Intraoperative Sarcomere Length Measurements
Muscle spasticity may cause severe joint deformity and dramatically affect quality of life. Evidence suggests that spastic muscles are themselves different from normal muscles, likely an effect of their abnormal neural input. For example, it has been shown that muscle fiber size variability and fiber type distribution different from that of normal muscle. Additionally, experiments have demonstrated that while some spastic muscles have a normal stretch reflex, intrinsic muscle stiffness is significantly higher compared to control muscle. These studies suggest that the properties of spastic muscle are not normal and yet, in spite of the prevalence of this entity, the muscle changes due to spasticity are poorly understood.
We have developed an intraoperative method to measure sarcomere length in human muscles during reconstructive surgery using laser diffraction, and have used this method to evaluate surgical reconstructive procedures that restore function in patients who have lost function after peripheral nerve injury or spinal cord injury. As the sarcomere length at the time of tendon transfer is probably important to optimize muscle function (previously demonstrated by our lab using mathematical modeling), studies of in vivo sarcomere length are being done in Sweden in close collaboration with Dr. Jan Fridén of the Göteborg University. Recent findings suggest that spasticity causes a major reorganization of the normal musclejoint relationships.
To further understand the properties of spastic muscle, it becomes necessary to test the mechanical properties of the cells, and also assess any protein differences that exist between them and normal muscle. Because with living human muscle, one does not have the luxury of being to dissect out full length muscle fibers (the patients wouldn't appreciate it), these tests need to be conducted on muscle biopsies. These muscle biopsies can then be dissected down to a single muscle fiber segment, which can then be tested for mechanics in a chamber such as the one below. Recent findings suggest that Spastic muscle cells are shorter and stiffer than normal cells.
Transfection of muscle tissue with plasmid DNA has potential therapeutic benefits for a variety of diseases, and can be used to replace proteins that are absent in disease state (such as dystrophin in patients with muscular dystrophy), or used to chronically secrete therapeutic proteins (such as erythropoetin in anemic patients). We can use transfection to introduce the proteins missing from mouse knockout models back into their muscles to see if we can rescue the functional losses or structural changes that we observe. We have also used this technique to show that by transfecting desmin back into desmin-null muscles, response to injury is restored to near normal levels.
Relationship Between Intramuscular Pressure and Muscle Force
Muscle force in living human beings is difficult to determine, because most methods are highly invasive. Electromyography (EMG) and joint kinematics are the most widely-used methods to assess muscle function, but are limited in their usefulness in dynamic motion. Intramuscular pressure, measured by placing a fiber optic pressure sensor into the muscle may be a new tool to bridge this gap. Recent results in the lab have shown that while IMP is a good predictor of muscle stress during isometric contractions, there is less correlation during dynamic contractions. These studies are being done in collaboration with Dr. Kenton R. Kaufman, Ph.D. from the Mayo Clinic.
Patients with skeletal muscle injuries and disease often suffer from muscle fibrosis and increased stiffness. Fibrotic muscle is characterized by an increase in the extracellular matrix, which could be a contributing factor to increased muscle stiffness. However, the ultrastructure of these extracellular matrix components and their connection to tendons and muscle fiber are unknown. To study the structure of the extracellular matrix and its connection to other muscle components we use serial block face scanning electron microscopy. Stacks of images from fibrotic muscles are generated and reconstructed to show fibrotic collagen structures within the muscle. Understanding the changes to extracellular matrix ultrastructure in fibrotic muscle may identify therapeutic targets to reduce fibrosis and muscle stiffness in patients with limited muscle function.
Understanding functional relationships among cellular structures is a fundamental problem facing biologists today. Elucidation of the mechanisms by which a protein or protein complex elicits a physiological response depends in part upon our ability to accurately define a protein’s physical connections to surrounding structures. While current approaches, such as solution biochemistry, theoretical analysis of protein structure and electron microscopy, yield critical information regarding the identity of proteins within a complex, they do not assess mechanical connections between proteins, or their relationship to cellular function. Conversely, within striated muscle, several systems have been developed to quantify mechanical properties of intact single cells and single myofibrils, however, the extension of these results to the mechanical performance of a single cell with an intact cytoskeletal lattice necessitates further study of connections between sub-cellular structures.
We have developed a system that allows simultaneous confocal imaging of protein interactions and measurement of mechanical properties during passive loading of muscle cells. Additionally, we developed image processing algorithms to quantify connectivity between subcellular structures. We have recently used this method to demonstrate the Structural and functional roles of desmin in mouse skeletal muscle during passive deformation.
BoNT/A is a common treatment used in the rehabilitation of children with cerebral palsy. Despite how widely used it has become over the past several years, there have been few studies characterizing the effects of injections on muscle structure or function. We have been studying the effect of BoNT/A on muscle structure and function in a rat model. Recently, we have shown Increased efficacy and decreased systemic-effects of botulinum toxin A injection after active or passive muscle manipulation and a Differential effect of dose and volume on muscle structure and function after botulinum toxin injection.
Last Updated: Tuesday, 18-Sep-2012 13:34:25 PDT
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