BBA - Molecular Basis of Disease (v.1792, #12)

Mitochondrial disease—the ever-widening circle by Howy Jacobs; Jan Smeitink (1095-1096).

The inheritance of pathogenic mitochondrial DNA mutations by L.M. Cree; D.C. Samuels; P.F. Chinnery (1097-1102).
Mitochondrial DNA mutations cause disease in > 1 in 5000 of the population, and ∼ 1 in 200 of the population are asymptomatic carriers of a pathogenic mtDNA mutation. Many patients with these pathogenic mtDNA mutations present with a progressive, disabling neurological syndrome that leads to major disability and premature death. There is currently no effective treatment for mitochondrial disorders, placing great emphasis on preventing the transmission of these diseases. An empiric approach can be used to guide genetic counseling for common mtDNA mutations, but many families transmit rare or unique molecular defects. There is therefore a pressing need to develop techniques to prevent transmission based on a solid understanding of the biological mechanisms. Several recent studies have cast new light on the genetics and cell biology of mtDNA inheritance, but these studies have also raised new controversies. Here we compare and contrast these findings and discuss their relevance for the transmission of human mtDNA diseases.
Keywords: mtDNA; Mitochondria; Genetic bottleneck; Inheritance;

Genetic causes of mitochondrial DNA depletion in humans by Agnès Rötig; Joanna Poulton (1103-1108).
Mitochondrial DNA (mtDNA) depletion is characterized by a profound reduction of mtDNA copy number. The maintenance of mtDNA copy number requires several nuclear-encoded factors involved in replication and in dNTP supply. In the past decade mutations in several of these factors have been reported in a growing number of syndromes. This article reviews the current knowledge of genes causing mitochondrial DNA depletion syndromes.
Keywords: Mitochondria; mtDNA depletion; Respiratory chain;

Collated mutations in mitochondrial DNA (mtDNA) depletion syndrome (excluding the mitochondrial gamma polymerase, POLG1) by J. Poulton; M. Hirano; A. Spinazzola; M. Arenas Hernandez; C. Jardel; A. Lombès; B. Czermin; R. Horvath; J.W. Taanman; A. Rotig; M. Zeviani; C. Fratter (1109-1112).
Keywords: mtDNA; mtDNA depletion; C10orf2; SUCLG1; SUCLA2; TYMP; RRM2B; MPV17; DGUOK; TK2;

OXPHOS gene expression and control in mitochondrial disorders by Fimmie Reinecke; Jan A.M. Smeitink; Francois H. van der Westhuizen (1113-1121).
The cellular consequences of deficiencies of the mitochondrial OXPHOS system include a variety of direct and secondary changes in metabolite homeostasis, such as ROS, Ca2+, ADP/ATP, and NAD/NADH. The adaptive responses to these changes include the transcriptional responses of nuclear and mitochondrial genes that are mediated by these metabolites, control of the mitochondria permeability transition pore, and a great variety of secondary signalling elements. Among the transcriptional responses reported over more than a decade using material harboring mtDNA mutations, deletions, or depletions, nuclear and mitochondrial DNA OXPHOS genes have mostly been up-regulated. However, it is evident from the limited data in a variety of disease models that expression responses are highly diverse and inconsistent. In this article, the mechanisms and controlling elements of these transcriptional responses are reviewed. In addition, the elements that need to be evaluated, in order to gain an improved perspective of the manner in which OXPHOS genes respond and impact on mitochondrial disease expression, are highlighted.
Keywords: Mitochondria; OXPHOS; Mitochondrial disorders; Gene expression; Mitochondria–nucleus communication; Signalling;

Mitochondrial proteome evolution and genetic disease by Martijn A. Huynen; Mattias de Hollander; Radek Szklarczyk (1122-1129).
Mitochondria are an essential organelle, not only to the human cell, but to all eukaryotic life. This essentiality is reflected in the large number of mutations in genes encoding mitochondrial proteins that lead to disease. Aside from their relevance to disease, mitochondria are, given their endosymbiotic origin, very interesting from an evolutionary point of view. Here, in the year that marks the bicentenary of Darwin's birth and the 150th anniversary of the publication of “On the origin of species” we review approaches that implicitly or explicitly use evolutionary analyses to find new genes involved in mitochondrial disease and to predict their function and involvement in pathways. We show how the phenotypic spectrum of mitochondrial disease is linked to the evolutionary origin of mitochondrial proteins, how combinations of evolutionary data and genomics data have been used to predict the mitochondrial proteome and functional links between the mitochondrial proteins and how the evolution of the mitochondrial proteome has been used to predict new mitochondrial disease genes. For the latter we review and reanalyze the eukaryotic evolution of the NADH:ubiquinone oxidoreductase (complex I) and the proteins involved in its assembly.
Keywords: Mitochondrial proteome; Evolution; Complex I;

Calcium and ATP handling in human NADH:Ubiquinone oxidoreductase deficiency by Federica Valsecchi; John J. Esseling; Werner J.H. Koopman; Peter H.G.M. Willems (1130-1137).
Proper cell functioning requires precise coordination between mitochondrial ATP production and local energy demand. Ionic calcium (Ca2+) plays a central role in this coupling because it activates mitochondrial oxidative phosphorylation (OXPHOS) during hormonal and electrical cell stimulation. To determine how mitochondrial dysfunction affects cytosolic and mitochondrial Ca2+/ATP handling, we performed life-cell quantification of these parameters in fibroblast cell lines derived from healthy subjects and patients with isolated deficiency of the first OXPHOS complex (CI). In resting patient cells, CI deficiency was associated with a normal mitochondrial ([ATP]m) and cytosolic ([ATP]c) ATP concentration, a normal cytosolic Ca2+ concentration ([Ca2+]c), but a reduced Ca2+ content of the endoplasmic reticulum (ER). Furthermore, cellular NAD(P)H levels were increased, mitochondrial membrane potential was slightly depolarized, reactive oxygen species (ROS) levels were elevated and mitochondrial shape was altered. Upon stimulation with bradykinin (Bk), the peak increases in [Ca2+]c, mitochondrial Ca2+ concentration ([Ca2+]m), [ATP]c and [ATP]m were reduced in patient cells. In agreement with these results, ATP-dependent Ca2+ removal from the cytosol was slower. Here, we review the interconnection between cytosolic, endoplasmic reticular and mitochondrial Ca2+ and ATP handling, and summarize our findings in patient fibroblasts in an integrative model.
Keywords: Mitochondria; Fibroblasts; ROS; Complex I; Life cell microscopy;

The molecular mechanism and cellular functions of mitochondrial division by Laura L. Lackner; Jodi M. Nunnari (1138-1144).
Mitochondria are highly dynamic organelles that continuously divide and fuse. These dynamic processes regulate the size, shape, and distribution of the mitochondrial network. In addition, mitochondrial division and fusion play critical roles in cell physiology. This review will focus on the dynamic process of mitochondrial division, which is highly conserved from yeast to humans. We will discuss what is known about how the essential components of the division machinery function to mediate mitochondrial division and then focus on proteins that have been implicated in division but whose functions remain unclear. We will then briefly discuss the cellular functions of mitochondrial division and the problems that arise when division is disrupted.
Keywords: Mitochondrial dynamics; Dnm1; Drp1; Fis1; Dynamin-related protein;

The tumor suppressor function of mitochondria: Translation into the clinics by José M. Cuezva; Álvaro D. Ortega; Imke Willers; Laura Sánchez-Cenizo; Marcos Aldea; María Sánchez-Aragó (1145-1158).
Recently, the inevitable metabolic reprogramming experienced by cancer cells as a result of the onset of cellular proliferation has been added to the list of hallmarks of the cancer cell phenotype. Proliferation is bound to the synchronous fluctuation of cycles of an increased glycolysis concurrent with a restrained oxidative phosphorylation. Mitochondria are key players in the metabolic cycling experienced during proliferation because of their essential roles in the transduction of biological energy and in defining the life–death fate of the cell. These two activities are molecularly and functionally integrated and are both targets of commonly altered cancer genes. Moreover, energetic metabolism of the cancer cell also affords a target to develop new therapies because the activity of mitochondria has an unquestionable tumor suppressor function. In this review, we summarize most of these findings paying special attention to the opportunity that translation of energetic metabolism into the clinics could afford for the management of cancer patients. More specifically, we emphasize the role that mitochondrial β-F1-ATPase has as a marker for the prognosis of different cancer patients as well as in predicting the tumor response to therapy.
Keywords: Cancer; Cell cycle; Cell death; Glycolysis; H+-ATP synthase; Markers of prognosis; Metabolic inhibitor; Oxidative phosphorylation; ROS;

Taking advantage of a series of questions raised by an association of patients with mitochondrial disease, this review, after a brief overview of basic concepts of mitochondrial bioenergetics and genetics, discusses the pros and cons of a number of practical options in the field of mitochondrial therapy. This makes it clear that, in contrast to the spectacular progress in our understanding of the biochemical and molecular bases of the mitochondrial diseases defined restrictively as disorders due to defects in the mitochondrial respiratory chain, we are still extremely limited in our ability to treat these conditions. We finally discussed the emerging genetic-based strategies that show some promise, even if much work remains to be done.
Keywords: Mitochondrial disease; Respiratory chain; Coenzyme Q10; Therapy;

Triosephosphate isomerase deficiency: New insights into an enigmatic disease by Ferenc Orosz; Judit Oláh; Judit Ovádi (1168-1174).
The triosephosphate isomerase (TPI) functions at a metabolic cross-road ensuring the rapid equilibration of the triosephosphates produced by aldolase in glycolysis, which is interconnected to lipid metabolism, to glycerol-3-phosphate shuttle and to the pentose phosphate pathway. The enzyme is a stable homodimer, which is catalytically active only in its dimeric form. TPI deficiency is an autosomal recessive multisystem genetic disease coupled with hemolytic anemia and neurological disorder frequently leading to death in early childhood. Various genetic mutations of this enzyme have been identified; the mutations result in decrease in the catalytic activity and/or the dissociation of the dimers into inactive monomers. The impairment of TPI activity apparently does not affect the energy metabolism at system level; however, it results in accumulation of dihydroxyacetone phosphate followed by its chemical conversion into the toxic methylglyoxal, leading to the formation of advanced glycation end products. By now, the research on this disease seems to enter a progressive stage by adapting new model systems such as Drosophila, yeast strains and TPI-deficient mouse, which have complemented the results obtained by prediction and experiments with recombinant proteins or erythrocytes, and added novel data concerning the complexity of the intracellular behavior of mutant TPIs. This paper reviews the recent studies on the structural and catalytic changes caused by mutation and/or nitrotyrosination of the isomerase leading to the formation of an aggregation-prone protein, a characteristic of conformational disorders.
Keywords: Neurodegeneration; Enzymopathy; Conformational disease; Glycolysis; Methylglyoxal; Advanced glycation end products (AGEs); Oxidative stress; Animal model;

Influence of natriuretic peptide receptor-1 on survival and cardiac hypertrophy during development by Nicola J.A. Scott; Leigh. J. Ellmers; John G. Lainchbury; Nobuyo Maeda; Oliver Smithies; A. Mark Richards; Vicky A. Cameron (1175-1184).
The heart adapts to an increased workload through the activation of a hypertrophic response within the cardiac ventricles. This response is characterized by both an increase in the size of the individual cardiomyocytes and an induction of a panel of genes normally expressed in the embryonic and neonatal ventricle, such as atrial natriuretic peptide (ANP). ANP and brain natriuretic peptide (BNP) exert their biological actions through activation of the natriuretic peptide receptor-1 (Npr1). The current study examined mice lacking Npr1 (Npr1 /) activity and investigated the effects of the absence of Npr1 signaling during cardiac development on embryo viability, cardiac structure and gene and protein expression. Npr1 /embryos were collected at embryonic day (ED) 12.5, 15.5 and neonatal day 1 (ND 1). Npr1 /embryos occurred at the expected Mendelian frequency at ED 12.5, but knockout numbers were significantly decreased at ED 15.5 and ND 1. There was no indication of cardiac structural abnormalities in surviving embryos. However, Npr1 /embryos exhibited cardiac enlargement (without fibrosis) from ED 15.5 as well as significantly increased ANP mRNA and protein expression compared to wild-type (WT) mice, but no concomitant increase in expression of the hypertrophy-related transcription factors, Mef2A, Mef2C, GATA-4, GATA-6 or serum response factor (SRF). However, there was a significant decrease in Connexin-43 (Cx43) gene and protein expression at mid-gestation in Npr1 /embryos. Our findings suggest that the mechanism by which natriuretic peptide signaling influences cardiac development in Npr1 / mice is distinct from that seen during the development of pathological cardiac hypertrophy and fibrosis. The decreased viability of Npr1 /embryos may result from a combination of cardiomegaly and dysregulated Cx43 protein affecting cardiac contractility.
Keywords: Akt1; Atrial natriuretic peptide; Calcineurin A; Cardiac hypertrophy; Connexin 43; Gene expression; Heart development; Npr1; Transcription factor;

Oxidative stress caused by an imbalance of the production of “reactive oxygen species” (ROS) and cellular scavenging systems is known to a play a key role in the development of various diseases and aging processes. Such elevated ROS levels can damage all components of cells, including proteins, lipids and DNA. Here, we study the influence of highly reactive ROS species on skeletal muscle proteins in a rat model of acute oxidative stress caused by X-ray irradiation at different time points. Protein preparations depleted for functional actin by polymerization were separated by gel electrophoresis in two dimensions by applying first non-reductive and then reductive conditions in SDS-PAGE. This diagonal redox SDS-PAGE revealed significant alterations to intra- and inter-molecular disulfide bridges for several proteins, but especially actin, creatine kinase and different isoforms of the myosin light chain. Though the levels of these reversible modifications were increased by oxidative stress, all proteins followed different kinetics. Moreover, a significant degree of protein was irreversibly oxidized (carbonylated), as revealed by western blot analyses performed at different time points.
Keywords: Carbonylation; Cysteine residue; Diagonal redox SDS-PAGE; Mass spectrometry (MS); Protein oxidation; Reactive oxygen species (ROS);

The R1441C mutation alters the folding properties of the ROC domain of LRRK2 by Yongchao Li; Laura Dunn; Elisa Greggio; Brian Krumm; Graham S. Jackson; Mark R. Cookson; Patrick A. Lewis; Junpeng Deng (1194-1197).
LRRK2 is a 250 kDa multidomain protein, mutations in which cause familial Parkinson's disease. Previously, we have demonstrated that the R1441C mutation in the ROC domain decreases GTPase activity. Here we show that the R1441C alters the folding properties of the ROC domain, lowering its thermodynamic stability. Similar to small GTPases, binding of different guanosine nucleotides alters the stability of the ROC domain, suggesting that there is an alteration in conformation dependent on GDP or GTP occupying the active site. GTP/GDP bound state also alters the self-interaction of the ROC domain, accentuating the impact of the R1441C mutation on this property. These data suggest a mechanism whereby the R1441C mutation can reduce the GTPase activity of LRRK2, and highlights the possibility of targeting the stability of the ROC domain as a therapeutic avenue in LRRK2 disease.
Keywords: LRRK2; ROCO protein; GTPase; Parkinson's disease; Differential scanning fluorimetry; Circular dichroism;

Mrp-8 and -14 mediate CNS injury in focal cerebral ischemia by Gina Ziegler; Vincent Prinz; Marcus W. Albrecht; Denise Harhausen; Uldus Khojasteh; Wolfgang Nacken; Matthias Endres; Ulrich Dirnagl; Wilfried Nietfeld; George Trendelenburg (1198-1204).
Several reports have recently demonstrated a detrimental role of Toll-like receptors (TLR) in cerebral ischemia, while there is little information about the endogenous ligands which activate TLR-signaling. The myeloid related proteins-8 and-14 (Mrp8/S100A8; Mrp14/S100A9) have recently been characterized as endogenous TLR4-agonists, and thus may mediate TLR-activation in cerebral ischemia. Interestingly, not only TLR-mRNAs, but also Mrp8 and Mrp14 mRNA were found to be induced in mouse brain between 3 and 48 h after transient 1 h focal cerebral ischemia/reperfusion. Mrp-protein was expressed in the ischemic hemisphere, and co-labeled with CD11b-positive cells. To test the hypothesis that Mrp-signaling contributes to the postischemic brain damage, we subjected Mrp14-deficient mice, which also lack Mrp8 protein expression, to focal cerebral ischemia. Mrp14-deficient mice had significantly smaller lesion volumes when compared to wild-type littermates (130 ± 16 mm3 vs. 105 ± 28 mm3) at 2 days after transient focal cerebral ischemia (1 h), less brain swelling, and a reduced macrophage/microglia cell count in the ischemic hemisphere. We conclude that upregulation and signaling of Mrp-8 and-14 contribute to neuroinflammation and the progression of ischemic damage.
Keywords: S100A8; S100A9; Toll-like receptor; MCAO; Knockout mice;

This study aimed to investigate the role of therapeutic dexamethasone (Dex) treatment on the mechanisms underlying chemokine expression during mild and severe acute pancreatitis (AP) experimentally induced in rats. Regardless of the AP severity, Dex (1 mg/kg), administered 1 h after AP, reduced the acinar cell activation of extracellular signal-regulated kinase (ERK) and c-Jun-NH2-terminal kinase (JNK) but failed to reduce p38-mitogen-activated protein kinase (MAPK) in severe AP. In both AP models, Dex inhibited the activation of nuclear factor-kappaB (NF-κB) and signal transducers and activators of transcription (STAT) factors. All of this resulted in pancreatic down-regulation of the chemokines monocyte chemoattractant protein-1 (MCP-1) and cytokine-induced neutrophil chemoattractant (CINC). Lower plasma chemokine levels as well as decreased amylasemia, hematocrit and plasma interleukin-1β (Il-1β) levels were found either in mild or severe AP treated with Dex. Pancreatic neutrophil infiltration was attenuated by Dex in mild but not in severe AP. In conclusion, by targeting MAPKs, NF-κB and STAT3 pathways, Dex treatment down-regulated the chemokine expression in different cell sources during mild and severe AP, resulting in decreased severity of the disease.
Keywords: Acute pancreatitis; Chemokines; Dexamethasone; MAPK; NF-κB; STAT3;