Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Lung inflammation.

<p>The amount of inflammatory cells (A) Macrophages, B) Neutrophils, and C) Eosinophils) of four different groups [Control (n = 9), Flu (n = 10), HDM (n = 9), and Flu + HDM (n = 9)] in BAL fluid at week 7 were counted using a haemocytometer. D) The total IgE of four different groups [Control (n = 8), Flu (n = 8), HDM (n = 8), and Flu + HDM (n = 9)] in serum at week 7 was measured using ELISA. Data are presented as mean ± SD, and were log10 transformed as appropriate to determine the statistical significance. Two-way ANOVA plus Holm-Sidak multiple comparison test was used to determine the statistical significance. *Significant differences (p<0.05).</p

Schematic representation of the experimental protocol.

<p>Adult female BALB/c mice were infected with influenza A or media only 21 days before they were sensitized with HDM. This involved intranasal exposure to 10 µg of HDM in saline or 50µL of saline for 5 days during weeks 1 and 4, followed by intranasal exposure to 100 µg of HDM in saline or 50µL of saline for 3 days in week 7. Serum samples were collected after the last challenge of week 1, 4, and 7. BAL samples were collected after the last challenge at week 7.</p

Serum vitamin D levels.

<p>Serum 25(OH)D levels of adult female BALB/c mice were measured using ELISA. Serum samples were from four different groups and collected at week 1 [Control (n = 5), Flu (n = 5), HDM (n = 5), and Flu + HDM (n = 5)], 4 [Control (n = 5), Flu (n = 5), HDM (n = 5), and Flu + HDM (n = 5)], and 7 [Control (n = 10), Flu (n = 10), HDM (n = 10), and Flu + HDM (n = 10)]. Data are presented as mean±SD. Two-way ANOVA plus Holm-Sidak multiple comparison test was used to determine the statistical significance.</p

Murine cytomegalovirus infection exacerbates complex IV deficiency in a model of mitochondrial disease

The influence of environmental insults on the onset and progression of mitochondrial diseases is unknown. To evaluate the effects of infection on mitochondrial disease we used a mouse model of Leigh Syndrome, where a missense mutation in the Taco1 gene results in the loss of the translation activator of cytochrome c oxidase subunit I (TACO1) protein. The mutation leads to an isolated complex IV deficiency that mimics the disease pathology observed in human patients with TACO1 mutations. We infected Taco1 mutant and wild-type mice with a murine cytomegalovirus and show that a common viral infection exacerbates the complex IV deficiency in a tissue-specific manner. We identified changes in neuromuscular morphology and tissue-specific regulation of the mammalian target of rapamycin pathway in response to viral infection. Taken together, we report for the first time that a common stress condition, such as viral infection, can exacerbate mitochondrial dysfunction in a genetic model of mitochondrial disease

Mutation in MRPS34 Compromises Protein Synthesis and Causes Mitochondrial Dysfunction

<div><p>The evolutionary divergence of mitochondrial ribosomes from their bacterial and cytoplasmic ancestors has resulted in reduced RNA content and the acquisition of mitochondria-specific proteins. The mitochondrial ribosomal protein of the small subunit 34 (MRPS34) is a mitochondria-specific ribosomal protein found only in chordates, whose function we investigated in mice carrying a homozygous mutation in the nuclear gene encoding this protein. The <i>Mrps34</i> mutation causes a significant decrease of this protein, which we show is required for the stability of the 12S rRNA, the small ribosomal subunit and actively translating ribosomes. The synthesis of all 13 mitochondrially-encoded polypeptides is compromised in the mutant mice, resulting in reduced levels of mitochondrial proteins and complexes, which leads to decreased oxygen consumption and respiratory complex activity. The <i>Mrps34</i> mutation causes tissue-specific molecular changes that result in heterogeneous pathology involving alterations in fractional shortening of the heart and pronounced liver dysfunction that is exacerbated with age. The defects in mitochondrial protein synthesis in the mutant mice are caused by destabilization of the small ribosomal subunit that affects the stability of the mitochondrial ribosome with age.</p></div

<i>Mrps34</i>^{<i>mut/mut</i>} mice have hypertrophic hearts and increased lipid accumulation in their livers.

<p>(A) Echocardiographic parameters of <i>Mrps34</i>^<i>wt/wt</i> (n = 5) and <i>Mrps34</i>^{<i>mut/mut</i>} (n = 5) mice. LVEDD, left ventricular end diastolic diameter; LVESD, left ventricular end systolic diameter; FS, fractional shortening; LVDPW, left ventricular posterior wall in diastole; LVSPW, left ventricular posterior wall in systole; IVDS, intraventricular septum in diastole; IVSS, intraventricular septum in systole. Values are means ± standard error. *p<0.05 compared with <i>Mrps34</i>^<i>wt/wt</i>. Liver sections cut at 8–12 μm thickness were stained with Haematoxylin and Eosin, oil red O and Haematoxylin or Gomori trichrome from young (B) and aged (C) <i>Mrps34</i>^<i>wt/wt</i> (n = 9) and <i>Mrps34</i>^{<i>mut/mut</i>} (n = 9) mice and visualized at 40X magnification. (D) Quantitative measurement of oil red staining using Image J. Data are means ± SEM of four different mice; *, <i>p</i> < 0.05 compared with control treatments by a 2-tailed paired Student’s <i>t</i> test. Serum ALT levels in young (E) and aged (F) <i>Mrps34</i>^<i>wt/wt</i> (n = 12) and <i>Mrps34</i>^{<i>mut/mut</i>} (n = 12) mice.</p

The <i>Mrps34</i> mutation causes reduced oxygen consumption and respiratory complex activities in heart and liver mitochondria.

<p>The activities of the five mitochondrial respiratory complexes were measured in mitochondria isolated from heart (A) and liver (B) of young <i>Mrps34</i>^<i>wt/wt</i> and <i>Mrps34</i>^{<i>mut/mut</i>} mice and aged mice (C and D), respectively. The respiratory complex activities were normalized relative to citrate synthase activity. Data are means ± SEM of three-four separate experiments; *, <i>p</i> < 0.05 compared with control treatments by a 2-tailed paired Student’s <i>t</i> test. State 3 and 4 respiration was measured in mitochondria isolated from hearts (E) and livers (F) of aged <i>Mrps34</i>^<i>wt/wt</i> and <i>Mrps34</i>^{<i>mut/mut</i>} mice using an OROBOROS oxygen electrode. Data are means ± SEM of three-four separate experiments; *, <i>p</i> < 0.05 compared with control treatments by a 2-tailed paired Student’s <i>t</i> test.</p

Decreased MRPS34 affects the stability of the 12S rRNA and specific mitochondrial mRNAs.

<p>(A) The abundance of mature mitochondrial transcripts in mitochondria isolated from young <i>Mrps34</i>^<i>wt/wt</i> and <i>Mrps34</i>^{<i>mut/mut</i>} livers and hearts was analyzed by northern blotting. (B) The abundance of mature mitochondrial transcripts in aged liver and heart was analyzed by northern blotting. 18S rRNA was used as a loading control. The data are representative of results obtained from at least 8 mice from each strain. Data are means ± SEM of three separate experiments; *, <i>p</i> < 0.05 compared with control treatments by a 2-tailed paired Student’s <i>t</i> test.</p