Deciphering how the body responds and repairs injuries has long been a source of fascination for the Nagy Lab.

Led by Laszlo Nagy, M.D., Ph.D., the Nagy Lab at Johns Hopkins All Children’s Hospital in St. Petersburg, Florida, spends considerable time seeking to understand a key component of that response. They are called macrophages, white blood cells that play an important role in defending against disease. Macrophages are best known for helping clear the body of pathogens, but an imbalance in macrophages can compromise the immune system and the response to inflammation. In the past, the Nagy Lab has studied many aspects of macrophage response, including how certain proteins send a signal to macrophages to initiate the repair response and how the body signals the need for a long-term macrophage response.

In their latest work in the Journal of Clinical Investigation, the Nagy Lab published an article exploring how macrophages organize themselves into distinct roles at different stages of the repair process.

The team used high-dimensional transcriptomics to study the RNA inside tissues and cells.

“It helps us understand which genes are active in different cell types at specific time points,” says Andreas Patsalos, Ph.D., an instructor of medicine at Johns Hopkins University School of Medicine and a member of the Nagy Lab who was first author on the manuscript. “By combining this with single-cell analysis and imaging techniques, we could see exactly where and when different macrophages appeared in the injured muscle. We found that macrophages form organized structures around injured muscle fibers. We called these ‘Regenerative Inflammation Zones’ or RIZs. These zones help the muscle heal by creating layers of cells that support different stages of repair.”

Nagy, co-director of the Johns Hopkins All Children's Institute for Fundamental Biomedical Research and professor of medicine in the Department of Medicine, Division of Endocrinology, Diabetes and Metabolism in the Johns Hopkins University School of Medicine, notes the study identified specific types of macrophages that express certain growth factors essential for muscle regeneration.

“One key player we discovered is GPNMB, a.k.a. osteoactivin,” he says. 

Glycoprotein nonmetastatic melanoma protein B (GPNMB) is a protein that's involved in many cellular functions. It is a marker found on a subset of repair-type macrophages that helps regenerate muscle. The Nagy Lab found that a transcription factor called ATF3 is crucial in regulating GPNMB-positive macrophages, ensuring they promote growth and healing effectively.

Glucocorticoids are a type of steroid hormones known for their potent anti-inflammatory properties and are commonly used to treat various inflammatory conditions. They may be produced naturally or synthetically, but the Nagy Lab discovered in certain muscle diseases, such as Duchenne muscular dystrophy, glucocorticoid treatment, even when given intermittently, can disrupt the healing process. They hope the discovery can help lead to better targeting of specific subsets of macrophages in muscular dystrophy and other inflammatory diseases.

“This finding really highlights the delicate balance required for effective muscle healing,” Nagy says. “It’s a complex dance of different macrophage types working together in a spatially organized fashion.”

The Nagy Lab's research received support from several organizations, including federal grants from the National Institutes of Health. Andreas Patsalos, Ph.D., also received funding from the Johns Hopkins All Children’s Foundation and the Muscular Dystrophy Association, both of which are dedicated to advancing medical research and improving pediatric patient care.