PEX11 promotes peroxisome division independently of peroxisome metabolism

Peroxisomal homeostasis in metabolic diseases and its implication in ferroptosis

Peroxisomes are dynamic organelles involved in various cellular processes, including lipid metabolism, redox homeostasis, and intracellular metabolite transfer. Accumulating evidence suggests that peroxisomal homeostasis plays a crucial role in human health and disease, particularly in metabolic disorders and ferroptosis. The abundance and function of peroxisomes are regulated by a complex interplay between biogenesis and degradation pathways, involving peroxins, membrane proteins, and pexophagy. Peroxisome-dependent lipid metabolism, especially the synthesis of ether-linked phospholipids, has been implicated in modulating cellular susceptibility to ferroptosis, a newly discovered form of iron-dependent cell death. This review discusses the current understanding of peroxisome homeostasis, its roles in redox regulation and lipid metabolism, and its implications in human diseases. We also summarize the main mechanisms of ferroptosis and highlight recent discoveries on how peroxisome-dependent metabolism and signaling influence ferroptosis sensitivity. A better understanding of the interplay between peroxisomal homeostasis and ferroptosis may provide new insights into disease pathogenesis and reveal novel therapeutic strategies for peroxisome-related metabolic disorders and ferroptosis-associated diseases.

Type I arginine methyltransferases play crucial roles in development and pathogenesis of Phytophthora capsici

Phytophthora capsici, a pathogenic oomycete, poses a serious threat to global vegetable production. This study investigated the role of protein arginine methylation, a notable post-translational modification, in the epigenetic regulation of P. capsici. We identified and characterized five protein arginine methyltransferases (PRMTs) in P. capsici, with a focus on four putative type I PRMTs exhibiting similar functional domain. Deletion of PcPRMT3, a homolog of PRMT3, significantly affected mycelial growth, asexual spore development, pathogenicity, and stress responses in P. capsici. Transcriptome analyses indicated that absence of PcPRMT3 disrupted multiple biological pathways. The PcPRMT3 deletion mutant displayed heightened susceptibility to oxidative stress, correlated with the downregulation of genes involved in peroxidase and peroxisome activities. Additionally, PcPRMT3 acted as a negative regulator, modulating the transcription levels of specific elicitins, which in turn affects the defense response of host plant against P. capsici. Furthermore, PcPRMT3 was found to affect global arginine methylation levels in P. capsici, implying potential alterations in the functions of its substrate proteins.

Nanobodies as novel tools to monitor the mitochondrial fission factor Drp1

In cells, mitochondria undergo constant fusion and fission. An essential factor for fission is the mammalian dynamin-related protein 1 (Drp1). Dysregulation of Drp1 is associated with neurodegenerative diseases including Parkinson's, cardiovascular diseases and cancer, making Drp1 a pivotal biomarker for monitoring mitochondrial status and potential pathophysiological conditions. Here, we developed nanobodies (Nbs) as versatile binding molecules for proteomics, advanced microscopy and live cell imaging of Drp1. To specifically enrich endogenous Drp1 with interacting proteins for proteomics, we functionalized high-affinity Nbs into advanced capture matrices. Furthermore, we detected Drp1 by bivalent Nbs combined with site-directed fluorophore labelling in super-resolution STORM microscopy. For real-time imaging of Drp1, we intracellularly expressed fluorescently labelled Nbs, so-called chromobodies (Cbs). To improve the signal-to-noise ratio, we further converted Cbs into a "turnover-accelerated" format. With these imaging probes, we visualized the dynamics of endogenous Drp1 upon compound-induced mitochondrial fission in living cells. Considering the wide range of research applications, the presented Nb toolset will open up new possibilities for advanced functional studies of Drp1 in disease-relevant models.

Megraw T, Ghaedi K. PPARgamma dependent PEX11beta counteracts the suppressive role of SIRT1 on neural differentiation of HESCs

The membrane peroxisomal proteins PEX11, play a crucial role in peroxisome proliferation by regulating elongation, membrane constriction, and fission of pre-existing peroxisomes. In this study, we evaluated the function of PEX11B gene in neural differentiation of human embryonic stem cell (hESC) by inducing shRNAi-mediated knockdown of PEX11B expression. Our results demonstrate that loss of PEX11B expression led to a significant decrease in the expression of peroxisomal-related genes including ACOX1, PMP70, PEX1, and PEX7, as well as neural tube-like structures and neuronal markers. Inhibition of SIRT1 using pharmacological agents counteracted the effects of PEX11B knockdown, resulting in a relative increase in PEX11B expression and an increase in differentiated neural tube-like structures. However, the neuroprotective effects of SIRT1 were eliminated by PPAR inhibition, indicating that PPARɣ may mediate the interaction between PEX11B and SIRT1. Our findings suggest that both SIRT1 and PPARɣ have neuroprotective effects, and also this study provides the first indication for a potential interaction between PEX11B, SIRT1, and PPARɣ during hESC neural differentiation.

An adaptive stress response that confers cellular resilience to decreased ubiquitination

Ubiquitination is a post-translational modification initiated by the E1 enzyme UBA1, which transfers ubiquitin to ~35 E2 ubiquitin-conjugating enzymes. While UBA1 loss is cell lethal, it remains unknown how partial reduction in UBA1 activity is endured. Here, we utilize deep-coverage mass spectrometry to define the E1-E2 interactome and to determine the proteins that are modulated by knockdown of UBA1 and of each E2 in human cells. These analyses define the UBA1/E2-sensitive proteome and the E2 specificity in protein modulation. Interestingly, profound adaptations in peroxisomes and other organelles are triggered by decreased ubiquitination. While the cargo receptor PEX5 depends on its mono-ubiquitination for binding to peroxisomal proteins and importing them into peroxisomes, we find that UBA1/E2 knockdown induces the compensatory upregulation of other PEX proteins necessary for PEX5 docking to the peroxisomal membrane. Altogether, this study defines a homeostatic mechanism that sustains peroxisomal protein import in cells with decreased ubiquitination capacity.

Peroxisomal compartmentalization of amino acid biosynthesis reactions imposes an upper limit on compartment size

Cellular metabolism relies on just a few redox cofactors. Selective compartmentalization may prevent competition between metabolic reactions requiring the same cofactor. Is such compartmentalization necessary for optimal cell function? Is there an optimal compartment size? Here we probe these fundamental questions using peroxisomal compartmentalization of the last steps of lysine and histidine biosynthesis in the fission yeast Schizosaccharomyces japonicus. We show that compartmentalization of these NAD+ dependent reactions together with a dedicated NADH/NAD+ recycling enzyme supports optimal growth when an increased demand for anabolic reactions taxes cellular redox balance. In turn, compartmentalization constrains the size of individual organelles, with larger peroxisomes accumulating all the required enzymes but unable to support both biosynthetic reactions at the same time. Our reengineering and physiological experiments indicate that compartmentalized biosynthetic reactions are sensitive to the size of the compartment, likely due to scaling-dependent changes within the system, such as enzyme packing density.

Histoplasma capsulatum requires peroxisomes for multiple virulence functions including siderophore biosynthesis

Peroxisomes are versatile eukaryotic organelles essential for many functions in fungi, including fatty acid metabolism, reactive oxygen species detoxification, and secondary metabolite biosynthesis. A suite of Pex proteins (peroxins) maintains peroxisomes, while peroxisomal matrix enzymes execute peroxisome functions. Insertional mutagenesis identified peroxin genes as essential components supporting the intraphagosomal growth of the fungal pathogen Histoplasma capsulatum. Disruption of the peroxins Pex5, Pex10, or Pex33 in H. capsulatum prevented peroxisome import of proteins targeted to the organelle via the PTS1 pathway. This loss of peroxisome protein import limited H. capsulatum intracellular growth in macrophages and attenuated virulence in an acute histoplasmosis infection model. Interruption of the alternate PTS2 import pathway also attenuated H. capsulatum virulence, although only at later time points of infection. The Sid1 and Sid3 siderophore biosynthesis proteins contain a PTS1 peroxisome import signal and localize to the H. capsulatum peroxisome. Loss of either the PTS1 or PTS2 peroxisome import pathway impaired siderophore production and iron acquisition in H. capsulatum, demonstrating compartmentalization of at least some biosynthetic steps for hydroxamate siderophore biosynthesis. However, the loss of PTS1-based peroxisome import caused earlier virulence attenuation than either the loss of PTS2-based protein import or the loss of siderophore biosynthesis, indicating additional PTS1-dependent peroxisomal functions are important for H. capsulatum virulence. Furthermore, disruption of the Pex11 peroxin also attenuated H. capsulatum virulence independently of peroxisomal protein import and siderophore biosynthesis. These findings demonstrate peroxisomes contribute to H. capsulatum pathogenesis by facilitating siderophore biosynthesis and another unidentified role(s) for the organelle during fungal virulence. IMPORTANCE The fungal pathogen Histoplasma capsulatum infects host phagocytes and establishes a replication-permissive niche within the cells. To do so, H. capsulatum overcomes and subverts antifungal defense mechanisms which include the limitation of essential micronutrients. H. capsulatum replication within host cells requires multiple distinct functions of the fungal peroxisome organelle. These peroxisomal functions contribute to H. capsulatum pathogenesis at different times during infection and include peroxisome-dependent biosynthesis of iron-scavenging siderophores to enable fungal proliferation, particularly after activation of cell-mediated immunity. The multiple essential roles of fungal peroxisomes reveal this organelle as a potential but untapped target for the development of therapeutics.

Molecular basis of the glycosomal targeting of PEX11 and its mislocalization to mitochondrion in trypanosomes

PEX19 binding sites are essential parts of the targeting signals of peroxisomal membrane proteins (mPTS). In this study, we characterized PEX19 binding sites of PEX11, the most abundant peroxisomal and glycosomal membrane protein from Trypanosoma brucei and Saccharomyces cerevisiae. TbPEX11 contains two PEX19 binding sites, one close to the N-terminus (BS1) and a second in proximity to the first transmembrane domain (BS2). The N-terminal BS1 is highly conserved across different organisms and is required for maintenance of the steady-state concentration and efficient targeting to peroxisomes and glycosomes in both baker's yeast and Trypanosoma brucei. The second PEX19 binding site in TbPEX11 is essential for its glycosomal localization. Deletion or mutations of the PEX19 binding sites in TbPEX11 or ScPEX11 results in mislocalization of the proteins to mitochondria. Bioinformatic analysis indicates that the N-terminal region of TbPEX11 contains an amphiphilic helix and several putative TOM20 recognition motifs. We show that the extreme N-terminal region of TbPEX11 contains a cryptic N-terminal signal that directs PEX11 to the mitochondrion if its glycosomal transport is blocked.

Genetic defects in peroxisome morphogenesis (Pex11β, dynamin-like protein 1, and nucleoside diphosphate kinase 3) affect docosahexaenoic acid-phospholipid metabolism

Peroxisomes are essential organelles involved in lipid metabolisms including plasmalogen biosynthesis and β-oxidation of very long-chain fatty acids. Peroxisomes proliferate by the growth and division of pre-existing peroxisomes. The peroxisomal membrane is elongated by Pex11β and then divided by the dynamin-like GTPase, DLP1 (also known as DRP1 encoded by DNM1L gene), which also functions as a fission factor for mitochondria. Nucleoside diphosphate kinase 3 (NME3) localized in both peroxisomes and mitochondria generates GTP for DLP1 activity. Deficiencies of either of these factors induce abnormal morphology of peroxisomes and/or mitochondria, and are associated with central nervous system dysfunction. To investigate whether the impaired division of peroxisomes affects lipid metabolisms, we assessed the phospholipid composition of cells lacking each of the different division factors. In fibroblasts from the patients deficient in DLP1, NME3, or Pex11β, docosahexaenoic acid (DHA, C22:6)-containing phospholipids were found to be decreased. Conversely, the levels of several fatty acids such as arachidonic acid (AA, C20:4) and oleic acid (C18:1) were elevated. Mouse embryonic fibroblasts from Drp1- and Pex11β-knockout mice also showed a decrease in the levels of phospholipids containing DHA and AA. Collectively, these results suggest that the dynamics of organelle morphology exert marked effects on the fatty acid composition of phospholipids.

Peroxisomes Are Highly Abundant and Heterogeneous in Human Parotid Glands

The parotid gland is one of the major salivary glands producing a serous secretion, and it plays an essential role in the digestive and immune systems. Knowledge of peroxisomes in the human parotid gland is minimal; furthermore, the peroxisomal compartment and its enzyme composition in the different cell types of the human parotid gland have never been subjected to a detailed investigation. Therefore, we performed a comprehensive analysis of peroxisomes in the human parotid gland's striated duct and acinar cells. We combined biochemical techniques with various light and electron microscopy techniques to determine the localization of parotid secretory proteins and different peroxisomal marker proteins in parotid gland tissue. Moreover, we analyzed the mRNA of numerous gene encoding proteins localized in peroxisomes using real-time quantitative PCR. The results confirm the presence of peroxisomes in all striated duct and acinar cells of the human parotid gland. Immunofluorescence analyses for various peroxisomal proteins showed a higher abundance and more intense staining in striated duct cells compared to acinar cells. Moreover, human parotid glands comprise high quantities of catalase and other antioxidative enzymes in discrete subcellular regions, suggesting their role in protection against oxidative stress. This study provides the first thorough description of parotid peroxisomes in different parotid cell types of healthy human tissue.

DRP1 mutations associated with EMPF1 encephalopathy alter mitochondrial membrane potential and metabolic programs

Mitochondria and peroxisomes are dynamic signaling organelles that constantly undergo fission, driven by the large GTPase dynamin-related protein 1 (DRP1; encoded by DNM1L). Patients with de novo heterozygous missense mutations in DNM1L present with encephalopathy due to defective mitochondrial and peroxisomal fission (EMPF1) - a devastating neurodevelopmental disease with no effective treatment. To interrogate the mechanisms by which DRP1 mutations cause cellular dysfunction, we used human-derived fibroblasts from patients who present with EMPF1. In addition to elongated mitochondrial morphology and lack of fission, patient cells display lower coupling efficiency, increased proton leak and upregulation of glycolysis. Mitochondrial hyperfusion also results in aberrant cristae structure and hyperpolarized mitochondrial membrane potential. Peroxisomes show a severely elongated morphology in patient cells, which is associated with reduced respiration when cells are reliant on fatty acid oxidation. Metabolomic analyses revealed impaired methionine cycle and synthesis of pyrimidine nucleotides. Our study provides insight into the role of mitochondrial dynamics in cristae maintenance and the metabolic capacity of the cell, as well as the disease mechanism underlying EMPF1.

Molecular insights into peroxisome homeostasis and peroxisome biogenesis disorders

Peroxisomes are single-membrane organelles essential for cell metabolism including the β-oxidation of fatty acids, synthesis of etherlipid plasmalogens, and redox homeostasis. Investigations into peroxisome biogenesis and the human peroxisome biogenesis disorders (PBDs) have identified 14 PEX genes encoding peroxins involved in peroxisome biogenesis and the mutation of PEX genes is responsible for the PBDs. Many recent findings have further advanced our understanding of the biology, physiology, and consequences of a functional deficit of peroxisomes. In this Review, we discuss cell defense mechanisms that counteract oxidative stress by 1) a proapoptotic Bcl-2 factor BAK-mediated release to the cytosol of H₂O₂-degrading catalase from peroxisomes and 2) peroxisomal import suppression of catalase by Ser232-phosphorylation of Pex14, a docking protein for the Pex5-PTS1 complex. With respect to peroxisome division, the important issue of how the energy-rich GTP is produced and supplied for the division process was recently addressed by the discovery of a nucleoside diphosphate kinase-like protein, termed DYNAMO1 in a lower eukaryote, which has a mammalian homologue NME3. In regard to the mechanisms underlying the pathogenesis of PBDs, a new PBD model mouse defective in Pex14 manifests a dysregulated brain-derived neurotrophic factor (BDNF)-TrkB pathway, an important signaling pathway for cerebellar morphogenesis. Communications between peroxisomes and other organelles are also addressed.

Peroxisomal Fitness: A Potential Protective Mechanism of Fenofibrate against High Fat Diet-Induced Non-Alcoholic Fatty Liver Disease in Mice

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) has been increasing in association with the epidemic of obesity and diabetes. Peroxisomes are single membrane-enclosed organelles that play a role in the metabolism of lipid and reactive oxygen species. The present study examined the role of peroxisomes in high-fat diet (HFD)-induced NAFLD using fenofibrate, a peroxisome proliferator-activated receptor α (PPARα) agonist.

METHODS

Eight-week-old male C57BL/6J mice were fed either a normal diet or HFD for 12 weeks, and fenofibrate (50 mg/kg/day) was orally administered along with the initiation of HFD.

RESULTS

HFD-induced liver injury as measured by increased alanine aminotransferase, inflammation, oxidative stress, and lipid accumulation was effectively prevented by fenofibrate. Fenofibrate significantly increased the expression of peroxisomal genes and proteins involved in peroxisomal biogenesis and function. HFD-induced attenuation of peroxisomal fatty acid oxidation was also significantly restored by fenofibrate, demonstrating the functional significance of peroxisomal fatty acid oxidation. In Ppara deficient mice, fenofibrate failed to maintain peroxisomal biogenesis and function in HFD-induced liver injury.

CONCLUSION

The present data highlight the importance of PPARα-mediated peroxisomal fitness in the protective effect of fenofibrate against NAFLD.

A sphingolipid-mTORC1 nutrient-sensing pathway regulates animal development by an intestinal peroxisome relocation-based gut-brain crosstalk

The mTOR-dependent nutrient-sensing and response machinery is the central hub for animals to regulate their cellular and developmental programs. However, equivalently pivotal nutrient and metabolite signals upstream of mTOR and developmental-regulatory signals downstream of mTOR are not clear, especially at the organism level. We previously showed glucosylceramide (GlcCer) acts as a critical nutrient and metabolite signal for overall amino acid levels to promote development by activating the intestinal mTORC1 signaling pathway. Here, through a large-scale genetic screen, we find that the intestinal peroxisome is critical for antagonizing the GlcCer-mTORC1-mediated nutrient signal. Mechanistically, GlcCer deficiency, inactive mTORC1, or prolonged starvation relocates intestinal peroxisomes closer to the apical region in a kinesin- and microtubule-dependent manner. Those apical accumulated peroxisomes further release peroxisomal-β-oxidation-derived glycolipid hormones that target chemosensory neurons and downstream nuclear hormone receptor DAF-12 to arrest the animal development. Our data illustrate a sophisticated gut-brain axis that predominantly orchestrates nutrient-sensing-dependent development in animals.

Recognition and Chaperoning by Pex19, Followed by Trafficking and Membrane Insertion of the Peroxisome Proliferation Protein, Pex11

Pex11, an abundant peroxisomal membrane protein (PMP), is required for division of peroxisomes and is robustly imported to peroxisomal membranes. We present a comprehensive analysis of how the Pichia pastoris Pex11 is recognized and chaperoned by Pex19, targeted to peroxisome membranes and inserted therein. We demonstrate that Pex11 contains one Pex19-binding site (Pex19-BS) that is required for Pex11 insertion into peroxisomal membranes by Pex19, but is non-essential for peroxisomal trafficking. We provide extensive mutational analyses regarding the recognition of Pex19-BS in Pex11 by Pex19. Pex11 also has a second, Pex19-independent membrane peroxisome-targeting signal (mPTS) that is preserved among Pex11-family proteins and anchors the human HsPex11γ to the outer leaflet of the peroxisomal membrane. Thus, unlike most PMPs, Pex11 can use two mechanisms of transport to peroxisomes, where only one of them depends on its direct interaction with Pex19, but the other does not. However, Pex19 is necessary for membrane insertion of Pex11. We show that Pex11 can self-interact, using both homo- and/or heterotypic interactions involving its N-terminal helical domains. We demonstrate that Pex19 acts as a chaperone by interacting with the Pex19-BS in Pex11, thereby protecting Pex11 from spontaneous oligomerization that would otherwise cause its aggregation and subsequent degradation.

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 Pex11β 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.

Peroxisomes in the mouse parotid glands: An in-depth morphological and molecular analysis

BACKGROUND

The parotid gland is a major salivary gland that has important roles in the digestive and immune system. Peroxisomes are ubiquitous, single-membrane-bound organelles that are present in all eukaryotic cells. Peroxisomes help mediate lipid and reactive oxygen species metabolism, as well as polyunsaturated fatty acid, cholesterol and plasmalogen synthesis. Much of the knowledge on peroxisomes has derived from metabolic organs, however no detailed knowledge is available on peroxisomes in the parotid glands. We thus aimed to comprehensively delineate the localization and characterization of peroxisomal proteins in the murine parotid gland.

METHODS

We characterized peroxisomes in the acinar and striated duct cells of the murine parotid gland by fluorescence and electron microscopy, as well as protein and mRNA expression analyses for important peroxisomal genes and proteins.

RESULTS

We found that peroxisomes are present in all cell types of the mouse parotid gland, however, exhibit notable cell-specific differences in their abundance and enzyme content. We also observed that mouse parotid glands contain high levels of peroxisomal β-oxidation enzymes (including Acox1, Mfp2 and Acaa1), catalase and other peroxisomal anti-oxidative enzymes.

CONCLUSIONS

This data suggests that peroxisomes are highly abundant in the murine parotid gland and might help to protect against oxidative stress. This comprehensive description of peroxisomes in the parotid gland lays the groundwork for further research concerning their role in the pathogenesis of parotid gland diseases and tumors.

Comparative Genomics of Peroxisome Biogenesis Proteins: Making Sense of the PEX Proteins

PEX genes encode proteins involved in peroxisome biogenesis and proliferation. Using a comparative genomics approach, we clarify the evolutionary relationships between the 37 known PEX proteins in a representative set of eukaryotes, including all common model organisms, pathogenic unicellular eukaryotes and human. A large number of previously unknown PEX orthologs were identified. We analyzed all PEX proteins, their conservation and domain architecture and defined the core set of PEX proteins that is required to make a peroxisome. The molecular processes in peroxisome biogenesis in different organisms were put into context, showing that peroxisomes are not static organelles in eukaryotic evolution. Organisms that lack peroxisomes still contain a few PEX proteins, which probably play a role in alternative processes. Finally, the relationships between PEX proteins of two large families, the Pex11 and Pex23 families, were analyzed, thereby contributing to the understanding of their complicated and sometimes incorrect nomenclature. We provide an exhaustive overview of this important eukaryotic organelle.

Peroxisomes and pancreatic beta-cell lipo-dysfunction

AIMS

Pancreatic beta-cell lipo-dysfunction decreases insulin secretion and predisposes to the development of type 2 diabetes. Through targeted Pex11β knockdown and peroxisome depletion, our aim was to investigate the specific contribution of peroxisomes to palmitate mediated pancreatic beta-cell dysfunction.

METHODS

MIN6 cells were transfected with probes targeted against Pex11β, a regulator of peroxisome abundance, or with scrambled control probes. Peroxisome abundance was measured by PMP-70 protein expression. 48 h post transfection, cells were incubated with 250 μM palmitate or BSA control for a further 48 h before measurement of glucose stimulated insulin secretion and of reactive oxygen species.

RESULTS

Pex11β knockdown decreased target gene expression by >80% compared with the scrambled control (P<0.001). This led to decreased PMP-70 expression (p<0.01) and a 22% decrease in peroxisome number (p<0.05). At 25 mM glucose, palmitate treatment decreased insulin secretion by 64% in the scrambled control cells (2.54±0.25 vs 7.07±0.83 [mean±SEM] ng/h/μg protein; Palmitate vs BSA P<0.001), but by just 37% in the Pex11β knockdown cells. Comparing responses in the presence of palmitate, insulin secretion at 25 mM glucose was significantly greater in the Pex11β knockdown cells compared with the scrambled controls (4.04±0.46 vs 2.54±0.25 ng/h/μg protein; p<0.05). Reactive oxygen species generation with palmitate was lower in the Pex11β knockdown cells compared with the scrambled controls (P<0.001).

CONCLUSION

Pex11β knockdown decreased peroxisome abundance, decreased palmitate mediated reactive oxygen species generation, and reversed the inhibitory effect of palmitate on insulin secretion. These findings reveal a distinct role of peroxisomes in palmitate mediated beta-cell dysfunction.

Mammalian Homologue NME3 of DYNAMO1 Regulates Peroxisome Division

Peroxisomes proliferate by sequential processes comprising elongation, constriction, and scission of peroxisomal membrane. It is known that the constriction step is mediated by a GTPase named dynamin-like protein 1 (DLP1) upon efficient loading of GTP. However, mechanism of fuelling GTP to DLP1 remains unknown in mammals. We earlier show that nucleoside diphosphate (NDP) kinase-like protein, termed dynamin-based ring motive-force organizer 1 (DYNAMO1), generates GTP for DLP1 in a red alga, Cyanidioschyzon merolae. In the present study, we identified that nucleoside diphosphate kinase 3 (NME3), a mammalian homologue of DYNAMO1, localizes to peroxisomes. Elongated peroxisomes were observed in cells with suppressed expression of NME3 and fibroblasts from a patient lacking NME3 due to the homozygous mutation at the initiation codon of NME3. Peroxisomes proliferated by elevation of NME3 upon silencing the expression of ATPase family AAA domain containing 1, ATAD1. In the wild-type cells expressing catalytically-inactive NME3, peroxisomes were elongated. These results suggest that NME3 plays an important role in peroxisome division in a manner dependent on its NDP kinase activity. Moreover, the impairment of peroxisome division reduces the level of ether-linked glycerophospholipids, ethanolamine plasmalogens, implying the physiological importance of regulation of peroxisome morphology.

Molecular Basis of Mitochondrial and Peroxisomal Division Machineries

Mitochondria and peroxisomes are ubiquitous subcellular organelles that are highly dynamic and possess a high degree of plasticity. These organelles proliferate through division of pre-existing organelles. Studies on yeast, mammalian cells, and unicellular algae have led to a surprising finding that mitochondria and peroxisomes share the components of their division machineries. At the heart of the mitochondrial and peroxisomal division machineries is a GTPase dynamin-like protein, Dnm1/Drp1, which forms a contractile ring around the neck of the dividing organelles. During division, Dnm1/Drp1 functions as a motor protein and constricts the membrane. This mechanochemical work is achieved by utilizing energy from GTP hydrolysis. Over the last two decades, studies have focused on the structure and assembly of Dnm1/Drp1 molecules around the neck. However, the regulation of GTP during the division of mitochondrion and peroxisome is not well understood. Here, we review the current understanding of Dnm1/Drp1-mediated divisions of mitochondria and peroxisomes, exploring the mechanisms of GTP regulation during the Dnm1/Drp1 function, and provide new perspectives on their potential contribution to mitochondrial and peroxisomal biogenesis.

Recent insights into peroxisome biogenesis and associated diseases

Peroxisomes are single-membrane organelles present in eukaryotes. The functional importance of peroxisomes in humans is represented by peroxisome-deficient peroxisome biogenesis disorders (PBDs), including Zellweger syndrome. Defects in the genes that encode the 14 peroxins that are required for peroxisomal membrane assembly, matrix protein import and division have been identified in PBDs. A number of recent findings have advanced our understanding of the biology, physiology and consequences of functional defects in peroxisomes. In this Review, we discuss a cooperative cell defense mechanisms against oxidative stress that involves the localization of BAK (also known as BAK1) to peroxisomes, which alters peroxisomal membrane permeability, resulting in the export of catalase, a peroxisomal enzyme. Another important recent finding is the discovery of a nucleoside diphosphate kinase-like protein that has been shown to be essential for how the energy GTP is generated and provided for the fission of peroxisomes. With regard to PBDs, we newly identified a mild mutation, Pex26-F51L that causes only hearing loss. We will also discuss findings from a new PBD model mouse defective in Pex14, which manifested dysregulation of the BDNF-TrkB pathway, an essential signaling pathway in cerebellar morphogenesis. Here, we thus aim to provide a current view of peroxisome biogenesis and the molecular pathogenesis of PBDs.

Pex11a deficiency causes dyslipidaemia and obesity in mice

Peroxisomes play a central role in lipid metabolism. We previously demonstrated that Pex11a deficiency impairs peroxisome abundance and fatty acid β‐oxidation and results in hepatic triglyceride accumulation. The role of Pex11a in dyslipidaemia and obesity is investigated here with Pex11a knockout mice (Pex11a^−/−). Metabolic phenotypes including tissue weight, glucose tolerance, insulin sensitivity, cholesterol levels, fatty acid profile, oxygen consumption, physical activity were assessed in wild‐type (WT) and Pex11a^−/− fed with a high‐fat diet. Molecular changes and peroxisome abundance in adipose tissue were evaluated through qRT‐PCR, Western blotting, and Immunofluorescence. Pex11a^−/− showed increased fat mass, decreased skeletal muscle, higher cholesterol levels, and more severely impaired glucose and insulin tolerance. Pex11a^−/− consumed less oxygen, indicating a decrease in fatty acid oxidation, which is consistent with the accumulation of very long‐ and long‐chain fatty acids. Adipose palmitic acid (C16:0) levels were elevated in Pex11a^−/−, which may be because of dramatically increased fatty acid synthase mRNA and protein levels. Furthermore, Pex11a deficiency increased ventricle size and macrophage infiltration, which are related to the reduced physical activity. These data demonstrate that Pex11a deficiency impairs physical activity and energy expenditure, decreases fatty acid β‐oxidation, increases de novo lipogenesis and results in dyslipidaemia and obesity.

Sex-steroids and hypolipidemic chemicals impacts on brown trout lipid and peroxisome signaling - Molecular, biochemical and morphological insights

Lipid metabolism involves complex pathways, which are regulated in a similar way across vertebrates. Hormonal and hypolipidemic deregulations cause lipid imbalance from fish to humans, but the underlying mechanisms are far from understood. This study explores the potential of using juvenile brown trout to evaluate the in vivo interferences caused by estrogenic (17α-ethinylestradiol - EE2), androgenic (testosterone - T), and hypolipidemic (clofibrate - CLF) compounds in lipidic and/or peroxisomal pathways. Studied endpoints were from blood/plasma biochemistry, plasma fatty acid profile, ultrastructure of hepatocytes and abundance of their peroxisomes to mRNA expression in the liver. Both T and CLF caused minimal effects when compared to EE2. Estrogenized fish had significantly higher hepatosomatic indexes, increased triglycerides and very-low density lipoproteins (VLDL) in plasma, compared with solvent control. Morphologically, EE2 fish showed increased lipid droplets in hepatocytes, and EE2 and T reduced volume density of peroxisomes in relation to the hepatic parenchyma. Polyunsaturated fatty acids (PUFA) in plasma, namely n-3 PUFA, increased with EE2. EE2 animals had increased mRNA levels of vitellogenin A (VtgA), estrogen receptor alpha (ERα), peroxisome proliferator-activated receptor alpha (PPARα), PPARαBa and acyl-CoA long chain synthetase 1 (Acsl1), while ERβ-1, acyl-CoA oxidase 1-3I (Acox1-3I), Acox3, PPARγ, catalase (Cat), urate oxidase (Uox), fatty acid binding protein 1 (Fabp1) and apolipoprotein AI (ApoAI) were down-regulated. In summary, in vivo EE2 exposure altered lipid metabolism and peroxisome dynamics in brown trout, namely by changing the mRNA levels of several genes. Our model can be used to study possible organism-level impacts, viz. in gonadogenesis.

Genomic and Proteomic Evidence for the Presence of a Peroxisome in the Apicomplexan Parasite Toxoplasma gondii and Other Coccidia

Apicomplexans are successful parasites responsible for severe human diseases including malaria, toxoplasmosis, and cryptosporidiosis. For many years, it has been discussed whether these parasites are in possession of peroxisomes, highly variable eukaryotic organelles usually involved in fatty acid degradation and cellular detoxification. Conflicting experimental data has been published. With the age of genomics, ever more high quality apicomplexan genomes have become available, that now allow a new assessment of the dispute. Here, we provide bioinformatic evidence for the presence of peroxisomes in Toxoplasma gondii and other coccidians. For these organisms, we have identified a complete set of peroxins, probably responsible for peroxisome biogenesis, division, and protein import. Moreover, via a global screening for peroxisomal targeting signals, we were able to show that a complete set of fatty acid β-oxidation enzymes is equipped with either PTS1 or PTS2 sequences, most likely mediating transport of these factors to putative peroxisomes in all investigated Coccidia. Our results further imply a life cycle stage-specific presence of peroxisomes in T. gondii and suggest several independent losses of peroxisomes during the evolution of apicomplexan parasites.

A role for Mitochondrial Rho GTPase 1 (MIRO1) in motility and membrane dynamics of peroxisomes

Peroxisomes are dynamic organelles which fulfil essential roles in lipid and ROS metabolism. Peroxisome movement and positioning allows interaction with other organelles and is crucial for their cellular function. In mammalian cells, such movement is microtubule-dependent and mediated by kinesin and dynein motors. The mechanisms of motor recruitment to peroxisomes are largely unknown, as well as the role this plays in peroxisome membrane dynamics and proliferation. Here, using a combination of microscopy, live-cell imaging analysis and mathematical modelling, we identify a role for Mitochondrial Rho GTPase 1 (MIRO1) as an adaptor for microtubule-dependent peroxisome motility in mammalian cells. We show that MIRO1 is targeted to peroxisomes and alters their distribution and motility. Using a peroxisome-targeted MIRO1 fusion protein, we demonstrate that MIRO1-mediated pulling forces contribute to peroxisome membrane elongation and proliferation in cellular models of peroxisome disease. Our findings reveal a molecular mechanism for establishing peroxisome-motor protein associations in mammalian cells and provide new insights into peroxisome membrane dynamics in health and disease.

Kinase MPK17 and the Peroxisome Division Factor PMD1 Influence Salt-induced Peroxisome Proliferation

Peroxisomes are small organelles that house many oxidative reactions. Peroxisome proliferation is induced under multiple stress conditions, including salt stress; however, factors regulating this process are not well defined. We have identified a role for Arabidopsis (Arabidopsis thaliana) MAP KINASE17 (MPK17) in affecting peroxisome division in a manner that requires the known peroxisome division factor PEROXISOME AND MITOCHONDRIAL DIVISION FACTOR1 (PMD1). MPK17 and PMD1 are involved in peroxisome proliferation in response to NaCl stress. Additionally, we found that PMD1 is an actin-binding protein and that a functioning actin cytoskeleton is required for NaCl-induced peroxisome division. Our data suggest roles for MPK17 and PMD1 in influencing the numbers and cellular distribution of peroxisomes through the cytoskeleton-peroxisome connection. These findings expand our understanding of peroxisome division and potentially identify factors connecting the actin cytoskeleton and peroxisome proliferation.

Coupling organelle inheritance with mitosis to balance growth and differentiation

Balancing growth and differentiation is essential to tissue morphogenesis and homeostasis. How imbalances arise in disease states is poorly understood. To address this issue, we identified transcripts differentially expressed in mouse basal epidermal progenitors versus their differentiating progeny and those altered in cancers. We used an in vivo RNA interference screen to unveil candidates that altered the equilibrium between the basal proliferative layer and suprabasal differentiating layers forming the skin barrier. We found that epidermal progenitors deficient in the peroxisome-associated protein Pex11b failed to segregate peroxisomes properly and entered a mitotic delay that perturbed polarized divisions and skewed daughter fates. Together, our findings unveil a role for organelle inheritance in mitosis, spindle alignment, and the choice of daughter progenitors to differentiate or remain stem-like.

Target acquired: Selective autophagy in cardiometabolic disease

The accumulation of damaged or excess proteins and organelles is a defining feature of metabolic disease in nearly every tissue. Thus, a central challenge in maintaining metabolic homeostasis is the identification, sequestration, and degradation of these cellular components, including protein aggregates, mitochondria, peroxisomes, inflammasomes, and lipid droplets. A primary route through which this challenge is met is selective autophagy, the targeting of specific cellular cargo for autophagic compartmentalization and lysosomal degradation. In addition to its roles in degradation, selective autophagy is emerging as an integral component of inflammatory and metabolic signaling cascades. In this Review, we focus on emerging evidence and key questions about the role of selective autophagy in the cell biology and pathophysiology of metabolic diseases such as obesity, diabetes, atherosclerosis, and steatohepatitis. Essential players in these processes are the selective autophagy receptors, defined broadly as adapter proteins that both recognize cargo and target it to the autophagosome. Additional domains within these receptors may allow integration of information about autophagic flux with critical regulators of cellular metabolism and inflammation. Details regarding the precise receptors involved, such as p62 and NBR1, and their predominant interacting partners are just beginning to be defined. Overall, we anticipate that the continued study of selective autophagy will prove to be informative in understanding the pathogenesis of metabolic diseases and to provide previously unrecognized therapeutic targets.

Fis1 depletion in osteoarthritis impairs chondrocyte survival and peroxisomal and lysosomal function

Cumulative evidence suggests the importance of organelle homeostasis in regulating metabolic functions in response to various cellular stresses. Particularly, the dynamism and health of the mitochondria-peroxisome network through fission and fusion are essential for cellular function; dysfunctional dynamism underlies the pathogenesis of several degenerative diseases including Parkinson's disease. Here, we investigated the role of Fis1 in cartilage homeostasis and its relevance to osteoarthritis (OA). We found that Fis1 is significantly suppressed in human OA chondrocytes compared to that in normal chondrocytes. Fis1 depletion through siRNA induced peroxisomal dysfunction. Moreover, Fis1 suppression altered miRNA profiles, especially those implicated in lysosomal regulation. Lysosomal destruction using LAMP-1-specific targeted nanorods or lysosomal dysfunction through chloroquine treatment resulted in enhanced chondrocyte apoptosis and/or suppression of autophagy. Accordingly, lysosomal activity and autophagy were severely decreased in OA chondrocytes despite abundant LAMP-1-positive organelles. Moreover, Fis1 morpholino-injected zebrafish embryos displayed lysosome accumulation, mitochondrial dysfunction, and peroxisome reduction. Collectively, these data suggest interconnected links among Fis1-modulated miRNA, lysosomes, and autophagy, which contributes to chondrocyte survival/apoptosis. This study represents the first functional study of Fis1 with its pathological relevance to OA. Our data suggest a new target for controlling cartilage-degenerative diseases, such as OA.

KEY MESSAGE

Fis1 suppression in OA chondrocytes induces accumulation and inhibition of lysosomes. Fis1 suppression alters miRNAs, especially those implicated in lysosomal regulation. Lysosomal destruction results in chondrocyte apoptosis and suppression of autophagy. Fis1 depletion in zebrafish causes lysosome accumulation, mitochondrial dysfunction, and peroxisome reduction. This is the first functional study of Fis1 and its pathological relevance to OA.

Super-resolution Microscopy Reveals Compartmentalization of Peroxisomal Membrane Proteins

Membrane-associated events during peroxisomal protein import processes play an essential role in peroxisome functionality. Many details of these processes are not known due to missing spatial resolution of technologies capable of investigating peroxisomes directly in the cell. Here, we present the use of super-resolution optical stimulated emission depletion microscopy to investigate with sub-60-nm resolution the heterogeneous spatial organization of the peroxisomal proteins PEX5, PEX14, and PEX11 around actively importing peroxisomes, showing distinct differences between these peroxins. Moreover, imported protein sterol carrier protein 2 (SCP2) occupies only a subregion of larger peroxisomes, highlighting the heterogeneous distribution of proteins even within the peroxisome. Finally, our data reveal subpopulations of peroxisomes showing only weak colocalization between PEX14 and PEX5 or PEX11 but at the same time a clear compartmentalized organization. This compartmentalization, which was less evident in cases of strong colocalization, indicates dynamic protein reorganization linked to changes occurring in the peroxisomes. Through the use of multicolor stimulated emission depletion microscopy, we have been able to characterize peroxisomes and their constituents to a yet unseen level of detail while maintaining a highly statistical approach, paving the way for equally complex biological studies in the future.

Putative modifier genes in mevalonate kinase deficiency

Mevalonate kinase deficiency (MKD) is an autosomal recessive auto‑inflammatory disease, caused by impairment of the mevalonate pathway. Although the molecular mechanism remains to be elucidated, there is clinical evidence suggesting that other regulatory genes may be involved in determining the phenotype. The identification of novel target genes may explain non‑homogeneous genotype‑phenotype correlations, and provide evidence in support of the hypothesis that novel regulatory genes predispose or amplify deregulation of the mevalonate pathway in this orphan disease. In the present study, DNA samples were obtained from five patients with MKD, which were then analyzed using whole exome sequencing. A missense variation in the PEX11γ gene was observed in homozygosis in P2, possibly correlating with visual blurring. The UNG rare gene variant was detected in homozygosis in P5, without correlating with a specific clinical phenotype. A number of other variants were found in the five analyzed DNA samples from the MKD patients, however no correlation with the phenotype was established. The results of the presents study suggested that further analysis, using next generation sequencing approaches, is required on a larger sample size of patients with MKD, who share the same MVK mutations and exhibit 'extreme' clinical phenotypes. As MVK mutations may be associated with MKD, the identification of specific modifier genes may assist in providing an earlier diagnosis.

Proliferation and fission of peroxisomes - An update

In mammals, peroxisomes perform crucial functions in cellular metabolism, signalling and viral defense which are essential to the health and viability of the organism. In order to achieve this functional versatility peroxisomes dynamically respond to molecular cues triggered by changes in the cellular environment. Such changes elicit a corresponding response in peroxisomes, which manifests itself as a change in peroxisome number, altered enzyme levels and adaptations to the peroxisomal structure. In mammals the generation of new peroxisomes is a complex process which has clear analogies to mitochondria, with both sharing the same division machinery and undergoing a similar division process. How the regulation of this division process is integrated into the cell's response to different stimuli, the signalling pathways and factors involved, remains somewhat unclear. Here, we discuss the mechanism of peroxisomal fission, the contributions of the various division factors and examine the potential impact of post-translational modifications, such as phosphorylation, on the proliferation process. We also summarize the signalling process and highlight the most recent data linking signalling pathways with peroxisome proliferation.

One of Three Pex11 Family Members Is Required for Peroxisomal Proliferation and Full Virulence of the Rice Blast Fungus Magnaporthe oryzae

Peroxisomes play important roles in metabolisms of eukaryotes and infection of plant fungal pathogens. These organelles proliferate by de novo formation or division in response to environmental stimulation. Although the assembly of peroxisomes was documented in fungal pathogens, their division and its relationship to pathogenicity remain obscure. In present work, we analyzed the roles of three Pex11 family members in peroxisomal division and pathogenicity of the rice blast fungus Magnaporthe oryzae. Deletion of MoPEX11A led to fewer but enlarged peroxisomes, and impaired the separation of Woronin bodies from peroxisomes, while deletion of MoPEX11B or MoPEX11C put no evident impacts to peroxisomal profiles. MoPEX11A mutant exhibited typical peroxisome related defects, delayed conidial germination and appressoria formation, and decreased appressorial turgor and host penetration. As a result, the virulence of MoPEX11A mutant was greatly reduced. Deletion of MoPEX11B and MoPEX11C did not alter the virulence of the fungus. Further, double or triple deletions of the three genes were unable to enhance the virulence decrease in MoPEX11A mutant. Our data indicated that MoPEX11A is the main factor modulating peroxisomal division and is required for full virulence of the fungus.

Hypoxia signaling pathways: modulators of oxygen-related organelles

Oxygen (O2) is an essential substrate in cellular metabolism, bioenergetics, and signaling and as such linked to the survival and normal function of all metazoans. Low O2 tension (hypoxia) is a fundamental feature of physiological processes as well as pathophysiological conditions such as cancer and ischemic diseases. Central to the molecular mechanisms underlying O2 homeostasis are the hypoxia-inducible factors-1 and -2 alpha (HIF-1α and EPAS1/HIF-2α) that function as master regulators of the adaptive response to hypoxia. HIF-induced genes promote characteristic tumor behaviors, including angiogenesis and metabolic reprogramming. The aim of this review is to critically explore current knowledge of how HIF-α signaling regulates the abundance and function of major O2-consuming organelles. Abundant evidence suggests key roles for HIF-1α in the regulation of mitochondrial homeostasis. An essential adaptation to sustained hypoxia is repression of mitochondrial respiration and induction of glycolysis. HIF-1α activates several genes that trigger mitophagy and represses regulators of mitochondrial biogenesis. Several lines of evidence point to a strong relationship between hypoxia, the accumulation of misfolded proteins in the endoplasmic reticulum, and activation of the unfolded protein response. Surprisingly, although peroxisomes depend highly on molecular O2 for their function, there has been no evidence linking HIF signaling to peroxisomes. We discuss our recent findings that establish HIF-2α as a negative regulator of peroxisome abundance and suggest a mechanism by which cells attune peroxisomal function with O2 availability. HIF-2α activation augments peroxisome turnover by pexophagy and thereby changes lipid composition reminiscent of peroxisomal disorders. We discuss potential mechanisms by which HIF-2α might trigger pexophagy and place special emphasis on the potential pathological implications of HIF-2α-mediated pexophagy for human health.

Pex11mediates peroxisomal proliferation by promoting deformation of the lipid membrane

Pex11p family proteins are key players in peroxisomal fission, but their molecular mechanisms remains mostly unknown. In the present study, overexpression of Pex11pβ caused substantial vesiculation of peroxisomes in mammalian cells. This vesicle formation was dependent on dynamin-like protein 1 (DLP1) and mitochondrial fission factor (Mff), as knockdown of these proteins diminished peroxisomal fission after Pex11pβ overexpression. The fission-deficient peroxisomes exhibited an elongated morphology, and peroxisomal marker proteins, such as Pex14p or matrix proteins harboring peroxisomal targeting signal 1, were discernible in a segmented staining pattern, like beads on a string. Endogenous Pex11pβ was also distributed a striped pattern, but which was not coincide with Pex14p and PTS1 matrix proteins. Altered morphology of the lipid membrane was observed when recombinant Pex11p proteins were introduced into proteo-liposomes. Constriction of proteo-liposomes was observed under confocal microscopy and electron microscopy, and the reconstituted Pex11pβ protein localized to the membrane constriction site. Introducing point mutations into the N-terminal amphiphathic helix of Pex11pβ strongly reduced peroxisomal fission, and decreased the oligomer formation. These results suggest that Pex11p contributes to the morphogenesis of the peroxisomal membrane, which is required for subsequent fission by DLP1.

Role of Pex11p in Lipid Homeostasis in Yarrowia lipolytica

Peroxisomes are essential organelles in the cells of most eukaryotes, from yeasts to mammals. Their role in β-oxidation is particularly essential in yeasts; for example, in Saccharomyces cerevisiae, fatty acid oxidation takes place solely in peroxisomes. In this species, peroxisome biogenesis occurs when lipids are present in the culture medium, and it involves the Pex11p protein family: ScPex11p, ScPex25p, ScPex27p, and ScPex34p. Yarrowia lipolytica has three Pex11p homologues, which are YALI0C04092p (YlPex11p), YALI0C04565p (YlPex11C), and YALI0D25498p (Pex11/25p). We found that these genes are regulated by oleic acid, and as has been observed in other organisms, YlPEX11 deletion generated giant peroxisomes when mutant yeast were grown in oleic acid medium. Moreover, ΔYlpex11 was unable to grow on fatty acid medium and showed extreme dose-dependent sensitivity to oleic acid. Indeed, when the strain was grown in minimum medium with 0.5% glucose and 3% oleic acid, lipid body lysis and cell death were observed. Cell death and lipid body lysis may be partially explained by an imbalance in the expression of the genes involved in lipid storage, namely, DGA1, DGA2, and LRO1, as well as that of TGL4, which is involved in lipid remobilization. TGL4 deletion and DGA2 overexpression resulted in decreased oleic acid sensitivity and delayed cell death of ΔYlpex11, which probably stemmed from the release of free fatty acids into the cytoplasm. All these results show that YlPex11p plays an important role in lipid homeostasis in Y. lipolytica.

Induction of peroxisomes by butyrate-producing probiotics

We previously found that peroxisomal biogenesis factor 11a (Pex11a) deficiency is associated with a reduction in peroxisome abundance and impaired fatty acid metabolism in hepatocytes, and results in steatosis. In the present study, we investigated whether butyrate induces Pex11a expression and peroxisome proliferation, and studied its effect on lipid metabolism. C57BL/6 mice fed standard chow or a high-fat diet (HFD) were treated with tributyrin, 4-phelybutyrate acid (4-PBA), or the butyrate-producing probiotics (Clostridium butyricum MIYAIRI 588 [CBM]) plus inulin (dietary fiber), and the body weight, white adipose tissue, serum triglycerides, mRNA expression, and peroxisome abundance were evaluated. Tributyrin or 4-PBA treatment significantly decreased body weight and increased hepatic mRNA expression of peroxisome proliferator-activated receptor-α (PPARα) and Pex11a. In addition, 4-PBA treatment increased peroxisome abundance and the expression of genes involved in peroxisomal fatty acid β-oxidation (acyl-coenzyme A oxidase 1 and hydroxysteroid [17-beta] dehydrogenase 4). CBM and inulin administration reduced adipose tissue mass and serum triglycerides, induced Pex11a, acyl-coenzyme A oxidase 1, and hydroxysteroid (17-beta) dehydrogenase 4 genes, and increased peroxisome abundance in mice fed standard chow or an HFD. In conclusion, elevation of butyrate availability (directly through administration of butyrate or indirectly via administration of butyrate-producing probiotics plus fiber) induces PPARα and Pex11a and the genes involved in peroxisomal fatty acid β-oxidation, increases peroxisome abundance, and improves lipid metabolism. These results may provide a new therapeutic strategy against hyperlipidemia and obesity.

Pex11a deficiency is associated with a reduced abundance of functional peroxisomes and aggravated renal interstitial lesions

Although proteinuria is known to be associated with the deterioration of chronic kidney disease, the molecular basis of this mechanism is not fully understood. We previously found that Pex11a deficiency was associated with a reduction of functional peroxisomes and impaired fatty acid metabolism in hepatocytes and resulted in steatosis. Proximal tubule cells are rich in peroxisomes. We assessed whether Pex11a deficiency might result in the derangement of peroxisome systems in proximal tubule cells and the aggravation of tubulointerstitial lesions in chronic kidney disease. Histological analyses showed that the number of functional peroxisomes in proximal tubule cells was reduced in Pex11a knockout (Pex11a(-/-)) mice. To clarify whether a decrease in the number of tubular peroxisomes might aggravate interstitial lesions, we assessed 2 models in which proximal tubule cells are overloaded with fatty acids (ie, deoxycorticosterone acetate and salt hypertension and the overload of fatty acid-bound albumin). Deoxycorticosterone acetate -salt-treated Pex11a(-/-) mice exhibited greater interstitial lesions than deoxycorticosterone acetate-salt-treated wild-type mice in terms of tubular lipid accumulation, blood pressure, urinary albumin, urinary N-acetyl-β-d-glucosaminidase, urinary 8-iso-prostane, and the histological evaluation of fibrosis and inflammation. An overload of fatty acid-bound albumin also resulted in more severe tubulointerstitial lesions in Pex11a(-/-) mice than in wild-type mice. Fenofibrate, a peroxisome proliferator-activated receptor-α agonist, restored the abundance of peroxisomes and reduced the tubulointerstitial lesions induced by deoxycorticosterone acetate-salt hypertension. In conclusion, our results indicate that proximal tubule peroxisomes play an important role in proteinuria-induced interstitial lesions. The activation of tubular peroxisomes might be an excellent therapeutic strategy against chronic kidney disease.

Peroxisomes: a nexus for lipid metabolism and cellular signaling

Peroxisomes are often dismissed as the cellular hoi polloi, relegated to cleaning up reactive oxygen chemical debris discarded by other organelles. However, their functions extend far beyond hydrogen peroxide metabolism. Peroxisomes are intimately associated with lipid droplets and mitochondria, and their ability to carry out fatty acid oxidation and lipid synthesis, especially the production of ether lipids, may be critical for generating cellular signals required for normal physiology. Here, we review the biology of peroxisomes and their potential relevance to human disorders including cancer, obesity-related diabetes, and degenerative neurologic disease.

Identification of the kinesin KifC3 as a new player for positioning of peroxisomes and other organelles in mammalian cells

The attachment of organelles to the cytoskeleton and directed organelle transport is essential for cellular morphology and function. In contrast to other cell organelles like the endoplasmic reticulum or the Golgi apparatus, peroxisomes are evenly distributed in the cytoplasm, which is achieved by binding of peroxisomes to microtubules and their bidirectional transport by the microtubule motor proteins kinesin-1 (Kif5) and cytoplasmic dynein. KifC3, belonging to the group of C-terminal kinesins, has been identified to interact with the human peroxin PEX1 in a yeast two-hybrid screen. We investigated the potential involvement of KifC3 in peroxisomal transport. Interaction of KifC3 and the AAA-protein (ATPase associated with various cellular activities) PEX1 was confirmed by in vivo colocalization and by coimmunoprecipitation from cell lysates. Furthermore, knockdown of KifC3 using RNAi resulted in an increase of cells with perinuclear-clustered peroxisomes, indicating enhanced minus-end directed motility of peroxisomes. The occurrence of this peroxisomal phenotype was cell cycle phase independent, while microtubules were essential for phenotype formation. We conclude that KifC3 may play a regulatory role in minus-end directed peroxisomal transport for example by blocking the motor function of dynein at peroxisomes. Knockdown of KifC3 would then lead to increased minus-end directed peroxisomal transport and cause the observed peroxisomal clustering at the microtubule-organizing center.

Peroxisome degradation in mammals: mechanisms of action, recent advances, and perspectives

Peroxisomes are remarkably dynamic organelles that participate in a diverse array of cellular processes, including the metabolism of lipids and reactive oxygen species. In order to regulate peroxisome function in response to changing nutritional and environmental stimuli, new organelles need to be formed and superfluous and dysfunctional organelles have to be selectively removed. Disturbances in any of these processes have been associated with the etiology and progression of various congenital neurodegenerative and age-related human disorders. The aim of this review is to critically explore our current knowledge of how peroxisomes are degraded in mammalian cells and how defects in this process may contribute to human disease. Some of the key issues highlighted include the current concepts of peroxisome removal, the peroxisome quality control mechanisms, the initial triggers for peroxisome degradation, the factors for dysfunctional peroxisome recognition, and the regulation of peroxisome homeostasis. We also dissect the functional and mechanistic relationship between different forms of selective organelle degradation and consider how lysosomal dysfunction may lead to defects in peroxisome turnover. In addition, we draw lessons from studies on other organisms and extrapolate this knowledge to mammals. Finally, we discuss the potential pathological implications of dysfunctional peroxisome degradation for human health.

Charcot-Marie-Tooth disease-associated mutants of GDAP1 dissociate its roles in peroxisomal and mitochondrial fission

Mitochondria and peroxisomes can be fragmented by the process of fission. The fission machineries of both organelles share a set of proteins. GDAP1 is a tail-anchored protein of mitochondria and induces mitochondrial fragmentation. Mutations in GDAP1 lead to Charcot-Marie-Tooth disease (CMT), an inherited peripheral neuropathy, and affect mitochondrial dynamics. Here, we show that GDAP1 is also targeted to peroxisomes mediated by the import receptor Pex19. Knockdown of GDAP1 leads to peroxisomal elongation that can be rescued by re-expressing GDAP1 and by missense mutated forms found in CMT patients. GDAP1-induced peroxisomal fission is dependent on the integrity of its hydrophobic domain 1, and on Drp1 and Mff, as is mitochondrial fission. Thus, GDAP1 regulates mitochondrial and peroxisomal fission by a similar mechanism. However, our results reveal also a more critical role of the amino-terminal GDAP1 domains, carrying most CMT-causing mutations, in the regulation of mitochondrial compared to peroxisomal fission.

Pex11α deficiency impairs peroxisome elongation and division and contributes to nonalcoholic fatty liver in mice

Hepatic triglyceride (TG) accumulation is considered to be a prerequisite for developing nonalcoholic fatty liver (NAFL). Peroxisomes have many important functions in lipid metabolism, including fatty acid β-oxidization. However, the pathogenic link between NAFL and peroxisome biogenesis remains unclear. To examine the molecular and physiological functions of the Pex11α gene, we disrupted this gene in mice. Body weights and hepatic TG concentrations in Pex11α(-/-) mice were significantly higher than those in wild-type (WT) mice fed a normal or a high-fat diet. Hepatic TG concentrations in fasted Pex11α(-/-) mice were significantly higher than those in fasted WT mice. Plasma TG levels increased at lower rates in Pex11α(-/-) mice than in WT mice after treatment with the lipoprotein lipase inhibitor tyloxapol. The number of peroxisomes was lower in the livers of Pex11α(-/-) mice than in those of WT mice. Ultrastructural analysis showed that small and regular spherically shaped peroxisomes were more prevalent in Pex11α(-/-) mice fed normal chow supplemented without or with fenofibrate. We observed a significantly higher ratio of empty peroxisomes containing only PMP70, a peroxisome membrane protein, but not catalase, a peroxisome matrix protein, in Pex11α(-/-) mice. The mRNA expression levels of peroxisomal fatty acid oxidation-related genes (ATP-binding cassette, subfamily D, member 2, and acyl-CoA thioesterase 3) were significantly higher in WT mice than those in Pex11α(-/-) mice under fed conditions. Our results demonstrate that Pex11α deficiency impairs peroxisome elongation and abundance and peroxisomal fatty acid oxidation, which contributes to increased lipid accumulation in the liver.