Tag Archive for: dysferlin

Microscopic visual of a diseased muscle section

Gene therapy offers potential long-term treatment for limb-girdle muscular dystrophy 2B

Microscopic visual of a diseased muscle section

Microscopic visual of a diseased muscle section. Credit: Daniel Bittel.

Children’s National Hospital experts developed a new pre-clinical gene therapy for a rare disorder, known as limb-girdle muscular dystrophy (LGMD) 2B, that addresses the primary cellular deficit associated with this disease. Using a single injection of a low dose gene therapy vector, researchers restored the ability of injured muscle fibers to repair in a way that reduced muscle degeneration and enhanced the functioning of the diseased muscle. The treatment was safe, attenuated fibro-fatty muscle degeneration, and restored myofiber size and muscle strength, according to the study published in the Journal of Clinical Investigation.

With an incidence of less than 1 in 100,000, LGMD2B is a rare disorder caused by a genetic mutation in a large gene called dysferlin. This faulty gene leads to muscle weakness in the arms, legs, shoulder and pelvic girdle. Affected children and adults face trouble walking, climbing stairs and getting out of chairs. Individuals typically lose the ability to walk within years after the onset of symptoms, and often need assistance with everyday tasks such as showering, dressing and transferring.

This study described a new approach that avoids the need for packaging a large gene, like dysferlin, or giving a large vector dose to target the muscles, which are bottlenecks faced in ongoing gene therapy efforts aimed at muscular dystrophies.

“Currently, patients with LGMD2B have no gene or drug-based therapies available to them, and we are amongst the few centers developing therapeutic approaches for this disease,” said Jyoti K. Jaiswal, M.Sc. Ph.D., senior investigator of the Center for Genetic Medicine Research at Children’s National. “We are working to further enhance the efficacy of this approach and perform a longer-term safety and efficacy study to enable the clinical translation of this therapy.”

The genetic defect in dysferlin that is associated with LGMD2B causes the encoded protein to be truncated or degraded. This hinders the muscle fiber’s ability to heal, which is required for healthy muscles. In recessive genetic disorders, like LGMD2B, common pre-clinical gene therapy approaches usually target the mutated gene in the muscle, making them capable of producing the missing proteins.

“The large size of the gene mutated in this disease, and impediments in body-wide delivery of gene therapy vectors to reach all the muscles, pose significant challenges for developing gene therapies to treat this disease,” said Jaiswal.

To overcome these challenges, the researchers found another way to slow down the disease’s progression. The authors built upon their previous discovery that acid sphingomyelinase (hASM) protein is required to repair injured muscle cells. In this current work, the research team administered a single in vivo dose of an Adeno-associated virus (AAV) vector that produces a secreted version of hASM in the liver, which then was delivered to the muscles via blood circulation at a level determined to be efficacious in repairing LGMD2B patient’s injured muscle cells.

“Increased muscle degeneration necessitates greater muscle regeneration, and we found that improved repair of dysferlin-deficient myofibers by hASM-AAV reduces the need for regeneration, causing a 2-fold decrease in the number of regenerated myofibers,” said Daniel Bittel, D.P.T., PhD., research postdoctoral fellow of the Center for Genetic Medicine Research at Children’s National and a lead author of this study.

Sreetama Sen Chandra, Ph.D., who was a research postdoctoral fellow at Children’s National at the time of this study and served as co-lead author, also added that “these findings are also of interest to patients with Niemann-Pick disease type A since the pre-clinical model for this disease also manifests poor sarcolemma repair.”

Children’s National researchers of the Center for Genetic Medicine Research and the Rare Disease Institute (RDI) are constantly pursuing high-impact opportunities in pediatric genomic and precision medicine. Both centers combine its strengths with public and private partners, including industry, universities, federal agencies, start-up companies and academic medical centers. They also serve as an international referral site for rare disorders.

Gene therapy Schematic

Gene therapy Schematic. Credit: Daniel Bittel.

sketch of muscle cells

Losing muscle to fat: misdirected fate of a multipotent stem cell drives LGMD2B

Fibro/adipogenic precursors (FAPs) control the onset and severity of disease in limb-girdle muscular dystrophy type 2 (LGMD2B)

Fibro/adipogenic precursors (FAPs) control the onset and severity of disease in limb-girdle muscular dystrophy type 2 (LGMD2B). a) Healthy and/or pre-symptomatic LGMD2B muscle contains resident FAPs. b) After myofiber injury, inflammatory cells invade and trigger FAP proliferation. c) In symptomatic LGMD2B muscle, there is a gradual accumulation of extracellular AnxA2, which prolongs the pro-inflammatory environment, causing excessive FAP proliferation. d) Blocking aberrant signaling due to AnxA2 buildup blocks FAP accumulation and thus preventing adipogenic loss of dysferlinopathic muscle. Credit: “Fibroadipogenic progenitors are responsible for muscle loss in limb girdle muscular dystrophy 2B.” Published online June 3, 2019, in Nature Communications. Marshall W. Hogarth, Aurelia Defour, Christopher Lazarski, Eduard Gallardo, Jordi Diaz Manera, Terence A. Partridge, Kanneboyina Nagaraju and Jyoti K. Jaiswal. https://rdcu.be/bFu9U.

Research led by faculty at Children’s National published online June 3, 2019, in Nature Communications shows that the sudden appearance of symptoms in limb-girdle muscular dystrophy type 2 (LGMD2B) is a result of impaired communication between different cell types that facilitate repair in healthy muscle. Of particular interest are the fibro/adipogenic precursors (FAPs), cells that typically play a helpful role in regenerating muscle after injury by removing debris and enhancing the fusion of muscle cells into new myofibers.

LGMD2B is caused by mutations in the DYSF gene that impair the function of dysferlin, a protein essential for repairing injured muscle fibers. Symptoms, like difficulty climbing or running, do not appear in patients until young adulthood. This late onset has long puzzled researchers, as the cellular consequences of dysferlin’s absence are present from birth and continue through development, but do not impact patients until later in life.

The study found that in the absence of dysferlin, muscle gradually increases the expression of the protein Annexin A2 which, like dysferlin, facilitates repair of injured muscle fiber. However, increasing Annexin A2 accumulates outside the muscle fiber and drives an increase in FAPs within the muscle as well as encourages these FAPs to differentiate into adipocytes, forming fatty deposits. Shutting down Annexin A2 or blocking the adipocyte fate of FAPs using an off-the-shelf medicine arrests the fatty replacement of dysferlinopathic muscle.

“We propose a feed-forward loop in which repeated myofiber injury triggers chronic inflammation which, over time, creates an environment that promotes FAPs to accumulate and differentiate into fat. This, in turn, contributes to more myofiber damage,” says Jyoti K. Jaiswal, MSc, Ph.D., a principal investigator in the Center for Genetic Medicine Research at Children’s National and the study’s senior author.

“Adipogenic accumulation becomes the nucleating event that results in an abrupt decline in muscle function in patients. This new view of LGMD2B disease opens previously unrealized avenues to intervene,” adds Marshall Hogarth, Ph.D., the study’s lead author.

Joyti Jaiswal

“We propose a feed-forward loop in which repeated myofiber injury triggers chronic inflammation which, over time, creates an environment that promotes FAPs to accumulate and differentiate into fat. This, in turn, contributes to more myofiber damage,” says Jyoti K. Jaiswal, MSc, Ph.D.

A research team led by Jaiswal collaborated with Eduard Gallardo and Jordi Diaz Manera, of Hospital de la Santa Creu in Barcelona, Spain, to examine muscle biopsies from people with LGMD2B who had mild to severe symptoms. They found that adipogenic deposits originate in the extracellular matrix space between muscle fibers, with the degree of accumulation tied to disease severity. They found a similar progressive increase in lipid accumulation between myofibers predicted disease severity in dysferlin-deficient experimental models. What’s more, this process can be accelerated by muscle injury, triggering increased adipogenic replacement in areas that otherwise would be occupied by muscle cells.

“Accumulation and adipogenic differentiation of FAPs is responsible for the decline in function for dysferlinopathic muscle. Reversing this could provide a therapy for LGMD2B, a devastating disease with no effective treatment,” predicts Jaiswal as the team continues research in this field.

Promising off-the-shelf drugs include batimastat, an anti-cancer drug that inhibits the extracellular matrix enzyme matrix metalloproteinase. This drug reduces FAP adipogenesis in vitro and lessens injury-triggered lipid formation in vivo. In experimental models, batimastat also increases muscle function.

In addition to Jaiswal, Hogarth, Gallardo and Diaz Manera, other study co-authors include Aurelia Defour, Christopher Lazarski, Terence A. Partridge and Kanneboyina Nagaraju, all of Children’s National.

Financial support for research described in this post was provided by the Muscular Dystrophy Association under awards MDA477331 and MDA277389, the National Institute of Arthritis and Musculoskeletal and Skin Diseases under award R01AR055686 and the National Institutes of Health under awards K26OD011171, R24HD050846 and P50AR060836.

Sen Chandra Sreetama and Jyoti K Jaiswal

Modified glucocorticoid stabilizes dysferlin-deficient muscle cell membrane in experimental models

Sen Chandra Sreetama and Jyoti K Jaiswal

Limb girdle muscular dystrophy type 2B (LGMD2B) – a disease so rare that researchers aren’t even sure how many people it affects – is characterized by chronic muscle inflammation and progressively weakened muscles in the pelvis and shoulder girdle. It can affect able-bodied people during their childbearing years and makes it difficult to tiptoe, walk, run or rise unaided from a squat. Ultimately, many with the muscle-wasting condition require wheelchair assistance. There is no therapy approved by the Food and Drug Administration for this condition.

In a head-to-head trial between the conventional glucocorticoid, prednisolone, and a modified glucocorticoid, vamorolone, in experimental models of LGMD2B, vamorolone improved dysferlin-deficient muscle cell membrane stability and repair. This correlated with increased muscle strength and decreased muscle degeneration, according to a Children’s-led study published online Aug. 27, 2018, in Molecular Therapy. By contrast, prednisolone worsened muscle weakness, impaired muscle repair and increased myofiber atrophy.

“These two steroids differ by only two chemical groups,” says Jyoti K. Jaiswal, MSC, Ph.D., a principal investigator at Children’s National Health System and senior study author. “One made muscle repair better. The other made muscle repair worse or about the same as untreated experimental models. This matches experience in the clinic as patients with LGMD2B experienced increased muscle weakness after being prescribed conventional glucocorticoids, such as prednisolone.”

Healthy muscle cells rely on the protein dysferlin to properly repair the sarcolemmal membrane, a cell membrane specialized for muscle cells that serves a vital role in ensuring that muscle fibers are strong enough and have the necessary resources to contract. Mutations in the DYSF gene that produces this essential protein causes LGMD2B.

Jaiswal likens the plasma membrane to a balloon that sits atop the myofiber, a long cell that when healthy can flex and contract. If, in the process of myofiber contraction, the plasma membrane experiences anything out of sync or overly stressful, it develops a tear that needs to be quickly sealed. An intact balloon keeps air inside; tear it, and air escapes. When the plasma membrane tears, calcium from the outside leaks in, causing the muscle cell to collapse into a ball and die. The body contends with the dead cell by breaking it up into fragments and sending in inflammatory cells to clear the debris.

Lack of dysferlin is associated with increased lipid mobility in the LGMD2B cell membrane

Lack of dysferlin is associated with increased lipid mobility in the limb girdle muscular dystrophy type 2B (LGMD2B) cell membrane, which is further increased by injury and prednisolone treatment, causing failure of these cells to undergo repair. By contrast, vamorolone treatment stabilizes the LGMD2B muscle cell membrane to near healthy cell level, enabling repair of injured cells.

The study team got the idea for the current research project during a previous study of the experimental treatment vamorolone for a different type of muscular dystrophy. “In Duchenne muscular dystrophy (DMD), treatment with vamorolone not only reduced inflammation, but the membranes of muscle fibers were stabilized. That was the team’s ah-hah moment,” he says.

Three different doses of vamorolone were tested on cells derived from patients with LGMD2B with higher cell membrane repair efficacy seen with rising treatment dose. The dysferlinopathic experimental models were treated for three months with daily doses of cherry syrup laced with either 30 mg/kg of vamorolone or prednisolone or cherry syrup alone as the placebo arm.

“Right now there are zero treatments,” he says. People with LGMD2B turn to rehabilitative therapies and movement aids to cope with loss of mobility. Doctors are cautioned not to prescribe steroids. Jaiswal says many patients with LGMD2B grew up doing strenuous exercise, former athletes whose first indication of a problem was muscle cramping and pain. How this progresses to muscle weakness and loss is an area of active research in Jaiswal’s lab. “While additional research is needed, our findings here suggest that modified steroids such as vamorlone may be an option for some patients,” Jaiswal says.

“There is a nuance here: In addition to genomic effects, steroids also have physical effects on the cell membrane which may make some of the approved steroids ‘good’ steroids for dysferlinopathy that could selectively be used for this disease,” adds Sen Chandra Sreetama, lead study author.  Further research could indicate whether vamorolone, which is in Phase II human clinical trials for DMD, or any off-the-shelf drug could slow decline in muscle function for patients with LGMD2B.

Additional Children’s study authors include Goutam Chandra; Jack H. Van der Meulen; Mohammad Mahad Ahmad; Peter Suzuki; Shivaprasad Bhuvanendran; and Kanneboyina Nagaraju and Eric P. Hoffman, both of ReveraGen BioPharma.

Research reported in this news release was supported by the Clark Charitable Foundation; Muscular Dystrophy Association, under award number MDA277389; National Institute of Arthritis and Musculoskeletal and Skin Diseases, under award number R01AR055686; National Institutes of Health (NIH), under award numbers K26OD011171 and R24HD050846; and the District of Columbia Intellectual and Developmental Disabilities Research Center under NIH award number 1U54HD090257.

Understanding individual and collective mechanisms behind cell membrane repair

Tissue repair signaling illustration

Signals released during plasma membrane repair initiate tissue repair: Extracellular vesicle signaling, an intracellular calcium increase that initiates plasma membrane repair in injured cells and an increase in cytosolic calcium that stimulates release of ATP by vesicle exocytosis or through plasma membrane channels.

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What’s known

All cells are surrounded by a cell membrane: a double layer of lipids with embedded proteins that separates the inside of the cell from the outside environment. At only 10 nanometers in thickness, this layer is quite fragile. Any breach can be fatal for a cell, causing chemical imbalances by exposing its interior to the extracellular milieu. Consequently, cells have evolved a set of responses to rapidly restore the integrity of the cell membrane in the event of a rupture, coordinating actions spurred by both immediate and longer-term signals. Research is providing a growing understanding of these repair mechanisms, which could go awry in degenerative diseases.

What’s new

Adam Horn, Ph.D., a postdoctoral fellow, and Jyoti K. Jaiswal, Ph.D., a principal investigator at Children’s Center for Neuroscience Research and the Center for Genetic Medicine Research, recently co-authored a literature review article summarizing these cell membrane repair mechanisms and the signals that trigger them. They delve into a variety of resourceful ways that cells fix tears or holes in this membrane, including one akin to blood clotting that stuffs a tear with proteins, organelles or vesicles; another in which the proteins that give a cell structure (the cytoskeleton) disassemble, relaxing tension that helps pull the damaged membrane together; or one in which the damaged portion in the membrane is shed. These repairs are driven by signals that largely rely on a large calcium influx into the cellular fluid, which spurs into action a variety of repair-related proteins. Better understanding each element could help researchers develop new and better ways to treat degenerative diseases in which cells inadequately repair damage.

Questions for future research

Q: How do the different types of signals coordinate individual and collective mechanisms of cell membrane repair?

Q: How is cell membrane repair coordinated among populations of cells at the tissue level?

Source: “Cellular Mechanisms and Signals That Coordinate Plasma Membrane Repair.” A. Horn and J.K. Jaiswal. Published by Cellular and Molecular Life Sciences July 26, 2018.