Article: Immortalized Parkinson’s Disease Lymphocytes Have Enhanced Mitochondrial Respiratory Activity
Disease Modes &l Mechanisms 2016 Nov 1;9(11):1295-1305.
doi: 10.1242/dmm.025684. Epub 2016 Sep 16
Authors: Sarah J Annesley 1, Sui T Lay 1, Shawn W De Piazza 1, Oana Sanislav 1, Eleanor Hammersley 2, Claire Y Allan 1, Lisa M Francione 1, Minh Q Bui 3, Zhi-Ping Chen 4, Kevin R W Ngoei 4, Flora Tassone 5, Bruce E Kemp 4, Elsdon Storey 6, Andrew Evans 7, Danuta Z Loesch 2, Paul R Fisher 8
1Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia.
2Department of Psychology and Counselling, School of Psychology and Public Health, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3986, Australia.
3Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Victoria 3010, Australia.
4Department of Medicine, University of Melbourne St. Vincent’s Institute of Medical Research, Fitzroy, Victoria 3065, Australia.
5UC Davis MIND Institute, Sacramento, CA 95817, USA.
6Department of Medicine (Neuroscience), Monash University, (Alfred Hospital Campus), Commercial Road, Melbourne, Victoria 3004, Australia.
7Department of Neurology, Royal Melbourne Hospital, Parkville, Victoria 3052, Australia.
8Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia P.Fisher@latrobe.edu.au.
Funders: This study was supported by research funds from La Trobe University’s Department of Microbiology (P.R.F.), School of Life Sciences (P.R.F.) and ‘Understanding Diseases’ Research Focus Area (A.J.S., P.R.F., D.L.); the National Institute of Child Health and Human Development [grant R01 HD 36071 to D.L.]; Michael J. Fox Foundation for Parkinson’s Research and Shake It Up Australia Foundation [grant 10862 to P.R.F., S.J.A., D.J.]; the Australian National Health and Medical Research Council [grant 1068798 and fellowship 1078752 to B.E.K.) and the Australian Research Council [grant DP130104548 to B.E.K.]. This work was supported in part by the Department of Health, State Government of Victoria Operational Infrastructure Support Program.
Mitochondrial dysfunction is theorized to be a contributing factor in PD. It is believed that reductions in mitochondrial respiratory function contribute to PD cytopathology
However, currently there is not a clear understanding of the link between cellular toxicity, mitochondrial changes and the disease process.
The research aim is to examine the role of mitochondrial dysfunction in Parkinson’s Disease- is a reduction in mitochondrial respiratory function causative? Or more likely a result of the disease process?
idiopathic Parkinson’s disease (iPD)- a progressive movement disorder resulting from the loss of nerve cells in the brain that produce a substance called dopamine.
Cytopathology- the study of individual cells in disease.
Mitochondria- membrane-bound cell organelles (mitochondrion, singular) that generate most of the chemical energy needed to power the cell’s biochemical reactions.
lymphocyte –type of white blood cell that is part of the immune system
Lymphoblast- immature white blood cell that gives rise to a type of immune cell known as a lymphocyte.
Reactive Oxygen Species (ROS) – a phrase used to describe a number of reactive molecules and free radicals derived from molecular oxygen
Immortalized cells– a population of cells from a multicellular organism due to mutation, which can escape normal cellular senescence and keep undergoing division. Thus, this kind of cells can grow in vitro for prolonged periods.
A series of investigatory tests using human lympothblasts were conducted. All individuals both with PD and normal, healthy controls were white, male Caucasians aged from 28 to 85 and were of European (mainly northern European) origin, residing in Australia.
ROS production in lymphoblasts from individuals with iPD and controls were measured. Further, analysis was conducted to determine if the flux of electrons from complexes I or II via complexes III and IV to molecular oxygen was elevated or reduced in iPD lymphoblasts compared with controls. Mitochondrial mass and mitochondrial gene copy number in iPD and control lymphoblasts were also measured to determine if elevated mitochondrial respiratory activity of these cells were a result of increased mitochondrial mass.
It was also investigated whether there was a correlation between the various components of mitochondrial respiration, the age of the patient and the duration of clinical disease.
The rates of mitochondrial respiration, ATP synthesis and maximum, uncoupled O2 consumption rates in lymphoblasts from individuals with iPD were fourfold those of control cells.
ROS production was significantly elevated in the cells from individuals with iPD compared with those from an age-matched control group.
However, no significant reduction in mitochondrial membrane potential in iPD lymphoblasts were found compared with controls.
The results showed that in iPD lymphoblasts, mitochondrial respiration and ATP synthesis rates are dramatically elevated. This suggests that ROS production is higher in individuals with PD because mitochondrial electron transport rates are elevated.
It is believed that ROS levels are elevated in PD lymphoblasts because of elevated respiration rates, not because of an impairment or blockade of mitochondrial electron transport in the electron transport chain.
Thus, the increased mitochondrial respiration rates in iPD cells are due to elevated activity of the mitochondria and not to increases in the steady-state mitochondrial mass or genome copy number.
Mitochondrial respiratory activity in iPD lymphoblasts is elevated regardless of patient age, disease duration or disease severity.
Mitochondrial respiratory complexes are functionally normal but dramatically more active in iPD lymphoblasts. Thus, mitochondrial respiratory function is not impaired in PD lymphoblasts.
It seems probable that the relatively rapid turnover of blood cells allows them to avoid the long-term adverse consequences of hyperactive mitochondria.
Finally, the apparently permanent nature of the dramatic elevation in PD lymphoblast respiratory activity suggests that lymphoblasts can occupy two distinct states, a ‘normal’ and a ‘hyperactive’ state characterized by two different metabolic rates.
This being the case, the beginning of the disease process could be initiated by an event that causes a switch from the normal to the hyperactive state.
Several components of mitochondrial respiration in lymphoblasts could provide biomarkers. needed to assist diagnosis and prognosis as well as to test the efficacy of potential treatment regimes.
It seems likely that respirometric assays of lymphoblasts would allow a clear distinction to be made between what might be called primary mitochondrial and non-mitochondrial forms of PD. Such distinctions might be important for diagnosis, prognosis and determination of treatment options in the future, perhaps not only for PD but also for other neurodegenerative diseases in which mitochondrial dysfunction has been implicated, including Alzheimer’s, Huntington’s and motor neuron diseases.
Rodents and non-human primates are used most frequently in PD research. However, the current animal models often fall short in replicating the true pathophysiology occurring in idiopathic PD, and thus results from animal models often do not translate to the clinic. As recommended, if one is attempting to identify blood biomarkers of PD, the investigation should be done directly in humans and therefore the results obtained from the study would be directly applicable to patients. It is encouraging to see human relevant basic research, which is much needed for this devastating disease, which does just this.