Peroxisomes are oxidative organelles

Salinomycin: Anti-tumor activity in a pre-clinical colorectal cancer model

Objectives

Salinomycin is a polyether antibiotic with selective activity against human cancer stem cells. The impact of salinomycin on patient-derived primary human colorectal cancer cells has not been investigated so far. Thus, here we aimed to investigate the activity of salinomycin against tumor initiating cells isolated from patients with colorectal cancer.

Methods

Primary tumor-initiating cells (TIC) isolated from human patients with colorectal liver metastases or from human primary colon carcinoma were exposed to salinomycin and compared to treatment with 5-FU and oxaliplatin. TICs were injected subcutaneously into NOD/SCID mice to induce a patient-derived mouse xenograft model of colorectal cancer. Animals were treated either with salinomycin, FOLFOX regimen, or salinomycin and FOLFOX. Human colorectal cancer cells were used to delineate an underlying molecular mechanism of salinomycin in this tumor entity.

Results

Applying TICs isolated from human patients with colorectal liver metastases or from human primary colon carcinoma, we demonstrated that salinomycin exerts increased antiproliferative activity compared to 5-fluorouracil and oxaliplatin treatment. Consistently, salinomycin alone or in combination with FOLFOX exerts superior antitumor activity compared to FOLFOX therapy in a patient-derived mouse xenograft model of colorectal cancer. Salinomycin induces apoptosis of human colorectal cancer cells, accompanied by accumulation of dysfunctional mitochondria and reactive oxygen species. These effects are associated with expressional down-regulation of superoxide dismutase-1 (SOD1) in response to salinomycin treatment.

Conclusion

Collectively, the results of this pre-clinical study indicate that salinomycin alone or in combination with 5-fluorouracil and oxaliplatin exerts increased antitumoral activity compared to common chemotherapy.

Peroxisomal dysfunction in neurodegenerative diseases

Peroxisomes and their (patho-)physiological importance in heath and disease have attracted increasing interest during last few decades. Together with mitochondria, peroxisomes comprise key metabolic platforms for oxidation of various fatty acids and redox regulation. In addition, peroxisomes contribute to bile acid, cholesterol, and plasmalogen biosynthesis. The importance of functional peroxisomes for cellular metabolism is demonstrated by the marked brain and systemic organ abnormalities occuring in peroxisome biogenesis disorders and peroxisomal enzyme deficiencies. Current evidences indicate that peroxisomal function is declined with aging, with peroxisomal dysfunction being linked to early onset of multiple age-related diseases including neurodegenerative diseases. Herein, we review recent progress toward understanding the physiological roles and pathological implications of peroxisomal dysfunctions, focusing on neurodegenerative disease.

Signals Getting Crossed in the Entanglement of Redox and Phosphorylation Pathways: Phosphorylation of Peroxiredoxin Proteins Sparks Cell Signaling

Reactive oxygen and nitrogen species have cell signaling properties and are involved in a multitude of processes beyond redox homeostasis. The peroxiredoxin (Prdx) proteins are highly sensitive intracellular peroxidases that can coordinate cell signaling via direct reactive species scavenging or by acting as a redox sensor that enables control of binding partner activity. Oxidation of the peroxidatic cysteine residue of Prdx proteins are the classical post-translational modification that has been recognized to modulate downstream signaling cascades, but increasing evidence supports that dynamic changes to phosphorylation of Prdx proteins is also an important determinant in redox signaling. Phosphorylation of Prdx proteins affects three-dimensional structure and function to coordinate cell proliferation, wound healing, cell fate and lipid signaling. The advent of large proteomic datasets has shown that there are many opportunities to understand further how phosphorylation of Prdx proteins fit into intracellular signaling cascades in normal or malignant cells and that more research is necessary. This review summarizes the Prdx family of proteins and details how post-translational modification by kinases and phosphatases controls intracellular signaling.

Redox Signaling from and to Peroxisomes: Progress, Challenges, and Prospects

SIGNIFICANCE

Peroxisomes are organelles that are best known for their role in cellular lipid and hydrogen peroxide (H₂O₂) metabolism. Emerging evidence suggests that these organelles serve as guardians and modulators of cellular redox balance, and that alterations in their redox metabolism may contribute to aging and the development of chronic diseases such as neurodegeneration, diabetes, and cancer. Recent Advances: H₂O₂ is an important signaling messenger that controls many cellular processes by modulating protein activity through cysteine oxidation. Somewhat surprisingly, the potential involvement of peroxisomes in H₂O₂-mediated signaling processes has been overlooked for a long time. However, recent advances in the development of live-cell approaches to monitor and modulate spatiotemporal fluxes in redox species at the subcellular level have opened up new avenues for research in redox biology and boosted interest in the concept of peroxisomes as redox signaling platforms.

CRITICAL ISSUES

This review first introduces the reader to what is known about the role of peroxisomes in cellular H₂O₂ production and clearance, with a focus on mammalian cells. Next, it briefly describes the benefits and drawbacks of current strategies used to investigate the complex interplay between peroxisome metabolism and cellular redox state. Furthermore, it integrates and critically evaluates literature dealing with the interrelationship between peroxisomal redox metabolism, cell signaling, and human disease.

FUTURE DIRECTIONS

As the precise molecular mechanisms underlying many of these associations are still poorly understood, a key focus for future research should be the identification of primary targets for peroxisome-derived H₂O₂.

Transport-exclusion pharmacology to localize lactate dehydrogenase activity within cells

BACKGROUND

Recent in vitro and in vivo work has shown that lactate provides an important source of carbon for metabolic reactions in cancer cell mitochondria. An interesting question is whether lactate is oxidized by lactate dehydrogenase (LDH) in the cytosol and/or in mitochondria. Since metabolic processes in the cytosol and mitochondria are affected by redox balance, the location of LDH may have important regulatory implications in cancer metabolism.

METHODS

Within most mammalian cells, metabolic processes are physically separated by membrane-bound compartments. Our general understanding of this spatial organization and its role in cellular function, however, suffers from the limited number of techniques to localize enzymatic activities within a cell. Here, we describe an approach to assess metabolic compartmentalization by monitoring the activity of pharmacological inhibitors that cannot be transported into specific cellular compartments.

RESULTS

Oxamate, which chemically resembles pyruvate, is transported into mitochondria and inhibits LDH activity in purified mitochondria. GSK-2837808A, in contrast, is a competitive inhibitor of NAD, which cannot cross the inner mitochondrial membrane. GSK-2837808A did not inhibit the LDH activity of intact mitochondria, but GSK-2837808A did inhibit LDH activity after the inner mitochondrial membrane was disrupted.

CONCLUSIONS

Our results are consistent with some mitochondrial LDH that is accessible to oxamate, but inaccessible to GSK-2837808A until mitochondria are homogenized. This strategy of using inhibitors with selective access to subcellular compartments, which we refer to as transport-exclusion pharmacology, is broadly applicable to localize other metabolic reactions within cells.

Bhlhe40 differentially regulates the function and number of peroxisomes and mitochondria in myogenic cells

PGC-1α is a key regulator of oxidative metabolism facilitating the expression of genes critical for the function and biogenesis of the two key oxidative organelles, mitochondria and peroxisomes, in skeletal muscle (SKM) and other organs. Our recent studies have found that the transcription factor Bhlhe40 negatively regulates PGC-1α gene expression and its coactivational activity, therefore, this factor should have profound influence on the biogenesis and metabolic activity of mitochondria and peroxisomes. Here we found that both the number and activity of peroxisomes were increased upon knockdown of Bhlhe40 expression but were repressed by its over-expression. Mitochondrial efficiency was significantly reduced by Bhlhe40 knockdown, resulting in the burst of ROS. Over-expression of a constitutively active PGC-1α-interactive domain (named as VBH135) of Bhlhe40 mimicked the effects of its knockdown on peroxisomes but simultaneously reduced ROS level. Furthermore, the efficiency, but not the number, of mitochondria was also increased by VBH135, suggesting differential regulation of peroxisomes and mitochondria by Bhlhe40. Unsaturated fatty acid oxidation, insulin response, and oxidative respiration were highly enhanced in Bhlhe40 knockdown or VBH135 over-expressed cells, suggesting the importance of Bhlhe40 in the regulation of unsaturated fatty acid and glucose oxidative metabolism. Expression profiling of genes important for either organelle also supports differential regulation of peroxisomes and mitochondria by Bhlhe40. These observations have established the important role of Bhlhe40 in SKM oxidative metabolism as the critical regulator of peroxisome and mitochondrion biogenesis and functions, and thus should provide a novel route for developing drugs targeting SKM metabolic diseases.

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Knockout of Bhlhe40 increased ROS but over-expression of Bhlhe40 reduced ROS.

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Peroxisome number was increased by Bhlhe40 knockout or VBH135 overexpression.

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Mitochondrial efficiency was reduced by Bhlhe40 knockout but increased by VBH135.

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Oxidative respiration was enhanced by Bhlhe40 knockdown or VBH135 overexpression.

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Bhlhe40 repressed PGC-1α coactivation of nuclear gene expression.

Pink Adipocytes

Adipocytes are lipid-rich parenchymal cells contained in a very plastic organ, whose composition can undergo striking physiologic changes. In standard conditions the organ contains white and brown adipocytes which play opposite roles: lipid storage to meet metabolic requirements and lipid burning for thermogenesis, respectively. During chronic cold exposure, white adipocytes transdifferentiate to brown, to increase thermogenesis, whereas in conditions of chronic positive energy balance brown adipocytes transdifferentiate to white, to increase energy stores. During pregnancy, lactation, and post-lactation, subcutaneous white adipocytes convert to milk-producing glands formed by lipid-rich elements that can be defined as pink adipocytes. Recent fate-mapping data support the conversion of pink to brown adipocytes and the reversible conversion of brown adipocytes to myoepithelial cells of alveoli.

Expanding the spectrum of PEX16 mutations and novel insights into disease mechanisms

Zellweger syndrome spectrum disorders are caused by mutations in any of at least 12 different PEX genes. This includes PEX16, an important regulator of peroxisome biogenesis. Using whole genome sequencing, we detected previously unreported, biallelic variants in PEX16 [NM_004813.2:c.658G>A, p.(Ala220Thr) and NM_004813.2:c.830G>A, p.(Arg277Gln)] in an individual with leukodystrophy, spastic paraplegia, cerebellar ataxia, and craniocervical dystonia with normal plasma very long chain fatty acids. Using olfactory-neurosphere derived cells, a population of neural stem cells, we showed patient cells had reduced peroxisome density and increased peroxisome size, replicating previously reported findings in PEX16 cell lines. Along with alterations in peroxisome morphology, patient cells also had impaired peroxisome function with reduced catalase activity. Furthermore, patient cells had reduced oxidative stress levels after exposure to hydrogen-peroxide (H2O2), which may be a result of compensation by H2O2 metabolising enzymes other than catalase to preserve peroxisome-related cell functions. Our findings of impaired catalase activity and altered oxidative stress response are novel. Our study expands the phenotype of PEX16 mutations by including dystonia and provides further insights into the pathological mechanisms underlying PEX16-associated disorders. Additional studies of the full spectrum of peroxisomal dysfunction could improve our understanding of the mechanism underlying PEX16-associated disorders.

Oxidative stress in chronic lung disease: From mitochondrial dysfunction to dysregulated redox signaling

The lung is a delicate organ with a large surface area that is continuously exposed to the external environment, and is therefore highly vulnerable to exogenous sources of oxidative stress. In addition, each of its approximately 40 cell types can also generate reactive oxygen species (ROS), as byproducts of cellular metabolism and in a more regulated manner by NOX enzymes with functions in host defense, immune regulation, and cell proliferation or differentiation. To effectively regulate the biological actions of exogenous and endogenous ROS, various enzymatic and non-enzymatic antioxidant defense systems are present in all lung cell types to provide adequate protection against their injurious effects and to allow for appropriate ROS-mediated biological signaling. Acute and chronic lung diseases are commonly thought to be associated with increased oxidative stress, evidenced by altered cellular or extracellular redox status, increased irreversible oxidative modifications in proteins or DNA, mitochondrial dysfunction, and altered expression or activity of NOX enzymes and antioxidant enzyme systems. However, supplementation strategies with generic antioxidants have been minimally successful in prevention or treatment of lung disease, most likely due to their inability to distinguish between harmful and beneficial actions of ROS. Recent studies have attempted to identify specific redox-based mechanisms that may mediate chronic lung disease, such as allergic asthma or pulmonary fibrosis, which provide opportunities for selective redox-based therapeutic strategies that may be useful in treatment of these diseases.

An unexpected friend - ROS in apoptosis-induced compensatory proliferation: Implications for regeneration and cancer

Apoptosis-induced compensatory proliferation (AiP) is a form of compensatory proliferation that is triggered by apoptotic cell death to maintain tissue homeostasis. As such, AiP is essential for many tissue repair processes including regeneration. The apoptotic effectors, termed caspases, not only execute apoptosis, but are also directly involved in the generation of the signals required for AiP. Reactive oxygen species (ROS) play an important role for regenerative processes. Recently, it was shown in Drosophila that apoptotic caspases can mediate the generation of ROS for promoting AiP. This review summarizes and discusses these findings in the context of regenerative processes and cancer.

Patient-Derived Stem Cell Models in SPAST HSP: Disease Modelling and Drug Discovery

Hereditary spastic paraplegia is an inherited, progressive paralysis of the lower limbs first described by Adolph Strümpell in 1883 with a further detailed description of the disease by Maurice Lorrain in 1888. Today, more than 100 years after the first case of HSP was described, we still do not know how mutations in HSP genes lead to degeneration of the corticospinal motor neurons. This review describes how patient-derived stem cells contribute to understanding the disease mechanism at the cellular level and use this for discovery of potential new therapeutics, focusing on SPAST mutations, the most common cause of HSP.

Peroxisomes: role in cellular ageing and age related disorders

Peroxisomes are dynamic organelles essential for optimum functioning of a eukaryotic cell. Biogenesis of these organelles and the diverse functions performed by them have been extensively studied in the past decade. Their ability to perform functions depending on the cell type and growth conditions is unique and remarkable. Oxidation of fatty acids and reactive oxygen species metabolism are the two most important functions of these ubiquitous organelles. They are often referred to as both source and sink of reactive oxygen species in a cell. Recent research connects peroxisome dysfunction to fatal oxidative damage associated with ageing-related diseases/disorders. It is now widely accepted that mitochondria and peroxisomes are required to maintain oxidative balance in a cell. However, our understanding on the inter-dependence of these organelles to maintain cellular homeostasis of reactive oxygen species is still in its infancy. Herein, we summarize findings that highlight the role of peroxisomes in cellular reactive oxygen species metabolism, ageing and age-related disorders.

Oxidative stress triggers aggregation of GFP-tagged Hsp31p, the budding yeast environmental stress response chaperone, and glyoxalase III

The Saccharomyces cerevisiae Hsp31p protein belongs to the ubiquitous DJ-1/ThiJ/PfpI family. The most prominent member of this family is human DJ-1; defects of this protein are associated with Parkinson's disease pathogenesis. Numerous recent findings reported by our group and others have revealed the importance of Hsp31p for survival in the post-diauxic phase of cell growth and under diverse environmental stresses. Hsp31p was shown to possess glutathione-independent glyoxalase III activity and to function as a protein chaperone, suggesting that it has multiple cellular roles. Our previous work also revealed that HSP31 gene expression was controlled by multiple stress-related transcription factors, which mediated HSP31 promoter responses to oxidative, osmotic, and thermal stresses, toxic products of glycolysis, and the diauxic shift. Nevertheless, the exact role of Hsp31p within budding yeast cells remains elusive. Here, we aimed to obtain insights into the function of Hsp31p based on its intracellular localization. We have demonstrated that the Hsp31p-GFP fusion protein is localized to the cytosol under most environmental conditions and that it becomes particulate in response to oxidative stress. However, the particles do not colocalize with other granular subcellular structures present in budding yeast cells. The observed particulate localization does not seem to be important for Hsp31p functionality. Instead, it is likely the result of oxidative damage, as the particle abundance increases when Hsp31p is nonfunctional, when the cellular oxidative stress response is affected, or when cellular maintenance systems that optimize the state of the proteome are compromised.

A FRET flow cytometry method for monitoring cytosolic and glycosomal glucose in living kinetoplastid parasites

The bloodstream lifecycle stage of the kinetoplastid parasite Trypanosoma brucei relies solely on glucose metabolism for ATP production, which occurs in peroxisome-like organelles (glycosomes). Many studies have been conducted on glucose uptake and metabolism, but none thus far have been able to monitor changes in cellular and organellar glucose concentration in live parasites. We have developed a non-destructive technique for monitoring changes in cytosolic and glycosomal glucose levels in T. brucei using a fluorescent protein biosensor (FLII¹²Pglu-700μδ6) in combination with flow cytometry. T. brucei parasites harboring the biosensor allowed for observation of cytosolic glucose levels. Appending a type 1 peroxisomal targeting sequence caused biosensors to localize to glycosomes, which enabled observation of glycosomal glucose levels. Using this approach, we investigated cytosolic and glycosomal glucose levels in response to changes in external glucose or 2-deoxyglucose concentration. These data show that procyclic form and bloodstream form parasites maintain different glucose concentrations in their cytosol and glycosomes. In procyclic form parasites, the cytosol and glycosomes maintain indistinguishable glucose levels (3.4 ± 0.4mM and 3.4 ± 0.5mM glucose respectively) at a 6.25mM external glucose concentration. In contrast, bloodstream form parasites maintain glycosomal glucose levels that are ~1.8-fold higher than the surrounding cytosol, equating to 1.9 ± 0.6mM in cytosol and 3.5 ± 0.5mM in glycosomes. While the mechanisms of glucose transport operating in the glycosomes of bloodstream form T. brucei remain unresolved, the methods described here will provide a means to begin to dissect the cellular machinery required for subcellular distribution of this critical hexose.

African sleeping sickness is caused by Trypanosoma brucei. Tens of millions of people living in endemic areas are at risk for the disease. Within the mammalian bloodstream, T. brucei parasites sustain all their energy needs by metabolizing glucose present in the host’s blood within specialized organelles known as glycosomes. In vitro, bloodstream parasites rapidly die if glucose is removed from their environment. This reliance on glucose for survival has made glucose metabolism in T. brucei an important area of study with the aim to develop targeted therapeutics that disrupt glucose metabolism. However, there have previously been no reported methods to study glucose uptake and distribution dynamics in intact glycosomes in live T. brucei. Here we describe development of approaches for observing changes in glucose concentration in glycosomes in live T. brucei. Results obtained using these methods provide new insights into how T. brucei acquires and transports glucose to sustain cell survival.

Supramolecular Encapsulation and Bioactivity Modulation of a Halonium Ion by Cucurbit[ n]uril ( n = 7, 8)

This is the first time that cucurbit[7]uril and cucurbit[8]uril have been demonstrated to serve as synthetic receptors for a halonium guest species, diphenyleneiodonium, modulating its bioactivities and alleviating its cardiotoxicity, which further expands the onium family of guest molecules for the cucurbit[ n]uril family and provides new insights for halonium-cucurbit[ n]uril host-guest chemistry and its potential applications in pharmaceutical chemistry.

Redox crosstalk at endoplasmic reticulum (ER) membrane contact sites (MCS) uses toxic waste to deliver messages

Many cellular redox reactions housed within mitochondria, peroxisomes and the endoplasmic reticulum (ER) generate hydrogen peroxide (H₂O₂) and other reactive oxygen species (ROS). The contribution of each organelle to the total cellular ROS production is considerable, but varies between cell types and also over time. Redox-regulatory enzymes are thought to assemble at a “redox triangle” formed by mitochondria, peroxisomes and the ER, assembling “redoxosomes” that sense ROS accumulations and redox imbalances. The redoxosome enzymes use ROS, potentially toxic by-products made by some redoxosome members themselves, to transmit inter-compartmental signals via chemical modifications of downstream proteins and lipids. Interestingly, important components of the redoxosome are ER chaperones and oxidoreductases, identifying ER oxidative protein folding as a key ROS producer and controller of the tri-organellar membrane contact sites (MCS) formed at the redox triangle. At these MCS, ROS accumulations could directly facilitate inter-organellar signal transmission, using ROS transporters. In addition, ROS influence the flux of Ca²⁺ ions, since many Ca²⁺ handling proteins, including inositol 1,4,5 trisphosphate receptors (IP₃Rs), SERCA pumps or regulators of the mitochondrial Ca²⁺ uniporter (MCU) are redox-sensitive. Fine-tuning of these redox and ion signaling pathways might be difficult in older organisms, suggesting a dysfunctional redox triangle may accompany the aging process.

The Role of Free Radicals in Autophagy Regulation: Implications for Ageing

Reactive oxygen and nitrogen species (ROS and RNS, resp.) have been traditionally perceived solely as detrimental, leading to oxidative damage of biological macromolecules and organelles, cellular demise, and ageing. However, recent data suggest that ROS/RNS also plays an integral role in intracellular signalling and redox homeostasis (redoxtasis), which are necessary for the maintenance of cellular functions. There is a complex relationship between cellular ROS/RNS content and autophagy, which represents one of the major quality control systems in the cell. In this review, we focus on redox signalling and autophagy regulation with a special interest on ageing-associated changes. In the last section, we describe the role of autophagy and redox signalling in the context of Alzheimer's disease as an example of a prevalent age-related disorder.

Disruption of peroxisome function leads to metabolic stress, mTOR inhibition, and lethality in liver cancer cells

Peroxisome houses a large number of enzymes involved in lipid and phytochemical oxidation as well as synthesis of bile acid and other specialized lipids. Peroxisome resident enzymes are imported into the organelle via a conserved cargo transport system composed of many peroxins, protein factors essential for the biogenesis of peroxisome. Among the peroxins, PEX5 plays a transporter role, and PEX2, 10, and 12 are thought to form a complex that functions as an E3 ubiquitin ligase to help recycle PEX5 in an ubiquitin modification-dependent process. Previous studies have demonstrated the importance of peroxins in postnatal development especially the development of nerve systems. These studies also show that peroxins or the function of peroxisomes is dispensable for cellular viability. In contrast, however, we report here that PEX2 and other peroxins are essential for the viability of liver cancer cells, probably through altering metabolism and signaling pathways. Our results suggest that peroxins may be potential targets of therapeutics against liver cancer.

Redox Regulation of Homeostasis and Proteostasis in Peroxisomes

Peroxisomes are highly dynamic intracellular organelles involved in a variety of metabolic functions essential for the metabolism of long-chain fatty acids, d-amino acids, and many polyamines. A byproduct of peroxisomal metabolism is the generation, and subsequent detoxification, of reactive oxygen and nitrogen species, particularly hydrogen peroxide (H₂O₂). Because of its relatively low reactivity (as a mild oxidant), H₂O₂ has a comparatively long intracellular half-life and a high diffusion rate, all of which makes H₂O₂ an efficient signaling molecule. Peroxisomes also have intricate connections to mitochondria, and both organelles appear to play important roles in regulating redox signaling pathways. Peroxisomal proteins are also subject to oxidative modification and inactivation by the reactive oxygen and nitrogen species they generate, but the peroxisomal LonP2 protease can selectively remove such oxidatively damaged proteins, thus prolonging the useful lifespan of the organelle. Peroxisomal homeostasis must adapt to the metabolic state of the cell, by a combination of peroxisome proliferation, the removal of excess or badly damaged organelles by autophagy (pexophagy), as well as by processes of peroxisome inheritance and motility. More recently the tumor suppressors ataxia telangiectasia mutate (ATM) and tuberous sclerosis complex (TSC), which regulate mTORC1 signaling, have been found to regulate pexophagy in response to variable levels of certain reactive oxygen and nitrogen species. It is now clear that any significant loss of peroxisome homeostasis can have devastating physiological consequences. Peroxisome dysregulation has been implicated in several metabolic diseases, and increasing evidence highlights the important role of diminished peroxisomal functions in aging processes.

Oxidised protein metabolism: recent insights

The ‘oxygen paradox’ arises from the fact that oxygen, the molecule that aerobic life depends on, threatens its very existence. An oxygen-rich environment provided life on Earth with more efficient bioenergetics and, with it, the challenge of having to deal with a host of oxygen-derived reactive species capable of damaging proteins and other crucial cellular components. In this minireview, we explore recent insights into the metabolism of proteins that have been reversibly or irreversibly damaged by oxygen-derived species. We discuss recent data on the important roles played by the proteasomal and lysosomal systems in the proteolytic degradation of oxidatively damaged proteins and the effects of oxidative damage on the function of the proteolytic pathways themselves. Mitochondria are central to oxygen utilisation in the cell, and their ability to handle oxygen-derived radicals is an important and still emerging area of research. Current knowledge of the proteolytic machinery in the mitochondria, including the ATP-dependent AAA+ proteases and mitochondrial-derived vesicles, is also highlighted in the review. Significant progress is still being made in regard to understanding the mechanisms underlying the detection and degradation of oxidised proteins and how proteolytic pathways interact with each other. Finally, we highlight a few unanswered questions such as the possibility of oxidised amino acids released from oxidised proteins by proteolysis being re-utilised in protein synthesis thus establishing a vicious cycle of oxidation in cells.

Spaceflight Activates Autophagy Programs and the Proteasome in Mouse Liver

Increased oxidative stress is an unavoidable consequence of exposure to the space environment. Our previous studies showed that mice exposed to space for 13.5 days had decreased glutathione levels, suggesting impairments in oxidative defense. Here we performed unbiased, unsupervised and integrated multi-‘omic analyses of metabolomic and transcriptomic datasets from mice flown aboard the Space Shuttle Atlantis. Enrichment analyses of metabolite and gene sets showed significant changes in osmolyte concentrations and pathways related to glycerophospholipid and sphingolipid metabolism, likely consequences of relative dehydration of the spaceflight mice. However, we also found increased enrichment of aminoacyl-tRNA biosynthesis and purine metabolic pathways, concomitant with enrichment of genes associated with autophagy and the ubiquitin-proteasome. When taken together with a downregulation in nuclear factor (erythroid-derived 2)-like 2-mediated signaling, our analyses suggest that decreased hepatic oxidative defense may lead to aberrant tRNA post-translational processing, induction of degradation programs and senescence-associated mitochondrial dysfunction in response to the spaceflight environment.

New insights into the distribution, protein abundance and subcellular localisation of the endogenous peroxisomal biogenesis proteins PEX3 and PEX19 in different organs and cell types of the adult mouse

Peroxisomes are ubiquitous organelles mainly involved in ROS and lipid metabolism. Their abundance, protein composition and metabolic function vary depending on the cell type and adjust to different intracellular and environmental factors such as oxidative stress or nutrition. The biogenesis and proliferation of these important organelles are regulated by proteins belonging to the peroxin (PEX) family. PEX3, an integral peroxisomal membrane protein, and the cytosolic shuttling receptor PEX19 are thought to be responsible for the early steps of peroxisome biogenesis and assembly of their matrix protein import machinery. Recently, both peroxins were suggested to be also involved in the autophagy of peroxisomes (pexophagy). Despite the fact that distribution and intracellular abundance of these proteins might regulate the turnover of the peroxisomal compartment in a cell type-specific manner, a comprehensive analysis of the endogenous PEX3 and PEX19 distribution in different organs is still missing. In this study, we have therefore generated antibodies against endogenous mouse PEX3 and PEX19 and analysed their abundance and subcellular localisation in various mouse organs, tissues and cell types and compared it to the one of three commonly used peroxisomal markers (PEX14, ABCD3 and catalase). Our results revealed that the abundance of PEX3, PEX19, PEX14, ABCD3 and catalase strongly varies in the analysed organs and cell types, suggesting that peroxisome abundance, biogenesis and matrix protein import are independently regulated. We further found that in some organs, such as heart and skeletal muscle, the majority of the shuttling receptor PEX19 is bound to the peroxisomal membrane and that a strong variability exists in the cell type-specific ratio of cytosol- and peroxisome-associated PEX19. In conclusion, our results indicate that peroxisomes in various cell types are heterogeneous with regards to their matrix, membrane and biogenesis proteins.

The peroxisomal import receptor PEX5 functions as a stress sensor, retaining catalase in the cytosol in times of oxidative stress

Accumulating evidence indicates that peroxisome functioning, catalase localization, and cellular oxidative balance are intimately interconnected. Nevertheless, it remains largely unclear why modest increases in the cellular redox state especially interfere with the subcellular localization of catalase, the most abundant peroxisomal antioxidant enzyme. This study aimed at gaining more insight into this phenomenon. Therefore, we first established a simple and powerful approach to study peroxisomal protein import and protein-protein interactions in living cells in response to changes in redox state. By employing this approach, we confirm and extend previous observations that Cys-11 of human PEX5, the shuttling import receptor for peroxisomal matrix proteins containing a C-terminal peroxisomal targeting signal (PTS1), functions as a redox switch that modulates the protein's activity in response to intracellular oxidative stress. In addition, we show that oxidative stress affects the import of catalase, a non-canonical PTS1-containing protein, more than the import of a reporter protein containing a canonical PTS1. Furthermore, we demonstrate that changes in the local redox state do not affect PEX5-substrate binding and that human PEX5 does not oligomerize in cellulo, not even when the cells are exposed to oxidative stress. Finally, we present evidence that catalase retained in the cytosol can protect against H₂O₂-mediated redox changes in a manner that peroxisomally targeted catalase does not. Together, these findings lend credit to the idea that inefficient catalase import, when coupled with the role of PEX5 as a redox-regulated import receptor, constitutes a cellular defense mechanism to combat oxidative insults of extra-peroxisomal origin.

Pro- and Antioxidant Functions of the Peroxisome-Mitochondria Connection and Its Impact on Aging and Disease

Peroxisomes and mitochondria are the main intracellular sources for reactive oxygen species. At the same time, both organelles are critical for the maintenance of a healthy redox balance in the cell. Consequently, failure in the function of both organelles is causally linked to oxidative stress and accelerated aging. However, it has become clear that peroxisomes and mitochondria are much more intimately connected both physiologically and structurally. Both organelles share common fission components to dynamically respond to environmental cues, and the autophagic turnover of both peroxisomes and mitochondria is decisive for cellular homeostasis. Moreover, peroxisomes can physically associate with mitochondria via specific protein complexes. Therefore, the structural and functional connection of both organelles is a critical and dynamic feature in the regulation of oxidative metabolism, whose dynamic nature will be revealed in the future. In this review, we will focus on fundamental aspects of the peroxisome-mitochondria interplay derived from simple models such as yeast and move onto discussing the impact of an impaired peroxisomal and mitochondrial homeostasis on ROS production, aging, and disease in humans.

The Central Role of Biometals Maintains Oxidative Balance in the Context of Metabolic and Neurodegenerative Disorders

Traditionally, oxidative stress as a biological aspect is defined as an imbalance between the free radical generation and antioxidant capacity of living systems. The intracellular imbalance of ions, disturbance in membrane dynamics, hypoxic conditions, and dysregulation of gene expression are all molecular pathogenic mechanisms closely associated with oxidative stress and underpin systemic changes in the body. These also include aspects such as chronic immune system activation, the impairment of cellular structure renewal, and alterations in the character of the endocrine secretion of diverse tissues. All of these mentioned features are crucial for the correct function of the various tissue types in the body. In the present review, we summarize current knowledge about the common roots of metabolic and neurodegenerative disorders induced by oxidative stress. We discuss these common roots with regard to the way that (1) the respective metal ions are involved in the maintenance of oxidative balance and (2) the metabolic and signaling disturbances of the most important biometals, such as Mg²⁺, Zn²⁺, Se²⁺, Fe²⁺, or Cu²⁺, can be considered as the central connection point between the pathogenesis of both types of disorders and oxidative stress.

Optimization of recombinant Zea mays transglutaminase production and its influence on the functional properties of yogurt

The requirements for the production of optimized Zea mays transglutaminase (TGZo) using Pichia pastoris GS115 (pPIC9K-tgzo) were optimized in this study. Plackett-Burman design was used to screen variables that significantly influence TGZo production. Oleic acid, methanol, and loading volume were identified as the most significant parameters. Central composite design was employed to determine the optimal level of these three parameters for TGZo production. Results showed that 1078 mU/mL of TGZo activity and 7.6 mg/L of TGZo production were obtained under conditions of 0.07% oleic acid, 1.31% methanol, and 7.36% loading volume. To explore the functional characteristics of TGZo, it was used in yogurt. It was found that the addition of TGZo could produce yogurt with stronger acid gel and higher consistency, cohesiveness, index of viscosity, and apparent viscosity than the untreated product. Therefore, TGZo can be used as a substitute for microbial transglutaminase in the yogurt, even in the food industry.

The Peroxisome-Mitochondria Connection: How and Why?

Over the past decades, peroxisomes have emerged as key regulators in overall cellular lipid and reactive oxygen species metabolism. In mammals, these organelles have also been recognized as important hubs in redox-, lipid-, inflammatory-, and innate immune-signaling networks. To exert these activities, peroxisomes must interact both functionally and physically with other cell organelles. This review provides a comprehensive look of what is currently known about the interconnectivity between peroxisomes and mitochondria within mammalian cells. We first outline how peroxisomal and mitochondrial abundance are controlled by common sets of cis- and trans-acting factors. Next, we discuss how peroxisomes and mitochondria may communicate with each other at the molecular level. In addition, we reflect on how these organelles cooperate in various metabolic and signaling pathways. Finally, we address why peroxisomes and mitochondria have to maintain a healthy relationship and why defects in one organelle may cause dysfunction in the other. Gaining a better insight into these issues is pivotal to understanding how these organelles function in their environment, both in health and disease.

Chemistry and biology of reactive species with special reference to the antioxidative defence status in pancreatic β-cells

BACKGROUND

Diabetes mellitus is a serious metabolic disease. Dysfunction and subsequent loss of the β-cells in the islets of Langerhans through apoptosis ultimately cause a life-threatening insulin deficiency. The underlying reason for the particular vulnerability of the β-cells is an extraordinary sensitivity to the toxicity of reactive oxygen and nitrogen species (ROS and RNS) due to its low antioxidative defense status.

SCOPE REVIEW

This review considers the different aspects of the chemistry and biology of the biologically most important reactive species and their chemico-biological interactions in the β-cell toxicity of proinflammatory cytokines in type 1 diabetes and of lipotoxicity in type 2 diabetes development.

MAJOR CONCLUSION

The weak antioxidative defense equipment in the different subcellular organelles makes the β-cells particularly vulnerable and prone to mitochondrial, peroxisomal and ER stress. Looking upon the enzyme deficiencies which are responsible for the low antioxidative defense status of the pancreatic β-cells it is the lack of enzymatic capacity for H₂O₂ inactivation at all major subcellular sites.

GENERAL SIGNIFICANCE

Diabetes is the most prevalent metabolic disorder with a steadily increasing incidence of both type 1 and type 2 diabetes worldwide. The weak protection of the pancreatic β-cells against oxidative stress is a major reason for their particular vulnerability. Thus, careful protection of the β-cells is required for prevention of the disease.

Endogenous catalase delays high-fat diet-induced liver injury in mice

Non-alcoholic fatty liver disease (NAFLD) has become the most prevalent liver disease in parallel with worldwide epidemic of obesity. Reactive oxygen species (ROS) contributes to the development and progression of NAFLD. Peroxisomes play an important role in fatty acid oxidation and ROS homeostasis, and catalase is an antioxidant exclusively expressed in peroxisome. The present study examined the role of endogenous catalase in early stage of NAFLD. 8-week-old male catalase knock-out (CKO) and age-matched C57BL/6J wild type (WT) mice were fed either a normal diet (ND: 18% of total calories from fat) or a high fat diet (HFD: 60% of total calories from fat) for 2 weeks. CKO mice gained body weight faster than WT mice at early period of HFD feeding. Plasma triglyceride and ALT, fasting plasma insulin, as well as liver lipid accumulation, inflammation (F4/80 staining), and oxidative stress (8-oxo-dG staining and nitrotyrosine level) were significantly increased in CKO but not in WT mice at 2 weeks of HFD feeding. While phosphorylation of Akt (Ser473) and PGC1α mRNA expression were decreased in both CKO and WT mice at HFD feeding, GSK3β phosphorylation and Cox4-il mRNA expression in the liver were decreased only in CKO-HF mice. Taken together, the present data demonstrated that endogenous catalase exerted beneficial effects in protecting liver injury including lipid accumulation and inflammation through maintaining liver redox balance from the early stage of HFD-induced metabolic stress.

Peroxisomal Dysfunction in Age-Related Diseases

Peroxisomes carry out many key functions related to lipid and reactive oxygen species (ROS) metabolism. The fundamental importance of peroxisomes for health in humans is underscored by the existence of devastating genetic disorders caused by impaired peroxisomal function or lack of peroxisomes. Emerging studies suggest that peroxisomal function may also be altered with aging and contribute to the pathogenesis of a variety of diseases, including diabetes and its related complications, neurodegenerative disorders, and cancer. With increasing evidence connecting peroxisomal dysfunction to the pathogenesis of these acquired diseases, the possibility of targeting peroxisomal function in disease prevention or treatment becomes intriguing. Here, we review recent developments in understanding the pathophysiological implications of peroxisomal dysfunctions outside the context of inherited peroxisomal disorders.

Antioxidant effect of thiazolidine molecules in cell culture media improves stability and performance

The ability of cell culture media components to generate reactive species as well as their sensitivity to oxidative degradation, affects the overall stability of media and the behavior of cells cultured in vitro. This study investigates the influence of thiazolidine molecules, formed from the condensation between cysteine and alpha-ketoacids, on the stability of these complex mixtures and on the performance of cell culture processes aiming to produce therapeutically relevant monoclonal antibodies. Results presented in this study indicate that 2-methyl-1,3-thiazolidine-2,4-dicarboxylic acid and 2-(2-carboxyethyl)-1,3-thiazolidine-2,4-dicarboxylic acid, obtained by condensation of cysteine with pyruvate or alpha-ketoglutarate, respectively, are able to stabilize cell culture media formulations, in particular redox sensitive molecules like folic acid, thiamine, l-methionine (met) and l-tryptophan (trp). The use of thiazolidine containing feeds in Chinese hamster ovary fed-batch processes showed prolonged culture duration and increased productivity. This enhanced performance was correlated with lower reactive species generation, extracellularly and intracellularly. Moreover, an anti-oxidative response was triggered via the induction of superoxide dismutase and an increase in the total glutathione pool, the major intracellular antioxidant. In total, the results confirm that cells in vitro are not cultured in an oxidant-free environment, a concept that has to be considered when studying the influence of reactive species in human diseases. Furthermore, this study indicates that thiazolidines are an interesting class of antioxidant molecules, capable of increasing cell culture media stability and process performance. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:759-770, 2017.

KillerRed as a Tool to Study the Cellular Responses to Peroxisome-Derived Oxidative Stress

Many biological processes and cell fate decisions are modulated by changes in redox environment. To gain insight into how subcellular compartmentalization of reactive oxygen species (ROS) formation contributes to (site-specific) redox signaling and oxidative stress responses, it is critical to have access to tools that allow tight spatial and temporal control of ROS production. Over the past decade, the use of genetically encoded photosensitizers has attracted growing interest of researchers because these proteins can be easily targeted to various subcellular compartments and allow for controlled release of ROS when excited by light. This chapter provides guidance and practical advice on the use of po-KR, a peroxisomal variant of the phototoxic red fluorescent protein KillerRed, to address fundamental questions about how mammalian cells cope with peroxisome-derived oxidative stress.

Statins Increase Mitochondrial and Peroxisomal Fatty Acid Oxidation in the Liver and Prevent Non-Alcoholic Steatohepatitis in Mice

BACKGROUND

Non-alcoholic fatty liver disease is the most common form of chronic liver disease in industrialized countries. Recent studies have highlighted the association between peroxisomal dysfunction and hepatic steatosis. Peroxisomes are intracellular organelles that contribute to several crucial metabolic processes, such as facilitation of mitochondrial fatty acid oxidation (FAO) and removal of reactive oxygen species through catalase or plasmalogen synthesis. Statins are known to prevent hepatic steatosis and non-alcoholic steatohepatitis (NASH), but underlying mechanisms of this prevention are largely unknown.

METHODS

Seven-week-old C57BL/6J mice were given normal chow or a methionine- and choline-deficient diet (MCDD) with or without various statins, fluvastatin, pravastatin, simvastatin, atorvastatin, and rosuvastatin (15 mg/kg/day), for 6 weeks. Histological lesions were analyzed by grading and staging systems of NASH. We also measured mitochondrial and peroxisomal FAO in the liver.

RESULTS

Statin treatment prevented the development of MCDD-induced NASH. Both steatosis and inflammation or fibrosis grades were significantly improved by statins compared with MCDD-fed mice. Gene expression levels of peroxisomal proliferator-activated receptor α (PPARα) were decreased by MCDD and recovered by statin treatment. MCDD-induced suppression of mitochondrial and peroxisomal FAO was restored by statins. Each statin's effect on increasing FAO and improving NASH was independent on its effect of decreasing cholesterol levels.

CONCLUSION

Statins prevented NASH and increased mitochondrial and peroxisomal FAO via induction of PPARα. The ability to increase hepatic FAO is likely the major determinant of NASH prevention by statins. Improvement of peroxisomal function by statins may contribute to the prevention of NASH.

Role of ROS and RNS Sources in Physiological and Pathological Conditions

There is significant evidence that, in living systems, free radicals and other reactive oxygen and nitrogen species play a double role, because they can cause oxidative damage and tissue dysfunction and serve as molecular signals activating stress responses that are beneficial to the organism. Mitochondria have been thought to both play a major role in tissue oxidative damage and dysfunction and provide protection against excessive tissue dysfunction through several mechanisms, including stimulation of opening of permeability transition pores. Until recently, the functional significance of ROS sources different from mitochondria has received lesser attention. However, the most recent data, besides confirming the mitochondrial role in tissue oxidative stress and protection, show interplay between mitochondria and other ROS cellular sources, so that activation of one can lead to activation of other sources. Thus, it is currently accepted that in various conditions all cellular sources of ROS provide significant contribution to processes that oxidatively damage tissues and assure their survival, through mechanisms such as autophagy and apoptosis.

Mechanism of impaired microtubule-dependent peroxisome trafficking and oxidative stress in SPAST-mutated cells from patients with Hereditary Spastic Paraplegia

Hereditary spastic paraplegia (HSP) is an inherited neurological condition that leads to progressive spasticity and gait abnormalities. Adult-onset HSP is most commonly caused by mutations in SPAST, which encodes spastin a microtubule severing protein. In olfactory stem cell lines derived from patients carrying different SPAST mutations, we investigated microtubule-dependent peroxisome movement with time-lapse imaging and automated image analysis. The average speed of peroxisomes in patient-cells was slower, with fewer fast moving peroxisomes than in cells from healthy controls. This was not because of impairment of peroxisome-microtubule interactions because the time-dependent saltatory dynamics of movement of individual peroxisomes was unaffected in patient-cells. Our observations indicate that average peroxisome speeds are less in patient-cells because of the lower probability of individual peroxisome interactions with the reduced numbers of stable microtubules: peroxisome speeds in patient cells are restored by epothilone D, a tubulin-binding drug that increases the number of stable microtubules to control levels. Patient-cells were under increased oxidative stress and were more sensitive than control-cells to hydrogen peroxide, which is primarily metabolised by peroxisomal catalase. Epothilone D also ameliorated patient-cell sensitivity to hydrogen-peroxide. Our findings suggest a mechanism for neurodegeneration whereby SPAST mutations indirectly lead to impaired peroxisome transport and oxidative stress.

The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1

Peroxisomes are ubiquitous eukaryotic organelles with the primary role of breaking down very long- and branched-chain fatty acids for subsequent β-oxidation in the mitochondrion. Like mitochondria, peroxisomes are major sites for oxygen utilization and potential contributors to cellular oxidative stress. The accumulation of oxidatively damaged proteins, which often develop into inclusion bodies (of oxidized, aggregated, and cross-linked proteins) within both mitochondria and peroxisomes, results in loss of organelle function that may contribute to the aging process. Both organelles possess an isoform of the Lon protease that is responsible for degrading proteins damaged by oxidation. While the importance of mitochondrial Lon (LonP1) in relation to oxidative stress and aging has been established, little is known regarding the role of LonP2 and aging-related changes in the peroxisome. Recently, peroxisome dysfunction has been associated with aging-related diseases indicating that peroxisome maintenance is a critical component of 'healthy aging'. Although mitochondria and peroxisomes are both needed for fatty acid metabolism, little work has focused on understanding the relationship between these two organelles including how age-dependent changes in one organelle may be detrimental for the other. Herein, we summarize findings that establish proteolytic degradation of damaged proteins by the Lon protease as a vital mechanism to maintain protein homeostasis within the peroxisome. Due to the metabolic coordination between peroxisomes and mitochondria, understanding the role of Lon in the aging peroxisome may help to elucidate cellular causes for both peroxisome and mitochondrial dysfunction.

Metabolic Interplay between Peroxisomes and Other Subcellular Organelles Including Mitochondria and the Endoplasmic Reticulum

Peroxisomes are unique subcellular organelles which play an indispensable role in several key metabolic pathways which include: (1.) etherphospholipid biosynthesis; (2.) fatty acid beta-oxidation; (3.) bile acid synthesis; (4.) docosahexaenoic acid (DHA) synthesis; (5.) fatty acid alpha-oxidation; (6.) glyoxylate metabolism; (7.) amino acid degradation, and (8.) ROS/RNS metabolism. The importance of peroxisomes for human health and development is exemplified by the existence of a large number of inborn errors of peroxisome metabolism in which there is an impairment in one or more of the metabolic functions of peroxisomes. Although the clinical signs and symptoms of affected patients differ depending upon the enzyme which is deficient and the extent of the deficiency, the disorders involved are usually (very) severe diseases with neurological dysfunction and early death in many of them. With respect to the role of peroxisomes in metabolism it is clear that peroxisomes are dependent on the functional interplay with other subcellular organelles to sustain their role in metabolism. Indeed, whereas mitochondria can oxidize fatty acids all the way to CO₂ and H₂O, peroxisomes are only able to chain-shorten fatty acids and the end products of peroxisomal beta-oxidation need to be shuttled to mitochondria for full oxidation to CO₂ and H₂O. Furthermore, NADH is generated during beta-oxidation in peroxisomes and beta-oxidation can only continue if peroxisomes are equipped with a mechanism to reoxidize NADH back to NAD⁺, which is now known to be mediated by specific NAD(H)-redox shuttles. In this paper we describe the current state of knowledge about the functional interplay between peroxisomes and other subcellular compartments notably the mitochondria and endoplasmic reticulum for each of the metabolic pathways in which peroxisomes are involved.

OsPEX11, a Peroxisomal Biogenesis Factor 11, Contributes to Salt Stress Tolerance in Oryza sativa

Peroxisomes are single membrane-bound organelles, whose basic enzymatic constituents are catalase and H₂O₂-producing flavin oxidases. Previous reports showed that peroxisome is involved in numerous processes including primary and secondary metabolism, plant development and abiotic stress responses. However, knowledge on the function of different peroxisome genes from rice and its regulatory roles in salt and other abiotic stresses is limited. Here, a novel prey protein, OsPEX11 (Os03g0302000), was screened and identified by yeast two-hybrid and GST pull-down assays. Phenotypic analysis of OsPEX11 overexpression seedlings demonstrated that they had better tolerance to salt stress than wild type (WT) and OsPEX11-RNAi seedlings. Compared with WT and OsPEX11-RNAi seedlings, overexpression of OsPEX11 had lower level of lipid peroxidation, Na⁺/K⁺ ratio, higher activities of antioxidant enzymes (SOD, POD, and CAT) and proline accumulation. Furthermore, qPCR data suggested that OsPEX11 acted as a positive regulator of salt tolerance by reinforcing the expression of several well-known rice transporters (OsHKT2;1, OsHKT1;5, OsLti6a, OsLti6b, OsSOS1, OsNHX1, and OsAKT1) involved in Na⁺/K⁺ homeostasis in transgenic plants under salinity. Ultrastructural observations of OsPEX11-RNAi seedlings showed that they were less sensitive to salt stress than WT and overexpression lines. These results provide experimental evidence that OsPEX11 is an important gene implicated in Na⁺ and K⁺ regulation, and plays a critical role in salt stress tolerance by modulating the expression of cation transporters and antioxidant defense. Thus, OsPEX11 could be considered in transgenic breeding for improvement of salt stress tolerance in rice crop.

Redox signaling: Potential arbitrator of autophagy and apoptosis in therapeutic response

Redox signaling plays important roles in the regulation of cell death and survival in response to cancer therapy. Autophagy and apoptosis are discrete cellular processes mediated by distinct groups of regulatory and executioner molecules, and both are thought to be cellular responses to various stress conditions including oxidative stress, therefore controlling cell fate. Basic levels of reactive oxygen species (ROS) may function as signals to promote cell proliferation and survival, whereas increase of ROS can induce autophagy and apoptosis by damaging cellular components. Growing evidence in recent years argues for ROS that below detrimental levels acting as intracellular signal transducers that regulate autophagy and apoptosis. ROS-regulated autophagy and apoptosis can cross-talk with each other. However, how redox signaling determines different cell fates by regulating autophagy and apoptosis remains unclear. In this review, we will focus on understanding the delicate molecular mechanism by which autophagy and apoptosis are finely orchestrated by redox signaling and discuss how this understanding can be used to develop strategies for the treatment of cancer.

Does PGC1α/FNDC5/BDNF Elicit the Beneficial Effects of Exercise on Neurodegenerative Disorders?

Neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases have high prevalence among the elderly. Many strategies have been established to alleviate the symptoms experienced by affected individuals. Recent studies have shown that exercise helps patients with neurological disorders to regain lost physical abilities. PGC1α/FNDC5/BDNF has emerged recently as a critical pathway for neuroprotection. PGC1α is a highly conserved co-activator of transcription factors that preserves and protects neurons against destruction. PGC1α regulates FNDC5 and its processed and secreted peptide Irisin, which has been proposed to play a critical role in energy expenditure and to promote neural differentiation of mouse embryonic stem cells. FNDC5 may also increase the expression of the neurotrophic factor BDNF, a neuroprotective agent, in the hippocampus. BDNF is secreted from hippocampus, amygdala, cerebral cortex and hypothalamus neurons and initiates intracellular signaling pathways through TrkB receptors. These pathways have positive feedback on CREB activities and lead to enhancement in PGC1α expression in neurons. Therefore, FNDC5 could behave as a key regulator in neuronal survival and development. This review presents recent findings on the PGC1α/FNDC5/BDNF pathway and its role in neuroprotection, and discusses the controversial promise of irisin as a mediator of the positive benefits of exercise.

Crosstalk between mitochondria and peroxisomes

Mitochondria and peroxisomes are small ubiquitous organelles. They both play major roles in cell metabolism, especially in terms of fatty acid metabolism, reactive oxygen species (ROS) production, and ROS scavenging, and it is now clear that they metabolically interact with each other. These two organelles share some properties, such as great plasticity and high potency to adapt their form and number according to cell requirements. Their functions are connected, and any alteration in the function of mitochondria may induce changes in peroxisomal physiology. The objective of this paper was to highlight the interconnection and the crosstalk existing between mitochondria and peroxisomes. Special emphasis was placed on the best known connections between these organelles: origin, structure, and metabolic interconnections.

Peroxisomal Pex11 is a pore-forming protein homologous to TRPM channels

More than 30 proteins (Pex proteins) are known to participate in the biogenesis of peroxisomes-ubiquitous oxidative organelles involved in lipid and ROS metabolism. The Pex11 family of homologous proteins is responsible for division and proliferation of peroxisomes. We show that yeast Pex11 is a pore-forming protein sharing sequence similarity with TRPM cation-selective channels. The Pex11 channel with a conductance of Λ=4.1 nS in 1.0M KCl is moderately cation-selective (PK(+)/PCl(-)=1.85) and resistant to voltage-dependent closing. The estimated size of the channel's pore (r~0.6 nm) supports the notion that Pex11 conducts solutes with molecular mass below 300-400 Da. We localized the channel's selectivity determining sequence. Overexpression of Pex11 resulted in acceleration of fatty acids β-oxidation in intact cells but not in the corresponding lysates. The β-oxidation was affected in cells by expression of the Pex11 protein carrying point mutations in the selectivity determining sequence. These data suggest that the Pex11-dependent transmembrane traffic of metabolites may be a rate-limiting step in the β-oxidation of fatty acids. This conclusion was corroborated by analysis of the rate of β-oxidation in yeast strains expressing Pex11 with mutations mimicking constitutively phosphorylated (S165D, S167D) or unphosphorylated (S165A, S167A) protein. The results suggest that phosphorylation of Pex11 is a mechanism that can control the peroxisomal β-oxidation rate. Our results disclose an unexpected function of Pex11 as a non-selective channel responsible for transfer of metabolites across peroxisomal membrane. The data indicate that peroxins may be involved in peroxisomal metabolic processes in addition to their role in peroxisome biogenesis.

Oxidative stress, mitochondrial and proteostasis malfunction in adrenoleukodystrophy: A paradigm for axonal degeneration

Peroxisomal and mitochondrial malfunction, which are highly intertwined through redox regulation, in combination with defective proteostasis, are hallmarks of the most prevalent multifactorial neurodegenerative diseases-including Alzheimer's (AD) and Parkinson's disease (PD)-and of the aging process, and are also found in inherited conditions. Here we review the interplay between oxidative stress and axonal degeneration, taking as groundwork recent findings on pathomechanisms of the peroxisomal neurometabolic disease adrenoleukodystrophy (X-ALD). We explore the impact of chronic redox imbalance caused by the excess of very long-chain fatty acids (VLCFA) on mitochondrial respiration and biogenesis, and discuss how this impairs protein quality control mechanisms essential for neural cell survival, such as the proteasome and autophagy systems. As consequence, prime molecular targets in the pathogenetic cascade emerge, such as the SIRT1/PGC-1α axis of mitochondrial biogenesis, and the inhibitor of autophagy mTOR. Thus, we propose that mitochondria-targeted antioxidants; mitochondrial biogenesis boosters such as the antidiabetic pioglitazone and the SIRT1 ligand resveratrol; and the autophagy activator temsirolimus, a derivative of the mTOR inhibitor rapamycin, hold promise as disease-modifying therapies for X-ALD.

The different facets of organelle interplay-an overview of organelle interactions

Membrane-bound organelles such as mitochondria, peroxisomes, or the endoplasmic reticulum (ER) create distinct environments to promote specific cellular tasks such as ATP production, lipid breakdown, or protein export. During recent years, it has become evident that organelles are integrated into cellular networks regulating metabolism, intracellular signaling, cellular maintenance, cell fate decision, and pathogen defence. In order to facilitate such signaling events, specialized membrane regions between apposing organelles bear distinct sets of proteins to enable tethering and exchange of metabolites and signaling molecules. Such membrane associations between the mitochondria and a specialized site of the ER, the mitochondria associated-membrane (MAM), as well as between the ER and the plasma membrane (PAM) have been partially characterized at the molecular level. However, historical and recent observations imply that other organelles like peroxisomes, lysosomes, and lipid droplets might also be involved in the formation of such apposing membrane contact sites. Alternatively, reports on so-called mitochondria derived-vesicles (MDV) suggest alternative mechanisms of organelle interaction. Moreover, maintenance of cellular homeostasis requires the precise removal of aged organelles by autophagy—a process which involves the detection of ubiquitinated organelle proteins by the autophagosome membrane, representing another site of membrane associated-signaling. This review will summarize the available data on the existence and composition of organelle contact sites and the molecular specializations each site uses in order to provide a timely overview on the potential functions of organelle interaction.

Peroxisomes sense and respond to environmental cues by regulating ROS and RNS signalling networks

BACKGROUND

Peroxisomes are highly dynamic, metabolically active organelles that used to be regarded as a sink for H2O2 generated in different organelles. However, peroxisomes are now considered to have a more complex function, containing different metabolic pathways, and they are an important source of reactive oxygen species (ROS), nitric oxide (NO) and reactive nitrogen species (RNS). Over-accumulation of ROS and RNS can give rise oxidative and nitrosative stress, but when produced at low concentrations they can act as signalling molecules.

SCOPE

This review focuses on the production of ROS and RNS in peroxisomes and their regulation by antioxidants. ROS production is associated with metabolic pathways such as photorespiration and fatty acid β-oxidation, and disturbances in any of these processes can be perceived by the cell as an alarm that triggers defence responses. Genetic and pharmacological studies have shown that photorespiratory H2O2 can affect nuclear gene expression, regulating the response to pathogen infection and light intensity. Proteomic studies have shown that peroxisomal proteins are targets for oxidative modification, S-nitrosylation and nitration and have highlighted the importance of these modifications in regulating peroxisomal metabolism and signalling networks. The morphology, size, number and speed of movement of peroxisomes can also change in response to oxidative stress, meaning that an ROS/redox receptor is required. Information available on the production and detection of NO/RNS in peroxisomes is more limited. Peroxisomal homeostasis is critical for maintaining the cellular redox balance and is regulated by ROS, peroxisomal proteases and autophagic processes.

CONCLUSIONS

Peroxisomes play a key role in many aspects of plant development and acclimation to stress conditions. These organelles can sense ROS/redox changes in the cell and thus trigger rapid and specific responses to environmental cues involving changes in peroxisomal dynamics as well as ROS- and NO-dependent signalling networks, although the mechanisms involved have not yet been established. Peroxisomes can therefore be regarded as a highly important decision-making platform in the cell, where ROS and RNS play a determining role.

Reactive oxygen species, nutrition, hypoxia and diseases: Problems solved?

Within the last twenty years the view on reactive oxygen species (ROS) has changed; they are no longer only considered to be harmful but also necessary for cellular communication and homeostasis in different organisms ranging from bacteria to mammals. In the latter, ROS were shown to modulate diverse physiological processes including the regulation of growth factor signaling, the hypoxic response, inflammation and the immune response. During the last 60–100 years the life style, at least in the Western world, has changed enormously. This became obvious with an increase in caloric intake, decreased energy expenditure as well as the appearance of alcoholism and smoking; These changes were shown to contribute to generation of ROS which are, at least in part, associated with the occurrence of several chronic diseases like adiposity, atherosclerosis, type II diabetes, and cancer. In this review we discuss aspects and problems on the role of intracellular ROS formation and nutrition with the link to diseases and their problematic therapeutical issues.

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Oxidative stress is linked to overnutrition, obesity and associated diseases or cancer.

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Reactive oxygen species (ROS) are crucially involved in modulation of signaling cascades.

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NOX proteins and hypoxia contribute to formation of ROS under different nutrient regimes.

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ROS are powerful post-transcriptional and epigenetic regulators.

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Treatment of obesity with antioxidants requires more, larger, and better monitored clinical trials.

Peroxisome-mitochondria interplay and disease

Peroxisomes and mitochondria are ubiquitous, highly dynamic organelles with an oxidative type of metabolism in eukaryotic cells. Over the years, substantial evidence has been provided that peroxisomes and mitochondria exhibit a close functional interplay which impacts on human health and development. The so-called "peroxisome-mitochondria connection" includes metabolic cooperation in the degradation of fatty acids, a redox-sensitive relationship, an overlap in key components of the membrane fission machineries and cooperation in anti-viral signalling and defence. Furthermore, combined peroxisome-mitochondria disorders with defects in organelle division have been revealed. In this review, we present the latest progress in the emerging field of peroxisomal and mitochondrial interplay in mammals with a particular emphasis on cooperative fatty acid β-oxidation, redox interplay, organelle dynamics, cooperation in anti-viral signalling and the resulting implications for disease.