Abnormal accumulation of desmin in gastrocnemius myofibers of patients with peripheral artery disease: associations with altered myofiber morphology and density, mitochondrial dysfunction and impaired limb function

Neurotrophic factor BDNF is upregulated in soft palate muscles of snorers and sleep apnea patients

Objectives

Neuromuscular injuries are suggested to contribute to upper airway collapse and swallowing dysfunction in patients with sleep apnea. Neurotrophins, a family of proteins involved in survival, development, and function of neurons, are reported to be upregulated in limb muscle fibers in response to overload and nerve damage. We aimed to investigate the expression of two important neurotrophins, brain‐derived neurotrophic factor (BDNF) and nerve growth factor (NGF), in muscle fibers of uvula from snorers and sleep apnea patients and to compare these findings with pharyngeal function.

Methods

Uvula muscle biopsies from 22 patients and 10 controls were analyzed for BDNF, NGF, and cytoskeletal protein desmin using immunohistochemistry. Pharyngeal swallowing function was assessed using videoradiography.

Results

BDNF, but not NGF, was significantly upregulated in a subpopulation of muscle fibers in snoring and sleep apnea patients. Two major immunoreaction patterns for BDNF were observed; a fine grainy point like BDNF staining was displayed in muscle fibers of both patients and controls (41 ± 23 vs. 25 ± 17%, respectively, P = .06), while an abnormal upregulated intense‐dotted or disorganized reaction was mainly observed in patients (8 ± 8 vs. 2 ± 2%, P = .02). The latter fibers, which often displayed an abnormal immunoreaction for desmin, were more frequent in patients with than without swallowing dysfunction (10 ± 8 vs. 3 ± 3%, P = .05).

Conclusion

BDNF is upregulated in the upper airway muscles of snorers and sleep apnea patients, and especially in patients with swallowing dysfunction. Upregulation of BDNF is suggested to be a response to denervation, reinnervation, and repair of injured muscle fibers. Our findings propose that damaged upper airway muscles might heal following treatment for snoring and sleep apnea.

Level of Evidence

NA

Damaged muscle fibers might masquerade as hybrid fibers - a cautionary note on immunophenotyping mouse muscle with mouse monoclonal antibodies

We report that, labeling mouse muscle tissue, with mouse monoclonal antibodies specific to slow or fast myosin heavy chain (sMyHC and fMyHC, respectively), can lead to artefactual labeling of damaged muscle fibers, as hybrid fibers (sMyHC+ and fMyHC+). We demonstrate that, such erroneous immunophenotyping of muscle may be avoided, by performing colabeling or serialsection- labeling, to identify damaged fibers. The quadriceps femorismuscle group (QF) in 7-month-old, male, C57BL/6J mice had: 1.21±0.21%, 98.34±1.06%, 0.07±0.01%, and 0.53±0.85% fibers, that were, sMyHC+, fMyHC+, hybrid, and damaged, respectively. All fibers in the tibialis anterior muscle (TA) of 3-month-old, male, C57BL/6J mice were fMyHC+; and at 3 days after injurious eccentric contractions, there was no fiber-type shift, but ~ 18% fibers were damaged.

Mitochondrial complex I defect resulting from exercise-induced lower limb ischemia in patients with peripheral arterial disease

This study aims to compare the structural and mitochondrial alterations between muscle segments affected by exercise-induced ischemia and segments of the same muscle without ischemia, in the same subject. In a prospective analysis, 34 patients presenting either peripheral arterial disease or chronic coronary syndrome without any evidence of peripheral arterial disease were eligible for inclusion based on findings indicating a need for either a femoro-popliteal bypass or a saphenous harvesting for coronary bypass. Before surgery, we assessed the level of exercise-induced ischemia in proximal and distal sections of the thigh by the measurement of transcutaneous oxygen pressure during an exercise treadmill test. Distal and proximal biopsies of the sartorius muscle were procured during vascular surgical procedures to assess mitochondrial function and morphometric parameters of the sartorius myofibers. Comparisons were made between the distal and proximal biopsies, with respect to these parameters. Thirteen of the study patients that initially presented with peripheral arterial disease had evidence of an isolated distal thigh exercise-induced ischemia, associated with a 35% decrease in the mitochondrial complex I enzymatic activity in the distal muscle biopsy. This defect was also associated with a decreased expression of the manganese superoxide dismutase enzyme and with alterations of the shapes of the myofibers. No functional or structural alterations were observed in the patients with coronary syndrome. We validated a specific model ischemia in peripheral arterial disease characterized by muscular alterations. This "Distal-Proximal-Sartorius Model" would be promising to explore the physiopathological consequences specific to chronic ischemia. NEW & NOTEWORTHY We compared proximal versus distal biopsies of the sartorius muscle in patients with superficial femoral artery stenosis or occlusion and proof of, distal only, regional blood flow impairment with exercise oximetry. We identified a decrease in the mitochondrial complex I enzymatic activity and antioxidant system impairment at the distal level only. We validate a model to explore the physiopathological consequences of chronic muscle ischemia.

Rapid growth rate results in remarkably hardened breast in broilers during the middle stage of rearing: A biochemical and histopathological study

The high incidence of meat of impaired quality poses a serious problem in the poultry industry. In recent years, the incidence of the pectoralis major muscle that appeared pale colored, remarkably hardened, and exudative, called "wooden breast" or "woody breast" has increased in slaughter houses. In the present study, 19-day-old Ross 308 broiler chickens affected (n = 10) and unaffected (n = 10) with remarkably hardened breast were selected from a commercial broiler farm, and reared to 55 days of age under a controlled environment. Among the affected birds, 5 of 10 birds appeared exhausted with markedly suppressed weight gain and 4 of 10 birds died during the rearing period. In contrast, all unaffected birds survived and most gained weight. Four of 10 unaffected birds lost the ability of back-to-back wing contact by the late stage of rearing. The biochemical analysis of blood plasma samples of 20-day-old birds revealed that creatine kinase and L-aspartate aminotransferase values in most affected birds were higher than those in unaffected birds; however, these values in unaffected birds increased rapidly with lost wing contactability and increasing age. Postmortem examinations revealed that the mean diameter of myofibers in affected birds was smaller than that in unaffected birds. Moreover, symptoms of degenerative and regenerative muscles were observed in most birds in both groups. Among them, a decrease in, or defect of, the characteristic polygonal shape of myofibers was the most common change within the pectoralis major muscles in both groups. The present study demonstrated that broilers affected with remarkably hardened breast during the middle stage of rearing would have suppressed physical status and weight gain, or would die. It was suggested that rapid growth in broilers might be a cause of remarkably hardened breast.

Cell therapy for peripheral artery disease

Patients with severe peripheral artery disease (PAD) who are not candidates for revascularization have poor prognosis. Cell therapy using peripheral blood-derived or bone marrow-derived mononuclear cells, mesenchymal stem cells, or marker-specific subsets of bone marrow cells with angiogenic properties may hold promise for no-option PAD patients. Injected cells may exert beneficial actions by enhancing local angiogenesis (either through maturation of endothelial progenitors, or through secretion of angiogenic mediators), or by transducing cytoprotective signals that preserve tissue structure. Despite extensive research, robust clinical evidence supporting the use of cell therapy in patients with critical limb ischemia is lacking. Larger, well-designed placebo-controlled clinical trials did not support the positive results of smaller less rigorous studies. There is a need for high-quality clinical studies to test the effectiveness of cell therapy in PAD patients. Moreover, fundamental cell biological studies are needed to identify the optimal cell types, and to develop strategies that may enhance homing, survival and effectiveness of the injected cells.

Iron limitation promotes the atrophy of skeletal myocytes, whereas iron supplementation prevents this process in the hypoxic conditions

There is clinical evidence that patients with heart failure and concomitant iron deficiency have increased skeletal muscle fatigability and impaired exercise tolerance. It was expected that a skeletal muscle cell line subjected to different degrees of iron availability and/or concomitant hypoxia would demonstrate changes in cell morphology and in the expression of atrophy markers. L6G8C5 rat skeletal myocytes were cultured in normoxia or hypoxia at optimal, reduced or increased iron concentrations. Experiments were performed to evaluate the iron content in cells, cell morphology, and the expression of muscle specific atrophy markers [Atrogin1 and muscle-specific RING-finger 1 (MuRF1)], a gene associated with the atrophy/hypertrophy balance [mothers against decapentaplegic homolog 4 (SMAD4)] and a muscle class-III intermediate filament protein (Desmin) at the mRNA and protein level. Hypoxic treatment caused, as compared to normoxic conditions, an increase in the expression of Atrogin-1 (P<0.001). Iron-deficient cells exhibited morphological abnormalities and demonstrated a significant increase in the expression of Atrogin-1 (P<0.05) and MuRF1 (P<0.05) both in normoxia and hypoxia, which indicated activation of the ubiquitin proteasome pathway associated with protein degradation during muscle atrophy. Depleted iron in cell culture combined with hypoxia also induced a decrease in SMAD4 expression (P<0.001) suggesting modifications leading to atrophy. In contrast, cells cultured in a medium enriched with iron during hypoxia exhibited inverse changes in the expression of atrophy markers (both P<0.05). Desmin was upregulated in cells subjected to both iron depletion and iron excess in normoxia and hypoxia (all P<0.05), but the greatest augmentation of mRNA expression occurred when iron depletion was combined with hypoxia. Notably, in hypoxia, an increased expression of Atrogin-1 and MuRF1 was associated with an increased expression of transferrin receptor 1, reflecting intracellular iron demand (R=0.76, P<0.01; R=0.86, P<0.01). Hypoxia and iron deficiency when combined exhibited the most detrimental impact on skeletal myocytes, especially in the context of muscle atrophy markers. Conversely, iron supplementation in in vitro conditions acted in a protective manner on these cells.

Optical probing of gastrocnemius in patients with peripheral artery disease characterizes myopathic biochemical alterations and correlates with stage of disease

Peripheral artery disease (PAD) is a condition caused by atherosclerotic blockages in the arteries supplying the lower limbs and is characterized by ischemia of the leg, progressive myopathy, and increased risk of limb loss. The affected leg muscles undergo significant changes of their biochemistry and metabolism including variations in the levels of many key proteins, lipids, and nucleotides. The mechanisms behind these changes are poorly understood. The objective of this study was to correlate the severity of the PAD disease stage and associated hemodynamic limitation (determined by the ankle brachial index, ABI) in the legs of the patients with alterations in the biochemistry of chronically ischemic leg muscle as determined by ATR‐Fourier transform infrared micro‐spectroscopy. Muscle (gastrocnemius) biopsies were collected from 13 subjects including four control patients (ABI≥0.9), five claudicating patients (0.4 ≤ ABI<0.9), and four critical limb ischemia (CLI) patients (ABI<0.4). Slide mounted specimens were analyzed by ATR‐Fourier transform infrared micro‐spectroscopy. An analysis of variance and a partial least squares regression model were used to identify significant differences in spectral peaks and correlate them with the ABI. The spectra revealed significant differences (P < 0.05) across control, claudicating, and CLI patients in the fingerprint and functional group regions. Infrared microspectroscopic probing of ischemic muscle biopsies demonstrates that PAD produces significant and unique changes to muscle biochemistry in comparison to control specimens. These distinctive biochemical profiles correlate with disease progression and may provide insight and direction for new targets in the diagnosis and therapy of muscle degeneration in PAD.

A systematic review of muscle morphology and function in intermittent claudication

OBJECTIVE

Intermittent claudication (IC) is frequently associated with deterioration in walking capacity and physical function, and it can often result in an impairment in balance. Whereas supervised exercise is recommended by the National Institute for Health and Care Excellence as the first-line treatment, the mechanism behind walking improvement is poorly understood. The existing literature suggests that there may be some physiologic change to the skeletal muscle contributing to the functional impairment, but these data are conflicting. We therefore sought to undertake a systematic review to clarify the muscle properties of patients with IC.

METHODS

A systematic review of randomized and nonrandomized trials that investigated the role of muscle function in patients diagnosed with IC was undertaken using MEDLINE, Cochrane Central Register of Controlled Trials, and Embase databases. The searches were limited from 1947 to June 2016 in the English language.

RESULTS

The search yielded a total of 506 articles, of which 206 were duplicate articles. Of the remaining 300, a total of 201 were excluded from full-text analysis; 99 full-text articles were assessed for eligibility, with 30 articles deemed appropriate for inclusion in the review. There were four main categories of functional outcome measures: muscle strength, muscle size, muscle fiber type, and muscle metabolism. A total of 2837 patients were included in the study. Nine studies reported on muscle strength, incorporating isometric, concentric, eccentric, and endurance measures. Eight studies reported on muscle size, incorporating circumference, computed tomography scans, and ultrasound imaging techniques. Eleven studies reported on muscle fibers, incorporating fiber type proportions, fiber size, and capillarity measures. Seven papers reported on muscle metabolism, incorporating adenosine diphosphate recovery and phosphocreatine recovery measures.

CONCLUSIONS

Previous literature has found clear evidence that strength (of the calf and thigh musculature) and calf characteristics are related to mortality and functional declines. However, this review has demonstrated the vast array of muscle groups assessed and multiple methods employed to determine strength; therefore, it is unclear exactly what measure of "strength" is impaired. Furthermore, the underlying morphologic causes of potential changes in strength are unclear. This information is essential for designing optimal exercise interventions. The data acquired during this systematic review are heterogeneous, with a substantial lack of high-quality intervention-based studies. Future research should endeavor to establish standardized testing procedures and to implement randomized controlled trials for targeted therapeutic interventions.

Muscle strength and control characteristics are altered by peripheral artery disease

OBJECTIVE

Peripheral artery disease (PAD), a common manifestation of atherosclerosis, is characterized by lower leg ischemia and myopathy in association with leg dysfunction. Patients with PAD have impaired gait from the first step they take with consistent defects in the movement around the ankle joint, especially in plantar flexion. Our goal was to develop muscle strength profiles to better understand the problems in motor control responsible for the walking impairment in patients with PAD.

METHODS

Ninety-four claudicating PAD patients performed maximal isometric plantar flexion contractions lasting 10 seconds in two conditions: pain free (patient is well rested and has no claudication symptoms) and pain induced (patient has walked and has claudication symptoms). Sixteen matched healthy controls performed the pain-free condition only. Torque curves were analyzed for dependent variables of muscle strength and motor control. Independent t-tests were used to compare variables between groups, and dependent t-tests determined differences between conditions.

RESULTS

Patients with PAD had significantly reduced peak torque and area under the curve compared with controls. Measures of control differed between PAD conditions only. Load rate and linear region duration were greater in the pain condition. Time to peak torque was shorter in the pain condition.

CONCLUSIONS

This study conclusively demonstrates that the plantar flexor muscles of the PAD patient at baseline and without pain are weaker in patients with PAD compared with controls. With the onset of claudication pain, patients with PAD exhibit altered muscle control strategies and further strength deficits are manifest compared to baseline levels. The myopathy of PAD legs appears to have a central role in the functional deterioration of the calf muscles, as it is evident both before and after onset of ischemic pain.

Crossroads between peripheral atherosclerosis, western-type diet and skeletal muscle pathophysiology: emphasis on apolipoprotein E deficiency and peripheral arterial disease

Atherosclerosis is a chronic inflammatory process that, in the presence of hyperlipidaemia, promotes the formation of atheromatous plaques in large vessels of the cardiovascular system. It also affects peripheral arteries with major implications for a number of other non-vascular tissues such as the skeletal muscle, the liver and the kidney. The aim of this review is to critically discuss and assimilate current knowledge on the impact of peripheral atherosclerosis and its implications on skeletal muscle homeostasis. Accumulating data suggests that manifestations of peripheral atherosclerosis in skeletal muscle originates in a combination of increased i)-oxidative stress, ii)-inflammation, iii)-mitochondrial deficits, iv)-altered myofibre morphology and fibrosis, v)-chronic ischemia followed by impaired oxygen supply, vi)-reduced capillary density, vii)- proteolysis and viii)-apoptosis. These structural, biochemical and pathophysiological alterations impact on skeletal muscle metabolic and physiologic homeostasis and its capacity to generate force, which further affects the individual's quality of life. Particular emphasis is given on two major areas representing basic and applied science respectively: a)-the abundant evidence from a well-recognised atherogenic model; the Apolipoprotein E deficient mouse and the role of a western-type diet and b)-on skeletal myopathy and oxidative stress-induced myofibre damage from human studies on peripheral arterial disease. A significant source of reactive oxygen species production and oxidative stress in cardiovascular disease is the family of NADPH oxidases that contribute to several pathologies. Finally, strategies targeting NADPH oxidases in skeletal muscle in an attempt to attenuate cellular oxidative stress are highlighted, providing a better understanding of the crossroads between peripheral atherosclerosis and skeletal muscle pathophysiology.

Mitochondrial Bioenergetics in the Metabolic Myopathy Accompanying Peripheral Artery Disease

Peripheral artery disease (PAD) is a serious but relatively underdiagnosed and undertreated clinical condition associated with a marked reduction in functional capacity and a heightened risk of morbidity and mortality. The pathophysiology of lower extremity PAD is complex, and extends beyond the atherosclerotic arterial occlusion and subsequent mismatch between oxygen demand and delivery to skeletal muscle mitochondria. In this review, we evaluate and summarize the available evidence implicating mitochondria in the metabolic myopathy that accompanies PAD. Following a short discussion of the available in vivo and in vitro methodologies to quantitate indices of muscle mitochondrial function, we review the current evidence implicating skeletal muscle mitochondrial dysfunction in the pathophysiology of PAD myopathy, while attempting to highlight questions that remain unanswered. Given the rising prevalence of PAD, the detriment in quality of life for patients, and the associated significant healthcare resource utilization, new alternate therapies that ameliorate lower limb symptoms and the functional impairment associated with PAD are needed. A clear understanding of the role of mitochondria in the pathophysiology of PAD may contribute to the development of novel therapeutic interventions.

Disruption of mitochondrial quality control in peripheral artery disease: New therapeutic opportunities

Peripheral artery disease (PAD) is a multifactorial disease initially triggered by reduced blood supply to the lower extremities due to atherosclerotic obstructions. It is considered a major public health problem worldwide, affecting over 200 million people. Management of PAD includes smoking cessation, exercise, statin therapy, antiplatelet therapy, antihypertensive therapy and surgical intervention. Although these pharmacological and non-pharmacological interventions usually increases blood flow to the ischemic limb, morbidity and mortality associated with PAD continue to increase. This scenario raises new fundamental questions regarding the contribution of intrinsic metabolic changes in the distal affected skeletal muscle to the progression of PAD. Recent evidence suggests that disruption of skeletal muscle mitochondrial quality control triggered by intermittent ischemia-reperfusion injury is associated with increased morbidity in individuals with PAD. The mitochondrial quality control machinery relies on surveillance systems that help maintaining mitochondrial homeostasis upon stress. In this review, we describe some of the most critical mechanisms responsible for the impaired skeletal muscle mitochondrial quality control in PAD. We also discuss recent findings on the central role of mitochondrial bioenergetics and quality control mechanisms including mitochondrial fusion-fission balance, turnover, oxidative stress and aldehyde metabolism in the pathophysiology of PAD, and highlight their potential as therapeutic targets.

Walking performance is positively correlated to calf muscle fiber size in peripheral artery disease subjects, but fibers show aberrant mitophagy: an observational study

BACKGROUND

Patients with lower extremity peripheral artery disease (PAD) have decreased mobility, which is not fully explained by impaired blood supply to the lower limb. Additionally, reports are conflicted regarding fiber type distribution patterns in PAD, but agree that skeletal muscle mitochondrial respiration is impaired.

METHODS

To test the hypothesis that reduced muscle fiber oxidative activity and type I distribution are negatively associated with walking performance in PAD, calf muscle biopsies from non-PAD (n = 7) and PAD participants (n = 26) were analyzed immunohistochemically for fiber type and size, oxidative activity, markers of autophagy, and capillary density. Data were analyzed using analysis of covariance.

RESULTS

There was a wide range in fiber type distribution among subjects with PAD (9-81 % type I fibers) that did not correlate with walking performance. However, mean type I fiber size correlated with 4-min normal- and fastest-paced walk velocity (r = 0.4940, P = 0.010 and r = 0.4944, P = 0.010, respectively). Although intensity of succinate dehydrogenase activity staining was consistent with fiber type, up to 17 % of oxidative fibers were devoid of mitochondria in their cores, and the core showed accumulation of the autophagic marker, LC3, which did not completely co-localize with LAMP2, a lysosome marker.

CONCLUSIONS

Calf muscle type I fiber size positively correlates with walking performance in PAD. Accumulation of LC3 and a lack of co-localization of LC3 with LAMP2 in the area depleted of mitochondria in PAD fibers suggests impaired clearance of damaged mitochondria, which may contribute to reduced muscle oxidative capacity. Further study is needed to determine whether defective mitophagy is associated with decline in function over time, and whether interventions aimed at preserving mitochondrial function and improving autophagy can improve walking performance in PAD.

Transforming growth factor-beta 1 produced by vascular smooth muscle cells predicts fibrosis in the gastrocnemius of patients with peripheral artery disease

Background

Lower leg ischemia, myopathy, and limb dysfunction are distinguishing features of peripheral artery disease (PAD). The myopathy of PAD is characterized by myofiber degeneration in association with extracellular matrix expansion, and increased expression of transforming growth factor-beta 1 (TGF-β1; a pro-fibrotic cytokine). In this study, we evaluated cellular expression of TGF-β1 in gastrocnemius of control (CTRL) and PAD patients and its relationship to deposited collagen, fibroblast accumulation and limb hemodynamics.

Methods

Gastrocnemius biopsies were collected from PAD patients with claudication (PAD-II; N = 25) and tissue loss (PAD-IV; N = 20) and from CTRL patients (N = 20). TGF-β1 in slide-mounted specimens was labeled with fluorescent antibodies and analyzed by quantitative wide-field, fluorescence microscopy. We evaluated co-localization of TGF-β1 with vascular smooth muscle cells (SMC) (high molecular weight caldesmon), fibroblasts (TE-7 antigen), macrophages (CD163), T cells (CD3) and endothelial cells (CD31). Collagen was stained with Masson Trichrome and collagen density was determined by quantitative bright-field microscopy with multi-spectral imaging.

Results

Collagen density increased from CTRL to PAD-II to PAD-IV specimens (all differences p < 0.05) and was prominent around microvessels. TGF-β1 expression increased with advancing disease (all differences p < 0.05), correlated with collagen density across all specimens (r = 0.864; p < 0.001), associated with fibroblast accumulation, and was observed exclusively in SMC. TGF-β1 expression inversely correlated with ankle-brachial index across PAD patients (r = −0.698; p < 0.001).

Conclusions

Our findings support a progressive fibrosis in the gastrocnemius of PAD patients that is caused by elevated TGF-β1 production in the SMC of microvessels in response to tissue hypoxia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0790-3) contains supplementary material, which is available to authorized users.

Abnormal myofiber morphology and limb dysfunction in claudication

BACKGROUND

Peripheral artery disease (PAD), which affects an estimated 27 million people in Europe and North America, is caused by atherosclerotic plaques that limit blood flow to the legs. Chronic, repeated ischemia in the lower leg muscles of PAD patients is associated with loss of normal myofiber morphology and myofiber degradation. In this study, we tested the hypothesis that myofiber morphometrics of PAD calf muscle are significantly different from normal calf muscle and correlate with reduced calf muscle strength and walking performance.

METHODS

Gastrocnemius biopsies were collected from 154 PAD patients (Fontaine stage II) and 85 control subjects. Morphometric parameters of gastrocnemius fibers were determined and evaluated for associations with walking distances and calf muscle strength.

RESULTS

Compared with control myofibers, PAD myofiber cross-sectional area, major and minor axes, equivalent diameter, perimeter, solidity, and density were significantly decreased (P < 0.005), whereas roundness was significantly increased (P < 0.005). Myofiber morphometric parameters correlated with walking distances and calf muscle strength. Multiple regression analyses demonstrated myofiber cross-sectional area, roundness, and solidity as the best predictors of calf muscle strength and 6-min walking distance, whereas cross-sectional area was the main predictor of maximum walking distance.

CONCLUSIONS

Myofiber morphometrics of PAD gastrocnemius differ significantly from those of control muscle and predict calf muscle strength and walking distances of the PAD patients. Morphometric parameters of gastrocnemius myofibers may serve as objective criteria for diagnosis, staging, and treatment of PAD.