I thought it would be fun to do a series on hot new trends in science and medicine based on different mechanisms of action, partly because this is what science is all about and partly because hearing about creative new scientific strategies gives me a sense of awe and wonder.
One idea that hit my mailbox today was a fascinating article on new targets for Alzheimers disease (AD) in SciBX, a Nature publication. For a limited time the leading articles are downloadable free of charge. You can find the link to the Alzheimers article here, which said:
According to Genentech's website:
It has long been observed that Alzheimer's patients develop a build up of amyloid plaques and neurofibrillary tangles made of misfolded proteins in their brain. The plaques are abnormal accumulations of sticky amyloid-beta
protein between the neurons. This situation arises when the
amyloid precursor protein is incorrectly cut into pieces. The tangles exist as a filamentous collection of twisted and hyperphosphorylated tau found in the cell body of a neuron.
The NIH has a beautiful illustration of the difference between a healthy and diseased neuron as well as other images on its website that are free to download:
A number of drugs have tried to slow the progression of the disease, with limited success. Once the plaques and tangles have formed, it is difficult to effect any change in the disease.
Earlier this year Yale researchers reported that cellular proteins called prions
activate the process by which amyloid-beta peptides impair brain
function in people with the disease. Cellular prion proteins are usually harmless and exist in all cells, but they can change shape and cause disease. Essentially, in Alzheimer's, they appear to start the cascade that makes the neurons sick.
These concepts raise several questions – can the amyloid plaques be stopped or slowed down from developing or can they be eliminated or reversed in some way.
The study by the Genentech team, which was reported in Nature, suggests a new mechanism for the pathogenesis of Alzheimer's disease by
outlining a process that could be an early step in the
The work also identifies a trio of new AD
targets, which the company is pursuing with preclinical programs. The
study suggests that the previously ignored amino-terminal portion of
amyloid precursor protein (APP), called N-APP, might be the main
culprit behind AD. APP is a transmembrane protein that gives rise to
N-APP and the much more commonly known amyloid (A), a fragment that
forms the amyloid fibres and plaques that are hallmarks of AD, although
the precise role of these in the disease pathology is
unclear. A schematic is shown below, from the Nature article:
Of course, none of this new research is going to help those of us who are struggling with parents with AD, but perhaps by the time we are seniors there will be some improvements in available therapies and earlier detection of this devastating disease. There is some justification for that raised hope because a newly discovered mutation, the A673V mutation, is associated with familial AD. The
inheritance pattern is recessive, meaning a patient needs two mutant
alleles in order to acquire the disease risk. This is unusual because most AD is sporadic and not inherited.
Regular readers of this blog will be familiar with wild type and mutant mutations seen in cancer conferring different prognosis. It seems that they also appear in AD. Interestingly, in combination with
wild type allele, A673V doesn’t cause AD. The presence of mutant protein prevents the wild type protein from forming amyloid fibrils, even under very favorable in vitro conditions.
As we learn more about the biology of Alzheimers Disease, hopefully new and better treatments will be developed. Perhaps we might even understand one day what actually causes or triggers the disease to begin it long slow process in the first place. Now that would be something.
Osherovich, L. (2009). Genentech's new parADigm Science-Business eXchange, 2 (8), 1-5 DOI: 10.1038/scibx.2009.300
Di Fede, G., Catania, M., Morbin, M., Rossi, G., Suardi, S., Mazzoleni, G., Merlin, M., Giovagnoli, A., Prioni, S., Erbetta, A., Falcone, C., Gobbi, M., Colombo, L., Bastone, A., Beeg, M., Manzoni, C., Francescucci, B., Spagnoli, A., Cantu, L., Del Favero, E., Levy, E., Salmona, M., & Tagliavini, F. (2009). A Recessive Mutation in the APP Gene with Dominant-Negative Effect on Amyloidogenesis Science, 323 (5920), 1473-1477 DOI: 10.1126/science.1168979