In a recent study published in the Proceedings of the National Academy of Sciences Journal, researchers examined the therapeutic effects of targeting integrins for treating Amyotrophic lateral sclerosis (ALS) disease.
Study: Elevated α5 integrin expression on myeloid cells in motor areas in amyotrophic lateral sclerosis is a therapeutic target. Image Credit: DavidHerraezCalzada/Shutterstock.com
ALS is a neurodegenerative disease that causes the motor cortex, brainstem, and spinal cord to lose motor neurons over time, leading to paralysis and death. In the United States, three approved treatments slow down the progression of ALS.
It is characterized by motor neuron degeneration. However, several studies show that immune cells from the blood and glial cells from the central nervous system (CNS) and peripheral nervous system (PNS) influence neurodegeneration in familial and sporadic ALS, challenging the neuron-centric theory.
There has been discussion about whether inflammation is a cause or result of ALS. A systems immunology analysis using mass cytometry (CyTOF) predicted the proinflammation role of α-integrins in late-stage of superoxide dismutase-1 G93A (SOD1G93A) mice microglia and peripheral nerve macrophages.
In the present study, researchers explored the potential of targeting α5 integrin as a therapeutic approach to modulate neuroinflammation in ALS.
About the study
This study used hSOD1G93A transgenic mouse lines for histopathology experiments. The mice carrying the human SOD1 transgene were identified through polymerase chain reaction (PCR) screening of tail deoxyribonucleic acid (DNA).
Nontransgenic mice were used as controls for histology experiments. The room temperature and humidity were maintained at 20 to 24 °C and between 45 and 65%, respectively. The animals were housed under a constant light cycle (12 hour light/dark).
Twenty female SOD1G93A mice were randomly divided into two groups of 10 mice, each receiving biweekly intraperitoneal injections of anti-α5 integrin antibody or isotype control (100 µg) starting at eight weeks old.
Motor behavior was assessed using the Vercelli score and the beam walk test. Microglial single cells were isolated and tagged with 20 unique mass-tag barcodes containing a combination of six palladium isotopes.
Additionally, antibody testing, panel design, antibody conjugation, and cell staining were carried out for the Mouse CyTOF experiment.
Furthermore, with the kin's consent, human postmortem single-cell isolation and tissue CyTOF analysis were performed immediately following the donor's autopsy from the Oregon Brain Bank (Oregon, USA).
Anti-α5 integrin antibody-treated SOD1G93A and isotype control mice underwent spinal cord histopathology tests. The Zeiss Apotome.2 on an Axio Imager with Zen v3.5 software was used to analyze both mice groups' spinal cords and sciatic nerves.
Further, the researchers examined the disease stage analysis as mice reached peak body weight and were defined by paralysis so severe that the animal could not move within 20 seconds when placed on its side. Kaplan-Meier analysis was used for survival curves and log-rank tests for statistical analysis.
In the current investigation, the single-cell proteome analysis of CyTOF showed
α5 integrin expression on microglia and peripheral nerve macrophages in SOD1G93A mice. Targeting α5 integrin with an anti-α5 integrin antibody improved motor performance and lifespan in these mice models.
The findings revealed an upregulation of the α5 integrin protein throughout the terminal stage of the disease. Additionally, α5 integrin-positive myeloid cells produced higher proinflammatory cytokines such as TNF- and IL-6.
The team also identified higher expression levels of α5 integrin across sporadic and genetic (C9orf72, SOD1, TARDBP, and TBK1) ALS subtypes compared to controls.
The presence of positive myeloid cells for α5 integrin promotes inflammation and axonal degeneration because these cells attract more macrophages.
Independent of sex, age, disease duration, genotype, or treatment, postmortem tissue analyses demonstrated that ALS patients had an increased α5 integrin-positive microglial cells in damaged motor regions.
The beam walk assay and the Vercelli scores both showed that treatment with an anti-α5 integrin antibody improved the motor capacities of SOD1G93A mice. According to the study findings, blood monocytes cannot infiltrate the spinal cord of SOD1G93A ALS mice during disease.
During CNS inflammation, monocyte mobilization channels from cranial and spinal bone marrow have been identified. As α5 integrin is known to play a role in leukocyte recruitment and adherence, it hinders the monocyte migration from the vertebral bone marrow.
Therefore, the anti-α5 integrin therapy could protect motor neurons by decreasing PNS and CNS inflammation by regulating microglial cells, peripheral monocytes, and macrophages in ALS.
To conclude, researchers found that α5 integrin was induced in the microglial cells of the CNS and macrophages in the sciatic nerve. The experimental outputs suggested modulating α5 integrin could effectively target both cell groups and reduce proinflammatory responses.
Furthermore, the study revealed a molecular link between inflammation and the pathological processes associated with ALS. By targeting α5 integrin and reducing inflammation, it could be possible to decrease neurodegenerative disease progression and alleviate its symptoms.
These findings provide important insights into the pathobiology of ALS and offer a promising avenue for future therapeutic interventions.
Chiot, A., Roemer, S.F., Ryner, L., Bogachuk, A., Emberley, K., Brownell, D., Jimenez, G.A., Leviten, M., Woltjer, R., Dickson, D.W., Steinman, L. & Ajami, B. (2023) Elevated α5 integrin expression on myeloid cells in motor areas in amyotrophic lateral sclerosis is a therapeutic target. Proceedings of the National Academy of Sciences, 120 (32). doi: 10.1073/pnas.2306731120. https://www.pnas.org/doi/10.1073/pnas.2306731120