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Is GSK-3B connected to Alzheimer's pathology?
Serenoa
Posted: Monday, October 13, 2014 8:41 PM
Joined: 4/24/2012
Posts: 484


New research is connecting this enzyme to the Amyloid Hypothesis.

 

 http://www.alzheimersreadingroom.com/2014/10/neuroscientist-replicates-alzheimers-disease.html
 

 

I read up on GSK-3 and found it is connected to many of the same biological pathways involved in Alzheimer's. Here's the Wiki:

 

http://en.wikipedia.org/wiki/GSK-3

 

Any thoughts on this? Lane?


Lane Simonian
Posted: Tuesday, October 14, 2014 12:28 AM
Joined: 12/12/2011
Posts: 4854


This is one of the better articles on GSK-3 and Alzheimer's disease. 


 

FASEB J. 2006 Jul;20(9):1431-42.

Peroxynitrite induces Alzheimer-like tau modifications and accumulation in rat brain and its underlying mechanisms.

Abstract

To investigate the upstream effector that led to tau hyperphosphorylation, nitration, and accumulation as seen in Alzheimer's disease brain, and the underlying mechanisms, we bilaterally injected SIN-1, a recognized peroxynitrite donor, into the hippocampus of rat brain. We observed that the level of nitrated and hyperphosphorylated tau was markedly increased in rat hippocampus 24 h after drug administration, and these alterations were prevented by preinjection of uric acid, a natural scavenger of peroxynitrite. Concomitantly, we detected a significant activation in glycogen synthase kinase-3beta (GSK-3beta) and p38 MAPKs, including p38alpha, p38beta, and p38delta, but no obvious change was measured in the activity of p38gamma, ERK, and c-Jun amino-terminal kinase (JNK). Both nitrated tau and hyperphosphorylated tau were aggregated in the hippocampus, in which the activity of 20S proteasome was significantly arrested in SIN-1-injected rats. Further studies demonstrated that the hyperphosphorylated tau was degraded as efficiently as normal tau by 20S proteasome, but the nitrated tau with an unorderly secondary structure became more resistant to the proteolysis. These results provide the first in vivo evidence showing that peroxynitrite simultaneously induces tau hyperphosphorylation, nitration, and accumulation, and that activation of GSK-3beta, p38alpha, p38beta, p38delta isoforms and the inhibition of proteasome activity are respectively responsible for the peroxynitrite-induced tau hyperphosphorylation and accumulation. Our findings reveal a common upstream stimulator and a potential therapeutic target for Alzheimer-like neurodegeneration.

 

One of the main pathways to inactivating GSK-3 is the phosphatidylinositol 3-kinase/Akt pathway but this pathway is inactivated in Alzheimer's disease. 


 

The mechanisms of peroxynitrite-induced apoptosis are not fully understood. We report here that peroxynitrite-induced apoptosis of PC12 cells requires the simultaneous activation of p38 and JNK MAP kinase, which in turn activates the intrinsic apoptotic pathway, as evidenced by Bax translocation to the mitochondria, cytochrome c release to the cytoplasm and activation of caspases, leading to cell death. Peroxynitrite induces inactivation of the Akt pathway. Furthermore, overexpression of constitutively active Akt inhibits both peroxynitrite-induced Bax translocation and cell death. Peroxynitrite-induced death was prevented by overexpression of Bcl-2 and by cyclosporin A, implicating the involvement of the intrinsic apoptotic pathway. Selective inhibition of mixed lineage kinase (MLK), p38 or JNK does not attenuate the decrease in Akt phosphorylation showing that inactivation of the Akt pathway occurs independently of the MLK/MAPK pathway. Together, these results reveal that peroxynitrite-induced activation of the intrinsic apoptotic pathway involves interactions with the MLK/MAPK and Akt signaling pathways. 


 

While it is true that if you inhibit GSK-3, you can have amyloid without tau tangles (as the authors of the most recent study note) this likely almost never happens in reality because if you inhibit the Akt pathway you are going to have both tangles and amyloid. 


Lane Simonian
Posted: Tuesday, October 14, 2014 8:41 PM
Joined: 12/12/2011
Posts: 4854


A different angle to the Tanzi research. 


 

Peroxynitrite nitration of the phosphatidylinositol 3-kinase/Akt pathway-- activation of GSK-3,--tau hyperphosphorylation and tau nitration. 


 

Abstract

Abnormally nitrated tau has been found recently in the neurofibrillary tangles of Alzheimer’s disease (AD). However, whether and how nitration of tau is involved in AD pathology is not known. Herein, we found that in vitro incubation of peroxynitrite with recombinant tau resulted in nitration and oligomerization of tau in a dosage-dependent manner. Moreover, the nitrated tau showed a significantly decreased binding activity to taxol-stabilized microtubulesin in vitro. Further study demonstrated that peroxynitrite also induced tau nitration in neuroblastoma N2a cell line, and the nitrated tau was accumulated in the cells. We conclude that abnormal nitration of tau contributes to the impaired biological activity of tau in binding to the microtubules and the aggregation of tau, implying a novel mechanism responsible for the neurodegeneration seen in AD brain.

 

Peroxynitrite-generated caspases--beta secretase--c-terminal fragment (which in turn increases peroxynitrite formation and is more toxic than amyloid oligomers and plaques). 


 

Over-activation of tyrosine receptor kinases, g protein-coupled receptor, or g proteins and/or peroxynitrite mediated cytochrome-c release--intracellular calcium release via inositol 1,4,5 triphosphate receptors--gamma secretease--amyloid oligomers. 

 

Nitration of amyloid oligomers--amyloid plaques. 


 

There are several set of possibilities: 

 

Only inhibit GSK3: amyloid but not tau tangles 

 

Relatively low levels of oxidative stress or scavenge peroxynitrites under conditions of medium to high oxidative stress: some amyloid and tau tangles but not Alzheimer's disease. 

 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3749371/ 


 

Inhibit intracellular calcium release under conditions of high oxidative stress (with caffeine and heparin for instance): little to no amyloid but Alzheimer's disease. 

 

http://www.sciencedebate.com/science-blog/alzheimer-s-disease-without-amyloid-plaques 


Serenoa
Posted: Tuesday, October 14, 2014 9:26 PM
Joined: 4/24/2012
Posts: 484


Thanks Lane. So we do have connections here. Interesting...

Lane Simonian
Posted: Wednesday, October 15, 2014 7:46 PM
Joined: 12/12/2011
Posts: 4854


Alzheimer's disease can be summed up in the following two quotes: 


 

The alternate hypothesis is that Aβ simply represents a bystander or a protector rather than the causative factor of disease (Smith et al., 2002; Lee et al., 2003, 2004b). Notably, all therapeutic studies that have an effect on Aβ levels in cells or animals have shown extremely poor or no efficacy in subsequent clinical trials. This includes indomethacin (Weggen et al., 2001), ibuprofen (Lim et al., 2000), sulindac sulfide (Weggen et al., 2001), a nitric oxide-releasing nonsterodial anti-inflammatory drug (Jantzen et al., 2002), and estrogen (Zheng et al., 2002). Clearly, the alternate hypothesis points to greater therapeutic efficacy by directing efforts to the upstream metabolic and oxidative abnormalities that are what led to Aβ.


[Clinical trials with over-the-counter supplements have concentrated either on items which suppress inflammation or on antioxidants which scavenger oxygen derived free radicals. Most of these items have proved to be worthless in the treatment of Alzheimer's disease. Similarly most drugs used to treat Alzheimer's disease do little to slow the deterioration, but instead offer a mild temporary symptom relief. However, evidence has been accumulating that the primary driver of Alzheimer's disease is a nitrogen derived free radical called peroxynitrites which may mediate both amyloid and tau accumulation as well as their toxicity. Excellent results have been obtained with peroxynitrite scavengers, with reversals of Alzheimer's disease being repeatedly demonstrated. IMHO, the only thing which may be preventing the abolition of Alzheimer's disease is the mental inertia of scientists as well as the bureaucrats who fund them. Unfortunately, most bureaucrats keep throwing money into repeatedly testing discredited interventions, while ignoring successful ones. Common sense is anything but...]

 

The bad news is that there are dozens of factors (diet, lifestyle, genetics, environmental toxins, medications, and viral and bacterial infections) that can cause oxidative stress.  The good news is that there are a half dozen or more plant compounds that can partially reverse the oxidative damage done to the brain in Alzheimer's disease. 


Lane Simonian
Posted: Wednesday, October 15, 2014 11:43 PM
Joined: 12/12/2011
Posts: 4854


Here is another good one involving peroxynitrites, GSK-3, hyperphosphorylated tau and antioxidants.


 2006 Sep;41(2):124-9.

Melatonin arrests peroxynitrite-induced tau hyperphosphorylation and the overactivation of protein kinases in rat brain.

Abstract

The purpose of this study was to examine the in vivo effect of melatonin (MEL) on peroxynitrite-induced tau hyperphosphorylation and the involvement of glycogen synthase kinase-3beta (GSK-3beta) and mitogen-activated protein kinase (MAPK) families. Melatonin was injected into the right cerebroventricle of the rats 1 hr before the bilateral hippocampal injection of 3-morpholino-sydnonimine chloride (SIN-1), the recognized donor of peroxynitrite. Thereafter, the phosphorylation level of tau and the activity of the kinases were analyzed. The injection of SIN-1 induced hyperphosphorylation of tau at pS396 epitope with a concomitant activation of GSK-3beta and selective MAPK isoforms including p38alpha, p38beta, and p38delta but not p38gamma. The effect of peroxynitrite was confirmed using uric acid, a recognized scavenger of peroxynitrite. Preinjection of MEL significantly arrested the peroxynitrite-induced hyperphosphorylation of tau and the activation of GSK-3beta and MAPKs. Melatonin also ameliorated peroxynitrite-induced oxidative stress. We conclude that MEL can efficiently arrest peroxynitrite-induced tau hyperphosphorylation, and the underlying mechanism may involve scavenging the reactive species and suppressing the activated GSK-3beta and p38 MAPK family.


Lane Simonian
Posted: Friday, October 17, 2014 4:31 PM
Joined: 12/12/2011
Posts: 4854


This one on tau is rather fascinating: 


 

Non-filamentous tau intermediates and neurotoxicity

The development of NFT is initiated by the formation of pre-tangles of oligomeric tau that assemble into insoluble filaments before aggregating to form NFT. Prior to, during or after this process, tau undergoes numerous, and potentially harmful, modifications. Therefore, though NFT may themselves be neurotoxic, the presence of some of these modifications may be indicative of tau-mediated damage that arose before their deposition. Indeed, tau-mediated neuronal death, in the absence of tau filaments, is observed in Drosophila and some transgenic mouse models overexpressing htau [65-67]. Mice overexpressing htau with the P301L mutation (rTg4510 mice) do develop age-related NFT, neuronal loss and memory impairments. Yet, the subsequent suppression of the mutant tau stabilizes neuronal loss and improves memory function even though NFT continue to accumulate [47]. In rTg4510, a regional dissociation between neuronal loss and the accumulation of NFT is observed; there is a loss of neurons in the dentate gyrus before NFT lesions appear and, conversely, NFT appear without major cell loss in the striatum [68]. Likewise, many of the neurons that accumulate NFT in aged transgenic mice overexpressing normal htau seem "healthy" in terms of nuclear morphology, while a number of dying neurons do not appear to have a significant load of tau filaments [69]. Furthermore, using models based on quantitative data on neuron loss and NFT formation as a function of disease duration, it is estimated that CA1 hippocampal neurons in AD can survive with NFT for approximately 20 years [70]. Together, these studies suggest that tau-mediated neuronal death does not require the formation of NFT. Rather, non-filamentous tau, as well as abnormally modified tau intermediates, may be neurotoxic. Indeed, tau can undergo numerous post-translational modifications and some of these modifications, like phosphorylation and glycosylation, are believed to occur early in the development of tau pathology [71,72]. However, it is not yet known which tau intermediates are critical for the development of the different stages of neurodegeneration and by which mechanisms these intermediates cause cellular injury.

 

There are a number of ways in which tau can become hyperphosphorylated but the one involving GSK-3 activation is the critical one, because the peroxynitrite-mediated nitration of the phosphatidylinositol-3 kinase not only causes the hyperphosphorylation of tau it also causes the nitration of tau.   


 

In addition to the incorporation of truncated tau into NFT, the PHF and NFT in AD brains are glycated[166] as well as ubiquitinated [167,168], but these modifications are believed to be later events in disease progression. Nitrated tau is also detected in cytoplasmic inclusions in AD, corticobasal degeneration, Pick's disease, progressive supranuclear palsy and FTPD-17 [169]. Tau-nY29, an antibody specific for tau when nitrated at Tyr29, detects soluble tau and PHF-tau from severely affected AD brains but fails to recognize tau from normal aged brains, suggesting that tau nitration is disease-specific [170]. The exact mechanisms by which nitrated tau contributes to pathology, however, remain poorly understood. Nitration can greatly affect protein folding and function[171,172]. Peroxynitrite (ONOO-), which is capable of both protein nitration and oxidation [173], leads to tau oligomerization in vitro and in neuroblastoma cells [174,175]. Yet, it is believed that this effect results from the oxidative role of peroxynitrite and the formation of dityrosine bonds in tau[175]. The overall effect of tau nitration by peroxynitrite in vitro is to delay the polymerization of tau into filaments [175,176]. The toxicity of tau nitration may instead result from the inhibitory effect of nitration on the ability of tau to promote tubulin assembly which could compromise microtubule function [177]. 

 

http://www.molecularneurodegeneration.com/content/4/1/13 


 

The principal damage done to the brain occurs before tau aggregates into tangles and before the c-terminal fragment is converted into amyloid oligomers and plaques.  Regarding the c-terminal fragment in Alzheimer's disease: 

 

In conclusion, the demonstration for the first time of the calcium homeostasis-distrupting effect of CT 105 peptide would support the evidence for its involvement in neurodegeneration characteristic of AD.  Also, it can be postulated that an altered processing or overproduction of APP could result in the intracellular production of the CT fragment, calcium homeostasis disruption, and triggering lethal process.  The AB-bearing CT fragment is not only the precursor of Ab production, but is also a more active and toxic product than AB.  Internal CT fragments may be further metabolized to AB, which is deposited in the brain where it inflicts additional toxicity to neurons.

 

http://www.fasebj.org/content/14/11/1508.full 


 

C-terminal fragments of amyloid precursor protein exert  

 neurotoxicity by inducing glycogen synthase kinase-3β 

 expression [via peroxynitrites--my addition] 


 

 2001 Jul;78(1):109-20.

C-terminal fragment of amyloid precursor protein induces astrocytosis.

Abstract

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.

 

http://www.ncbi.nlm.nih.gov/pubmed/11432978 

 


 

So while amyloid and tau tangles may add to the neurotoxicity in Alzheimer's disease, they are not the primary cause and while most people with Alzheimer's disease will have both amyloid and tangles in their brain, some have the disease with little of either.