Mild Muscular Features in Tenascin-X Knockout Mice,A Model of Ehlers–Danlos Syndrome

Introduction: Tenascin-X (TNX) is an extracellular matrix (ECM) glycoprotein, the absence of which in humans leads to a recessive form of Ehlers–Danlos syndrome (EDS), a group of inherited connective tissue disorders characterized by joint hypermobility, skin hyperextensibility, and tissue fragility. A mouse model of TNX-deficient type EDS has been used to characterize the dermatological, orthopedic, and obstetrical features. The growing insight in the clinical overlap between myopathies and inherited connective tissue disorders asks for a study of the muscular characteristics of inherited connective tissue diseases. Therefore, this study aims to define the muscular phenotype of TNX knockout (KO) mice. Materials and methods: We performed a comprehensive study on the muscular phenotype of these TNX KO mice, consisting of standardized clinical assessment, muscle histology, and gene expression profiling of muscle tissue. Furthermore, peripheral nerve composition was studied by histology and electron microscopy. Results: The main findings are the presence of mild muscle weakness, mild myopathic features on histology, and functional upregulation of genes encoding proteins involved in ECM degradation and synthesis. Additionally, sciatic nerve samples showed mildly reduced collagen fibril density of endoneurium. Discussion: The muscular phenotype of TNX KO mice consists of mild muscle weakness with histological signs of myopathy and of increased turnover of the ECM in muscle. Furthermore, mildly reduced diameter of myelinated fibers and reduction of collagen fibril density of endoneurium may correspond with polyneuropathy in TNX-deficient EDS patients. This comprehensive assessment can serve as a starting point for further investigations on neuromuscular function in TNX KO mice.     

REM sleep deprivation impairs muscle regeneration in rats

Introduction: The aim was observe the influence of sleep deprivation (SD) and sleep recovery on muscle regeneration process in rats submitted to cryolesion.

Methods: Thirty-two Wistar rats were randomly allocated in four groups: control (CTL), SD for 96?h (SD96), control plus sleep recovery period (CTL?+?R) and SD96h plus 96?h of sleep recovery (SD96?+?R). The animals were submitted to muscle injury by cryolesioning, after to SD and sleep recovery.

Results: The major outcomes of this study were the reduction of muscular IGF-1 in both legs (injured and uninjured) and a delay in muscle regeneration process of animals submitted to SD compared to animals that slept, with increase connective tissue, inflammatory infiltrate and minor muscle fibers.

Conclusions: SD impairs muscle regeneration in rats, moreover reduces muscular IGF-1 and sleep recovery was able to restore it to basal levels, but it was not enough to normalize the muscle regeneration.     

Vertical Clinging and Leaping Ahead: How Bamboo Has Shaped the Anatomy and Physiology of Hapalemur

Hapalemur sps. and Prolemur simus (bamboo lemurs, collectively) stand out from the relatively homogeneous lemurids because they are bamboo feeders and vertical clingers and leapers. This unique diet presents equally unique challenges, like its verticality, toughness, and toxicity. The bamboo lemurs share the generalized anatomy of the other lemurids, but also display some well-documented skeletal adaptations, perhaps to overcome the problems presented by their specialization. Soft-tissue adaptations, however, remain largely unexplored. Explored here are possible soft-tissue adaptations in Hapalemur griseus. We compare H. griseus with other lemurids, Propithecus, Galago, Tarsier, and a tree shrew. Based on the available anatomical and physiological data, we hypothesize that Hapalemur and Prolemur species will have differences in hindlimb morphology when compared with other lemurids. We predict that H. griseus will have more hindlimb muscle mass and will amplify muscle mass differences with increased type II muscle fibers. Relative hindlimb muscle mass in H. griseus is less than other prosimians sampled, yet relative sural muscle mass is significantly heavier (P < 0.01) in H. griseus. Results show that the soleus muscle of H. griseus has a higher amount of type II (fast) fibers in plantarflexors. These findings indicate although H. griseus shares some generalized lemurid morphology, its diet of bamboo may have pushed this generalized lemurid to an anatomical extreme. We suspect additional bamboo-specific adaptations in their anatomy and physiology will be uncovered with further examination into the anatomy of the bamboo lemurs. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc. Anat Rec, 303:295–307, 2020. © 2019 American Association for Anatomy     

Morphological peculiarities in the integument of enigmatic anomalurid gliders (Anomaluridae,Rodentia)

Scaly-tailed squirrels, the most poorly known group of gliding mammals, hold the record for variety of remarkable integument peculiarities. One of the most striking of these features is the scales on the tail, which apparently allow them to reduce energy costs when positioning themselves on a tree trunk. No less interesting is a peculiar spur that supports the flying membrane: the unciform element (‘spur’). Despite the peculiarity of such elements, their nature has not yet been studied. Using anatomical, histological methods and scanning electron microscopy we studied the structure of the skin and its derivatives in five of the six species from both genera of extant gliding scaly-tailed squirrels (Anomaluridae, Rodentia): Idiurus macrotis, Idiurus zenkeri, Anomalurus beecrofti, Anomalurus pusillus and Anomalurus derbianus. In addition to the common mammalian skin structures, such as hair, vibrissae, sebaceous glands, meibomian glands of eyelids and eccrine sweat glands of the palmar and plantar pads, these animals have unique species-specific skin derivatives (the tail scaly organ and its specific glands, vibrissae of the withers, patagium and its hair brush) that play a significant role in their adaptation to gliding and to their environment in general. The structure of the elbow spur is also described and hypotheses on its evolutionary origin from the tendon of the triceps muscle are presented.     

Forelimb musculature and function in the therizinosaur Nothronychus (Maniraptora,Theropoda)

Therizinosaurs are unusual theropods from the Upper Cretaceous of Asia and North America. North American representatives include Falcarius utahensis from central Utah, Nothronychus mckinleyi from west central New Mexico, and N. graffami from southern Utah. Nothronychus was quite large, with well-developed forelimbs and pectoral girdle. In many respects, however, these structures were typical for conventional carnivorous theropods, although therizinosaurs have been hypothesized to be herbivorous using anatomical and functional inferences. There is no indication of increased range of motion within the forelimbs, as might be predicted for derived non-avian theropods. The muscular anatomy of the pectoral girdle and forelimb of Nothronychus is reconstructed using visible muscle scars, data from extant birds and crocodilians, and models for other theropods. The osteology and inferred musculature is a mosaic of primitive and derived characters for theropods. A fossa pneumotricipitales may have been present in the proximal humerus. There was a well-developed fossa brachialis in the distal humerus. The epicleidium of the furcula is deflected, reflecting either taphonomic deformation or possibly accommodation of M. supracoracoideus in a triosseal canal, but such a development has yet to be described in any non-avian theropod. In many respects, the other muscular results were quite similar to those inferred for dromaeosaurs.     

The vastus lateralis muscle: An anatomical investigation

Anterior knee pain or patellofemoral pain syndrome is commonly encountered by clinicians, but the pathogenesis of this condition is not well understood. While much research has centred around the relationship between vastus medialis and anterior knee pain, little is known about the most lateral of the quadriceps muscle group, vastus lateralis (VL). Knowledge of the anatomical organization of VL is not only necessary to understand its precise function, but to also assist in the development of clinical and biomechanical models of knee dysfunction. The purpose of this study was to investigate the detailed morphology of VL, specifically to provide data relating to architecture, attachment sites, innervation, and the presence of anatomical partitioning within the muscle. The VL muscle was examined in 10 cadaveric lower limbs using macrodissection techniques. On the basis of architecture and innervation, this muscle comprised four partitions with each receiving its own unique nerve branch. The mean fascicular length of VL was 7 cm and the mean fascicular and muscle physiological cross‐sectional areas were 1.2 cm² and 21.6 cm², respectively. In addition to inserting proximally at the base of the greater trochanter and distally into the superolateral border and base of the patella, three additional attachment sites were identified: the lateral intermuscular septum, iliotibial band, and the rectus tendon. The results of this study suggest that the gross morphology of VL is more complex than previously described, and the information provided regarding architecture will contribute to knowledge regarding the function of VL as well as its role in knee joint dysfunction. Clin. Anat. 23:575–585, 2010. © 2010 Wiley‐Liss, Inc.     

Protection of dystrophic muscle cells using Idebenone correlates with the interplay between calcium,oxidative stress and inflammation

There is strong cross-talk between abnormal intracellular calcium concentration, high levels of reactive oxygen species (ROS) and an exacerbated inflammatory process in the dystrophic muscles of mdx mice, the experimental model of Duchenne muscular dystrophy (DMD). In this study, we investigated effects of Idebenone, a potent anti-oxidant, on oxidative stress markers, the anti-oxidant defence system, intracellular calcium concentrations and the inflammatory process in primary dystrophic muscle cells from mdx mice. Dystrophic muscle cells were treated with Idebenone (0.05 μM) for 24 h. The untreated mdx muscle cells were used as controls. The MTT assay showed that Idebenone did not have a cytotoxic effect on the dystrophic muscle cells. The Idebenone treatment was able to reduce the levels of oxidative stress markers, such as H₂O₂ and 4-HNE, as well as decreasing intracellular calcium influx in the dystrophic muscle cells. Regarding Idebenone effects on the anti-oxidant defence system, an up-regulation of catalase levels, glutathione reductase (GR), glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity was observed in the dystrophic muscle cells. In addition, the Idebenone treatment was also associated with reduction in inflammatory molecules, such as nuclear factor kappa-B (NF-κB) and tumour necrosis factor (TNF) in mdx muscle cells. These outcomes supported the use of Idebenone as a protective agent against oxidative stress and related signalling mechanisms involved in dystrophinopathies, such as DMD.     

Muscle moment arms and sensitivity analysis of a mouse hindlimb musculoskeletal model

Musculoskeletal modelling has become a valuable tool with which to understand how neural, muscular, skeletal and other tissues are integrated to produce movement. Most musculoskeletal modelling work has to date focused on humans or their close relatives, with few examples of quadrupedal animal limb models. A musculoskeletal model of the mouse hindlimb could have broad utility for questions in medicine, genetics, locomotion and neuroscience. This is due to this species’ position as a premier model of human disease, having an array of genetic tools for manipulation of the animal in vivo, and being a small quadruped, a category for which few models exist. Here, the methods used to develop the first three‐dimensional (3D) model of a mouse hindlimb and pelvis are described. The model, which represents bones, joints and 39 musculotendon units, was created through a combination of previously gathered muscle architecture data from microdissections, contrast‐enhanced micro‐computed tomography (CT) scanning and digital segmentation. The model allowed muscle moment arms as well as muscle forces to be estimated for each musculotendon unit throughout a range of joint rotations. Moment arm analysis supported the reliability of musculotendon unit placement within the model, and comparison to a previously published rat hindlimb model further supported the model's reliability. A sensitivity analysis performed on both the force‐generating parameters and muscle's attachment points of the model indicated that the maximal isometric muscle moment is generally most sensitive to changes in either tendon slack length or the coordinates of insertion, although the degree to which the moment is affected depends on several factors. This model represents the first step in the creation of a fully dynamic 3D computer model of the mouse hindlimb and pelvis that has application to neuromuscular disease, comparative biomechanics and the neuromechanical basis of movement. Capturing the morphology and dynamics of the limb, it enables future dissection of the complex interactions between the nervous and musculoskeletal systems as well as the environment.     

Anatomical mapping of the nasal muscles and application to cosmetic surgery

We present an anatomical mapping of the most important muscles influencing the nose, incorporating constant anatomical structures, and their spatial correlations. At our disposal were the midfaces of 18 bodies of both sexes, obtained by informed consent from body donors aged between 60 and 80 years. Macroscopically, we dissected the nasal regions of eight corpses, six midfaces were prepared according to plastination histology, four by creating plastinated slices. On their way from their periosteal origin to the edge of the skin, the muscles of the nose cross the subcutaneous adipose tissue, dividing it into superficial and deep layers. The individual muscle fibers insert into the skin directly at the reticular corium. Sometimes, they reach the border of the epidermis which represents a special arrangement of corial muscle attachments. The course of the anatomical fibers of individual nasal muscles presented macroscopically and microscopically in this study offers surgeons a detailed overview of the anatomically important muscular landmarks of the midface. Clin. Anat. 27:1178–1184, 2014. © 2014 Wiley Periodicals, Inc.     

The musculus pterygoïdeus proprius: an in-vivo approach with magnetic resonance imaging

There is a limited understanding of the normal function of the pterygoïdeus proprius muscle and the role that this muscle may have in temporomandibular disorders. Despite a well‐described anatomical in‐vitro approach to this muscle, there are still difficulties in investigating the fossa pterygopalatina. This study reveals an alternative in‐vivo approach by magnetic resonance imaging to visualise the muscle in the fossa pterygopalatina on 78 head halves, describe the connections with the musculus temporalis and pterygoïdeus lateralis as well as report the incidence without dealing with the known inconveniences of the dissection approach. The results show an incidence of 12.82% for the musculus pterygoïdeus proprius equally divided between both genders. Two different types of bridging between the musculus temporalis and musculus pterygoïdeus lateralis were also found: (i) ‘O’ shape (6.41%) and (ii) ‘Y’ shape (6.41%). This study suggests the use of magnetic resonance imaging to investigate the different connections between vascular and muscular structures in the fossa pterygopalatina. Further research with this approach to link the appearance of the muscle with neurovascular entrapment syndromes is warranted.     

Combined spiroergometry and 31P–MRS of human calf muscle during high‐intensity exercise

Simultaneous measurements of pulmonary oxygen consumption (VO₂), carbon dioxide exhalation (VCO₂) and phosphorus magnetic resonance spectroscopy (³¹P–MRS) are valuable in physiological studies to evaluate muscle metabolism during specific loads. Therefore, the aim of this study was to adapt a commercially available spirometric device to enable measurements of VO₂ and VCO₂ whilst simultaneously performing ³¹P–MRS at 3 T. Volunteers performed intense plantar flexion of their right calf muscle inside the MR scanner against a pneumatic MR‐compatible pedal ergometer. The use of a non‐magnetic pneumotachograph and extension of the sampling line from 3 m to 5 m to place the spirometric device outside the MR scanner room did not affect adversely the measurements of VO₂ and VCO₂. Response and delay times increased, on average, by at most 0.05 s and 0.79 s, respectively. Overall, we were able to demonstrate a feasible ventilation response (VO₂ = 1.05 ± 0.31 L/min; VCO₂ = 1.11 ± 0.33 L/min) during the exercise of a single calf muscle, as well as a good correlation between local energy metabolism and muscular acidification (τ_{PCr fast} and pH; R² = 0.73, p < 0.005) and global respiration (τ_{PCr fast} and VO₂; R² = 0.55, p = 0.01). This provides improved insights into aerobic and anaerobic energy supply during strong muscular performances.     

Limitations of relaxation kinetics on muscular work

Aim: Positive net work produced during cyclic contractions is partially limited by relaxation kinetics, which to date, have not been directly investigated. Therefore, the purpose of this investigation was to determine the influence of relaxation kinetics on cyclic work. Methods: Soleus muscles of four cats were isolated and subjected to a series of work loops (0.5, 1, 1.5 and 2 Hz cycle frequencies) during which stimulation terminated prior to the end of the shortening phase to allow for complete muscle relaxation and matched discrete sinusoidal shortening contractions during which stimulation remained on until the completion of the shortening phase. Muscle length changes during these protocols were centred on optimum length and were performed across muscle lengths that represented walking gait. Results: When muscle excursions were centred on L_o relaxation kinetics decreased muscular work by 2.8 ± 0.8%, 12.1 ± 4.1%, 27.9 ± 4.5% and 40.1 ± 5.9% for 0.5, 1, 1.5 and 2 Hz respectively. However, relaxation kinetics did not influence muscular work when muscle excursions represented walking gait. In addition, muscular work produced at muscle lengths associated with walking gait was less than the work produced across L_o (55.7 ± 20.0%, 53.5 ± 21.0%, and 50.1 ± 22.0% for 0.5, 1 and 1.5 Hz respectively). Conclusion: These results imply that relaxation kinetics are an important factor that limit the ability of muscle to produce work; however, the influence of relaxation kinetics on physiological function may depend on the relation between the optimum length and natural excursion of a muscle.     

PDGFRα signalling promotes fibrogenic responses in collagen‐producing cells in Duchenne muscular dystrophy

Fibrosis is a characteristic of Duchenne muscular dystrophy (DMD), yet the cellular and molecular mechanisms responsible for DMD fibrosis are poorly understood. Utilizing the Collagen1a1‐GFP transgene to identify cells producing Collagen‐I matrix in wild‐type mice exposed to toxic injury or those mutated at the dystrophin gene locus (mdx) as a model of DMD, we studied mechanisms of skeletal muscle injury/repair and fibrosis. PDGFRα is restricted to Sca1+, CD45? mesenchymal progenitors. Fate‐mapping experiments using inducible CreER/LoxP somatic recombination indicate that these progenitors expand in injury or DMD to become PDGFRα+, Col1a1‐GFP+ matrix‐forming fibroblasts, whereas muscle fibres do not become fibroblasts but are an important source of the PDGFRα ligand, PDGF‐AA. While in toxin injury/repair of muscle PDGFRα, signalling is transiently up‐regulated during the regenerative phase in the DMD model and in human DMD it is chronically overactivated. Conditional expression of the constitutively active PDGFRα D842V mutation in Collagen‐I+ fibroblasts, during injury/repair, hindered the repair phase and instead promoted fibrosis. In DMD, treatment of mdx mice with crenolanib, a highly selective PDGFRα/β tyrosine kinase inhibitor, reduced fibrosis, improved muscle strength, and was associated with decreased activity of Src, a downstream effector of PDGFRα signalling. These observations are consistent with a model in which PDGFRα activation of mesenchymal progenitors normally regulates repair of the injured muscle, but in DMD persistent and excessive activation of this pathway directly drives fibrosis and hinders repair. The PDGFRα pathway is a potential new target for treatment of progressive DMD. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.     

Comparative hindlimb myology of foot‐propelled swimming birds

Several groups of birds have convergently evolved the ability to swim using their feet despite facing trade‐offs with walking. However, swimming relative to terrestrial performance varies across these groups. Highly specialized divers, such as loons and grebes, excel at swimming underwater but struggle to stand on land, whereas species that primarily swim on the water surface, such as Mallards, retain the ability to move terrestrially. The identification of skeletal features associated with a swimming style and conserved across independent groups suggests that the hindlimb of foot‐propelled swimming birds has adapted to suit the physical challenges of producing propulsive forces underwater. But in addition to skeletal features, how do hindlimb muscles reflect swimming ability and mode? This paper presents the first comparative myology analysis associated with foot‐based swimming. Our detailed dissections of 35 specimens representing eight species reveal trends in hindlimb muscle size and attachment location across four independent lineages of extant swimming birds. We expand upon our dissections by compiling data from historical texts and provide a key to any outdated muscle nomenclature used in these sources. Our results show that highly diving birds tuck the femur and proximal tibiotarsus next to the ribcage and under the skin covering the abdomen, streamlining the body. Several hindlimb muscles exhibit dramatic anatomical variation in diving birds, including the flexor cruris lateralis (FCL ) and iliofibularis (IF ), which reduce in size and shift distally along the tibiotarsus. The femorotibialis medius (FTM ) extends along an expanded cnemial crest. The resulting increased moment arms of these muscles likely help stabilize the hip and knee while paddling. Additionally, distal ankle plantarflexors, including the gastrocnemius and digital flexors, are exceptionally large in diving birds in order to power foot propulsion. These patterns exist within distantly related lineages of diving birds and, to a lesser extent, in surface swimmers. Together, our findings verify conserved muscular adaptations to a foot‐propelled swimming lifestyle. The association of muscle anatomy with skeletal features and biomechanical movement demands can inform functional interpretation of fossil birds and reveal selective pressures underlying avian diversification.     

Flight feather attachment in rock pigeons (Columba livia): covert feathers and smooth muscle coordinate a morphing wing

Mechanisms for passively coordinating forelimb movements and flight feather abduction and adduction have been described separately from both in vivo and ex vivo studies. Skeletal coordination has been identified as a way for birds to simplify the neuromotor task of controlling flight stroke, but an understanding of the relationship between skeletal coordination and the coordination of the aerodynamic control surface (the flight feathers) has been slow to materialize. This break between the biomechanical and aerodynamic approaches – between skeletal kinematics and airfoil shape – has hindered the study of dynamic flight behaviors. Here I use dissection and histology to identify previously overlooked interconnections between musculoskeletal elements and flight feathers. Many of these structures are well‐placed to directly link elements of the passive musculoskeletal coordination system with flight feather movements. Small bundles of smooth muscle form prominent connections between upper forearm coverts (deck feathers) and the ulna, as well as the majority of interconnections between major flight feathers of the hand. Abundant smooth muscle may play a role in efficient maintenance of folded wing posture, and may also provide an autonomically regulated means of tuning wing shape and aeroelastic behavior in flight. The pattern of muscular and ligamentous linkages of flight feathers to underlying muscle and bone may provide predictable passive guidance for the shape of the airfoil during flight stroke. The structures described here provide an anatomical touchstone for in vivo experimental tests of wing surface coordination in an extensively researched avian model species.