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Showing posts with label TSC. Show all posts
Showing posts with label TSC. Show all posts

Thursday 2 October 2014

Dendritic Spines in Autism – Why, and potentially how, to modify them





This blog is getting rather more detailed than I had anticipated.  

Today’s post is about something very complex, but not fully understood by anyone, so I will be somewhat superficial in my coverage.  Just click on the links to learn more detail.

There are two words that may be new to you – Morphology and Dendritic Spines.





Morphology, in biology, the study of the size, shape, and structure of animals, plants, and microorganisms and of the relationships of the parts comprising them.

For today it is really could be thought of as the variability in size and shape of something.


A dendritic spine is a small protrusion from a neuron's dendrite that typically receives input from a single synapse. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body. Most spines have a bulbous head (the spine head), and a thin neck that connects the head of the spine to the shaft of the dendrite. The dendrites of a single neuron can contain hundreds to thousands of spines. In addition to spines providing an anatomical substrate for memory storage and synaptic transmission, they may also serve to increase the number of possible contacts between neurons.







Now we combine our two new words and have a better summary of what this post is about:

Morphology of dendritic spines and mental disease

It turns out that shape of dendritic spines may play a key role in mental disease, including autism.

The shape is not fixed and live imaging studies have revealed that spines are remarkably dynamic, changing size and shape over timescales of seconds to minutes and of hours to days.

The shape is important as it impacts on function, malformations lead to dysfunctions that can affect a myriad of brain functions.

Here are some variations in the shape of dendritic spines.









In case you are thinking this is all rather abstract, let’s jump forward to a patent for a possible new treatment for autism.


Afraxis Patent

  
SUMMARY OF THE INVENTION

Described herein are p21 -activated kinase (PA ) inhibitors that alleviate, ameliorate, delay onset of, inhibit progression of, or reduce the severity of at least one of the symptoms associated with autism.

Claims  

WHAT IS CLAIMED IS:

1. A method for treating autism comprising administering to an individual in need thereof a therapeutically effective amount of a p21 -activated kinase (PAK) inhibitor.
2. The method of claim 1, wherein the PAK inhibitor modulates dendritic spine morphology or synaptic function.
3. The method of claim 2, wherein the PAK inhibitor modulates dendritic spine density.
4. The method of claim 2 or 3, wherein the PAK inhibitor modulates dendritic spine length.
5. The method of any of claims 1-4, wherein the PAK inhibitor modulates dendritic spine neck diameter.
6. The method of any one of claims 1-5, wherein the PAK inhibitor modulates dendritic spine head volume.
7. The method of any one of claims 1-6, wherein the PAK inhibitor modulates dendritic spine head diameter.
8. The method of claim 1 or 2, wherein the PAK inhibitor modulates the ratio of the number of mature dendritic spines to the number of immature dendritic spines.
9. The method of claim 1 or 2, wherein the PAK inhibitor modulates the ratio of the dendritic spine head diameter to dendritic spine length.
10. The method of claim 1 or 2, wherein the PAK inhibitor modulates synaptic function.

Etc …

Of course, plenty of patents turn out to be worthless nonsense, but I think the people at Afraxis do know what they are doing; time will tell.



Morphology or Number of Dendritic Spines?

The PAK1 researchers and others believe the morphology (shape) of the dendritic spines is the problem, others believe the problem is that there are just too many of them.

Research has shown that a particular gene (NrCAM) can increase/decrease the number of dendritic spines.

Studies at University of North Carolina showed that knocking out the NrCAM gene caused mice to exhibit the same sorts of social behaviors associated with autism in humans.

Researchers from Columbia University found an overabundance of the protein MTOR in mice bred to develop a rare form of autism. By using a drug to limit MTOR in mice, the Columbia researchers were able to decrease the number of dendritic spines and thus prune the overabundance of synaptic connections during adolescence. As a result, the social behaviors associated with autism were decreased. However, the drug (Rapamycin) used to limit MTOR can cause serious side effects.



Dr. Tang measured synapse density in a small section of tissue in each brain by counting the number of tiny spines that branch from these cortical neurons; each spine connects with another neuron via a synapse.
By late childhood, she found, spine density had dropped by about half in the control brains, but by only 16 percent in the brains from autism patients.
“It’s the first time that anyone has looked for, and seen, a lack of pruning during development of children with autism,” Dr. Sulzer said, “although lower numbers of synapses in some brain areas have been detected in brains from older patients and in mice with autistic-like behaviors.”
Using mouse models of autism, the researchers traced the pruning defect to a protein called mTOR. When mTOR is overactive, they found, brain cells lose much of their “self-eating” ability. And without this ability, the brains of the mice were pruned poorly and contained excess synapses. “While people usually think of learning as requiring formation of new synapses, “Dr. Sulzer says, “the removal of inappropriate synapses may be just as important.”

“What’s remarkable about the findings,” said Dr. Sulzer, “is that hundreds of genes have been linked to autism, but almost all of our human subjects had overactive mTOR and decreased autophagy, and all appear to have a lack of normal synaptic pruning. This says that many, perhaps the majority, of genes may converge onto this mTOR/autophagy pathway, the same way that many tributaries all lead into the Mississippi River. Overactive mTOR and reduced autophagy, by blocking normal synaptic pruning that may underlie learning appropriate behavior, may be a unifying feature of autism.”


Maness, a member of the UNC Neuroscience Center and the Carolina Institute for Developmental Disabilities, also said that there are likely many other proteins downstream of NrCAM that depend on the protein to maintain the proper amount of dendritic spines. Decreasing NrCAM could allow for an increase in the levels of some of these proteins, thus kick starting the creation of dendritic spines.

Knocking out the gene NrCAM increases the number of dendritic spines  
   
Gene linked to increased dendritic spines -- asignpost of autism

  
The view from Japan

RIKEN is a large research institute in Japan, with an annual budget of US$760 million.  Their Brain Science Institute (BSI) has a mission to produce innovative research and technology leading to scientific discoveries of the brain.  So RIKEN  BSI is like MIT just for the brain.

Science does tend to stratify by geography.  Just as we saw that NGF (Nerve Growth Factor) is the preserve of the Italians, when it comes to PAK it is the Japanese.
As you can see below the Japanese are firmly behind PAK1. 

Abstract
The serine/threonine kinase p21-activated kinase 1 (Pak1) modulates actin and microtubule dynamics. The neuronal functions of Pak1, despite its abundant expression in the brain, have not yet been fully delineated. Previously, we reported that Pak1 mediates initiation of dendrite formation. In the present study, the role of Pak1 in dendritogenesis, spine formation and maintenance was examined in detail. Overexpression of constitutively active-Pak1 in immature cortical neurons increased not only the number of the primary branching on apical dendrites but also the number of basal dendrites. In contrast, introduction of dominant negative-Pak caused a reduction in both of these morphological features. The length and the number of secondary apical branch points of dendrites were not significantly different in cultured neurons expressing these mutant forms, suggesting that Pak1 plays a role in dendritogenesis. Pak1 also plays a role in the formation and maintenance of spines, as evidenced by the altered spine morphology, resulting from overexpression of mutant forms of Pak1 in immature and mature hippocampal neurons. Thus, our results provide further evidence of the key role of Pak1 in the regulation of dendritogenesis, dendritic arborization, the spine formation, and maintenance.


SHANK3 and Dendritic Spines

Mutations of the SHANK3 gene are known to cause autism. 

Researchers in France found that SHANK3 mutations lead to modification of dendritic spine morphology and they identified the mechanism.



You may recall in my earlier posts on growth factors that it was this type of autism that responded to treatment with IGF1.



If you take a broader look at today’s subject you will see that various growth factors are indeed closely involved.  Here is some comment from Wayman Lab at Washington State University:- 


"Not surprisingly, abnormalities in dendritic arborization and spinogenesis, which diminish neuronal connectivity, are a common feature of the cognitively compromised aging brain as well as numerous forms of mental retardation including Fragile X, Fetal alcohol, Downs and Retts syndromes.

It is clear that changes in synaptic activity and neurotropic factors (e.g., BDNF) are effective initiators of the remodeling process and result in long-term alterations in dendrite and spine structure. What is not known are the molecular mechanisms that underlie how they stimulate dendritic spine formation."


Take your pick

So it looks like three different methods may exist to potentially modify dendritic spine numbers and morphology:-


1.   PAK1

Much work is ongoing regarding PAK1.  It is my current favorite.
For those interested here is a recent study using FRAX486 on Fragile X mice.


Abnormal dendritic spines are a common feature in FXS, idiopathic autism, and intellectual disability. Thus, this neuroanatomical abnormality may contribute to disease symptoms and severity. Here we take a hypothesis-driven, mechanism-based approach to the search for an effective therapy for FXS. We hypothesize that a treatment that rescues the dendritic spine defect may also ameliorate behavioral symptoms. Thus, we targeted a protein that regulates spines through modulation of actin cytoskeleton dynamics: p21-activated kinase (PAK). In a healthy brain, PAK and FMRP - the protein product of fmr1 - antagonize one another to regulate spine number and shape. Inhibition of PAK with a strategy utilizing mouse genetics reverses spine abnormalities as well as cognitive and behavioral symptoms in fmr1 KO mice, as we demonstrated in our previous publication. This discovery highlights PAK as a potential target for drug discovery research. In this thesis work, we build on this finding to test whether the small molecule FRAX486 - selected for its ability to inhibit PAK - can rescue behavioral, morphological, and physiological phenotypes in fmr1 KO mice. Our results demonstrate that seizures and behavioral abnormalities such as hyperactivity, repetitive movements, and habituation to a novel environment can all be rescued by FRAX486. Moreover, FRAX486 reverses spine phenotypes in adult mice, thereby supporting the hypothesis that a drug treatment which reverses the spine abnormalities can also treat neurological and behavioral symptoms.


2. mTOR

In spite of its noted toxicity, Rapamycin, is about to be tested in a clinical trial on a rare type of autism called TSC:-



Funnily enough the trial is taking place at the Kennedy Krieger Institute.

When commenting on the use of Bumetanide for autism, I recall the President of the Institute was quoted as saying:-


"So many things cure cancer in mice and rats, and so many things cure all kinds of things and then when we give them to humans they have adverse effects and don't fix the problems we thought they could fix," says Gary Goldstein, president and CEO of the Kennedy Krieger Institute, a Baltimore-based clinic and research center. "I wouldn't give it to my child, I can tell you that."

I found it a little odd that he gave the green light to trialing Rapamycin in children, given the long list of very nasty side effects.

  
3.  NrCAM 

Manesslab at UNC is clearly the centre for research into finding therapeutic agents surrounding NrCAM.  It looks like this is still some way from trials in humans.

“Too many spines and too many excitatory connections that are not pruned between early childhood and adolescence could be one of the chief problems underlying autism. Our goal is to understand the molecular mechanisms involved in pruning and find promising targets for therapeutic agents.”



Conclusion

It should not be surprising that multiple pathways may have the same therapeutic benefit on dendritic spines.  We only need one to be safe and effective.

The link back to human growth factors is interesting since we know these are disturbed in autism and other mental conditions, but the dysfunction varies by sub-type.  In fact, Nerve Growth Factor (NGF) would likely be an effective therapy for dementia and perhaps even Retts syndrome.

In the next post we will learn some more interesting things about growth factor anomalies in autism.  It turns out that something called Akt, also known as protein kinase B (PKB), may be behind them all. A related protein called protein kinase C (PKC), is known to affect the morphology of dendritic spines. There is also protein kinase A (PKA).  Both PKA and PKB have been shown to have reduced activity in regressive autism, this will also be covered later. 






Tuesday 7 May 2013

Pep up those Purkinje cells

In the previous post we established that both oxidative stress and neuroinflammation can be measured.  We learned from the clever people at Johns Hopkins that the site of the greatest inflammation is in the  cerebelleum; as they put it:-

Based on our observations, selective processes of neuronal degeneration and neuroglial activation appear to occur predominantly in the Purkinje cell layer (PCL) and granular cell layer (GCL) areas of the cerebellum in autistic subjects.

Now, you may recall that I recommended an excellent book called "Autism: Oxidative Stress, Inflammation and Immune Abnormalities".  The book is from 2010, and since then the authors have been busy.  In 2012 they published a study called:   Brain Region-Specific Glutathione Redox Imbalance in Autism
This study tells us which parts of the brain are most affected by oxidative stress.  The abnormal level of GSH redox (the marker for oxidative stress) was highest in the cerebellum and in the temporal cortex.
This is good to hear, since I have assumed that oxidative stress and neuroinflammation are essentially part of the same process and that what halts one, will likely halt the other.
 

Purkinje Cells
Purkinje cells are a class of GABAergic (controlled by the neurotransmitter GABA) located in the cerebellum.
Purkinje cells are some of the largest neurons in the human brain, perhaps this makes them target of stress and inflammation.
Purkinje cells send inhibitory projections to the deep cerebellar nuclei, and constitute the sole output of all motor coordination (and maybe more?) from the cerebellum.

In humans, Purkinje cells are affected in a variety of diseases ranging from toxic exposure (alcohol, lithium), to autoimmune diseases and to genetic mutations (spinocerebellar ataxias, Unverricht-Lundborg disease and autism) and neurodegenerative diseases that are not thought to have a known genetic basis (cerebellar type of multiple system atrophy, sporadic ataxias).

Purkinje Damage in Autism
It has been shown that there is a 35 to 50% reduction in the number of Purkinje cells in the autistic cerebellum when compared with a normal cerebellum.  (this comes from a paper on glutamate neuro-transmitter abnormalities)

Here is an excellent and  very readable study all about Purkinje damage in autism, from 10 years ago:-
 Purkinje cell vulnerability and autism: a possible etiological connection

It is proposed that the cell death in the Purkinje cell layer produces the autistic-like behaviours.

Functions of the and temporal lobe and cerebellum
(where the oxidative stress was measured to be highest)

The temporal lobe seem very much related to the problematic areas of autistim, namely:-
·         Processing sensory input

·         Language comprehension
It also contains the hippocampus.  The hippocampus has made an earlier appearance on this blog since one of its main functions is the realease of hormones including TRH (thyrotropin releasing hormone) CRH (Corticotropin releasing hormone) GHRH (growth hormone releasing hormone).  Disfunction of the hippocampus is known to occur in epilepsy (often comorbid with autism).
If you want to read all about the temporal lobe, try this : Anatomy of the temporal lobe.

The cerebellum is commonly associated with motor control function, but it may have a role in cognitive function, such as language.  Damage to the cerebellum is known to causes disorders in fine movement (sloppy handwriting in autism?)
So it would appear at first glance that inflammation in the temporal lobe and cerebellum could indeed account for many autistic-like behaviors.  

 
Pep up those Purkinje cells  -  Indirect or direct action?
As is often the case, there is the direct approach and the indirect approach.  I usually favour the subtle indirect approach; this would be to work on reducing the oxidation and inflammation. 

There may also a direct approach, using a drug developed as an anti-fungal agent, that turned out to be a potent immunosuppressant.    It prevents activation of T cells and B cells by inhibiting their response to interleukin (IL-2). 

Since nothing in neuroscience is clear cut, there is of course a far more complicated alternative explanation of what is going on.  It could be a genetic disorder that is causing the failure in the Purkinje cells.  Take a look:-

Tuberous sclerosis complex (TSC) is a dominant tumour suppressor disorder caused by mutations in either TSC1 or TSC2. TSC causes substantial neuropathology, often leading to autism spectrum disorders (ASDs) in up to 60% of patients. The anatomic and neurophysiologic links between these two disorders are not well understood…. These studies provide compelling evidence that Purkinje cell loss and/or dysfunction may be an important link between TSC and ASD as well as a general anatomic phenomenon that contributes to the ASD phenotype.


The good news is that TSC already has a viable therapy (in mice at least, and in clinical trials), with a drug called rapamycin/sirolimus.  If you look on the web, you will find people experimenting with it.
There have been several studies using mutant mice. 

Autism in mice

In a study of sirolimus as a treatment for TSC, researchers observed a major improvement regarding effects related to autism. The researchers discovered sirolimus regulates one of the same proteins the TSC gene does, but in different parts of the body. They decided to treat mice three to six months old (adulthood in mice lifespans); this increased the autistic mice's intellect to about that of normal mice in as little as three days.

Here are two studies:- 


Before heading down to the pharmacy to ask about Rapamycin, click on this to see a warning or two.  Also TSC is a genetic condition that usually leads to autism.  This does not mean that if you have autism you also have TSC.  It does mean that better understanding TSC may help to better undertand autism.


It looks like the indirect approach is best again.  Just keep taking the NAC !!