ALS therapy target: Integrin that spurs immune cells to ‘eat’ neurons
Blocking alpha-5 integrin treats mouse model, 'optimized' antibody now sought
A “velcro-like” protein called alpha-5 integrin consistently is found at high levels in immune cells near motor neurons being damaged or killed in people with amyotrophic lateral sclerosis (ALS) and those of mice in a disease model, a study reports.
Blocking the protein in the mice slowed disease progression, and it helped in restoring their motor skills and overall health.
“We demonstrated that targeting α5 [alpha-5] integrin with an anti-α5 integrin antibody extended survival and improved [the animals’] motor performance,” the researchers wrote, suggesting that therapies targeting the integrin might treat ALS.
The study, “Elevated α5 integrin expression on myeloid cells in motor areas in amyotrophic lateral sclerosis is a therapeutic target,” was published in PNAS. It was a collaborative effort between Pasithea Therapeutics and researchers at Stanford Medical School, the Mayo Clinic, and Oregon Health & Science University.
Treatment ideally to ‘kill the big eaters before they kill the motor neuron’
Last year, Pasithea used an award worth AU$1 million (about $660,000) from FightMND, an Australian nonprofit supporting disease research, to further its work into anti-integrin antibodies as potential ALS treatments.
ALS occurs when motor neurons, the nerve cells that control voluntary movement, become damaged and progressively die. Without motor neurons, muscles become weak and waste away, leading to such disease symptoms as difficulty walking and breathing, slurred speech, and trouble chewing and swallowing.
Although the exact causes of ALS are not known, immune cells like microglia and macrophages are believed to play a role.
Microglia and macrophages work to engulf and destroy dead cells, harmful invaders, and debris. While macrophages can be found in various tissues outside the brain, microglia are the brain’s resident immune cells.
Microglia are important for maintaining the health of the brain and spinal cord. But in ALS they become overly active, causing excessive inflammation and damage to motor neurons. Peripheral macrophages, those outside the brain, also are involved in disease progression.
“The motor neurons are ‘eaten’ by cells called macrophages and microglia,” Lawrence Steinman, MD, a neurologist and professor at Stanford Medical School, said in an email exchange with ALS News Today. “We have pictures of these ‘big eaters’ ingesting motor neurons.”
But determining exactly how inflammation damages motor neurons is hard, because microglia are very diverse. Examining them one by one is crucial to understanding the disease better.
In a study co-led by Steinman, researchers used a technique called single-cell mass cytometry, which uses tagged antibodies to look at individual cells, allowing them to detail a cell’s characteristics with high precision.
An initial analysis used a model of ALS where mice carry a mutated version of the SOD1 gene and develop symptoms similar to those of ALS patients. Mutations in this gene are linked to both familial ALS and sporadic disease forms.
Researchers analyzed 78,293 single cells isolated from these mice, including 21,250 myeloid cells from the brain and spinal cord, a group of immune cells that include microglia. The alpha-5 integrin was present at high levels in myeloid cells of mice with late-stage disease, marked by paralysis, but not in healthy mice, results showed.
An integrin is a type of protein found on the surface of cells, which helps them attach to nearby cells. These proteins also receive and transmit chemical signals that tell the cells how to behave in response to cues from their surroundings.
“We show that a particular [velcro-like] molecule called alpha-5 integrin is present at the site of disease in ALS,” said Steinman, who is also co-founder and chairman of Pasithea.
Microglial cells positive for integrin seen in damaged motor areas of patients
In animals with late-stage ALS, considerably more microglia tested positive for alpha-5 integrin in the ventral horn of the spinal cord, which houses the cell bodies of lower motor neurons, than in healthy mice (25.6% vs. 0.06%).
A similar observation was made for macrophages found along the sciatic nerve (49.6% vs. 11.7%), a long nerve that runs from the lower back down through the lower limbs.
Notably, these integrin-positive cells produced significantly higher levels of inflammatory molecules than their integrin-negative counterparts. This included “higher levels of the IL-6 cytokine, which is known to participate in macrophage recruitment toward neurons,” the researchers wrote.
To determine if these findings also held true for people with ALS, the researchers looked at post-mortem samples from 132 patients, and compared them with samples from 10 healthy individuals.
Most of these patient samples (75%) had markedly higher levels of microglia positive for the alpha-5 integrin. These positive cells typically were located close to motor neurons and in empty regions where a motor neuron previously was found.
They “appear at the scene of where motor neurons are being destroyed,” Steinman said.
“Importantly, findings … show that ALS patients irrespective of sex, age, disease duration, genotype, or treatment consistently had increased α5 integrin-positive microglial cells, specifically in damaged motor areas, suggesting that modulation of α5 integrin-positive immune cells may prove beneficial for ALS across a wide range of ALS etiologies [causative factors],” the researchers wrote.
Better health, motor skills evident in mice treated with anti-integrin antibody
Returning to the ALS mouse model, the scientists tested whether an antibody to block the alpha-5 integrin could ease disease manifestations and improve outcomes. Mice were treated twice a week starting before symptoms were apparent through to a late disease stage.
While mice treated with the antibody developed the disease around the same time as animals given a placebo, their symptoms appeared later and treated mice lived significantly longer, “consistent with microglia/macrophages playing a major role in ALS disease progression but not in its initiation,” the scientists wrote.
In a beam walking test, a measure of coordination and balance, treated mice experienced fewer slips and moved across the beam faster than placebo mice, suggesting better motor function. They also showed “better general health and reduced symptoms.”
“These results provide novel data on the role and spatial distribution of α5 integrin in ALS and provide efficacy data of anti-α5 integrin treatment in the [SOD1] mouse model, the gold standard preclinical ALS model,” Tiago Reis Marques, MD, PhD, Pasithea Therapeutics’ CEO, said in a company press release.
“We believe this treatment may be used as a monotherapy or in combination with existing standard of care in both sporadic and genetic” ALS, he said, adding that company work is ongoing and aims “to select the most optimized antibody as our lead candidate later this year.”
Likewise, the researchers noted that five approved treatments for different diseases target integrins, suggesting that a “clinical trial to test α5 integrin as a drug target in ALS might be worthwhile.”
“We are dedicated to pursuing this to develop a potential treatment for ALS,” Steinman said. “The basic idea is to ‘kill the big eaters’ before they kill the motor neuron.”