Glenn A. Walter, Ph.D.
My lab focuses on the pathophysiology of muscle damage and the development of novel molecular and cellular imaging techniques. In addition, we develop stem-cell therapies and utilize viral delivery of therapeutic genes to mitigate muscle damage and restore the regenerative potential of dystrophic and atrophied muscle. The lab also studies the physiological effects of muscle atrophy and therapeutic gene transfer to both skeletal and cardiac muscle. Our research is funded by grants from the National Institutes of Health, National Science Foundation, the Howard Hughes Medical Institute, and the Muscular Dystrophy Association.
Bioengineering of Muscle Structure and Metabolism
Thermodynamic bioengineering with invertebrate genes. We have shown that arginine kinase (AK) can serve as a noninvasive monitoring system for viral mediated gene delivery. The general implication of these results are twofold. First arginine kinase can be used as a noninvasive marker for gene transfer in vertebrate skeletal muscles. Secondly, skeletal muscles that express a combination of creatine kinase and arginine kinase provide an extended thermodynamic buffering range. Thus the coexpression of AK and CK should prove beneficial to skeletal cells under conditions of prolonged ischemia or fatiguing conditions. Following the introduction of AK into the mammalian muscle cytoplasm a large PArg pool is expected to be formed without disturbing the normal levels of ATP or PCr. However, upon depletion of PCr which would occur in ischemia, creatine kinase can no longer buffer changes in ATP. At this point, the PArg pool will continue to buffer changes in ATP levels. In addition, the AK reaction will tend to slow the fall of pH.
Restoration of membrane integrity and sarcolemmal integrity. We use a combination of unsuppressed 1H-MRS, multi-echo and dynamic, macromolecule contrast enhanced MRI, to investigate the intrinsic properties that lead to changes in muscle T2 in dystrophy and following damage, ischemia, and exercise. Contraction-induced injury can be characterized using a variety of methods. However, many of the histological methods have the disadvantage they are invasive and require the animal to be sacrificed. MRI/MRS due to its noninvasive nature and short acquisition periods, can be used to follow both primary (0-3 day) and secondary (3-21 day) injury processes within the same mouse providing a tool for longitudinal studies in both control and dystrophic animals. Differences in T2 provide sensitive markers of muscle damage producing differences in image contrast with a spatial resolution on the order of that of a single muscle fiber. MRI for detection of muscle injury has the added advantage that large muscle volumes can be sampled instead of a small number of muscle fibers or muscles. This is particular important due to monitoring of gene transfer efficacy and expression in clinical settings currently requires invasive techniques. This can be problematic in subjects with extensive muscle damage and necrosis such as children with Duchene muscular dystrophy and LGMD.
Augmenting angiogenesis and perfusion in skeletal muscle. We are using MRI and MRS methods to measure the effectiveness of gene mediated collateral formation as a potential therapy for chronically ischemic muscle. We have found that sufficient signal-to-noise and spatial resolution is achievable at field strengths greater than 4T to examine heterogeneity in muscle perfusion. This work has been extended to study whether the lack of NOS in dystrophic muscle is associated with poor muscle perfusion and exercise ischemia in the murine and human muscular dystrophies. Animal models are used to test different molecule weight contrast agents as to the appropriateness for blood perfusion measures as confirmed by ex vivo microsphere methods.
Monitoring of transgene delivery and cell migration
Common techniques to monitor muscle stem-cell transplants typically rely on ex vivo genetic modification to allow expression of reporter genes. The statement of specific reporter genes allows for graft identification during post-mortem analysis. Using these conventional techniques, however, even simple and practical questions are difficult and labor-intensive to answer. For example, to determine the distribution of the graft, the entire organ must be harvested and sectioned, followed by identification of individual cells by conventional microscopy. More complex questions, such as cell homing, identification of migration events, and engraftment rates, may be impossible to accurately and quantitatively address using conventional microscopy. Novel techniques that allow non-invasive, continuous imaging of stem cell transplants have recently been proposed and evaluated in a limited number of cell delivery models. We have previously found that magnetic resonance (MR) methods can be used to noninvasively monitor the widespread expression of a MR marker gene (arginine kinase) and therapeutic genes for the muscular dystrophies and cardiomyopathies. On the other hand, cell-based therapies represent a greater challenge for noninvasive monitoring due to the variability and limited stem cell incorporation. We found that MR imaging (MRI) has the ability to provide extremely sensitive, high-resolution images of magnetically labeled cells in both skeletal and cardiac muscle. As such, the application of MRI of stem cell investigations is of great importance to enhance the development of stem cell therapies. We have evaluated the application of magnetically labeled stem cells for the noninvasive monitoring of therapeutic stem cell transplants in murine dystrophies, senescent muscle, and cardiac dysfunction. Additional studies have revealed that MRI can be implemented to track the migration of a small number of labeled cells following arterial delivery to regions of targeted gene expression and tissue damage. These MR labeling strategies are not limited to muscle applications but can be readily extended to the noninvasive cell tracking in the brain, liver, and retina in both small animal models and humans.
Currently offering post-doctoral positions in MR cell and molecular imaging. If interested please send a current biosketch and research statement to email@example.com
Sites related to our research
- UF Muscle Physiology Lab: http://mpl.phhp.ufl.edu
- National High Field Magnet Lab (NHFML) Home Page: http://www.magnet.fsu.edu
- My profile at the NHFML website: click here
- MBI IMAGING FACILITY (AMRIS): http://www.mbi.ufl.edu/facilities/amris/
- Powell Gene Therapy Center: http://www.gtc.ufl.edu
- Program in Regenerative Medicine: http://stemcell.ufl.edu/Main_Site/gwalter/walter.html
Selected peer-reviewed publications
- Vandenborne, K., McCully, K., Kakihira, H., Prammer, M., Bolinger, L., Detre, J., De Meirleir, K., Walter, G., Chance, B., Leigh, J.S.: Metabolic heterogeneity in human calf muscle during maximal exercise. Proc Natl Acad Sci USA 88: 5714-5718, 1991.
- Goelman, G., Walter, G. and J.S. Leigh. Hadamard spectroscopic imaging technique as applied to study human calf muscles. Magn. Reson. Med., 25, 349-354, 1992.
- Mancini, D.M., Walter, G., Reichek, N., Lenkinski, R., Mccully, K., Mullen, J. and Wilson, J.R. Contribution of skeletal muscle atrophy to exercise intolerance and altered muscle metabolism in heart failure. Circulation, 85, 1364-1373, 1992.
- Vandenborne, K., Walter, G., Leigh, J.S., Goelman, G.: pH heterogeneity in localized spectra of single human muscles. Am J Physiol 265 (Cell Physiol 34): C1132-C1139, 1993.
- Vandenborne, K., Walter, G., Ploutz-Snyder, L., Staron, R., Fry, A., De Meirleir, K., Dudley, G., Leigh, J.S.: Energy rich phosphates in slow and fast human skeletal muscle. Am J Physiol (268): C869-C876, 1995.
- Walter, G., Vandenborne, K., McCully, K., Leigh, J.S.: Noninvasive measurement of phosphocreatine recovery kinetics in single muscles. Am J Physiol 272 (Cell Physiol 41): C525-534, 1997.
- Elliott, M.A., Walter, G.A., Gulish, H., Sadi, A.S., Lawson, D.D., Jaffe, W., Insko, E.K., Leigh, J.S., Vandenborne, K.: Volumetric measurement of human calf muscle from MRI. MAGMA 5: 93-98, 1997.
- Vandenborne, K., Elliot, M.A., Walter, G.A., Sadi, A.S., Okereke, E., Shaffer, M., Tahernia, D., Esterhai, J: Longitudinal study of skeletal muscle adaptations during immobilization and rehabilitation. Muscle Nerve 21: 1006-1012, 1998.
- Elliott, M.A., Walter, G.A., Swift, A., Vandenborne, K., Schotland, J.C., Leigh, J.S.: Spectral quantitation by principle-component analysis using complex singular value decomposition. Mag. Res. Med.,41:450-455, 1999.
- Walter, G., Vandenborne, K., Elliott, M., Leigh, J.S.: Non-invasive measurement of ATP synthesis rates in single human muscles. J Physiol (London), 519:901-910, 1999.
- Walter, G., Barton, E.and H.L. Sweeney, Noninvasive measurement of gene expression in muscle PNAS 97:5151-5155, 2000.
- Vandenborne, K., Walter, G., Ploutz-Snyder, L., Dudley, G., Elliott, M.A., De Meirleir, K., Leigh, J.S.: Relationship between muscle T2 relaxation properties and metabolic state: a combined localized 31P-spectroscopy and 1H-imaging study. Eur J Physiol, 82:76-82,2000.
- Shaffer M, Okereke E, Esterhai J, Elliott M, Walter GA, Yim S, Vandenborne K. The effects of immobilization on plantar flexion strength, endurance, and functional ability following an ankle fracture. Physical Therapy, 80(8), 769-181, 2000.
- Russ, D.W., Vandenborne, H.E., Walter, G.A., Elliott, M.E., and S. Binder-Macleod. Effects of stimulation frequency and force on fatigue and metabolism in human skeletal. J Appl Physiol 92: 1978-1986, 2002.
- Russ, D.W., Vandenborne, H.E., Walter, G.A., Elliott, M.E., and S. Binder-Macleod. Metabolic costs of isometric force generationand maintenance of human skeletal muscle. Am J Physiol Endocrinol Metab 282: E448-E457, 2002.
- Fraites, T J., Schleissing, MR, Shanely, RA, Walter,GA, Cloutier, DA, Zolotukhin,I, Pauly, DF, Raben, N, Plotz, PH, Powers,, SK, Kessler, PD and Barry J. Byrne. Correction of the enzymatic and functional deficit in a model of Pompe’s disease using adeno-associated virus vectors. Molecular Therapy 5(2):571-578, 2002.
- Walter, G., Cahill, KC, Feng, H., Douglas, T., Huard, J., Sweeney, H.L., J.W.M Bulte. Noninvasive monitoring of stem cell transfer for muscle disorders. Magn Reson Med Feb;51(2):273-7, 2004.
- White, L.J., McCoy, S.C., Castellano,V., Gutierrez, G., Stevens, J.E., GA Walter, and K Vandenborne. Resistance training improves strength and functional capacity in persons with multiple sclerosis. Mult Scler Dec;10(6):668-74, 2004.
- Stevens, J., Walter, G., Esterhai, J., Elliott, M., Shaffer, M., Yim, S., Vandenborne, K. Longitudinal study of skeletal muscle adaptations during immobilization and rehabilitation after ankle fracture. Med. Sci. Sports Exer., 36(10): 1695-1701, 2004.
- Cahill, KS, Gaidosh, G., Silver, X., Huard, J., Byrne, B.J., and G. Walter. Noninvasive monitoring and tracking of muscle stem cell transplants. Transplantion 78(11), pp. 1626-1633, 2004.
- Falcón, BL, Bourassa E., Stewart J., Katovich M.J., Walter G., Speth, R.C. Sumners, C. and M.K. Raizada Angiotensin II type 2 receptor gene transfer elicits cardioprotective effects in an angiotensin II infusion rat model of hypertension. Physiol Genomics;19(3):255-61, 2004.
- Cahill, KS, Germain, S., Byrne, BB and G. A Walter. Non-invasive analysis of myoblast transplants in rodent cardiac muscle. International Journal of Cardiovascular Imaging. 20(6):December 2004.
- Pathare NC, Walter, G.A., Stevens JE, Yang Z, Okereke E, Gibbs JD, Esterhai JL, Scarborough, JT, Gibbs, CP, Sweeney HL, and K Vandenborne. Changes in inorganic phosphate and force production in human skeletal muscle following cast immobilization. J Appl Physiol 98: 307-314, 2005.
- Frimel, T.N, Walter,G.A., Gibbs, J.D., Gaidosh, GS. and Vandenborne K. Noninvasive monitoring of muscle damage during reloading following limb disuse. Muscle Nerve 32(5):605-612, 2005
- Frimel, T.N, Kapadia, F., Gaidosh, GS. Li, Y., Walter, G.A., and Vandenborne K. A model of muscle atrophy using cast immobilization in mice. Muscle Nerve 32(5)672-674, 2005.
- Swadeshmukul Santra, Heesun Yang, Jessie T. Stanley, Paul H. Holloway, Brij M. Moudgil, Glenn Walter, and Robert A. Mericle, Rapid and effective labeling of brain tissue using TAT-conjugated CdS:Mn/ZnS quantum dots, Chemical Communications, Jul:7(25):3144-3146, 2005.
- Walter, G.,Bloy,D., Cordier, L, and H. Lee Sweeney. Noninvasive monitoring of gene correction in muscle Magn Reson Med. Dec;54(6):1369-76, 2005.
- Conlon TJ, Walter G, Owen R, Cossette T, Erger K, Gutierrez G, Goetzman E, Matern D, Vockley J, Flotte TR. Systemic correction of a fatty acid oxidation defect by intramuscular injectionof a recombinant adeno-associated virus vector. Hum Gene Ther. Jan;17(1):71-80, 2006.
- Liu M, Bose P, Walter GA, Anderson DK, Thompson FJ, Vandenborne K. Changes in muscle T2 relaxation properties following spinal cord injury and locomotor training. Eur J Appl Physiol. Apr 25, 2006.
- Prithvi K. Shah, Jennifer E. Stevens, Chris M. Gregory, Neeti C. Pathare, Arun Jayaraman, Scott C. Bickel, Mark Bowden, Andrea L. Behrman, Glenn A. Walter, Gary A. Dudley, and Krista Vandenborne. Lower extremity muscle cross-sectional area after incomplete spinal cord injury. Arch Phys Med Rehabil. Jun;87(6):772-8, 2006.
- Stevens, JE, Pathare, NC*, Tillman,SM, Scarborough, MT, Gibbs, P., Shah,P. Jayaraman,A*, Walter,GA, and Vandenborne K. Relative contributions of muscle activation and muscle size to plantarflexor torque during rehabilitation after immobilization. J Orthop Res Aug;24(8):1729-36, 2006.
- Pathare N, Vandenborne K, Liu M, Stevens JE, Li Y, Frimel TN, Walther GA. Alterations in inorganic phosphate in mouse hindlimb muscles during limb disuse. NMR Biomed. Feb;21(2):101-10, 2008.
- Aslanidi G, Kroutov V, Philipsberg G, Lamb K, Campbell-Thompson M, Walter GA, Kurenov S, Ignacio Aguirre J, Keller P, Hankenson K, Macdougald OA, Zolotukhin S. Ectopic expression of Wnt10b decreases adiposity and improves glucose homeostasis in obese rats. Am J Physiol Endocrinol Metab. Sep;293(3):E726-36, 2007.
- Pacak CA, Walter GA, Gaidosh G, Bryant N, Lewis MA, Germain S, Mah CS, Campbell KP, Byrne BJ. Long-term skeletal muscle protection after gene transfer in a mouse model of LGMD-2D. Mol Ther. Oct;15(10):1775-81, 2007.
- Chen YW, Gregory CM, Scarborough MT, Shi R, Walther GA, Vandenborne K. Transcriptional pathways associated with skeletal muscle disuse atrophy in humans. Physiol Genomics. Nov 14;31(3):510-20, 2007.
- Der Sarkissian S, Grobe JL, Yuan L, Narielwala DR, Walter GA, Katovich MJ, Raizada MK.Cardiac overexpression of angiotensin converting enzyme 2 protects the heart from ischemia-induced pathophysiology. Hypertension. Mar;51(3):712-8, 2008.
- Liu M, Bose P, Walter GA, Thompson FJ, Vandenborne K. A longitudinal study of skeletal muscle following spinal cord injury and locomotor training. Spinal Cord. Feb 1, 2008. [on line]
- Shah PK, Gregory CM, Stevens JE, Pathare NC, Jayaraman A, Behrman AL, Walter GA, Vandenborne K. Non-invasive assessment of lower extremity muscle composition after incomplete spinal cord injury. Spinal Cord. Mar 18, 2008. [on line].
- Beattie SG, Goetzman E, Conlon T, Germain S, Walter G, Campbell-Thompson M,Matern D, Vockley J, Flotte TR. Biochemical correction of short-chain Acyl-Coenzyme A Dehydrogenase deficiency after portal vein injection of rAAV8-SCAD. Hum Gene Ther. 2008 May 26.
- Sharma P, Brown SC, Bengtsson N, Zhang Q, Walter GA, Grobmyer SR, Santra S, Jiang H, Scott EW, Moudgil BM. Gold speckled multimodal nanoparticles for noninvasive bio-imaging. Chemistry of Materials (In Press).