Thursday, 17 May 2012

OVERCOMING MITOCHONDRIAL GENETIC DISORDERS

For years the role played by the mitochondria in human diseases has been sorely overlooked. However, recent studies have set in motion an array of important discoveries exploring a possible remedy for debilitating mitochondrial genetic disorders.

In order to understand the incapacitating and broad nature of these diseases, it is first important to understand the process by which they arise. Mitochondria are double membrane-bound organelles found in eukaryotes.

Structure of Mitochondria (Villarreal 2006).

They are commonly referred to as the ‘powerhouse’ of the cell owing to their ability to produce adenosine triphosphate (ATP) by cellular respiration.  Aerobic cellular respiration is comprised of three main reactions: glycolysis, the Krebs cycle, and the electron transport chain (ETC). Together these reactions result in a maximum yield of 36 ATP molecules. 


Aerobic Respiration in Mitochondria (Hyperbaric-Oxygen 2011).
Mitochondrial diseases (mito diseases) are due to mutations, or genetic disorders, in the mitochondrial DNA (mtDNA). Interestingly, mtDNA is maternally inherited; that is, it is hereditary from the mother only.  “The products of most mitochondrial genes help make up the protein complexes of the electron transport chain and ATP synthase” (Reece et al. 2011). Therefore, genetic defects in these proteins reduce the number of ATP molecules generated in aerobic respiration and result in what is referred to as mito diseases.

Recent studies conducted at UCLA, specifically by Dr. Michael Teitell have heavily contributed to providing a treatment for Mito diseases. Their research revealed that polynucleotide phosphorylase (PNPASE) regulates RNA import into the mitochondria; and that reduced PNPASE decreased RNA import and RNA processing. According to UCLA (2012), reduced RNA processing inhibited the translation of proteins required to maintain the mitochondrial electron transport chain that consumes oxygen during cell respiration to produce energy. This led researchers to consider the role of PNPASE in causing mito diseases. Generally, mito disorders are characterised by defective energy production and metabolism processes, leaving organs and cells with insufficient levels of energy to function.

These discoveries lead the way to formulating a treatment for mito diseases. For the most part, mito disorders principally affect the nervous system and cardiac muscles, as these regions of the body are the most vulnerable to energy deficiency. Below is an extensive list of diseases believed to be caused by mutations in mtDNA.

·         Alcheimer’s Disease

·         Aging

·         Cancer

·         Deafness

·         Dementia

·         Diabetes

·         Exercise Intolerance

·         Epilepsy

·         Leigh Syndrome

·         Parkinson’s Disease

·         Rett Syndrome

·         SIDS

As we can see, RNA is a vital component of mtDNA replication, transcription and translation. Using their newfound knowledge, Teitell and Koehler developed a strategy to target and import specific RNA molecules encoded in the nucleus into the mitochondria and, once there, to express proteins needed to repair mitochondrial gene mutations (UCLA 2012). This strategy involves using gene therapy, where copied genes are transferred into a cell so as to repair a defective gene. This astounding breakthrough should alleviate mitochondrial genetic diseases. Although these proposed strategies haven’t yet been put into practice, the prospect remains positive. 

REFERENCES:
Hyperbaric-Oxygen 2011, Aerobic Cellular Respiration, viewed 18 March 2012, http://www.hyperbaric-oxygen-info.com/aerobic-cellular-respiration.html.

Reece, J, Meyers, N, Urry, L, Cain, M, Wasserman, S, Minorsky, P, Jackson, R & Cooke, B 2011, Campbell Biology: Australian Version. 9th edn. Pearsons.

Teitell, MA 2010, ‘PNPASE Regulates RNA import into Mitochondria’, Cell, vol. 142, no. 3, viewed 17 March 2012, http://www.sciencedirect.com/science/article/pii/S0092867410007257.

University of California - Los Angeles Health Science (UCLA), 2012, ‘Overcoming Mitochondrial Genetic Disorders,’ Medical News Today, viewed 17 March 2011, http://www.medicalnewstoday.com/releases/242814.php.

Villarreal, MR 2006, Animal Mitochondrion Diagram, Wikimedia, viewed 18 March 2012, http://commons.wikimedia.org/wiki/File:Animal_mitochondrion_diagram_en.svg.

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