Functions of mitochondria: from intracellular power stations to mediators of a senescence program

Catalpolaglycone disrupts mitochondrial thermogenesis by specifically binding to a conserved lysine residue of UCP2 on the proton leak tunnel

BACKGROUND

Catalpol (CAT), a naturally occurring iridoid glycoside sourced from the root of Rehmannia glutinosa, affects mitochondrial metabolic functions. However, the mechanism of action of CAT against pyrexia and its plausible targets remain to be fully elucidated.

PURPOSE

This study aimed to identify the specific targets of CAT for blocking mitochondrial thermogenesis and to unveil the unique biological mechanism of action of the orthogonal binding mode between the hemiacetal group and lysine residue on the target protein in vivo.

METHODS

Lipopolysaccharide (LPS)/ carbonyl cyanide 3-chlorophenylhydrazone (CCCP)-induced fever models were established to evaluate the potential antipyretic effects of CAT. An alkenyl-modified CAT probe was designed to identify and capture potential targets. Binding capacity was tested using in-gel imaging and a cellular thermal shift assay. The underlying antipyretic mechanisms were explored using biochemical and molecular biological methods. Catalpolaglycone (CA) was coupled with protein profile identification and molecular docking analysis to evaluate and identify its binding mode to UCP2.

RESULTS

After deglycation of CAT in vivo, the hemiacetal group in CA covalently binds to Lys239 of UCP2 in the mitochondria of the liver via an ɛ-amine nucleophilic addition. This irreversible binding affects proton leakage and improves mitochondrial membrane potential and ADP/ATP transformation efficiency, leading to an antipyretic effect.

CONCLUSION

Our findings highlight the potential role of CA in modulating UCP2 activity or function within the mitochondria and open new avenues for investigating the therapeutic effects of CA on mitochondrial homeostasis.

Tracing Slow Phenoptosis to the Prenatal Stage in Social Vertebrates

Vladimir Skulachev's coining of the term "phenoptosis" 25 years ago (Skulachev, V. P., Biochemistry (Moscow), 62, 1997) highlighted the theoretical possibility that aging is a programmed process to speed the exit of individuals posing some danger to their social group. While rapid "acute phenoptosis" might occur at any age (e.g., to prevent spread of deadly infections), "slow phenoptosis" is generally considered to occur later in life in the form of chronic age-related disorders. However, recent research indicates that risks for such chronic disorders can be greatly raised by early life adversity, especially during the prenatal stage. Much of this research uses indicators of biological aging, the speeding or slowing of natural physiological deterioration in response to environmental inputs, leading to divergence from chronological age. Studies using biological aging indicators commonly find it is accelerated not only in older individuals with chronic disorders, but also in very young individuals with health problems. This review will explain how accelerated biological aging equates to slow phenoptosis. Its occurrence even in the prenatal stage is theoretically supported by W. D. Hamilton's proposal that offsprings detecting they have dangerous mutations should then automatically speed their demise, in order to improve their inclusive fitness by giving their parents the chance to produce other fitter siblings.

Small-Molecule Fluorogenic Probe for the Detection of Mitochondrial Temperature In Vivo

Mitochondria, as energy factories, participate in many metabolic processes and play vital roles in cell life. Most human diseases are caused by mitochondrial dysfunction, and mitochondrial temperature is an important indicator of mitochondrial function. Despite the biological importance of mitochondria, there are few tools for detecting changes in mitochondrial temperature in living organisms. Here, we report on a thermosensitive rhodamine B (RhB)-derived fluorogenic probe (RhBIV) that enables fluorescent labeling of cell mitochondria at concentrations as low as 1 μM. We demonstrate that this probe exhibits a temperature-dependent response in cell mitochondria. Furthermore, in mice, it has a long half-life (t_1/2) and is primarily enriched in the liver. This unique thermosensitive probe offers a simple, nondestructive method for longitudinal monitoring of mitochondrial temperature both in vitro and in vivo to elucidate fundamental physiological and pathological processes related to mitochondrial function.

Luteinizing Hormone Regulation of Inter-Organelle Communication and Fate of the Corpus Luteum

The corpus luteum is an endocrine gland that synthesizes the steroid hormone progesterone. luteinizing hormone (LH) is a key luteotropic hormone that stimulates ovulation, luteal development, progesterone biosynthesis, and maintenance of the corpus luteum. Luteotropic and luteolytic factors precisely regulate luteal structure and function; yet, despite recent scientific progress within the past few years, the exact mechanisms remain largely unknown. In the present review, we summarize the recent progress towards understanding cellular changes induced by LH in steroidogenic luteal cells. Herein, we will focus on the effects of LH on inter-organelle communication and steroid biosynthesis, and how LH regulates key protein kinases (i.e., AMPK and MTOR) responsible for controlling steroidogenesis and autophagy in luteal cells.

Effect of mitoquinone on liver metabolism and steatosis in obese and diabetic rats

Previous work by ourselves and others showed that mitoquinone (mitoQ) reduced oxidative damage and prevented hepatic fat accumulation in mice made obese with high-fat (HF) feeding. Here we extended these studies to examine the effect of mitoQ on parameters affecting liver function in rats treated with HF to induce obesity and in rats treated with HF plus streptozotocin (STZ) to model a severe form of type 2 diabetes. In prior reported work, we found that mitoQ significantly improved glycemia based on glucose tolerance data in HF rats but not in the diabetic rats. Here we found only non-significant reductions in insulin and glucose measured in the fed state at sacrifice in the HF mice treated with mitoQ. Metabolomic data showed that mitoQ altered several hepatic metabolic pathways in HF-fed obese rats toward those observed in control normal chow-fed non-obese rats. However, mitoQ had little effect on pathways observed in the diabetic rats, wherein diabetes itself induced marked pathway aberrations. MitoQ did not alter respiration or membrane potential in isolated liver mitochondria. MitoQ reduced liver fat and liver hydroperoxide levels but did not improve liver function as marked by circulating levels of aspartate and alanine aminotransferase (ALT). In summary, our results for HF-fed rats are consistent with past findings in HF-fed mice indicating decreased liver lipid hydroperoxides (LPO) and improved glycemia. However, in contrast to the HF obese mice, mitoQ did not improve glycemia or reset perturbed metabolic pathways in the diabetic rats.

Effect of a mitochondrial-targeted coenzyme Q analog on pancreatic β-cell function and energetics in high fat fed obese mice

We recently reported that mitoquinone (mitoQ, 500 μmol/L) added to drinking water of C57BL/6J mice attenuated weight gain and reduced oxidative stress when administered to high-fat (HF) fed mice. Here, we examined the effects of mitoQ administered to HF fed mice on pancreatic islet morphology, dynamics of insulin secretion, and islet mitochondrial metabolism. C57BL/6J mice were fed HF for 130 days while we administered vehicle (cyclodextrin [CD]) or mitoQ added to the drinking water at up to 500 μmol/L. MitoQ-treated mice vs vehicle gained significantly less weight, expended significantly more energy as determined by indirect calorimetry, and trended to consume less (nonsignificant) food. As we and others reported before, mitoQ-treated mice drank less water but showed no difference in percent body fluid by nuclear magnetic resonance. Circulating insulin and glucose-stimulated insulin secretion by isolated islets were decreased in mitoQ-treated mice while insulin sensitivity (plasma insulin x glucose) was greater. Islet respiration as basal oxygen consumption (OCR), OCR directed at ATP synthesis, and maximal uncoupled OCR were also reduced in mitoQ-treated mice. Quantitative morphologic studies revealed that islet size was reduced in the mitoQ-treated mice while visual inspection of histochemically stained sections suggested that mitoQ reduced islet lipid peroxides. MitoQ markedly improved liver function as determined by plasma alanine aminotransferase. In summary, mitoQ treatment reduced the demand for insulin and reduced islet size, likely consequent to the action of mitoQ to mitigate weight gain and improve liver function.

Apoptosis induction in K562 human myelogenous leukaemia cells is connected to the modulation of Wnt/β-catenin signalling by BHX, a novel pyrazoline derivative

OBJECTIVES

The goal of this study was to explore the effects of BHX on human chronic myeloid leukaemia (CML) cells and to elucidate the underlying molecular mechanism.

MATERIALS AND METHODS

CML cell line K562 cells were treated with BHX. The effects of BHX on cell proliferation, apoptosis and cell cycle were detected. Subsequently, the caspase, ATP activity, Ca²⁺ , ROS and mitochondrial membrane potential (MMP) levels treated with various concentrations of BHX were analysed. The variation of relevant proteins and genes was detected. Further, toxicity of BHX on peripheral blood cells, bone marrow-nucleated cells (BMNC) and organ index were investigated on mice.

RESULTS

Results showed that BHX suppressed K562 cell proliferation in a dose-dependent manner and induced apoptosis and G0/G1 phase arrest. BHX induced mitochondria-mediated apoptosis, which was associated with downregulation of MMP, activation of caspase-3 and caspase-9, generation of intracellular ROS and elevation of Ca²⁺ in K562 cells. In treated cells, ATP levels were decreased, expression of total β-catenin, phosphorylated β-catenin and β-catenin in the nucleus was decreased, and expression of cell cycle-related proteins was decreased. Further analysis revealed that BHX lowered the transcriptional level of β-catenin. Lastly, BHX treatment significantly reduced the number of white blood cells, but had no effect on BMNC and organ index.

CONCLUSIONS

These findings provide further insight into the potential use of BHX as an anti-cancer agent against human leukaemia.

A Systematic Review of the Immune-Regulating and Anticancer Activities of Pseudolaric Acid B

Cortex pseudolaricis, the root bark of Pseudolarix kaempferi Gord, has been used to treat tinea and other skin diseases for the antimicrobial activities in Traditional Chinese Medicine (TCM). Pseudolaric acid B (PAB) has been identified as the major component responsible for the action of C. pseudolaricis. Recently, PAB has been demonstrated to be used as novel treatments for cancer, immune disorders, inflammatory diseases, and immunosuppression. However, the mechanisms through which PAB exerts its properties are not understood well, and little attention in the literature has been given to review its pharmacological activities before. In this review, we performed a systematic summary of the literature with respect to the anticancer, immunosuppressive and anti-inflammatory properties of PAB and its derivatives. Currently available data suggest that PAB is a promising immunosuppressive and anti-inflammatory agent candidate and should be explored further in cancer treatment and prevention.

Renal Tubular Mitochondrial Abnormalities in Complex II/III Respiratory Chain Deficiency

Defects in the respiratory chain may present with a wide spectrum of clinical signs and symptoms. In this "Images in Pathology" discussion we correlate the clinical, histologic, and ultrastructural findings in a 12-year-old male with a complex II/III respiratory chain deficiency and kidney dysfunction.

Age-Related Changes in Ultrastructure of Mitochondria. Effect of SkQ1

For many years, investigators have attempted to identify unique ultrastructural conditions of mitochondria related to aging. However, this did not result in definitive results. At present, this issue has again become of topical interest due to development of the mitochondrial theory of aging and of engineering of a novel antioxidant class known as mitochondria-targeted antioxidants. The review briefly discusses experimental results that, from our perspective, allow the most objective understanding regarding age-related changes in mitochondrial ultrastructure.

SkQ1 Ophthalmic Solution for Dry Eye Treatment: Results of a Phase 2 Safety and Efficacy Clinical Study in the Environment and During Challenge in the Controlled Adverse Environment Model

Introduction

This Phase 2 clinical trial assessed the efficacy and safety of the novel antioxidative, renewable compound SkQ1 for topical treatment of dry eye signs and symptoms.

Methods

In a single-center, randomized, double-masked, placebo-controlled, 29-day study, 91 subjects with mild to moderate dry eye instilled the study drug twice daily and recorded dry eye symptoms daily. Subjects were randomized 1:1:1 into one of three ophthalmic solution treatment groups: SkQ1 1.55 µg/mL, SkQ1 0.155 µg/mL, or 0.0 µg/mL (placebo). Subjects were exposed to a controlled adverse environment chamber at 3 of the 4 study visits (Day −7, Day 1, and Day 29). Investigator assessments occurred at all study visits.

Results

SkQ1 was safe and efficacious in treating dry eye signs and symptoms. Statistically significant improvements with SkQ1 compared to placebo occurred for the dry eye signs of corneal fluorescein staining and lissamine green staining in the central region and lid margin redness, and for the dry eye symptoms of ocular discomfort, dryness, and grittiness. In addition, SkQ1 demonstrated greater efficacy compared to placebo, although the differences were not statistically significant, for corneal fluorescein staining in other regions and/or time points (total staining score, central region, corneal sum score, and temporal region), lissamine green staining for the central and nasal regions, and blink rate scores.

Conclusions

This Phase 2 study indicated that SkQ1 is safe and efficacious for the treatment of dry eye signs and symptoms and supported previous study results.

Trial registration

Clinicaltrials.gov identifier: NCT02121301.

Funding

Miotech S.A.

Electronic supplementary material

The online version of this article (doi:10.1007/s12325-015-0274-5) contains supplementary material, which is available to authorized users.

Results of a Multicenter, Randomized, Double-Masked, Placebo-Controlled Clinical Study of the Efficacy and Safety of Visomitin Eye Drops in Patients with Dry Eye Syndrome

INTRODUCTION

This article presents the results of an international, multicenter, randomized, double-masked, placebo-controlled clinical study of Visomitin (Mitotech LLC, Moscow, Russian Federation) eye drops in patients with dry eye syndrome (DES). Visomitin is the first registered (in Russia) drug with a mitochondria-targeted antioxidant (SkQ1) as the active ingredient.

METHODS

In this multicenter (10 sites) study of 240 subjects with DES, study drug (Visomitin or placebo) was self-administered three times daily (TID) for 6 weeks, followed by a 6-week follow-up period. Seven in-office study visits occurred every 2 weeks during both the treatment and follow-up periods. Efficacy measures included Schirmer's test, tear break-up time, fluorescein staining, meniscus height, and visual acuity. Safety measures included adverse events, slit lamp biomicroscopy, tonometry, blood pressure, and heart rate. Tolerability was also evaluated.

RESULTS

This clinical study showed the effectiveness of Visomitin eye drops in the treatment of signs and symptoms of DES compared with placebo. The study showed that a 6-week course of TID topical instillation of Visomitin significantly improved the functional state of the cornea; Visomitin increased tear film stability and reduced corneal damage. Significant reduction of dry eye symptoms (such as dryness, burning, grittiness, and blurred vision) was also observed.

CONCLUSION

Based on the results of this study, Visomitin is effective and safe for use in eye patients with DES for protection from corneal damage.

FUNDING

Mitotech LLC.

A mitochondrial-targeted coenzyme q analog prevents weight gain and ameliorates hepatic dysfunction in high-fat-fed mice

We hypothesized that the mitochondrial-targeted antioxidant, mitoquinone (mitoQ), known to have mitochondrial uncoupling properties, might prevent the development of obesity and mitigate liver dysfunction by increasing energy expenditure, as opposed to reducing energy intake. We administered mitoQ or vehicle (ethanol) to obesity-prone C57BL/6 mice fed high-fat (HF) or normal-fat (NF) diets. MitoQ (500 µM) or vehicle (ethanol) was added to the drinking water for 28 weeks. MitoQ significantly reduced total body mass and fat mass in the HF-fed mice but had no effect on these parameters in NF mice. Food intake was reduced by mitoQ in the HF-fed but not in the NF-fed mice. Average daily water intake was reduced by mitoQ in both the NF- and HF-fed mice. Hypothalamic expression of neuropeptide Y, agouti-related peptide, and the long form of the leptin receptor were reduced in the HF but not in the NF mice. Hepatic total fat and triglyceride content did not differ between the mitoQ-treated and control HF-fed mice. However, mitoQ markedly reduced hepatic lipid hydroperoxides and reduced circulating alanine aminotransferase, a marker of liver function. MitoQ did not alter whole-body oxygen consumption or liver mitochondrial oxygen utilization, membrane potential, ATP production, or production of reactive oxygen species. In summary, mitoQ added to drinking water mitigated the development of obesity. Contrary to our hypothesis, the mechanism involved decreased energy intake likely mediated at the hypothalamic level. MitoQ also ameliorated HF-induced liver dysfunction by virtue of its antioxidant properties without altering liver fat or mitochondrial bioenergetics.

Mitochondrial uncoupling reduces exercise capacity despite several skeletal muscle metabolic adaptations

The effects of mitochondrial uncoupling on skeletal muscle mitochondrial adaptation and maximal exercise capacity are unknown. In this study, rats were divided into a control group (CTL, n = 8) and a group treated with 2,4-dinitrophenol, a mitochondrial uncoupler, for 28 days (DNP, 30 mg·kg−1·day−1in drinking water, n = 8). The DNP group had a significantly lower body mass ( P < 0.05) and a higher resting oxygen uptake (V̇o2, P < 0.005). The incremental treadmill test showed that maximal running speed and running economy ( P < 0.01) were impaired but that maximal V̇o2(V̇o2max) was higher in the DNP-treated rats ( P < 0.05). In skinned gastrocnemius fibers, basal respiration (V0) was higher ( P < 0.01) in the DNP-treated animals, whereas the acceptor control ratio (ACR, Vmax/V0) was significantly lower ( P < 0.05), indicating a reduction in OXPHOS efficiency. In skeletal muscle, DNP activated the mitochondrial biogenesis pathway, as indicated by changes in the mRNA expression of PGC1-α and -β, NRF-1 and −2, and TFAM, and increased the mRNA expression of cytochrome oxidase 1 ( P < 0.01). The expression of two mitochondrial proteins (prohibitin and Ndufs 3) was higher after DNP treatment. Mitochondrial fission 1 protein (Fis-1) was increased in the DNP group ( P < 0.01), but mitofusin-1 and -2 were unchanged. Histochemical staining for NADH dehydrogenase and succinate dehydrogenase activity in the gastrocnemius muscle revealed an increase in the proportion of oxidative fibers after DNP treatment. Our study shows that mitochondrial uncoupling induces several skeletal muscle adaptations, highlighting the role of mitochondrial coupling as a critical factor for maximal exercise capacities. These results emphasize the importance of investigating the qualitative aspects of mitochondrial function in addition to the amount of mitochondria.

Pseudolaric acid B-induced autophagy contributes to senescence via enhancement of ROS generation and mitochondrial dysfunction in murine fibrosarcoma L929 cells

Pseudolaric acid B (PAB) is the primary biologically active compound isolated from the root bark of P. kaempferi Gordon. Our previous study demonstrated that PAB induced mitotic catastrophe in L929 cells and indicated that only a small percentage (12%) of the cells undergoing mitotic catastrophe displayed an apoptotic phenotype after PAB treatment for 72 h. In this study, we found that a minority of the cells undergoing mitotic catastrophe ended in apoptosis, and a majority of them entered a period of senescence. Further data confirmed that PAB induced autophagy, reactive oxygen species (ROS) generation, and mitochondrial dysfunction in L929 cells. Subsequently, we found that autophagy inhibitors significantly delayed the senescence process, indicating that autophagy facilitated senescence. Moreover, ROS scavenger significantly decreased the autophagic level and improved mitochondrial function. Additionally, autophagy inhibitors effectively reduced ROS levels and ameliorated mitochondrial function. In conclusion, autophagy promoted senescence via enhancement of ROS generation and mitochondrial dysfunction in PAB-treated L929 cells.

Mitochondrial gene expression in the human annulus: in vivo data from annulus cells and selectively harvested senescent annulus cells

BACKGROUND CONTEXT

Mitochondrial dysfunction is recognized during cell senescence and apoptosis, two important components of human disc aging/degeneration. We hypothesize that mitochondrial dysfunction is present in the degenerating and senescent annulus cells. The objective of the present study was to analyze gene expression profiles related to mitochondrial function in vivo.

PURPOSE

This study had two objectives in the analysis of gene expression patterns related to mitochondria in the human annulus: First, to assess human annulus cells in a genome-wide microarray analysis approach to evaluate mitochondrial gene expression in annulus tissue from degenerated compared with healthier discs. Second, to use laser capture microdissection (LCM) to selectively isolate senescent versus nonsenescent annulus cells to evaluate their mitochondrial gene expression patterns.

STUDY DESIGN

Following approval by our Human Subjects Institutional Review Board, annulus cells from 20 human lumbar discs were analyzed for gene groups related to mitochondrial function; a subset was also analyzed, which focused on senescent versus nonsenescent annulus cells in a study of annulus cells from 10 lumbar discs.

PATIENT SAMPLE

Human annulus tissue was used in molecular studies following institutional review board approval.

OUTCOME MEASURES

Gene expression levels identified with microarray analyses were statistically evaluated using GeneSifter Web-based software (VizX Labs, Seattle, WA, USA).

METHODS

Human annulus specimens were assessed for gene expression related to mitochondrial function. Approaches used whole annulus tissue and senescent or nonsenescent annulus cells selectively harvested using LCM. Microarray data were analyzed using gene ontology searches and GeneSifter Web-based software.

RESULTS

Analysis of annulus cells compared mitochondrial gene expression patterns in annulus cells from more degenerated discs with patterns in annulus cells derived from healthier discs. Important findings included significant upregulation of p53 and several proapoptotic genes (including apoptosis-inducing factor, mitochondrion-associated 1, BCL2-like 11 [an apoptosis facilitator]; caspase 7 apoptosis-related cysteine peptidase; proteasome 26S subunit nonadenosine triphosphatase 10, programmed cell death 6, and reticulon 3). Methionine sulfoxide reductase (Msr), a repair enzyme that reduces methionine sulfoxide residues in proteins damaged by oxidation, was also significantly upregulated (2.02-fold increase). The gene "membrane-associated ring finger (C3HC4) 5" was significantly upregulated and relevant because it is believed to play a role in preventing cell senescence acting to regulate mitochondrial quality control. Nitric oxide synthase 3 (endothelial nitric oxide synthase [eNOS]) showed a 5.9-fold downregulation in more degenerated versus healthier annulus cells. In LCM-harvested senescent cells, Msr was significantly downregulated in senescent versus nonsenescent cells, a finding previously recognized in other types of senescent cells.

CONCLUSIONS

Novel data showed that significant gene expression patterns are present in the human annulus related to mitochondrial dysfunction; changes were identified in important genes involving apoptosis, eNOS and Msr expressions, and solute carrier genes. Because current research efforts are focusing on bioactive compounds for mitochondria, we suggest that future biologic cell-based therapies for annulus degeneration should also consider mitochondrial-focused therapies.

Metabolic manipulators: a well founded strategy to combat mitochondrial dysfunction

Whilst the pathophysiology and genetics of mitochondrial disease are slowly being unraveled, currently no effective remedy for mitochondrial disorders is available. One particular strategy in mitochondrial medicine presently under study is metabolic manipulation. This approach is aimed at counteracting the deranged cell biological homeostasis caused by mitochondrial dysfunction, using dietary modifications or small molecule therapy. Cell biological alterations caused by mitochondrial dysfunction include increased reactive oxygen species production, enhanced lipid peroxidation and altered cellular calcium homeostasis. This review covers the five principles of metabolic manipulation: (1) prevention of oxidative damage by reactive oxygen species, (2) amelioration of lipid peroxidation, (3) correction of altered membrane potential, (4) restoration of calcium homeostasis, and (5) transcription regulation interference. We hypothesize that a combination of compounds targeting different metabolic pathways will abolish cellular disturbance arising as a consequences of mitochondrial dysfunction, and thereby improve or stabilize clinical features. However, only a handful of compounds have reached efficacy testing in mammals, and it remains unknown to what extent metabolic manipulation will affect the whole organism. Until a potent remedy is found, patients will remain dependent on supportive, not curative, interventions.