Brittany K. Miller

Bio: Brittany K. Miller is an academic researcher from University of North Carolina at Chapel Hill. The author has contributed to research in topics: Duchenne muscular dystrophy & Pyrazinamide. The author has an hindex of 5, co-authored 7 publications receiving 218 citations. Previous affiliations of Brittany K. Miller include Children's National Medical Center.

VBP15, a novel anti-inflammatory and membrane-stabilizer, improves muscular dystrophy without side effects

Abstract: Absence of dystrophin makes skeletal muscle more susceptible to injury, resulting in breaches of the plasma membrane and chronic inflammation in Duchenne muscular dystrophy (DMD). Current management by glucocorticoids has unclear molecular benefits and harsh side effects. It is uncertain whether therapies that avoid hormonal stunting of growth and development, and/or immunosuppression, would be more or less beneficial. Here, we discover an oral drug with mechanisms that provide efficacy through anti-inflammatory signaling and membrane-stabilizing pathways, independent of hormonal or immunosuppressive effects. We find VBP15 protects and promotes efficient repair of skeletal muscle cells upon laser injury, in opposition to prednisolone. Potent inhibition of NF-κB is mediated through protein interactions of the glucocorticoid receptor, however VBP15 shows significantly reduced hormonal receptor transcriptional activity. The translation of these drug mechanisms into DMD model mice improves muscle strength, live-imaging and pathology through both preventive and post-onset intervention regimens. These data demonstrate successful improvement of dystrophy independent of hormonal, growth, or immunosuppressive effects, indicating VBP15 merits clinical investigation for DMD and would benefit other chronic inflammatory diseases.

Long-term treatment with naproxcinod significantly improves skeletal and cardiac disease phenotype in the mdx mouse model of dystrophy

Abstract: In Duchenne muscular dystrophy (DMD) patients and the mouse model of DMD, mdx, dystrophin deficiency causes a decrease and mislocalization of muscle-specific neuronal nitric oxide synthase (nNOSμ), leading to functional impairments. Previous studies have shown that nitric oxide (NO) donation associated with anti-inflammatory action has beneficial effects in dystrophic mouse models. In this study, we have systematically investigated the effects of naproxcinod, an NO-donating naproxen derivative, on the skeletal and cardiac disease phenotype in mdx mice. Four-week-old mdx and C57BL/10 mice were treated with four different concentrations (0, 10, 21 and 41 mg/kg) of naproxcinod and 0.9 mg/kg of prednisolone in their food for 9 months. All mice were subjected to twice-weekly treadmill sessions, and functional and behavioral parameters were measured at 3, 6 and 9 months of treatment. In addition, we evaluated in vitro force contraction, optical imaging of inflammation, echocardiography and blood pressure (BP) at the 9-month endpoint prior to sacrifice. We found that naproxcinod treatment at 21 mg/kg resulted in significant improvement in hindlimb grip strength and a 30% decrease in inflammation in the fore- and hindlimbs of mdx mice. Furthermore, we found significant improvement in heart function, as evidenced by improved fraction shortening, ejection fraction and systolic BP. In addition, the long-term detrimental effects of prednisolone typically seen in mdx skeletal and heart function were not observed at the effective dose of naproxcinod. In conclusion, our results indicate that naproxcinod has significant potential as a safe therapeutic option for the treatment of muscular dystrophies.

An orphaned Mce‐associated membrane protein of Mycobacterium tuberculosis is a virulence factor that stabilizes Mce transporters

Abstract: Mycobacterium tuberculosis proteins that are exported out of the bacterial cytoplasm are ideally positioned to be virulence factors; however, the functions of individual exported proteins remain largely unknown. Previous studies identified Rv0199 as an exported membrane protein of unknown function. Here, we characterized the role of Rv0199 in M. tuberculosis virulence using an aerosol model of murine infection. Rv0199 appears to be a member of a Mce-associated membrane (Mam) protein family leading us to rename it OmamA, for orphaned Mam protein A. Consistent with a role in Mce transport, we showed OmamA is required for cholesterol import, which is a Mce4-dependent process. We further demonstrated a function for OmamA in stabilizing protein components of the Mce1 transporter complex. These results indicate a function of OmamA in multiple Mce transporters and one that may be analogous to the role of VirB8 in stabilizing Type IV secretion systems, as structural similarities between Mam proteins and VirB8 proteins are predicted by the Phyre 2 program. In this study, we provide functional information about OmamA and shed light on the function of Mam family proteins in Mce transporters.

The Sec Pathways and Exportomes of Mycobacterium tuberculosis.

Abstract: All bacteria utilize pathways to export proteins from the cytoplasm to the bacterial cell envelope or extracellular space. Many exported proteins function in essential physiological processes or in virulence. Consequently, the responsible protein export pathways are commonly essential and/or are important for pathogenesis. The general Sec protein export pathway is conserved and essential in all bacteria, and it is responsible for most protein export. The energy for Sec export is provided by the SecA ATPase. Mycobacteria and some Gram-positive bacteria have two SecA paralogs: SecA1 and SecA2. SecA1 is essential and works with the canonical Sec pathway to perform the bulk of protein export. The nonessential SecA2 exports a smaller subset of proteins and is required for the virulence of pathogens such as Mycobacterium tuberculosis. In this article, we review our current understanding of the mechanism of the SecA1 and SecA2 export pathways and discuss some of their better-studied exported substrates. We focus on proteins with established functions in M. tuberculosis pathogenesis and proteins that suggest potential roles for SecA1 and SecA2 in M. tuberculosis dormancy.

Structural Similarities and Differences between Two Functionally Distinct SecA Proteins, Mycobacterium tuberculosis SecA1 and SecA2.

Abstract: While SecA is the ATPase component of the major bacterial secretory (Sec) system, mycobacteria and some Gram-positive pathogens have a second paralog, SecA2. In bacteria with two SecA paralogs, each SecA is functionally distinct, and they cannot compensate for one another. Compared to SecA1, SecA2 exports a distinct and smaller set of substrates, some of which have roles in virulence. In the mycobacterial system, some SecA2-dependent substrates lack a signal peptide, while others contain a signal peptide but possess features in the mature protein that necessitate a role for SecA2 in their export. It is unclear how SecA2 functions in protein export, and one open question is whether SecA2 works with the canonical SecYEG channel to export proteins. In this study, we report the structure of Mycobacterium tuberculosis SecA2 (MtbSecA2), which is the first structure of any SecA2 protein. A high level of structural similarity is observed between SecA2 and SecA1. The major structural difference is the absence of the helical wing domain, which is likely to play a role in how MtbSecA2 recognizes its unique substrates. Importantly, structural features critical to the interaction between SecA1 and SecYEG are preserved in SecA2. Furthermore, suppressor mutations of a dominant-negative secA2 mutant map to the surface of SecA2 and help identify functional regions of SecA2 that may promote interactions with SecYEG or the translocating polypeptide substrate. These results support a model in which the mycobacterial SecA2 works with SecYEG. Importance SecA2 is a paralog of SecA1, which is the ATPase of the canonical bacterial Sec secretion system. SecA2 has a nonredundant function with SecA1, and SecA2 exports a distinct and smaller set of substrates than SecA1. This work reports the crystal structure of SecA2 of Mycobacterium tuberculosis (the first SecA2 structure reported for any organism). Many of the structural features of SecA1 are conserved in the SecA2 structure, including putative contacts with the SecYEG channel. Several structural differences are also identified that could relate to the unique function and selectivity of SecA2. Suppressor mutations of a secA2 mutant map to the surface of SecA2 and help identify functional regions of SecA2 that may promote interactions with SecYEG.

Duchenne muscular dystrophy.

Abstract: Duchenne muscular dystrophy is a severe, progressive, muscle-wasting disease that leads to difficulties with movement and, eventually, to the need for assisted ventilation and premature death. The disease is caused by mutations in DMD (encoding dystrophin) that abolish the production of dystrophin in muscle. Muscles without dystrophin are more sensitive to damage, resulting in progressive loss of muscle tissue and function, in addition to cardiomyopathy. Recent studies have greatly deepened our understanding of the primary and secondary pathogenetic mechanisms. Guidelines for the multidisciplinary care for Duchenne muscular dystrophy that address obtaining a genetic diagnosis and managing the various aspects of the disease have been established. In addition, a number of therapies that aim to restore the missing dystrophin protein or address secondary pathology have received regulatory approval and many others are in clinical development.

The Pathogenesis and Therapy of Muscular Dystrophies

Abstract: Current molecular genomic approaches to human genetic disorders have led to an explosion in the identification of the genes and their encoded proteins responsible for these disorders. The identification of the gene altered by mutations in Duchenne and Becker muscular dystrophy was one of the earliest examples of this paradigm. The nearly 30 years of research partly outlined here exemplifies the road that similar current gene discovery protocols will be expected to travel, albeit much more rapidly owing to improved diagnosis of genetic disorders and an understanding of the spectrum of mutations thought to cause them. The identification of the protein dystrophin has led to a new understanding of the muscle cell membrane and the proteins involved in membrane stability, as well as new candidate genes for additional forms of muscular dystrophy. Animal models identified with naturally occurring mutations and developed by genetic manipulation have furthered the understanding of disease progression and underlying pathology. The biochemistry and molecular analysis of patient samples have led to the different dystrophin-dependent and -independent therapies that are currently close to or in human clinical trials. The lessons learned from decades of research on dystrophin have benefited the field of human genetics.

Large-scale serum protein biomarker discovery in Duchenne muscular dystrophy

Abstract: Serum biomarkers in Duchenne muscular dystrophy (DMD) may provide deeper insights into disease pathogenesis, suggest new therapeutic approaches, serve as acute read-outs of drug effects, and be useful as surrogate outcome measures to predict later clinical benefit In this study a large-scale biomarker discovery was performed on serum samples from patients with DMD and age-matched healthy volunteers using a modified aptamer-based proteomics technology Levels of 1,125 proteins were quantified in serum samples from two independent DMD cohorts: cohort 1 (The Parent Project Muscular Dystrophy–Cincinnati Children’s Hospital Medical Center), 42 patients with DMD and 28 age-matched normal volunteers; and cohort 2 (The Cooperative International Neuromuscular Research Group, Duchenne Natural History Study), 51 patients with DMD and 17 age-matched normal volunteers Forty-four proteins showed significant differences that were consistent in both cohorts when comparing DMD patients and healthy volunteers at a 1% false-discovery rate, a large number of significant protein changes for such a small study These biomarkers can be classified by known cellular processes and by age-dependent changes in protein concentration Our findings demonstrate both the utility of this unbiased biomarker discovery approach and suggest potential new diagnostic and therapeutic avenues for ameliorating the burden of DMD and, we hope, other rare and devastating diseases

Immune-mediated pathology in Duchenne muscular dystrophy

Abstract: Immunological and inflammatory processes downstream of dystrophin deficiency as well as metabolic abnormalities, defective autophagy, and loss of regenerative capacity all contribute to muscle pathology in Duchenne muscular dystrophy (DMD). These downstream cascades offer potential avenues for pharmacological intervention. Modulating the inflammatory response and inducing immunological tolerance to de novo dystrophin expression will be critical to the success of dystrophin-replacement therapies. This Review focuses on the role of the inflammatory response in DMD pathogenesis and opportunities for clinical intervention.

Duchenne Muscular Dystrophy: From Diagnosis to Therapy

Abstract: Duchenne muscular dystrophy (DMD) is an X-linked inherited neuromuscular disorder due to mutations in the dystrophin gene. It is characterized by progressive muscle weakness and wasting due to the absence of dystrophin protein that causes degeneration of skeletal and cardiac muscle. The molecular diagnostic of DMD involves a deletions/duplications analysis performed by quantitative technique such as microarray-based comparative genomic hybridization (array-CGH), Multiple Ligation Probe Assay MLPA. Since traditional methods for detection of point mutations and other sequence variants require high cost and are time consuming, especially for a large gene like dystrophin, the use of next-generation sequencing (NGS) has become a useful tool available for clinical diagnosis. The dystrophin gene is large and finely regulated in terms of tissue expression, and RNA processing and editing includes a variety of fine tuned processes. At present, there are no effective treatments and the steroids are the only fully approved drugs used in DMD therapy able to slow disease progression. In the last years, an increasing variety of strategies have been studied as a possible therapeutic approach aimed to restore dystrophin production and to preserve muscle mass, ameliorating the DMD phenotype. RNA is the most studied target for the development of clinical strategies and Antisense Oligonucleotides (AONs) are the most used molecules for RNA modulation. The identification of delivery system to enhance the efficacy and to reduce the toxicity of AON is the main purpose in this area and nanomaterials are a very promising model as DNA/RNA molecules vectors. Dystrophinopathies therefore represent a pivotal field of investigation, which has opened novel avenues in molecular biology, medical genetics and novel therapeutic options.