Rapid disuse atrophy of diaphragm fibers in mechanically ventilated humans.

BACKGROUND: The combination of complete diaphragm inactivity and mechanical ventilation (for more than 18 hours) elicits disuse atrophy of myofibers in animals. We hypothesized that the same may also occur in the human diaphragm. METHODS: We obtained biopsy specimens from the costal diaphragms of 14 brain-dead organ donors before organ harvest (case subjects) and compared them with intraoperative biopsy specimens from the diaphragms of 8 patients who were undergoing surgery for either benign lesions or localized lung cancer (control subjects). Case subjects had diaphragmatic inactivity and underwent mechanical ventilation for 18 to 69 hours; among control subjects diaphragmatic inactivity and mechanical ventilation were limited to 2 to 3 hours. We carried out histologic, biochemical, and gene-expression studies on these specimens. RESULTS: As compared with diaphragm-biopsy specimens from controls, specimens from case subjects showed decreased cross-sectional areas of slow-twitch and fast-twitch fibers of 57% (P=0.001) and 53% (P=0.01), respectively, decreased glutathione concentration of 23% (P=0.01), increased active caspase-3 expression of 100% (P=0.05), a 200% higher ratio of atrogin-1 messenger RNA (mRNA) transcripts to MBD4 (a housekeeping gene) (P=0.002), and a 590% higher ratio of MuRF-1 mRNA transcripts to MBD4 (P=0.001). CONCLUSIONS: The combination of 18 to 69 hours of complete diaphragmatic inactivity and mechanical ventilation results in marked atrophy of human diaphragm myofibers. These findings are consistent with increased diaphragmatic proteolysis during inactivity.

Harnessing Augmented Reality and CT to Teach First-Year Medical Students Head and Neck Anatomy.

RATIONALE AND OBJECTIVES: Three-dimensional (3D) visualization has been shown to benefit new generations of medical students and physicians-in-training in a variety of contexts. However, there is limited research directly comparing student performance after using 3D tools to those using two-dimensional (2D) screens. MATERIALS AND METHODS: A CT was performed on a donated cadaver and a 3D CT hologram was created. A total of 30 first-year medical students were randomly assigned into two groups to review head and neck anatomy in a teaching session that incorporated CT. The first group used an augmented reality headset, while the second group used a laptop screen. The students were administered a five-question anatomy test before and after the session. Two-tailed t-tests were used for statistical comparison of pretest and posttest performance within and between groups. A feedback survey was distributed for qualitative data. RESULTS: Pretest vs. posttest comparison of average percentage of questions answered correctly demonstrated both groups showing significant in-group improvement (p < 0.05), from 59% to 95% in the augmented reality group, and from 57% to 80% in the screen group. Between-group analysis indicated that posttest performance was significantly better in the augmented reality group (p = 0.022, effect size = 0.73). CONCLUSION: Immersive 3D visualization has the potential to improve short-term anatomic recall in the head and neck compared to traditional 2D screen-based review, as well as engage millennial learners to learn better in anatomy laboratory. Our findings may reflect additional benefit gained from the stereoscopic depth cues present in augmented reality-based visualization.

Ets-2 repressor factor silences extrasynaptic utrophin by N-box mediated repression in skeletal muscle.

Utrophin is the autosomal homologue of dystrophin, the protein product of the Duchenne's muscular dystrophy (DMD) locus. Utrophin expression is temporally and spatially regulated being developmentally down-regulated perinatally and enriched at neuromuscular junctions (NMJs) in adult muscle. Synaptic localization of utrophin occurs in part by heregulin-mediated extracellular signal-regulated kinase (ERK)-phosphorylation, leading to binding of GABPalpha/beta to the N-box/EBS and activation of the major utrophin promoter-A expressed in myofibers. However, molecular mechanisms contributing to concurrent extrasynaptic silencing that must occur to achieve NMJ localization are unknown. We demonstrate that the Ets-2 repressor factor (ERF) represses extrasynaptic utrophin-A in muscle. Gel shift and chromatin immunoprecipitation studies demonstrated physical association of ERF with the utrophin-A promoter N-box/EBS site. ERF overexpression repressed utrophin-A promoter activity; conversely, small interfering RNA-mediated ERF knockdown enhanced promoter activity as well as endogenous utrophin mRNA levels in cultured muscle cells in vitro. Laser-capture microscopy of tibialis anterior NMJ and extrasynaptic transcriptomes and gene transfer studies provide spatial and direct evidence, respectively, for ERF-mediated utrophin repression in vivo. Together, these studies suggest "repressing repressors" as a potential strategy for achieving utrophin up-regulation in DMD, and they provide a model for utrophin-A regulation in muscle.

First-Year Radiology Residents Teaching Anatomy to First-Year Medical Students: A Symbiotic Relationship.

OBJECTIVES: Our institution has developed an educational program in which first-year radiology residents teach first-year medical students during gross anatomy laboratory sessions. The purpose of this study is to assess the impact of this program on medical student knowledge and perceptions of radiology, and on resident attitudes toward teaching. MATERIALS AND METHODS: First-year resident pairs taught small groups of medical students during weekly 15-minute interactive sessions, and were evaluated on teaching skills by senior residents. A survey about attitudes toward radiology and a knowledge quiz were sent to the medical students, and a survey about attitudes toward teaching was sent to the first-year radiology residents, both pre-course and post-course. RESULTS: Students' radiology knowledge significantly increased between the pre-course and post-course survey across all categories tested (P < 0.001). Additionally, there were significant improvements in terms of students' confidence in radiologic anatomy skills, perceived importance of radiology for medical training, familiarity with the field of radiology, and perception that radiologists are friendly (P < 0.001). Radiology residents felt more confident in their teaching proficiency (P < 0.001) by the conclusion of the course. CONCLUSIONS: Resident-led small-group teaching sessions during anatomy laboratory are mutually beneficial for medical students and radiology residents. The program also allows radiology residents to be exposed early on in residency to teaching and academic medicine.

Influence of hyperthyroid conditions on gene expression in extraocular muscles of rats.

Extraocular muscles (EOMs) are a highly specialized type of tissue with a wide range of unique properties, including characteristic innervation, development, and structural proteins. Even though EOMs are frequently and prominently affected by thyroid-associated diseases, little is known about the direct effects of thyroid hormone on these muscles. To create a comprehensive profile of changes in gene expression levels in EOMs induced by thyroid hormone, hyperthyroid conditions were simulated by treating adult Sprague-Dawley rats with intraperitoneal injections of the thyroid hormone 3,3',5-triiodo-L-thyronine (T(3)); subsequently, microarray analysis was used to determine changes in mRNA levels in EOMs from T(3)-treated animals relative to untreated control animals. The expression of 468 transcripts was found to be significantly altered, with 466 of these transcripts downregulated in EOMs from T(3)-treated animals. The biological processes into which the affected genes could be grouped included cellular metabolism, transport, biosynthesis, protein localization, and cell homeostasis. Moreover, 15 distinct biochemical canonical pathways were represented among the genes with altered transcription levels. Strikingly, myostatin (Gdf8), a potent negative regulator of muscle growth, was found to be strongly downregulated in EOMs from T(3)-treated animals. Together, these findings suggest that pathological concentrations of thyroid hormone have a unique effect on gene expression in EOMs, which is likely to play a hitherto neglected role in thyroid-associated ophthalmopathies.

Transcriptional and functional differences in stem cell populations isolated from extraocular and limb muscles.

The extraocular muscles (EOMs) are a distinct muscle group that displays an array of unique contractile, structural, and regenerative properties. They also have differential sensitivity to certain diseases and are enigmatically spared in Duchenne muscular dystrophy (DMD). The EOMs are so distinct from other skeletal muscles that the term "allotype" has been coined to highlight EOM group-specific properties. We hypothesized that increased and distinct stem cells may underlie the continual myogenesis noted in EOM. The side population (SP) stem cells were isolated and studied. EOMs had 15x higher SP cell content compared with limb muscles. Expression profiling revealed 348 transcripts that define the EOM-SP transcriptome. Over 92% of transcripts were SP specific, because they were absent in previous whole muscle microarray studies. Cultured EOM-SP cells revealed superior in vitro proliferative capacity. Finally, assays of the committed progenitors or satellite cells performed on myofibers isolated from EOM and limb muscles independently validated the increased proliferative capacity of these muscles. We suggest a model in which unique EOM stem cells contribute to the continual myogenesis noted in EOM and consistent with a role for their sparing in DMD. We believe the greater numbers of stem cells, their unique transcriptome, the greater proliferative capacity of EOM stem cells, and the greater number of satellite cells also offer clues for novel cell-based therapeutic strategies.

Identification of acetylcholine receptor subunits differentially expressed in singly and multiply innervated fibers of extraocular muscles.

PURPOSE: To identify the acetylcholine receptor (AChR) isoforms among the neuromuscular junctions (NMJs) of singly and multiply innervated fibers (SIFs and MIFs) of rat extraocular muscles (EOMs). METHODS: EOMs were dissected from adult rats and serially sectioned. Sections were simultaneously stained for acetylcholinesterase and with an antibody to the slow myosin heavy chain to identify NMJ topography and fiber types in the same section. Synapses and subsynaptic regions of SIFs and MIFs were isolated by laser capture microdissection and the AChR subunits identified by RT-PCR. RESULTS: The en plaque endings of SIFs expressed only the adult epsilon subunit, not the fetal gamma subunit, of the AChR, whereas the en grappe endings of the MIFs expressed only the gamma subunit, and not the epsilon subunit. Although the expression of the epsilon subunit was confined to the NMJ region of the SIFs, the gamma subunit was expressed both synaptically and extrasynaptically within the MIFs. The gamma subunit in MIFs correlated with the expression of the myogenic regulatory factor myogenin. Moreover, an unusual neuronal AChR subunit, alpha9, was found in the EOMs, but not in the limb muscles. CONCLUSIONS: The adult epsilon and fetal gamma subunits of the AChRs are segregated into distinct synapses on distinct fiber types. The maintenance of the fetal subunit in a population of fibers is probably linked to the expression of myogenin and is a unique attribute of the EOM allotype.

Parasternal intercostal muscle remodeling in severe chronic obstructive pulmonary disease.

Studies in experimental animals indicate that chronic increases in neural drive to limb muscles elicit a fast-to-slow transformation of fiber-type proportions and myofibrillar proteins. Since neural drive to the parasternal intercostal muscles (parasternals) is chronically increased in patients with severe chronic obstructive pulmonary diseases (COPDs), we carried out the present study to test the hypothesis that the parasternals of COPD patients exhibit an increase in the proportions of both slow fibers and slow myosin heavy chains (MHCs). Accordingly, we obtained full thickness parasternal muscle biopsies from the third interspace of seven COPD patients (mean +/- SE age: 59 +/- 4 yr) and seven age-matched controls (AMCs). Fiber typing was done by immunohistochemistry, and MHC proportions were determined by SDS-PAGE followed by densitometry. COPD patients exhibited higher proportions of slow fibers than AMCs (73 +/- 4 vs. 51 +/- 3%; P < 0.01). Additionally, COPD patients exhibited higher proportions of slow MHC than AMCs (56 +/- 4 vs. 46 +/- 4%, P < 0.04). We conclude that the parasternal muscles of patients with severe COPD exhibit a fast-to-slow transformation in both fiber-type and MHC proportions. Previous workers have demonstrated that remodeling of the external intercostals, another rib cage inspiratory muscle, elicited by severe COPD is characterized by a slow-to-fast transformation in both fiber types and MHC isoform proportions. The physiological significance of this difference in remodeling between these two inspiratory rib cage muscles remains to be elucidated.

Effect of chronic obstructive pulmonary disease on calcium pump ATPase expression in human diaphragm.

We have previously demonstrated that human diaphragm remodeling elicited by severe chronic obstructive pulmonary disease (COPD) is characterized by a fast-to-slow myosin heavy chain isoform transformation. To test the hypothesis that COPD-induced diaphragm remodeling also elicits a fast-to-slow isoform shift in the sarcoendoplasmic reticulum Ca(2+) ATPase (SERCA), the other major ATPase in skeletal muscle, we obtained intraoperative biopsies of the costal diaphragm from 10 severe COPD patients and 10 control subjects. We then used isoform-specific monoclonal antibodies to characterize diaphragm fibers with respect to the expression of SERCA isoforms. Compared with control diaphragms, COPD diaphragms exhibited a 63% decrease in fibers expressing only fast SERCA (i.e., SERCA1; P < 0.001), a 190% increase in fibers containing both fast and slow SERCA isoforms (P < 0.01), and a 19% increase (P < 0.05) in fibers expressing only the slow SERCA isoform (i.e., SERCA2). Additionally, immunoblot experiments carried out on diaphragm homogenates indicated that COPD diaphragms expressed only one-third the SERCA1 content noted in control diaphragms; in contrast, COPD and control diaphragms did not differ with respect to SERCA2 content. The combination of these histological and immunoblot results is consistent with the hypothesis that diaphragm remodeling elicited by severe COPD is characterized by a fast-to-slow SERCA isoform transformation. Moreover, the combination of these SERCA data and our previously reported myosin heavy chain isoform data (Levine S, Nguyen T, Kaiser LR, Rubinstein NA, Maislin G, Gregory C, Rome LC, Dudley GA, Sieck GC, and Shrager JB. Am J Respir Crit Care Med 168: 706-713, 2003) suggests that diaphragm remodeling elicited by severe COPD should decrease ATP utilization by the diaphragm.

Structural details of rat extraocular muscles and three-dimensional reconstruction of the rat inferior rectus muscle and muscle-pulley interface.

Light microscopy, electron microscopy and morphometry revealed structural details and allowed generation of a three-dimensional reconstruction of the pulley and muscle-pulley interface of extraocular muscle. The inferior rectus orbital layer was bifurcate in shape and extended anterior to the pulley. The putative pulley structure itself was asymmetric; loosely attached at the orbital aspect it adhered tightly to the global aspect of muscle. Orbital multiply innervated fiber proportion increased anterior to the pulley insertion site. Additionally longitudinal variation in juxtaposition of orbital and global layers was noted. These newly described structural details provide novel mechanistic insight for extraocular muscle function in rats.

Expression profiling reveals metabolic and structural components of extraocular muscles.

The extraocular muscles (EOM) are anatomically and physiologically distinct from other skeletal muscles. EOM are preferentially affected in mitochondrial myopathies, but spared in Duchenne's muscular dystrophy. The anatomical and pathophysiological properties of EOM have been attributed to their unique molecular makeup: an allotype. We used expression profiling to define molecular features of the EOM allotype. We found 346 differentially expressed genes in rat EOM compared with tibialis anterior, based on a twofold difference cutoff. Genes required for efficient, fatigue-resistant, oxidative metabolism were increased in EOM, whereas genes for glycogen metabolism were decreased. EOM also showed increased expression of genes related to structural components of EOM such as vessels, nerves, mitochondria, and neuromuscular junctions. Additionally, genes related to specialized functional roles of EOM such as the embryonic and EOM-specific myosin heavy chains and genes for muscle growth, development, and/or regeneration were increased. The EOM expression profile was validated using biochemical, structural, and molecular methods. Characterization of the EOM expression profile begins to define gene transcription patterns associated with the unique anatomical, metabolic, and pathophysiological properties of EOM.

Layer-specific differences of gene expression in extraocular muscles identified by laser-capture microscopy.

In mammals, separate muscles are typically specialized as a whole to provide distinct functional roles leading to well-recognized adaptations. This is exemplified in the lower limb by the slow, fatigue-resistant soleus, which provides a postural role vs. the fast, fatiguable tibialis anterior (TA), which provides rapid movements. A unique characteristic of extraocular muscles (EOMs) is their compartmentalization into two distinct layers, the orbital layer (OL) and global layer (GL), presumably to subserve diverse functions within the same muscle. However, molecular evidence of this diversity has been limited. We used laser-capture microscopy coupled with microarray-based expression profiling to identify molecular differences between the OL and GL of rat EOMs. We found that 210 genes were differentially regulated between these layers at a twofold expression cutoff. Differences in genes related to metabolic pathways and related to structural elements of muscle and nerve formed the largest functional clusters. Layer-specific differential expression was validated at both mRNA and protein level for MYH3, MYH6, and ACTN3. The expected layer-specific differences among genes encoding vascular elements were not evident by profiling; morphometric analysis demonstrated that the differences exist, but at a magnitude below the cutoff level established by our statistical methods. Comparison of these results with previous results comparing whole EOMs and TA suggest evolutionary mechanisms may play a role in achieving functional distinctions between OL and GL.

The development of longitudinal variation of Myosin isoforms in the orbital fibers of extraocular muscles of rats.

PURPOSE: To examine the appearance of longitudinal variation of extraocular and embryonic myosin heavy chain (MyHC) isoforms during the development of orbital singly innervated fibers of rat extraocular muscles (EOMs). METHODS: EOMs were dissected from rat pups of various ages and stained with isoform-specific monoclonal antibodies to the embryonic and extraocular MyHC isoforms and to neurofilaments, as well as with labeled alpha-bungarotoxin. The orbital layers of whole muscles were examined by confocal microscopy. RNase protection assays for the embryonic (Myh3) and extraocular (Myh13) MyHC isoform mRNAs were also performed. RESULTS: At 10 days postpartum, the EOM MyHC RNA was first detected by RNase protection assay. At 11 days postpartum, the extraocular isoform was detected in the orbital fibers as two thin stripes just proximal and distal to the neuromuscular junction (NMJ). Over the next few weeks, the area occupied by the extraocular isoform increased to include the entire central region of the orbital fibers at and surrounding the NMJ. At the same time, the embryonic isoform became excluded from the region of the NMJ. CONCLUSIONS: The orbital layer fibers of rat EOMs contain a longitudinal variation in MyHC isoforms not seen in other skeletal muscles. Development of this longitudinal variation begins as a late event postpartum; and the first appearance of it may be closely linked to neural contact. This targeting of MyHC isoforms to distinct domains is unique to EOMs.

Myosin heavy chain and physiological adaptation of the rat diaphragm in elastase-induced emphysema.

BACKGROUND: Several physiological adaptations occur in the respiratory muscles in rodent models of elastase-induced emphysema. Although the contractile properties of the diaphragm are altered in a way that suggests expression of slower isoforms of myosin heavy chain (MHC), it has been difficult to demonstrate a shift in MHCs in an animal model that corresponds to the shift toward slower MHCs seen in human emphysema. METHODS: We sought to identify MHC and corresponding physiological changes in the diaphragms of rats with elastase-induced emphysema. Nine rats with emphysema and 11 control rats were studied 10 months after instillation with elastase. MHC isoform composition was determined by both reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemistry by using specific probes able to identify all known adult isoforms. Physiological adaptation was studied on diaphragm strips stimulated in vitro. RESULTS: In addition to confirming that emphysematous diaphragm has a decreased fatigability, we identified a significantly longer time-to-peak-tension (63.9 +/- 2.7 ms versus 53.9 +/- 2.4 ms). At both the RNA (RT-PCR) and protein (immunocytochemistry) levels, we found a significant decrease in the fastest, MHC isoform (IIb) in emphysema. CONCLUSION: This is the first demonstration of MHC shifts and corresponding physiological changes in the diaphragm in an animal model of emphysema. It is established that rodent emphysema, like human emphysema, does result in a physiologically significant shift toward slower diaphragmatic MHC isoforms. In the rat, this occurs at the faster end of the MHC spectrum than in humans.

Identification of the neuromuscular junction transcriptome of extraocular muscle by laser capture microdissection.

PURPOSE: To examine and characterize the profile of genes expressed at the synapses or neuromuscular junctions (NMJs) of extraocular muscles (EOMs) compared with those expressed at the tibialis anterior (TA). METHODS: Adult rat eyeballs with rectus EOMs attached and TAs were dissected, snap frozen, serially sectioned, and stained for acetylcholinesterase (AChE) to identify the NMJs. Approximately 6000 NMJs for rectus EOM (EOMsyn), 6000 NMJs for TA (TAsyn), equal amounts of NMJ-free fiber regions (EOMfib, TAfib), and underlying myonuclei and RNAs were captured by laser capture microdissection (LCM). RNA was processed for microarray-based expression profiling. Expression profiles and interaction lists were generated for genes differentially expressed at synaptic and nonsynaptic regions of EOM (EOMsyn versus EOMfib) and TA (TAsyn versus TAfib). Profiles were validated by using real-time quantitative polymerase chain reaction (qPCR). RESULTS: The regional transcriptomes associated with NMJs of EOMs and TAs were identified. Two hundred seventy-five genes were preferentially expressed in EOMsyn (compared with EOMfib), 230 in TAsyn (compared with TAfib), and 288 additional transcripts expressed in both synapses. Identified genes included novel genes as well as well-known, evolutionarily conserved synaptic markers (e.g., nicotinic acetylcholine receptor (AChR) alpha (Chrna) and epsilon (Chrne) subunits and nestin (Nes). CONCLUSIONS: Transcriptome level differences exist between EOM synaptic regions and TA synaptic regions. The definition of the synaptic transcriptome provides insight into the mechanism of formation and functioning of the unique synapses of EOM and their differential involvement in diseases noted in the EOM allotype.

Gene expression in the lamellar dermis-epidermis during the developmental phase of carbohydrate overload-induced laminitis in the horse.

OBJECTIVE: Gene expression in the lamellar dermis and epidermis was compared between healthy horses and horses in the developmental phase of carbohydrate overload-induced laminitis, in order to better understand the local biochemical and cellular events involved in the pathogenesis of laminitis. ANIMALS: Six healthy adult horses, with no history or clinical evidence of laminitis. PROCEDURES: Horses were randomly divided into two groups: control (n=3) and laminitis (n=3). Control horses received no treatment and were humanely euthanatized at the same time as the laminitis group. Horses in the laminitis group were given oligofructose (10g/kg bwt by nasogastric tube) and humanely euthanatized 24-30h later, before any clinical signs of laminitis were apparent. Sections of lamellar dermis and epidermis were harvested from the dorsal hoof wall of each horse immediately after death and cryopreserved until analysis. A bovine microarray chip, comprising approximately 15,000 genes, was used to compare gene expression between laminitis and control groups. RESULTS: A total of 155 genes were up-regulated in the laminitis group. No genes were down-regulated. Genes coding for the production of pro-inflammatory biochemical or cellular processes and those involved in protein degradation/turnover predominated. Several regulatory or anti-inflammatory genes were also up-regulated. CONCLUSIONS AND CLINICAL RELEVANCE: Generation of inflammatory mediators within the lamellar tissues occurred before the development of substantial dermal-epidermal separation, inflammatory infiltrate, or vascular changes, and before the horses began showing signs of foot pain. While further studies are needed, early and targeted anti-inflammatory therapy may halt or prevent the development of laminitis in at-risk individuals.

Combination of peptide OFFGEL fractionation and label-free quantitation facilitated proteomics profiling of extraocular muscle.

Several label-free quantitation strategies have been introduced that obliterate the need for expensive isotopically labeled molecules. However label-free approaches have considerably higher demands in respect of repeatability of sample preparation and fractionation than multiplexing isotope labeling-based strategies. OFFGEL fractionation promises the necessary separation efficiency and repeatability. To test this platform, 12-fraction peptide OFFGEL electrophoresis and online reversed-phase LC connected to a quadrupole TOF mass spectrometer were used to determine differences of the physiological, pathological and biochemical distinct extraocular muscle allotype in comparison to hind-limb muscle. Close to 70% of the peptides separated by OFFGEL electrophoresis were detected only in a single fraction. To determine the separation repeatability of four samples, we compared the ion volumes of multiple peptides deriving from the thick filament-associated protein titin over several fractions and determined a coefficient of variation below 20%. Of the 474 proteins identified, 61 proteins were differently expressed between the two muscle allotypes and were involved in metabolism, muscle contraction, stress response, or gene expression. Several expression differences were validated using immunohistochemistry and Western blot analysis. We therefore consider peptide OFFGEL fractionation an effective and efficient addition to our label-free quantitative proteomics workflow.

Quantitative proteomics profiling of sarcomere associated proteins in limb and extraocular muscle allotypes.

The sarcomere is the major structural and functional unit of striated muscle. Approximately 65 different proteins have been associated with the sarcomere, and their exact composition defines the speed, endurance, and biology of each individual muscle. Past analyses relied heavily on electrophoretic and immunohistochemical techniques, which only allow the analysis of a small fraction of proteins at a time. Here we introduce a quantitative label-free, shotgun proteomics approach to differentially quantitate sarcomeric proteins from microgram quantities of muscle tissue in a fast and reliable manner by liquid chromatography and mass spectrometry. The high sequence similarity of some sarcomeric proteins poses a problem for shotgun proteomics because of limitations in subsequent database search algorithms in the exclusive assignment of peptides to specific isoforms. Therefore multiple sequence alignments were generated to improve the identification of isoform specific peptides. This methodology was used to compare the sarcomeric proteome of the extraocular muscle allotype to limb muscle. Extraocular muscles are a unique group of highly specialized muscles with distinct biochemical, physiological, and pathological properties. We were able to quantitate 40 sarcomeric proteins; although the basic sarcomeric proteins in extraocular muscle are similar to those in limb muscle, key proteins stabilizing the connection of the Z-bands to thin filaments and the costamere are augmented in extraocular muscle and may represent an adaptation to the eccentric contractions known to normally occur during eye movements. Furthermore, a number of changes are seen that closely relate to the unique nature of extraocular muscle.

Human diaphragm remodeling associated with chronic obstructive pulmonary disease: clinical implications.

Diaphragm remodeling associated with chronic obstructive pulmonary disease (COPD) consists of a fast-to-slow fiber type transformation as well as adaptations within each fiber type. To try to explain disparate findings in the literature regarding the relationship between fiber type proportions and FEV1, we obtained costal diaphragm biopsies on 40 subjects whose FEV1 ranged from 118 to 16% of the predicted normal value. First, we noted that our exponential regression model indicated that changes in FEV1 can account for 72% of the variation in the proportion of Type I fibers. Second, to assess the impact of COPD on diaphragm force generation, we measured maximal specific force generated by single permeabilized fibers prepared from the diaphragms of two patients with normal pulmonary function tests and two patients with severe COPD. We noted that fibers prepared from the diaphragms of severe COPD patients generated a lower specific force than control fibers (p < 0.001) and Type I fibers generated a lower specific force than Type II fibers (p < 0.001). Our finding of an exponential relationship between the proportion of Type I fibers and FEV1 accounts for discrepancies in the literature. Moreover, our single-fiber results suggest that COPD-associated diaphragm remodeling decreases diaphragmatic force generation by adaptations within each fiber type as well as by fiber type transformations.