HRG-9 homologues regulate haem trafficking from haem-enriched compartments

TANGO2 is an acyl-CoA binding protein

Loss of TANGO2 in humans precipitates metabolic crises during periods of heightened energy demand, such as fasting, infections, or high fever. TANGO2 has been implicated in various functions, including lipid metabolism and heme transport, and its cellular localization remains uncertain. In our study, we demonstrate that TANGO2 localizes to the mitochondrial lumen via a structural region containing LIL residues. Mutations in these LIL residues cause TANGO2 to relocate to the periphery of lipid droplets. We further show that purified TANGO2 binds acyl-coenzyme A, and mutations in the highly conserved NRDE sequence of TANGO2 inhibit this binding. Collectively, our findings suggest that TANGO2 serves as an acyl-coenzyme A binding protein. These insights may provide new avenues for addressing the severe cardiomyopathies and rhabdomyolysis associated with defective TANGO2 in humans.

Mitochondrial mayhem: Disrupting conserved N-terminal motifs in TANGO2 impacts its localization and function

TANGO2 deficiency in humans leads to progressive neurological impairment, punctuated by life-threatening metabolic crises. In this issue, Lujan and colleagues demonstrate that TANGO2 localizes within the mitochondrial lumen and binds acyl-CoA species, potentially implicating it as a lipid trafficking protein.

Enhancing heme import to synthesize active myoglobin and hemoglobin in Pichia pastoris

Myoglobin and hemoglobin are both heme-binding proteins that have widespread applications in food processing and medical treatments. Pichia pastoris is often chosen to produce heterologous hemoproteins. However, due to the insufficient heme supply, the inactive hemoproteins take a large proportion of synthesized products. To overcome this problem, the intracellular heme supply was increased by improving heme uptake efficiency. At first, an efficient method was created for the screen of potential heme importers from various microorganisms by knocking out HEM1 gene to obtain a deficient P. pastoris strain X33-ΔKu70-ΔHEM1 (HEMEX) in heme synthesis. Based on the significantly improved cell growth, two effective heterogenous heme importers (Caflc1 and Shu1) were selected when the exogenous heme was supplemented. Finally, the titers of porcine myoglobin (PMB) and soybean hemoglobin (SHB) increased by 112.28% and 5.78-fold, respectively, through the overexpression of heme importers. The applied strategy provides a promising approach to synthesize other valuable hemoproteins in P. pastoris.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-025-04286-6.

TANGO-2: A Rare Genetic Condition With Severe Clinical Presentation of Encephalopathy, Rhabdomyolysis, and Cardiac Rhythm Disorders in 2 Children

Biallelic pathogenic or likely pathogenic variants in Transport and Golgi Organization 2 (TANGO-2) are associated with a spectrum of clinical features including encephalopathy, rhabdomyolysis, cardiac rhythm disorders, and neurologic regression. We are reporting on 2 unrelated children with biallelic TANGO-2 pathogenic variants. These variants were identified through a Next Generation Sequencing (NGS) panel of genes associated with hereditary rhabdomyolysis. Both children had a history of developmental delay, especially in their motor milestones. They also experienced episodic transient weakness with acute illness. One of the children's siblings had similar complaints and died at an early age. During their illness, both children developed extreme lethargy with very high CPK levels, lactic acidosis, rising trends of transaminases, and recurrent hypoglycemia. Both patients developed ventricular tachyarrhythmias, and the echocardiogram showed cardiomyopathy. Despite intensive symptomatic management, both patients died of cardiac failure because of fatal ventricular arrhythmia. Genetic testing revealed the presence of biallelic pathogenic variants TANGO-2. This rare genetic condition should be suspected in any patient with episodic recurrent weakness, rhabdomyolysis, abdominal pain, and cardiac arrhythmias, because of its diverse clinical presentation. However, early diagnosis is challenging because there are no specific biochemical markers for the disease. There is strong evidence that vitamin B supplementation can significantly reduce the number of metabolic crises in these children. Although this is not a targeted therapy, it can be a potentially life-saving treatment for these patients.

Identification of FLVCR1 as the iron metabolism-related gene of statin-associated diabetes

AIMS

Long-term statin use has been linked to increased diabetes risk. Iron metabolism disruption may explain this association. The objective of this study was to identify the co-expression gene modules and the iron metabolism-related gene (IMG) linking statin administration and diabetes, making the hunt for novel therapeutic targets necessary.

METHODS

Weighted gene co-expression network analysis (WGCNA) was applied to the GSE130991 dataset to detect co-expressed gene modules. Enrichment analysis and single sample gene set enrichment analysis (ssGSEA) were conducted to characterize the biological processes and iron metabolism differences, respectively. Candidate IMGs were identified by intersecting WGCNA hub genes, differentially expressed genes (DEGs) from the statin-using and non-using obese individuals within the GSE130991 liver tissue dataset, and IMGs from Molecular Signatures Database Molecular Signatures Database (MisgDB). Mediation analysis was utilized to identify the definitive IMG. Expression validation was conducted through reverse transcription quantitative PCR (RT-qPCR) experiments and cross-referencing with additional datasets.

RESULTS

A shared gene module was identified between statin-users and diabetes patients, with functional enrichment analysis indicating involvement in iron ion binding. ssGSEA revealed differentially expressed iron metabolism in both statin-users and diabetes patients. Five IMG genes (CYP51A1, SC5D, MSMO1, SCD, and FLVCR1) were shortlisted, with FLVCR1 emerging as the key intermediary biomarker. FLVCR1 was positively correlated with insulin resistance and demonstrated robust predictive capabilities for diabetes. An increase in FLVCR1 mRNA levels was observed following statin treatment, as confirmed by RT-qPCR experiments and the GSE24188 dataset. Elevated FLVCR1 mRNA was also noted in diabetes patients across datasets GSE130991, GSE23343, and GSE95849.

CONCLUSION

In this study, bioinformatics evidence supporting the association between statin use and diabetes was presented. FLVCR1 was identified as the iron metabolism-related mediator gene implicated in this relationship. Overall, our findings provide a theoretical foundation for new directions for future research exploring the complex interplay between statin treatment, iron metabolism regulation, and diabetes pathogenesis.

Cellular mechanisms of acute rhabdomyolysis in inherited metabolic diseases

Acute rhabdomyolysis (RM) constitutes a life-threatening emergency resulting from the (acute) breakdown of skeletal myofibers, characterized by a plasma creatine kinase (CK) level exceeding 1000 IU/L in response to a precipitating factor. Genetic predisposition, particularly inherited metabolic diseases, often underlie RM, contributing to recurrent episodes. Both sporadic and congenital forms of RM share common triggers. Considering the skeletal muscle's urgent need to rapidly adjust to environmental cues, sustaining sufficient energy levels and functional autophagy and mitophagy processes are vital for its preservation and response to stressors. Crucially, the composition of membrane lipids, along with lipid and calcium transport, and the availability of adenosine triphosphate (ATP), influence membrane biophysical properties, membrane curvature in skeletal muscle, calcium channel signaling regulation, and determine the characteristics of autophagic organelles. Consequently, a genetic defect involving ATP depletion, aberrant calcium release, abnormal lipid metabolism and/or lipid or calcium transport, and/or impaired anterograde trafficking may disrupt autophagy resulting in RM. The complex composition of lipid membranes also alters Toll-like receptor signaling and viral replication. In response, infections, recognized triggers of RM, stimulate increased levels of inflammatory cytokines, affecting skeletal muscle integrity, energy metabolism, and cellular trafficking, while elevated temperatures can reduce the activity of thermolabile enzymes. Overall, several mechanisms can account for RMs and may be associated in the same disease-causing RM.

Tango6 regulates HSPC proliferation and definitive haematopoiesis via Ikzf1 and Cmyb in caudal haematopoietic tissue

Haematopoietic stem and progenitor cells (HSPCs) arise from the aorta-gonad-mesonephros and migrate to the caudal haematopoietic tissue (CHT) in zebrafish, where nascent HSPCs undergo tightly controlled proliferation and differentiation to promote definitive haematopoiesis. Effective expansion of HSPCs requires the coordination of well-established vesicle trafficking systems and appropriate transcription factors. However, the underlying molecules are yet to be identified. Using large-scale genetic screening of zebrafish larvae, Tango6 of the coat protein complex I (COPI) vesicle trafficking system was found to be indispensable for HSPC proliferation and definitive haematopoiesis. Homozygous tango6cq72 mutants display defective expansion of HSPCs in the CHT and compromised haematopoiesis. However, haematopoietic overexpression of Tango6 promoted haematopoietic expansion. tango6 deficiency caused a decline in RNA polymerase II subunit B and accumulation of DNA damage, which suppressed cell expansion in a P53-dependent manner. ikzf1 and cmyb (myb), two indispensable haematopoietic transcription factors, are targets of P53 and are used by tango6 in haematopoiesis. The haematopoietic phenotype was partially recovered by compensating for loss of ikzf1 and cmyb in tango6cq72 mutants. This study reveals a vesicle trafficking-mediated Tango6-P53-Ikzf1/Cmyb axis in zebrafish definitive haematopoiesis.

Application of Ti4+ embedded functional composite materials in simultaneous enrichment of glycopeptides and phosphopeptides

Glycosylation and phosphorylation of proteins represent crucial forms of post-translational modifications (PTMs), playing pivotal roles in various biological processes. Research indicates a strong correlation between the development of type 2 diabetes (T2D) and abnormal protein translation in the body. Therefore, studying glycosylation and phosphorylation at the molecular level can be used for monitoring disease progression and refining research methodologies. In this study, the material is modified and functionally engineered by utilizing graphene oxide (GO) as the substrate, and incorporating titanium ions (Ti4+) into chondroitin sulfate. The composite was successfully applied to the selective enrichment of glycopeptides and phosphopeptides by utilizing the bifunctionality of hydrophilic interaction chromatography and metal ion chelation chromatography. This approach allowed for the capture of 57 glycopeptides and 2 phosphopeptides from normal human serum, and 141 glycopeptides and 10 phosphopeptides from T2D serum, respectively. This approach effectively tackles the challenges of detecting low-abundance glycopeptides and phosphopeptides in complex environments, enabling the successful capture from serum samples. The design and application of this material provide new insights into the development of PTMs and their connection to the study of T2D diabetes.

TANGO2-related rhabdomyolysis symptoms are associated with abnormal autophagy functioning

Patients with pathogenic variants in the TANGO2 gene suffer from severe and recurrent rhabdomyolysis episodes precipitated by fasting. Autophagy functioning was analyzed in vitro, in primary skeletal myoblasts from TANGO2 patients, in basal and fasting conditions, and TANGO2 mutations were associated with reduced LC3-II levels upon starvation. In zebrafish larvae, tango2 inhibition induced locomotor defects which were exacerbated by exposure to atorvastatin, a compound known to cause rhabdomyolysis. Importantly, rhabdomyolysis features of tango2 knockdown were associated with autophagy and mitophagy defects in zebrafish. Calpeptin treatment was sufficient to rescue the locomotor properties thanks to its beneficial effect on autophagy functioning in zebrafish and to improve LC3-II levels in starved primary muscle cells of TANGO2 patients. Overall, we demonstrated that TANGO2 plays an important role in autophagy thus giving rise to new therapeutic perspectives in the prevention of RM life-threatening episodes.

Essentiality of SLC7A11-mediated nonessential amino acids in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) remains a rapidly growing global health burden. Here, we report that the nonessential amino acid (NEAA) transporter SLC7A11 plays a key role in MASLD. In patients with MASLD, we found high expression levels of SLC7A11 that were correlated directly with clinical grade. Using both loss-of-function and gain-of-function genetic models, we found that Slc7a11 deficiency accelerated MASLD progression via classic cystine/cysteine deficiency-induced ferroptosis, while serine deficiency and a resulting impairment in de novo cysteine production were attributed to ferroptosis-induced MASLD progression in mice overexpressing hepatic Slc7a11. Consistent with these findings, we found that both serine supplementation and blocking ferroptosis significantly alleviated MASLD, and the serum serine/glutamate ratio was significantly lower in these preclinical disease models, suggesting that it might serve as a prognostic biomarker for MASLD in patients. These findings indicate that defects in NEAA metabolism are involved in the progression of MASLD and that serine deficiency-triggered ferroptosis may provide a therapeutic target for its treatment.

Bifidobacterium animalis Probio-M8 improves sarcopenia physical performance by mitigating creatine restrictions imposed by microbial metabolites

Sarcopenia is a major health challenge due to an aging population. Probiotics may improve muscle function through gut-muscle axis, but their efficacy and mechanisms in treating sarcopenia remain unclear. This study investigated the impact of Bifidobacterium animalis subsp. lactis Probio-M8 (Probio-M8) on old mice and sarcopenia patients. We analyzed 43 subjects, including gut microbiome, fecal metabolome, and serum metabolome, using a multi-omics approach to assess whether Probio-M8 can improve sarcopenia by modulating gut microbial metabolites. Probio-M8 significantly improved muscle function in aged mice and enhanced physical performance in sarcopenia patients. It reduced pathogenic gut species and increased beneficial metabolites such as indole-3-lactic acid, acetoacetic acid, and creatine. Mediating effect analyses revealed that Probio-M8 effectively reduced n-dodecanoyl-L-homoserine lactone level in gut concurrent with increased creatine circulation, to significantly enhance host physical properties. These findings provide new insights into probiotics as a potential treatment for sarcopenia by modulating gut microbiota metabolism.

Heme's relevance genuine? Re-visiting the roles of TANGO2 homologs including HRG-9 and HRG-10 in C. elegans

Mutations in the TANGO2 gene cause severe illness in humans, including life-threatening metabolic crises. However, the function of TANGO2 protein remains unknown. Using Caenorhabditis elegans and other models, it has recently been proposed that TANGO2 transports heme within and between cells, from areas with high heme concentrations to those with lower concentrations. Here, we demonstrate that heme-related observations in nematodes may be better explained by a previously unreported metabolic phenotype in these worms, characterized by reduced feeding, decreased lifespan and brood sizes, and poor motility. We also show that several genes not implicated in heme transport are upregulated in the low heme state and conversely demonstrate that hrg-9 in particular is highly responsive to oxidative stress, independent of heme status. Collectively, these data implicate bioenergetic failure and oxidative stress as key factors in the pathophysiology of TANGO2 deficiency, in alignment with observations from human patients. Our group performed several experiments in yeast and zebrafish deficient in TANGO2 homologs and was unable to replicate prior findings from these models. Overall, we believe there is insufficient evidence to support heme transport as the primary function for TANGO2.

Fighting ischemia-reperfusion injury: Focusing on mitochondria-derived ferroptosis

Ischemia-reperfusion injury (IRI) is a major cause of mortality and morbidity. Current treatments for IRI have limited efficacy and novel therapeutic strategies are needed. Mitochondrial dysfunction not only initiates IRI but also plays a significant role in ferroptosis pathogenesis. Recent studies have highlighted that targeting mitochondrial pathways is a promising therapeutic approach for ferroptosis-induced IRI. The association between ferroptosis and IRI has been reviewed many times, but our review provides the first comprehensive overview with a focus on recent mitochondrial research. First, we present the role of mitochondria in ferroptosis. Then, we summarize the evidence on mitochondrial manipulation of ferroptosis in IRI and review recent therapeutic strategies aimed at targeting mitochondria-related ferroptosis to mitigate IRI. We hope our review will provide new ideas for the treatment of IRI and accelerate the transition from bench to bedside.

Intestinal immunity in C. elegans is activated by pathogen effector-triggered aggregation of the guard protein TIR-1 on lysosome-related organelles

Toll/interleukin-1/resistance (TIR)-domain proteins with enzymatic activity are essential for immunity in plants, animals, and bacteria. However, it is not known how these proteins function in pathogen sensing in animals. We discovered that the lone enzymatic TIR-domain protein in the nematode C. elegans (TIR-1, homolog of mammalian sterile alpha and TIR motif-containing 1 [SARM1]) was strategically expressed on the membranes of a specific intracellular compartment called lysosome-related organelles. The positioning of TIR-1 on lysosome-related organelles enables intestinal epithelial cells in the nematode C. elegans to survey for pathogen effector-triggered host damage. A virulence effector secreted by the bacterial pathogen Pseudomonas aeruginosa alkalinized and condensed lysosome-related organelles. This pathogen-induced morphological change in lysosome-related organelles triggered TIR-1 multimerization, which engaged its intrinsic NAD+ hydrolase (NADase) activity to activate the p38 innate immune pathway and protect the host against microbial intoxication. Thus, TIR-1 is a guard protein in an effector-triggered immune response, which enables intestinal epithelial cells to survey for pathogen-induced host damage.

The mrp-3 gene is involved in haem efflux and detoxification in a blood-feeding nematode

BACKGROUND

Haem is essential but toxic for metazoan organisms. Auxotrophic nematodes can acquire sufficient haem from the environment or their hosts in the meanwhile eliminate or detoxify excessive haem through tightly controlled machinery. In previous work, we reported a role of the unique transporter protein HRG-1 in the haem acquisition and homeostasis of parasitic nematodes. However, little is known about the haem efflux and detoxification via ABC transporters, particularly the multiple drug resistance proteins (MRPs).

RESULTS

Here, we further elucidate that a member of the mrp family (mrp-3) is involved in haem efflux and detoxification in a blood-feeding model gastrointestinal parasite, Haemonchus contortus. This gene is haem-responsive and dominantly expressed in the intestine and inner membrane of the hypodermis of this parasite. RNA interference of mrp-3 resulted in a disturbance of genes (e.g. hrg-1, hrg-2 and gst-1) that are known to be involved in haem homeostasis and an increased formation of haemozoin in the treated larvae and lethality in vitro, particularly when exposed to exogenous haem. Notably, the nuclear hormone receptor NHR-14 appears to be associated the regulation of mrp-3 expression for haem homeostasis and detoxification. Gene knockdown of nhr-14 and/or mrp-3 increases the sensitivity of treated larvae to exogenous haem and consequently a high death rate (> 80%).

CONCLUSIONS

These findings demonstrate that MRP-3 and the associated molecules are essential for haematophagous nematodes, suggesting novel intervention targets for these pathogens in humans and animals.

Oxidative damage and cardiotoxicity induced by 2-aminobenzothiazole in zebrafish (Danio rerio)

There is limited information available on cardiovascular toxicity of 2-Aminobenzothiazole (NTH), a derivative of benzothiazole (BTH) commonly used in tire production, in aquatic organisms. In the present study, the zebrafish embryos were exposed to varying concentrations of NTH (0, 0.05, 0.5, and 5 mg/L) until adulthood and the potential cardiovascular toxicity was assessed. NTH exposure resulted in striking aberrations in cardiac development, including heart looping failure and interference with atrioventricular canal differentiation. RNA-sequencing analysis indicated that NTH causes oxidative damage to the heart via ferroptosis, leading to oxygen supply disruption, cardiac malformation, and ultimately, zebrafish death. Quantitative real-time polymerase chain reaction (qPCR) analysis demonstrated the dysregulation of genes associated with early heart development, contraction, and oxidative stress. Additionally, reactive oxygen species accumulation and glutathione/malondialdehyde levels changes suggested a potential link between cardiac developmental toxicity and oxidative stress. In adult zebrafish, NTH exposure led to ventricular enlargement, decreased heart rate, reduced blood flow, and prolonged RR, QRS, and QTc intervals. To the best of our knowledge, this study is the first to provide evidence of cardiac toxicity and the adverse effects of ontogenetic NTH exposure in zebrafish, revealing the underlying toxic mechanisms connected with oxidative stress damage. These findings may provide crucial insights into the environmental risks associated with NTH and other BTHs.

Heme homeostasis and its regulation by hemoproteins in bacteria

Heme is an important cofactor and a regulatory molecule involved in various physiological processes in virtually all living cellular organisms, and it can also serve as the primary iron source for many bacteria, particularly pathogens. However, excess heme is cytotoxic to cells. In order to meet physiological needs while preventing deleterious effects, bacteria have evolved sophisticated cellular mechanisms to maintain heme homeostasis. Recent advances in technologies have shaped our understanding of the molecular mechanisms that govern the biological processes crucial to heme homeostasis, including synthesis, acquisition, utilization, degradation, trafficking, and efflux, as well as their regulation. Central to these mechanisms is the regulation of the heme, by the heme, and for the heme. In this review, we present state-of-the-art findings covering the biochemical, physiological, and structural characterization of important, newly identified hemoproteins/systems involved in heme homeostasis.

Single-tissue proteomics in Caenorhabditis elegans reveals proteins resident in intestinal lysosome-related organelles

The nematode intestine is the primary site for nutrient uptake and storage as well as the synthesis of biomolecules; lysosome-related organelles known as gut granules are important for many of these functions. Aspects of intestine biology are not well understood, including the export of the nutrients it imports and the molecules it synthesizes, as well as the complete functions and protein content of the gut granules. Here, we report a mass spectrometry (MS)-based proteomic analysis of the intestine of the Caenorhabditis elegans and of its gut granules. Overall, we identified approximately 5,000 proteins each in the intestine and the gonad and showed that most of these proteins can be detected in samples extracted from a single worm, suggesting the feasibility of individual-level genetic analysis using proteomes. Comparing proteomes and published transcriptomes of the intestine and the gonad, we identified proteins that appear to be synthesized in the intestine and then transferred to the gonad. To identify gut granule proteins, we compared the proteome of individual intestines deficient in gut granules to the wild type. The identified gut granule proteome includes proteins known to be exclusively localized to the granules and additional putative gut granule proteins. We selected two of these putative gut granule proteins for validation via immunohistochemistry, and our successful confirmation of both suggests that our strategy was effective in identifying the gut granule proteome. Our results demonstrate the practicability of single-tissue MS-based proteomic analysis in small organisms and in its future utility.

Technological challenges and future perspectives of plant-based meat analogues: From the viewpoint of proteins

The global demand for high-quality animal protein faces challenges, prompting a surge in interest in plant-based meat analogues (PBMA). PBMA have emerged as a promising solution, although they encounter technological obstacles. This review discusses the technological challenges faced by PBMA from the viewpoint of plant proteins, emphasizing textural, flavor, color, and nutritional aspects. Texturally, PBMA confront issues, such as deficient fibrous structure, chewiness, and juiciness. Addressing meat flavor and mitigating beany flavor in plant protein are imperative. Furthermore, achieving a distinctive red or pink meat color remains a challenge. Plant proteins exhibit a lower content of essential amino acids. Future research directions encompass (1) shaping myofibril fibrous structures through innovative processing; (2) effectively eliminating the beany flavor; (3) developing biotechnological methodologies for leghemoglobin and plant-derived pigments; (4) optimizing amino acid composition to augment the nutritional profiles. These advancements are crucial for utilization of plant proteins in development of high-quality PBMA.

TANGO2 deficiency disease is predominantly caused by a lipid imbalance

TANGO2 deficiency disease (TDD) is a rare genetic disorder estimated to affect ∼8000 individuals worldwide. It causes neurodegeneration often accompanied by potentially lethal metabolic crises that are triggered by diet or illness. Recent work has demonstrated distinct lipid imbalances in multiple model systems either depleted for or devoid of the TANGO2 protein, including human cells, fruit flies and zebrafish. Importantly, vitamin B5 supplementation has been shown to rescue TANGO2 deficiency-associated defects in flies and human cells. The notion that vitamin B5 is needed for synthesis of the lipid precursor coenzyme A (CoA) corroborates the hypothesis that key aspects of TDD pathology may be caused by lipid imbalance. A natural history study of 73 individuals with TDD reported that either multivitamin or vitamin B complex supplementation prevented the metabolic crises, suggesting this as a potentially life-saving treatment. Although recently published work supports this notion, much remains unknown about TANGO2 function, the pathological mechanism of TDD and the possible downsides of sustained vitamin supplementation in children and young adults. In this Perspective, we discuss these recent findings and highlight areas for immediate scientific attention.

Crucial Involvement of Heme Biosynthesis in Vegetative Growth, Development, Stress Response, and Fungicide Sensitivity of Fusarium graminearum

Heme biosynthesis is a highly conserved pathway from bacteria to higher animals. Heme, which serves as a prosthetic group for various enzymes involved in multiple biochemical processes, is essential in almost all species, making heme homeostasis vital for life. However, studies on the biological functions of heme in filamentous fungi are scarce. In this study, we investigated the role of heme in Fusarium graminearum. A mutant lacking the rate-limiting enzymes in heme synthesis, coproporphyrinogen III oxidase (Cpo) or ferrochelatase (Fc), was constructed using a homologous recombination strategy. The results showed that the absence of these enzymes was lethal to F. graminearum, but the growth defect could be rescued by the addition of hemin, so we carried out further studies with the help of hemin. The results demonstrated that heme was required for the activity of FgCyp51, and its absence increased the sensitivity to tebuconazole and led to the upregulation of FgCYP51 in F. graminearum. Additionally, heme plays an indispensable role in the life cycle of F. graminearum, which is essential for vegetative growth, conidiation, external stress response (especially oxidative stress), lipid accumulation, fatty acid β-oxidation, autophagy, and virulence.

Heme allocation in eukaryotic cells relies on mitochondrial heme export through FLVCR1b to cytosolic GAPDH

Heme is an iron-containing cofactor essential for life. In eukaryotes heme is generated in the mitochondria and must leave this organelle to reach protein targets in other cell compartments. Mitochondrial heme binding by cytosolic GAPDH was recently found essential for heme distribution in eukaryotic cells. Here, we sought to uncover how mitochondrial heme reaches GAPDH. Experiments involving a human cell line and a novel GAPDH reporter construct whose heme binding in live cells can be followed by fluorescence revealed that the mitochondrial transmembrane protein FLVCR1b exclusively transfers mitochondrial heme to GAPDH through a direct protein-protein interaction that rises and falls as heme transfers. In the absence of FLVCR1b, neither GAPDH nor downstream hemeproteins received any mitochondrial heme. Cell expression of TANGO2 was also required, and we found it interacts with FLVCR1b to likely support its heme exporting function. Finally, we show that purified GAPDH interacts with FLVCR1b in isolated mitochondria and triggers heme transfer to GAPDH and its downstream delivery to two client proteins. Identifying FLVCR1b as the sole heme source for GAPDH completes the path by which heme is exported from mitochondria, transported, and delivered into protein targets within eukaryotic cells.

Activation of intestinal immunity by pathogen effector-triggered aggregation of lysosomal TIR-1/SARM1

TIR-domain proteins with enzymatic activity are essential for immunity in plants, animals, and bacteria. However, it is not known how these proteins function in pathogen sensing in animals. We discovered that a TIR-domain protein (TIR-1/SARM1) is strategically expressed on the membranes of a lysosomal sub-compartment, which enables intestinal epithelial cells in the nematode C. elegans to survey for pathogen effector-triggered host damage. We showed that a redox active virulence effector secreted by the bacterial pathogen Pseudomonas aeruginosa alkalinized and condensed a specific subset of lysosomes by inducing intracellular oxidative stress. Concentration of TIR-1/SARM1 on the surface of these organelles triggered its multimerization, which engages its intrinsic NADase activity, to activate the p38 innate immune pathway and protect the host against microbial intoxication. Thus, lysosomal TIR-1/SARM1 is a sensor for oxidative stress induced by pathogenic bacteria to activate metazoan intestinal immunity.

Mechanisms controlling cellular and systemic iron homeostasis

In mammals, hundreds of proteins use iron in a multitude of cellular functions, including vital processes such as mitochondrial respiration, gene regulation and DNA synthesis or repair. Highly orchestrated regulatory systems control cellular and systemic iron fluxes ensuring sufficient iron delivery to target proteins is maintained, while limiting its potentially deleterious effects in iron-mediated oxidative cell damage and ferroptosis. In this Review, we discuss how cells acquire, traffick and export iron and how stored iron is mobilized for iron-sulfur cluster and haem biogenesis. Furthermore, we describe how these cellular processes are fine-tuned by the combination of various sensory and regulatory systems, such as the iron-regulatory protein (IRP)-iron-responsive element (IRE) network, the nuclear receptor co-activator 4 (NCOA4)-mediated ferritinophagy pathway, the prolyl hydroxylase domain (PHD)-hypoxia-inducible factor (HIF) axis or the nuclear factor erythroid 2-related factor 2 (NRF2) regulatory hub. We further describe how these pathways interact with systemic iron homeostasis control through the hepcidin-ferroportin axis to ensure appropriate iron fluxes. This knowledge is key for the identification of novel therapeutic opportunities to prevent diseases of cellular and/or systemic iron mismanagement.

Fluorometric Methods to Measure Bioavailable and Total Heme

Heme b (iron protoporphyrin IX) is an essential but potentially cytotoxic cofactor, signaling molecule, and nutritional source of iron. Its importance in cell biology and metabolism is underscored by the fact that numerous diseases, including various cancers, neurodegenerative disorders, infectious diseases, anemias, and porphyrias, are associated with the dysregulation of heme synthesis, degradation, trafficking, and/or transport. Consequently, methods to measure, image, and quantify heme in cells are required to better understand the physiology and pathophysiology of heme. Herein, we describe fluorescence-based protocols to probe heme bioavailability and trafficking dynamics using genetically encoded fluorescent heme sensors in combination with various modalities, such as confocal microscopy, flow cytometry, and microplate readers. Additionally, we describe a protocol for measuring total heme and its precursor protoporphyrin IX using a fluorometric assay that exploits porphyrin fluorescence. Together, the methods described enable the monitoring of total and bioavailable heme to study heme homeostatic mechanisms in virtually any cell type and organism.

Nitric oxide and thiols: Chemical biology, signalling paradigms and vascular therapeutic potential

Nitric oxide (• NO) interactions with biological thiols play crucial, but incompletely determined, roles in vascular signalling and other biological processes. Here, we highlight two recently proposed signalling paradigms: (1) the formation of a vasodilating labile nitrosyl ferrous haem (NO-ferrohaem) facilitated by thiols via thiyl radical generation and (2) polysulfides/persulfides and their interaction with • NO. We also describe the specific (bio)chemical routes in which • NO and thiols react to form S-nitrosothiols, a broad class of small molecules, and protein post-translational modifications that can influence protein function through catalytic site or allosteric structural changes. S-Nitrosothiol formation depends upon cellular conditions, but critically, an appropriate oxidant for either the thiol (yielding a thiyl radical) or • NO (yielding a nitrosonium [NO+ ]-donating species) is required. We examine the roles of these collective • NO/thiol species in vascular signalling and their cardiovascular therapeutic potential.

Fluorescence dynamics of lysosomal-related organelle flashing in the intestinal cells of Caenorhabditis elegans

The biological roles of the autofluorescent lysosome-related organelles ("gut granules") in the intestinal cells of many nematodes, including Caenorhabditis elegans, have been shown to play an important role in metabolic and signaling processes, but they have not been fully characterized. We report here a previously undescribed phenomenon in which the autofluorescence of these granules increased and then decreased in a rapid and dynamic manner that may be associated with nutrient availability. We observed that two distinct types of fluorophores are likely present in the gut granules. One displays a "flashing" phenomenon, in which fluorescence decrease is preceded by a sharp increase in fluorescence intensity that expands into the surrounding area, while the other simply decreases in intensity. Gut granule flashing was observed in the different life stages of C. elegans and was also observed in Steinernema hermaphroditum, an evolutionarily distant nematode. We hypothesize that the "flashing" fluorophore is pH-sensitive, and the fluorescence intensity change results from the fluorophore being released from the lysosome-related organelles into the relatively higher pH environment of the cytosol. The visually spectacular dynamic fluorescence phenomenon we describe might provide a handle on the biochemistry and genetics of these lysosome-related organelles.

Thiol-catalyzed formation of NO-ferroheme regulates intravascular NO signaling

Nitric oxide (NO) is an endogenously produced signaling molecule that regulates blood flow and platelet activation. However, intracellular and intravascular diffusion of NO are limited by scavenging reactions with several hemoproteins, raising questions as to how free NO can signal in hemoprotein-rich environments. We explore the hypothesis that NO can be stabilized as a labile ferrous heme-nitrosyl complex (Fe2+-NO, NO-ferroheme). We observe a reaction between NO, labile ferric heme (Fe3+) and reduced thiols to yield NO-ferroheme and a thiyl radical. This thiol-catalyzed reductive nitrosylation occurs when heme is solubilized in lipophilic environments such as red blood cell membranes or bound to serum albumin. The resulting NO-ferroheme resists oxidative inactivation, is soluble in cell membranes and is transported intravascularly by albumin to promote potent vasodilation. We therefore provide an alternative route for NO delivery from erythrocytes and blood via transfer of NO-ferroheme and activation of apo-soluble guanylyl cyclase.

Intrinsic and extrinsic regulation of rhabdomyolysis susceptibility by Tango2

Rhabdomyolysis is a clinical emergency characterized by severe muscle damage, resulting in the release of intracellular muscle components, which leads to myoglobinuria and, in severe cases, acute kidney failure. Rhabdomyolysis is caused by genetic factors linked to increased disease susceptibility in response to extrinsic triggers. Recessive mutations in TANGO2 result in episodic rhabdomyolysis, metabolic crises, encephalopathy and cardiac arrhythmia. The underlying mechanism contributing to disease onset in response to specific triggers remains unclear. To address these challenges, we created a zebrafish model of Tango2 deficiency. Here, we demonstrate that the loss of Tango2 in zebrafish results in growth defects, early lethality and increased susceptibility of skeletal muscle defects in response to extrinsic triggers, similar to TANGO2-deficient patients. Using lipidomics, we identified alterations in the glycerolipid pathway in tango2 mutants, which is critical for membrane stability and energy balance. Therefore, these studies provide insight into key disease processes in Tango2 deficiency and have increased our understanding of the impacts of specific defects on predisposition to environmental triggers in TANGO2-related disorders.

Bacterial TANGO2 homologs are heme-trafficking proteins that facilitate biosynthesis of cytochromes c

Heme, an essential molecule for virtually all living organisms, acts primarily as a cofactor in a large number of proteins. However, how heme is mobilized from the site of synthesis to the locations where hemoproteins are assembled remains largely unknown in cells, especially bacterial ones. In this study, with Shewanella oneidensis as the model, we identified HtpA (SO0126) as a heme-trafficking protein and homolog of TANGO2 proteins found in eukaryotes. We showed that HtpA homologs are widely distributed in all domains of living organisms and have undergone parallel evolution. In its absence, the cytochrome (cyt) c content and catalase activity decreased significantly. We further showed that both HtpA and representative TANGO2 proteins bind heme with 1:1 stoichiometry and a relatively low dissociation constant. Protein interaction analyses substantiated that HtpA directly interacts with the cytochrome c maturation system. Our findings shed light on cross-membrane transport of heme in bacteria and extend the understanding of TANGO2 proteins. IMPORTANCE The intracellular trafficking of heme, an essential cofactor for hemoproteins, remains underexplored even in eukaryotes, let alone bacteria. Here we developed a high-throughput method by which HtpA, a homolog of eukaryotic TANGO2 proteins, was identified to be a heme-binding protein that enhances cytochrome c biosynthesis and catalase activity in Shewanella oneidensis. HtpA interacts with the cytochrome c biosynthesis system directly, supporting that this protein, like TANGO2, functions in intracellular heme trafficking. HtpA homologs are widely distributed, but a large majority of them were found to be non-exchangeable, likely a result of parallel evolution. By substantiating the heme-trafficking nature of HtpA and its eukaryotic homologs, our findings provide general insight into the heme-trafficking process and highlight the functional conservation along evolution in all living organisms.

Notes from the Underground: Heme Homeostasis in C. elegans

Heme is an iron-containing tetrapyrrole that plays a critical role in various biological processes, including oxygen transport, electron transport, signal transduction, and catalysis. However, free heme is hydrophobic and potentially toxic to cells. Organisms have evolved specific pathways to safely transport this essential but toxic macrocycle within and between cells. The bacterivorous soil-dwelling nematode Caenorhabditis elegans is a powerful animal model for studying heme-trafficking pathways, as it lacks the ability to synthesize heme but instead relies on specialized trafficking pathways to acquire, distribute, and utilize heme. Over the past 15 years, studies on this microscopic animal have led to the identification of a number of heme-trafficking proteins, with corresponding functional homologs in vertebrates. In this review, we provide a comprehensive overview of the heme-trafficking proteins identified in C. elegans and their corresponding homologs in related organisms.

Live or death in cells: from micronutrition metabolism to cell fate

Micronutrients and cell death have a strong relationship and both are essential for human to maintain good body health. Dysregulation of any micronutrients causes metabolic or chronic diseases, including obesity, cardiometabolic condition, neurodegeneration, and cancer. The nematode Caenorhabditis elegans is an ideal genetic organism for researching the mechanisms of micronutrients in metabolism, healthspan, and lifespan. For example, C. elegans is a haem auxotroph, and the research of this special haem trafficking pathway contributes important reference to mammal study. Also, C. elegans characteristics including anatomy simply, clear cell lineage, well-defined genetics, and easily differentiated cell forms make it a powerful tool for studying the mechanisms of cell death including apoptosis, necrosis, autophagy, and ferroptosis. Here, we describe the understanding of micronutrient metabolism currently and also sort out the fundamental mechanisms of different kinds of cell death. A thorough understanding of these physiological processes not only builds a foundation for developing better treatments for various micronutrient disorders but also provides key insights into human health and aging.

Vitamin B5, a coenzyme A precursor, rescues TANGO2 deficiency disease-associated defects in Drosophila and human cells

Mutations in the Transport and Golgi Organization 2 (TANGO2) gene are associated with intellectual deficit, neurodevelopmental delay and regression. Individuals can also present with an acute metabolic crisis that includes rhabdomyolysis, cardiomyopathy, and cardiac arrhythmias, the latter of which are potentially lethal. While preventing metabolic crises has the potential to reduce mortality, no treatments currently exist for this condition. The function of TANGO2 remains unknown but is suspected to be involved in some aspect of lipid metabolism. Here, we describe a model of TANGO2-related disease in the fruit fly Drosophila melanogaster that recapitulates crucial disease traits. Pairing a new fly model with human cells, we examined the effects of vitamin B5, a coenzyme A (CoA) precursor, on alleviating the cellular and organismal defects associated with TANGO2 deficiency. We demonstrate that vitamin B5 specifically improves multiple defects associated with TANGO2 loss-of-function in Drosophila and rescues membrane trafficking defects in human cells. We also observed a partial rescue of one of the fly defects by vitamin B3, though to a lesser extent than vitamin B5. Our data suggest that a B complex supplement containing vitamin B5/pantothenate may have therapeutic benefits in individuals with TANGO2-deficiency disease. Possible mechanisms for the rescue are discussed that may include restoration of lipid homeostasis.

A multifunctional peroxidase-based reaction for imaging, sensing and networking of spatial biology

Peroxidase is a heme-containing enzyme that reduces hydrogen peroxide to water by extracting electron(s) from aromatic compounds via a sequential turnover reaction. This reaction can generate various aromatic radicals in the form of short-lived "spray" molecules. These can be either covalently attached to proximal proteins or polymerized via radical-radical coupling. Recent studies have shown that these peroxidase-generated radicals can be utilized as effective tools for spatial research in biological systems, including imaging studies aimed at the spatial localization of proteins using electron microscopy, spatial proteome mapping, and spatial sensing of metabolites (e.g., heme and hydrogen peroxide). This review may facilitate the wider utilization of these peroxidase-based methods for spatial discovery in cellular biology.

Haem transporter HRG-1 is essential in the barber's pole worm and an intervention target candidate

Parasitic roundworms (nematodes) have lost genes involved in the de novo biosynthesis of haem, but have evolved the capacity to acquire and utilise exogenous haem from host animals. However, very little is known about the processes or mechanisms underlying haem acquisition and utilisation in parasites. Here, we reveal that HRG-1 is a conserved and unique haem transporter in a broad range of parasitic nematodes of socioeconomic importance, which enables haem uptake via intestinal cells, facilitates cellular haem utilisation through the endo-lysosomal system, and exhibits a conspicuous distribution at the basal laminae covering the alimentary tract, muscles and gonads. The broader tissue expression pattern of HRG-1 in Haemonchus contortus (barber's pole worm) compared with its orthologues in the free-living nematode Caenorhabditis elegans indicates critical involvement of this unique haem transporter in haem homeostasis in tissues and organs of the parasitic nematode. RNAi-mediated gene knockdown of hrg-1 resulted in sick and lethal phenotypes of infective larvae of H. contortus, which could only be rescued by supplementation of exogenous haem in the early developmental stage. Notably, the RNAi-treated infective larvae could not establish infection or survive in the mammalian host, suggesting an indispensable role of this haem transporter in the survival of this parasite. This study provides new insights into the haem biology of a parasitic nematode, demonstrates that haem acquisition by HRG-1 is essential for H. contortus survival and infection, and suggests that HRG-1 could be an intervention target candidate in a range of parasitic nematodes.

Thiol catalyzed formation of NO-ferroheme regulates canonical intravascular NO signaling

Nitric oxide (NO) is an endogenously produced physiological signaling molecule that regulates blood flow and platelet activation. However, both the intracellular and intravascular diffusion of NO is severely limited by scavenging reactions with hemoglobin, myoglobin, and other hemoproteins, raising unanswered questions as to how free NO can signal in hemoprotein-rich environments, like blood and cardiomyocytes. We explored the hypothesis that NO could be stabilized as a ferrous heme-nitrosyl complex (Fe 2+ -NO, NO-ferroheme) either in solution within membranes or bound to albumin. Unexpectedly, we observed a rapid reaction of NO with free ferric heme (Fe 3+ ) and a reduced thiol under physiological conditions to yield NO-ferroheme and a thiyl radical. This thiol-catalyzed reductive nitrosylation reaction occurs readily when the hemin is solubilized in lipophilic environments, such as red blood cell membranes, or bound to serum albumin. NO-ferroheme albumin is stable, even in the presence of excess oxyhemoglobin, and potently inhibits platelet activation. NO-ferroheme-albumin administered intravenously to mice dose-dependently vasodilates at low- to mid-nanomolar concentrations. In conclusion, we report the fastest rate of reductive nitrosylation observed to date to generate a NO-ferroheme molecule that resists oxidative inactivation, is soluble in cell membranes, and is transported intravascularly by albumin to promote potent vasodilation.

Humidity-Responsive Polymer Cushion-Supported Biomimetic Membrane: A Model System for X-ray Studies

An effort aimed at replacing the conventional water column by a relative humidity (RH) environment for structural investigation of a soft polymer cushion-supported model phospholipid membrane has been reported. An RH-responsive well-hydrated polymer cushion layer capable of approximately 2-fold swellability under RH 96% has been employed for phospholipid model membrane fabrication. To validate the proposed method, supported lipid bilayers (SLBs) of phosphocholine and phosphoethanolamine were deposited and structurally characterized at molecular level by the X-ray scattering method. In addition, the molecular interaction of the porphyrin-based hemin molecule, having a drug-like structure, with the supported membrane has been studied for further validation. The swelling behavior of the polymer cushion has been studied at a range of RH values prior to the bilayer deposition. The RH environment, in comparison to the conventional water column, enhanced the dynamic range approximately by 100-fold and the structural resolution by 2-fold. Thus, the bilayer structural features can be assessed without being overwhelmed by the background signals from the traditional water column. This facilitates in extracting reliable layer parameters and exogenous molecule-induced minute changes from the model fit. The proposed method will have far-reaching implications in biosensor engineering, protein-lipid, and drug-lipid interaction studies, X-ray microscopy, imaging, and photon correlation spectroscopy studies from SLBs where acquiring sufficient scattered intensity is still a challenge. This study also predicts that lab-based rotating-anode X-ray instruments can potentially be an alternative to the hard-access synchrotron experiments on biomimetic membranes, keeping the dynamic range and structural resolution uncompromised.