Krista Vandenborne - US grants

musculoskeletal system; enzymes; biomedical resource;

musculoskeletal system; technology /technique development; magnetic resonance imaging; model design /development; enzymes; computers; biomedical resource;

musculoskeletal system; technology /technique development; magnetic resonance imaging; enzymes; computers; biomedical resource;

musculoskeletal system; epidemiology; magnetic resonance imaging; nervous system; rehabilitation; carbohydrates; biomedical resource;

musculoskeletal system; technology /technique development; magnetic resonance imaging; enzymes; computers; biomedical resource;

disease /disorder etiology; muscle strength; muscle function; chronic fatigue syndrome; veterans; enzyme deficiency; muscle metabolism; AMP deaminase; clinical research; questionnaires; nuclear magnetic resonance spectroscopy; human subject; electromyography;

The major goal of this study is to implement innovative, noninvasive imaging techniques to study the mechanisms involved in the loss and recovery of muscle strength and overall functional ability after limb disuse. We will focus our investigation on a number of intrinsic properties of skeletal muscle. Particular attention will be focused on the muscle contractile area, muscle specific force, and the inorganic phosphate concentration. For this purpose, Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy measurements in combination with force measurements will be performed on skeletal muscle during the course of cast immobilization and the subsequent recovery, in both patients and animals. The loss of muscle strength with limb disuse has been related to a decrease in muscle contractile area as well as a decrease in muscle specific force (force/contractile area). We hypothesize that an increase in the basal inorganic phosphate (Pi) content contributes to the decline in muscle specific force after limb disuse. Conversely, we hypothesize that the recovery of muscle specific force is associated with a decrease in basal inorganic phosphate content. This hypothesis is tested using two approaches: a) We will determine the relationship between muscle specific force and in vivo basal inorganic phosphate content during the course of cast immobilization, reloading and the subsequent recovery and b) using skinned muscle fibers we will determine the direct effect of the inorganic phosphate concentration on the force output per fiber diameter. Skinned fiber studies will be performed on experimental muscles (casted, reloaded and recovered) at control Pi concentrations and elevated Pi concentrations, as determined in vivo by 31P-spectroscopy. However the ultimate goal of this study is to determine how in vivo determined pathophysiological changes affect the overall functional ability. For this purpose, the ability to perform simple functional tasks such as stairclimbing, walking and one legged heel rises will be assessed during the experimental timecourse. We anticipate that the investigation of muscle dysfunction from a cellular to a whole body level as proposed in this study will help provide the understanding necessary for the development of preventive and therapeutic interventions designed to minimize the loss of functional ability that accompanies limb disuse.

9. Gene expression vector- New investigator. Normal aging is associated with a loss of muscle mass and strength, and a decrease in functional ability. During periods of forced bed rest, immobilization or non weight-bearing, elderly individuals often fall victim to an even further decline in muscle function, with devastating consequences for the individual's functional ability and overall well-being. As such the objective of this study is to investigate the potential of virus mediated gene transfer of IGF-1 to guard senescent from secondary atrophy caused by disuse or forced inactivity. Specifically, we hypothesize that in both young adult and elderly muscle virus mediated gene transfer the IGF-1 ameliorates the loss of muscle strength and muscle size induced by immobilization, but not the shift in fiber type distribution. In addition, we hypothesize that virus-mediated gene transfer of IGF-1 expedites the recovery in muscle size and strength following immobilization-induced atrophy. For this purpose the left or right hindlimb (randomized) muscles of both young adult (3 months) and elderly mice (21 months) will be infected with a recombinant adeno-associated virus vector for IGF-1.2 months post-injection, both hindlimbs (injected and control) of the animals will be immobilized in a plaster cast for a period of 4 weeks. At day 28 the cast will be removed and metabolic, morphological and functional characteristics of injected and contralateral control muscles will be determined. Measurements will include muscle cross-sectional area, muscle weight, in vitro force generation and fatiguability, fiber cross- sectional area, fiber type composition, and in vitro oxidative and glycolytic enzyme activity. In order to study the effect of IGF-1 on the recovery of muscle function following immobilization the same measurements will be repeated in a cohort of mice, 1 month and 2 months post-immobilization. We anticipate that the ability to locally manipulate muscle adaptation and growth in the elderly population, especially in the face of secondary atrophy, will be of great clinical importance.

Patients with mammographically visible or palpable findings underwent T1- and fat-saturated T2 weighted spin-echo and contrast agent-enhanced fat-saturated gradient-echo MR imaging. Patients underwent subsequent excisional biopsy for histopathologic confirmation. An interpretational model was constructed using 98 cases and was tested prospectively using 94 different cases. Sensitivity, specificity, predictive values, and receiver operating characteristics curves were computed for all models. Individual features with highly predictive values were MR visibility, enhancement degree and pattern, focal mass border characteristics, and focal mass internal septations. The model was built in a stepwise fashion to result in a decision tree in which individual architectural features occupied decision nodes. The diagnostic performance of all models was assessed and comprised assessment of the performance of each model's individual terminal nodes (positive predictive value PPV and negative predictive value NPV), as well as performance of each model as a whole. Perhaps the most valuable aspect of our interpretation model is its ability to identify hierarchical combinations of features with high NPV's for malignancy. We were interested in individual features and feature combinations with a greater than 95% likelihood of being benign. If similar results are seen in prospective validation studies performed in other clinical settings, biopsy may not be necessary in patients with findings that fall into these five feature categories. In addition, the categories of ductal and regional enhancement, in particular, could benefit from further subcategorization. Thus far in our investigation, ductal enhancement has been sufficiently highly associated with malignancy, that if a case shows ductal enhancement the case is considered suspicious for malignancy. A larger sample size will allow the construction of an even more detailed model.

Muscle weakness is a common clinical phenomina observed following bed rest, surgery, cast immobilization and injury or disease. The consequences of loss of muscle strength are far reaching and include decrease of motor control and overall fitness, development of functional limitations and impairment, and long term disability. As such, the objective of this study is to investigate the potential of virus-mediated gene transfer of IGF-1 to guard skeletal muscle from the deleterious impact of disuse or forced inactivity and to accelerate the subsequent recovery in muscle size and strength. For this purpose the left or right hindlimb (randomized) muscles of young adult mice will be injected with a recombinant adeno-associated virus vector for IGF-1. 3 months post-injection, both hindlimbs (injected and control) of the animals will be immobilized in a plaster cast for a period of 2 weeks. After removal of the cast the animals are allowed to reambulate and resume their normal cage activity. Cage restricted levels of weight-bearing activity have been shown to be sufficient to induce muscle regeneration and hypertrophy. Morphometric and functional measurements will be performed bilaterally (injected and control limb) at baseline, 3 months post-injection, following 2 weeks of cast immobilization, during reloading and at several time points during reambulation (2, 4 and 10 weeks). Morphological measures will include fiber cross- sectional area and fiber number, wet weight and protein content. Functional measures (twitch and tetanic force) will be performed in vitro on superfused muscles. The secondary objective of this study is to elucidate the mechanisms by which IGF-1 overexpression modulates muscle size and function under varying loading/activity conditions. For this purpose we will measure IGF-1 peptide levels, in vivo protein synthesis and degradation rates, and markers of muscle regeneration and satellite cell proliferation. We anticipate that the ability to locally manipulate muscle regeneration and hypertrophy during disuse and subsequent rehabilitation will be of great clinical importance. In addition, we anticipate that this study will help elucidate the role of IGF-1 in the regulation of muscle size under varying loading/activation conditions.

DESCRIPTION (provided by applicant): Across the nation there is a growing need for well-trained scientists and clinicians with a commitment to rehabilitation research. The goal of this application is to develop a unique interdisciplinary pre-doctoral training program in rehabilitation and neuromuscular plasticity. This program is unique in that it emphasizes the interaction and joint training of medical rehabilitation clinicians and basic scientists with a common interest in translational research in neuromuscular plasticity. Trainees are selected from a pool of outstanding students with diverse backgrounds and are admitted by one of three graduate programs: Interdisciplinary Biomedical Sciences, Rehabilitation Sciences, or Health and Human Performance. In order to maximize the cross-fertilization, each trainee will have dual advisors: a medical rehabilitation clinician and a basic scientist. The program faculty members have been selected in terms of their suitability to fill either one or both of these roles. This innovative program, coordinated by the Department of Physical Therapy, focuses on the following central themes (1) characterization of pathophysiology of central nervous system damage and neural regeneration during rehabilitation; (2) characterization of muscular adaptations, motor dysfunction and impairment during CNS injury and rehabilitation; and (3) interaction between neural and muscular adaptations following CNS injury and during rehabilitation. The training program is a well-defined, closely mentored program that includes required and elective courses, laboratory research, seminars, journal clubs, oral presentations and a yearly retreat. An administrative structure has been devised which assures optimal recruitment and selection of trainees, oversight of individual training programs, and overall program evaluation. The research facilities that are available for this training program are extensive and state of the art. In addition, the trainees have access to a highly qualified technical staff to learn clinical and experimental techniques and procedures. This training program in rehabilitation and neuromuscular plasticity will provide the interdisciplinary environment that is fundamental to the advancement of rehabilitation research and will uniquely prepare trainees for translational research in neuromuscular plasticity.

DESCRIPTION (provided by applicant): Muscle atrophy and weakness secondary to disuse are common clinical phenomena, which can significantly impact activities of daily living and present a major challenge in rehabilitation. Rehabilitation programs designed to maximize strength gains may not be optimal, and the speed and extent of recovery is highly variable between individuals. We will identify the molecular (transcriptional) signatures associated with muscle remodeling in response to rehabilitation in a patient cohort. The key hypothesis of this proposal is that the rate and extent of functional recovery during rehabilitation following limb disuse correlates with the extent of induction of four remodeling signatures eccentric/damage, TGFbeta/MAPK, atrophy and aerobic conditioning) previously identified by this investigative team. 60 patients with a closed malleolus fracture, treated conservatively using a short leg cast for a period of 6 weeks will be recruited. Following cast-immobilization, subjects will be enrolled in a standardized 6-week rehabilitation program (3 sessions/week) focusing on progressive resistance training of the ankle plantar flexor muscles. The phenotypic response (Aim 1) to cast-immobilization and rehabilitation will be assessed in all individuals using isokinetic testing, magnetic resonance imaging and functional assessment tests. Phenotypic measurements will be performed before, during and immediately after the rehabilitation intervention. Ankle plantar flexor muscle size and strength measurements will also be performed on the uninvolved limb (serves as a control) at 6 months post-immobilization. In Aim 2, four longitudinal biopsies will be taken from the medial gastrocnemius of each individual and expression profiled over the entire human genome (U133A/B). The first 30 individuals will be used as the data generation "test set" (years 1-3), and the second 30 individuals as a "validation set" (years 3-5). In Aim 3, we will determine the correlation between the phenotypes defined in Aim 1 (percentage change in size, muscle strength, functional performance), and the "relative induction/repression" of the four remodeling signatures (eccentric/damage, TGFbeta/MAPK, muscle atrophy and aerobic conditioning). The development of effective therapeutic interventions targeting restoration of muscle function necessitates an in-depth understanding of the cellular and molecular mechanisms mediating muscle atrophy and subsequent repair. We anticipate that this study will provide essential feedback for the design and development of effective, individualized, rehabilitation interventions.

ABSTRACT NOT PROVIDED

[unreadable] DESCRIPTION (provided by applicant): The Interdisciplinary Training Program in Rehabilitation and Neuromuscular Plasticity was initiated in 2003 to help build a critical mass of well-trained scientists prepared to conduct innovative rehabilitation research. This pre-doctoral training program is unique in that it emphasizes the interaction and joint training of rehabilitation clinicians and basic scientists with a common interest in translational research in neuromuscular plasticity. Trainees are selected from a pool of outstanding students with diverse backgrounds and are admitted by one of three graduate programs: Interdisciplinary Biomedical Sciences, Rehabilitation Sciences or Health and Human Performance. The program capitalizes on several existing strengths at the University of Florida including a cadre of well established rehabilitation investigators, outstanding research facilities and interdisciplinary centers, three Rehabilitation Centers of Excellence, and a newly funded K12 Rehabilitation Research Career Development Program. The Neuromuscular Plasticity Training program (NMPT) is specifically designed to provide predoctoral trainees with the foundation and skills needed to become independent investigators and future leaders in rehabilitation. Upon entering the program, each trainee prepares an individualized career development plan under the guidance of an experienced Faculty Mentor and Translational Research Co- Advisor. The individualized plan consists of a structured didactic program, specialized courses, journal clubs and seminars, laboratory research and multiple scientific dissemination experiences. Trainees learn cutting edge research methodologies and acquire extensive research experience. Most importantly, they generate, analyze, present and publish research data. In addition to the close mentorship provided by the faculty mentor and translational research co-advisor, the trainees benefit from close interactions with clinical and basic science faculty participating in established Collaborative Translational Research Partnerships. The University of Florida Neuromuscular Plasticity Training Program provides the interdisciplinary training environment that is fundamental to the advancement of rehabilitation research and will uniquely prepare trainees for translational research in neuromuscular plasticity and rehabilitation. To ensure that the program meets its short- and long-term objectives a carefully designed review process will be implemented. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): MR monitoring of PTC124 treatment in DMD. This application addresses broad challenge area (03) Biomarkers Discovery and Validation and Specific Challenge Topic;03-AR 104: Imaging Biomarkers. DMD is one of the most devastating genetically linked neuromuscular diseases and is characterized by the absence of dystrophin, resulting in progressive muscle weakness, loss of walking ability and premature death. Despite the poor prognosis for patients with muscular dystrophy, therapeutic interventions have been lacking, and outcome measures for clinical trials have been limited to measures of muscle function and quality of life, serum biomarkers of muscle breakdown and invasive muscle biopsies. Additional noninvasive biomarkers that are sensitive to changes in muscle structure and composition are needed to facilitate the rapid translation of promising new interventions from preclinical studies to clinical trials. Therefore, the objective of this study is to validate the potential of magnetic resonance imaging (MRI) and spectroscopy (MRS) to monitor disease progression and the response to therapeutic interventions in children with DMD. The proposed study capitalizes on the recently initiated PTC124 phase 2a extension study, which involves the long-term administration (96 weeks) of PTC124, a novel stop codon suppression drug. Up to 15% of boys with DMD fail to make dystrophin because of a point mutation that creates a premature stop codon in the dystrophin mRNA. Stop codon suppression drugs, such as PTC124, allow the stop codon to be ignored and the entire dystrophin to be translated. Phase 1 and 2a testing have shown that orally bioavailable PTC124 is well tolerated, induces partial restoration of full-length dystrophin production and reduces muscle fragility in both mdx mice and boys with nonsense-mutation-mediated DMD. In the proposed study we will enroll 20 ambulatory boys participating in the phase 2a extension study to determine the ability of MRI/MRS to monitor the short and long term effect of PTC124 treatment on skeletal muscle. Magnetic resonance measurements of muscle damage/inflammation, muscle contractile tissue and intramuscular lipid accumulation will be performed in the lower extremity muscles prior to, and at multiple time points following initiation of PTC124 treatment. A subgroup of boys (n=20) not currently treated with PTC124 will be tested at the same time points and serve as controls. Ultimately, imaging data will be correlated with functional and histological outcome measures of disease progression/regression. This study provides an unprecedented opportunity to validate the potential of MRI/MRS to monitor the efficacy of therapeutic interventions targeting the restoration of dystrophin production in boys with DMD. We anticipate that the MR techniques developed and validated in this proposal will be suitable for clinical trials in a wide range of muscular dystrophies. The University of Florida and the University of Pennsylvania contribute substantially to the local and regional economy. In 2008, UF created 2,525 jobs and recent studies have shown that UF contributes nearly $6 billion annually to Florida's economy. The university employs about 34,000 people directly on its main campus and via UF organizations, such as the Institute of Food and Agricultural Sciences, is responsible for the creation of 74,894 jobs statewide. Penn Medicine created about 37,000 jobs and $5.4 billion in regional economic activity in 2008, with the area's highly trained workforce producing more than 24,600 applications for just 840 open Penn staff research positions. The current proposal will create or retain at least 14 jobs across two different states and all the infrastructure is in place to immediately initiate the project. Public Health Relevance: The goal of this project is to develop a way to observe whether or not new therapies are effective in correcting the disease process in muscles of boys with Duchenne muscular dystrophy (DMD) without the need to take muscle biopsies. To date, the only relatively noninvasive method of monitoring the disease process is unreliable and measures blood levels of creatine kinase. We have evidence in mouse models of both DMD and limb girdle muscular dystrophy, that magnetic resonance imaging can be used to track disease progression and monitor the efficacy of therapeutic interventions. We will extend our past mouse studies to boys who are participating in the Phase 2a clinical trial of PTC124, a promising new drug for DMD boys with premature stop codons. The availability of a reliable, nondestructive monitoring method that can be routinely and repeatedly implemented in patients will greatly benefit clinical trials in muscle diseases.

The long-range of this project is to develop novel therapeutic strategies that ameliorate muscle atrophy and accelerate muscle rehabilitation following pathological conditions such as spinal cord injury. This application is consistent with the vision of the Christopher and Dana Reeve Paralysis Act (CDRPA) which promotes the interaction of scientists conducting similar work to further enhance understanding and expedite the search for effective treatment interventions for millions of Americans living with paralysis. "The CDRPA encourages coordination of research to prevent redundancies and hopefully hasten discovery of better treatments and cures and, as importantly, to improve the daily lives today for those living with paralysis". The proposed application presents a unique collaboration between a group of productive scientists with diverse, yet complimentary expertise and a common interest in the recovery of muscle and motor function. This team of national experts explores a new area of research focusing on complimentary treatment strategies utilizing pharmacological/molecular therapies modulating muscle growth in conjunction with emerging rehabilitation interventions. The specific objectives of this 2 year application are: 1) To identify novel pharmacological strategies to ameliorate muscle atrophy induced by disuse/unloading and promote muscle recovery;2) To validate a new animal model of incomplete spinal cord injury for the assessment of rehabilitation strategies. This Project will provide important preclinical data in an area of rapid pharmacological development and will set the stage for a more clinical relevant model of spinal cord injury. The drugs that are targeted are either approved for human use or they are in clinical development and will allow rapid translation to animal models. This proposal provides some unique opportunities and presents an important step forward in the translation towards human trials. The results of the individual studies will also make important new contributions to the science base of muscle rehabilitation and spinal cord injury.

DESCRIPTION (provided by applicant): The overall objective of this proposal is to validate the potential of noninvasive magnetic resonance imaging (MRI) and spectroscopy (MRS) to monitor disease progression and to serve as a surrogate outcome measure for clinical trials in Duchenne muscular dystrophy (DMD). DMD is one of the most devastating genetically linked neuromuscular diseases and is characterized by the absence of dystrophin, resulting in progressive muscle weakness, loss of walking ability and premature death. Despite the poor prognosis for patients with muscular dystrophy, therapeutic interventions have been lacking, and outcome measures for clinical trials have been limited to measures of muscle function and quality of life, serum biomarkers of muscle breakdown and invasive muscle biopsies. Additional quantitative outcome measures that are noninvasive and sensitive to changes in muscle structure and composition are needed to facilitate the rapid translation of promising new interventions from preclinical studies to clinical trials. As such, this proposal targets the development and validation of magnetic resonance as a noninvasive biomarker of disease progression in muscular dystrophy. Using a multi-site research design this study will examine the intramuscular lipid content, muscle damage/inflammation and contractile area in the lower extremity muscles of 100 ambulatory boys with DMD and 50 healthy age matched boys using a combination of MRI and MRS technologies. In order to assess the sensitivity of each MR measure to disease progression, all boys with DMD will be re-evaluated in yearly or 6 month intervals. In addition, we will correlate changes in MR measures with standard measures of disease progression, such as loss in muscle strength and functional ability. Using MRI/MRS we will also examine the effect of initiating corticosteroid treatment on skeletal muscle characteristics and composition. Finally, we will deposit immortalized fibroblasts from carefully characterized DMD boys participating in this study in established tissue repositories. We anticipate that the MR techniques developed and validated in this proposal will be suitable for clinical trials in a wide range of muscular dystrophies and other neuromuscular diseases. In addition, MR characterization may serve as a powerful tool to further advance our understanding of the pathogenesis of muscular dystrophy and help guide the design of future trials.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Insulin-like growth factor I (IGF-I) is a potent myogenic factor that plays a critical role in muscle regeneration and muscle hypertrophy. The purpose of this study was to evaluate the effect of IGF-I overexpression on the recovery of muscle size and function during reloading/reambulation after a period of cast immobilization in predominantly fast twitch muscles. In addition, we investigated concomitant molecular responses in IGF-I receptor and binding proteins (BPs). Recombinant adeno-associated virus vector for IGF-I (rAAV-IGF-IA) was injected into the anterior compartment of one of the hindlimbs of young (3 wk) C57BL6 female mice. At 20 wk of age, both hindlimbs were cast immobilized in a shortened position for 2 wk to unload the tibialis anterior (TA) and extensor longus digitorum (EDL) muscles. The TA and EDL muscles were removed bilaterally after 2 wk of cast immobilization and after 1 and 3 wk of free cage reambulation.

? DESCRIPTION (provided by applicant): Over the last decade tremendous progress has been made in identifying therapeutic targets for Duchenne muscular dystrophy (DMD), a devastating progressive neuromuscular disease. However the design of clinical trials has been challenging, with sparse natural history data, a limited patient pool to recruit from, and few sensitive noninvasive outcome measures. Recent setbacks in several clinical trials have underscored the crucial need for transitional outcome measures that are sensitive across various stages of disease progression, including in non-ambulatory boys, and can reliably be implemented at multiple sites. In the initial funding cycle of this grant, we successfully implemented the first multicenter MR study in DMD and demonstrated that lower extremity quantitative MR measures (e.g. MRS fat fraction and MRI/MRS T2) are sensitive to disease progression in ambulatory boys, responsive to corticosteroid treatment, and reliable across multiple sites. In Aim 1 of this renewal application, we propose to extend the natural history MR biomarker study (iDMD) in the lower extremity muscles. Given the age distribution of the iDMD subject cohort (n=136; ages 7-18 years) we have an unprecedented opportunity to examine the sensitivity of quantitative MR measures (including 8-point Dixon and UTE) at different stages of disease progression, assess their value in predicting loss of ambulation, and obtain extremely valuable long term natural history data. In Aim 2, we will develop and validate upper extremity MR biomarkers and outcome measures in the same subject cohort. Specifically, we will perform a detailed MRI/MRS characterization of the forearm, upper arm and shoulder girdle. No prior MR imaging studies in DMD have been performed on upper extremity muscles that are essential for function, such as the biceps and deltoid, leaving a considerable gap in knowledge. MR measures in boys with DMD will be repeated at yearly intervals. In addition, we will correlate changes in MRI/MRS measures with loss in upper extremity function and strength. Finally, in Aim 3 we will build on our current infrastructure to establish a National Tissue and Data Resource, linking biological samples (fibroblasts, blood/urine) with genetic, detailed MRI/MRS, strength, functional, and demographic data collected in iDMD and making them available to the larger DMD community. This project addresses several critical barriers in therapeutic development and has the potential to significantly improve future clinical trials in DMD, as well as other neuromuscular diseases.

? DESCRIPTION (provided by applicant): Over the last decade tremendous progress has been made in identifying therapeutic targets for Duchenne muscular dystrophy (DMD), a devastating progressive neuromuscular disease. However the design of clinical trials has been challenging, with sparse natural history data, a limited patient pool to recruit from, and few sensitive noninvasive outcome measures. Recent setbacks in several clinical trials have underscored the crucial need for transitional outcome measures that are sensitive across various stages of disease progression, including in non-ambulatory boys, and can reliably be implemented at multiple sites. In the initial funding cycle of this grant, we successfully implemented the first multicenter MR study in DMD and demonstrated that lower extremity quantitative MR measures (e.g. MRS fat fraction and MRI/MRS T2) are sensitive to disease progression in ambulatory boys, responsive to corticosteroid treatment, and reliable across multiple sites. In Aim 1 of this renewal application, we propose to extend the natural history MR biomarker study (iDMD) in the lower extremity muscles. Given the age distribution of the iDMD subject cohort (n=136; ages 7-18 years) we have an unprecedented opportunity to examine the sensitivity of quantitative MR measures (including 8-point Dixon and UTE) at different stages of disease progression, assess their value in predicting loss of ambulation, and obtain extremely valuable long term natural history data. In Aim 2, we will develop and validate upper extremity MR biomarkers and outcome measures in the same subject cohort. Specifically, we will perform a detailed MRI/MRS characterization of the forearm, upper arm and shoulder girdle. No prior MR imaging studies in DMD have been performed on upper extremity muscles that are essential for function, such as the biceps and deltoid, leaving a considerable gap in knowledge. MR measures in boys with DMD will be repeated at yearly intervals. In addition, we will correlate changes in MRI/MRS measures with loss in upper extremity function and strength. Finally, in Aim 3 we will build on our current infrastructure to establish a National Tissue and Data Resource, linking biological samples (fibroblasts, blood/urine) with genetic, detailed MRI/MRS, strength, functional, and demographic data collected in iDMD and making them available to the larger DMD community. This project addresses several critical barriers in therapeutic development and has the potential to significantly improve future clinical trials in DMD, as well as other neuromuscular diseases.

Project Summary The proposed research is for the second competitive renewal of a long-term project to develop imaging biomarkers for Duchenne muscular dystrophy (DMD). Noninvasive outcome measures that provide unbiased patient assessments and reliably evaluate drug responses in clinical trials are essential to develop curative therapies for muscular dystrophies. In the previous funding cycles, we developed and validated lower extremity quantitative magnetic resonance imaging (qMR) biomarkers for ambulatory patients with DMD and modeled the disease trajectory in upper and lower extremity muscles. These qMR biomarkers are now used as primary and secondary endpoints in a number of international clinical trials. In this application one major objective is to extend our DMD work by focusing on older DMD patients with advanced disease progression. More than 50% of the DMD population is nonambulant, yet there are few outcome measures that permit their inclusion in clinical trials. We propose to 1) develop composite qMR biomarkers using quantitative whole-body imaging and 2) validate novel qMR biomarkers that assess respiratory muscle quality and can predict a decline in respiratory function, a major cause of death in muscular dystrophies. We hypothesize that composite qMR biomarkers?statistical constructs that optimally combine fat fraction measures in multiple muscles?are responsive across a wide range of motor abilities in DMD. We will leverage the large (older) DMD cohort currently enrolled in the ImagingDMD natural history study to test these two new qMR biomarkers for advanced disease stages. We also propose to extend our biomarker development work to patients with Becker muscular dystrophy (BMD), the milder allelic form of the disease. Breakthroughs in gene delivery and exon skipping technology have resulted in production of truncated dystrophin in variable amounts, effectively converting the DMD phenotype into BMD. These therapeutic developments are expected to change the landscape for the next generation of DMD patients. Thus, to assist future trials targeting dystrophin restoration, we will examine the critical relationship between dystrophin expression, mutation site and qMR biomarkers of muscle quality in BMD patients, setting the stage for informed in vivo monitoring of dystrophin rescue across muscles. This project addresses critical barriers in therapeutic development and provides the potential for a paradigm shift in clinical trial design in DBMD. In addition, this project will help inform future molecular based therapies and will address a missing piece in translational gene restoration in DMD. All natural history data are shared with the community.