Analysis of cytochrome C oxidase subunits III and IV expression in developing rat brain

Pyruvate Dehydrogenase Complex in Neonatal Hypoxic-Ischemic Brain Injury

The disruption of cerebral energy metabolism in relation to brain damage has been the subject of extensive research. However, the pyruvate dehydrogenase complex (PDHC), which is primarily characterized by poor cerebral energy metabolism following brain trauma, has received relatively little study in comparison to newborn hypoxic-ischemic brain injury. Mitochondrial PDHC, a multienzyme complex that functions as a crucial hub in energy metabolism and acts as a central metabolic node to mediate pyruvate oxidation after glycolysis and fuel the Krebs cycle to meet energy demands, has been reported to be one cause of energy metabolism dysfunction according to recent studies. Here we assess the potential mechanisms of neonatal hypoxic-ischemic brain injury-related brain dysfunction mediated by PDHC and further discuss the neuroprotective effects of therapeutic medicines that target PDHC activation. We also provide a summary of recent research on medicines that target PDHC in neonates with hypoxic-ischemic brain damage. Through an understanding of the mechanisms by which it is modulated and an investigation of the neuroprotective techniques available to activate brain PDHC and improve neonatal hypoxic-ischemic impairment, our review emphasizes the significance of PDHC impairment in neonatal hypoxic-ischemic brain injury.

Mitochondria: hub of injury responses in the developing brain

Progress in the field of mitochondrial biology in the past few years has shown that mitochondrial activities go beyond bioenergetics. These new aspects of mitochondrial physiology and pathophysiology have important implications for the immature brain. A picture emerges in which mitochondrial biogenesis, mitophagy, migration, and morphogenesis are crucial for brain development and synaptic pruning, and play a part in recovery after acute insults. Mitochondria also affect brain susceptibility to injury, and mitochondria-directed interventions can make the immature brain highly resistant to acute injury. Finally, the mitochondrion is a platform for innate immunity, contributes to inflammation in response to infection and acute damage, and participates in antiviral and antibacterial defence. Understanding of these new aspects of mitochondrial function will provide insights into brain development and neurological disease, and enable discovery and development of new strategies for treatment.

Cortical metabolic deficits in a rat model of cholinergic basal forebrain degeneration

Evidence indicates that the degeneration of basal forebrain cholinergic neurons may represent an important factor underlying the progressive cognitive decline characterizing Alzheimer's disease (AD). However, the nature of the relationship between cholinergic depletion and AD is not fully elucidated. This study aimed at clarifying some aspects of the relation existing between deficits in cerebral energy metabolism and degeneration of cholinergic system in AD, by investigating the neuronal metabolic activity of several cortical areas after depletion of basal forebrain cholinergic neurons. In cholinergically depleted rats, we evaluated the neuronal metabolic activity by assaying cytochrome oxidase (CO) activity in frontal, parietal and posterior parietal cortices at four different time-points after unilateral injection of 192 IgG-saporin in the nucleus basalis magnocellularis. Unilateral depletion of cholinergic cells in the basal forebrain induced a bilateral decrease of metabolic activity in all the analyzed areas. Frontal and parietal cortices showed decreased metabolic activity even 3 days after the lesion, when the cholinergic degeneration was still incomplete. In posterior parietal cortex metabolic activity decreased only 7 days after the lesion. The possible molecular mechanisms underlying these findings were also investigated. Real-time PCR showed an increase of CO mRNA levels at 3, 7 and 15 days after the lesion both in frontal and parietal cortices, followed by normalization at 30 days. Western Blot analysis did not show any change in CO protein levels at any time-point after the lesion. Our findings support a link between metabolic deficit and cholinergic hypofunctionality characterizing AD pathology. The present model of cholinergic hypofunctionality provides a useful means to study the complex mechanisms linking two fundamental and interrelated phenomena characterizing AD from the early stages.

Pre-microRNA and mature microRNA in human mitochondria

Background

Because of the central functions of the mitochondria in providing metabolic energy and initiating apoptosis on one hand and the role that microRNA (miRNA) play in gene expression, we hypothesized that some miRNA could be present in the mitochondria for post-transcriptomic regulation by RNA interference. We intend to identify miRNA localized in the mitochondria isolated from human skeletal primary muscular cells.

Methodology/Principal Findings

To investigate the potential origin of mitochondrial miRNA, we in-silico searched for microRNA candidates in the mtDNA. Twenty five human pre-miRNA and 33 miRNA aligments (E-value<0.1) were found in the reference mitochondrial sequence and some of the best candidates were chosen for a co-localization test. In situ hybridization of pre-mir-302a, pre-let-7b and mir-365, using specific labelled locked nucleic acids and confocal microscopy, demonstrated that these miRNA were localized in mitochondria of human myoblasts. Total RNA was extracted from enriched mitochondria isolated by an immunomagnetic method from a culture of human myotubes. The detection of 742 human miRNA (miRBase) were monitored by RT-qPCR at three increasing mtRNA inputs. Forty six miRNA were significantly expressed (2^nd derivative method Cp>35) for the smallest RNA input concentration and 204 miRNA for the maximum RNA input concentration. In silico analysis predicted 80 putative miRNA target sites in the mitochondrial genome (E-value<0.05).

Conclusions/Significance

The present study experimentally demonstrated for the first time the presence of pre-miRNA and miRNA in the human mitochondria isolated from skeletal muscular cells. A set of miRNA were significantly detected in mitochondria fraction. The origin of these pre-miRNA and miRNA should be further investigate to determine if they are imported from the cytosol and/or if they are partially processed in the mitochondria.

Triacylglycerol-induced impairment in mitochondrial biogenesis and function in J774.2 and mouse peritoneal macrophage foam cells

The aim of this study was to detect mitochondrial alterations in J774.2 macrophages and mouse peritoneal macrophages (MPM) foam cells. J774.2 and MPM cells were exposed to triacylglycerol (TG) emulsion (1 mg/ml) for induction of fat accumulation. Impairment of mitochondrial function was reflected by reduced cellular ATP production and decreased expression of subunits of mitochondrial complexes I and III. The expression of subunit IV of complex IV remained unchanged, however, the content of its precursor in cells increased. Inhibitors of mitochondrial complexes, rotenone (0.1 microM) and myxothiazol (25 nM), protected the viability in TG-loaded macrophages. The exposure to TG caused downregulation of PPARgamma coactivator (PGC)-1alpha and nuclear respiratory factor (NRF)-1. Activation of peroxisome proliferator-activated receptors attenuated reactive oxygen species production in the foam cells. Treatment with antioxidant N-acetylcysteine (NAC) prevented lipid-mediated mitochondrial and cellular damage. In conclusion, this study demonstrates the important role of mitochondrial biogenesis dysfunction in TG-induced lipotoxicity in macrophages.

Cadmium and mitochondria

The heavy metal cadmium (Cd) a pollutant associated with several modern industrial processes, is absorbed in significant quantities from cigarette smoke, water, food and air contaminations. It is known to have numerous undesirable effects on health in both experimental animals and humans, targeting kidney, liver and vascular system. The molecular mechanism accounting for most of the biological effects of Cd are not well-understood and the toxicity targets are largely unidentified. The present review focuses on important recent advances about the effects of cadmium on mitochondria of mammalian cells. Mitochondria are the proverbial powerhouses of the cell, running the fundamental biochemical processes that produce energy from nutrients using oxygen. They are among the key intracellular targets for different stressors including Cd. This review provides new additional informations on the cellular and molecular aspects of the interaction between Cd and cells, emphasizing alterations of mitochondria as important events in Cd cytotoxicity, thus representing an important basis for understanding the mechanisms of cadmium effect on the cells.

Proteins participating to the post-transcriptional regulation of the mitochondrial cytochrome c oxidase subunit IV via elements located in the 3'UTR

In developing rat brain cytochrome c oxidase subunit IV (COXIV) expression is also regulated at post-transcriptional level and two 3'UTR-COXIV RNA-binding factors have been identified. Here, we report the enrichment and identification of the factors from just born rat brains by affinity chromatography of biotinylated 3'UTR-COXIV RNA-protein complexes on streptavidin-conjugated paramagnetic particles. We successfully isolated two main proteins of about 86 and 42kDa, whose sequences were highly attributable to Hsp90 and Actin. The purified proteins maintain RNA-binding ability and specificity for COXIV messenger and, interacting with the 3'UTR, then could negatively modulate mRNA translation. We also studied the content of Hsp90 and Actin during postnatal brain development and demonstrated that in just born rat brain, when the COXIV protein appears at low level, Hsp90 was not phosphorylated. Vice versa in the adult tissue, when COXIV accumulates, Hsp90 appeared phosphorylated in serine therefore it could be unable to bind COXIV messenger, suggesting that the phosphorylation event could provoke the loss of Hsp90 binding to mRNA. We hypothesize a new post-transcriptional mechanism regulating a messenger encoded by nuclear genome for a mitochondrial protein and that Hsp90 and Actin, could represent key players in COXIV translation.

Mitochondrial compartment: a possible target of cadmium effects on breast epithelial cells

Cadmium-breast epithelial cell interactions were studied by analyzing some mitochondria-related aspects of stress response. We treated immortalized non-tumor breast cells with 5 or 50 microM CdCl(2) for 24 or 96 h demonstrating that the exposure did not cause a significant mitochondrial proliferation, while it induced a significant increase in the respiratory activity and mitochondrial polarization. In addition, we found that hsp60 was up-regulated while hsp70 and COXII and COXIV were down-regulated. The mRNA for hsp70 remained constant and only the inducible form of the 70-kDa heat shock protein was over expressed. The mRNAs for COXII and COXIV remained constant after 24 h and increased after longer incubations while the respective proteins decreased. These findings provide additional information on the cellular and molecular aspects of the interaction between Cd and epithelial cells, and on alterations of mitochondria as early events in Cd cytotoxicity.

Nuclear-mitochondrial interaction

The biogenesis of mitochondria depends on the coordinated expression of nuclear and mitochondrial genomes. Consequently, the control of mitochondrial biogenesis and function depends on extremely complex processes requiring a variety of well orchestrated regulatory mechanisms. It is clear that the interplay of transcription factors and coactivators contributes to the expression of both nuclear and mitochondrial respiratory genes. In addition, the regulation of mitochondria biogenesis depends on proteins that, interacting with messenger RNAs for mitochondrial proteins, influence their metabolism and expression. Moreover, a tight regulation of the import and final assembly of mitochondrial protein is essential to endow mitochondria with functional complexes. These studies represent the basis for understanding the mechanisms involved in the nucleus-mitochondrion communication, a cross-talk essential for the cell.

Localization of the transcriptional coactivator PGC-1alpha to GABAergic neurons during maturation of the rat brain

The transcriptional coactivator peroxisome proliferator activated receptor gamma coactivator 1alpha (PGC-1alpha) can activate a number of transcription factors to regulate mitochondrial biogenesis and cell-specific responses to cold, fasting, and exercise. Recent studies indicate that PGC-1alpha knockout mice exhibit behavioral abnormalities and progressive vacuolization in various brain regions. To investigate the roles for PGC-1alpha in the nervous system, we evaluated the temporal and cell-specific expression of PGC-1alpha in the normal developing rat brain. Western blot of whole brain homogenates with a PGC-1alpha-specific antibody revealed that PGC-1alpha protein was most abundant in the embryonic and early postnatal forebrain and cerebellum. Using quantitative reverse-transcriptase polymerase chain reaction (RT-PCR), we determined that PGC-1alpha mRNA expression increased most markedly between postnatal days 3 (P3) and 14 in the cortex, striatum, and hippocampus. Immunohistochemical and immunofluorescence analyses of brain tissue indicated that while PGC-1alpha was found in most neuronal populations from embryonic day 15 to P3, it was specifically concentrated in GABAergic populations from P3 to adulthood. Interestingly, PGC-1alpha colocalized with the developmentally regulated chemoattractant reelin in the cortex and hippocampus, and the survival-promoting transcription factor myocyte enhancing factor 2 was highly concentrated in GABAergic populations in the striatum and cerebellum at times of PGC-1alpha expression. These results implicate PGC-1alpha as a regulator of metabolism and/or survival in GABAergic neurons during a phase of mitochondrial and synaptic changes in the developing brain and suggest that PGC-1alpha may be a good target for increasing metabolism in GABAergic populations in neurodevelopmental and neurodegenerative disorders.