Apolipoprotein E epsilon 4 (APOE4) directly and independently exacerbates accumulation of alpha-synuclein in patients with Lewy body dementia, whereas APOE2 may have a protective effect, based on two recent studies involving mouse models and human patients.
Dr. Eliezer Masliah
These insights confirm the importance of APOE in synucleinopathies, and may lead to new treatments, according to Eliezer Masliah, MD, director of the division of neuroscience at the National Institute on Aging.
“These [studies] definitely implicate a role of APOE4,” Dr. Masliah said in an interview.
According to Dr. Masliah, previous studies linked the APOE4 genotype with cognitive decline in synucleinopathies, but underlying molecular mechanisms remained unknown.
“We [now] have more direct confirmation [based on] different experimental animal models,” Dr. Masliah said. “It also means that APOE4 could be a therapeutic target for dementia with Lewy bodies.”
The two studies were published simultaneously in Science Translational Medicine. The first study was conducted by Albert A. Davis, MD, PhD, of Washington University, St. Louis, and colleagues; the second was led by Na Zhao, MD, PhD, of the Mayo Clinic in Jacksonville, Fla.
“The studies are very synergistic, but used different techniques,” said Dr. Masliah, who was not involved in the studies.
Both studies involved mice that expressed a human variant of APOE: APOE2, APOE3, or APOE4. Three independent techniques were used to concurrently overexpress alpha-synuclein; Dr. Davis and colleagues used a transgenic approach, as well as striatal injection of alpha-synuclein preformed fibrils, whereas Dr. Zhao and colleagues turned to a viral vector. Regardless of technique, each APOE variant had a distinct impact on the level of alpha-synuclein accumulation.
“In a nutshell, [Dr. Davis and colleagues] found that those mice that have synuclein and APOE4 have a much more rapid progression of the disease,” Dr. Masliah said. “They become Parkinsonian much faster, but also, they become cognitively impaired much faster, and they have more synuclein in the brain. Remarkably, on the opposite side, those that were expressing APOE2, which we know is a protective allele, actually were far less impaired. So that’s really a remarkable finding.”
The study at the Mayo Clinic echoed these findings.
“Essentially, [Dr. Zhao and colleagues] had very similar results,” Dr. Masliah said. “[In mice expressing] APOE4, synuclein accumulation was worse and pathology was worse, and with APOE2, there was relative protection.”
Both studies found that the exacerbating effect of APOE4 translated to human patients.
Dr. Davis and colleagues evaluated data from 251 patients in the Parkinson’s Progression Markers Initiative. A multivariate model showed that patients with the APOE4 genotype had faster cognitive decline, an impact that was independent of other variables, including cerebrospinal fluid concentrations of amyloid beta and tau protein (P = .0119). This finding was further supported by additional analyses involving 177 patients with Parkinson’s disease from the Washington University Movement Disorders Center, and another 1,030 patients enrolled in the NeuroGenetics Research Consortium study.
Dr. Zhao and colleagues evaluated postmortem samples from patients with Lewy body dementia who had minimal amyloid pathology. Comparing 22 APOE4 carriers versus 22 age- and sex-matched noncarriers, they found that carriers had significantly greater accumulations of alpha-synuclein (P less than .05).
According to the investigators, these findings could have both prognostic and therapeutic implications.
“[I]t is intriguing to speculate whether APOE and other potential genetic risk or resilience genes could be useful as screening tools to stratify risk for individual patients,” Dr. Davis and colleagues wrote in their paper. They went on to suggest that APOE genotyping may one day be used to personalize treatments for patients with neurodegenerative disease.
According to Dr. Masliah, several treatment strategies are under investigation.
“There are some pharmaceutical companies and also some academic groups that have been developing antibodies against APOE4 for Alzheimer’s disease, but certainly that could also be used for dementia with Lewy bodies,” he said. “There are other ways. One could [be] to suppress the expression of APOE4 with antisense or other technologies.
“There is also a very innovative technology that has been developed by the group at the Gladstone Institutes in San Francisco, which is to switch APOE4 to APOE3.” This technique, Dr. Masliah explained, is accomplished by breaking a disulfide bond in APOE4, which opens the structure into an isoform that mimics APOE3. “They have developed small molecules that actually can break that bond and essentially chemically switch APOE4 to APOE3,” he said.
Although multiple techniques are feasible, Dr. Masliah stressed that these therapeutic efforts are still in their infancy.
“We need to better understand the mechanisms as to how APOE4 and alpha-synuclein interact,” he said. “I think we need a lot more work in this area.”
The Davis study was funded by the American Academy of Neurology/American Brain Foundation, the BrightFocus Foundation, the Mary E. Groff Charitable Trust, and others; the investigators reported additional relationships with Biogen, Alector, Parabon, and others. The Zhao study was funded by the National Institutes of Health and the Lewy Body Dementia Center Without Walls; the investigators reported no competing interests. Dr. Masliah reported no conflicts of interest.
SOURCES: Davis AA et al. Sci Transl Med. 2020 Feb 5. doi: 10.1126/scitranslmed.aay3069; Zhao N et al. Sci Transl Med. 2020 Feb 5. doi: 10.1126/scitranslmed.aay1809.