Whilst the cause of Parkinson’s disease remains unknown for the vast majority of sufferers, new research on the inherited form of Parkinson’s disease may offer the potential to yield new insights into treatments.
Parkinson’s disease is caused by the death of dopamine neurons within the brain. This occurs in the substantia nigra in the basal ganglia, a part of the brain responsible for co-ordinating smooth and balanced movement. Dopamine is a powerful neurotransmitter, a special chemical messenger that works within the brain to allow normal motor output. In Parkinson’s disease, the death of these dopamine cells results in the turning down of motor output, resulting in slow, stiff movements.
The factors contributing to the death of these neurons is not yet fully understood, but is thought to be due to a variety of environmental, genetic and possibly ageing factors. In approximately 10% of cases the cause is known to be genetic, related to mutation in a gene called parkin.
The process underlying the death of these cells has been difficult to isolate as the brain is such a highly integrated, complex organ. However, a team of scientists in the US have replicated human dopamine neurons in a laboratory for the first time using the skin cells of Parkinson’s sufferers with the faulty parkin gene. Nerve cells from the Parkinson’s population showed changes in the way they handle dopamine compared to those of healthy controls.
The Parkinson’s cells showed increased stress caused by a build up of damaging molecules. In healthy cells, the parkin gene tightly controls the production of monoamine oxidase (MAO), keeping it at very low levels. MAO catalyses dopamine oxidation and can be toxic. In the cells with the faulty parkin gene, MAO was poorly regulated and expressed at much higher levels, causing the death of dopamine cells. The action of dopamine in supporting neural computation was also disrupted by mutations of the parkin gene.
When the normal parkin gene was given to the faulty cells the effects were reversed.
This research offers several implications for the development and testing of treatment therapies for Parkinson’s disease. Testing new treatments for Parkinson’s disease has always been a challenge. Animal studies have been fraught with difficulty as animal models with the faulty parkin gene do not develop the disease, possibly due to the differences in neural processing required for bipedal movement in humans and quadrupedal movement in most other animals.
By isolating these faulty cells the effects of potential treatments can be studied at the cellular level, and new research may be directed at drug therapies that could mimic the protective functions of healthy parkin genes.
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