Protein building block may be a therapeutic target for childhood AAV
Study: Increasing glutamine levels could help curb inflammation
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Children with ANCA-associated vasculitis (AAV) have higher numbers of two specific subsets of neutrophils, a type of immune cell implicated in AAV, that produce high levels of molecules linked to inflammation and other damaging processes, a small study showed.
Notably, these overactive neutrophils appear to have difficulty processing glutamine, a protein building block used as an energy source and known to influence neutrophils’ maturation and function. Adding glutamine to lab-grown immature immune cells prevented them from maturing into these overactive neutrophils.
While the study was exploratory, its findings suggest that “glutamine metabolism could serve as a potential therapeutic target for AAV,” researchers wrote.
Their study, “Single-Cell RNA-Sequencing of Peripheral Blood Reveals Neutrophil Heterogeneity in Childhood ANCA-Associated Vasculitis,” was published in the Journal of Inflammation Research by a team of researchers in China.
Glutamine metabolism plays key role in modulating neutrophil behavior
In most cases, AAV is driven by abnormal antibodies that react against the body’s own healthy neutrophils, causing them to become overly active. As a result, they cause inflammation and damage to neighboring small blood vessels. Depending on where this occurs, AAV can cause many different symptoms.
“Accumulating evidence underscores the crucial role of glutamine metabolism in modulating neutrophil behavior and broader immune responses,” the researchers wrote. “Glutamine is not only a key energy source but also contributes to [cellular processes] impacting neutrophil [maturation], activation, and [function].”
While rare, AAV can occur in children, who are treated based on data from studies of adult patients. Newborns and children “exhibit distinct metabolic requirements and nutrient sensitivities compared to adults, which may influence disease mechanisms and treatment responses,” the team wrote.
To evaluate how glutamine metabolism influences neutrophil subsets and function in pediatric AAV, the researchers collected blood from 12 children with the autoimmune disease, ages 5 to 17, and three healthy children who served as controls.
2 subsets of neutrophils more abundant in children with AAV
They then studied single cells using RNA sequencing, a technique that reveals which cell types are present and which genes are active in each cell. Interestingly, the overall numbers of immune cells, including neutrophils, were similar between the AAV and control groups.
Neutrophils could be divided into seven subsets, and two of them were more abundant in the blood of children with AAV. While both subsets were positive for a cell surface protein called CD11B, which is involved in neutrophils’ immune functions, one subset was also positive for CD10. This protein breaks down molecules at the cell surface and is used as a marker of final neutrophil maturation.
Both subsets of neutrophils produced high levels of molecules linked to inflammation, including toxic enzymes and weblike structures called neutrophil extracellular traps that can damage blood vessels.
Given that in healthy people, neutrophils fully develop in the bone marrow before entering the bloodstream, the higher numbers of immature neutrophils (CD11B-positive and CD10-negative) in the blood of AAV patients suggest an abnormal maturation pathway.
The researchers also showed that immature CD10-negative neutrophils can develop into more mature, CD10-positive neutrophils in the blood. This indicates that neutrophils can change over time during the disease course.
Proteins that regulate gene activity altered in the 2 groups of neutrophils
The researchers also examined changes in transcription factors, proteins that regulate gene activity. They found that CEBPA, CEBPD, and other transcription factors were altered in the two neutrophil groups, possibly causing them to become overly activated.
Lab experiments in lab-grown HL-60 cells, a type of human blood cancer cell that can be matured into neutrophils, showed that exposure to blood from children with AAV increased the proportion of these overactive neutrophils.
“We hypothesized that in the AAV setting, there would be an excess of immature [CD10-negative CD11B-positive] neutrophil subsets in the … blood and that the … blood microenvironment promotes the [maturation] of immature neutrophils toward [CD10-positive CD11B-positive] neutrophils,” the team wrote.
The researchers also studied neutrophils’ metabolism, the process by which cells produce and use energy. While these two groups of neutrophils produced more energy from glucose (sugar) and fats, their glutamine metabolism was reduced. Glutamine is a protein building block essential for making antioxidants, such as glutathione, which protects cells from damage.
Increasing neutrophil glutamine metabolism by increasing … blood glutamine concentrations and GGT levels may be an important potential target of AAV.
Glutamine metabolism was also significantly lower in the mature neutrophil subset of children with AAV than in those from healthy children. Similar findings were obtained when the team examined blood glutamine levels.
Notably, blood samples from six of the children with AAV and 21 additional AAV cases showed increased levels of glutamine-related enzymes, such as gamma-glutamyl transpeptidase (GGT), after treatment.
This suggested that restoring glutamine metabolism is part of the therapeutic effect. Lab experiments showed that adding glutamine to lab-grown HL-60 cells reduced the proportion of overactive neutrophils, supporting this idea.
“Increasing neutrophil glutamine metabolism by increasing … blood glutamine concentrations and GGT levels may be an important potential target of AAV,” the researchers wrote. They noted, however, that “given the exploratory nature of this research, these findings should be interpreted as preliminary.”
