Expression of fiber type specific proteins during ontogeny of canine temporalis muscle

Masticatory Myositis in a Guinea Pig (Cavia porcellus): A Case Report

Masticatory myositis is an autoimmune neuromuscular disorder that affects the muscles of mastication. The affected individual has difficulties in opening or closing the mouth, pain, and swelling in the acute phase, and significant atrophy of the affected musculature in the chronic phase. A guinea pig (Cavia porcellus) with a history of chronic hyporexia, recurrent cheek teeth overgrowth, and loss of facial silhouette, was suspected of having masticatory myositis. The disease was confirmed by computed tomography and histopathological examination of muscle fragments. The patient was treated with a protocol involving corticosteroids and gabapentin, and occlusal correction procedures.

Developmental, Physiological and Phylogenetic Perspectives on the Expression and Regulation of Myosin Heavy Chains in Craniofacial Muscles

This review deals with the developmental origins of extraocular, jaw and laryngeal muscles, the expression, regulation and functional significance of sarcomeric myosin heavy chains (MyHCs) that they express and changes in MyHC expression during phylogeny. Myogenic progenitors from the mesoderm in the prechordal plate and branchial arches specify craniofacial muscle allotypes with different repertoires for MyHC expression. To cope with very complex eye movements, extraocular muscles (EOMs) express 11 MyHCs, ranging from the superfast extraocular MyHC to the slowest, non-muscle MyHC IIB (nmMyH IIB). They have distinct global and orbital layers, singly- and multiply-innervated fibres, longitudinal MyHC variations, and palisade endings that mediate axon reflexes. Jaw-closing muscles express the high-force masticatory MyHC and cardiac or limb MyHCs depending on the appropriateness for the acquisition and mastication of food. Laryngeal muscles express extraocular and limb muscle MyHCs but shift toward expressing slower MyHCs in large animals. During postnatal development, MyHC expression of craniofacial muscles is subject to neural and hormonal modulation. The primary and secondary myotubes of developing EOMs are postulated to induce, via different retrogradely transported neurotrophins, the rich diversity of neural impulse patterns that regulate the specific MyHCs that they express. Thyroid hormone shifts MyHC 2A toward 2B in jaw muscles, laryngeal muscles and possibly extraocular muscles. This review highlights the fact that the pattern of myosin expression in mammalian craniofacial muscles is principally influenced by the complex interplay of cell lineages, neural impulse patterns, thyroid and other hormones, functional demands and body mass. In these respects, craniofacial muscles are similar to limb muscles, but they differ radically in the types of cell lineage and the nature of their functional demands.

Case report: Atypical and chronic masticatory muscle myositis in a 5-month old Cavalier King Charles Spaniel. Clinical and diagnostic findings, treatment and successful outcome

Masticatory muscle myositis (MMM) is the second most common inflammatory myopathy diagnosed in dogs, but it is rarely described in puppies. The disease is characterized by the production of autoantibodies against 2M myofibers contained in masticatory muscle, although the cause of this production is still unclear. The aim of the present case report was to describe the clinical presentation, diagnostic findings, treatment, and follow-up of an atypical case of chronic masticatory muscle myositis in a very young dog. A 5-month old Cavalier king Charles Spaniel (CKCS) was presented to the AniCura Istituto Veterinario Novara with a two weeks, progressive history of lethargy and difficulty in food prehension. Neurological examination revealed bilateral masticatory muscle atrophy, mandibular ptosis with the jaw kept open, inability to close the mouth without manual assistance, jaw pain, and bilateral reduction of palpebral reflex and menace reaction; vision was maintained. A myopathy was suspected. Computed tomography (CT), magnetic resonance imaging (MRI), enzyme-linked immunosorbent assay test for 2M antibodies, and histopathological examination of masticatory muscle biopsy confirmed the diagnosis of MMM. Glucocorticoids treatment was started and clinical signs promptly improved. To the authors' knowledge, this is the first case describing mandibular ptosis in a dog affected by chronic MMM, successfully managed with medical treatment and the first report describing the CT and MRI findings in a young CKCS affected by MMM.

Inherited neuroaxonal dystrophy in dogs causing lethal, fetal-onset motor system dysfunction and cerebellar hypoplasia

Neuroaxonal dystrophy in brainstem, spinal cord tracts, and spinal nerves accompanied by cerebellar hypoplasia was observed in a colony of laboratory dogs. Fetal akinesia was documented by ultrasonographic examination. At birth, affected puppies exhibited stereotypical positioning of limbs, scoliosis, arthrogryposis, pulmonary hypoplasia, and respiratory failure. Regional hypoplasia in the central nervous system was apparent grossly, most strikingly as underdeveloped cerebellum and spinal cord. Histopathologic abnormalities included swollen axons and spheroids in brainstem and spinal cord tracts; reduced cerebellar foliation, patchy loss of Purkinje cells, multifocal thinning of the external granular cell layer, and loss of neurons in the deep cerebellar nuclei; spheroids and loss of myelinated axons in spinal roots and peripheral nerves; increased myocyte apoptosis in skeletal muscle; and fibrofatty connective tissue proliferation around joints. Breeding studies demonstrated that the canine disorder is a fully penetrant, simple autosomal recessive trait. The disorder demonstrated a type and distribution of lesions homologous to that of human infantile neuroaxonal dystrophy (INAD), most commonly caused by mutations of phospholipase A2 group VI gene (PLA2G6), but alleles of informative markers flanking the canine PLA2G6 locus did not associate with the canine disorder. Thus, fetal-onset neuroaxonal dystrophy in dogs, a species with well-developed genome mapping resources, provides a unique opportunity for additional disease gene discovery and understanding of this pathology.

MTM1 mutation associated with X-linked myotubular myopathy in Labrador Retrievers

Mutations in the MTM1 gene encoding myotubularin cause X-linked myotubular myopathy (XLMTM), a well-defined subtype of human centronuclear myopathy. Seven male Labrador Retrievers, age 14-26 wk, were clinically evaluated for generalized weakness and muscle atrophy. Muscle biopsies showed variability in fiber size, centrally placed nuclei resembling fetal myotubes, and subsarcolemmal ringed and central dense areas highlighted with mitochondrial specific reactions. Ultrastructural studies confirmed the centrally located nuclei, abnormal perinuclear structure, and mitochondrial accumulations. Wild-type triads were infrequent, with most exhibiting an abnormal orientation of T tubules. MTM1 gene sequencing revealed a unique exon 7 variant in all seven affected males, causing a nonconservative missense change, p.N155K, which haplotype data suggest derives from a recent founder in the local population. Analysis of a worldwide panel of 237 unaffected Labrador Retrievers and 59 additional control dogs from 25 other breeds failed to identify this variant, supporting it as the pathogenic mutation. Myotubularin protein levels and localization were abnormal in muscles from affected dogs, and expression of GFP-MTM1 p.N155K in COS-1 cells showed that the mutant protein was sequestered in proteasomes, where it was presumably misfolded and prematurely degraded. These data demonstrate that XLMTM in Labrador Retrievers is a faithful genetic model of the human condition.

Locked Jaw Syndrome in Dogs and Cats: 37 Cases (1998–2005)

A consecutive series of cases of dogs and cats with locked jaw syndrome (inability to open or close the mouth) are reported in this study. Dogs were significantly overrepresented (84.0 %) and adult dogs were more frequently affected (81.0 %). Temporomandibular joint ankylosis due to fracture was the most common cause (54.0 %) of locked jaw syndrome. Additional potential causes of locked jaw syndrome are masticatory muscle myositis, neoplasia, trigeminal nerve paralysis and central neurological lesions, temporomandibular joint luxation and dysplasia, osteoarthritis, retrobulbar abscess, tetanus, and severe ear disease. Treatment of locked jaw is directed towards the primary cause. It is important to treat the tonic spasm in order to minimize periarticular fibrosis. Surgical intervention is recommended for temporomandibular joint ankylosis. Masticatory muscle myositis treatment is initiated by gradually opening the mouth, with medical treatment based on immunosuppressive therapy. Fracture and masticatory muscle myositis are associated with a relatively good prognosis in regard to short-term outcome as compared to animals with central neurologic lesions or osteosarcoma which have a poor prognosis.

Autoantibodies in Canine Masticatory Muscle Myositis Recognize a Novel Myosin Binding Protein-C Family Member

Inflammatory myopathies are a group of autoimmune diseases that affect muscles. In humans, the most common inflammatory myopathies are polymyositis, dermatomyositis, and inclusion body myositis. Autoantibodies may be found in humans with inflammatory myopathies, and these play an important role in diagnosis and disease classification. However, these Abs are typically not muscle specific. Spontaneously occurring canine inflammatory myopathies may be good parallel disorders and provide insights into human myositis. In dogs with inflammatory myopathy, muscle-specific autoantibodies have been found, especially in masticatory muscle myositis. We have identified the major Ag recognized by the autoantibodies in canine masticatory muscle myositis. This Ag is a novel member of the myosin binding protein-C family, which we call masticatory myosin binding protein-C (mMyBP-C). mMyBP-C is localized not only within the masticatory muscle fibers, but also at or near their cell surface, perhaps making it accessible as an immunogen. The gene for mMyBP-C also exists in humans, and mMyBP-C could potentially play a role in certain human inflammatory myopathies. Understanding the role of mMyBP-C in this canine inflammatory myopathy may advance our knowledge of mechanisms of autoimmune inflammatory muscle diseases, not only in dogs, but also in humans.

Computed tomographic appearance of masticatory myositis in dogs: 7 cases (1999–2006)

OBJECTIVE

To document computed tomography (CT) features in dogs with masticatory myositis.

DESIGN

Retrospective case series.

ANIMALS

7 dogs with an immunologic diagnosis of masticatory myositis and an absence of clinical abnormalities of any skeletal muscles other than the masticatory muscles.

PROCEDURES

History; clinical, hematologic, biochemical, immunologic, cytologic, and histologic findings; and pre- and postcontrast CT imaging features of masticatory muscles and head and neck lymph nodes were extracted from medical records.

RESULTS

On CT images, changes in size (atrophy or swelling) were common for all masticatory muscles except the digastricus muscles, which were involved only in 1 dog. Pre-contrast attenuation changes, most often hypoattenuation with varied distribution patterns, were seen in masticatory muscles of 4 dogs. Contrast enhancement with a predominantly inhomogeneous distribution pattern was seen in the temporalis, masseter, and pterygoid muscles of all dogs. Head and neck lymph nodes were enlarged in all but 1 dog and had contrast enhancement with predominantly central or homogeneous distribution patterns. Muscle biopsy was performed in 6 dogs, with biopsy specimens obtained from areas that had the most obvious contrast enhancement on CT images. For all 6 dogs, biopsy specimens had histologic features indicative of masticatory myositis.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that CT may be a useful adjunct in the diagnosis of masticatory myositis in dogs, including selection of sites for diagnostic muscle biopsy.

From dog to man: the broad spectrum of inflammatory myopathies

The purpose of this review is to describe the various forms of inflammatory myopathy that occur spontaneously in dogs, and discuss the similarities and differences between inflammatory myopathy in dogs and humans. Some interesting muscle-specific autoantigens have recently been discovered in canine autoimmune myositis, and they are associated with specific forms of inflammatory myopathy. These autoantigens may now be investigated in humans. Furthermore, the association of distinct inflammatory myopathies with certain breeds of dogs point to important genetic components of inflammatory myopathy that can now be studied using dogs as both parallel disorders and animal models. Other canine myositides, associated with infectious and histiocytic diseases, may also be relevant to similar human disorders.

`Superfast' or masticatory myosin and the evolution of jaw-closing muscles of vertebrates

There are four fibre types in mammalian limb muscles, each expressing a different myosin isoform that finely tunes fibre mechanics and energetics for locomotion. Functional demands on jaw-closer muscles are complex and varied,and jaw muscles show considerable phylogenetic plasticity, with a repertoire for myosin expression that includes limb, developmental, α-cardiac and masticatory myosins. Masticatory myosin is a phylogenetically ancient motor with distinct light chains and heavy chains. It confers high maximal muscle force and power. It is highly jaw-specific in expression and is found in several orders of eutherian and marsupial mammals including carnivores,chiropterans, primates, dasyurids and diprotodonts. In exceptional species among these orders, masticatory myosin is replaced by some other isoform. Masticatory myosin is also found in reptiles and fish. It is postulated that masticatory myosin diverged early during gnathostome evolution and is expressed in primitive mammals. During mammalian evolution, mastication of food became important, and in some taxa jaw closers replaced masticatory myosin with α-cardiac, developmental, slow or fast limb myosins to adapt to the variety of diets and eating habits. This occurred early in some taxa(rodents, ungulates) and later in others (macropods, lesser panda, humans). The cellular basis for the uniqueness of jaw-closing muscles lies in their developmental origin.

Post-translational phosphorylation of the slow/beta myosin heavy chain isoform in adult rabbit masseter muscle

Four different phenotypes of slow muscle fibers, characterized by differential epitope expression in the slow/beta myosin heavy chain (MyHC) isoform, have been identified in adult rabbit masseter muscle. We investigated the role of post-translational phosphorylation in the expression of these four phenotypes. Serial cryostat sections were treated either with alkaline phosphatase to dephosphorylate proteins in the tissue, or with a brain kinase solution and ATP to phosphorylate them, and then stained, using four antibodies that bind specifically to the slow/beta MyHC isoform. In sections pre-treated with phosphatase, immunoreactivity to antibody A4.840 was abolished, but it could be restored by subsequent kinase/ATP treatment or ATP alone, indicating that the expression of its epitope requires phosphorylation. Phosphatase treatment resulted in an exposure of the epitope for antibody A4.951 in cells that normally bind this antibody only weakly or not at all, but since heat treatment alone produced similar effects, the role of phosphorylation in this enhancement is less certain. Immunoreactivity to antibodies S58 and BA-D5 were not influenced by phosphatase pre-treatment. Kinase/ATP treatment was only effective in changing antibody binding when tissues already had been phosphatase treated. We interpret these results to mean that sites of potential phosphorylation may already be occupied by O-linked glycosylation.

A review of immunologic diseases of the dog

The following review is based on notes used in the teaching of clinical immunology to veterinary students. Immune diseases of the dog are placed into six different categories: (1) type I or allergic conditions; (2) type II or auto- and allo-antibody diseases; (3) type III or immune complex disorders; (4) type IV or cell-mediated immune diseases; (5) type V conditions or gammopathies; and (6) type VI or immunodeficiency disorders. Separate discussions of transplantation immunology and the use of drugs to regulate unwanted immune responses are also included.

Mammalian skeletal muscle fiber type transitions

Mammalian skeletal muscle is an extremely heterogeneous tissue, composed of a large variety of fiber types. These fibers, however, are not fixed units but represent highly versatile entities capable of responding to altered functional demands and a variety of signals by changing their phenotypic profiles. This adaptive responsiveness is the basis of fiber type transitions. The fiber population of a given muscle is in a dynamic state, constantly adjusting to the current conditions. The full range of adaptive ability spans fast to slow characteristics. However, it is now clear that fiber type transitions do not proceed in immediate jumps from one extreme to the other, but occur in a graded and orderly sequential manner. At the molecular level, the best examples of these stepwise transitions are myofibrillar protein isoform exchanges. For the myosin heavy chain, this entails a sequence going from the fastest (MHCIIb) to the slowest (MHCI) isoform, and vice-versa. Depending on the basal protein isoform profile and hence the position within the fast-slow spectrum, the adaptive ranges of different fibers vary. A simple transition scheme has emerged from the multitude of data collected on fiber type conversions under a variety of conditions.

Bite-force development, metabolic and circulatory response to electrical stimulation in the canine and porcine masseter muscles

The development of fatigue was investigated by electrical stimulation in 15 domestic pigs (1 yr old, 70-90 kg body weight) and seven adult dogs (3 yr old, 45 kg body weight). After anaesthesia, silver electrodes were implanted in the anterior and posterior parts of the right masseter muscles. The contralateral muscle was used as control. The bite force was measured. Muscle biopsies were obtained from the anterior, central and posterior parts, and were immediately frozen in liquid nitrogen. A fluorometrical analysis by enzymatic methods for glycogen, glucose, creatine phosphate, NAD, NADH, lactate and pyruvate was made. Blood flow was measured by 133Xe wash-out; oxygen consumption was monitored with an oxygen electrode. The porcine masseter was continuously stimulated for 60 min (100 V, 4 Hz and 2 ms). The canine masseter was intermittently stimulated (100 V, 20 Hz and 2 ms). The contraction was repeated four times, with a 10-min rest between. The porcine masseter could sustain longer endurance times than the canine masseter, which was easily fatigued. A marked substrate depletion was evident. The precontractional contents of glycogen, glucose and creatine phosphate were reduced. Lactate accumulation was evident (2-4 times more in the porcine and 4-8 times more in the canine masseter). The NADH concentration increased and the NAD content decreased. Blood-flow impairment (80% reduction in the dog, 60% in the pig) was observed. After the contraction phase, there was a hyperaemia (58% elevation of blood flow in the pig masseter, 45% in the canine). The oxygen tension followed in magnitude and time the blood-flow changes. These circulatory variables returned to normal after recovery. The high degree of substrate depletion, blood-flow impairment and a simultaneous decrease in oxygen transport to the contracted muscle, in combination with a prominent lactate accumulation, may induce a decrease in bite-force production.

Histomorphometric and histopathological study of the human cricopharyngeus muscle: in health and in motor neuron disease

Abnormalities in muscle histology have been reported frequently for the cricopharyngeus muscle of patients with oculopharyngeal muscular dystrophy, motor neuron disease and other neurological disorders in which dysphagia is a common clinical sign. However, there are few detailed reports of the normal structure of this muscle nor quantitative baseline data with which to compare the diseased state. In this study, cricopharyngeus muscles from 21 healthy individuals and four patients with motor neuron disease underwent quantitative histological and histochemical examination. In addition to the extensive connective tissue content (40%), comprising abundant elastic fibres, cricopharyngeus muscles from normal individuals possessed small calibre striated muscle fibres (mean narrow diameter 30 microns) of widely varying size (coefficient of variation 41%). The majority of fibres were histochemically type I (82%) and highly oxidative. All muscles comprised numerous muscle fibres with aberrant histological and histochemical features (internalized nuclei, 'ragged red' crescents, splits, degenerating fibres, 'moth-eaten' fibres, or nemaline rods.) The histomorphometric and histopathological features were similar in males and females and some showed a correlation with age. There were increases in fibre size and roundedness and decreases in the numerical density and percentage of type I and split fibres in the specimens from older individuals. Cricopharyngeus muscles from patients with motor neuron disease were not significantly different from the controls for most parameters. It is therefore suggested that previous descriptions of specific cricopharyngeal pathology accompanying neuromuscular disease or dysphagia be interpreted with caution. The importance of obtaining normal structural, morphometric and histopathological data from muscles other than the usually biopsied limb muscles, is emphasized.

Regeneration of cat posterior temporalis muscle in culture

Cat posterior temporalis muscle has a rapid speed of contraction associated with a unique superfast myosin isoform. Superfast myosin expression appears to be an intrinsic property of the muscle fibres and satellite cells, though in culture they failed to express superfast myosin. We have, therefore, cultured this muscle in a system which had previously been shown to encourage the expression of an adult phenotype. The presence of nerve cells resulted in effective regeneration of cat posterior temporalis muscle and even the formation of functional neuromuscular junctions. However, superfast myosin was not found even in mature, contracting, innervated cultures. Thyroid hormone, a known regulator of myosin isoform expression, also failed to elicit superfast myosin expression. Different culture conditions may allow a different outcome, but under circumstances in which mouse muscle expresses an adult phenotype, cat posterior temporalis muscle fails to do so.