In 1985, the discovery of a neurotoxin called 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) changed the lives of six Californians. The young people were recreation drug users, who happened to purchase a synthetic form of heroin that, unfortunately, caused them all to simultaneously develop Parkinson’s disease (Palfreman, 2014). Parkinson’s is a progressive disorder that attacks the nervous system (specifically dopaminergic neurons), making it increasingly difficult to perform motor functioning (i.e. movement, speech etc) over time. Typically the disease is developed in older adults, thus raising the question as to why six young people in California were all diagnosed at essentially the exact same time. Research later proved that the concoction created in place of heroin was incidentally the MPTP neurotoxin, which as a result caused the development of Parkinson’s disease. Mustafa et al. (2016) recently looked into the role of the tumour necrosis factor like weak inducer of apoptosis (TWEAK) and its receptor protein Fn-14 in the MPTP model of Parkinson’s disease. Simply put, the target of their study was to see if reducing the efficiency of the TWEAK/Fn14 functioning in certain areas of the brain (substantia nigra, striatum) would affect the functioning of the disease. Neuronal death is associated with increased functioning of the TWEAK-Fn14 signalling process, and so the study focused on the role of TWEAK-Fn14 in Parkinson’s disease using the MPTP neurotoxin in mice.
There were several different procedures and analyses that were undergone, beginning with engineering knockout mice. Knockout mice are simply specimens to which DNA has been genetically engineered so that it does not express particular proteins… in this case the TWEAK or Fn14 proteins. These and wild-type mice both received an MPTP dose, then after seven days they were sacrificed and their brain tissue collected. Some wild-types were treated with a TWEAK neutralizing antibody before they were treated with the MPTP toxin. Human tissues were experimented with as well, with samples obtained from a tissue donor bank. It was observed that the average age of the individuals’ disease onset was roughly 70 years old, none of whom had any family history with Parkinson’s. The Western blot procedure is typically used to detect specific proteins in a sample of tissue. In this experiment, it was used on both the animal and human sample in order to isolate total protein i.e. the entire protein concentration in the tissue. The “blots” (samples) were then treated with TWEAK and ?-actin antibodies so that the proteins of interest could later be targeted. Next, and immunohistochemistry study was performed, which is done to detect antigens (i.e. proteins) by specifically targeting the principle antibodies that are bound to the desired protein. The stain used in this procedure is called a Nissl stain. Invented by Franz Nissl, the Nissl stain works to distinguish between neurons and glia (the two major components of neuroanatomy) making it easy to observe dissections of brain matter under a microscope. The last of the laboratory procedures is the HPLC (high performance liquid chromatography) analysis. This was done in order to detect striatal levels of dopamine. Recall that Parkinson’s is typically classified as a dopaminergic neuron degenerator, and thus levels of dopamine could indicate whether or not experimental procedures were effective.
The results were interpreted based on levels of expression of TWEAK proteins at different time points. It was observed that in acute MPTP treated mice, there was no change in nigral protein levels of TWEAK compared to the control group at any of the various time points. But there was however an observed increase in striatal levels on 2, 4 and 7 days post-treatment of MPTP. Based on the HPLC test, TWEAK and Fn14 removal had no significant effect on the levels of dopamine within the striatum. Any other observed effects were minor, and thus concluded as non-significant. Overall, the results showed that there is only a minor role of the TWEAK protein in Parkinson’s disease but for future endeavours it could certainly be considered as useful in multi-target therapy.
Sources Cited
Mustafa, S. Martin, H.L., Burkly, L., Costa, A., Martins, M.L., Schwaninger, M., Teismann, P. 2016. The Role of TWEAK/Fn14 Signaling in the MPTP-Model of Parkinson’s Disease. Neuroscience 319. pp 116-122.
Palfreman, J. 2014. Author Reflects on Impact of “The Case of the Frozen Addicts” as 2nd Edition Released. The Michael J. Fox Foundation- Foxfeed blog.
<https://www.michaeljfox.org/foundation/news-detail.php?author-reflects-on- impact-of-the-case-of-the-frozen-addicts-as-second-edition-released>.
