passionless Droning about autism

Adventures in Expected Findings Part II – Brain region-specific deficit in mitochondrial electron transport chain complexes in children with autism

Posted on: January 27, 2011


Hello friends –

Hot on the heels of Mitochondrial Dysfunction in Autism, another study on mitochondrial function in the autism population was just released, this time giving us insight into what is happening inside the gated community behind the blood brain barrier.  How potentially inconvenient.  Brain region-specific deficit in mitochondrial electron transport chain complexes in children with autism came out the other day; I’ve yet to receive a full copy (one has been promised to my real world email), but the abstract is juicy enough to warrant a small posting.

Mitochondria play important roles in generation of free radicals, ATP formation, and in apoptosis. We studied the levels of mitochondrial electron transport chain (ETC) complexes, i.e., complexes I, II, III, IV, and V, in brain tissue samples from the cerebellum and the frontal, parietal, occipital, and temporal cortices of subjects with autism and age-matched control subjects. The subjects were divided into two groups according to their ages: Group A (children, ages 4-10 years) and Group B (adults, ages 14-39 years). In Group A, we observed significantly lower levels of complexes III and V in the cerebellum (p < 0.05), of complex I in the frontal cortex (p < 0.05), and of complexes II (p < 0.01), III (p < 0.01), and V (p < 0.05) in the temporal cortex of children with autism as compared to age-matched control subjects, while none of the five ETC complexes was affected in the parietal and occipital cortices in subjects with autism. In the cerebellum and temporal cortex, no overlap was observed in the levels of these ETC complexes between subjects with autism and control subjects. In the frontal cortex of Group A, a lower level of ETC complexes was observed in a subset of autism cases, i.e., 60% (3/5) for complexes I, II, and V, and 40% (2/5) for complexes III and IV. A striking observation was that the levels of ETC complexes were similar in adult subjects with autism and control subjects (Group B). A significant increase in the levels of lipid hydroperoxides, an oxidative stress marker, was also observed in the cerebellum and temporal cortex in the children with autism. These results suggest that the expression of ETC complexes is decreased in the cerebellum and the frontal and temporal regions of the brain in children with autism, which may lead to abnormal energy metabolism and oxidative stress. The deficits observed in the levels of ETC complexes in children with autism may readjust to normal levels by adulthood. (my emphasis)

A few things immediately jump out at me.  Firstly, the Chauhan’s are authors of this paper, who have been around the autism / oxidative stress block since the get go, as authors of the very nice Oxidative stress in autism: increased lipid peroxidation and reduced serum levels of ceruloplasmin and transferrin–the antioxidant proteins, a really nice paper that was one of the first I saw that broke the autism groups into classic and regressive phenotypes with findings of increased oxidative stress in the latter.

Secondly, one of the biggest concerns with Mitochondrial Dysfunction in Autism when it was released a few weeks ago was, whether or not the findings taken from lymphocytes, cells outside of the brain, could be reliably used as proxies for what is happening within the CNS.  Based on the findings in Brain region-specific deficit in mitochondrial electron transport chain complexes in children with autism it would seem that, at least in children, there is an increased frequency of mitochondrial problems in the brain.  Of course, if we acknowledge the reality of the interconnectedness of immune activation, oxidative stress, mitochondrial impairment and what we already know about the CNS in autism, these findings shouldn’t really be all that surprising.  None the less, it is nice to have some direct evidence of this.

Unfortunately, we still don’t know what is causing the problems with mitochondria function in the brain; it is possible, though exceedingly unlikely that all of the participants in this study also had a diagnosable electron chain disorder (I haven’t gotten a full copy of the paper yet).  I think it is possible that there is a feedback loop in place involving the immune response, oxidative stress, and mitochondria that for some reason our children’s physiology cannot shake loose from. 

The very small sample size of the children in this study, five, is an unfortunate reality for nearly all brain based studies in the autism world.  Though I’ve yet to read the full paper, my prediction is that it is liberally peppered with cautious language regarding interpreting the findings widely without further confirmation.  That is probably pretty good thinking.

But, if we look closely, and we taken notice of the where of mitochondrial problems in the autism group was observed, we may have evidence of participatory processes.  Specifically, Chauhan found decreased electron chain transport measurements in the cerebellum, frontal cortex, and temporal cortex.

In Group A, we observed significantly lower levels of complexes III and V in the cerebellum (p < 0.05), of complex I in the frontal cortex (p < 0.05), and of complexes II (p < 0.01), III (p < 0.01), and V (p < 0.05) in the temporal cortex of children with autism as compared to age-matched control subjects, while none of the five ETC complexes was affected in the parietal and occipital cortices in subjects with autism.

(my emphasis)

There have been a few other studies (that I know of) that have looked for brain region specific abnormalities that might be of interest to u.  Brain Region-Specific Changes in Oxidative Stress and Neurotrophin Levels in Autism Spectrum Disorders (ASD), which found increased markers of oxidative stress in the cerebellum:

Consistent with our earlier report, we found an increase in NT-3 levels in the cerebellar hemisphere in both autistic cases. We also detected an increase in NT-3 level in the dorsolateral prefrontal cortex (BA46) in the older autistic case and in the Wernicke’s area and cingulate gyrus in the younger case. These preliminary results reveal, for the first time, brain region-specific changes in oxidative stress marker 3-NT and neurotrophin-3 levels in ASD.

(My emphasis)

Interesting note: the ‘Wernicke’s area’ of the brain plays a large part in language skills, and in fact, damage to the Wernicke’s area can cause a type of aphasia. 

The number of studies that tie together oxidative stress and mitochondrial function are many and numerous to the point of cumbersomeness, I have a short list of them on a previous post about mitochondria function in autism, here

Two of the really nice neuroimmune studies in the autism realm, Neuroglial Activation and Neuroinflammation in the Brain of Patients with Autism, and Immune Transcriptome Alterations In the Temporal Cortex of Subjects With Autism both provide evidence of an ongoing immune response in some of the specific areas of the CNS where Chauhan found impaired mitochondrial function, the cerebellum and the temporal cortex.

From Vargas:

We demonstrate an active neuroinflammatory process in the cerebral cortex, white matter, and notably

in cerebellum of autistic patients.

And

The neuroglial activation in the autism brain tissues was particularly striking in the cerebellum, and the changes were associated with upregulation of selective cytokines in this and other regions of the brain.

 

From Garbett:

 

Expression profiling of the superior temporal gyrus of six autistic subjects and matched controls revealed increased transcript levels of many immune system related genes. We also noticed changes in transcripts related to cell communication, differentiation, cell cycle regulation and chaperone systems.

 

Detangling if these findings are related, and if so, the direction of causality is for another series of studies to discern.  Calls towards the possibility that relationships like this are spurious are common, but I hate to invoke coincidences for no good reason other than coincidences do occur.  My suspicion is that the immune findings and impaired mitochondria findings are related, but a cautious suspicion is all that is warranted at this time.  I do believe that the relationship between immune activation and mitochondria function is being evaluated now; though I do not know if it is being addressed directly in the CNS, which would be ideal.

 

Curiously from my perspective, however, is the finding that young adults and adults with ASD in Chauhan did not exhibit decreased electron chain function.  The original microglia paper from Vargas, Neuroglial Activation and Neuroinflammation in the Brain of Patients with Autism found extensive evidence of an ongoing immune response in the CNS of people with autism into adulthood.  From the standpoint of a theory wherein an immune response were driving the mitochondrial impairment due to increased oxidative stress, the findings in Chauhan of normal mitochondria function are contradictory to what was found in Vargas.  (?) 

 

A few other thoughts occurred to me as I considered the age differences found in Chauhan.  If mitochondrial dysfunction is part of the pathogenic force driving behaviors associated with autism, it is possible that a decrease as adulthood is reached conforms with a general improvement in adaptation many people seem to report.  Alternatively, if we are actually observing a true increase in the number of people with behaviors that can be classified as autistic, that is, the number of children with autism is a new phenomena, the age findings in Chauhan could be artifacts of different underlying causes of autism in the adults versus the children.  I’m a big believer in a wide range of physiological roads to the end point of autistic behaviors, so such a situation doesn’t really bother me conceptually, though it is very, very problematic to put to any kind of designed experiment. 

 

Lastly, for a while now I’ve been putting some thought towards something that’s really been bugging me about the neuroimmune findings in autism when put in context with other ‘classic’ neurological diseases that also exhibit a strong immune component; i.e., Alzheimer’s or Parkinson’s, both of which have strong immune findings as well, but are more strikingly degenerative in nature when compared to autism.  Generally you talk about a child with autism gradually getting better, or in some cases reaching a plateau; but very rarely (or never) is there the steady and unforgiving decrease in function that you see in diseases like Alzheimer’s.  I’m struggling with this reality and how our findings fit in.  I’m not sure how, or if, the age differences in Chauhan are meaningful towards this apparent paradox, but my pattern recognition unit sure is trying to tell me something, I just can’t tell if it’s sending me on (another) snipe hunt or not.

 

When the entire paper lands in my inbox, I may write another post about it.  I’m interested in seeing if any other blogs pick up on this paper or not and what their take on it is.  I’m still sort of in the dark on the machinations of the press cycle as it relates to autism news, but this paper doesn’t seem to have gotten the press release treatment that Mitochondrial Dysfunction in Autism did, even though its findings are just as interesting. 

 

          pD

Advertisements

3 Responses to "Adventures in Expected Findings Part II – Brain region-specific deficit in mitochondrial electron transport chain complexes in children with autism"

I would be interested to know which papers you have found interesting regarding Parkinson’s, including those indicating a “strong immune component” or other similarities to autism such as mito issues or oxi stress, if you have time to post any links.

Hi Twyla –

There are a great many. This search for Parkinson’s and cytokines gave me over 300 hits.

http://www.ncbi.nlm.nih.gov/pubmed?term=parkinsons%20cytokine

As we all know, the details are important, we can’t just count hits in pubmed and think we’ve made a case, but in this instance, the details are there.

Association between sporadic Parkinson disease and interleukin-1 beta -511 gene polymorphisms in the Turkish population

The pathogenesis of Parkinson Disease (PD) remains poorly understood; however, inflammation is thought to play an important role in disease progression. Recent reports suggest that IL-1, a major proinflammatory cytokine, might play a role in PD progression. The purpose of this study was to determine the relationship between IL-1 gene family polymorphisms [IL-1 alpha (-889), IL-1Ra (VNTR) and IL-1 beta (-511, +3953)] and PD in the Turkish population. In this study, we examined the genotypes of IL-1 gene family polymorphisms in 365 individuals, of which 199 were healthy control subjects and 166 were PD patients. No significant differences were found in the genotype distribution or in the allele frequencies of IL-1 alpha (-889), IL-1Ra (VNTR) and IL-1 beta (+3953) between PD cases and control subjects. However, distribution of the IL-1 beta -511 2/2 (T/T) genotype was found to be significantly lower in PD patients than in healthy controls (p = 0.018, x2: 8.242, OR: 2.211, 95% CI: 1.261-3.877). In addition, the IL-1 beta -511 allele 1 (C) frequency was significantly elevated in PD patients versus controls (p = 0.048, x2: 3.87, OR: 1.178, 95% CI: 0.999-1.388). These results suggest that IL-1 alpha (-889), IL-1Ra and IL-1 beta (+3953) gene polymorphisms have no association with PD, while allele 1 (C) of IL-1 beta (-511) is associated with PD and may provide a susceptibility factor for this disease in the Turkish population. Furthermore, the 2/2 (T/T) genotype of IL-1 beta (-511) may protect individuals from PD.

Future directions for immune modulation in neurodegenerative disorders: focus on Parkinson’s disease

One common feature of neurodegenerative diseases is neuroinflammation. In the case of Parkinson’s disease (PD), neuroinflammation appears early and persists throughout the disease course. The principal cellular mediator of brain inflammation is the resident microglia which share many features with related hematopoietically derived macrophages. Microglia can become activated by misfolded proteins including the PD relevant example, alpha-synuclein, a presynaptic protein. When activated, microglia release pro-inflammatory diffusible mediators that promote dysfunction and contribute to the death of the PD vulnerable dopaminergic neurons in the midbrain. Recently, the orphan nuclear receptor Nurr1, well known as a critical determinant in dopaminergic neuron maturation, has been ascribed two new properties. First, it promotes the production and release of the neuropeptide vasoactive intestinal peptide that functions both to stimulate dopaminergic neuron survival and inhibit neuroinflammation. Second, Nurr1 suppresses the expression and release of pro-inflammatory cytokines in glial cells. Herein, we discuss these new findings in context of strategies to attenuate neuroinflammation in PD.

There are a zillion more.

Thanks for stopping by my blog.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Join 36 other followers

%d bloggers like this: