Zebrafish larvae with intact skeletal muscle structure and function (top) and impaired skeletal muscle structure (as seen with reduced birefringence, right panel) and function due to loss of Ddx27 (bottom).

Uncovering the genetics of skeletal muscle growth and regeneration

Study finds gene responsible for regulating skeletal muscle growth and regeneration by modulating protein building processes

Skeletal muscle has a remarkable capacity to regenerate – a capacity that is diminished in many skeletal muscle diseases and aging. To investigate the mechanism behind skeletal muscle growth and regeneration, researchers from Brigham and Women’s Hospital bombarded zebrafish with chemical mutagen and screened for larvae with defective skeletal muscle structure. Using genetic mapping, they found that zebrafish larvae with a mutation in DDX27 showed reduced muscle growth and impaired regeneration. Their results are published in PLOS Genetics.

“A major hindrance in the development of effective therapies for skeletal muscle diseases thus far has been a lack of understanding of the biological processes that promote muscle growth and repair,” said corresponding author Vandana Gupta, PhD, of the Division of Genetics at BWH. “Our study is one of the first efforts to provide specificity to the processes controlling protein synthesis in muscles, which will hopefully allow for the development of effective targeted treatments for skeletal muscle diseases.”

Loss of muscle mass is a debilitating feature that is a common manifestation of a wide array of diseases, and leads to reduced muscle function and increased morbidity and mortality. Maintenance of skeletal mass relies on a dynamic balance between protein synthesis and degradation. A number of conditions such as myopathies, sarcopenia, cancer cachexia, disuse atrophy, sepsis and chronic kidney diseases lead to a disruption of this balance in favor of reduced protein synthesis.

The researchers discovered that DDX27 is involved in ribosome biogenesis and protein synthesis in skeletal muscle. Loss of DDX27 affects the function of skeletal muscle by disrupting the regulation and production of proteins that are crucial for muscle function. Looking ahead the researchers hope to further explore the mechanism by which protein synthesis is changed in different disease conditions and develop approaches to target DDX27 regulated pathways to restore muscle growth and regeneration in skeletal muscle disorders.

“If we can promote muscle growth in patients with skeletal muscle disorders, we would be able to restore muscle strength and mobility in these patients, and reducing morbidity,” said Gupta. “Our study is just the beginning of an effort to develop regenerative therapies for myopathies that could have a wide impact in a large patient population.”

Paper cited: Alexis H Bennett et al. “RNA helicase, DDX27 regulates skeletal muscle growth and regeneration by modulation of translational processes” PLOS Genetics DOI: https://doi.org/10.1101/125484


Study Explores Emerging Role of NAD+ in Innate and Adaptive Immune Responses

In a pre-clinical model, researchers find that NAD+ can trigger a response that protects against lethal infections

Researchers at Brigham and Women’s Hospital (BWH) have discovered a new cellular and molecular pathway that regulates CD4+ T cell response—a finding that may lead to new ways to treat diseases that result from alterations in these cells. Their discovery, published online in the Journal of Allergy and Clinical Immunology, shows that administering nicotinamide adenine dinucleotide (NAD+), a natural molecule found in all living cells, shuts off the capacity of dendritic cells and macrophages to dictate CD4+ T fate. Researchers found that NAD+ administration regulated CD4+ T cells via mast cells (MCs), cells that have been mainly described in the context of allergy, exclusively.

“This is a novel cellular and molecular pathway that is distinct from the two major pathways that were previously known. Since it is distinct and since it has the ability to regulate the immune system systemically, we can use it as an alternative to bypass the current pathways,” said Abdallah ElKhal, PhD, BWH Department of Surgery, senior study author.

CD4+ T helper cells and dendritic cells play a central role in immunity. Alterations or aberrant dendritic cells and T cell responses can lead to many health conditions including autoimmune diseases, infections, allergy, primary immunodeficiencies and cancer.

As of today, two major pathways have been described to regulate CD4+ T cell response. The first pathway was described by Peter C. Doherty and Rolf M. Zinkernagel (1996 Nobel prize winners) showing the requirement of MHC-TCR signaling machinery. More recently, a second mechanism involving the Pathogen or Damage Associated Molecular Patterns (PAMPs or DAMPs) was unraveled by Bruce A. Beutler and Jules A. Hoffmann (2011 Nobel Prize winners). Of importance, both pathways require antigen presenting cells (APCs) in particular dendritic cells (DCs) or macrophages (Mφ). Elkhal’s novel pathway is distinct from the two previous ones and may offer a path forward for novel therapeutic approaches.

For the current study, BWH researchers performed pre-clinical trials using an experimental infection model. They showed that mast cell-mediated CD4+ T cell response protects against lethal doses of infection (Listeria monocytogenes). Mice treated with NAD+ had a dramatically increased survival rate when compared to the non-treated group.

“Collectively, our study unravels a novel cellular and molecular pathway that regulates innate and adaptive immunity via MCs, exclusively, and underscores the therapeutic potential of NAD+ in the context of a myriad of diseases including autoimmune diseases, hemophilia, primary immunodeficiencies and antimicrobial resistance,” said Elkhal.

This work was supported by the National Institutes of Health R01NS073635 and R01MH110438, R01 HL096795 and U01 HL126497, R01AG039449. Co-authors were supported by the Swiss Society of Cardiac Surgery, FIS-ISCIII (grant PI10/02 511) and Fundación Ramón Areces (CIVP16A1843).

Preventing the Misdiagnosis of Cellulitis

Study finds that early dermatology consultation for presumptive cellulitis can improve patient outcomes, reduce costs and reduce unnecessary hospitalization.

Cellulitis – a bacterial infection of the skin – is a common medical condition, yet there is no diagnostic tool for it currently available. The only way to diagnose cellulitis is based on the appearance of the affected area and the patient’s reported symptoms. Many other medical conditions cause skin inflammation that mimics the appearance of cellulitis (known as pseudocellulitis) and are commonly misdiagnosed. A new study by researchers from Brigham and Women’s Hospital demonstrates that early consultation by a dermatologist for patients with presumed cellulitis was a cost-effective intervention to prevent misdiagnoses and improve health-related outcomes. Their results are published in JAMA Dermatology.

“This is a big win-win for both the patients and for the hospitals,” said corresponding author Arash Mostaghimi, MD, MPA, MPH, Director of Inpatient Dermatology. “Our findings show that early intervention by dermatologists for patients with presumptive cellulitis, not only improves outcomes for the patients, but saves the hospitals on costs associated with unnecessary hospitalization and opens up beds in the emergency department.”
Previous work by Mostaghimi and his colleagues evaluated a series of patients in BWH’s Emergency Department with presumptive diagnosis of cellulitis and determined that a third of these patients had pseudocellulitis. Alarmed by this statistic, the dermatology consult team partnered with the inpatient group and ED to provide dermatology consultation for 165 patients in the ED observation unit who were about to be admitted with presumptive diagnosis of cellulitis. A third of these patients were diagnosed with pseudocellulitis by dermatology consultation. The dermatologists recommended the discontinuation of antibiotics in 82.4 percent of these patients, and discharge from planned observation or inpatient admissions in half of the patients. None of the patients diagnosed with pseudocellulitis showed worsening of their condition after discharge.

Extrapolating from their findings, the researchers estimate that dermatology consultation for presumed cellulitis could nationally prevent between 97,000 to 256,000 in hospitalization days and 34,000 to 91,000 cases of unnecessary antibiotic exposure. It could also result in $80 million to $210 million in net cost savings annually.

While the results of their proof-of-concept study show the benefits of early dermatology consultation, the major challenge now is scalability. The researchers have already implemented protocols at BWH to involve dermatology experts early in the care of patients with presumptive cellulitis, but this is hard to do in settings that do not have access to 24/7 dermatology consultation, such as primary care offices, nursing homes and rehabilitation centers. Mostaghimi and his team are currently developing tools to allow them to provide high quality dermatology consultation remotely, which they call “teledermatology,” to improve health-related outcomes of pseudocellulitis diagnoses on a much larger scale.

This study was funded by the National Center for Advancing Translational Sciences, National Institutes of Health, and by the Brigham and Women’s Physician Organization Brigham Care Redesign Incubator and Startup Program (BCRISP).

Paper cited: David G. Li et al. “Outcomes of Early Dermatology Consultation for Inpatients Diagnosed with Cellulitis” JAMA Dermatology DOI: TBD