Effects of electrically induced contractile activity on cultured embryonic chick breast muscle cells

Promoting endogenous repair of skeletal muscle using regenerative biomaterials

Skeletal muscles normally have a remarkable ability to repair themselves; however, large muscle injuries and several myopathies diminish this ability leading to permanent loss of function. No clinical therapy yet exists that reliably restores muscle integrity and function following severe injury. Consequently, numerous tissue engineering techniques, both acellular and with cells, are being investigated to enhance muscle regeneration. Biomaterials are an essential part of these techniques as they can present physical and biochemical signals that augment the repair process. Successful tissue engineering strategies require regenerative biomaterials that either actively promote endogenous muscle repair or create an environment supportive of regeneration. This review will discuss several acellular biomaterial strategies for skeletal muscle regeneration with a focus on those under investigation in vivo. This includes materials that release bioactive molecules, biomimetic materials and immunomodulatory materials.

Oxygen consumption in human, tissue-engineered myobundles during basal and electrical stimulation conditions

During three-dimensional culture of skeletal muscle in vitro, electrical stimulation provides an important cue to enhance skeletal muscle mimicry of the in vivo structure and function. However, increased respiration can cause oxygen transport limitations in these avascular three-dimensional constructs, leading to a hypoxic, necrotic core, or nonuniform cell distributions in larger constructs. To enhance oxygen transport with convection, oxygen concentrations were measured using an optical sensor at the inlet and outlet of an 80 μl fluid volume microphysiological system (MPS) flow chamber containing three-dimensional human skeletal muscle myobundles. Finite element model simulations of convection around myobundles and oxygen metabolism by the myobundles in the 80 μl MPS flow chamber agreed well with the oxygen consumption rate (OCR) at different flow rates, suggesting that under basal conditions, mass transfer limitations were negligible for flow rates above 1.5 μl s^-1. To accommodate electrodes for electrical stimulation, a modified 450 μl chamber was constructed. Electrical stimulation for 30 min increased the measured rate of oxygen consumption by the myobundles to slightly over 2 times the basal OCR. Model simulations indicate that mass transfer limitations were significant during electrical stimulation and, in the absence of mass transfer limitations, electrical stimulation induced about a 20-fold increase in the maximum rate of oxygen consumption. The results indicate that simulated exercise conditions increase respiration of skeletal muscle and mass transfer limitations reduce the measured levels of oxygen uptake, which may affect previous studies that model exercise with engineered muscle.

Electrical pulse stimulation of cultured skeletal muscle cells as a model for in vitro exercise - possibilities and limitations

The beneficial health-related effects of exercise are well recognized, and numerous studies have investigated underlying mechanism using various in vivo and in vitro models. Although electrical pulse stimulation (EPS) for the induction of muscle contraction has been used for quite some time, its application on cultured skeletal muscle cells of animal or human origin as a model of in vitro exercise is a more recent development. In this review, we compare in vivo exercise and in vitro EPS with regard to effects on signalling, expression level and metabolism. We provide a comprehensive overview of different EPS protocols and their applications, discuss technical aspects of this model including critical controls and the importance of a proper maintenance procedure and finally discuss the limitations of the EPS model.

Optimisation of conductive polymer biomaterials for cardiac progenitor cells

The characterisation of biomaterials for cardiac tissue engineering applications is vital for the development of effective treatments for the repair of cardiac function.

Regeneration and repair of human digits and limbs: fact and fiction

A variety of digit and limb repair and reconstruction methods have been used in different clinical settings, but regeneration remains an item on every plastic surgeon's "wish list." Although surgical salvage techniques are continually being improved, unreplantable digits and limbs are still abundant. We comprehensively review the structural and functional salvage methods in clinical practice, from the peeling injuries of small distal fingertips to multisegmented amputated limbs, and the developmental and tissue engineering approaches for regenerating human digits and limbs in the laboratory. Although surgical techniques have forged ahead, there are still situations in which digits and limbs are unreplantable. Advances in the field are delineated, and the regeneration processes of salamander limbs, lizard tails, and mouse digits and each component of tissue engineering approaches for digit- and limb-building are discussed. Although the current technology is promising, there are many challenges in human digit and limb regeneration. We hope this review inspires research on the critical gap between clinical and basic science, and leads to more sophisticated digit and limb loss rescue and regeneration innovations.

Biomaterials based strategies for skeletal muscle tissue engineering: existing technologies and future trends

Skeletal muscles have a robust capacity to regenerate, but under compromised conditions, such as severe trauma, the loss of muscle functionality is inevitable. Research carried out in the field of skeletal muscle tissue engineering has elucidated multiple intrinsic mechanisms of skeletal muscle repair, and has thus sought to identify various types of cells and bioactive factors which play an important role during regeneration. In order to maximize the potential therapeutic effects of cells and growth factors, several biomaterial based strategies have been developed and successfully implemented in animal muscle injury models. A suitable biomaterial can be utilized as a template to guide tissue reorganization, as a matrix that provides optimum micro-environmental conditions to cells, as a delivery vehicle to carry bioactive factors which can be released in a controlled manner, and as local niches to orchestrate in situ tissue regeneration. A myriad of biomaterials, varying in geometrical structure, physical form, chemical properties, and biofunctionality have been investigated for skeletal muscle tissue engineering applications. In the current review, we present a detailed summary of studies where the use of biomaterials favorably influenced muscle repair. Biomaterials in the form of porous three-dimensional scaffolds, hydrogels, fibrous meshes, and patterned substrates with defined topographies, have each displayed unique benefits, and are discussed herein. Additionally, several biomaterial based approaches aimed specifically at stimulating vascularization, innervation, and inducing contractility in regenerating muscle tissues are also discussed. Finally, we outline promising future trends in the field of muscle regeneration involving a deeper understanding of the endogenous healing cascades and utilization of this knowledge for the development of multifunctional, hybrid, biomaterials which support and enable muscle regeneration under compromised conditions.

Use of flow, electrical, and mechanical stimulation to promote engineering of striated muscles

The field of tissue engineering involves design of high-fidelity tissue substitutes for predictive experimental assays in vitro and cell-based regenerative therapies in vivo. Design of striated muscle tissues, such as cardiac and skeletal muscle, has been particularly challenging due to a high metabolic demand and complex cellular organization and electromechanical function of the native tissues. Successful engineering of highly functional striated muscles may thus require creation of biomimetic culture conditions involving medium perfusion, electrical and mechanical stimulation. When optimized, these external cues are expected to synergistically and dynamically activate important intracellular signaling pathways leading to accelerated muscle growth and development. This review will discuss the use of different types of tissue culture bioreactors aimed at providing conditions for enhanced structural and functional maturation of engineered striated muscles.

Musculature tissue engineering to repair abdominal wall hernia

Hernia repair is one of the most frequently performed operations in surgical clinics. Tissue engineering provides insights for the treatment of abdominal wall hernias and other disorders involving deficiencies in the musculature. The present review summarizes the mechanisms of muscle development and regeneration and provides an overview of tissue engineering strategies for the construction of muscles.

Development and progress of engineering of skeletal muscle tissue

Engineering skeletal muscle tissue remains still a challenge, and numerous studies have indicated that this technique may be of great importance in medicine in the near future. This article reviews some of the recent findings resulting from tissue engineering science related to the contractile behavior and the phenotypes of muscle tissue cells in different three-dimensional environment, and discusses how tissue engineering could be used to create and regenerate skeletal muscle, as well as the extended applications and the related patents concerned with engineered skeletal muscle.

Bioreactors for guiding muscle tissue growth and development

Muscle tissue bioreactors are devices which are employed to guide and monitor the development of engineered muscle tissue. These devices have a modern history that can be traced back more than a century, because the key elements of muscle tissue bioreactors have been studied for a very long time. These include barrier isolation and culture of cells, tissues and organs after isolation from a host organism; the provision of various stimuli intended to promote growth and maintain the muscle, such as electrical and mechanical stimulation; and the provision of a perfusate such as culture media or blood derived substances. An accurate appraisal of our current progress in the development of muscle bioreactors can only be made in the context of the history of this endeavor. Modern efforts tend to focus more upon the use of computer control and the application of mechanical strain as a stimulus, as well as substrate surface modifications to induce cellular organization at the early stages of culture of isolated muscle cells.

Tissue engineering in head and neck reconstructive surgery: what type of tissue do we need?

Craniofacial tissue loss due to congenital defects, disease or injury is a major clinical problem. The head and neck region is composed of several tissues. The most prevalent method of reconstruction is autologous grafting. Often, there is insufficient host tissue for adequate repair of the defect side, and extensive donor site morbidity may result from the secondary surgical procedure. The field of tissue engineering has the potential to create functional replacements for damaged or pathologic tissues.

Impact of electrical stimulation on three-dimensional myoblast cultures - a real-time RT-PCR study

Several focal skeletal muscle diseases, including tumours and trauma lead to a limited loss of functional muscle tissue. There is still no suitable clinical approach for treating such defects. A promising approach could be the tissue engineering of skeletal muscle. However, a clinically reliable differentiation stimulus for three-dimensional (3-D) cultures is necessary for this process, and this condition has not yet been established. In order to quantify and analyze the differentiation potential of electrical cell stimulation, primary myoblasts were stimulated within a 3-D fibrin- matrix. Gene expression of MyoD, myogenin and AChR-epsilon were measured by real-time RT-PCR over a time period of eight days, showing immediate down-regulation of all marker genes. For tissue engineering approaches, cell multiplication is crucial for acquisition of sufficient tissue volumes for reconstruction. Therefore, all experiments were performed with high and low passaged myoblasts, demonstrating higher transcript rates of marker genes in lowpassage cells. Our findings strongly suggest a reconsideration of electrical stimulation in muscle tissue engineering.

Application of Animal Models: Chronic Electrical Stimulation-Induced Contractile Activity

Unilateral, chronic low-frequency electrical stimulation (CLFS) is an experimental model that evokes numerous biochemical and physiological adaptations in skeletal muscle. These occur within a short time frame and are restricted to the stimulated muscle. The humoral effects of whole body exercise are eliminated and the nonstimulated contralaterai limb can often be used as a control muscle, if possible effects on the contralateral side are considered. CLFS induces a fast-to-slow transformation of muscle because of alterations in calcium dynamics and myofibrillar proteins, and a white-to-red transformation because of changes in mitochondrial enzymes, myoglobin, and the induction of angiogenesis. These adaptations occur in a coordinated time-dependent manner and result from altered gene expression, including transcriptional and posttranscriptional processes. CLFS techniques have also been applied to myocytes in cell culture, which provide a greater opportunity for the delivery of pharmacological agents or for the application of gene transfer methodologies. Clinical applications of the CLFS technique have been limited, but they have shown potential therapeutic value in patients in whom voluntary muscle contraction is not possible due to debilitating disease and/or injury. Thus the CLFS technique has great value for studying various aspects of muscle adaptation, and its wider scientific application to a variety of neuromuscular-based disorders in humans appears to be warranted. Key words: skeletal muscle, muscle plasticity, endurance training, mitochondrial biogenesis, fiber types

Skeletal muscle tissue engineering

The reconstruction of skeletal muscle tissue either lost by traumatic injury or tumor ablation or functional damage due to myopathies is hampered by the lack of availability of functional substitution of this native tissue. Until now, only few alternatives exist to provide functional restoration of damaged muscle tissues. Loss of muscle mass and their function can surgically managed in part using a variety of muscle transplantation or transposition techniques. These techniques represent a limited degree of success in attempts to restore the normal functioning, however they are not perfect solutions. A new alternative approach to addressing difficult tissue reconstruction is to engineer new tissues. Although those tissue engineering techniques attempting regeneration of human tissues and organs have recently entered into clinical practice, the engineering of skeletal muscle tissue ist still a scientific challenge. This article reviews some of the recent findings resulting from tissue engineering science related to the attempt of creation and regeneration of functional skeletal muscle tissue.

Engineering of muscle tissue

The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Tissue engineering and regenerative medicine is an emerging interdisciplinary field that applies the principles of biology and engineering to the development of viable substitutes that restore, maintain, or improve the function of human tissues and organs. Tissue engineering science has provided critical new knowledge that will deepen our understanding of the phenotype of an important category of cell types-the muscle cells-and this knowledge may enable meaningful advances in musculoskeletal tissue engineering. There are two principle strategies for the replacement of impaired muscle tissues. One approach uses the application of isolated and differentiated cells (in vivo tissue engineering), using a transport matrix for the cell delivery; the other uses in vitro-designed and pre-fabricated tissue equivalents (in vitro tissue engineering). Future developments and the decision regarding which approach is more promising depend on the elucidation of the relationships among cell growth and differentiation, the three-dimensional environment, the architecture of the cells, and gene expression of the developmental process and the survival of the cells and integration in the host in in vivo experiments. As the techniques of tissue engineering become more sophisticated and as issues such as vascularization and innervation are addressed, the usefulness of these methods for reconstructive surgery may grow significantly.

Fast-to-slow transformation and nuclear import/export kinetics of the transcription factor NFATc1 during electrostimulation of rabbit muscle cells in culture

Contractile activity imposed by chronic electrical stimulation of a primary skeletal muscle cell culture grown on microcarriers over several days led to an increase of slow myosin heavy chain I (MHCI) and a decrease of fast MHCII expression at mRNA and protein levels, indicating an ongoing fast-to-slow transformation. Only patterns with periods of continuous stimulation of > or = 5 min in a 45 min cycle were capable of inducing a fibre type transformation, and this was independent of the applied stimulation frequency over the range 1-10 Hz. We have shown before that the calcineurin-NFATc1 signalling pathway is indispensable in mediating MHCI upregulation during fibre type transformation. Therefore, subcellular localization of NFATc1 was studied immunocytochemically. This revealed that only one stimulation train lasting for > or = 5 min was sufficient to induce nuclear import of this factor, which was about complete after 20 min of continuous stimulation. For both induction of NFATc1 import and MHCI mRNA upregulation, the minimum stimulation interval of > or = 5 min was sufficient and stimulation frequency was not crucial between 1 and 10 Hz. Repetition of stimulation cycles, with pauses (40 min) shorter than the time required for complete export of NFATc1, led to an accumulation of NFATc1 in the nuclei with each cycle and thus to an amplification of the transformation signal during extended periods of electrostimulation. The temporal behaviour of NFATc import/export appears to determine the effectiveness of various electrostimulation protocols in inducing fast-to-slow fibre transformation.

Effect of electrical stimulation on beta-adrenergic receptor population and cyclic amp production in chicken and rat skeletal muscle cell cultures

Expression of the beta-adrenergic receptor (betaAR) and its coupling to cyclic AMP (cAMP) synthesis are important components of the signaling system that controls muscle atrophy and hypertrophy, and the goal of this study was to determine if electrical stimulation in a pattern simulating slow muscle contraction would alter the betaAR response in primary cultures of avian and mammalian skeletal muscle cells. Specifically, chicken skeletal muscle cells and rat skeletal muscle cells that had been grown for 7 d in culture were subjected to electrical stimulation for an additional 2 d at a pulse frequency of 0.5 pulses/sec and a pulse duration of 200 msec. In chicken skeletal muscle cells, the betaAR population was not significantly affected by electrical stimulation; however, the ability of these cells to synthesize cyclic AMP was reduced by approximately one-half. In contrast, the betaAR population in rat muscle cells was increased slightly but not significantly by electrical stimulation, and the ability of these cells to synthesize cyclic AMP was increased by almost twofold. The basal levels of intracellular cyclic AMP in neither rat muscle cells nor chicken muscle cells were affected by electrical stimulation.

Expression of fast myosin heavy chain transcripts in developing and dystrophic chicken skeletal muscle

The expression of fast myosin heavy chain (MyHC) genes was examined in vivo during fast skeletal muscle development in the inbred White Leghorn chicken (line 03) and in adult muscles from the genetically related dystrophic White Leghorn chicken (line 433). RNA dotblot and northern hybridization was employed to monitor MyHC transcript levels utilizing specific oligonucleotide probes. The developmental pattern of MyHC gene expression in the pectoralis major (PM) and the gastrocnemius muscles was similar during embryonic development with three embryonic MyHC isoform genes, Cemb1, Cemb2, and Cemb3, sequentially expressed. Following hatching, MyHC expression patterns in each muscle differed. The expression of MyHC genes was also studied in muscle cell cultures derived from 12-day embryonic pectoralis muscles. In vitro, Cvent, Cemb1, and Cemb2 MyHC genes were expressed; however, little if any Cemb3 MyHC gene expression could be detected, even though Cemb3 was the predominant MyHC gene expressed during late embryonic development in vivo. In most adult muscles other than the PM and anterior latissimus dorsi (ALD), the Cemb3 MyHC gene was the major adult MyHC isoform. In addition, two general patterns of expression were identified in fast muscle. The fast muscles of the leg expressed neonatal (Cneo) and Cemb3 MyHC genes, while other fast muscles expressed adult (Cadult) and Cemb3 MyHC genes. MyHC gene expression in adult dystrophic muscles was found to reflect the expression patterns found in corresponding normal muscles during the neonatal or early post-hatch developmental period, providing additional evidence that avian muscular dystrophy inhibits muscle maturation.

Innervation regulates myosin heavy chain isoform expression in developing skeletal muscle fibers

The influence of innervation on primary and secondary myogenesis and its relation to fiber type diversity were investigated in two specific wing muscles of quail embryo, the posterior (PLD) and anterior latissimus dorsi (ALD). In the adult, these muscles are composed almost exclusively of pure populations of fast and slow fibers, respectively. When slow ALD and fast PLD muscles developed in ovo in an aneurogenic environment induced after neural tube ablation, the cardiac ventricular myosin heavy chain (MHC) isoform was not expressed. The adult slow MHC isoform, SM2, appeared by embryonic day 7 (ED 7) in normal innervated slow ALD but was not expressed in denervated muscle. Analysis of in vitro differentiation of myoblasts from fast PLD and slow ALD muscles isolated from ED 7 control and neuralectomized quail embryos showed no fundamental differences in the pattern of MHC isoform expression. Newly differentiated fibers accumulated cardiac ventricular, embryonic fast, slow SM1 and SM3 MHC isoforms. Nevertheless, the expression of slow SM2 isoform in myotubes formed from slow ALD myoblasts only occurred when myoblasts were cultured in the presence of embryonic spinal cord. Our studies demonstrate that the neural tube influences primary as well as secondary myotube differentiation in avian forelimb and facilitates the expression of different MHC, particularly slow SM2 MHC gene expression in slow myoblasts.

Effects of chronic electrical stimulation on myosin heavy chain expression in satellite cell cultures derived from rat muscles of different fiber-type composition

Myotube cultures were established from satellite cells of three rat muscles of different fiber-type composition, slow-twitch soleus, diaphragm, and fast-twitch tibialis anterior (TA). Effects of chronic electrical stimulation were studied by exposing these cultures for up to 13 days to a stimulus pattern consisting of 250 ms impulse trains of 40 Hz, repeated every 4 s. Changes in myosin expression were assessed at the mRNA level by Northern blotting and in situ hybridization. Expression of slow myosin at the protein level was analysed by immunoblotting and immunohistochemistry with two antibodies, one specific to adult slow myosin, the other reacting with developmental and adult slow myosin heavy chain (MHCI) isoforms. In all three myotube cultures stimulation enhanced the mRNA and protein expression of a developmental isoform of slow myosin (MHCI). However, the three myotube cultures differed in the extent of the increase in MHCI. It was greatest in soleus-derived myotubes, least in TA-derived myotubes, and intermediate in diaphragm-derived myotubes. In addition to the increase in slow myosin, long-term stimulation led to an isoform switch, as indicated by an increase in myotubes reacting with the antibody specific for the adult MHCI. Our results suggest that enhanced contractile activity promotes the expression of the slow phenotype predetermined in satellite cells of slow-twitch, type I fibers. The different extents of increased slow myosin expression may thus be explained as reflecting different percentages of type I fibers and consequently of slow-type satellite cells in the corresponding donor muscles.

Electrical stimulation of contractile activity accelerates growth of cultured neonatal cardiocytes

An electrical stimulation system was designed to regulate synchronized contractile activity of neonatal rat cardiocytes and to examine the effects of mechanical contraction on cardiocyte growth. Continuous electrical stimulation at a pulse duration of 5 milliseconds and frequency of 3 Hz resulted in a time-dependent accumulation of cell protein that reached 34% above initial values, as measured by the protein-to-DNA ratio. The growth response did not occur using voltage amplitudes that were subthreshold for contraction and was independent of contraction frequencies set at > or = 0.5 Hz. The RNA-to-DNA ratio increased in parallel to cell protein, indicating that the capacity for protein synthesis was enhanced by contraction. Rates of 28S rRNA synthesis were accelerated twofold in contracting cardiocytes. By comparison, protein and RNA accumulation did not occur in electrically stimulated cardiocytes in which contraction was blocked by either 10 mumol/L verapamil or by 5 mmol/L 2,3-butanedione monoxime, an inhibitor of actomyosin crossbridge cycling. Electrical stimulation of cardiocyte contraction did not enhance alpha-cardiac actin or myosin heavy chain (alpha+beta) mRNA transcript levels relative to 28S rRNA during the period of rapid growth that occurred over the first 48 hours. It is concluded that (1) electrical stimulation of contraction accelerates cardiocyte growth and RNA accumulation, (2) mechanical contraction is involved in regulating the growth of electrically stimulated cardiocytes, and (3) the levels of alpha-actin and myosin heavy chain mRNA increase in proportion to rRNA during the growth of contracting cardiocytes.

Effects of chronic stimulation with different impulse patterns on the expression of myosin isoforms in rat myotube cultures

In order to study maturation and differentiation of aneural myotubes in vitro, long-term myotube cultures were established from hindlimb musculature of newborn rats. The developmental state of the myotubes was judged by their myosin heavy chain (HC) patterns. Newly formed myotubes only expressed the embryonic isoform, HCemb, older myotubes expressed the neonatal isoform HCneo, as well as the fast adult isoforms HCIIb and HCIId. HCIId increased continuously, reaching a relative concentration of 47% in 37-day-old cultures. The third fast isoform, HCIIa, was not detected and also the slow isoform HCI was absent. Effects of chronic (20 days) electrostimulation were studied by exposing the cultures to various stimulus patterns. Bursts of 250 ms duration at various pulse frequencies were applied at low and high burst frequencies. Although HCemb remained the predominant isoform under all conditions, different stimulus patterns induced specific changes in the patterns of fast and slow HC isoforms. Bursts of 250 ms duration at 15 Hz, 40 Hz, or 100 Hz, repeated every second or every 4 s, induced the expression of slow myosin, i.e., HCl. Bursts of 250 ms duration at 100 Hz, repeated every 100 s, enhanced the expression of HCIId, but not of HCI. Because slow myosin was induced at high burst frequency with low and high pulse rates, we suggest that burst frequency rather than pulse frequency has a specifying effect on myosin expression. Our results show that the basal program of myosin expression during myogenesis in vitro can be modulated by electrostimulation, suggesting a possible influence of neuromuscular activity on the development of adult fiber types.