MitoNews volume 8, issue 02

Table of Contents

I. Mitochondrial Biogenesis

II. Neurodegeneration: Bioenergetics and Complex I

III. Drug Toxicity and Mitochondria

Mitochondrial biogenesis is the cellular process of making new mitochondria. There is strong evidence that decreasing mitochondrial mass or function may be causal in neuromuscular, neurodegenerative or diabetic disorders. Therefore an understanding the regulation of mitochondrial biogenesis is key to the etiology of these diseases and potential therapies.

PGC1a(Peroxisome proliferator-activated receptor gamma coactivator 1-alpha, PPARGC1A) is a coactivator of multiple transcription factors in the regulation of metabolism and in particular mitochondrial biogenesis. Pathways sensing AMP/ATP, Ca++, NAD+/NADH and ROS converge on PGC1a transactivation toeffect metabolic change.

Several interesting research papers this month focus on measuring mitochondrial biogenesis in cell culture and animal model systems.

Using a mouse model of Duchenne muscular dystrophy, a progressive muscle wasting disease caused by non functional dystorphin protein, authors Selsby et al. showed that viral driven overexpression of PGC1a in a mouse model resulted in increased expression of a dystrophin related protein, uturophin, and an increase in mitochondria. Increasing mitochondrial content was confirmed by Western blotting with antibodies including COX1 and UCP1, while HSP60 remained unchanged. Interestingly an upstream deacetylase regulator of PGC1a, Sirt1, was also increased. A well known activator of Sirt1, resveratrol was also administered with improvement in muscle fatigue resistance but not in utorphoin expression. Suggesting that a more potent Sirt-1 activator may be of therapeutic value.

Rescue of Dystrophic Skeletal Muscle by PGC-1a Involves a Fast to Slow Fiber Type Shift in the mdx Mouse. Selsby JT, Morine KJ, Pendrak K, Barton ER, Sweeney HL.

Pearen et al showed in a mouse model that over expression of the novel nuclear derived orphan receptor 1 (Nor-1) resulted in increased mitochondrial function and a striking increase in respiratory chain enzyme expression using rodent OXPHOS antibody cocktail. Type II diabetes and insulin resistance have been associated with decreased oxidative phosphorylation and mitochondrial content, interestingly the increased oxidative capacity measured in these mice correlated with improved glucose tolerance.

The Nuclear Receptor, Nor-1, Markedly Increases Type II Oxidative Muscle Fibers and Resistance to Fatigue. Pearen MA, Eriksson NA, Fitzsimmons RL, Goode JM, Martel N, Andrikopoulos S, Muscat GE.

Proliferating CD8+ effector T cells undergo a metabolic shift to aerobic glycolysis to support growth and division. However Van der Windt et al showed that CD8+ memory T cells maintain a spare mitochondrial respiratory capacity (SRC) thought to be important in their long term survival. This SRC is derived from additional interleukin 15 (IL15) stimulated mitochondrial biogenesis shown by Western blotting Western blotting and in particular increased expression of the fatty acid oxidation rate limiting enzyme CPT1a.In the absence of infection and associated pro-glycolysis signals the authors propose that the effector cells become bioenergetically unstable and die while the memory cells survive due to SRC. Therefore agents that promote mitochondrial biogenesis may hold promise as immunotherapeutics.

Mitochondrial respiratory capacity is a critical regulator of CD8(+) T cell memory development. van der Windt GJ, Everts B, Chang CH, Curtis JD, Freitas TC, Amiel E, Pearce EJ, Pearce EL.

Also this month see:

The influence of age and aerobic fitness: effects on mitochondrial respiration in skeletal muscle. Larsen S, Hey-Mogensen M, Rabøl R, Stride N, Helge JW, Dela F.

Thyrotropin-Releasing Hormone Controls Mitochondrial Biology in Human Epidermis. Knuever J, Poeggeler B, Gáspár E, Klinger M, Hellwig-Burgel T, Hardenbicker C, Tóth BI, Bíró T, Paus R.

There is growing evidence that bioenergetic deficiency may have a role in neurodegenerative diseases. The strongest evidence links Complex I deficiency and Parkinson's disease. Common rodent models of Parkinsonian syndrome utilize rotenone, MPTP or 6-OHDA, all inhibitors of Complex I.

In an article this month by Kuan et al, the authors showed that a small RNA transcript 2.7, delivered by a modified rabies virus protein, can rescue rotenone treated cultured cells and was neuroprotective in a rat 6-OHDA PD model. The effect of toxins on Complex I was ameliorated as measured by Complex I microplate activity assay. While the mechanism of action remains unclear, the RNA was shown to specifically bind Complex I by co-immunoprecipitation experiments using Complex I immunocapture kit.

A novel neuroprotective therapy for Parkinson's disease using a viral noncoding RNA that protects mitochondrial Complex I activity. Kuan WL, Poole E, Fletcher M, Karniely S, Tyers P, Wills M, Barker RA, Sinclair JH

Also this month see:

Melatonin plus physical exercise are highly neuroprotective in the 3xTg-AD mouse. García-Mesa Y, Giménez-Llort L, López LC, Venegas C, Cristòfol R, Escames G, Acuña-Castroviejo D, Sanfeliu C.

Accumulation of vesicle-associated human tau in distal dendrites drives degeneration and tau secretion in an in situ cellular tauopathy model. Lee S, Kim W, Li Z, Hall GF.

Complex I inhibition by Sorafenib induces cell death in neuroblastoma cells. Sorafenib is a newly discovered drug approved in 2005 for use against a wide range of cancers. The exact mechanism of Sorafenib-induced cell death is unknown. In work published this month Bull and coworkers identified that Sorafenib induces cell death in human neuroblastoma cell line SHSY5Y. The mechanism of action was investigated using a quantitative proteomic approach employing stable isotope labeling with amino acids (SILAC) and mass spectrometry. These researchers found that in addition to triggering apoptosis, a large fraction of the regulated proteins were mitochondrial and, in particular, 16 of 46 subunits of the NADH dehydrogenase (Complex I) were down regulated. Using the Complex I dipstick assay, measured activity was completely abolished after 12 hours and could not be rescued by caspase inhibitors or Bcl2 overexpression. Complex I subunit down regulation was confirmed by Western blotting and may occur before mitochondrial outer membrane permeabilization (MOMP). It is possible that Complex I, and other down regulated mitochondrial ribosomal and transport proteins, are important initiators of apoptosis and occur upstream of MOMP and the caspase cascade.

Also this month see:

Bioenergetics failure and oxidative stress in brain stem mediates cardiovascular collapse associated with fatal methamphetamine intoxication. Li FC, Yen JC, Chan SH, Chang AY.

Survival and mitochondrial function in septic patients according to mitochondrial DNA haplogroup. Lorente L, Iceta R, Martin MM, Lopez-Gallardo E, Sole-Violan J, Blanquer J, Labarta L, Diaz C, Jimenez A, Montoya J, Ruiz-Pesini E.