Engineering Cell Membrane-Cloaked Catalysts as Multifaceted Artificial Peroxisomes for Biomedical Applications.

Artificial peroxisomes (APEXs) or peroxisome mimics have caught a lot of attention in nanomedicine and biomaterial science in the last decade, which have great potential in clinically diagnosing and treating diseases. APEXs are typically constructed from a semipermeable membrane that encloses natural enzymes or enzyme-mimetic catalysts to perform peroxisome-/enzyme-mimetic activities. The recent rapid progress regarding their biocatalytic stability, adjustable activity, and surface functionality has significantly promoted APEXs systems in real-life applications. In addition, developing a facile and versatile system that can simulate multiple biocatalytic tasks is advantageous. Here, the recent advances in engineering cell membrane-cloaked catalysts as multifaceted APEXs for diverse biomedical applications are highlighted and commented. First, various catalysts with single or multiple enzyme activities have been introduced as cores of APEXs. Subsequently, the extraction and function of cell membranes that are used as the shell are summarized. After that, the applications of these APEXs are discussed in detail, such as cancer therapy, antioxidant, anti-inflammation, and neuron protection. Finally, the future perspectives and challenges of APEXs are proposed and outlined. This progress review is anticipated to provide new and unique insights into cell membrane-cloaked catalysts and to offer significant new inspiration for designing future artificial organelles.

Dengue and Zika Virus Capsid Proteins Contain a Common PEX19-Binding Motif.

Flaviviruses such as dengue virus (DENV) and Zika virus (ZIKV) have evolved sophisticated mechanisms to suppress the host immune system. For instance, flavivirus infections were found to sabotage peroxisomes, organelles with an important role in innate immunity. The current model suggests that the capsid (C) proteins of DENV and ZIKV downregulate peroxisomes, ultimately resulting in reduced production of interferons by interacting with the host protein PEX19, a crucial chaperone in peroxisomal biogenesis. Here, we aimed to explore the importance of peroxisomes and the role of C interaction with PEX19 in the flavivirus life cycle. By infecting cells lacking peroxisomes we show that this organelle is required for optimal DENV replication. Moreover, we demonstrate that DENV and ZIKV C bind PEX19 through a conserved PEX19-binding motif, which is also commonly found in cellular peroxisomal membrane proteins (PMPs). However, in contrast to PMPs, this interaction does not result in the targeting of C to peroxisomes. Furthermore, we show that the presence of C results in peroxisome loss due to impaired peroxisomal biogenesis, which appears to occur by a PEX19-independent mechanism. Hence, these findings challenge the current model of how flavivirus C might downregulate peroxisomal abundance and suggest a yet unknown role of peroxisomes in flavivirus biology.

Hypothyroidism Intensifies Both Canonic and the De Novo Pathway of Peroxisomal Biogenesis in Rat Brown Adipocytes in a Time-Dependent Manner.

Despite peroxisomes being important partners of mitochondria by carrying out fatty acid oxidation in brown adipocytes, no clear evidence concerning peroxisome origin and way(s) of biogenesis exists. Herein we used methimazole-induced hypothyroidism for 7, 15, and 21 days to study peroxisomal remodeling and origin in rat brown adipocytes. We found that peroxisomes originated via both canonic, and de novo pathways. Each pathway operates in euthyroid control and over the course of hypothyroidism, in a time-dependent manner. Hypothyroidism increased the peroxisomal number by 1.8-, 3.6- and 5.8-fold on days 7, 15, and 21. Peroxisomal presence, their distribution, and their degree of maturation were heterogeneous in brown adipocytes in a Harlequin-like manner, reflecting differences in their origin. The canonic pathway, through numerous dumbbell-like and "pearls on strings" structures, supported by high levels of Pex11ß and Drp1, prevailed on day 7. The de novo pathway of peroxisomal biogenesis started on day 15 and became dominant by day 21. The transition of peroxisomal biogenesis from canonic to the de novo pathway was driven by increased levels of Pex19, PMP70, Pex5S, and Pex26 and characterized by numerous tubular structures. Furthermore, specific peroxisomal origin from mitochondria, regardless of thyroid status, indicates their mutual regulation in rat brown adipocytes.

How cytosolic compartments play safeguard functions against neuroinflammation and cell death in cerebral ischemia.

Ischemic stroke is the second leading cause of mortality and disability globally. Neuronal damage following ischemic stroke is rapid and irreversible, and eventually results in neuronal death. In addition to activation of cell death signaling, neuroinflammation is also considered as another pathogenesis that can occur within hours after cerebral ischemia. Under physiological conditions, subcellular organelles play a substantial role in neuronal functionality and viability. However, their functions can be remarkably perturbed under neurological disorders, particularly cerebral ischemia. Therefore, their biochemical and structural response has a determining role in the sequel of neuronal cells and the progression of disease. However, their effects on cell death and neuroinflammation, as major underlying mechanisms of ischemic stroke, are still not understood. This review aims to provide a comprehensive overview of the contribution of each organelle on these pathological processes after ischemic stroke.

PxdA interacts with the DipA phosphatase to regulate peroxisome hitchhiking on early endosomes.

In canonical microtubule-based transport, adaptor proteins link cargoes to dynein and kinesin motors. Recently, an alternative mode of transport known as "hitchhiking" was discovered, where cargoes achieve motility by hitching a ride on already-motile cargoes, rather than attaching to a motor protein. Hitchhiking has been best studied in two filamentous fungi, Aspergillus nidulans and Ustilago maydis. In U. maydis, ribonucleoprotein complexes, peroxisomes, lipid droplets (LDs), and endoplasmic reticulum hitchhike on early endosomes (EEs). In A. nidulans, peroxisomes hitchhike using a putative molecular linker, peroxisome distribution mutant A (PxdA), which associates with EEs. However, whether other organelles use PxdA to hitchhike on EEs is unclear, as are the molecular mechanisms that regulate hitchhiking. Here we find that the proper distribution of LDs, mitochondria, and preautophagosomes do not require PxdA, suggesting that PxdA is a peroxisome-specific molecular linker. We identify two new pxdA alleles, including a point mutation (R2044P) that disrupts PxdA's ability to associate with EEs and reduces peroxisome movement. We also identify a novel regulator of peroxisome hitchhiking, the phosphatase DipA. DipA colocalizes with EEs and its association with EEs relies on PxdA. Together, our data suggest that PxdA and the DipA phosphatase are specific regulators of peroxisome hitchhiking on EEs.

Mitochondrial Miro GTPases coordinate mitochondrial and peroxisomal dynamics.

Mitochondria and peroxisomes are highly dynamic, multifunctional organelles. Both perform key roles for cellular physiology and homoeostasis by mediating bioenergetics, biosynthesis, and/or signalling. To support cellular function, they must be properly distributed, of proper size, and be able to interact with other organelles. Accumulating evidence suggests that the small atypical GTPase Miro provides a central signalling node to coordinate mitochondrial as well as peroxisomal dynamics. In this review, I summarize our current understanding of Miro-dependent functions and molecular mechanisms underlying the proper distribution, size and function of mitochondria and peroxisomes.

Fusion of Mitochondria to 3-D Networks, Autophagy and Increased Organelle Contacts are Important Subcellular Hallmarks during Cold Stress in Plants.

Low temperature stress has a severe impact on the distribution, physiology, and survival of plants in their natural habitats. While numerous studies have focused on the physiological and molecular adjustments to low temperatures, this study provides evidence that cold induced physiological responses coincide with distinct ultrastructural alterations. Three plants from different evolutionary levels and habitats were investigated: The freshwater alga Micrasterias denticulata, the aquatic plant Lemna sp., and the nival plant Ranunculus glacialis. Ultrastructural alterations during low temperature stress were determined by the employment of 2-D transmission electron microscopy and 3-D reconstructions from focused ion beam-scanning electron microscopic series. With decreasing temperatures, increasing numbers of organelle contacts and particularly the fusion of mitochondria to 3-dimensional networks were observed. We assume that the increase or at least maintenance of respiration during low temperature stress is likely to be based on these mitochondrial interconnections. Moreover, it is shown that autophagy and degeneration processes accompany freezing stress in Lemna and R. glacialis. This might be an essential mechanism to recycle damaged cytoplasmic constituents to maintain the cellular metabolism during freezing stress.

Review: Morphology, behaviour and interactions of organelles.

High quality transmission electron micrographs have played a major role in shaping our views on organelles in plant cells. However, these snapshots of dead, fixed and sectioned tissue do not automatically convey an appreciation of the dynamic nature of organelles in living cells. Advances in the imaging of subcellular structures in living cells using multicoloured, targeted fluorescent proteins reveal considerable changes in organelle pleomorphy that might be limited to small regions of the cell. The fresh data and insights also challenge several existing ideas on organelle behaviour and interactivity. Here, using succinct examples from plastids, mitochondria, peroxisomes, and the endoplasmic reticulum I present an evolving view of subcellular dynamics in the plant cell.

DNM1, a Dynamin-Related Protein That Contributes to Endocytosis and Peroxisome Fission, Is Required for the Vegetative Growth, Sporulation, and Virulence of Metarhizium robertsii.

Although dynamins and dynamin-related proteins (DRPs), a large GTPase superfamily, are involved in the budding of transport vesicles and division of organelles in eukaryotic cells, the function of these proteins in entomopathogenic fungi has not been reported to date. Here, DNM1, a DRP in Metarhizium robertsii, was characterized using gene disruption and complementation strategies. Mutant phenotype assays showed that the ΔDnm1 strain displayed increased defects in radial growth (∼24%) and conidial production (∼42%) compared to those of the wild type (WT), and reduced conidiation levels were accompanied by the repression of several key conidiation-related genes, including flbA, wetA, and flbD Additionally, mutant bioassays revealed that disruption of Dnm1 impaired the virulence (both topical inoculation and injection) of M. robertsii in the insect Galleria mellonella Further analysis demonstrated that deleting Dnm1 in fungi suppressed the transcriptional levels of several virulence genes in the insect hemocoel. Moreover, we found that DNM1 colocalized with peroxisomes and mitochondria. Importantly, disruption of Dnm1 abolished normal fungal endocytosis, resulting in significantly decreased numbers of, as well as morphological changes in, peroxisomes. These findings indicate that deletion of Dnm1 causes significant changes in the vegetative growth, sporulation, and virulence of M. robertsii due to changes in cell function and peroxisomes.IMPORTANCEDnm1 was found to be involved in fungal development and virulence, mediated peroxisomal fission, and normal endocytosis. This finding provides new insights into the cellular processes and pathogenicity in entomopathogenic fungi.

Short-term inhibition of autophagy benefits pancreatic ß-cells by augmenting ether lipids and peroxisomal function, and by countering depletion of n-3 polyunsaturated fatty acids after fat-feeding.

OBJECTIVE: Investigations of autophagy in ß-cells have usually focused on its homeostatic function. More dynamic roles in inhibiting glucose-stimulated insulin secretion (GSIS), potentially involving remodelling of cellular lipids, have been suggested from in vitro studies but not evaluated in vivo. METHODS: We employed temporally-regulated deletion of the essential autophagy gene, Atg7, in ß-cells. Mice were fed chow or high-fat diets (HFD), in conjunction with deletion of Atg7 for the last 3 weeks (short-term model) or 9 weeks (long-term model). Standard in vivo metabolic phenotyping was undertaken, and 450 lipid species in islets quantified ex vivo using mass spectroscopy (MS). MIN6 cells were also employed for lipidomics and secretory interventions. RESULTS: ß-cell function was impaired by inhibiting autophagy in the longer-term, but conversely improved by 3-week deletion of Atg7, specifically under HFD conditions. This was accompanied by augmented GSIS ex vivo. Surprisingly, the HFD had minimal effect on sphingolipid and neutral lipid species, but modulated >100 phospholipids and ether lipids, and markedly shifted the profile of polyunsaturated fatty acid (PUFA) sidechains from n3 to n6 forms. These changes were partially countered by Atg7 deletion, consistent with an accompanying upregulation of the PUFA elongase enzyme, Elovl5. Loss of Atg7 separately augmented plasmalogens and alkyl lipids, in association with increased expression of Lonp2, a peroxisomal chaperone/protease that facilitates maturation of ether lipid synthetic enzymes. Depletion of PUFAs and ether lipids was also observed in MIN6 cells chronically exposed to oleate (more so than palmitate). GSIS was inhibited by knocking down Dhrs7b, which encodes an enzyme of peroxisomal ether lipid synthesis. Conversely, impaired GSIS due to oleate pre-treatment was selectively reverted by Dhrs7b overexpression. CONCLUSIONS: A detrimental increase in n6:n3 PUFA ratios in ether lipids and phospholipids is revealed as a major response of ß-cells to high-fat feeding. This is partially reversed by short-term inhibition of autophagy, which results in compensatory changes in peroxisomal lipid metabolism. The short-term phenotype is linked to improved GSIS, in contrast to the impairment seen with the longer-term inhibition of autophagy. The balance between these positive and negative inputs could help determine whether ß-cells adapt or fail in response to obesity.

Inter-organelle Communication in the Pathogenesis of Mitochondrial Dysfunction and Insulin Resistance.

PURPOSE OF REVIEW: Impairments in mitochondrial function in patients with insulin resistance and type 2 diabetes have been disputed for decades. This review aims to briefly summarize the current knowledge on mitochondrial dysfunction in metabolic tissues and to particularly focus on addressing a new perspective of mitochondrial dysfunction, the altered capacity of mitochondria to communicate with other organelles within insulin-resistant tissues. RECENT FINDINGS: Organelle interactions are temporally and spatially formed connections essential for normal cell function. Recent studies have shown that mitochondria interact with various cellular organelles, such as the endoplasmic reticulum, lysosomes and lipid droplets, forming inter-organelle junctions. We will discuss the current knowledge on alterations in these mitochondria-organelle interactions in insulin resistance and diabetes, with a focus on changes in mitochondria-lipid droplet communication as a major player in ectopic lipid accumulation, lipotoxicity and insulin resistance.

Peroxisome Elevation Induces Stem Cell Differentiation and Intestinal Epithelial Repair.

Epithelial-repair-dependent mucosal healing (MH) is associated with a more favorable prognosis for patients with inflammatory bowel disease (IBD). MH is accomplished via repair and regeneration of the intestinal epithelium. However, the mechanism underlying MH is ill defined. We found a striking upregulation of peroxisomes in the injured crypts of IBD patients. By increasing peroxisome levels in Drosophila midguts, we found that peroxisome elevation enhanced RAB7-dependent late endosome maturation, which then promoted stem and/or progenitor-cell differentiation via modulation of Janus Kinase (JAK) and Signal Transducer and Activator of Transcription (STAT)-SOX21A signaling. This in turn enhanced ISC-mediated regeneration. Importantly, RAB7 and SOX21 were upregulated in the crypts of IBD patients. Moreover, administration of drugs that increased peroxisome levels reversed the symptoms of dextran sulfate sodium (DSS)-induced colitis in mice. This study demonstrates a peroxisome-mediated epithelial repair mechanism, which opens a therapeutic avenue for the enhancement of MH in IBD patients.

Peroxisomes: versatile organelles with diverse roles in plants.

Peroxisomes are small, ubiquitous organelles that are delimited by a single membrane and lack genetic material. However, these simple-structured organelles are highly versatile in morphology, abundance and protein content in response to various developmental and environmental cues. In plants, peroxisomes are essential for growth and development and perform diverse metabolic functions, many of which are carried out coordinately by peroxisomes and other organelles physically interacting with peroxisomes. Recent studies have added greatly to our knowledge of peroxisomes, addressing areas such as the diverse proteome, regulation of division and protein import, pexophagy, matrix protein degradation, solute transport, signaling, redox homeostasis and various metabolic and physiological functions. This review summarizes our current understanding of plant peroxisomes, focusing on recent discoveries. Current problems and future efforts required to better understand these organelles are also discussed. An improved understanding of peroxisomes will be important not only to the understanding of eukaryotic cell biology and metabolism, but also to agricultural efforts aimed at improving crop performance and defense.

Staying in Healthy Contact: How Peroxisomes Interact with Other Cell Organelles.

Peroxisomes share extensive metabolic connections with other cell organelles. Membrane contact sites (MCSs) establish and maintain such interactions, and they are vital for organelle positioning and motility. In the past few years peroxisome interactions and MCSs with other cellular organelles have been explored extensively, resulting in the identification of new MCSs, the tethering molecules involved, and their functional characterization. Defective tethering and compartmental communication can lead to pathological conditions that can be termed 'organelle interaction diseases'. We review peroxisome-organelle interactions in mammals and summarize the most recent knowledge of mammalian peroxisomal organelle contacts in health and disease.

Peroxisome Maintenance Depends on De Novo Peroxisome Formation in Yeast Mutants Defective in Peroxisome Fission and Inheritance.

There is an ongoing debate on how peroxisomes form: by growth and fission of pre-existing peroxisomes or de novo from another membrane. It has been proposed that, in wild type yeast cells, peroxisome fission and careful segregation of the organelles over mother cells and buds is essential for organelle maintenance. Using live cell imaging we observed that cells of the yeast Hansenula polymorpha, lacking the peroxisome fission protein Pex11, still show peroxisome fission and inheritance. Also, in cells of mutants without the peroxisome inheritance protein Inp2 peroxisome segregation can still occur. In contrast, peroxisome fission and inheritance were not observed in cells of a pex11 inp2 double deletion strain. In buds of cells of this double mutant, new organelles likely appear de novo. Growth of pex11 inp2 cells on methanol, a growth substrate that requires functional peroxisomes, is retarded relative to the wild type control. Based on these observations we conclude that in H. polymorpha de novo peroxisome formation is a rescue mechanism, which is less efficient than organelle fission and inheritance to maintain functional peroxisomes.

Peroxisome Plasticity at the Virus-Host Interface.

Peroxisomes are multifunctional organelles with roles in cellular metabolism, cytotoxicity, and signaling. The plastic nature of these organelles allows them to respond to diverse biological processes, such as virus infections, by remodeling their biogenesis, morphology, and composition to enhance specific functions. During virus infections in humans, peroxisomes act as important immune signaling organelles, aiding the host by orchestrating antiviral signaling. However, more recently it was discovered that peroxisomes can also benefit the virus, facilitating virus-host interactions that rewire peroxisomes to support cellular processes for virus replication and spread. Here, we describe recent studies that uncovered this double-edged character of peroxisomes during infection, highlighting mechanisms that viruses have coevolved to take advantage of peroxisome plasticity. We also provide a perspective for future studies by comparing the established roles of peroxisomes in plant infections and discussing the promise of virology studies as a venue to reveal the uncharted biology of peroxisomes.

Diverse Cellular Roles of Autophagy.

Macroautophagy is an intracellular degradation system that delivers diverse cytoplasmic materials to lysosomes via autophagosomes. Recent advances have enabled identification of several selective autophagy substrates and receptors, greatly expanding our understanding of the cellular functions of autophagy. In this review, we describe the diverse cellular functions of macroautophagy, including its essential contribution to metabolic adaptation and cellular homeostasis. We also discuss emerging findings on the mechanisms and functions of various types of selective autophagy.

Molecular and phenotypic responses of male crucian carp (Carassius auratus) exposed to perfluorooctanoic acid.

Perfluorooctanoic acid (PFOA) has long been produced and widely used due to its excellent water and oil repellent properties. However, this trend has facilitated to the ubiquitous existence of PFOA in environmental matrix, and the potential ecotoxicity on aquatic organisms has not been fully elucidated. To study the tissue-specific bioconcentration and the nervous system- and energy-related biochemical effects of PFOA, as well as the phenotypic alterations by this chemical, male crucian carp (Carassius auratus) were exposed to gradient concentrations of PFOA (nominal 0.2, 10, 500 and 25,000 µg/L) in a flow-through apparatus for 7 days. PFOA was enriched in tissues following an order of blood > kidney ≥ liver > gill > brain > muscle. The bioconcentration factors ranged from 0.1 to 60.4. Acetylcholinesterase activity in the fish brain was inhibited, while liver carboxylesterase was induced in most cases and attenuated with time. The acyl-CoA oxidase activity was dose-dependently elevated and accompanied by a decline of ATP contents. PFOA treatments also inhibited the activity of the electron transport system (ETS). At the transcriptional level, ETS component complexes II and IV were concordantly depressed, and ATP synthesis was also downregulated. The mRNA level of peroxisome proliferator activated receptor α was increasingly upregulated, with related downstream genes upregulated in varying degrees. The phenotypes showed patterns of increased liver pathology and reduced swimming activity. In summary, PFOA leads to adverse effects in Carassius auratus related to multiple aspects, which may be associated with the nervous system, fundamental energy metabolism and other unpredictable factors. The results obtained in this study are expected to help clarify the PFOA toxic mechanisms on energy relevance.

Peroxisome development in yeast is associated with the formation of Pex3-dependent peroxisome-vacuole contact sites.

Using electron and fluorescence microscopy techniques, we identified various physical contacts between peroxisomes and other cell organelles in the yeast Hansenula polymorpha. In exponential glucose-grown cells, which typically contain a single small peroxisome, contacts were only observed with the endoplasmic reticulum and the plasma membrane. Here we focus on a novel peroxisome-vacuole contact site that is formed when glucose-grown cells are shifted to methanol containing media, conditions that induce strong peroxisome development. At these conditions, the small peroxisomes rapidly increase in size, a phenomenon that is paralleled by the formation of distinct intimate contacts with the vacuole. Localization studies showed that the peroxin Pex3 accumulated in patches at the peroxisome-vacuole contact sites. In wild-type cells growing exponentially on medium containing glucose, peroxisome-vacuole contact sites were never observed. However, upon overproduction of Pex3 peroxisomes also associated to vacuoles at these growth conditions. Our observations strongly suggest a role for Pex3 in the formation of a novel peroxisome-vacuole contact site. This contact likely plays a role in membrane growth as it is formed solely at conditions of strong peroxisome expansion.