Some COVID-19 vaccines successfully used lipid nanoparticles (LNPs) to deliver messenger RNA (mRNA) to cells. Now, a new study from MIT suggests that a different type of LNP could be used as a potential therapy for Alzheimer’s disease (AD). In experiments with multiple mouse models and cultured human cells, researchers developed a specialized LNP formulation that efficiently delivered small interfering RNA (siRNA) to microglia, the brain’s immune cells. This approach successfully reduced the expression of a protein linked to excessive inflammation in Alzheimer’s disease.

In previous research, the team demonstrated that blocking the effects of PU.1 protein activity could mitigate AD-related neuroinflammation and pathology. Their latest open-access study, published in Advanced Materials, takes this further by directly suppressing the Spi1 gene, which encodes PU.1. More broadly, the findings introduce a novel method for delivering RNA to microglia, which have historically been difficult to target.

A Collaborative Effort

Co-senior author Li-Huei Tsai, a professor of neuroscience at MIT and director of The Picower Institute for Learning and Memory and the Aging Brain Initiative, hypothesized that LNPs could effectively transport siRNA into microglia. Given that these cells naturally absorb lipid molecules while clearing waste from the brain, Tsai shared her idea with Robert Langer, a professor at MIT’s Koch Institute for Integrative Cancer Research and a leading expert in nanoparticle drug delivery. Their collaboration aimed to explore whether LNPs could reduce PU.1 expression via siRNA delivery.

“I vividly remember the moment I met with Bob to discuss testing LNPs for targeting inflammatory microglia,” Tsai recalled. “I am deeply grateful to The JPB Foundation for supporting this idea even before we had preliminary evidence.”

Leading the research were Jason Andresen, a graduate student in Langer’s lab, and William Ralvenius, a former postdoc in Tsai’s lab. The study’s co-corresponding authors include Owen Fenton, a former Langer Lab postdoc now at the University of North Carolina, along with Tsai and Langer.

Engineering the Optimal Nanoparticle

The simplest approach would have been to use an existing siRNA delivery system, but the researchers found that none of the eight commercially available reagents could safely and effectively deliver RNA to cultured human microglia-like cells. This necessitated the design of a custom LNP.

LNPs consist of four primary components, and by modifying two of them and adjusting the lipid-to-RNA ratio, the team created seven different formulations. They tested these on cultured microglia in an inflammatory state—the condition in which treatment would be most needed.

Among the seven candidates, one formulation, dubbed “MG-LNP,” emerged as the most effective in delivering RNA while maintaining cellular safety.

Since promising in vitro results do not always translate to success in living organisms, the team then tested MG-LNP in mice. They compared two injection methods: systemic administration and direct delivery into cerebrospinal fluid (CSF). The latter proved far superior, ensuring targeted microglia delivery while minimizing effects on other organs. Again, MG-LNP outperformed the other formulations, reinforcing its potential as a delivery vehicle for brain therapies.

Targeting Inflammation in Alzheimer’s Disease

Once MG-LNP’s effectiveness was established, the researchers tested whether delivering PU.1-suppressing siRNA could reduce inflammation in microglia. In cultured cells, a low dose of MG-LNP-mediated siRNA delivery reduced PU.1 expression by 42%—a crucial balance since some PU.1 is necessary for microglial survival. Importantly, the treatment did not harm the cells and effectively lowered multiple inflammatory markers. MG-LNP also outperformed RNAiMAX, a commercially available transfection reagent.

“These results support MG-LNP as a viable method for delivering anti-PU.1 siRNA as a potential therapy for neuroinflammatory diseases,” the researchers wrote.

The final phase of the study tested MG-LNP’s efficacy in two mouse models of brain inflammation. In one, systemic inflammation was induced using lipopolysaccharide (LPS), which mimics an infection. In the second model, mice developed severe neurodegeneration and inflammation due to hyperactivation of the CDK5 enzyme by a protein called p25. In both cases, MG-LNP successfully reduced PU.1 expression and inflammatory markers, mirroring the effects observed in cell cultures.

The researchers concluded that MG-LNP delivery of anti-PU.1 siRNA could serve as an anti-inflammatory therapeutic for systemic inflammation and AD-like neuroinflammation. While these results provide strong proof-of-principle, further testing is needed before the approach can be evaluated in human patients.

Funding and Contributors

In addition to Andresen, Ralvenius, Langer, Tsai, and Fenton, other authors of the study include Margaret Huston, Jay Penney, and Julia Maeve Bonner.

The research was supported by The JPB Foundation, The Picower Institute for Learning and Memory, the Robert and Renee Belfer Family, Eduardo Eurnekian, Lester A. Gimpelson, Jay L. and Carroll Miller, the Koch Institute, the Swiss National Science Foundation, and the Alzheimer’s Association.

Source: https://news.mit.edu/2023/nanoparticle-delivered-rna-reduces-neuroinflammation-lab-tests-1215