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Smoking-derived nicotine (N) and oral contraceptive (OC) synergistically exacerbate ischemic brain damage in females, and the underlying mechanisms remain elusive. In a previous study, we showed that N + OC exposure altered brain glucose metabolism in females. Since lipid metabolism complements glycolysis, the current study aims to examine the metabolic fingerprint of fatty acids in the brain of female rats exposed to N+/−OC. Adolescent and adult Sprague–Dawley female rats were randomly (n = 8 per group) exposed to either saline or N (4.5 mg/kg) +/−OC (combined OC or placebo delivered via oral gavage) for 16–21 days. Following exposure, brain tissue was harvested for unbiased metabolomic analysis (performed by Metabolon Inc., Morrisville, NC, USA) and the metabolomic profile changes were complemented with Western blot analysis of key enzymes in the lipid pathway. Metabolomic data showed significant accumulation of fatty acids and phosphatidylcholine (PC) metabolites in the brain. Adolescent, more so than adult females, exposed to N + OC showed significant increases in carnitine-conjugated fatty acid metabolites compared to saline control animals. These changes in fatty acyl carnitines were accompanied by an increase in a subset of free fatty acids, suggesting elevated fatty acid β-oxidation in the mitochondria to meet energy demand. In support, β-hydroxybutyrate was significantly lower in N + OC exposure groups in adolescent animals, implying a complete shunting of acetyl CoA for energy production via the TCA cycle. The reported changes in fatty acids and PC metabolism due to N + OC could inhibit post-translational palmitoylation of membrane proteins and synaptic vesicle formation, respectively, thus exacerbating ischemic brain damage in female rats. [ABSTRACT FROM AUTHOR]

Mitochondrial respiratory chain complexes I, III, and IV can associate into larger structures termed supercomplexes or respirasomes, thereby generating structural interdependences among the individual complexes yet to be understood. In patients, nonsense mutations in complex IV subunit genes cause severe encephalomyopathies randomly associated with pleiotropic complex I defects. Using complexome profiling and biochemical analyses, we have explored the structural rearrangements of the respiratory chain in human cell lines depleted of the catalytic complex IV subunit COX1 or COX2. In the absence of a functional complex IV holoenzyme, several supercomplex I+III2 species coexist, which differ in their content of COX subunits and COX7A2L/HIGD2A assembly factors. The incorporation of an atypical COX1‐HIGD2A submodule attenuates supercomplex I+III2 turnover rate, indicating an unexpected molecular adaptation for supercomplexes stabilization that relies on the presence of COX1 independently of holo‐complex IV formation. Our data set the basis for complex I structural dependence on complex IV, revealing the co‐existence of alternative pathways for the biogenesis of "supercomplex‐associated" versus individual complex IV, which could determine physiological adaptations under different stress and disease scenarios. Synopsis: The mitochondrial respiratory chain (MRC) drives aerobic energy transduction in eukaryotic cells and consists of five multisubunit enzyme complexes that can associate to form supercomplexes (SCs). Availability of complex IV subunit COX1 and assembly factor HIGD2A promotes the formation of submodules that directly bind and stabilize respiratory SC I+III2 in human cells. Human cells lacking complex IV display diverse SC I+III2 species.Alternative SC I+III2 species differ in their COX subunits and assembly factors content.SC I+III2 stability is enhanced upon binding of an atypical COX1‐HIGD2A submodule.Functional preservation of SC I+III2 requires COX1 but is independent of holo‐COX formation.Different assembly lines exist to synthesize free‐ versus SC‐associated complex IV. [ABSTRACT FROM AUTHOR]

Here, we review and update the recent advances in the metabolic control during the adaptive response of budding yeast to hyperosmotic and salt stress, which is one of the best understood signaling events at the molecular level. This environmental stress can be easily applied and hence has been exploited in the past to generate an impressively detailed and comprehensive model of cellular adaptation. It is clear now that this stress modulates a great number of different physiological functions of the cell, which altogether contribute to cellular survival and adaptation. Primary defense mechanisms are the massive induction of stress tolerance genes in the nucleus, the activation of cation transport at the plasma membrane, or the production and intracellular accumulation of osmolytes. At the same time and in a coordinated manner, the cell shuts down the expression of housekeeping genes, delays the progression of the cell cycle, inhibits genomic replication, and modulates translation efficiency to optimize the response and to avoid cellular damage. To this fascinating interplay of cellular functions directly regulated by the stress, we have to add yet another layer of control, which is physiologically relevant for stress tolerance. Salt stress induces an immediate metabolic readjustment, which includes the up-regulation of peroxisomal biomass and activity in a coordinated manner with the reinforcement of mitochondrial respiratory metabolism. Our recent findings are consistent with a model, where salt stress triggers a metabolic shift from fermentation to respiration fueled by the enhanced peroxisomal oxidation of fatty acids. We discuss here the regulatory details of this stress-induced metabolic shift and its possible roles in the context of the previously known adaptive functions. [ABSTRACT FROM AUTHOR]

Repair and removal of damaged mitochondria is a key process for eukaryotic cell homeostasis. Here we investigate in the yeast model how different protein complexes of the mitochondrial electron transport chain are subject to specific degradation upon high respiration load and organelle damage. We find that the turnover of subunits of the electron transport complex I equivalent and complex III is preferentially stimulated upon high respiration rates. Particular mitochondrial proteases, but not mitophagy, are involved in this activated degradation. Further mitochondrial damage by valinomycin treatment of yeast cells triggers the mitophagic removal of the same respiratory complexes. This selective protein degradation depends on the mitochondrial fusion and fission apparatus and the autophagy adaptor protein Atg11, but not on the mitochondrial mitophagy receptor Atg32. Loss of autophagosomal protein function leads to valinomycin sensitivity and an overproduction of reactive oxygen species upon mitochondrial damage. A specific event in this selective turnover of electron transport chain complexes seems to be the association of Atg11 with the mitochondrial network, which can be achieved by overexpression of the Atg11 protein even in the absence of Atg32. Furthermore, the interaction of various Atg11 molecules via the C-terminal coil domain is specifically and rapidly stimulated upon mitochondrial damage and could therefore be an early trigger of selective mitophagy in response to the organelles dysfunction. Our work indicates that autophagic quality control upon mitochondrial damage operates in a selective manner. [ABSTRACT FROM AUTHOR]

Mpc proteins are highly conserved from yeast to humans and are necessary for the uptake of pyruvate at the inner mitochondrial membrane, which is used for leucine and valine biosynthesis and as a fuel for respiration. Our analysis of the yeast MPC gene family suggests that amino acid biosynthesis, respiration rate and oxidative stress tolerance are regulated by changes in the Mpc protein composition of the mitochondria. Mpc2 and Mpc3 are highly similar but functionally different: Mpc2 is most abundant under fermentative non stress conditions and important for amino acid biosynthesis, while Mpc3 is the most abundant family member upon salt stress or when high respiration rates are required. Accordingly, expression of the MPC3 gene is highly activated upon NaCl stress or during the transition from fermentation to respiration, both types of regulation depend on the Hog1 MAP kinase. Overexpression experiments show that gain of Mpc2 function leads to a severe respiration defect and ROS accumulation, while Mpc3 stimulates respiration and enhances tolerance to oxidative stress. Our results identify the regulated mitochondrial pyruvate uptake as an important determinant of respiration rate and stress resistance. [ABSTRACT FROM AUTHOR]

The biogenesis and function of eukaryotic cytochrome c oxidase or mitochondrial respiratory chain complex IV (CIV) undergo several levels of regulation to adapt to changing environmental conditions. Adaptation to hypoxia and oxidative stress involves CIV subunit isoform switch, changes in phosphorylation status, and modulation of CIV assembly and enzymatic activity by interacting factors. The latter include the Hypoxia Inducible Gene Domain (HIGD) family yeast respiratory supercomplex factors 1 and 2 (Rcf1 and Rcf2) and two mammalian homologs of Rcf1, the proteins HIGD1A and HIGD2A. Whereas Rcf1 and Rcf2 are expressed constitutively, expression of HIGD1A and HIGD2A is induced under stress conditions, such as hypoxia and/or low glucose levels. In both systems, the HIGD proteins localize in the mitochondrial inner membrane and play a role in the biogenesis of CIV as a free unit or as part as respiratory supercomplexes. Notably, they remain bound to assembled CIV and, by modulating its activity, regulate cellular respiration. Here, we will describe the current knowledge regarding the specific and overlapping roles of the several HIGD proteins in physiological and stress conditions. [ABSTRACT FROM AUTHOR]

Summary The mitochondrial respiratory chain is organized in a dynamic set of supercomplexes (SCs). The COX7A2L protein is essential for mammalian SC III 2 +IV assembly. However, its function in respirasome (SCs I+III 2 +IV n) biogenesis remains controversial. To unambiguously determine the COX7A2L role, we generated COX7A2L -knockout (COX7A2L -KO) HEK293T and U87 cells. COX7A2L -KO cells lack SC III 2 +IV but have enhanced complex III steady-state levels, activity, and assembly rate, normal de novo complex IV biogenesis, and delayed respirasome formation. Nonetheless, the KOs have normal respirasome steady-state levels, and only larger structures (SCs I 1-2 +III 2 +IV 2-n or megacomplexes) were undetected. Functional substrate-driven competition assays showed normal mitochondrial respiration in COX7A2L -KO cells in standard and nutritional-, environmental-, and oxidative-stress-challenging conditions. We conclude that COX7A2L establishes a regulatory checkpoint for the biogenesis of CIII 2 and specific SCs, but the COX7A2L-dependent MRC remodeling is essential neither to maintain mitochondrial bioenergetics nor to cope with acute cellular stresses. Graphical Abstract Highlights • COX7A2L -knockout human cells lack SC III 2 +IV and some megacomplexes • COX7A2L -KO cells have enhanced CIII 2 steady-state levels and assembly rate • COX7A2L -KO cells have slower respirasome assembly but normal steady-state levels • COX7A2L-dependent MRC remodeling does not affect mitochondrial bioenergetics The role of COX7A2L in mitochondrial respiratory chain supercomplex biogenesis and function remains controversial. By analyzing COX7A2L -knockout human cells, Lobo-Jarne et al. report that this protein promotes specific respiratory chain complex assembly and organization remodeling but does not affect mitochondrial bioenergetics in physiological, nutritional, or oxidative stress conditions. [ABSTRACT FROM AUTHOR]