Biomedical subjects

Richard L Lieber

Publications and source records attributed to Richard L Lieber.

At least 37 records · Page 2Linked to original sources

PubMed2004

Structural and functional roles of desmin in mouse skeletal muscle during passive deformation.

Mechanical interactions between desmin and Z-disks, costameres, and nuclei were measured during passive deformation of single muscle cells. Image processing and continuum kinematics were used to quantify the structural connectivity among these structures. Analysis of both wild-type and desmin-null fibers revealed that the costamere protein talin colocalized with the Z-disk protein alpha-actinin, even at very high strains and stresses. These data indicate that desmin is not essential for mechanical coupling of the costamere complex and the sarcomere lattice. Within the sarcomere lattice, significant differences in myofibrillar connectivity were revealed between passively deformed wild-type and desmin-null fibers. Connectivity in wild-type fibers was significantly greater compared to desmin-null fibers, demonstrating a significant functional connection between myofibrils that requires desmin. Passive mechanical analysis revealed that desmin may be partially responsible for regulating fiber volume, and consequently, fiber mechanical properties. Kinematic analysis of alpha-actinin strain fields revealed that knockout fibers transmitted less shear strain compared to wild-type fibers and experienced a slight increase in fiber volume. Finally, linkage of desmin intermediate filaments to muscle nuclei was strongly suggested based on extensive loss of nuclei positioning in the absence of desmin during passive fiber loading.

Actinin↗

PubMed2004

Implications of muscle design on surgical reconstruction of upper extremities.

The basic anatomic and physiologic properties of human upper extremity muscles have been elucidated using a novel intraoperative sarcomere length measuring device in conjunction with quantitative anatomic and biomechanic models of these same muscles. We reviewed the genesis of these studies which began with development of the optical tools, validation using animal models, and application to human upper extremity surgery. Human muscles have a remarkable degree of specialization, even among synergists. Mechanical properties of human tendons provide another source of specialization such that the muscle-tendon unit does not simply retain the properties of a muscle plus a tendon. The operating range of different muscles is also a method whereby the balance of the joint can be maintained in the face of altered moment arms and muscle forces. The derivation of these principles is explained along with their importance in surgical tendon transfers where one muscle substitutes function for another.

Animals↗

PubMed2003

Rapid muscle-specific gene expression changes after a single bout of eccentric contractions in the mouse.

Eccentric contractions (ECs), in which a muscle is forced to lengthen while activated, result in muscle injury and, eventually, muscle strengthening and prevention of further injury. Although the mechanical basis of EC-induced injury has been studied in detail, the biological response of muscle is less well characterized. This study presents the development of a minimally invasive model of EC injury in the mouse, follows the time course of torque recovery after an injurious bout of ECs, and uses Affymetrix microarrays to compare the gene expression profile 48 h after ECs to both isometrically stimulated muscles and contralateral muscles. Torque dropped by approximately 55% immediately after the exercise bout and recovered to initial levels 7 days later. Thirty-six known genes were upregulated after ECs compared with contralateral and isometrically stimulated muscles, including five muscle-specific genes: muscle LIM protein (MLP), muscle ankyrin repeat proteins (MARP1 and -2; also known as cardiac ankyrin repeat protein and Arpp/Ankrd2, respectively), Xin, and myosin binding protein H. The time courses of MLP and MARP expression after the injury bout (determined by quantitative real-time polymerase chain reaction) indicate that these genes are rapidly induced, reaching a peak expression level of 6-11 times contralateral values 12-24 h after the EC bout and returning to baseline within 72 h. Very little gene induction was seen after either isometric activation or passive stretch, indicating that the MLP and MARP genes may play an important and specific role in the biological response of muscle to EC-induced injury.

Animals↗

PubMed2003

Asynchronous functional, cellular and transcriptional changes after a bout of eccentric exercise in the rat.

Thirty eccentric contractions (ECs) were imposed upon rat dorsiflexors (n = 46) by activating the peroneal nerve and plantarflexing the foot ~40 deg, corresponding to a sarcomere length change over the range 2.27-2.39 microm for the tibialis anterior and 2.52-2.66 microm for the extensor digitorum longus. Animals were allowed to recover for one of 10 time periods ranging from 0.5 to 240 h, at which time muscle contractile properties, immunohistochemical labelling and gene expression were measured. Peak isometric torque dropped significantly by ~40 % from an initial level of 0.0530 +/- 0.0009 Nm to 0.0298 +/- 0.0008 Nm (P < 0.0001) immediately after EC, and then recovered in a linear fashion to control levels 168 h later. Immunohistochemical labelling of cellular proteins revealed a generally asynchronous sequence of events at the cellular level, with the earliest event measured being loss of immunostaining for the intermediate filament protein, desmin. Soon after the first signs of desmin loss, infiltration of inflammatory cells occurred, followed by a transient increase in membrane permeability, manifested as inclusion of plasma fibronectin. The quantitative polymerase chain reaction (QPCR) was used to measure transcript levels of desmin, vimentin, embryonic myosin heavy chain (MHC), myostatin, myoD and myogenin. Compared to control levels, myostatin transcripts were significantly elevated after only 0.5 h, myogenic regulatory factors significantly elevated after 3 h and desmin transcripts were significantly increased 12 h after EC. None of the measured parameters provide a mechanistic explanation for muscle force loss after EC. Future studies are required to investigate whether there is a causal relationship among desmin loss, increased cellular permeability, upregulation of the myoD and desmin genes, and, ultimately, an increase in the desmin content per sarcomere of the muscle.

Animals↗

PubMed2003

Spastic muscle cells are shorter and stiffer than normal cells.

The mechanical properties of isolated single muscle fiber segments were measured in muscle cells obtained from patients undergoing surgery for correction of flexion contractures secondary to static perinatal encephalopathy (cerebral palsy). "Normal" muscle cells from patients with intact neuromuscular function were also mechanically tested. Fiber segments taken from subjects with spasticity developed passive tension at significantly shorter sarcomere lengths (1.84 +/- 0.05 microm, n = 15) than fibers taken from normal subjects (2.20 +/- 0.04 microm, n = 35). Elastic modulus of the stress-strain relationship in fibers from patients with spasticity (55.00 +/- 6.61 kPa) was almost double that measured in normal fibers (28.25 +/- 3.31 kPa). The fact that these muscle cells from patients with spasticity have a shorter resting sarcomere length and increased modulus compared with normal muscle cells suggests dramatic remodeling of intracellular or extracellular muscle structural components such as titin and collagen. Such changes in muscles of patients with spasticity may have implications for therapy.

Adult↗

PubMed2003

Inferior mechanical properties of spastic muscle bundles due to hypertrophic but compromised extracellular matrix material.

The passive mechanical properties of small muscle fiber bundles obtained from surgical patients with spasticity (n = 9) and patients without neuromuscular disorders (n = 21) were measured in order to determine the relative influence of intracellular and extracellular components. For both types of patient, tangent modulus was significantly greater in bundles compared to identical tests performed on isolated single cells (P < 0.05). However, the relative difference between bundles and single cells was much greater in normal tissue than spastic tissue. The tangent modulus of normal bundles (462.5 +/- 99.6 MPa) was 16 times greater than normal single cells (28.2 +/- 3.3 MPa), whereas the tangent modulus of spastic bundles (111.2 +/- 35.5 MPa) was only twice that of spastic muscle cells (55.0 +/- 6.6 MPa). This relatively small influence of the extracellular matrix (ECM) in spastic muscle was even more surprising because spastic muscle cells occupied a significantly smaller fraction of the total specimen area (38.5 +/- 13.6%) compared to normal muscle (95.0 +/- 8.8%). Based on these data, normal muscle ECM is calculated to have a modulus of 8.7 GPa, and the ECM from spastic muscle of only 0.20 GPa. These data indicate that spastic muscle, although composed of cells that are stiffer compared to normal muscle, contains an ECM of inferior mechanical strength. The present findings illustrate some of the profound changes that occur in skeletal muscle secondary to spasticity. The surgical implications of these results are discussed.

Adult↗

PubMed2003

Performance characteristics of a pressure microsensor.

A new fiber optic microsensor has been developed for pressure measurement. The pressure microsensor is extremely small (360 micro m). Performance characteristics of the microsensor were evaluated over a pressure range from 0 to 250mmHg. Five sensors were compared to a National Institute of Standards and Technology traceable reference pressure. The microsensor had an accuracy, repeatability, and linearity better than 2% full-scale output (FSO) and a hysteresis of 4.5% FSO.

Calibration↗

PubMed2003

Correlation between active and passive isometric force and intramuscular pressure in the isolated rabbit tibialis anterior muscle.

The purpose of this study was to quantify the relationship between intramuscular pressure (IMP) and muscle force during isometric muscle contraction of the rabbit tibialis anterior (TA) absent the effect of either bone or fascia. To quantify this relationship, length-tension experiments were performed on the isolated TA of the New Zealand White rabbit (mass=2.5+/-0.5kg, n=12). The knee was fixed in a custom jig, the distal tendon of the TA was attached to a servomotor, and a 360 microm fiber optic pressure transducer was inserted into the TA. The peroneal nerve was stimulated to define optimal length (L(0)). The length-tension curve was created using 40Hz isometric contractions with 2-min rest intervals between each contraction. Measurements began at L(0)-50%L(f) and progressed to L(0)+50%L(f), changing the length-tension in 5% L(f) increments after each contraction. Qualitatively, the length-tension curve for isometric contractions was mimicked by the length-pressure curve for both active and passive conditions. Linear regression was performed individually for each animal for the ascending and descending limb of the length-tension curve and for active and passive conditions. Pressure-force coefficients of determination ranged from 0.138-0.963 for the active ascending limb and 0.343-0.947 for the active descending limb. Passive pressure coefficients of determination ranged from 0.045-0.842 for the ascending limb and 0.672-0.982 for the descending limb. These data indicate that IMP measurement provide a fairly accurate index of relative muscle force, especially at muscle lengths longer than optimal.

Animals↗

PubMed2003

Analysis of posterior deltoid function one year after surgical restoration of elbow extension.

PURPOSE: The purpose of this study was to measure the extent and timing of elbow extension torque recovery after posterior deltoid-to-triceps tendon transfer. METHODS: Elbow extension moment was measured in 40 limbs from 23 patients who underwent surgical restoration using the posterior deltoid-to-triceps tendon transfer at times ranging from 8 weeks to 1 year after surgery. For comparison purposes, elbow extension moment also was measured in healthy controls and persons with C7 spinal cord injuries. RESULTS: Maximum extension moment was 5.89 +/- 0.24 Nm (mean +/- standard error of mean, n = 40), which corresponds to approximately 65% of the predicted posterior deltoid force and provided an adequate moment to oppose gravity. Based on the shape of the moment-joint angle curve and using a biomechanical model, it was predicted that posterior deltoid was inserted at a relatively short muscle length of 123.1 mm and thus operated exclusively on the ascending limb of the length-tension relationship. CONCLUSIONS: These observations support an evolving model of muscle architecture in which connective tissue septa restrict muscle fiber elongation during surgical tensioning of the tendon transfer. This relatively short length would result in a significant force loss should any of the repair sites slip or stretch during rehabilitation. These data have implications for the reconstruction and rehabilitation of this patient population.

Adolescent↗

PubMed2003

Simultaneous imaging and functional assessment of cytoskeletal protein connections in passively loaded single muscle cells.

We describe a novel system that permits simultaneous confocal imaging of protein interactions and measurement of cell mechanical properties during passive loading. A mechanical apparatus was designed to replace the stage of a confocal microscope, enabling cell manipulation, force transduction, and imaging. In addition, image processing algorithms were developed to quantify the degree of connectivity between subcellular structures. Using this system, we examined the interactions among three cellular structures thought to be linked by the muscle's intermediate filament system: Z-disks, nuclei, and the costamere protein complexes located at the muscle cell surface. Fast Fourier transforms (FFTs) and autocorrelations (ACs) were implemented to quantify image periodicity and relative phase shifts among structures. We demonstrated in sample wild-type muscle cells that there was significant connectivity among Z-disks in the same fiber at various sarcomere lengths, as well as between Z-disks and the costamere complexes. This approach can be applied to any cell system in which structural periodicity and mechanical connectivity are of interest.

Actinin↗

PubMed2002

Finite element model of intramuscular pressure during isometric contraction of skeletal muscle.

The measurement of in vivo intramuscular pressure (IMP) has recently become practical and IMP appears well correlated with muscle tension. A numerical model of skeletal muscle was developed to examine the mechanisms producing IMP. Unipennate muscle is modelled as a two-dimensional material continuum that is incompressible and nonlinearly anisotropic. The finite element technique is used to calculate IMP and muscle stress during passive stretch and during isometric contraction. A novel element models the contractile portion of muscle, incorporating sarcomere length-force and velocity-force relations. A range of unipennate muscle geometries can be modelled. The model was configured to simulate the rabbit tibialis anterior muscle over a range of lengths. Simulated IMP and stress results were validated against animal experimentation data. The simulation agreed well with the experimental data over the range of 0.8-1.1 of the optimal length. Severe pressure gradients were produced near the musculo-tendinous junctions while IMP was more uniform in the central muscle belly. IMP and muscle stress in relaxed (unstimulated) muscle increased nonlinearly with muscle length. IMP and stress in isometrically contracting muscle showed a local maximum at optimal length and were reduced at shorter lengths. At muscle lengths longer than optimal, stress and IMP increased predominately due to tension in the passive elastic structures.

Animals↗

PubMed2002

Spasticity causes a fundamental rearrangement of muscle-joint interaction.

Sarcomere length was measured in flexor carpi ulnaris (FCU) muscles from patients with severely spastic wrist flexion contractures (n = 6), as well as from patients with radial nerve injury and a normally innervated FCU (n = 12). Spastic FCU muscles had extremely long sarcomere lengths with the wrist fully flexed (3.48 +/- 0.44 microm) compared to the FCU muscles of patients with radial nerve injury (2.41 +/- 0.31 microm). In three of the patients with spastic wrist flexion contractures, the slope of the FCU sarcomere length-joint angle relationship was measured and found to be, essentially, normal (0.017 +/- 0.005 microm/degree, n = 3) suggesting that serial sarcomere number (and therefore muscle fiber length) was unchanged in spite of the dramatic absolute sarcomere length change. These results indicate that spasticity results in a major alteration of normal muscle-joint anatomical relationships that has not previously been recognized to our knowledge. We hypothesize that the results are explained either by the inability of muscle fibers to add serial sarcomeres in response to growth, or the selective loss of FCU muscle length secondary to the central nervous system lesion.

Adaptation, Physiological↗

PubMed2002

Mechanical considerations in the design of surgical reconstructive procedures.

Tendon transfers are used to restore arm and hand function after injury to the peripheral nerves or after spinal cord injury. Traditional guidelines to choose the length at which the transferred muscle should be attached have a poor scientific foundation. We postulate that passive tension only becomes significant at relatively long lengths and that passive tension as the major factor in intra-operative decision making may result in overstretch of the muscle-tendon unit (MTU) and accompanying low-active force generation. It appears unwise to rely on unknown factors, such as slippage or stress relaxation, to correct an overstretched transfer. Instead, we suggest the use of intra-operative sarcomere length measurements to predict and set the optimal MTU length during reconstructive upper limb surgery.

Biomechanical Phenomena↗

PubMed2002

Differential expression of neural cell adhesion molecule (NCAM) after tenotomy in rabbit skeletal muscle.

Tenotomy is a commonly encountered event in orthopaedic surgery. In 23 rabbit extensor digitorum longus (EDL) muscles, within 24 h after tenotomy, a marked drop in maximum force production occurred. This was not explainable based on architectural changes and histological examination using standard markers for muscle injury, i.e., haematoxylin and eosin morphology, developmental myosin heavy chain (MHC) immunolabeling, and quantitation of muscle fiber type percentage, area and distribution. The expression of neural cell adhesion molecule (NCAM), a glycoprotein expressed during muscle development was measured as a function of time in these muscles. NCAM expression was increased as early as one day after tenotomy with 2.2+/-1.2% of the fibers showing positive expression. This expression level increased significantly to 15.4+/-15.2% after 7 days and then subsided to 13.2+/-10.6% 21 days after tenotomy. Two-way analysis of variance demonstrated a significant effect of time and a significant time x tenotomy method interaction. These results suggest that tenotomy leads to possible changes in muscle-nerve connections and/or excitation-contraction (EC) coupling.

Animals↗

PubMed2002

In vitro cyclic tensile testing of combined peripheral and core flexor tenorrhaphy suture techniques.

Early tenorrhaphy mobilization increases repair site strength and decreases adhesions. Preliminary unpublished data suggest that early active mobilization improves clinical outcome compared with traditional passive motion protocols. We loaded cadaver flexor profundus tendon repairs to 8.0 kg (78.4 N) for up to 5,000 cycles to simulate the loads and cycle number of our active flexor tendon rehabilitation protocol. 3-0 Ethibond (Ethicon, Somerville, NJ) and 6-0 Prolene (Surgi-pro; US Surgical, Norwalk, CT) were used for core and peripheral sutures, respectively. Four different groups were tested: 2-strand Tajima core suture with either a running interlocking (2R) or a Silfverskiöld cross-stitch (2S) peripheral suture and 4-strand Tajima plus horizontal mattress core suture with either a running interlocking (4R) or a Silfverskiöld peripheral suture (4S). Repairs failed in the suture midsubstance or at the knot. There was considerable variability within groups and no significant difference in the number of cycles to failure between the 2R, 4R, and 2S repairs, which failed after 2 +/- 2, 304 +/- 249, and 560 +/- 987 cycles, respectively. All 4S repairs were intact after 5,000 cycles. Our data suggest that flexor tenorrhaphy with the 4S repair can withstand the cyclic loads we estimate would be present during an active rehabilitation protocol.

Biomechanical Phenomena↗

PubMed2002

Mechanisms of muscle injury gleaned from animal models.

Eccentric contractions of skeletal muscles produce injury and, ultimately, muscle strengthening. Current data suggest that the earliest events associated with injury are mechanical in nature and may be based primarily on the sarcomere strain experienced by the muscle. In this review, recent experimental data, primarily from rabbit dorsiflexor muscles, are used to provide general information regarding the factors that cause injury and means for preventing injury. Mechanical experiments reveal that excessive sarcomere strain is the primary cause of injury. We hypothesize that excessive strain permits extracellular or intracellular membrane disruption that may permit hydrolysis of structural proteins, leading to the myofibrillar disruption that is commonly observed. Inflammation that occurs after injury further degrades the tissue, but prevention of the inflammation leads to a long-term loss in muscle function. Simple preventative treatments such as increasing muscle oxidative capacity (getting into shape) or cyclic stress-relaxation of tissue (stretching out) have no measurable effect on the magnitude of muscle injury that occurs. Ultimately, an improved understanding of the damage mechanism may improve our ability to provide rehabilitative and strengthening prescriptions that have a rational scientific basis.

Animals↗

PubMed2002

Studies of myosin isoforms in muscle cells: single cell mechanics and gene transfer.

Myosin, the motor protein in skeletal muscle, is composed of two subunits, myosin heavy chain and myosin light chain. All vertebrates express a family of myosin heavy chain and myosin light chain isoforms that together are primary determinants of force, velocity, and power in muscle fibers. Therefore, appropriate expression of myosin isoforms in skeletal muscle is critical to proper motor function. Myosin isoform expression is highly plastic and undergoes significant changes in response to muscular injury, muscle disuse, and disease. Therefore, myosin isoform function and plasticity are highly relevant to clinical orthopaedic research, musculoskeletal surgery, and sports medicine. Muscle from frogs offers a special opportunity to study the structural basis of contractile protein function because single intact fibers can be isolated that maintain excellent mechanical stability, allowing for high-resolution studies of contractile performance in intact cells. The current authors summarize recent studies defining the myosin isoforms in muscle from frogs and the relationship between myosin isoforms and mechanical performance of intact single muscle cells. Preliminary studies also are described that show the potential for simple plasmid-based in vivo gene transfer approaches as a model system to elucidate the structural basis of muscle protein function in intact cells.

Animals↗

PubMed2002

Cytoskeletal disruption after eccentric contraction-induced muscle injury.

Skeletal muscle cytoskeletal proteins are receiving more attention recently based on their importance in maintaining muscle integrity, their role in transmitting force throughout the cell, and their involvement in muscle diseases. In this report, the authors focus on the intermediate filament system of skeletal muscle composed of the protein desmin. Desmin is shown to transmit force from myofibrillar force generators to the muscle surface and to the muscle-tendon junction. This protein is lost rapidly during high-intensity exercise using a rabbit model. Mice were genetically engineered that lack the desmin gene and these muscles were shown to generate lower stress but actually to experience less injury during intense exercise. Finally, direct imaging of muscle cells with fluorescently labeled cytoskeletal proteins shows that lack of the desmin protein results in tremendous disorganization of the myofibrillar lattice which may help to explain desmin myopathies.

Animals↗