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'Chaperone' compounds offer new approach to Alzheimer's treatment
Posted: Tuesday, April 22, 2014 10:07 PM
Joined: 12/6/2011
Posts: 3326

A team of researchers from Columbia University Medical Center (CUMC), Weill Cornell Medical College, and Brandeis University has devised a wholly new approach to the treatment of Alzheimer's disease involving the so-called retromer protein complex. Retromer plays a vital role in neurons, steering amyloid precursor protein (APP) away from a region of the cell where APP is cleaved, creating the potentially toxic byproduct amyloid-beta, which is thought to contribute to the development of Alzheimer's. 


Using computer-based virtual screening, the researchers identified a new class of compounds, called pharmacologic chaperones, that can significantly increase retromer levels and decrease amyloid-beta levels in cultured hippocampal neurons, without apparent cell toxicity. The study was published today in the online edition of the journal Nature Chemical Biology. 


“Our findings identify a novel class of pharmacologic agents that are designed to treat neurologic disease by targeting a defect in cell biology, rather than a defect in molecular biology,” said Scott Small, MD, the Boris and Rose Katz Professor of Neurology, Director of the Alzheimer's Disease Research Center in the Taub Institute for Research on Alzheimer's Disease and the Aging Brain at CUMC, and a senior author of the paper. “This approach may prove to be safer and more effective than conventional treatments for neurologic disease, which typically target single proteins.” 


In 2005, Dr. Small and his colleagues showed that retromer is deficient in the brains of patients with Alzheimer’s disease. In cultured neurons, they showed that reducing retromer levels raised amyloid-beta levels, while increasing retromer levels had the opposite effect. Three years later, he showed that reducing retromer had the same effect in animal models, and that these changes led to Alzheimer's-like symptoms. Retromer abnormalities have also been observed in Parkinson’s disease. 


In discussions at a scientific meeting, Dr. Small and co-senior authors Gregory A. Petsko, DPhil, Arthur J. Mahon Professor of Neurology and Neuroscience in the Feil Family Brain and Mind Research Institute and Director of the Helen and Robert Appel Alzheimer’s Disease Research Institute at Weill Cornell Medical College, and Dagmar Ringe, PhD, Harold and Bernice Davis Professor in the Departments of Biochemistry and Chemistry and in the Rosenstiel Basic Medical Sciences Research Center at Brandeis University, began wondering if there was a way to stabilize retromer (that is, prevent it from degrading) and bolster its function. “The idea that it would be beneficial to protect a protein’s structure is one that nature figured out a long time ago,” said Dr. Petsko. “We’re just learning how to do that pharmacologically.”

Other researchers had already determined retromer’s three-dimensional structure. “Our challenge was to find small molecules—or pharmacologic chaperones—that could bind to retromer’s weak point and stabilize the whole protein complex,” said Dr. Ringe.


This was accomplished through computerized virtual, or in silico, screening of known chemical compounds, simulating how the compounds might dock with the retromer protein complex. (In conventional screening, compounds are physically tested to see whether they interact with the intended target, a costlier and lengthier process.) The screening identified 100 potential retromer-stabilizing candidates, 24 of which showed particular promise. Of those, one compound, called R55, was found to significantly increase the stability of retromer when the complex was subjected to heat stress. 


The researchers then looked at how R55 affected neurons of the hippocampus, a key brain structure involved in learning and memory. “One concern was that this compound would be toxic,” said Dr. Diego Berman, assistant professor of clinical pathology and cell biology at CUMC and a lead author. “But R55 was found to be relatively non-toxic in mouse neurons in cell culture.” 


More important, a subsequent experiment showed that the compound significantly increased retromer levels and decreased amyloid-beta levels in cultured neurons taken from healthy mice and from a mouse model of Alzheimer's. The researchers are currently testing the clinical effects of R55 in the actual mouse model . 


“The odds that this particular compound will pan out are low, but the paper provides a proof of principle for the efficacy of retromer pharmacologic chaperones,” said Dr. Petsko. “While we’re testing R55, we will be developing chemical analogs in the hope of finding compounds that are more effective.” 


Vincent J Mecozzi, Diego E Berman, Sabrina Simoes, Chris Vetanovetz, Mehraj R Awal, Vivek M Patel, Remy T Schneider, Gregory A Petsko, Dagmar Ringe, Scott A Small. Pharmacological chaperones stabilize retromer to limit APP processing. Nature Chemical Biology, 2014; DOI: 10.1038/nchembio.1508  

Biff C
Posted: Wednesday, April 23, 2014 12:52 PM
Joined: 8/20/2013
Posts: 56

Good find Myriam - you beat me to posting this.   While others focus on another aspect of the disease, this appears to be a significant step.  I think I am going to pound the table on this aspect for a while.


Again, it deals with the natural inter-cellualar processes that effect the Amyloid Precursor Protein (APP) and the eventual formation of Amyloid Beta (AB).


This seems to dovetail nicely with the study on SORLA as reported here:

Both being mechanisms that control the intracellular trafficking of APP, rather than cleaning it up after it is formed.


The same research was reported on in the ALZForum.




R55 nestles between retromer subunits (turquoise/orange) and cements their connection, lowering β- and raising α-secretase cleavage of APP. [Image courtesy of Mecozzi et al., Nature Chemical Biology. 



What I find to be of significance is the number of other researchers who commented on this work.  These are the other researchers in the AD fight, not bloggers.  When your competitors for research funds praise your work, you likely are on to something.


Some of those comments:


James J. Lah 

 Scott Small, Dagmar Ringe, Greg Petsko, and their colleagues are to be congratulated on a beautiful piece of science. This paper represents the combination of expert structural biology and AD cell biology to produce simultaneous advances in both arenas. Their results demonstrate rather convincingly that the identified compound (R55) is capable of stabilizing the retromer complex through binding at a Vps35-Vps29 interaction site. The effects of R55 on APP processing also support the notion that enhanced retromer function will tend to shunt APP through a non-amyloidogenic pathway, reduce APP-BACE interaction, and limit Aβ production. 


Samuel Gandy 

The first is that I have become convinced that the conventional one target-one drug approach is willfully naive.  That simple approach made sense before we had the computational tools to begin to address the true complexity of diseases.  Genetic predispositions have been present in humans since conception, and many equilibria will shift as a result. Instituting a one target-one drug intervention in adulthood in hopes of a clinical benefit may well turn out to be a quixotic endeavor. 


Matthew M J Farrer

This study raises some intriguing possibilities. Loss of retromer expression has long been noted in AD, with consequent effects on APP processing and Aβ production. However, retromer recycling appears as a nexus for parkinsonism and dementia. Deficits in neuron transmission and early endosome protein sorting and trafficking are highlighted by the recent discoveries of mutations in DNAJC13 and VPS35, most likely mediated by dominant-negative loss of functional WASH complex. That a chemical chaperone can restore functional retromer activity is a remarkable proof of concept. Further R&D might have broad clinical applications in PD-MCI and dementia. These are exciting times.    



Olav Andersen 

The paper by Mecozzi et al. elegantly demonstrates how a small drug, R55, is able to stabilize the retromer complex, enabling enhanced neuronal transport of APP (and sorLA) out of early endosomal compartments thereby escaping amyloidogenic processing. These novel data strongly support previous studies from several groups, and adds yet additional evidence that retromer plays a pivotal role in the neuronal trafficking of APP together with sorLA. 



So the bottom line is not scavenging some compound that has a part in the Amyloid Cascade, but rather finding the processes that lead to it and stopping those processes.  So be it "sorting" by the SORLA receptor or pharmcological "chaperones" this represents a move in a new direction If we can handle the APP in the cell and boost/repair the natural cellular process that handle APP it sure looks like we can avoid the formation of AB plaques. 






Lane Simonian
Posted: Wednesday, April 23, 2014 2:53 PM
Joined: 12/12/2011
Posts: 5140

The key is likely this: when protein kinase C activity occurs outside of lipid rafts it produces a N-terminal fragment of the amyloid precursor protein that is easily disposed of.   


Activation of PKC resulted in increased shedding of the ectodomains of both APP and SorL1, and this was paralleled by an apparent increase in the level of the phosphorylated form of SorL1. ROCK2, the neuronal isoform of another protein kinase, was found to form complexes with SorL1, and both ROCK2 inhibition and ROCK2 knockdown enhanced generation of both soluble APP and Aβ. 


APP phosphorylation at serine 655 was discovered in 1988 [4], and its physiological role includes regulation of the interaction of APP with the retromer trafficking complex [15] and activation of PKC is associated with increased retromer-mediated transport of APP to the TGN and decreased Aβ generation [15]. 



However, when protein kinase C activity occurs in lipid rafts (which may be increased by cholesterol, saturated fats, and mutations in the Sorl1 gene), you get a c-terminal fragment of the amyloid precursor protein which cannot be easily disposed of.  When this is combined with the release of intracellular calcium, the result is amyloid oligomers and plaques. 



Protein Kinase C Activation Increases Release of Secreted Amyloid 

Precursor Protein without Decreasing Ab Production in Human 

Primary Neuron Cultures. 


Overexpression and altered metabolism of amyloid precursor 

protein (APP) resulting in increased 4 kDa amyloid b peptide 

(Ab) production are believed to play a major role in Alzheimer’s 

disease (AD). Therefore, reducing Ab production in the brain is 

a possible therapy for AD. Because AD pathology is fairly 

restricted to the CNS of humans, we have established human 

cerebral primary neuron cultures to investigate the metabolism 

of APP. In many cell lines and rodent primary neuron cultures, 

phorbol ester activation of protein kinase C (PKC) increases the 

release of the secreted large N-terminal fragment of amyloid 

precursor protein (sAPP) and decreases Ab release (Buxbaum 

et al,. 1993; Gadzuba et al., 1993; Huang et al, 1993).  In contrast, 

we find that PKC activation in human primary neurons increases 

the rate of sAPP release and the production of APP C-terminal 

fragments and 4 kDa Ab.  Our results indicate species--and cell 

type-specific regulation of APP metabolism.  Therefore, our 

results curtail the use of PKC activators in controlling human 

brain Ab levels. 



If all one is doing is inhibiting the beta-secretase that leads to the c-terminal fragment of the amyloid precursor protein or increasing the removal of c-terminal fragments, one is not treating the cause of the disease.  The following gets the order partially mixed up, but the solution is likely the correct one. 



 2001 Jul;78(1):109-20.

C-terminal fragment of amyloid precursor protein induces astrocytosis.


One of the pathophysiological features of Alzheimer's disease is astrocytosis around senile plaques. Reactive astrocytes may produce proinflammatory mediators, nitric oxide, and subsequent reactive oxygen intermediates such as peroxynitrites. In the present study, we investigated the possible role of the C-terminal fragment of amyloid precursor protein (CT-APP), which is another constituent of amyloid senile plaque and an abnormal product of APP metabolism, as an inducer of astrocytosis. We report that 100 nM recombinant C-terminal 105 amino acid fragment (CT105) of APP induced astrocytosis morphologically and immunologically. CT105 exposure resulted in activation of mitogen-activated protein kinase (MAPK) pathways as well as transcription factor NF-kappaB. Pretreatment with PD098059 and/or SB203580 decreased nitric oxide (NO) production and nuclear factor-kappa B (NF-kappaB) activation. But inhibitors of NF-kappaB activation did not affect MAPKs activation whereas they abolished NO production and attenuated astrocytosis. Furthermore, conditioned media derived from CT105-treated astrocytes enhanced neurotoxicity and pretreatment with NO and peroxynitrite scavengers attenuated its toxicity. These suggest that CT-APP may participate in Alzheimer's pathogenesis through MAPKs- and NF-kappaB-dependent astrocytosis and iNOS induction.


The c-terminal fragment of the amyloid precursor protein (which is all one needs to have for Alzheimer's disease), amyloid oligomers, and amyloid plaques are largely the result not the cause of peroxynitrite formation. Removing them may slow down the progression of the disease, but ultimately does not stop that progression.  Instead, one needs to work upstream from each of them early on and scavenge peroxynitrites at all stages of the disease.