Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease best known for the progressive death of motor neurons. But a growing body of evidence suggests that ALS involves far more than neuronal loss. The blood-brain barrier and blood-spinal cord barrier—the tightly sealed endothelial layers that protect the central nervous system from harmful blood-borne substances—show significant damage in both ALS patients and animal models of the disease.
When this barrier breaks down, motor neurons are exposed to toxic plasma components including proinflammatory cytokines, and degeneration accelerates. If the barrier cannot be repaired, even therapies that target motor neurons directly may struggle to provide lasting benefit. This makes endothelial cell repair a compelling, if underexplored, therapeutic target in ALS.
A 2022 study published in eNeuro by researchers at the University of South Florida now provides important evidence that a familiar cardiovascular protein—Apolipoprotein A1 (ApoA1)—may offer a path toward vascular protection in ALS.1
The Dyslipidemia Connection
Altered lipid metabolism has been observed in ALS patients for decades. Patients often show elevated serum levels of LDL, HDL, apolipoprotein B (ApoB), and ApoA1—sometimes years before clinical diagnosis. Paradoxically, several studies have found that hyperlipidemia correlates with longer survival after ALS diagnosis, suggesting the body may be mobilizing lipid resources to support cellular energy demands or to protect damaged tissues.
ApoA1 is the principal protein component of high-density lipoprotein (HDL), the particle commonly referred to as “good cholesterol.” Beyond its role in lipid transport, ApoA1 is well established as an anti-inflammatory, antioxidative, and antithrombotic agent in the cardiovascular system, where it protects blood vessel linings from injury and inflammation.
The USF team, led by Dr. Svitlana Garbuzova-Davis, asked a straightforward question: if the blood-spinal cord barrier is breaking down in ALS, and if ApoA1 is known to protect endothelial cells in cardiovascular disease, could it do the same for the damaged endothelium in ALS?
Modeling ALS-Like Vascular Damage In Vitro
To test this hypothesis, the researchers created an in vitro system designed to mimic the pathological vascular environment in ALS. They cultured mouse brain endothelial cells (mBECs)—the cell type that forms the blood-CNS barrier—and exposed them to plasma collected from symptomatic G93A SOD1 mutant mice, the most widely used animal model of ALS. This plasma contains the proinflammatory cytokines and other disease-state factors that circulate in ALS.
The effect was dramatic. Exposure to 3% ALS mouse plasma increased endothelial cell death from roughly 6% under normal culture conditions to nearly 50%, confirming that the ALS plasma environment is acutely toxic to barrier-forming cells.
The team then introduced human ApoA1 at three concentrations—10, 50, and 100 μg/ml—to determine whether the protein could rescue the damaged cells.
A Dose-Dependent Rescue
The results were clear and dose-dependent. At 10 μg/ml, ApoA1 reduced cell death from approximately 50% to 31%. At 50 μg/ml, death dropped to roughly 19%. At the highest dose of 100 μg/ml, cell death fell to approximately 14%—a reduction of nearly 73% compared to ALS plasma alone, nearly restoring cell viability to healthy baseline levels.
To understand the mechanism behind this protection, the researchers inhibited the PI3K/Akt signaling pathway—a critical intracellular cascade involved in cell survival and angiogenesis—using the well-characterized inhibitor wortmannin. When this pathway was blocked, even the highest dose of ApoA1 failed to protect the cells, with death rates rising back to approximately 40%. This confirmed that ApoA1’s protective effect in this model operates through PI3K/Akt-dependent signaling.
The team also examined whether ApoA1’s benefit was specific or whether other apolipoproteins might produce a similar effect. When they substituted recombinant human apolipoprotein E (ApoE) at 50 μg/ml under the same conditions, there was no significant reduction in cell death. This specificity is noteworthy, particularly given that ApoE has been extensively studied in other neurodegenerative diseases such as Alzheimer’s and Parkinson’s, yet appears to have no protective role in this ALS endothelial model.
How ApoA1 Protects: Cellular Integration
Perhaps the most striking finding of the study was the mechanism by which ApoA1 exerts its effect. Using immunocytochemistry, the researchers demonstrated that ApoA1 physically incorporates into the cytosol of endothelial cells exposed to ALS plasma. Cells cultured in basal media or ALS plasma alone showed no ApoA1 immunostaining, but cells treated with 100 μg/ml ApoA1 showed clear cytosolic accumulation of the protein.
To confirm that this integration was essential to the protective effect, the team immunoprecipitated ApoA1 with a blocking antibody before adding it to the culture. When ApoA1 was prevented from entering the cells, the protective effect disappeared entirely—cell death rates returned to levels comparable to ALS plasma exposure alone. This confirmed that ApoA1 must be taken up by the endothelial cells to confer protection.
Why Protein Purity Mattered
A critical design consideration in this study was the choice of ApoA1 reagent. The researchers selected purified ApoA1 from human plasma with low endotoxin levels sourced from Athens Bioscience, Inc. (formerly known as Athens Research & Technology, Inc.; Cat# 16-16-120101-LEL).
This choice was essential for experimental integrity. Endotoxins—bacterial lipopolysaccharides that commonly contaminate protein preparations—are potent inflammatory agents and can be directly cytotoxic to endothelial cells. In a study designed to measure whether ApoA1 protects cells from ALS-associated damage, any endotoxin contamination in the ApoA1 preparation could introduce confounding inflammation or toxicity, making it impossible to determine whether observed effects were genuinely attributable to the protein itself.
By using human plasma-derived ApoA1 with verified low endotoxin levels, the researchers ensured that the dose-dependent protective effects they observed reflected authentic ApoA1 biology—not artifacts from contaminating substances.
From Single Protein to Cell Therapy
The study also explored a biologically important question: where does ApoA1 come from in a therapeutic context? The researchers co-cultured human bone marrow-derived endothelial progenitor cells (hBM-EPCs) with mBECs using a transwell system that prevented direct cell-to-cell contact. This allowed them to test whether factors secreted by the progenitor cells could protect the endothelial cells at a distance.
Immunocytochemical staining confirmed that hBM-EPCs contain and actively secrete ApoA1. When the progenitor cells were co-cultured with mBECs exposed to ALS plasma, there was no significant increase in endothelial cell death—the hBM-EPCs provided protection. But when a blocking antibody against ApoA1 was added to the co-culture, cell death rose significantly, to over 21%. This demonstrated that ApoA1 secreted by the progenitor cells is a key factor in their protective effect.
These findings have important implications for the ongoing exploration of cell-based therapies for ALS. If endothelial progenitor cell transplants can repair the blood-spinal cord barrier in part by secreting ApoA1, this identifies both a mechanism of action for cell therapy and a potential alternative approach—direct administration of purified ApoA1 as a biologic strategy to restore barrier integrity.
The Proteins Behind the Science
Athens Bioscience, Inc. has manufactured high-purity native human proteins from its facility in Athens, Georgia for four decades. The ApoA1 used in this study is part of a comprehensive portfolio of more than 170 purified human proteins, including apolipoproteins and lipoproteins available in Standard, Low Endotoxin Level (LEL), and Immunogen Grade (IMM) formats to serve research, diagnostic, and pharmaceutical applications.
For researchers investigating vascular dysfunction in neurodegenerative disease, the quality of protein reagents directly determines whether experimental results reflect genuine biology or preparation artifacts. When a study depends on distinguishing ApoA1-mediated cellular protection from endotoxin-induced inflammation, starting material purity is not optional—it is foundational to valid conclusions.
References
1. Garbuzova-Davis, S., Willing, A.E., & Borlongan, C.V. (2022). “Apolipoprotein A1 Enhances Endothelial Cell Survival in an In Vitro Model of ALS.” eNeuro, 9(4), ENEURO.0140-22.2022. https://doi.org/10.1523/ENEURO.0140-22.2022
Explore Athens’ full portfolio of apolipoproteins and lipoproteins at www.athensbioscience.com.
Athens Products Referenced in This Study:
Apolipoprotein A1, Human Plasma, Low Endotoxin Level (Cat# 16-16-120101-LEL)