(-3), and (11.95±3.23)×10(-3). There were no differences in levels of GABA+(P=0.196), Glu(P=0.590), and NAA(P=0.292) between sleep bruxism patients and healthy controls, nor in inbilateral CMA(GABA+: P=0.837; Glu: P=0.510; NAA: P=0.628). CONCLUSIONS: The results indicate the absence of any alteration of the cortical control of the central jaw motor system in the levels of GABA, Glu and NAA in patients with sleep bruxism.

Nucleotide and protein sequences for dog masticatory tropomyosin identify a novel Tpm4 gene product.

Jaw-closing muscles of several vertebrate species, including members of Carnivora, express a unique, "masticatory", isoform of myosin heavy chain, along with isoforms of other myofibrillar proteins that are not expressed in most other muscles. It is generally believed that the complement of myofibrillar isoforms in these muscles serves high force generation for capturing live prey, breaking down tough plant material and defensive biting. A unique isoform of tropomyosin (Tpm) was reported to be expressed in cat jaw-closing muscle, based upon two-dimensional gel mobility, peptide mapping, and immunohistochemistry. The objective of this study was to obtain protein and gene sequence information for this unique Tpm isoform. Samples of masseter (a jaw-closing muscle), tibialis (predominantly fast-twitch fibers), and the deep lateral gastrocnemius (predominantly slow-twitch fibers) were obtained from adult dogs. Expressed Tpm isoforms were cloned and sequencing yielded cDNAs that were identical to genomic predicted striated muscle Tpm1.1St(a,b,b,a) (historically referred to as αTpm), Tpm2.2St(a,b,b,a) (ßTpm) and Tpm3.12St(a,b,b,a) (γTpm) isoforms (nomenclature reflects predominant tissue expression ("St"-striated muscle) and exon splicing pattern), as well as a novel 284 amino acid isoform observed in jaw-closing muscle that is identical to a genomic predicted product of the Tpm4 gene (δTpm) family. The novel isoform is designated as Tpm4.3St(a,b,b,a). The myofibrillar Tpm isoform expressed in dog masseter exhibits a unique electrophoretic mobility on gels containing 6 M urea, compared to other skeletal Tpm isoforms. To validate that the cloned Tpm4.3 isoform is the Tpm expressed in dog masseter, E. coli-expressed Tpm4.3 was electrophoresed in the presence of urea. Results demonstrate that Tpm4.3 has identical electrophoretic mobility to the unique dog masseter Tpm isoform and is of different mobility from that of muscle Tpm1.1, Tpm2.2 and Tpm3.12 isoforms. We conclude that the unique Tpm isoform in dog masseter is a product of the Tpm4 gene and that the 284 amino acid protein product of this gene represents a novel myofibrillar Tpm isoform never before observed to be expressed in striated muscle.

Distribution of transient receptor potential melastatin-8-containing nerve fibers in rat oral and craniofacial structures.

The transient receptor potential melastatin-8 (TRPM8) is a cold and menthol receptor located in the sensory ganglia. Immunohistochemistry for TRPM8 was performed on oral and craniofacial structures of the rat. TRPM8-immunoreactive (-IR) nerve fibers were detected in the oral mucous membrane. In the gingiva, TRPM8-IR nerve fibers were abundant beneath and within crestal and outer epithelia. Such nerve fibers were also common beneath and within taste buds in the incisive papilla. In addition, TRPM8-immunoreactivity was expressed by some taste bud cells in the papilla. Lips, periodontal ligaments and salivary glands as well as masticatory muscles and temporomandibular joints were mostly devoid of TRPM8-IR nerve fibers. A double immunofluorescence study indicated different distribution patterns of nerve fibers containing TRPM8 and calcitonin gene-related peptide in oral and craniofacial tissues. Retrograde tracing method also indicated that TRPM8-IR nerve fibers in the gingiva and incisive papilla originate from small sensory neurons in the trigeminal ganglion. TRPM8 may be associated with cool, cold nociceptive (

Muscle characterization of reactive oxygen species in oral diseases.

IMPORTANCE AND OBJECTIVE: Reactive Oxygen Species (ROS) are oxygen-derived molecules that are unstable and highly reactive. They are important signaling mediators of biological processes. In contrast, excessive ROS generation, defective oxidant scavenging or both have been implicated in the pathogenesis of several conditions. This biological paradox of ROS function contributes to the integrity of cells and tissues. So, the aim of this review was examined for published literature related to 'reactive oxygen species and dentistry and muscle'. MATERIALS AND METHODS: A PubMed search was performed by using the following key words: 'reactive oxygen species and dentistry and muscle'. RESULTS: Involvement of ROS in pathologic conditions can be highlighted in oral diseases like periodontitis, orofacial pain, temporomandibular disorders and oral cancer. Also, several studies have correlated the increase in ROS production with the initiation of the muscle fatigue process and the process of muscle injury. However, studies evaluating the relation of ROS and orofacial muscles, which can prove very important to understand the fatigue muscle in this region during oral movements, have not yet been conducted. CONCLUSIONS: It is concluded that the data on skeletal muscles, especially those of mastication, are not commonly published in this data source; therefore, further studies in this field are strongly recommended.

Differential expression of genes involved in the calcium homeostasis in masticatory muscles of MDX mice.

Duchenne Muscular Dystrophy (DMD) and its murine model, mdx, are characterized by Ca(2+) induced muscle damage and muscle weakness followed by distorted dentofacial morphology. In both, DMD patients and in mdx mice, could be proven so far that only the extraocular muscles (EOM) are not affected by muscular dystrophy. The EOMs are protected against calcium overload by enhanced expression of genes involved in the Ca(2+) homeostasis. We could recently demonstrate that masticatory muscles of mdx mice are differentially affected by muscle dystrophy. The dystrophic masseter and temporalis shows muscle histology comparable to all other skeletal muscles in this animal model, whereas dystrophic tongue muscles seem to develop a milder phenotype. Due to this fact it is to hypothesize that an altered Ca(2+) homeostasis seems to underlie the mdx masticatory muscle pathology. Aim of this study was to examine the mRNA and protein levels of the sarcoplasmic reticulum Ca(2+) ATPases SERCA1 and SERCA2, the plasma membrane Ca(2+) ATPases Atp2b1 and Atp2b4, the sodium/calcium exchanger NCX1, the ryanodine receptor 1, parvalbumin, sarcolipin, phospholamban and the L-type Ca(2+) channel alpha-1 subunit (Cacna1s) in Musculus masseter, temporalis, and tongue of 100 day old control and mdx mice. In mdx masseter muscle significant increased mRNA levels of NCX1 and Cacna1s were found compared to control mice. In contrast, the mRNA amount of RYR1 was significant reduced in mdx temporalis muscle, whereas ATP2b4 was significant increased. In mdx tongue a down-regulation of the ATP2b1, sarcolipin and parvalbumin mRNA expression was found, whereas the phospholamban mRNA level was significantly increased compared to controls. These data were verified by western blot analyses. Our findings revealed that mdx masticatory muscles showed an unequally altered expression of genes involved in the Ca(2+) homeostasis that can support the differences in masticatory muscles response to dystrophin deficiency.

[Application of near infrared spectroscopy in study of occlusal splints and resistance of masticatory muscles to fatigue pain].

OBJECTIVE: To analyze the influence of occlusal splint on resistance capability of masticatory muscles to fatigue. METHODS: In the study, 25 young male volunteers were randomly divided to 5 groups according to different splint placements: (1) no splint, (2) 1.5 mm thick soft splint, (3) 2 mm thick resin stability splint, (4) 4 mm thick resin stability splint, (5) buccolingual mock splint. Near infrared spectroscopy (NIRS) was used to measure blood oxygen content in human masticatory muscles during constant strong biting before and after the splint placement at seven time points: before, baseline after, 1 week after, and 2 weeks after splint placement, and immediately after, 1 week after, and 5 weeks after removing of splints. The strength of the biting force was maintained constantly at 30% level of the maximum biting force of each subject by biofeedback to the displayed value of an electro-myographic monitor. The time points of muscular fatigue and pain that appeared were recorded and the correlation between the subjective feeling and the NIRS measurement result was analyzed. RESULTS: The NIRS measurement curve had a point of inflection that had no significant difference with the time point of the muscle pain that appeared. Two weeks after placement of soft splint, the time point of the muscular fatigue and pain that appeared were 2.75 s and 8.00 s delayed respectively compared with that before placement of splint (P<0.01) while they were earlier in the groups of hard splints and there was no significant difference (P>0.05) in the group of mock splint. CONCLUSION: The metabolic status of human masticatory muscles could be monitored in real time by using NIRS; soft splint delayed the appearing of muscle fatigue and muscle pain after two weeks of placement.

Molecular and cellular changes associated with the evolution of novel jaw muscles in parrots.

Vertebrates have achieved great evolutionary success due in large part to the anatomical diversification of their jaw complex, which allows them to inhabit almost every ecological niche. While many studies have focused on mechanisms that pattern the jaw skeleton, much remains to be understood about the origins of novelty and diversity in the closely associated musculature. To address this issue, we focused on parrots, which have acquired two anatomically unique jaw muscles: the ethmomandibular and the pseudomasseter. In parrot embryos, we observe distinct and highly derived expression patterns for Scx, Bmp4, Tgfß2 and Six2 in neural crest-derived mesenchyme destined to form jaw muscle connective tissues. Furthermore, immunohistochemical analysis reveals that cell proliferation is more active in the cells within the jaw muscle than in surrounding connective tissue cells. This biased and differentially regulated mode of cell proliferation in cranial musculoskeletal tissues may allow these unusual jaw muscles to extend towards their new attachment sites. We conclude that the alteration of neural crest-derived connective tissue distribution during development may underlie the spatial changes in jaw musculoskeletal architecture found only in parrots. Thus, parrots provide valuable insights into molecular and cellular mechanisms that may generate evolutionary novelties with functionally adaptive significance.

Association between the lack of teeth and the expression of myosins in masticatory muscles of microphthalmic mouse.

The purposes of the present study were to elucidate the influences of the deficiency of teeth on masticatory muscles, such as the masseter, temporalis and digastric muscles and compare the influence among masticatory muscles. We analysed the expressions of myosin heavy chain (MyHC) isoform messenger RNA (mRNA) and protein in these muscles in the microphthalmic (mi/mi) mouse, whose teeth cannot erupt because of a mutation in the mitf gene locus. The expression levels of MyHC mRNA and protein in the masseter, temporalis, digastric, tibialis anterior and gastrocnemius muscles of +/+ and mi/mi mice were analysed with real-time polymerase chain reaction and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively. The mi/mi masseter muscle at 8 weeks of age expressed 4.1-fold (p < 0.05) and 3.3-fold (p < 0.01) more MyHC neonatal mRNA and protein than that in the +/+, respectively; the expression level of MyHC neonatal protein was 19% of the total MyHC protein in the masseter muscle of mi/mi mice. In the digastric muscle, the expression levels of MyHC I mRNA and protein in the mi/mi mice were 4.7-fold (p < 0.05) and 5-fold (p < 0.01) higher than those in the +/+ mice. In the temporalis, tibialis anterior and gastrocnemius muscles, there was no significant difference in the expression levels of any MyHC isoform mRNA and protein between +/+ and mi/mi mice. These results indicate associations between the lack of teeth and the expression of MyHC in the masseter and digastric muscles but not such associations in the temporalis muscle, suggesting that the influence of tooth deficiency varies among the masticatory muscles.

Mechanisms underlying the sparing of masticatory versus limb muscle function in an experimental critical illness model.

Acute quadriplegic myopathy (AQM) is a common debilitating acquired disorder in critically ill intensive care unit (ICU) patients that is characterized by tetraplegia/generalized weakness of limb and trunk muscles. Masticatory muscles, on the other hand, are typically spared or less affected, yet the mechanisms underlying this striking muscle-specific difference remain unknown. This study aims to evaluate physiological parameters and the gene expression profiles of masticatory and limb muscles exposed to factors suggested to trigger AQM, such as mechanical ventilation, immobilization, neuromuscular blocking agents, corticosteroids (CS), and sepsis for 5 days by using a unique porcine model mimicking the ICU conditions. Single muscle fiber cross-sectional area and force-generating capacity, i.e., maximum force normalized to fiber cross-sectional area (specific force), revealed maintained masseter single muscle fiber cross-sectional area and specific-force after 5 days' exposure to all triggering factors. This is in sharp contrast to observations in limb and trunk muscles, showing a dramatic decline in specific force in response to 5 days' exposure to the triggering factors. Significant differences in gene expression were observed between craniofacial and limb muscles, indicating a highly complex and muscle-specific response involving transcription and growth factors, heat shock proteins, matrix metalloproteinase inhibitor, oxidative stress responsive elements, and sarcomeric proteins underlying the relative sparing of cranial vs. spinal nerve innervated muscles during exposure to the ICU intervention.

Caveolin-1, caveolin-3 and VEGF expression in the masticatory muscles of mdx mice.

Duchenne muscular dystrophy (DMD) and murine X-linked muscular dystrophy (mdx), its murine model, are characterized by muscle damage and muscle weakness associated with inflammation and new vessel formation. Caveolins, dystrophin-associated proteins, are involved in the pathogenesis of DMD, because increased numbers of caveolae are found in DMD and mdx hindlimb muscles. Caveolae influence angiogenesis due to their content of vascular endothelial growth factor (VEGF) receptors. Orofacial muscles in mdx mice undergo muscle necrosis followed by muscle regeneration. To ascertain the role of caveolins and VEGF in the pathogenesis of dystrophic masticatory muscles, we examined the expression of caveolin-1 (cav-1), caveolin-3 (cav-3) and VEGF in control and mdx mice. In mdx masticatory muscles, no changes in transcript and protein levels of VEGF were found, whereas cav-1 and cav-3 expression was increased. Using immunohistochemistry, a strong sarcolemmal staining of caveolin-3 in regenerated muscle fibers was found. Furthermore, immunohistochemistry with the caveolin-1 antibody showed an increase in the amount of blood vessels in areas with regenerating muscle fibers. Dystrophic masticatory muscles showed changes comparable to those of hindlimb muscles in the expression of cav-1 and cav-3. The angiogenesis seems to be unaffected in the jaw muscles of mdx mice. We speculate that the increased caveolin expression could cause extensive and efficient muscle regeneration.