by Cynthia Tranchemontagne Biochemistry 658; Spring, 2012

Mitochondria  Aerobic Respiration generate ATP: the form of energy needed to carry out cellular functions and drive anabolism  Numerous Complex Enzymes crucial to the citric acid cycle and electron transport chain in the aerobic pathways  Contains DNA- mtDNA takes about 3000 genes to code for a mitochondrion only 37 genes are located in the mitochondria the rest reside in nuclear DNA- nDNA

Mitochondrial Disease Mitochondrial dysfunction Caused by mutations in mtDNA or the nDNA that code for the mitochondrion - inherited -spontaneous Connection to age- it is thought that deteriorating mitochondrial function is responsible for many of the aspect s of aging `-unclear as to which causes which Mito What? Mystery and lack of awareness Oversimplification of the function of mitochondria Catabolic processes intimately linked with anabolic processes of the 3000 genes that code for a mitochondrion, only about 3% are involved in making ATP!

Mitochondrial Disease Hundreds of different Mitochondrial Diseases Cell differentiation according to function and tissue type- -Same differentiation in mitochondria, giving them specialized processes specific to the tissue type Broad range of tissue types/organ systems affected by disease Multitude of symptoms difficult to diagnose and differentiate as mitochondrial dysfunction Type/location of mutation may affect mitochondrial function in certain tissues, but not in others Multiple mutations are often involved Genocopies / Phenocopies

Leigh’s Syndrome  Neurometabolic disorder  Develops in infancy or childhood  Onset frequently follows a viral infection  Cause: Pyruvate Dehydrogenase Deficiency  Also caused by Respiratory chain enzyme defects: Complexes I, II, IV, and V Original Research Study-  Development of a tool to monitor Pyruvate Dehydrogenase (PDH) activity  Tested on tissue from a patient with Leigh’s Syndrome

Pyruvate Dehydrogenase Complex  One of the largest multienzyme complexes in eukaryotic cells  Mitochondrial matrix  Conversion of pyruvate to acetyl-CoA necessary for entrance to the citric acid cycle for aerobic respiration  Key control point in cellular metabolism the one control point for the citric acid cycle that exists OUTSIDE the cycle  5 enzyme complex, compact arrangement: -3 involved in the conversion: PDH, dihydrolipoyl transacetylase,dihydrolipoyl dehydrogenase -2 involved in control of PDH: pyruvate dehydrogenase kinase (PDK) pyruvate dehydrogenase phosphatase (PDP)

Tight Regulation through Reversible Phosphorylation Control Enzymes PDK 4 isoforms  Phosphorylates PDH  Activated by acetyl-CoA, NADH, ATP  When activated, inhibits PDH activity PDP 2 isoforms  Hydrolysis of ester linkage: Dephosphorylation  Activated by pyruvate, ADP  Leads to reactivation of PDH This regulatory mechanism is currently implicated in varied patterns of metabolic activity in other conditions, as well, such as: Pyruvate Dehydrogenase Deficiency Cancer Obesity Insulin Resistance

Original Research Study Original Research Study: monitoring phosphorylation of the pyruvate dehydrogenase complex Developed: 3 site-specific antibodies to the 3 phosphorylation sites on the E1 α subunit of PDH Purpose : monitor regulatory phosphorylation mechanism for the purpose of understanding its expression and deficiency characteristic to various disorders Mitochondria isolated from rat kidney tissue Confirmed that the phosphorylation of PDH is site specific Different isoforms of PDK & PDP exhibit specificity Found that different tissue types exhibit varying levels of different isoforms Demonstrated varied levels of expression of one specific phosphorylation site across different tissue types Demonstrated use of the site-specific antibodies: Demonstrated pharmacological inhibition of PDKs - shows promise for the development of small molecule treatments for the regulation of PDH activity Demonstrated the use of antibodies to monitor and assess this control mechanism in a patient with Leigh’s Syndrome- low levels of phosphorylation were observed

Treatments No cure for Leigh’s Syndrome and other Mitochondrial Diseases Treatments are geared towards slowing progression of disease and managing symptoms Avoidance of Physiological Stress- no strenuous exercise, no large meals Dietary management and adjustments are key- depends on the pathway(s) that is(are) inhibited For ex) if lipid metabolism not effected at all- then a high fat, low carbohydrate diet would utilize metabolic pathways that are functioning Vitamin / Mineral Supplements Therapies- PT, Speech Therapy, Respiratory Therapy

References Campbell, M. K., & Farrell, S. O. (2012). Biochemistry (7 th ed.). Belmont, CA: Brooks/Cole. Rardin, M. J., Wiley, S. E., Naviaux, R. K., Murphy A. N., & Dixon, J. E. (June 15, 2009). Monitoring phosphorylation of the pyruvate dehydrogenase complex. Analytical Biochemistry. Vol. 389 (Issue 2). Retrieved from The Mitochondrial Medicine Society. Accessed on: April 20, United Mitochondrial Disease Foundation. Accessed on: April 19, 2012.