A lay persons guide to the results of a recent research paper - Part II

Today’s article is Part II of a guest post from Ms. Karia Orr. 

There are different types of nuclear receptors but AR belongs to Class I and behaves as shown the diagram below. The cytoplasm is the cytosol (liquid) plus all the other organelles (intracellular components/structures) contained within the cytosol. Ribosome’s are the organelles in cells that make protein following the instructions in mRNA which is a kind of copy of DNA. AR binds to DNA in the nucleus as mentioned and as a result turns genes either on or off. This then results in changes to the copies of the mRNA which head off outside the nucleus to the Ribosome and provide blueprints for the manufacture of proteins. The proteins then have different roles depending on what they are made of and what their destination is. Think of the ribosome’s as a Global distributing car manufacturing plant that makes different models of cars and car components each with a specific blueprint coded in the mRNA.

Basically, the researchers needed to look at every bit of the AR at the amino acid level and this is one heck of a long rosary chain! In essence you need to change one bead (amino acid) at a time and then see what happens. Change a different bead on a fresh new identical chain and do the same ad infinitum. This takes ages as you need to look at the adult creature (so change a bead, wait for the organism to mature in the case of KD then test) but as a fruit fly matures quickly, they utilized this well studied creature. There are some mammalian models out there being used to study KD but this would have taken the researchers 2 decades and a few billion. The research behind this paper took 5 years. Moving on, what have they found using our friend the fruit fly?

Well, previous findings were confirmed, i.e. the androgen has to bind to the receptor for the whole toxic business to begin. In science things have to be confirmed quite a few times and in different ways for them to become fact so this is good! The really interesting stuff to a geek like myself is that the researchers found that:

• Nuclear translocation of mutant AR is insufficient to initiate neurodegeneration, it is necessary for the receptor to head off to the nucleus as it does normally but this does not cause the neurodegeneration. Knowing that activation of the mutant receptor does not create some yucky stuff in the cytoplasm of the cell that causes the toxicity is good to know.
  
• So what next? They found out the step that initiates the neurodegeneration- DNA binding by mutant AR (remember normal AR normally binds to DNA anyhow and is doing it as you read this!).
  
• They also identified and pin pointed coregulators that assist the mutant AR in its toxic dirty work once it has bound to the DNA.

Co-regulators are all over the place in the body and they are specific wee beasties. Think of the way vitamin D is needed by our bodies to absorb calcium. It is, and if you don’t have enough vitamin D you could eat calcium till the cows come home and you will not absorb much. In this example vitamin D could be classed as a co-regulator in calcium absorption. The researchers identified co-regulators to mutant AR dirty work called AF-2 that comes along after AR has bound to the DNA. Remember we talked about locks and keys earlier? Well, Mutant AR has an interaction site where AF-2 binds once AR had bound to the DNA and the researchers disrupted this binding site to show that it was essential for mutant AR to initiate neurodegeneration. If AF-2 doesn’t bind or you stop it binding to mutant AR bound to the DNA, you don’t get toxicity. Additionally if you stop mutant AR binding to the DNA you do not get the toxicity. So, what does this mean in plain English? In essence, it means the researchers have found a potential drug target and this is discussed below. Basically, in discovering drugs it really helps to know what your target is. This does not always happen in drug discovery but it seriously makes life a lot easier. Drug discovery is like a giant 3D complicated jigsaw puzzle with only a very basic diagram to follow and the more knowledge you have, the easier (relatively speaking) it is.

Treatment in the Future
 
First of all it is impossible to put defined timeframes on gene therapy or drug discovery. Gene therapy is the golden goose and with something like KD we are definitely at least a minimum of 15years away as gene therapy is in its infancy.

So what about drugs? Well, the future is a bit brighter here as the paper has identified areas of mutant AR that confer toxicity to your neurons. This had to be confirmed more in higher species but the data is very promising and has identified some pharmacological targets. Also bear in mind that KD belongs to a family of other disease’s so as we find out more about one, it adds to the overall jigsaw of drug discovery in this area and everything moves forward. Experiments and/or trials that fail are also good as it means we have eliminated something and therefore re-evaluated our jigsaw pieces if you like.

So, what about this AF-2 stuff we talked about earlier? As it happens AF-2 is being studied in other disease areas (prostate cancer, hyperandrogenic syndromes and male pattern baldness amongst others) so we know a bit about it and have some drugs that wreck its plans! Therefore, the next steps of research are likely to take some of these AF-2 drugs and see what happens when you put them into a genetically modified mutant AR mouse. Will they halt or slow down the toxicity? Well there is a drug that has been put into a mouse model of KD and did show promising results but this needs to be repeated and replicated in species a bit higher up the evolutionary tree than our other friend, the mouse (see http://www.nature.com/nm/journal/v13/n3/abs/nm1547.html for more info). This waits to be seen but it’s a good step forward to have a pharmacological target to test. Remember your AR does lots of good things so you really don’t want to block its effects all together. What we want to do is let it do what it normally should do but stop this toxicity business which is only a fraction of what it does.

In summary this research paper is quite exciting, we have found out more information and have a pharmacological target to test. This target has been studied in other diseases and we know some information about it and we have some established tool to use to investigate. This opens up a lot of areas for research and as KD is related to other diseases’ the information overlaps and will assist other areas which will in turn assist knowledge on KD. The future is promising.