Mitochondrial respiration promotes Cdc37-dependent stability of the Cdk1 homolog Cdc28.

Cdc28, the homolog of mammalian Cdk1, is a conserved key regulatory kinase for all major cell cycle transitions in yeast. We have found that defects in mitochondrial respiration (including deletion of ATP2, an ATP synthase subunit) inhibit growth of cells carrying a degron allele of Cdc28 (cdc28td) or Cdc28 temperature-sensitive mutations (cdc28-1 and cdc28-1N) at semi-permissive temperatures. Loss of cell proliferation in the atp2Δcdc28td double mutant is associated with aggravated cell cycle arrest and mitochondrial dysfunction, including mitochondrial hyperpolarization and fragmentation. Unexpectedly, in mutants defective in mitochondrial respiration, steady-state protein levels of mutant cdc28 are strongly reduced, accounting for the aggravated growth defects. Stability of Cdc28 is promoted by the Hsp90-Cdc37 chaperone complex. Our results show that atp2Δcdc28td double-mutant cells, but not single mutants, are sensitive to chemical inhibition of the Hsp90-Cdc37 complex, and exhibit reduced levels of additional Hsp90-Cdc37 client kinases, suggesting an inhibition of this complex. In agreement, overexpression of CDC37 improved atp2Δcdc28td cell growth and Cdc28 levels. Overall, our study shows that simultaneous disturbance of mitochondrial respiration and Cdc28 activity reduces the capacity of Cdc37 to chaperone client kinases, leading to growth arrest.

Prediction and biological analysis of yeast VDAC1 phosphorylation.

The mitochondrial outer membrane protein porin 1 (Por1), the yeast orthologue of mammalian voltage-dependent anion channel (VDAC), is the major permeability pathway for the flux of metabolites and ions between cytosol and mitochondria. In yeast, several Por1 phosphorylation sites have been identified. Protein phosphorylation is a major modification regulating a variety of biological activities, but the potential biological roles of Por1 phosphorylation remains unaddressed. In this work, we analysed 10 experimentally observed phosphorylation sites in yeast Por1 using bioinformatics tools. Two of the residues, T100 and S133, predicted to reduce and increase pore permeability, respectively, were validated using biological assays. In accordance, Por1T100D reduced mitochondrial respiration, while Por1S133E phosphomimetic mutant increased it. Por1T100A expression also improved respiratory growth, while Por1S133A caused defects in all growth conditions tested, notably in fermenting media. In conclusion, we found phosphorylation has the potential to modulate Por1, causing a marked effect on mitochondrial function. It can also impact on cell morphology and growth both in respiratory and, unpredictably, also in fermenting conditions, expanding our knowledge on the role of Por1 in cell physiology.

Agreement Between Maximal Lactate Steady State and Critical Power in Different Sports: A Systematic Review and Bayesian's Meta-Regression.

ABSTRACT: Borszcz, FK, de Aguiar, RA, Costa, VP, Denadai, BS, and de Lucas, RD. Agreement between maximal lactate steady state and critical power in different sports: A systematic review and Bayesian's meta-regression. J Strength Cond Res 38(6): e320-e339, 2024-This study aimed to systematically review the literature and perform a meta-regression to determine the level of agreement between maximal lactate steady state (MLSS) and critical power (CP). Considered eligible to include were peer-reviewed and "gray literature" studies in English, Spanish, and Portuguese languages in cyclical exercises. The last search was made on March 24, 2022, on PubMed, ScienceDirect, SciELO, and Google Scholar. The study's quality was evaluated using 4 criteria adapted from the COSMIN tool. The level of agreement was examined by 2 separate meta-regressions modeled under Bayesian's methods, the first for the mean differences and the second for the SD of differences. The searches yielded 455 studies, of which 36 studies were included. Quality scale revealed detailed methods and small samples used and that some studies lacked inclusion/exclusion criteria reporting. For MLSS and CP comparison, likely (i.e., coefficients with high probabilities) covariates that change the mean difference were the MLSS time frame and delta criteria of blood lactate concentration, MLSS number and duration of pauses, CP longest predictive trial duration, CP type of predictive trials, CP model fitting parameters, and exercise modality. Covariates for SD of the differences were the subject's maximal oxygen uptake, CP's longest predictive trial duration, and exercise modality. Traditional MLSS protocol and CP from 2- to 15-minute trials do not reflect equivalent exercise intensity levels; the proximity between MLSS and CP measures can differ depending on test design, and both MLSS and CP have inherent limitations. Therefore, comparisons between them should always consider these aspects.

Identifying Roadkill Hotspots for Mammals in the Brazilian Atlantic Forest using a Functional Group Approach.

A critical step to design wildlife mitigating measures is the identification of roadkill hotspots. However, the effectiveness of mitigations based on roadkill hotspots depends on whether spatial aggregations are recurrent over time, spatially restricted, and most importantly, shared by species with diverse ecological and functional characteristics. We used a functional group approach to map roadkill hotspots for mammalian species along the BR-101/North RJ, a major road crossing important remnants of the Brazilian Atlantic Forest. We tested if functional groups present distinct hotspot patterns, and if they converge into the same road sectors, in that case, favoring optimal mitigating actions. Roadkill rates were monitored and recorded between October/2014 and September/2018 and species were classified into six functional groups based on their home range, body size, locomotion mode, diet, and forest-dependency. Hotspots along the roads were mapped for comparison of spatial patterns between functional groups. Results demonstrated that the roadkill index varied idiosyncratically for each functional group throughout the months and that no group presented seasonality. Seven hotspots were shared by two or more functional groups, highlighting the importance of these road stretches to regional mammal fauna. Two of the stretches are associated with aquatic areas extending from one side of the road to the other, and the remaining are connected to patches of native vegetation on both sides. This work brings a promising approach, yet hardly used in ecological studies on roads to analyze roadkill dynamics, assigning more importance to ecological instead of taxonomical characteristics, normally used to identify spatiotemporal patterns.

Optimism and fear of COVID-19 in higher education students: the mediating role of general anxiety.

Higher education students have faced several changes in their lives due to the COVID-19 pandemic. This study aims to explore the effect of dispositional optimism in students' fear of COVID-19 and to test the mediating role of general anxiety in the relationship between optimism and fear. Using an online survey, data were collected during the second wave of the pandemic in Portugal. The sample included 312 higher education students (76% females) aged 18-25 years old, who completed measures of dispositional optimism, general anxiety and fear of COVID-19. The results showed that higher optimism and lower general anxiety reduce fear of COVID-19. Moreover, the link between optimism and fear is fully mediated by general anxiety, showing that optimism reduces fear of COVID-19 indirectly through the reduction of students' anxiety. The role of optimism, anxiety and fear in higher education students is discussed and topics for further research are presented.

Definition of the Region of Interest for the Assessment of Alveolar Bone Repair Using Micro-computed Tomography.

The objective of this study was to evaluate the influence of the extraction socket (distal or lingual root) and the type of region of interest (ROI) definition (manual or predefined) on the assessment of alveolar repair following tooth extraction using micro-computed tomography (micro-CT). The software package used for scanning, reconstruction, reorientation, and analysis of images (NRecon®, DataViewer®, CT-Analyzer®) was acquired through Bruker < https://www.bruker.com > . The sample comprised the micro-CT volumes of seven Wistar rat mandibles, in which the right first molar was extracted. The reconstructed images were analyzed using the extraction sockets, i.e., the distal and intermediate lingual root and the method of ROI definition: manual (MA), central round (CR), and peripheral round (PR). The bone volume fraction (BV/TV) values obtained were analyzed by two-way ANOVA with Tukey's post hoc test (α = 5%). The distal extraction socket resulted in significantly lower BV/TV values than the intermediate lingual socket for MA (P = 0.001), CR (P < 0.001), and PR (P < 0.001). Regarding the ROI, when evaluating the distal extraction socket, the BV/TV was significantly higher (P < 0.001) for MA than for CR and PR, with a lower BV/TV for CR. However, no significant difference was observed for MA (P = 0.855), CR (P = 0.769), or PR (P = 0.453) in the intermediate lingual extraction socket. The bone neoformation outcome (BV/TV) for alveolar bone repair after tooth extraction is significantly influenced by the ROI and the extraction socket. Using the predefined method with a standardized ROI in the central region of the distal extraction socket resulted in the assessment of bone volume, demonstrating the most critical region of the bone neoformation process.

The APC/C Activator Cdh1p Plays a Role in Mitochondrial Metabolic Remodelling in Yeast.

Cdh1p is one of the two substrate adaptor proteins of the anaphase promoting complex/cyclosome (APC/C), a ubiquitin ligase that regulates proteolysis during cell cycle. In this work, using a proteomic approach, we found 135 mitochondrial proteins whose abundance was significantly altered in the cdh1Δ mutant, with 43 up-regulated proteins and 92 down-regulated proteins. The group of significantly up-regulated proteins included subunits of the mitochondrial respiratory chain, enzymes from the tricarboxylic acid cycle and regulators of mitochondrial organization, suggesting a metabolic remodelling towards an increase in mitochondrial respiration. In accordance, mitochondrial oxygen consumption and Cytochrome c oxidase activity increased in Cdh1p-deficient cells. These effects seem to be mediated by the transcriptional activator Yap1p, a major regulator of the yeast oxidative stress response. YAP1 deletion suppressed the increased Cyc1p levels and mitochondrial respiration in cdh1Δ cells. In agreement, Yap1p is transcriptionally more active in cdh1Δ cells and responsible for the higher oxidative stress tolerance of cdh1Δ mutant cells. Overall, our results unveil a new role for APC/C-Cdh1p in the regulation of the mitochondrial metabolic remodelling through Yap1p activity.

Iron Limitation Restores Autophagy and Increases Lifespan in the Yeast Model of Niemann-Pick Type C1.

Niemann-Pick type C1 (NPC1) is an endolysosomal transmembrane protein involved in the export of cholesterol and sphingolipids to other cellular compartments such as the endoplasmic reticulum and plasma membrane. NPC1 loss of function is the major cause of NPC disease, a rare lysosomal storage disorder characterized by an abnormal accumulation of lipids in the late endosomal/lysosomal network, mitochondrial dysfunction, and impaired autophagy. NPC phenotypes are conserved in yeast lacking Ncr1, an orthologue of human NPC1, leading to premature aging. Herein, we performed a phosphoproteomic analysis to investigate the effect of Ncr1 loss on cellular functions mediated by the yeast lysosome-like vacuoles. Our results revealed changes in vacuolar membrane proteins that are associated mostly with vesicle biology (fusion, transport, organization), autophagy, and ion homeostasis, including iron, manganese, and calcium. Consistently, the cytoplasm to vacuole targeting (Cvt) pathway was increased in ncr1∆ cells and autophagy was compromised despite TORC1 inhibition. Moreover, ncr1∆ cells exhibited iron overload mediated by the low-iron sensing transcription factor Aft1. Iron deprivation restored the autophagic flux of ncr1∆ cells and increased its chronological lifespan and oxidative stress resistance. These results implicate iron overload on autophagy impairment, oxidative stress sensitivity, and cell death in the yeast model of NPC1.

Selection of plasma donors for the production of anti-SARS-CoV-2 immunoglobulin-based therapies: Strategies for quantitative antibody measurements.

Even after two years of the pandemic, a completely effective treatment against SARS-CoV-2 has not yet been established. Considering this fact and the emergence of successive new viral variants, the development of therapies based on natural polyclonal antibodies recovered from convalescent plasma remains relevant. This study presents a comparison between different methods of screening antibodies in samples of 41 individuals previously diagnosed with COVID-19. We found a significant correlation between Abbot Architect anti-SARS-CoV-2 IgG and Abbott Allinity SARS-CoV-2 IgG II Quantitative assay intensity of reactivity and neutralizing antibody (nAb) titers. Thus, we propose an initial antibody screening with IgG anti-N Abbott Architect test, with an index of, for example, > 3.25 or SARS-CoV-2 IgG II Quantitative Abbott Allinity assay > 137.65 AU/mL as good predictors of Nab ≥ 1:80. For the quantitative method, this threshold demonstrated a 100 % sensitivity and 80 % specificity, with 97.3 % accuracy. An interesting observation was the increase in the neutralizing activity of the anti-SARS-CoV-2 antibodies with the longest interval between the end of the symptoms and the collection, demonstrating that the delay in plasma collection does not affect the achievement of adequate nAbs levels. These results demonstrate the possibility of using faster and more widely available commercial serological tests with a good correlation with viral neutralization tests in culture, allowing for optimized large-scale donor selection, which will be of utmost importance for the development of therapies such as hyperimmune immunoglobulin.

Functional Threshold Power Estimated from a 20-minute Time-trial Test is Warm-up-dependent.

This study investigated the influence of different warm-up protocols on functional threshold power. Twenty-one trained cyclists (˙VO2max=60.2±6.8 ml·kg-1·min-1) performed an incremental test and four 20-min time trials preceded by different warm-up protocols. Two warm-up protocols lasted 45 min, with a 5-min time trial performed either 15 min (Traditional) or 25 min (Reverse) before the 20-min time trial. The other two warm-up protocols lasted 25 min (High Revolutions-per minute) and 10 min (Self-selected), including three fast accelerations and self-selected intensity, respectively. The power outputs achieved during the 20-min time trial preceded by the Traditional and Reverse warm-up protocols were significantly lower than the High Revolutions-per-minute and Self-selected protocols (256±30; 257±30; 270±30; 270±30 W, respectively). Participants chose a conservative pacing strategy at the onset (negative) for the Traditional and Reverse but implemented a fast-start strategy (U-shaped) for the High revolutions-per-minute and Self-selected warm-up protocols. In conclusion, 20-min time-trial performance and pacing are affected by different warm-ups. Consequently, the resultant functional threshold power may be different depending on whether the original protocol with a 5-min time trial is followed or not.

Is Functional Overreaching or Acute Fatigue the Key to the Effects of Concentrated Block Training in Running?

ABSTRACT: Borszcz, FK, Vieira, MT, Tramontin, AF, Visentainer, LH, and Costa, VP. Is functional overreaching or acute fatigue the key to the effects of concentrated block training in running? J Strength Cond Res 36(12): 3485-3496, 2022-This study examined the effects of 5 consecutive days of high- and moderate-intensity training on performance and physiological measures in moderately trained individuals. The relationship of the training organization with the state of overreaching and acute fatigue was investigated. Twenty-four male soldiers (age, 19.3 ± 0.4 years; V̇o2peak, 58.7 ± 3.8 ml·kg-1·min-1) were assigned to 2 training groups for 5 consecutive days of either high- or moderate-intensity training. The subjects underwent incremental and 12-minute time trial tests before, immediately after, 1 and 2 weeks after training. The high- and moderate-intensity sessions were 30 minutes in duration and performed at fixed velocities of 13.3 and 10 km·h-1 (near second and first ventilatory thresholds), respectively. Acute fatigue and overreaching criteria were set as concomitant nonimpairment and impairment, respectively, in the incremental peak velocity and 12-minute time trial performances at posttest immediately after the training block. Data analyses were completed using hierarchical Bayesian's models. In subjects who wer trained at moderate intensity, no performance impairment occurred (i.e., acute fatigue); for the high-intensity training, 5 subjects showed impairment in performance and were classified as overreached. Only in subjects who were acutely fatigued, clear beneficial effects were observed in incremental test peak velocity and 12-minute time trial performances. In moderately trained runners, a block of 5 consecutive days of moderate-intensity training was demonstrated to be a useful strategy for the improvement of performance. However, high-intensity training does not seem to be a safe strategy because of the observations of overreaching and inferior probabilities of performance improvements.

SicknessMiner: a deep-learning-driven text-mining tool to abridge disease-disease associations.

BACKGROUND: Blood cancers (BCs) are responsible for over 720 K yearly deaths worldwide. Their prevalence and mortality-rate uphold the relevance of research related to BCs. Despite the availability of different resources establishing Disease-Disease Associations (DDAs), the knowledge is scattered and not accessible in a straightforward way to the scientific community. Here, we propose SicknessMiner, a biomedical Text-Mining (TM) approach towards the centralization of DDAs. Our methodology encompasses Named Entity Recognition (NER) and Named Entity Normalization (NEN) steps, and the DDAs retrieved were compared to the DisGeNET resource for qualitative and quantitative comparison. RESULTS: We obtained the DDAs via co-mention using our SicknessMiner or gene- or variant-disease similarity on DisGeNET. SicknessMiner was able to retrieve around 92% of the DisGeNET results and nearly 15% of the SicknessMiner results were specific to our pipeline. CONCLUSIONS: SicknessMiner is a valuable tool to extract disease-disease relationship from RAW input corpus.

Predicting Maximal Lactate Steady State from Carminatti's Shuttle Run Test in Soccer Players.

The objective of the present study was to determine the validity of Carminatti's shuttle run incremental test-T-Car derived parameters in estimating the maximal lactate steady state determined in shuttle run format. Eighteen soccer players performed a T-Car test, and several trials to determine the maximal lactate steady state. From T-Car were derived the heart rate deflection point, peak speed, maximal heart rate and parameters resulting from percentage of peak measures. The validity was accessed by Bland-Altman plots, linear regressions, and two one-sided tests of equivalence analysis. The results showed the speed at 80.4% of T-Car peak speed, the heart rate deflection point and the 91.4% of maximal heart rate were equivalent to maximal lactate steady state (Mean difference; ±90% compatibility interval; -0.8; ±1.5%, -0.4; ±1.1%, and 0.0; ±2.7%, respectively). Additionally, peak speed during the T-Car test was a stronger predictor of maximal lactate steady state (MLSS [km/h]=2.57+0.65 × sPeak; r=0.82 [90% CI; 0.62-0.92], standard error of the estimate=3.6%; 90% CI ×/÷1.4). Therefore, soccer players can use the T-Car derived parameters as a noninvasive and practical alternative to estimate the specific maximal lactate steady state for soccer.

Influence of material and loading location on stress distribution of inlays.

PURPOSE: To evaluate the stress distribution of inlays fabricated with restorative materials of different elastic moduli under two functional loading conditions by using three-dimensional (3D) finite element analysis (FEA) models of a second maxillary premolar. METHODS: A 3D model of a sound maxillary left second premolar and its supporting bone was generated in a previous study and reutilized under permission of the authors for the present study. Inlay models obtained from the sound tooth were then assigned according to the type and inherent elastic modulus of the restorative material used, as follows: microhybrid composite (Filtek Z250); indirect resin composite (Paradigm); lithium disilicate reinforced glass ceramic (IPS e.max Press); and type III gold alloy. The geometric models were then exported for 3D FEA. All materials were considered isotropic, homogeneous, and linear-elastic. A static load of 100 N was applied in two conditions: axially at both cusps (axial loading) and at the mesial marginal ridge (proximal loading). Maximum principal and von Mises stresses were used to analyze the stress distribution pattern in inlays and sound premolar models. RESULTS: Under axial loading condition, either resin composite, ceramic or type III gold alloy inlays generated a similar biomechanical behavior, especially in terms of stress distribution in the remaining tooth structure and cusp deflection. However, higher tensile stresses were observed along the proximal gingival margin of the preparation under proximal loading in the Z250 and Paradigm models, as well as a greater cusp deflection. In contrast, a deflection like the sound model was observed in the ceramic and gold inlay models. CLINICAL SIGNIFICANCE: Restorative materials with higher elastic modulus, such as dental ceramics and type III gold alloys, seem to be the best choice for maxillary premolars restored with inlays in the presence of occlusal contact on the marginal ridge.

Target of Rapamycin Complex 1 (TORC1), Protein Kinase A (PKA) and Cytosolic pH Regulate a Transcriptional Circuit for Lipid Droplet Formation.

Lipid droplets (LDs) are ubiquitous organelles that fulfill essential roles in response to metabolic cues. The identification of several neutral lipid synthesizing and regulatory protein complexes have propelled significant advance on the mechanisms of LD biogenesis in the endoplasmic reticulum (ER). However, our understanding of signaling networks, especially transcriptional mechanisms, regulating membrane biogenesis is very limited. Here, we show that the nutrient-sensing Target of Rapamycin Complex 1 (TORC1) regulates LD formation at a transcriptional level, by targeting DGA1 expression, in a Sit4-, Mks1-, and Sfp1-dependent manner. We show that cytosolic pH (pHc), co-regulated by the plasma membrane H+-ATPase Pma1 and the vacuolar ATPase (V-ATPase), acts as a second messenger, upstream of protein kinase A (PKA), to adjust the localization and activity of the major transcription factor repressor Opi1, which in turn controls the metabolic switch between phospholipid metabolism and lipid storage. Together, this work delineates hitherto unknown molecular mechanisms that couple nutrient availability and pHc to LD formation through a transcriptional circuit regulated by major signaling transduction pathways.

Reliability of the Functional Threshold Power in Competitive Cyclists.

Functional threshold power (FTP) is defined as the highest power that a cyclist can maintain in a quasi-steady state without fatigue for approximately 1 hour. To improve practicality, a 20-minute time-trial test was proposed, where FTP is represented by 95% of the mean power produced. It is preceded by a specific 45-min warm-up, with periods of low intensity, fast accelerations, and a 5-min time-trial. Thus, the aim of this study was to determine the reliability of this protocol, including the reliability of the warm-up, pacing strategy, and FTP determination. For this purpose, 25 trained cyclists performed a familiarization and two other tests separated by seven days. The coefficient of variation (CV [%]), intraclass correlation coefficient (ICC), and change in the mean between test and retest were calculated. The results show that the 20-min time-trial was reliable (CV=2.9%, ICC=0.97), despite a less reliable warm-up (CV=5.5%, ICC=0.84). The changes in the mean between the test and retest were trivial to small for all measurements, and the pacing strategy was consistent across all trials. These results suggest that FTP determination with a 20-min protocol was reliable in trained cyclists.

Influence of 2,4-D residues on the soil microbial community and growth of tree species.

The 2,4-D (2,4-dichlorophenoxyacetic acid) has low half-life in the soil, but it is capable of altering the soil microbial community. The objective of this study was to evaluate the influence of 2,4-D residues on the structure of the soil microbial community and the growth of tree species. The tolerance and phytoremediation potential of tree species were evaluated. The microbial analysis was performed by T-RFLP. The 2,4-D herbicide reduced the plant height of K. lathrophyton, number of leaves of C. ferrea and K. lathrophyton and root dry matter allocation for C. brasiliense, I. striata, P. heptaphyllum, and T. guianensis. Cucumis sativus intoxication on soil contaminated with 2,4-D was not significant. The structure of Fungi community in the rhizospheric soils of C. ferrea was altered. The herbicide 2,4-D increased the diversity of Fungi in rhizospheric soils of P. heptahyllum and R. grandis. Most tree species were tolerant, and the evaluation time was sufficient to remedy 2,4-D. The structures of the microbial communities Archaea, Bacteria, and Fungi were little influenced by 2,4-D. The diversity of the Archaea domain was not affected, the diversity of the Bacteria in Inga striata decreased while the fungi increased in Protium heptaphyllum and Richeria grandis with 2,4-D.

Effects of Physical Exercise on the Expression of MicroRNAs: A Systematic Review.

Silva, FCd, Iop, RdR, Andrade, A, Costa, VP, Gutierres Filho, PJB, and Silva, Rd. Effects of physical exercise on the expression of microRNAs: A systematic review 34(1): 270-280, 2020-Studies have detected changes in the expression of miRNAs after physical exercise, which brings new insight into the molecular control of adaptation to exercise. Therefore, the objective of the current systematic review of experimental and quasiexperimental studies published in the past 10 years was to assess evidence related to acute effects, chronic effects, and both acute and chronic effects of physical exercise on miRNA expression in humans, as well as its functions, evaluated in serum, plasma, whole blood, saliva, or muscle biopsy. For this purpose, the following electronic databases were selected: MEDLINE by Pubmed, SCOPUS, Web of Science, and also a manual search in references of the selected articles to April 2017. Experimental and quasiexperimental studies were included. Results indicate that, of the 345 studies retrieved, 40 studies met the inclusion criteria and two articles were included as a result of the manual search. The 42 studies were analyzed, and it can be observed acute and chronic effects of physical exercises (aerobic and resistance) on the expression of several miRNAs in healthy subjects, athletes, young, elderly and in patients with congestive heart failure, chronic kidney disease, diabetes mellitus type 2 associated with morbid obesity, prediabetic, and patients with intermittent claudication. It is safe to assume that miRNA changes, both in muscle tissues and bodily fluids, are presumably associated with the benefits induced by acute and chronic physical exercise. Thus, a better understanding of changes in miRNAs as a response to physical exercise might contribute to the development of miRNAs as therapeutic targets for the improvement of exercise capacity in individuals with any given disease. However, additional studies are necessary to draw accurate conclusions.

Signaling pathways governing iron homeostasis in budding yeast.

Iron is an essential element for eukaryotes as it participates as a redox-active co-factor in many biological processes. Since iron is also potentially toxic, iron levels are carefully regulated. In the yeast Saccharomyces cerevisiae, iron homeostasis is maintained by the transcriptional control of the iron acquisition systems (iron regulon), mainly by the iron-responsive transcriptional factors Aft1p and Yap5p. Intracellular iron is stored in the vacuole, mobilized for other locations when necessary, particularly for the mitochondria, the major site of iron-utilizing pathways. Mitochondria also play an additional role as a sensor for the regulation of cellular iron acquisition and intracellular distribution. Mounting evidence suggest that iron acquisition systems are not only responsive to iron levels but also to signaling pathways. The most recognized is the activation of the iron regulon at the diauxic shift, oppositely regulated by PKA and SNF1 kinases, major regulators of glucose signaling. Hog1p, a MAP kinase involved in stress responses, also negatively regulates iron uptake by phosphorylating Aft1p. In this review, we address organellar signaling and signal transduction pathways that play a major role in the coordination of iron homeostasis with cell growth and division.

The NAD+-dependent deacetylase SIRT2 attenuates oxidative stress and mitochondrial dysfunction and improves insulin sensitivity in hepatocytes.

Insulin resistance is a major predictor of the development of metabolic disorders. Sirtuins (SIRTs) have emerged as potential targets that can be manipulated to counteract age-related diseases, including type 2 diabetes. SIRT2 has been recently shown to exert important metabolic effects, but whether SIRT2 regulates insulin sensitivity in hepatocytes is currently unknown. The aim of this study is to investigate this possibility and to elucidate underlying molecular mechanisms. Here, we show that SIRT2 is downregulated in insulin-resistant hepatocytes and livers, and this was accompanied by increased generation of reactive oxygen species, activation of stress-sensitive ERK1/2 kinase, and mitochondrial dysfunction. Conversely, SIRT2 overexpression in insulin-resistant hepatocytes improved insulin sensitivity, mitigated reactive oxygen species production and ameliorated mitochondrial dysfunction. Further analysis revealed a reestablishment of mitochondrial morphology, with a higher number of elongated mitochondria rather than fragmented mitochondria instigated by insulin resistance. Mechanistically, SIRT2 was able to increase fusion-related protein Mfn2 and decrease mitochondrial-associated Drp1. SIRT2 also attenuated the downregulation of TFAM, a key mtDNA-associated protein, contributing to the increase in mitochondrial mass. Importantly, we found that SIRT2 expression in PBMCs of human subjects was negatively correlated with obesity and insulin resistance. These results suggest a novel function for hepatic SIRT2 in the regulation of insulin sensitivity and raise the possibility that SIRT2 activators may offer novel opportunities for preventing or treating insulin resistance and type 2 diabetes.