Fibre size, atrophy, and hypertrophy factors in vastus lateralis muscle from 18- to 29-year-old men

Muscle Changes During Atrophy

Muscle atrophy typically is a direct effect of protein degradation induced by a diversity of pathophysiologic states such as disuse, immobilization, denervation, aging, sepsis, cachexia, glucocorticoid treatment, hereditary muscular disorders, cancer, diabetes and obesity, kidney and heart failure, and others. Muscle atrophy is defined by changes in the muscles, consisting in shrinkage of myofibers, changes in the types of fiber and myosin isoforms, and a net loss of cytoplasm, organelles and overall a protein loss. Although in the literature there are extensive studies in a range of animal models, the paucity of human data is a reality. This chapter is focused on various aspects of muscle wasting and describes the transitions of myofiber types during the progression of muscle atrophy in several pathological states. Clinical conditions associated with muscle atrophy have been grouped based on the fast-to-slow or slow-to-fast fiber-type shifts. We have also summarized the ultrastructural and histochemical features characteristic for muscle atrophy in clinical and experimental models for aging, cancer, diabetes and obesity, and heart failure and arrhythmia.

Molecular determinants of force production in human skeletal muscle fibers: effects of myosin isoform expression and cross-sectional area

Skeletal muscle contractile performance is governed by the properties of its constituent fibers, which are, in turn, determined by the molecular interactions of the myofilament proteins. To define the molecular determinants of contractile function in humans, we measured myofilament mechanics during maximal Ca(2+)-activated and passive isometric conditions in single muscle fibers with homogenous (I and IIA) and mixed (I/IIA and IIA/X) myosin heavy chain (MHC) isoforms from healthy, young adult male (n = 5) and female (n = 7) volunteers. Fibers containing only MHC II isoforms (IIA and IIA/X) produced higher maximal Ca(2+)-activated forces over the range of cross-sectional areas (CSAs) examined than MHC I fibers, resulting in higher (24-42%) specific forces. The number and/or stiffness of the strongly bound myosin-actin cross bridges increased in the higher force-producing MHC II isoforms and, in all isoforms, better predicted force than CSA. In men and women, cross-bridge kinetics, in terms of myosin attachment time and rate of myosin force production, were independent of CSA, although women had faster (7-15%) kinetics. The relative proportion of cross bridges and/or their stiffness was reduced as fiber size increased, causing a decline in specific force. Results from our examination of molecular mechanisms across the range of physiological CSAs explain the variation in specific force among the different fiber types in human skeletal muscle, which may have relevance to understanding how various physiological and pathophysiological conditions modulate single-fiber and whole muscle contractility.

Automated image segmentation of haematoxylin and eosin stained skeletal muscle cross-sections

The ability to accurately and efficiently quantify muscle morphology is essential to determine the physiological relevance of a variety of muscle conditions including growth, atrophy and repair. There is agreement across the muscle biology community that important morphological characteristics of muscle fibres, such as cross-sectional area, are critical factors that determine the health and function (e.g. quality) of the muscle. However, at this time, quantification of muscle characteristics, especially from haematoxylin and eosin stained slides, is still a manual or semi-automatic process. This procedure is labour-intensive and time-consuming. In this paper, we have developed and validated an automatic image segmentation algorithm that is not only efficient but also accurate. Our proposed automatic segmentation algorithm for haematoxylin and eosin stained skeletal muscle cross-sections consists of two major steps: (1) A learning-based seed detection method to find the geometric centres of the muscle fibres, and (2) a colour gradient repulsive balloon snake deformable model that adopts colour gradient in Luv colour space. Automatic quantification of muscle fibre cross-sectional areas using the proposed method is accurate and efficient, providing a powerful automatic quantification tool that can increase sensitivity, objectivity and efficiency in measuring the morphometric features of the haematoxylin and eosin stained muscle cross-sections.

Myosin heavy chain composition of the human sternocleidomastoid muscle

The sternocleidomastoid (SCM) muscle is one of the neck muscles responsible for head posture and control of head movement. It functions in rotation, inclination, protraction, extension and flexion of the head, whilst chewing and in exerting increased respiratory efforts. This study is the first one describing the myosin heavy chain (MyHC) isoform composition of the SCM muscle of presumably healthy young males for the purpose of better understanding the contractile properties of the muscle as well as to help in evaluation of pathologically altered structure of the muscle. Autopsy samples were processed immunohistochemically to reveal the MyHC isoform composition. The muscle fibres expressed MyHC-1 (31.5%), -2a (29.7%) and -2x (4.3%) or co-expressed MyHC-2a with MyHC-2x (26.8%), MyHC-1 with MyHC-2a (4.1%) and/or MyHC-1, -2a with -2x (1.1%). In addition to the MyHC isoforms, characteristic of adult limb muscles, a very low percentage of muscle fibres (0.2-2.7%) expressed MyHC-neo, which is normally not found in adult limb muscles. Only two samples exhibited MyHC-neo at a rather higher percentage (6.3% and 7.5%) of muscle fibres. The high share of hybrid fibres and the presence of MyHC-neo in the SCM muscle differ from that of adult limb muscles where hybrid fibres are rare and the expression of immature MyHC isoforms occurs only in pathological or experimental conditions. Since the SCM muscle shares the same embryogenic potential as limb muscles, its distinct MyHC expression appears to be associated with twin innervation and with the intrinsic specialisation to perform multiple functions.

Characterization of fiber types in different muscles of the hindlimb in female weanling and adult Wistar rats

We analyzed lesser diameter and distribution of fiber types in different skeletal muscles from female Wistar rats using a histoenzymology Myofibrillar Adenosine Tri-phosphatase (mATPase) method. Fragments from muscles were frozen and processed by mATPase in different pH. Adult and weanling rat soleus muscles presented a predominance of type I fibers and larger fiber diameters. In the plantar muscle in adult rats, the type IIB fibers demonstrated greater lesser diameter while in the weanling animals, types I and IIB fibers were larger. The plantar muscle of animals of both ages was composed predominantly of the type IID fibers. The type IID fibers were observed in similar amounts in the lateral gastrocnemius and the medial gastrocnemius muscles. Type IIB fibers showed predominance and presented higher size in comparison with other types in the EDL muscle. The present study shows that data on fiber type distribution and fiber lesser diameter obtained in adult animals cannot always be applied to weanling animals of the same species. Using the mATPase, despite the difficult handling, is an important tool to determine the different characteristics of the specific fibers in the skeletal muscle tissue.

Software for muscle fibre type classification and analysis

Fibre type determination requires a large series of differently stained muscle sections. The manual identification of individual fibres through the series is tedious and time consuming. This paper presents a software that enables (i) adjusting the position of individual fibres through a series of differently stained sections (image registration) and identification of individual fibres through the series as well as (ii) muscle fibre classification and (iii) quantitative analysis. The data output of the system is the following: numerical and areal proportions of fibre types, fibre type size and optical density (grey level) of the final reaction product in every fibre. The muscle fibre type can be determined stepwise, based on one set of stained sections while further, newly stained sections can be added to the already defined muscle fibre profile. Several advantages of the presented software application in skeletal muscle research are presented. The system is semiquantitative, flexible, and user friendly.

Fibre type related changes in the metabolic profile and fibre diameter of human vastus medialis muscle after anterior cruciate ligament rupture

Vastus medialis muscles of patients with chronic anterior instability of the knee after anterior cruciate ligament rupture were analysed to investigate changes in defined muscle fibres of the diseased leg in comparison to the healthy leg of the same patient. Metabolic and morphological parameters were obtained by cytophotometrical measurements of the activities of succinate dehydrogenase (a marker of oxidative metabolism) and glycerol-3-phosphate dehydrogenase (a marker of glycolytic metabolism) of slow-oxidative (SO), fast-oxidative glycolytic (FOG) and fast-glycolytic (FG) fibre types in serial sections and by measuring the minimal fibre diameters of type I (slow) and type II (fast) fibres. We found decreased glycolytic activity and a shift to more oxidative metabolism in each fibre type suggesting diminished fast force and shift to endurance force development. The latter was interpreted as a sign of active compensation for the knee instability. Significantly decreased minimal fibre diameters to 85.9% in type I fibres, and to 88.7% in type II fibres of the diseased muscle were measured, indicating the fibre atrophy. Our findings suggest that the atrophied muscle fibres of the affected vastus medialis muscle adapt to the altered conditions by changing their metabolic profile. Muscle fibres of different types were found to be affected similarly.

The effects of aging on biceps brachii muscle fibers: a morphometrical study from biopsies and autopsies

OBJECTIVES: In order to study the morphology and size of muscle fibers, cross sections of biceps brachii samples from autopsies, up to 9 hours after death, and biopsies of 72 subjects were compared. The subjects aged 13 to 84 years in both sexes. METHODS: The samples obtained from autopsies (n=47) were from subjects with sudden death, or who died after acute disease without evidence of neuromuscular involvement. The biopsies (n=25) were from patients with symptoms suggestive of inflammatory or metabolic myopathy, not confirmed morphologically. The lesser diameter of muscle fibers was measured using the ATPase reaction. RESULTS: Morphological analysis showed that aging changes were present from the sixth decade in autopsies, and consisted of atrophy and/or type-grouping. The statistical models adjusted for females in both autopsies and biopsies were linear straight with no variation in fiber size with increasing age. The models adjusted for males in both groups were quadratic, indicating that age influenced the size of different type fibers. In males type 2 were larger than type 1 fibers, and than fibers in females. CONCLUSIONS: These values might be useful as controls, helping interpretation of changes in fiber size in samples obtained from biopsies and autopsies.

Quadriceps muscle wasting persists 5 months after total hip arthroplasty for osteoarthritis of the hip: a pilot study

AIMS

To determine whether additional muscle fibre wasting of the ipsilateral vastus lateralis muscle occurs in the early postoperative period after total hip arthroplasty for osteoarthritis of the hip and whether there is an improvement in preoperative measures of quadriceps muscle thickness, strength, pain and function over a 5-month postoperative period.

METHODS

Twelve patients had ipsilateral needle quadriceps biopsy for muscle morphology and bilateral quadriceps muscle thickness ultrasound preoperatively, 5 days and 4 weeks postoperatively and a further muscle thickness measurement at 5 months. Seven additional patients and five age-matched control subjects had bilateral quadriceps muscle ultrasound thickness preoperatively, 6 weeks and 5 months postoperatively, with assessment of quadriceps muscle dynamometry, pain scores and Timed Up and Go (TUG) test.

RESULTS

Preoperatively, all 19 patients demonstrated significant atrophy of the ipsilateral compared with the contralateral quadriceps muscle (P = 1.8 x 10(-7)) on muscle ultrasound, which persisted at 5 months follow up (P = 0.009). Muscle morphology preoperatively showed type 2A and 2B muscle fibre atrophy on needle muscle biopsy, with further atrophy of all three fibre types (P = 0.029) at 5 days postoperatively associated with a fibre type shift from type 1 to 2A fibres (P = 0.0011) at 1 month. There was improvement in hip pain postoperatively and a significant improvement in the TUG test (P = 0.007). However, there was no improvement in muscle strength on dynamometry.

CONCLUSIONS

There is significant ipsilateral quadriceps atrophy and weakness with 2A and 2B fibre atrophy preoperatively in patients with osteoarthritis of the hip with exacerbation and further atrophy of all three fibre types 5 days postoperatively. Postoperative follow up showed that the reduction in ipsilateral quadriceps muscle thickness persisted at 5 months despite physical rehabilitation. Patients did note significant improvement in pain postoperatively and improvement on functional assessment with the TUG test. Other therapeutic strategies may have to be developed to reverse disuse muscle atrophy.

Effects on skeletal muscle fibres of diabetes and Ginkgo biloba extract treatment

Combined cytophotometric and morphometric analysis of muscle fibre properties and myosin heavy chain electrophoresis were performed on extensor digitorum longus and soleus muscles from healthy rats and rats with streptozotocin-induced diabetes. Moreover, the protective effect of Ginkgo biloba extract, a potent oxygen radical scavenger, on diabetic muscles was investigated. Changes in fibre type-related enzyme activities, fibre type distribution, fibre cross areas and myosin isoforms were found. In muscles of diabetic rats, a metabolic shift was measured mainly in fibres with oxidative metabolism. Fast-oxidative glycolytic fibres showed a shift to more glycolytic metabolism and about a third transformed into fast-glycolytic fibres. Slow-oxidative fibres became more oxidative. Fibre atrophy was measured in diabetic muscles dependent on fibre type and muscle. Different fibre types atrophied to a different degree. Therefore, a decreased area percentage of slow fibres and an increased area percentage of fast fibres of the whole muscle cross section in both muscles were found. This is supported by reduced slow and increased fast myosin heavy chain isoforms. These alterations of diabetic muscle fibres could be due to less motion of diabetic rats and diabetic neuropathy. After treatment with Ginkgo biloba extract, enzyme activities were increased mainly in oxidative fibres of diabetic muscles, which was interpreted as protective effect. Generally, the soleus muscle with predominant oxidative metabolism was more vulnerable to diabetic alterations and Ginkgo biloba extract treatment than the extensor digitorum longus muscle with predominant glycolytic metabolism.