By Diana Ortega Cruz
In previous articles at Knowing Neurons, we have discussed the neurobiology of Alzheimer’s Disease (AD), the most common form of dementia. This neurodegenerative disease has long been characterized by two pathological proteins: tau and amyloid-beta. After the controversial FDA approval of Aducanumab, a drug that eliminates amyloid-beta (Aβ) in the brain but with questionable cognitive effects, AD has recently become a hot topic again after the publication of an article in Science magazine that revealed potential fraudulent Aβ research. Several media sources have questioned whether this news dilutes the relevance of Aβ in Alzheimer’s and imply that millions have been invested in drug development based on fabricated findings. While this potential fraud may place some specific lines of AD research at risk, claims from the media and the Science article itself might have overstated its importance for the field. In this post, I’ll explain why.
enfermedad de Alzheimer receives its name from Alois Alzheimer, the first neurologist that described a strong shrinkage in the brain of a patient that died presenting memory problems and hallucinations. After closely examining the tissue under the microscope, he observed the presence of two types of abnormal deposits, one within neurons and another in between them (Alzheimer, 1911). Several decades later, more advanced techniques were developed and used to reveal that these deposits were formed by the proteins tau and Aβ, respectively (Grundke-Iqbal et al., 1986, Glenner & Wong, 1984). Currently, clinical diagnoses of AD are based on established criteria for which evidence of abnormal tau or Aβ is necessary (Dubois, et al., 2014). Two main techniques are approved for detection of these pathologies in the patient: positron emission tomography (TEP) and cerebrospinal fluid extraction. Beyond clinical diagnosis, and mainly for research purposes, a confirmed diagnosis of AD is obtained by analysis of brain tissue after the patient passes away – known as neuropathological diagnosis. The presence of both tau and Aβ deposits is required to hold a confirmed neuropathological diagnosis of AD (Montine et al., 2012). Therefore, these two pathologies have been key to identifying AD and are thereby considered the two hallmarks that define the disease.
It has been long debated whether cognitive symptoms and brain damage observed in AD are caused by tau or Aβ, thus building either the “tau hypothesis” or “amyloid hypothesis”. Until today, neither hypothesis has sufficed to explain brain changes in AD by itself (Gallardo & Holtzman, 2019). This debate, particularly the theory that Aβ is the predominant driving factor in the progression of AD, is the topic questioned in the recent Science report. In the words of Nobel laureate Thomas C. Südhof in a recent interview: “The question here is not whether they’re important, I think everybody would agree they’re important. The question is whether they, by themselves alone, drive the disease process, or whether they’re part of a larger ensemble of events that cause the disease.”
“…The question is whether they, by themselves alone, drive the disease process, or whether they’re part of a larger ensemble of events that cause the disease.”
The alleged fraud discussed in the buzzing Science article is related to Aβ*56, an oligomer type of Aβ claimed to directly affect cognition in rats in a paper from the influential scientific journal, Nature (Lesné et al., 2006). Aβ plaques form by protein aggregation: several abnormal protein units aggregate into an oligomer, which in turn cluster into fibrils that form the plaques. In this process, Aβ can take multiple oligomeric states (Finder & Glockshuber, 2007). The study in question described the oligomer type Aβ*56 for the first time and reported that increased levels of this oligomer were associated with a significant drop in memory function. Firstly, Lesné and colleagues studied a model of AD by using a mouse line which expressed an abnormal variant of Aβ. Young mice of this line typically have normal memory function, while middle-aged mice display memory deficits. The authors extracted protein samples from these mice and evaluated the presence of Aβ*56 through a common experiment to assess proteins in a sample, known as a western blot. This technique separates proteins based on their size and labels those of interest using specific antibodies, resulting in bands like those in Figure 2a of the paper (shown below). Analysis of protein samples from mice of different ages appeared to show that increasing Aβ*56 levels coincided with the expected age of onset of AD in this mouse line. To further test the role of the Aβ*56 oligomer in memory impairment, the researchers isolated the oligomer and inject it into young, healthy rats. As they hypothesized, injection of Aβ*56 resulted in a decrease in memory function in these rats. Given the association of Aβ*56 levels with disease onset in the AD mouse model, together with the drop in memory function observed after injecting the oligomer, this study presented compelling evidence for the contribution of Aβ*56 to AD development.
It was not until recently that the neuroscientist and physician, Matthew Schrag, reported irregularities with Figure 2a, as shown in the Science report. Schrag noticed that bands from samples of differently aged mice looked very similar, and suspected they could have been duplicated. A manipulation of this type can falsely show the presence of a protein or higher/lower levels compared to a different sample. Using software tools, Schrag found such bands were much more similar than commonly expected for bands from different samples, since these bands typically display irregular shapes. Schrag had previously found posts in a research forum called PubPeer in which other researchers reported duplicated bands in figures from later papers citing Lesné’s work (Larson et al., 2012a, Larson et al., 2012b, Amar et al., 2017), an observation that he also confirmed.
The concerns raised about these papers have severe consequences: other labs have based their investigations on the findings reported in these papers. Lesné’s paper has obtained around 3,000 citations since its publication, which indicates the work has been quite influential. However, some researchers have been unable to replicate these findings and have suggested there was insufficient proof of a link between oligomer presence and cognitive deterioration (Shankar et al., 2009). Other groups may have obtained similar results and refrained from publishing them to avoid contradicting such influential work by Lesné and colleagues. Thus, precious resources and effort in the field of Alzheimer’s research might have been wrongly oriented due to Lesné’s 2006 paper. Honest communication of procedures and results is the pillar of research, so fraudulent activity severely hinders its progress. This should never be tolerated in any field of science. Ongoing investigations will reveal if the reported accusations are true – and in such case, authors will hopefully take responsibility. To avoid situations like these going forward, encouraging the appreciation and publication of unexpected or negative results would help to identify fabricated or irreproducible work.
…the independent contribution of the amyloid Aβ*56 oligomer to cognitive deficits in AD should be questioned…
All in all, it is safe to say that this news does not threaten the role of amyloid-beta as a key element of AD. The Science report does, however, show that the independent contribution of the amyloid Aβ*56 oligomer to cognitive deficits in AD should be questioned, and fraudulent activity should be accordingly investigated. Yet, media reports on the topic included hyperbolic statements that do not help the field, patients or caregivers: the relevance of amyloid-beta as a key element in this disease is not at stake. The original tau and amyloid hypotheses have been refined by recent advances in neuroimágenes and biomarkers, supporting the idea that both proteins – as well as other mechanisms such as inflammation – come together to influence AD development. Research can only contribute to progression in society if it is reproducible, and fraud could be prevented through more open publishing procedures and less reductionist press headlines.
Escrito por Diana Ortega Cruz
Imagen por Himani Arora
Edited by Lauren Wagner, Justin McMahon, and Talia Oughourlian
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