ARTICLE IN BRIEF
Investigators found that monocytes from patients with amyotrophic lateral sclerosis (ALS) exhibited a microRNA inflammatory signature similar to that observed in the ALS mouse model. They conclude that recruitment of inflammatory monocytes plays an important role in disease progression and that modulation of these cells is a potential therapeutic approach.
A decade ago, scientists and doctors in working on amyotrophic lateral sclerosis (ALS) were beginning to suspect that inflammation was critical to the disease process. It wasn't a popular idea. But a growing body of evidence is mounting in support of this theory and is leading to the identification of possible immune system biomarkers and even novel treatments.
Now, a team of Harvard scientists has outlined a clearer picture of the role that innate immunity plays in ALS. The finding, published in the Sept. 4 Journal of Clinical Investigation, suggests a specific microRNA gene signature rich with immune system regulators, and a recruitment of inflammatory monocytes that play a critical role in disease progression.
Oleg Butovsky, PhD, Howard L. Weiner, MD, and their colleagues have spent several years unraveling the immune systems role in ALS, first in animals and then looking for similar pathways in patients.
According to Dr. Butovsky, a senior scientist at the Center for Neurologic Diseases at the Brigham and Women's Hospital and Harvard Medical School, the inflammatory signature is similar to that of the mouse model of the most common familial form of the disease — mutant superoxide dismutase-1 (SOD1) — that leads to the death of motor neurons.
“We think we have a direct link between the animal models and patients,” said Dr. Butovsky. The published findings were presented earlier this year at the AAN annual meeting.
Dr. Butovsky explained that the recruitment of inflammatory monocytes seems to play an important role in disease progression. He and colleagues identified a microRNA (miRNA) signature specific to ALS, which they believe could potentially be used as a biomarker and a therapeutic approach to protect motor neurons in patients with ALS. [miRNAs are non-coding areas of the RNA that play a critical role in regulation of gene expression.]
Dr. Butovsky and Dr. Weiner, the Robert L. Kroc professor of neurology at Harvard Medical School and director of the Partners Multiple Sclerosis Center and co-director of Brigham's Center for Neurologic Diseases, are now working on developing methods to specifically target peripheral monocytes in order to modulate their phenotype to help prevent this proinflammatory response.
They identified a proinflammatory gene signal in Ly6CHi monocytes in the SOD1 mice a month before the onset of symptoms; a five percent drop in weight is an early symptom of disease in ALS mice. Then, they found a progressive recruitment of a monocyte with specific cell markers that enters the spinal cord, but not the brain, and damages the motor neuron.
Once they identified markers for this monocyte, they created an antibody and used it to down-regulate the proinflammatory monocytes. This led to a substantial reduction in the numbers of monocytes recruited to the spinal cord. This technique protected the motor neurons from damage and prolonged survival; the SOD mice live an average of 135 days and their treated mice lived on average 146 days.
STRATEGY FOR TRIAL
They went on to look at blood samples from ALS patients and found a common inflammatory signature that could ultimately lead to a biomarker for the disease and pave the way for studies of immune-modulating medicines.
The investigators measured monocytes from 18 patients with sporadic ALS and four with familial ALS with SOD1 mutation, eight with MS, 13 with Alzheimer's disease, and 33 age-matched controls. miRNA profiling of peripheral monocytes in ALS patients — (CD14+/CD16-) — demonstrated an inflammatory phenotype analogous to that seen in the SOD1 mouse, and that profile was distinct from that obtained from patients with a classic inflammatory disease, MS.
The investigators found 19 miRNAs are common and similarly affected in SOD1 mice and ALS patients.
While there were some dysregulated miRNAs shared in ALS and MS samples, there was no overlap between ALS and the Alzheimer's disease samples. There were also some miRNAs that distinguish ALS from MS, Dr. Butovsky said. “We see more profound activation in the blood from ALS patients than we do in MS patients,” he added.
The Boston researchers are now working on developing a blood biomarker of this inflammatory signature that could help monitor disease progression and response to therapies. They are also testing the benefits of modulating these monocytes as a potential treatment.
Some of the therapeutic ideas that they are now working on include targeting the CD14+/CD16- pathway. Dr. Butovsky said that this could stop recruitment of proinflammatory cells to the spinal cord. Another way is to target NF kappa B, which is proinflammatory.
The Harvard team has also generated ALS-specific gene chips, which are now being tested by other groups. They are now conducting a larger study in ALS patients to test blood at the beginning of the disease and the end stages to see what genes and miRNAs are affected early and how the signature changes over time.
“Monocytes (and inflammatory processes in general) are good treatment targets for ALS (and other neurodegeneration diseases),” said Richard M. Ransohoff, MD, director of the Neuroinflammation Research Center at the Cleveland Clinic. Dr. Ransohoff is now collaborating with the Harvard team in testing biomarkers that would be specific for microglia. “We have many approved drugs, which work against specific inflammatory targets and have known safety profiles. We don't have drugs that rescue damaged neurons so for near-term treatment strategies, inflammation is very important.”
Stanley H. Appel, MD, the Edwards Distinguished Endowed Chair for ALS and director of the Methodist Neurological Institute in Houston, said: “I agree that neuroinflammation and immunomodulation play a significant role in the mouse SOD1 ALS model as well as in human sporadic ALS. The miRNAs they identified provide a unique opportunity to monitor pathogenic pathways in ALS models, and it is a major contribution to have documented that inflammation-related miRNAs are prominent in the mouse SOD1 model, and may also reflect the enhanced inflammation in human sporadic ALS.”
Dr. Appel and his colleagues have been studying neuroinflammation in ALS and their evidence, he added, suggests that while “monocytes, macrophages, and microglia may be the final executioner, they are getting their marching orders from T cells of the immune system.”
He added that “future studies need to address whether the miRNAs are early or late markers of ALS, do they correlate with the rate of disease progression or disease burden, and can alterations in miRNAs influence disease duration and survival?”