A high-throughput assay for mitochondrial membrane potential in permeabilized yeast cells

Obesity-driven mitochondrial dysfunction in human adipose tissue-derived mesenchymal stem/stromal cells involves epigenetic changes

Obesity exacerbates tissue degeneration and compromises the integrity and reparative potential of mesenchymal stem/stromal cells (MSCs), but the underlying mechanisms have not been sufficiently elucidated. Mitochondria modulate the viability, plasticity, proliferative capacity, and differentiation potential of MSCs. We hypothesized that alterations in the 5-hydroxymethylcytosine (5hmC) profile of mitochondria-related genes may mediate obesity-driven dysfunction of human adipose-derived MSCs. MSCs were harvested from abdominal subcutaneous fat of obese and age/sex-matched non-obese subjects (n = 5 each). The 5hmC profile and expression of nuclear-encoded mitochondrial genes were examined by hydroxymethylated DNA immunoprecipitation sequencing (h MeDIP-seq) and mRNA-seq, respectively. MSC mitochondrial structure (electron microscopy) and function, metabolomics, proliferation, and neurogenic differentiation were evaluated in vitro, before and after epigenetic modulation. hMeDIP-seq identified 99 peaks of hyper-hydroxymethylation and 150 peaks of hypo-hydroxymethylation in nuclear-encoded mitochondrial genes from Obese- versus Non-obese-MSCs. Integrated hMeDIP-seq/mRNA-seq analysis identified a select group of overlapping (altered levels of both 5hmC and mRNA) nuclear-encoded mitochondrial genes involved in ATP production, redox activity, cell proliferation, migration, fatty acid metabolism, and neuronal development. Furthermore, Obese-MSCs exhibited decreased mitochondrial matrix density, membrane potential, and levels of fatty acid metabolites, increased superoxide production, and impaired neuronal differentiation, which improved with epigenetic modulation. Obesity elicits epigenetic changes in mitochondria-related genes in human adipose-derived MSCs, accompanied by structural and functional changes in their mitochondria and impaired fatty acid metabolism and neurogenic differentiation capacity. These observations may assist in developing novel therapies to preserve the potential of MSCs for tissue repair and regeneration in obese individuals.

Metabolic Syndrome Induces Epigenetic Alterations in Mitochondria-Related Genes in Swine Mesenchymal Stem Cells

Autologous mesenchymal stem/stromal cells (MSCs) have demonstrated important therapeutic effects in several diseases. Cardiovascular risk factors may impair MSC mitochondrial structure and function, but the underlying mechanisms remain unknown. We hypothesized that metabolic syndrome (MetS) induces epigenetic alterations in mitochondria-related genes in swine MSCs. Pigs were fed a Lean or MetS diet (n = 6 each) for 16 weeks. MSCs were collected from subcutaneous abdominal fat, and DNA hydroxymethylation (5 hmC) profiles of mitochondria-related genes (MitoCarta-2.0) were analyzed by hydroxymethylated DNA immunoprecipitation and next-generation sequencing (hMeDIP-seq) in Lean- and MetS-MSCs untreated or treated with the epigenetic modulator vitamin (Vit)-C (n = 3 each). Functional analysis of genes with differential 5 hmC regions was performed using DAVID6.8. Mitochondrial structure (electron microscopy), oxidative stress, and membrane potential were assessed. hMeDIP-seq identified 172 peaks (associated with 103 mitochondrial genes) with higher and 416 peaks (associated with 165 mitochondrial genes) with lower 5 hmC levels in MetS-MSCs versus Lean-MSCs (≥2-fold, p < 0.05). Genes with higher 5 hmC levels in MetS + MSCs were primarily implicated in fatty acid metabolism, whereas those with lower 5 hmC levels were associated with electron transport chain activity. Vit-C increased 5 hmC levels in mitochondrial antioxidant genes, improved mitochondrial structure and membrane potential, and decreased oxidative stress. MetS alters 5 hmC levels of mitochondria-related genes in swine MSCs. Vit-C modulated 5 hmC levels in these genes and preserved mitochondrial structure and function in MetS-MSCs. These observations may contribute to development of strategies to overcome the deleterious effects of MetS on MSCs.

Effects of Elamipretide on Autophagy in Renal Cells of Pigs with Metabolic Syndrome

Autophagy eliminates excessive nutrients and maintains homeostasis. Obesity and metabolic syndrome (MetS) dysregulate autophagy, possibly partly due to mitochondria injury and inflammation. Elamipretide (ELAM) improves mitochondrial function. We hypothesized that MetS blunts kidney autophagy, which ELAM would restore. Domestic pigs were fed a control or MetS-inducing diet for 16 weeks. During the 4 last weeks, MetS pigs received subcutaneous injections of ELAM (0.1 mg/kg/day, MetS + ELAM) or vehicle (MetS), and kidneys were then harvested to measure protein expression of autophagy mediators and apoptosis. Systemic and renal venous levels of inflammatory cytokines were measured to calculate renal release. The function of isolated mitochondria was assessed by oxidative stress, energy production, and pro-apoptotic activity. MetS slightly downregulated renal expression of autophagy mediators including p62, ATG5-12, mTOR, and AMPK vs. control. Increased mitochondrial H₂O₂ production accompanied decreased ATP production, elevated apoptosis, and renal fibrosis. In MetS + ELAM, mito-protection restored autophagic protein expression, improved mitochondrial energetics, and blunted renal cytokine release and fibrosis. In vitro, mitoprotection restored mitochondrial membrane potential and reduced oxidative stress in injured proximal tubular epithelial cells. Our study suggests that swine MetS mildly affects renal autophagy, possibly secondary to mitochondrial damage, and may contribute to kidney structural damage in MetS.

Renal Ischemia Induces Epigenetic Changes in Apoptotic, Proteolytic, and Mitochondrial Genes in Swine Scattered Tubular-like Cells

BACKGROUND

Scattered tubular-like cells (STCs) are dedifferentiated renal tubular cells endowed with progenitor-like characteristics to repair injured parenchymal cells. STCs may be damaged and rendered ineffective by renal artery stenosis (RAS), but the underlying processes remain unclear. We hypothesized that RAS alters the epigenetic landscape on DNA and the ensuing gene transcriptional profile of swine STCs.

METHODS

CD24+/CD133+ STCs were isolated from pig kidneys after 10 weeks of RAS or sham (n = 3 each) and their whole 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) profiles were examined by 5mC and 5hmC immunoprecipitation sequencing (MeDIP-/hMeDIP-seq, respectively). A subsequent integrated (MeDIP/hMeDIP-seq/mRNA-seq) analysis was performed by comparing all online available gene sets using Gene Set Enrichment Analysis. Apoptosis, proteolysis, and mitochondrial structure and function were subsequently evaluated in vitro.

RESULTS

Differential expression (DE) analysis revealed 239 genes with higher and 236 with lower 5mC levels and 275 genes with higher and 315 with lower 5hmC levels in RAS-STCs compared to Normal-STCs (fold change ≥1.4 or ≤0.7, p ≤ 0.05). Integrated MeDIP-/hMeDIP-seq/mRNA-seq analysis identified several overlapping (DE-5mC/mRNA and DE-5hmC/mRNA levels) genes primarily implicated in apoptosis, proteolysis, and mitochondrial functions. Furthermore, RAS-STCs exhibited decreased apoptosis, mitochondrial matrix density, and ATP production, and increased intracellular amino acid concentration and ubiquitin expression.

CONCLUSIONS

Renal ischemia induces epigenetic changes in apoptosis-, proteolysis-, and mitochondria-related genes, which correlate with alterations in the transcriptomic profile and corresponding function of swine STCs. These observations may contribute to developing novel targeted interventions to preserve the reparative potency of STCs in renal disease.

Metabolic Syndrome Impairs 3D Mitochondrial Structure, Dynamics, and Function in Swine Mesenchymal Stem Cells

Transplantation of autologous mesenchymal stem cells (MSCs) is an effective therapy for several diseases. Mitochondria modulate several important aspects of MSC function, but might be damaged by comorbidities and cardiovascular risk factors. We hypothesized that metabolic syndrome (MetS) compromises 3D mitochondrial structure, dynamics, and function in swine adipose tissue-derived MSCs. Domestic pigs were fed a Lean or MetS diet (n = 6 each) for 16 weeks. MSCs were collected from subcutaneous abdominal fat and their mitochondria analyzed using state-of-the-art Serial Block Face Electron Microscopy and 3D reconstruction. Mitochondrial dynamics (fusion/fission) were assessed by mRNA sequencing and Western blotting, and bioenergetics by membrane potential (TMRE), cytochrome-c oxidase (COX)-IV activity, and Seahorse Analyzer. Expression of mitochondria-associated microRNAs (mitomiRs) was measured by quantitative polymerase chain reaction (qPCR). MetS pigs developed obesity, hypertension, insulin resistance, and hyperlipidemia. Mitochondrial density was similar between the groups, but 3D mitochondrial and matrix volumes were lower in MetS-MSCs versus Lean-MSCs. Mitochondrial fission was higher, but fusion lower in MetS-MSCs versus Lean-MSCs, as were membrane potential, COX-IV activity, and ATP production. Contrarily, expression of the mitomiRs miR15a, miR-137, and miR-181c, which target mitochondrial genes that support mitochondrial structure, energy pathways, and dynamics, was higher in MetS-MSCs compared to Lean-MSCs, suggesting a potential to modulate their expression. MetS damages MSC 3D mitochondrial structure, dynamics, and function, and may modulate genes encoding for mitochondrial proteins. These observations support development of mitoprotective strategies to preserve the regenerative potency of MSCs and their suitability for autologous transplantation in patients with MetS.

Apoptosis, Induced by Human α-Synuclein in Yeast, Can Occur Independent of Functional Mitochondria

Human α-synuclein expression in baker’s yeast reportedly induces mitochondria-dependent apoptosis. Surprisingly, we find that, under de-repressing conditions of the inducible MET25/GAL1 promoters, yeast cells expressing chromosomally-integrated copies of the human α-synuclein gene are not killed, but spontaneously form respiration-deficient rho-minus (ρ⁻) petites. Although yeast cells can undergo cell death (apoptosis) from loss of mitochondrial function, they can also survive without functional mitochondria. Such cells are referred to as ρ⁰ or ρ⁻ petites. This study reports that minimal expression of human α-synuclein in yeast, from MET25/GAL1 promoter, gives rise to ρ⁻ petites. Interestingly, the full expression of α-synuclein, from the same promoters, in α-synuclein-triggered ρ⁻ petites and also in ρ⁰ petites (produced by treating ρ⁺ cells with the mutagen ethidium bromide) initiates apoptosis. The percentages of petites increase with increasing α-synuclein gene copy-number. ρ⁻ petites expressing α-synuclein from fully-induced MET25/GAL1 promoters exhibit increased ROS levels, loss of mitochondrial membrane potential, and nuclear DNA fragmentation, with increasing copies of α-synuclein. Our results indicate that, for the first time in yeast, α-synuclein-triggered apoptosis can occur independently of functional mitochondria. The observation that α-synuclein naturally forms petites and that they can undergo apoptosis may have important implications in understanding the pathogenesis of Parkinson’s disease.

Bioorthogonal Turn-On BODIPY-Peptide Photosensitizers for Tailored Photodynamic Therapy

Photodynamic therapy (PDT) leads to cancer remission via the production of cytotoxic species under photosensitizer (PS) irradiation. However, concomitant damage and dark toxicity can both hinder its use. With this in mind, we have implemented a versatile peptide-based platform of bioorthogonally activatable BODIPY-tetrazine PSs. Confocal microscopy and phototoxicity studies demonstrated that the incorporation of the PS, as a bifunctional module, into a peptide enabled spatial and conditional control of singlet oxygen (1 O2 ) generation. Comparing subcellular distribution, PS confined in the cytoplasmic membrane achieved the highest toxicities (IC50 =0.096±0.003 μm) after activation and without apparent dark toxicity. Our tunable approach will inspire novel probes towards smart PDT.

Experimental Renovascular Disease Induces Endothelial Cell Mitochondrial Damage and Impairs Endothelium-Dependent Relaxation of Renal Artery Segments

BACKGROUND

Mitochondria modulate endothelial cell (EC) function, but may be damaged during renal disease. We hypothesized that the ischemic and metabolic constituents of swine renovascular disease (RVD) induce mitochondrial damage and impair the function of renal artery ECs.

METHODS

Pigs were studied after 16 weeks of metabolic syndrome (MetS), renal artery stenosis (RAS), or MetS + RAS, and Lean pigs served as control (n = 6 each). Mitochondrial morphology, homeostasis, and function were measured in isolated primary stenotic-kidney artery ECs. EC functions were assessed in vitro, whereas vasoreactivity of renal artery segments was characterized in organ baths.

RESULTS

Lean + RAS and MetS + RAS ECs showed increased mitochondrial area and decreased matrix density. Mitochondrial biogenesis was impaired in MetS and MetS + RAS compared with their respective controls. Mitochondrial membrane potential similarly decreased in MetS, Lean + RAS, and MetS + RAS groups, whereas production of reactive oxygen species increased in MetS vs. Lean, but further increased in both RAS groups. EC tube formation was impaired in MetS, RAS, and MetS + RAS vs. Lean, but EC proliferation and endothelial-dependent relaxation of renal artery segments were blunted in MetS vs. Lean, but further attenuated in Lean + RAS and MetS + RAS.

CONCLUSIONS

MetS and RAS damage mitochondria in pig renal artery ECs, which may impair EC function. Coexisting MetS and RAS did not aggravate EC mitochondrial damage in the short time of our in vivo studies, suggesting that mitochondrial injury is associated with impaired renal artery EC function.

Galectin-3 mediates survival and apoptosis pathways during Trypanosoma cruzi-host cell interplay

Neglected tropical diseases, such as Chagas disease caused by the protozoa Trypanosoma cruzi, affect millions of people worldwide but lack effective treatments that are accessible to the entire population, especially patients with the debilitating chronic phase. The recognition of host cells, invasion and its intracellular replicative success are essential stages for progression of the parasite life cycle and the development of Chagas disease. It is predicted that programmed cell death pathways (apoptosis) would be activated in infected cells, either via autocrine secretion or mediated by cytotoxic immune cells. This process should play a key role in resolving infections by hindering the evolutionary success of the parasite. In this research, we performed assays to investigate the role of the lectin galectin-3 (Gal3) in parasite-host signaling pathways. Using cells with endogenous levels of Gal3 compared to Gal3-deficient cells (induced by RNA interference), we demonstrated that T. cruzi mediated the survival pathways and the subverted apoptosis through Gal3 promoting a pro-survival state in infected cells. Infected Gal3-depleted cells showed increased activation of caspase 3 and pro-apoptotic targets, such as poly (ADP-ribose) polymerase (PARP), and lower accumulation of anti-apoptotic proteins, such as c-IAP1, survivin and XIAP. During the early stages of infection, Gal3 translocates from the cytoplasm to the nucleus and must act in survival pathways. In a murine model of experimental infection, Gal3 knockout macrophages showed lower infectivity and viability. In vivo infection revealed a lower parasitemia and longer survival and an increased spleen cellularity in Gal3 knockout mice with consequences on the percentage of T lymphocytes (CD4⁺ CD11b⁺) and macrophages. In addition, cytokines such as IL-2, IL-4, IL-6 and TNF-α are increased in Gal3 knockout mice when compared to wild type genotype. These data demonstrate a Gal3-mediated complex interplay in the host cell, keeping infected cells alive long enough for infection and intracellular proliferation of new parasites. However, a continuous knowledge of these signaling pathways should contribute to a better understanding the mechanisms of cell death subversion that are promoted by protozoans in the pathophysiology of neglected diseases such as Chagas disease.

Renovascular disease induces mitochondrial damage in swine scattered tubular cells

Scattered tubular-like cells (STCs) contribute to repair neighboring injured renal tubular cells. Mitochondria mediate STC biology and function but might be injured by the ambient milieu. We hypothesized that the microenviroment induced by the ischemic and metabolic components of renovascular disease impairs STC mitochondrial structure and function in swine, which can be attenuated with mitoprotection. CD24⁺/CD133⁺ STCs were quantified in pig kidneys after 16 wk of metabolic syndrome (MetS) or lean diet (Lean) with or without concurrent renal artery stenosis (RAS) (n = 6 each). Pig STCs were isolated and characterized, and mitochondrial structure, membrane potential, and oxidative stress were assessed in cells untreated or incubated with the mitoprotective drug elamipretide (1 nM for 6 h). STC-protective effects were assessed in vitro by their capacity to proliferate and improve viability of injured pig tubular epithelial cells. The percentage of STCs was higher in MetS, Lean + RAS, and MetS + RAS kidneys compared with Lean kidneys. STCs isolated from Lean + RAS and MetS + RAS pigs showed mitochondrial swelling and decreased matrix density, which were both restored by mitoprotection. In addition, mitochondrial membrane potential and ATP production were reduced and production of reactive oxygen species elevated in MetS, Lean + RAS, and MetS + RAS STCs. Importantly, mitoprotection improved mitochondrial structure and function as well as the capacity of MetS + RAS STCs to repair injured tubular cells in vitro. Renovascular disease in swine is associated with a higher prevalence of STCs but induces structural and functional alterations in STC mitochondria, which impair their reparative potency. These observations suggest a key role for mitochondria in the renal reparative capacity of STCs.

Inhibitors of Aβ42-induced endoplasmic reticular unfolded protein response (UPRER), in yeast, also rescue yeast cells from Aβ42-mediated apoptosis

Aggregated Aβ peptides which cause amyloid deposits, a characteristic of Alzheimer's disease (AD), activate a stress response in the endoplasmic reticulum (ER), known as the unfolded protein response, UPR^ER. Nascent UPR^ER induction helps in reducing ER stress by eliminating accumulated misfolded/aggregated secretory proteins. However, prolonged UPR^ER induction may trigger apoptosis. Here we show that, when expressed in yeast with an NH₂-terminal secretory signal sequence (ss), the 42-amino acid human Aβ42 (h_Aβ42), but not the mouse/ratAβ42 (m_Aβ42) which reportedly does not misfold/aggregate, induces UPR^ER as monitored via an eGFP reporter. We also show that expression of ss-h_Aβ42, not ss-m_Aβ42, blocks yeast cell growth, with cells expressing ss-h_Aβ42 manifesting distinctive features of apoptosis such as loss of mitochondrial membrane potential, increase in ROS levels and DNA fragmentation. Screening for suppressors of ss-h_Aβ42-activated UPR^ER-eGFP induction, in a computationally-designed 29-compound methoxy-stilbene library, revealed three compounds that reduce >95% of UPR^ER-eGFP induction at 5 μM concentration, with EC₅₀ values of 40-50 nM. Surprisingly, the compounds also rescue yeast cells from ss-h_Aβ42-mediated apoptosis, with EC₅₀-s of 50-60 nM. These results provide direct evidence, probably for the first time, that there is a direct correlation between deactivation of UPR^ER and attenuation of apoptosis.

Aegeline, a natural product from the plant Aegle marmelos, mimics the yeast SNARE protein Sec22p in suppressing α-synuclein and Bax toxicity in yeast

Herein, we have identified yeast Sec22p (ySec22p), a SNARE protein essential for endoplasmic reticulum to Golgi trafficking, as a suppressor of Bax-induced yeast apoptosis and corroborated published observations that ySec22p suppresses α-synuclein's toxicity in yeast. It has been suggested that compounds which enhance expression, in neurons, of human homologues of ySec22p (Sec22Bp/Sec22p/Sec22A) would prevent synucleinopathies, such as Parkinson's disease. With the aim of finding a small molecule that would mimic ySec22p, a library of natural products consisting of 394-compounds was screened using yeast cells that express either human α-synuclein or human Bax. The antioxidant aegeline, an alkaloid-amide occurring in the leaves of the plant Aegle marmelos Correa, was the only molecule that overcame apoptosis induced by both α-synuclein and Bax in yeast. Besides, aegeline also prevented growth block in cells expressing the more toxic A53T α-synuclein mutant. Restoration of cell growth occurred through inhibition of increased ROS levels, mitochondrial membrane potential loss and nuclear DNA fragmentation, characteristics of apoptosis manifested in α-synuclein or Bax-expressing cells. These results highlight the importance of yeast systems to identify rapidly molecules that may prevent the onset of apoptosis that occurs in Parkinson's disease.

Uncoupling proteins: Martin Klingenberg's contributions for 40 years

The uncoupling protein (UCP1) is a proton (H⁺) transporter in the mitochondrial inner membrane. By dissipating the electrochemical H⁺ gradient, UCP1 uncouples respiration from ATP synthesis, which drives an increase in substrate oxidation via the TCA cycle flux that generates more heat. The mitochondrial uncoupling-mediated non-shivering thermogenesis in brown adipose tissue is vital primarily to mammals, such as rodents and new-born humans, but more recently additional functions in adult humans have been described. UCP1 is regulated by β-adrenergic receptors through the sympathetic nervous system and at the molecular activity level by nucleotides and fatty acid to meet thermogenesis needs. The discovery of novel UCP homologs has greatly contributed to the understanding of human diseases, such as obesity and diabetes. In this article, we review the progress made towards the molecular mechanism and function of the UCPs, in particular focusing on the influential contributions from Martin Klingenberg's laboratory. Because all members of the UCP family are potentially promising drug targets, we also present and discuss possible approaches and methods for UCP-related drug discovery.

Nonantioxidant Tetramethoxystilbene Abrogates α-Synuclein-Induced Yeast Cell Death but Not That Triggered by the Bax or βA4 Peptide

The overexpression of α-synuclein (α-syn) and its aggregation is the hallmark of Parkinson's disease. The α-syn aggregation results in the formation of Lewy bodies that causes neuronal cell death. Therefore, the small molecules that can protect neuronal cells from α-syn toxicity or inhibit the aggregation of α-syn could emerge as anti-Parkinson agents. Herein, a library of methoxy-stilbenes was screened for their ability to restore the cell growth from α-syn toxicity, using a yeast strain that stably expresses two copies of a chromosomally integrated human α-syn gene. Tetramethoxy-stilbene 4s, a nonantioxidant, was the most capable of restoring cell growth. It also rescues the more toxic cells that bear three copies of wild-type or A53T-mutant α-syn, from cell growth block. Its EC₅₀ values for growth restoration of the 2-copy wild-type and the 3-copy mutant α-syn strains are 0.95 and 0.35 μM, respectively. Stilbene 4s mitigates mitochondrial membrane potential loss, negates ROS production, and prevents nuclear DNA-fragmentation, all hallmarks of apoptosis. However, 4s does not rescue cells from the death-inducing effects of Bax and βA4, which suggest that 4s specifically inhibits α-syn-mediated toxicity in the yeast. Our results signify that simultaneous use of multiple yeast-cell-based screens can facilitate revelation of compounds that may have the potential for further investigation as anti-Parkinson's agents.

Obesity-induced mitochondrial dysfunction in porcine adipose tissue-derived mesenchymal stem cells

Transplantation of autologous mesenchymal stem cells (MSCs) may be a viable option for treatment of several diseases. MSCs efficacy depends on adequate function of their mitochondria, which might be impaired in a noxious milieu. We hypothesized that obesity compromises MSCs mitochondrial structure and function, possibly via micro-RNA (miRNA)-based mechanisms. MSCs were collected from swine abdominal adipose tissue after 16 weeks of Lean or Obese diet (n = 7 each). Mitochondrial structure was assessed by electron microscopy and function by membrane potential and cytochrome-c oxidase (COX)-IV activity. Oxidative stress was assessed by Mito-SOX and dihydroethidium staining. Next-generation sequencing (RNA-seq) was performed to identify miRNAs expression in MSCs, and predicted mitochondrial target genes were then identified (MitoCarta). Compared to Lean-MSCs, mitochondria from Obese-MSCs were smaller and showed cristae remodeling and loss. Mitochondrial membrane potential and COX-IV activity decreased in Obese-MSCs, associated with increased mitochondrial oxidative stress. RNA-seq generated reads for 413 miRNAs, of which 5 miRNAs were upregulated in Obese-MSCs (fold change >2, p < 0.05) and found to target 43 specific mitochondrial genes. Obesity impairs MSC mitochondrial structure and function, possibly mediated partly through miRNA-induced mitochondrial gene regulation, leading to increased oxidative stress. Importantly, these alterations may limit the therapeutic use of autologous MSCs in subjects with obesity.

Impact of Membrane Phospholipid Alterations in Escherichia coli on Cellular Function and Bacterial Stress Adaptation

Bacteria have evolved multiple strategies to sense and rapidly adapt to challenging and ever-changing environmental conditions. The ability to alter membrane lipid composition, a key component of the cellular envelope, is crucial for bacterial survival and adaptation in response to environmental stress. However, the precise roles played by membrane phospholipids in bacterial physiology and stress adaptation are not fully elucidated. The goal of this study was to define the role of membrane phospholipids in adaptation to stress and maintenance of bacterial cell fitness. By using genetically modified strains in which the membrane phospholipid composition can be systematically manipulated, we show that alterations in major Escherichia coli phospholipids transform these cells globally. We found that alterations in phospholipids impair the cellular envelope structure and function, the ability to form biofilms, and bacterial fitness and cause phospholipid-dependent susceptibility to environmental stresses. This study provides an unprecedented view of the structural, signaling, and metabolic pathways in which bacterial phospholipids participate, allowing the design of new approaches in the investigation of lipid-dependent processes involved in bacterial physiology and adaptation.IMPORTANCE In order to cope with and adapt to a wide range of environmental conditions, bacteria have to sense and quickly respond to fluctuating conditions. In this study, we investigated the effects of systematic and controlled alterations in bacterial phospholipids on cell shape, physiology, and stress adaptation. We provide new evidence that alterations of specific phospholipids in Escherichia coli have detrimental effects on cellular shape, envelope integrity, and cell physiology that impair biofilm formation, cellular envelope remodeling, and adaptability to environmental stresses. These findings hold promise for future antibacterial therapies that target bacterial lipid biosynthesis.

Oncometabolite d-2-hydroxyglutarate impairs α-ketoglutarate dehydrogenase and contractile function in rodent heart

Hematologic malignancies are frequently associated with cardiac pathologies. Mutations of isocitrate dehydrogenase 1 and 2 (IDH1/2) occur in a subset of acute myeloid leukemia patients, causing metabolic and epigenetic derangements. We have now discovered that altered metabolism in leukemic cells has a profound effect on cardiac metabolism. Combining mathematical modeling and in vivo as well as ex vivo studies, we found that increased amounts of the oncometabolite d-2-hydroxyglutarate (D2-HG), produced by IDH2 mutant leukemic cells, cause contractile dysfunction in the heart. This contractile dysfunction is associated with impaired oxidative decarboxylation of α-ketoglutarate, a redirection of Krebs cycle intermediates, and increased ATP citrate lyase (ACL) activity. Increased availability of D2-HG also leads to altered histone methylation and acetylation in the heart. We propose that D2-HG promotes cardiac dysfunction by impairing α-ketoglutarate dehydrogenase and induces histone modifications in an ACL-dependent manner. Collectively, our results highlight the impact of cancer cell metabolism on function and metabolism of the heart.

Sinulolides A-H, new cyclopentenone and butenolide derivatives from soft coral Sinularia sp

Eight new compounds, sinulolides A-H (1-8), along with two known compounds, α-methoxy-2,3-dimethyl-butenolide (9) and sinularone D (10), were isolated from the soft coral Sinularia sp. The structures of these compounds were elucidated on the basis of extensive spectroscopic analysis. The absolute configurations were determined on the basis of electronic circular dichroism (ECD) data analysis. Compounds 5 and 10 exhibited moderate effects for the inhibition of NF-κB activation.

Bioactivities of six sterols isolated from marine invertebrates

CONTEXT

Epidioxy sterols and sterols with special side chains, such as hydroperoxyl sterols, usually obtained from marine natural products, are attractive for bioactivities.

OBJECTIVE

To isolate and screen bioactive and special sterols from China Sea invertebrates.

MATERIALS AND METHODS

Two hydroperoxyl sterols (1 and 2) from the sponge Xestospongia testudinaria Lamarck (Petrosiidae), three epidioxy sterols (3-5) from the sea urchin Glyptocidaris crenularis A. Agassiz (Glyptocidaridae), sponge Mycale sp. (Mycalidae) and gorgonian Dichotella gemmacea Milne Edwards and Haime (Ellisellidae) and an unusual sterol with 25-acetoxy-19-oate (6) also from D. gemmacea were obtained and identified. Using high-throughput screening, their bioactivities were tested toward Forkhead box O 3a (Foxo3a), 3-hydroxy-3-methylglutaryl CoA reductase gene fluorescent protein (HMGCR-GFP), nuclear factor kappa B (NF-κB) luciferase, peroxisome proliferator-activated receptor-γ co-activator 1α (PGC-1α), protein-tyrosine phosphatase 1B (PTP1B), mitochondrial membrane permeabilization (MMP) and adenosine monophosphate-activated protein kinase.

RESULTS

Their structures were determined by comparing their nuclear magnetic resonance data with those reported in the literature. Three epidioxy sterols (3-5) showed inhibitory activities toward Foxo3a, HMGCR-GFP and NF-κB-luciferase with the IC50 values 4.9-6.8 μg/mL. The hydroperoxyl sterol 29-hydroperoxystigmasta-5,24(28)-dien-3-ol (2) had diverse inhibitory activities against Foxo3a, HMGCR-GFP, NF-κB-luciferase, PGC-1α, PTP1B and MMP, with IC50 values of 3.8-19.1 μg/mL.

DISCUSSION AND CONCLUSION

The bioactivities of 3-5 showed that 5α,8α-epidioxy is the active group. Otherwise, the most plausible biosynthesis pathway for 1 and 2 in sponge involves the abstraction of an allylic proton by an activated oxygen, such as O2, along with migration of carbon-carbon double bond. Therefore, the bioactive and unstable steroid should be biosynthesized in sponge under a special ecological environment to act as a defensive strategy against invaders.

A two-hybrid approach to identify inhibitors of the RAS-RAF interaction

MCP compounds were developed with the idea to inhibit RAS/RAF interaction. They were identified by carrying out high-throughput screens of chemical compounds for their ability to inhibit RAS/RAF interaction in the yeast two-hybrid assay. A number of compounds including MCP1, MCP53, and MCP110 were identified as active compounds. Their inhibition of the RAS signaling was demonstrated by examining RAF and MEK activities, phosphorylation of ERK as well as characterizing their effects on events downstream of RAF. Direct evidence for the inhibition of RAS/RAF interaction was obtained by carrying out co-IP experiments. MCP compounds inhibit proliferation of a wide range of human cancer cell lines. Combination studies with other drugs showed that MCP compounds synergize with MAPK pathway inhibitors as well as with microtubule-targeting chemotherapeutics. In particular, a strong synergy with paclitaxel was observed. Efficacy to inhibit tumor formation was demonstrated using mouse xenograft models. Combination of MCP110 and paclitaxel was particularly effective in inhibiting tumor growth in a mouse xenograft model of colorectal carcinoma.

A high-throughput assay for modulators of NNT activity in permeabilized yeast cells

Nicotinamide nucleotide transhydrogenase (NNT) mutant mice show glucose intolerance with impaired insulin secretion during glucose tolerance tests. Uncoupling of the β cell mitochondrial metabolism due to such mutations makes NNT a novel target for therapeutics in the treatment of pathologies such as type 2 diabetes. The authors propose that increasing NNT activity would help reduce deleterious buildup of reactive oxygen species in the inner mitochondrial matrix. They have expressed human Nnt cDNA for the first time in Saccharomyces cerevisiae, and transhydrogenase activity in mitochondria isolated from these cells is six times greater than is seen in wild-type mitochondria. The same mitochondria have partially uncoupled respiration, and the cells have slower growth rates compared to cells that do not express NNT. The authors have used NNT's role as a redox-driven proton pump to develop a robust fluorimetric assay in permeabilized yeast. Screening in parallel a library of known pharmacologically active compounds (National Institute of Neurological Disorders and Stroke collection) against NNT ± cells, they demonstrate a robust and reproducible assay suitable for expansion into larger and more diverse compound sets. The identification of NNT activators may help in the elucidation of the role of NNT in mammalian cells and assessing its potential as a therapeutic target for insulin secretion disorders.

Yeast screens for inhibitors of Ras-Raf interaction and characterization of MCP inhibitors of Ras-Raf interaction

Because of the central role of Ras in cancer cell signaling, there has been considerable interest in developing small molecule inhibitors of the Ras signaling pathways as potential chemotherapeutic agents. This chapter describes the use of a two-hybrid approach to identify the MCP compounds, small molecules that disrupt the interaction between Ras and its effector Raf. We first outline the reagent development and selection/counter selection methods required to successfully apply a two-hybrid approach to isolation of MCP compounds. Separately, we describe the collateral benefits of this screening approach in yielding novel antifungal compounds. We then discuss secondary physiological validation approaches to confirm the MCP compounds specifically target Ras-Raf signaling. Finally, we develop a decision tree for subsequent preclinical characterization and optimization of this class of pathway-targeted reagent.

Uncoupling protein 1 affects the yeast mitoproteome and oxygen free radical production

Uncoupling protein 1 (UCP1) is a mitochondrial inner membrane protein that dissipates the proton electrochemical gradient built up by the respiratory chain. Its activity is stimulated by free fatty acids and inhibited by purine nucleotides. Here we investigated how active and regulated recombinant UCP1 expressed in yeast at approximately 1 and approximately 10 microg/mg of total mitochondrial proteins induced changes in the mitochondrial proteome and in oxygen free radical production. Using two-dimensional differential in-gel electrophoresis (2D-DIGE), we found that most of the proteins involved in the response to ectopically expressed UCP1 are related to energy metabolism. We also quantified the cellular H(2)O(2) release in the absence or in the presence of UCP1. Our results suggest that UCP1 has a dual influence on free radical generation. On one side, FFA-activated UCP1 was able to decrease the superoxide anion production, demonstrating that a decrease in the generation of reactive oxygen species is an obligatory outcome of UCP1 activity even in a heterologous context. On the other side, an increase in UCP1 content was concomitant with an increase in the basal release of superoxide anion by mitochondria as a side consequence of the overall increase in oxidative metabolism.

Frataxin and mitochondrial carrier proteins, Mrs3p and Mrs4p, cooperate in providing iron for heme synthesis

Frataxin is a conserved mitochondrial protein implicated in cellular iron metabolism. Deletion of the yeast frataxin homolog (YFH1) was combined with deletions of MRS3 and MRS4, mitochondrial carrier proteins implicated in iron homeostasis. As previously reported, the Deltayfh1 mutant accumulated iron in mitochondria, whereas the triple mutant (DeltaDeltaDelta) did not. When wild-type, Deltamrs3/4, Deltayfh1, and DeltaDeltaDelta strains were incubated anaerobically, all strains were devoid of heme and protected from iron and oxygen toxicity. The cultures were then shifted to air for a short time (4-5 h) or a longer time (15 h), and the evolving mutant phenotypes were analyzed (heme-dependent growth, total heme, cytochromes, heme proteins, and iron levels). A picture emerges from these data of defective heme formation in the mutants, with a markedly more severe defect in the DeltaDeltaDelta than in the individual Deltamrs3/4 or Deltayfh1 mutants (a "synthetic" defect in the genetic sense). The defect(s) in heme formation could be traced to lack of iron. Using a real time assay of heme biosynthesis, porphyrin precursor and iron were presented to permeabilized cells, and the appearance and disappearance of fluorescent porphyrins were followed. The Mrs3/4p carriers were required for rapid iron transport into mitochondria for heme synthesis, whereas there was also evidence for an alternative slower system. A different role for Yfh1p was observed under conditions of low mitochondrial iron and aerobic growth (revealed in the DeltaDeltaDelta), acting to protect bioavailable iron within mitochondria and to facilitate its use for heme synthesis.

Development of a high throughput screening assay for mitochondrial membrane potential in living cells

The mitochondrion plays a pivotal role in energy metabolism in eukaryotic cells. The electrochemical potential across the mitochondrial inner membrane is regulated to cope with cellular energy needs and thus reflects the bioenergetic state of the cell. Traditional assays for mitochondrial membrane potential are not amenable to high-throughput drug screening. In this paper, I describe a high-throughput assay that measures the mitochondrial membrane potential of living cells in 96- or 384-well plates. Cells were first treated with test compounds and then with a fluorescent potentiometric probe, the cationic-lipophilic dye tetramethylrhodamine methyl ester (TMRM). The cells were then washed to remove free compounds and probe. The amount of TMRM retained in the mitochondria, which is proportional to the mitochondrial membrane potential, was measured on an LJL Analyst fluorescence reader. Under optimal conditions, the assay measured only the mitochondrial membrane potential. The chemical uncouplers carbonylcyanide m-chlorophenyl hydrazone and dinitrophenol decreased fluorescence intensity, with IC(50) values (concentration at 50% inhibition) similar to those reported in the literature. A Z' factor of greater than 0.5 suggests that this cell-based assay can be adapted for high-throughput screening of chemical libraries. This assay may be used in screens for drugs to treat metabolic disorders such as obesity and diabetes, as well as cancer and neurodegenerative diseases.