Wolfram Syndrome protein, Miner1, regulates sulphydryl redox status, the unfolded protein response, and Ca2+ homeostasis

Wolfram syndrome 2 gene (CISD2) deficiency disrupts Ca2+-mediated insulin secretion in β-cells

OBJECTIVE

Diabetes, characterized by childhood-onset, autoantibody-negativity and insulin-deficiency, is a major manifestation of Wolfram syndrome 2 (WFS2), which is caused by recessive mutations of CISD2. Nevertheless, the mechanism underlying β-cell dysfunction in WFS2 remains elusive. Here we delineate the essential role of CISD2 in β-cells.

METHODS

We use β-cell specific Cisd2 knockout (Cisd2KO) mice, a CRISPR-mediated Cisd2KO MIN6 β-cell line and transcriptomic analysis.

RESULTS

Four findings are pinpointed. Firstly, β-cell specific Cisd2KO in mice disrupts systemic glucose homeostasis via impairing β-granules synthesis and insulin secretion; hypertrophy of the β-islets and the presence of a loss of identity that affects certain β-cells. Secondly, Cisd2 deficiency leads to impairment of glucose-induced extracellular Ca2+ influx, which compromises Ca2+-mediated insulin secretory signaling, causing mitochondrial dysfunction and, thereby impairing insulin secretion in the MIN6-Cisd2KO β-cells. Thirdly, transcriptomic analysis of β-islets reveals that Cisd2 modulates proteostasis and ER stress, mitochondrial function, insulin secretion and vesicle transport. Finally, the activated state of two potential upstream regulators, Glis3 and Hnf1a, is significantly suppressed under Cisd2 deficiency; notably, their downstream target genes are deeply involved in β-cell function and identity.

CONCLUSIONS

These findings provide mechanistic insights and form a basis for developing therapeutics for the effective treatment of diabetes in WFS2 patients.

Reciprocal rescue of Wolfram syndrome by two causative genes

Wolfram syndrome (WS) is marked by juvenile-onset diabetes mellitus, optic atrophy, diabetes insipidus, and sensorineural hearing loss. The causative genes, WFS1 and CISD2, correspond to WS types 1 and 2, respectively. Here, we establish their mutual indispensability for inositol 1,4,5-triphosphate receptor (IP3R) activity, demonstrating their ability to restore reduced IP3R activity in WFS1- or CISD2-deficient mammalian cells. Additionally, our Drosophila WS models lacking dWFS1 or dCISD exhibit diabetes-like phenotypes analogous to WS patients, and overexpression of dWFS1 and dCISD in the flies alleviates their phenotypes. We have engineered a peptide containing the CDGSH domain of CISD2, critical for its interaction with IP3R. Overexpression of our CISD2 peptide or treatment with its cell-penetrating peptide (CPP)-conjugated form restores calcium homeostasis in WFS1- or CISD2-deficient cells, and overexpressing the homologous dCISD peptide suppresses diabetes-like phenotypes in WS model flies. These findings underscore the intricate involvements of WFS1 and CISD2 in ER calcium regulation and provide potential therapeutic prospects for WS-related diabetes.

ER calcium depletion as a key driver for impaired ER-to-mitochondria calcium transfer and mitochondrial dysfunction in Wolfram syndrome

Wolfram syndrome is a rare genetic disease caused by mutations in the WFS1 or CISD2 gene. A primary defect in Wolfram syndrome involves poor ER Ca2+ handling, but how this disturbance leads to the disease is not known. The current study, performed in primary neurons, the most affected and disease-relevant cells, involving both Wolfram syndrome genes, explains how the disturbed ER Ca2+ handling compromises mitochondrial function and affects neuronal health. Loss of ER Ca2+ content and impaired ER-mitochondrial contact sites in the WFS1- or CISD2-deficient neurons is associated with lower IP3R-mediated Ca2+ transfer from ER to mitochondria and decreased mitochondrial Ca2+ uptake. In turn, reduced mitochondrial Ca2+ content inhibits mitochondrial ATP production leading to an increased NADH/NAD+ ratio. The resulting bioenergetic deficit and reductive stress compromise the health of the neurons. Our work also identifies pharmacological targets and compounds that restore Ca2+ homeostasis, enhance mitochondrial function and improve neuronal health.

Mitochondrial CISD1/Cisd accumulation blocks mitophagy and genetic or pharmacological inhibition rescues neurodegenerative phenotypes in Pink1/parkin models

BACKGROUND

Mitochondrial dysfunction and toxic protein aggregates have been shown to be key features in the pathogenesis of neurodegenerative diseases, such as Parkinson's disease (PD). Functional analysis of genes linked to PD have revealed that the E3 ligase Parkin and the mitochondrial kinase PINK1 are important factors for mitochondrial quality control. PINK1 phosphorylates and activates Parkin, which in turn ubiquitinates mitochondrial proteins priming them and the mitochondrion itself for degradation. However, it is unclear whether dysregulated mitochondrial degradation or the toxic build-up of certain Parkin ubiquitin substrates is the driving pathophysiological mechanism leading to PD. The iron-sulphur cluster containing proteins CISD1 and CISD2 have been identified as major targets of Parkin in various proteomic studies.

METHODS

We employed in vivo Drosophila and human cell culture models to study the role of CISD proteins in cell and tissue viability as well as aged-related neurodegeneration, specifically analysing aspects of mitophagy and autophagy using orthogonal assays.

RESULTS

We show that the Drosophila homolog Cisd accumulates in Pink1 and parkin mutant flies, as well as during ageing. We observed that build-up of Cisd is particularly toxic in neurons, resulting in mitochondrial defects and Ser65-phospho-Ubiquitin accumulation. Age-related increase of Cisd blocks mitophagy and impairs autophagy flux. Importantly, reduction of Cisd levels upregulates mitophagy in vitro and in vivo, and ameliorates pathological phenotypes in locomotion, lifespan and neurodegeneration in Pink1/parkin mutant flies. In addition, we show that pharmacological inhibition of CISD1/2 by rosiglitazone and NL-1 induces mitophagy in human cells and ameliorates the defective phenotypes of Pink1/parkin mutants.

CONCLUSION

Altogether, our studies indicate that Cisd accumulation during ageing and in Pink1/parkin mutants is a key driver of pathology by blocking mitophagy, and genetically and pharmacologically inhibiting CISD proteins may offer a potential target for therapeutic intervention.

Not So Rare: Diseases Based on Mutant Proteins Controlling Endoplasmic Reticulum-Mitochondria Contact (MERC) Tethering

Mitochondria-endoplasmic reticulum contacts (MERCs), also called endoplasmic reticulum (ER)-mitochondria contact sites (ERMCS), are the membrane domains, where these two organelles exchange lipids, Ca2+ ions, and reactive oxygen species. This crosstalk is a major determinant of cell metabolism, since it allows the ER to control mitochondrial oxidative phosphorylation and the Krebs cycle, while conversely, it allows the mitochondria to provide sufficient ATP to control ER proteostasis. MERC metabolic signaling is under the control of tethers and a multitude of regulatory proteins. Many of these proteins have recently been discovered to give rise to rare diseases if their genes are mutated. Surprisingly, these diseases share important hallmarks and cause neurological defects, sometimes paired with, or replaced by skeletal muscle deficiency. Typical symptoms include developmental delay, intellectual disability, facial dysmorphism and ophthalmologic defects. Seizures, epilepsy, deafness, ataxia, or peripheral neuropathy can also occur upon mutation of a MERC protein. Given that most MERC tethers and regulatory proteins have secondary functions, some MERC protein-based diseases do not fit into this categorization. Typically, however, the proteins affected in those diseases have dominant functions unrelated to their roles in MERCs tethering or their regulation. We are discussing avenues to pharmacologically target genetic diseases leading to MERC defects, based on our novel insight that MERC defects lead to common characteristics in rare diseases. These shared characteristics of MERCs disorders raise the hope that they may allow for similar treatment options.

TMTC4 is a hair cell-specific human deafness gene

Transmembrane and tetratricopeptide repeat 4 (Tmtc4) is a deafness gene in mice. Tmtc4-KO mice have rapidly progressive postnatal hearing loss due to overactivation of the unfolded protein response (UPR); however, the cellular basis and human relevance of Tmtc4-associated hearing loss in the cochlea was not heretofore appreciated. We created a hair cell-specific conditional KO mouse that phenocopies the constitutive KO with postnatal onset deafness, demonstrating that Tmtc4 is a hair cell-specific deafness gene. Furthermore, we identified a human family in which Tmtc4 variants segregate with adult-onset progressive hearing loss. Lymphoblastoid cells derived from multiple affected and unaffected family members, as well as human embryonic kidney cells engineered to harbor each of the variants, demonstrated that the human Tmtc4 variants confer hypersensitivity of the UPR toward apoptosis. These findings provide evidence that TMTC4 is a deafness gene in humans and further implicate the UPR in progressive hearing loss.

Depletion of WFS1 compromises mitochondrial function in hiPSC-derived neuronal models of Wolfram syndrome

Mitochondrial dysfunction involving mitochondria-associated ER membrane (MAM) dysregulation is implicated in the pathogenesis of late-onset neurodegenerative diseases, but understanding is limited for rare early-onset conditions. Loss of the MAM-resident protein WFS1 causes Wolfram syndrome (WS), a rare early-onset neurodegenerative disease that has been linked to mitochondrial abnormalities. Here we demonstrate mitochondrial dysfunction in human induced pluripotent stem cell-derived neuronal cells of WS patients. VDAC1 is identified to interact with WFS1, whereas loss of this interaction in WS cells could compromise mitochondrial function. Restoring WFS1 levels in WS cells reinstates WFS1-VDAC1 interaction, which correlates with an increase in MAMs and mitochondrial network that could positively affect mitochondrial function. Genetic rescue by WFS1 overexpression or pharmacological agents modulating mitochondrial function improves the viability and bioenergetics of WS neurons. Our data implicate a role of WFS1 in regulating mitochondrial functionality and highlight a therapeutic intervention for WS and related rare diseases with mitochondrial defects.

CDGSH iron sulfur domain 2 over-expression alleviates neuronal ferroptosis and brain injury by inhibiting lipid peroxidation via AKT/mTOR pathway following intracerebral hemorrhage in mice

Ferroptosis has been implicated in the pathogenesis of secondary brain injury following intracerebral hemorrhage (ICH), and regulating this process is considered a potential therapy for alleviating further brain injury. A previous study showed that CDGSH iron sulfur domain 2 (CISD2) can inhibit ferroptosis in cancer. Thus, we investigated the effects of CISD2 on ferroptosis and the mechanisms underlying its neuroprotective role in mice after ICH. CISD2 expression markedly increased after ICH. CISD2 over-expression significantly decreased the number of Fluoro-Jade C-positive neurons and alleviated brain edema and neurobehavioral deficits at 24 h after ICH. In addition, CISD2 over-expression up-regulated the expression of p-AKT, p-mTOR, ferritin heavy chain 1, glutathione peroxidase 4, ferroportin, glutathione, and glutathione peroxidase activity, which are markers of ferroptosis. Additionally, CISD2 over-expression down-regulated the levels of malonaldehyde, iron content, acyl-CoA synthetase long-chain family member 4, transferrin receptor 1, and cyclooxygenase-2 at 24 h after ICH. It also alleviated mitochondrial shrinkage and decreased the density of the mitochondrial membrane. Furthermore, CISD2 over-expression increased the number of GPX4-positive neurons following ICH induction. Conversely, knockdown of CISD2 aggravated neurobehavioral deficits, brain edema, and neuronal ferroptosis. Mechanistically, MK2206, an AKT inhibitor, suppressed p-AKT and p-mTOR and reversed the effects of CISD2 over-expression on markers of neuronal ferroptosis and acute neurological outcome. Taken together, CISD2 over-expression alleviated neuronal ferroptosis and improved neurological performance, which may be mediated through the AKT/mTOR pathway after ICH. Thus, CISD2 may be a potential target to mitigate brain injury via the anti-ferroptosis effect after ICH.

Coupling of autophagy and the mitochondrial intrinsic apoptosis pathway modulates proteostasis and ageing in Caenorhabditis elegans

Mitochondria preserve metabolic homeostasis and integrate stress signals, to trigger cytoprotective, or cell death pathways. Mitochondrial homeostasis and function decline with age. The mechanisms underlying the deterioration of mitochondrial homeostasis during ageing, or in age-associated pathologies, remain unclear. Here, we show that CISD-1, a mitochondrial iron-sulfur cluster binding protein, implicated in the pathogenesis of Wolfram neurodegenerative syndrome type 2, modulates longevity in the nematode Caenorhabditis elegans by engaging autophagy and the mitochondrial intrinsic apoptosis pathway. The anti-apoptotic protein CED-9 is the downstream effector that mediates CISD-1-dependent effects on proteostasis, neuronal integrity and lifespan. Moreover, intracellular iron abundance is critical for CISD-1 function, since mild iron supplementation is sufficient to decelerate ageing and partly ameliorate the disturbed mitochondrial bioenergetics and proteostasis of CISD-1 deficient animals. Our findings reveal that CISD-1 serves as a mechanistic link between autophagy and the apoptotic pathway in mitochondria to differentially modulate organismal proteostasis and ageing, and suggest novel approaches which could facilitate the treatment of Wolfram Syndrome or related diseases.

Psychiatric Diagnoses and Medications in Wolfram Syndrome

Background

Wolfram Syndrome is a rare genetic disorder usually resulting from pathogenic variation in the WFS1 gene, which leads to an exaggerated endoplasmic reticulum (ER) stress response. The disorder is typically characterized by diabetes insipidus, diabetes mellitus, optic nerve atrophy, hearing loss, and neurodegenerative features. Existing literature suggests it may also have psychiatric manifestations.

Objective

To examine lifetime psychiatric diagnoses and medication history in Wolfram Syndrome.

Method

Child, adolescent, and young adult Wolfram Syndrome participants (n=39) were assessed by a child & adolescent psychiatrist to determine best estimate DSM-5 lifetime psychiatric diagnoses as well as psychoactive medication history. In addition, the Child & Adolescent Symptom Inventory-5 (CASI-5) Parent Checklist was used to determine likely psychiatric diagnoses based on symptom counts in Wolfram Syndrome patients (n=33), type 1 diabetes (n=15), and healthy comparison (n=18) groups.

Results

Study participants with Wolfram Syndrome had high lifetime rates of anxiety disorders (77%). Also, 31% had an obsessive-compulsive spectrum disorder, 33% had a mood disorder, 31% had a neurodevelopmental or disruptive behavior disorder, and 31% had a sleep-wake disorder. More than half of Wolfram Syndrome participants had taken at least one psychoactive medication, and one third had taken at least one selective serotonin reuptake inhibitor (SSRI). Some individuals reported poor response to sertraline but better response after switching to another SSRI (fluoxetine or citalopram). In general, people with Wolfram Syndrome often reported benefit from psychotherapy and/or commonly used psychoactive medications appropriate for their psychiatric diagnoses.

Conclusions

Wolfram Syndrome may be associated with elevated risk for anxiety and obsessive-compulsive spectrum disorders, which seem generally responsive to usual treatments for these disorders.

A practical guide for the analysis, standardization and interpretation of oxygen consumption measurements

Measurement of oxygen consumption is a powerful and uniquely informative experimental technique. It can help identify mitochondrial mechanisms of action following pharmacologic and genetic interventions, and characterize energy metabolism in physiology and disease. The conceptual and practical benefits of respirometry have made it a frontline technique to understand how mitochondrial function can interface with-and in some cases control-cell physiology. Nonetheless, an appreciation of the complexity and challenges involved with such measurements is required to avoid common experimental and analytical pitfalls. Here we provide a practical guide to oxygen consumption measurements covering the selection of experimental models and instrumentation, as well as recommendations for the collection, interpretation and normalization of data. These guidelines are provided with the intention of aiding experimental design and enhancing the overall reputability, transparency and reliability of oxygen consumption measurements.

Effects of Curcumin on Mitochondrial Function, Endoplasmic Reticulum Stress, and Mitochondria-Associated Endoplasmic Reticulum Membranes in the Jejunum of Oxidative Stress Piglets

Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) are not only critical for the communication between two organelles but also crucial for cellular processes such as energy metabolism, calcium signaling, and mitochondrial dynamics. The effects of curcumin on jejunal mitochondria, ER, and MAMs in piglets under diquat-induced oxidative stress were assessed. Twenty-four piglets (35 days old, weaned at 21 days, 9.54 ± 0.28 kg, six piglets per group) were used in the study: (1) control group; (2) control + curcumin group; (3) diquat group; and (4) diquat + curcumin group. Curcumin was mixed with the basic diet at 200 mg/kg and fed to piglets. Piglets were administered intraperitoneally of 0.9% saline solution or diquat at 10 mg/kg body weight on the first day. Compared with the diquat group, curcumin improved jejunal morphology and barrier function. Meanwhile, curcumin improved mitochondrial function and ultrastructure, alleviated endoplasmic reticulum stress (ERS), and inhibited apoptosis induced by diquat. Moreover, curcumin prevented excessive MAM formation and alleviated MAM disorder. In conclusion, dietary curcumin ameliorated jejunal damage and mitochondrial dysfunction, attenuated ERS, and alleviated MAM disorder in oxidative stress piglets induced by diquat.

Dysregulated Ca2+ Homeostasis as a Central Theme in Neurodegeneration: Lessons from Alzheimer's Disease and Wolfram Syndrome

Calcium ions (Ca²⁺) operate as important messengers in the cell, indispensable for signaling the underlying numerous cellular processes in all of the cell types in the human body. In neurons, Ca²⁺ signaling is crucial for regulating synaptic transmission and for the processes of learning and memory formation. Hence, the dysregulation of intracellular Ca²⁺ homeostasis results in a broad range of disorders, including cancer and neurodegeneration. A major source for intracellular Ca²⁺ is the endoplasmic reticulum (ER), which has close contacts with other organelles, including mitochondria. In this review, we focus on the emerging role of Ca²⁺ signaling at the ER–mitochondrial interface in two different neurodegenerative diseases, namely Alzheimer’s disease and Wolfram syndrome. Both of these diseases share some common hallmarks in the early stages, including alterations in the ER and mitochondrial Ca²⁺ handling, mitochondrial dysfunction and increased Reactive oxygen species (ROS) production. This indicates that similar mechanisms may underly these two disease pathologies and suggests that both research topics might benefit from complementary research.

Mitochondria-associated membranes: A hub for neurodegenerative diseases

In eukaryotic cells, organelles could coordinate complex mechanisms of signaling transduction metabolism and gene expression through their functional interactions. The functional domain between ER and mitochondria, called mitochondria-associated membranes (MAM), is closely associated with various physiological functions including intracellular lipid transport, Ca²⁺ transfer, mitochondria function maintenance, and autophagosome formation. In addition, more evidence suggests that MAM modulate cellular functions in health and disease. Studies have also demonstrated the association of MAM with numerous diseases, including neurodegenerative diseases, cancer, viral infection, obesity, and diabetes. In fact, recent evidence revealed a close relationship of MAM with Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and other neurodegenerative diseases. In this view, elucidating the role of MAM in neurodegenerative diseases is particularly important. This review will focus the main tethering protein complexes of MAM and functions of MAM. Besides, the role of MAM in the regulation of neurodegenerative diseases and the potential molecular mechanisms is introduced to provide a new understanding of the pathogenesis of these diseases.

Anti-Inflammatory CDGSH Iron-Sulfur Domain 2: A Biomarker of Central Nervous System Insult in Cellular, Animal Models and Patients

Spinal cord injury (SCI) promotes brain inflammation; conversely, brain injury promotes spinal neuron loss. There is a need to identify molecular biomarkers and therapeutic targets for central nervous system (CNS) injury. CDGSH iron-sulfur structural domain 2 (CISD2), an NF-κB antagonist, is downregulated after injury in vivo and in vitro. We aimed to examine the diagnostic value of CISD2 in patients with CNS insult. Plasma and cerebrospinal fluid (CSF) CISD2 levels were decreased in 13 patients with CNS insult and were negatively correlated with plasma IL6 levels (associated with disease severity; r = −0.7062; p < 0.01). SCI-induced inflammatory mediators delivered through CSF promoted mouse brain inflammation at 1 h post-SCI. Anti-CISD2 antibody treatment exacerbated SCI-induced inflammation in mouse spine and brain. Lipopolysaccharide-stimulated siCISD2-transfected EOC microglial cells exhibited proinflammatory phenotypes (enhanced M1 polarization, decreased M2 polarization, and increased intranuclear NF-κB p65 translocation). Plasma and CSF CISD2 levels were increased in three patients with CNS insult post-therapeutic hypothermia. CISD2 levels were negatively correlated with plasma and CSF levels of inflammatory mediators. CISD2 inhibition and potentiation experiments in cells, animals, and humans revealed CISD2 as a biomarker for CNS insult and upregulation of CISD2 anti-inflammatory properties as a potential therapeutic strategy for CNS insult.

Current Drug Repurposing Strategies for Rare Neurodegenerative Disorders

Rare diseases are life-threatening or chronically debilitating low-prevalent disorders caused by pathogenic mutations or particular environmental insults. Due to their high complexity and low frequency, important gaps still exist in their prevention, diagnosis, and treatment. Since new drug discovery is a very costly and time-consuming process, leading pharmaceutical companies show relatively low interest in orphan drug research and development due to the high cost of investments compared to the low market return of the product. Drug repurposing–based approaches appear then as cost- and time-saving strategies for the development of therapeutic opportunities for rare diseases. In this article, we discuss the scientific, regulatory, and economic aspects of the development of repurposed drugs for the treatment of rare neurodegenerative disorders with a particular focus on Huntington’s disease, Friedreich’s ataxia, Wolfram syndrome, and amyotrophic lateral sclerosis. The role of academia, pharmaceutical companies, patient associations, and foundations in the identification of candidate compounds and their preclinical and clinical evaluation will also be discussed.

Use of Zebrafish Models to Boost Research in Rare Genetic Diseases

Rare genetic diseases are a group of pathologies with often unmet clinical needs. Even if rare by a single genetic disease (from 1/2000 to 1/more than 1,000,000), the total number of patients concerned account for approximatively 400 million peoples worldwide. Finding treatments remains challenging due to the complexity of these diseases, the small number of patients and the challenge in conducting clinical trials. Therefore, innovative preclinical research strategies are required. The zebrafish has emerged as a powerful animal model for investigating rare diseases. Zebrafish combines conserved vertebrate characteristics with high rate of breeding, limited housing requirements and low costs. More than 84% of human genes responsible for diseases present an orthologue, suggesting that the majority of genetic diseases could be modelized in zebrafish. In this review, we emphasize the unique advantages of zebrafish models over other in vivo models, particularly underlining the high throughput phenotypic capacity for therapeutic screening. We briefly introduce how the generation of zebrafish transgenic lines by gene-modulating technologies can be used to model rare genetic diseases. Then, we describe how zebrafish could be phenotyped using state-of-the-art technologies. Two prototypic examples of rare diseases illustrate how zebrafish models could play a critical role in deciphering the underlying mechanisms of rare genetic diseases and their use to identify innovative therapeutic solutions.

Iron Metabolism in Pancreatic Beta-Cell Function and Dysfunction

Iron is an essential element involved in a variety of physiological functions. In the pancreatic beta-cells, being part of Fe-S cluster proteins, it is necessary for the correct insulin synthesis and processing. In the mitochondria, as a component of the respiratory chain, it allows the production of ATP and reactive oxygen species (ROS) that trigger beta-cell depolarization and potentiate the calcium-dependent insulin release. Iron cellular content must be finely tuned to ensure the normal supply but also to prevent overloading. Indeed, due to the high reactivity with oxygen and the formation of free radicals, iron excess may cause oxidative damage of cells that are extremely vulnerable to this condition because the normal elevated ROS production and the paucity in antioxidant enzyme activities. The aim of the present review is to provide insights into the mechanisms responsible for iron homeostasis in beta-cells, describing how alteration of these processes has been related to beta-cell damage and failure. Defects in iron-storing or -chaperoning proteins have been detected in diabetic conditions; therefore, the control of iron metabolism in these cells deserves further investigation as a promising target for the development of new disease treatments.

Intracellular targeting of Cisd2/Miner1 to the endoplasmic reticulum

Background

Cisd1 and Cisd2 proteins share very similar structures with an N-terminal membrane-anchoring domain and a C-terminal cytosolic domain containing an iron-cluster binding domain and ending with a C-terminal KKxx sequence. Despite sharing a similar structure, Cisd1 and Cisd2 are anchored to different compartments: mitochondria for Cisd1 and endoplasmic reticulum for Cisd2. The aim of this study was to identify the protein motifs targeting Cisd2 to the ER and ensuring its retention in this compartment.

Results

We used new recombinant antibodies to localize Cisd1 and Cisd2 proteins, as well as various protein chimeras. Cisd2 is targeted to the ER by its N-terminal sequence. It is then retained in the ER by the combined action of a C-terminal COPI-binding KKxx ER retrieval motif, and of an ER-targeting transmembrane domain. As previously reported for Cisd1, Cisd2 can alter the morphology of the compartment in which it accumulates.

Conclusion

Although they share a very similar structure, Cisd1 and Cisd2 use largely different intracellular targeting motifs to reach their target compartment (mitochondria and endoplasmic reticulum, respectively).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-021-00387-1.

Uniting the divergent Wolfram syndrome-linked proteins WFS1 and CISD2 as modulators of Ca2+ signaling

[Figure: see text].

A Combined Drug Treatment That Reduces Mitochondrial Iron and Reactive Oxygen Levels Recovers Insulin Secretion in NAF-1-Deficient Pancreatic Cells

Decreased insulin secretion, associated with pancreatic β-cell failure, plays a critical role in many human diseases including diabetes, obesity, and cancer. While numerous studies linked β-cell failure with enhanced levels of reactive oxygen species (ROS), the development of diabetes associated with hereditary conditions that result in iron overload, e.g., hemochromatosis, Friedreich's ataxia, and Wolfram syndrome type 2 (WFS-T2; a mutation in CISD2, encoding the [2Fe-2S] protein NAF-1), underscores an additional link between iron metabolism and β-cell failure. Here, using NAF-1-repressed INS-1E pancreatic cells, we observed that NAF-1 repression inhibited insulin secretion, as well as impaired mitochondrial and ER structure and function. Importantly, we found that a combined treatment with the cell permeant iron chelator deferiprone and the glutathione precursor N-acetyl cysteine promoted the structural repair of mitochondria and ER, decreased mitochondrial labile iron and ROS levels, and restored glucose-stimulated insulin secretion. Additionally, treatment with the ferroptosis inhibitor ferrostatin-1 decreased cellular ROS formation and improved cellular growth of NAF-1 repressed pancreatic cells. Our findings reveal that suppressed expression of NAF-1 is associated with the development of ferroptosis-like features in pancreatic cells, and that reducing the levels of mitochondrial iron and ROS levels could be used as a therapeutic avenue for WFS-T2 patients.

Novel mutations in malonyl-CoA-acyl carrier protein transacylase provoke autosomal recessive optic neuropathy

Inherited optic neuropathies are rare eye diseases of optic nerve dysfunction that present in various genetic forms. Previously, mutation in three genes encoding mitochondrial proteins has been implicated in autosomal recessive forms of optic atrophy that involve progressive degeneration of optic nerve and retinal ganglion cells (RGC). Using whole exome analysis, a novel double homozygous mutation p.L81R and pR212W in malonyl CoA-acyl carrier protein transacylase (MCAT), a mitochondrial protein involved in fatty acid biosynthesis, has now been identified as responsible for an autosomal recessive optic neuropathy from a Chinese consanguineous family. MCAT is expressed in RGC that are rich in mitochondria. The disease variants lead to structurally unstable MCAT protein with significantly reduced intracellular expression. RGC-specific knockdown of Mcat in mice, lead to an attenuated retinal neurofiber layer, that resembles the phenotype of optic neuropathy. These results indicated that MCAT plays an essential role in mitochondrial function and maintenance of RGC axons, while novel MCAT p.L81R and p.R212W mutations can lead to optic neuropathy.

Clinical Spectrum Associated with Wolfram Syndrome Type 1 and Type 2: A Review on Genotype-Phenotype Correlations

Wolfram syndrome is a rare neurodegenerative disorder that is typically characterized by diabetes mellitus and optic atrophy. Other common features are diabetes insipidus and hearing loss, but additional less-frequent findings may also be present. The phenotype spectrum is quite wide, and penetrance may be incomplete. The syndrome is progressive, and thus, the clinical picture may change during follow-up. Currently, two different subtypes of this syndrome have been described, and they are associated with two different disease-genes, wolframin (WFS1) and CISD2. These genes encode a transmembrane protein and an endoplasmic reticulum intermembrane protein, respectively. These genes are detected in different organs and account for the pleiotropic features of this syndrome. In this review, we describe the phenotypes of both syndromes and discuss the most pertinent literature about the genotype–phenotype correlation. The clinical presentation of Wolfram syndrome type 1 suggests that the pathogenic variant does not predict the phenotype. There are few papers on Wolfram syndrome type 2 and, thus, predicting the phenotype on the basis of genotype is not yet supported. We also discuss the most pertinent approach to gene analysis.

Glutathione Metabolism and the Novel Role of Mitochondrial GSH in Retinal Degeneration

Glutathione (GSH) is present ubiquitously, and its role as a crucial cellular antioxidant in tissues, including the retina, is well established. GSH's antioxidant function arises from its ability to scavenge reactive oxygen species or to serve as an essential cofactor for GSH S-transferases and peroxidases. This review summarizes the general functions, retinal distribution, disorders linked to GSH deficiency, and the emerging role for mitochondrial GSH (mGSH) in retinal function. Though synthesized only in the cytosol, the presence of GSH in multiple cell organelles suggests the requirement for its active transport across organellar membranes. The localization and distribution of 2-oxoglutarate carrier (OGC) and dicarboxylate carrier (DIC), two recently characterized mitochondrial carrier proteins in RPE and retina, show that these transporters are highly expressed in human retinal pigment epithelium (RPE) cells and retinal layers, and their expression increases with RPE polarity in cultured cells. Depletion of mGSH levels via inhibition of the two transporters resulted in reduced mitochondrial bioenergetic parameters (basal respiration, ATP production, maximal respiration, and spare respiratory capacity) and increased RPE cell death. These results begin to reveal a critical role for mGSH in maintaining RPE bioenergetics and cell health. Thus, augmentation of mGSH pool under GSH-deficient conditions may be a valuable tool in treating retinal disorders, such as age-related macular degeneration and optic neuropathies, whose pathologies have been associated with mitochondrial dysfunction.

New Insights of the NEET Protein CISD2 Reveals Distinct Features Compared to Its Close Mitochondrial Homolog mitoNEET

Human CISD2 and mitoNEET are two NEET proteins anchored in the endoplasmic reticulum and mitochondria membranes respectively, with an Fe–S containing domain stretching out in the cytosol. Their cytosolic domains are close in sequence and structure. In the present study, combining cellular and biochemical approaches, we compared both proteins in order to possibly identify specific roles and mechanisms of action in the cell. We show that both proteins exhibit a high intrinsic stability and a sensitivity of their cluster to oxygen. In contrast, they differ in according to expression profiles in tissues and intracellular half-life. The stability of their Fe–S cluster and its ability to be transferred in vitro are affected differently by pH variations in a physiological and pathological range for cytosolic pH. Finally, we question a possible role for CISD2 in cellular Fe–S cluster trafficking. In conclusion, our work highlights unexpected major differences in the cellular and biochemical features between these two structurally close NEET proteins.

Cisd2 Protects the Liver from Oxidative Stress and Ameliorates Western Diet-Induced Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) and its more severe form, nonalcoholic steatohepatitis (NASH), are the most common chronic liver diseases worldwide. However, drugs to treat NAFLD and NASH are an unmet clinical need. This study sought to provide evidence that Cisd2 is a molecular target for the development of treatments targeting NAFLD and NASH. Several discoveries are pinpointed. The first is that Cisd2 dosage modulates the severity of Western diet-induced (WD-induced) NAFLD. Specifically, Cisd2 haploinsufficiency accelerates NAFLD development and exacerbates progression toward NASH. Conversely, an enhanced Cisd2 copy number attenuates liver pathogenesis. Secondly, when a WD is fed to mice, transcriptomic analysis reveals that the major alterations affecting biological processes are related to inflammation, lipid metabolism, and DNA replication/repair. Thirdly, among these differentially expressed genes, the most significant changes involve Nrf2-mediated oxidative stress, cholesterol biosynthesis, and fatty acid metabolism. Finally, increased Cisd2 expression protects the liver from oxidative stress and reduces the occurrence of mitochondrial DNA deletions. Taken together, our mouse model reveals that Cisd2 plays a crucial role in protecting the liver from WD-induced damages. The development of therapeutic agents that effectively enhance Cisd2 expression is one potential approach to the treatment of WD-induced fatty liver diseases.

Molecular Mechanisms behind Inherited Neurodegeneration of the Optic Nerve

Inherited neurodegeneration of the optic nerve is a paradigm in neurology, as many forms of isolated or syndromic optic atrophy are encountered in clinical practice. The retinal ganglion cells originate the axons that form the optic nerve. They are particularly vulnerable to mitochondrial dysfunction, as they present a peculiar cellular architecture, with axons that are not myelinated for a long intra-retinal segment, thus, very energy dependent. The genetic landscape of causative mutations and genes greatly enlarged in the last decade, pointing to common pathways. These mostly imply mitochondrial dysfunction, which leads to a similar outcome in terms of neurodegeneration. We here critically review these pathways, which include (1) complex I-related oxidative phosphorylation (OXPHOS) dysfunction, (2) mitochondrial dynamics, and (3) endoplasmic reticulum-mitochondrial inter-organellar crosstalk. These major pathogenic mechanisms are in turn interconnected and represent the target for therapeutic strategies. Thus, their deep understanding is the basis to set and test new effective therapies, an urgent unmet need for these patients. New tools are now available to capture all interlinked mechanistic intricacies for the pathogenesis of optic nerve neurodegeneration, casting hope for innovative therapies to be rapidly transferred into the clinic and effectively cure inherited optic neuropathies.

Beneficial Impacts of Alpha-Eleostearic Acid from Wild Bitter Melon and Curcumin on Promotion of CDGSH Iron-Sulfur Domain 2: Therapeutic Roles in CNS Injuries and Diseases

Neuroinflammation and abnormal mitochondrial function are related to the cause of aging, neurodegeneration, and neurotrauma. The activation of nuclear factor κB (NF-κB), exaggerating these two pathologies, underlies the pathogenesis for the aforementioned injuries and diseases in the central nervous system (CNS). CDGSH iron-sulfur domain 2 (CISD2) belongs to the human NEET protein family with the [2Fe-2S] cluster. CISD2 has been verified as an NFκB antagonist through the association with peroxisome proliferator-activated receptor-β (PPAR-β). This protective protein can be attenuated under circumstances of CNS injuries and diseases, thereby causing NFκB activation and exaggerating NFκB-provoked neuroinflammation and abnormal mitochondrial function. Consequently, CISD2-elevating plans of action provide pathways in the management of various disease categories. Various bioactive molecules derived from plants exert protective anti-oxidative and anti-inflammatory effects and serve as natural antioxidants, such as conjugated fatty acids and phenolic compounds. Herein, we have summarized pharmacological characters of the two phytochemicals, namely, alpha-eleostearic acid (α-ESA), an isomer of conjugated linolenic acids derived from wild bitter melon (Momordica charantia L. var. abbreviata Ser.), and curcumin, a polyphenol derived from rhizomes of Curcuma longa L. In this review, the unique function of the CISD2-elevating effect of α-ESA and curcumin are particularly emphasized, and these natural compounds are expected to serve as a potential therapeutic target for CNS injuries and diseases.

Molecular mechanisms of β-cell dysfunction and death in monogenic forms of diabetes

Monogenetic forms of diabetes represent 1%-5% of all diabetes cases and are caused by mutations in a single gene. These mutations, that affect genes involved in pancreatic β-cell development, function and survival, or insulin regulation, may be dominant or recessive, inherited or de novo. Most patients with monogenic diabetes are very commonly misdiagnosed as having type 1 or type 2 diabetes. The severity of their symptoms depends on the nature of the mutation, the function of the affected gene and, in some cases, the influence of additional genetic or environmental factors that modulate severity and penetrance. In some patients, diabetes is accompanied by other syndromic features such as deafness, blindness, microcephaly, liver and intestinal defects, among others. The age of diabetes onset may also vary from neonatal until early adulthood manifestations. Since the different mutations result in diverse clinical presentations, patients usually need different treatments that range from just diet and exercise, to the requirement of exogenous insulin or other hypoglycemic drugs, e.g., sulfonylureas or glucagon-like peptide 1 analogs to control their glycemia. As a consequence, awareness and correct diagnosis are crucial for the proper management and treatment of monogenic diabetes patients. In this chapter, we describe mutations causing different monogenic forms of diabetes associated with inadequate pancreas development or impaired β-cell function and survival, and discuss the molecular mechanisms involved in β-cell demise.

CISD2 plays a role in age-related diseases and cancer

CDGSH iron-sulfur domain 2 (Cisd2) is an evolutionarily conserved protein that plays an important regulatory role in aging-related diseases and cancers. Since its discovery, Cisd2 has been identified as a regulatory factor for the aging of the human body and the regulation of mammalian lifespan. Cisd2 is also an oncoprotein that regulates the occurrence and development of cancer. Cisd2 mediates the occurrence of diseases related to human aging and the proliferation, differentiation, metastasis, and invasion of various cancer cells through various mechanisms. Multiple studies have shown that Cisd2 expression is related to the clinical characteristics of aging-related diseases and patients with cancer, and its expression profile is a novel diagnostic and prognostic biomarker for a variety of human diseases. Modulating the expression or function of Cisd2 may be a potential treatment strategy for different diseases. In this review, we summarize the role of Cisd2 in human aging-related diseases and various cancers, as well as the biological functions, underlying mechanisms, and potential clinical significance.

Behavioral characterization of a novel Cisd2 mutant mouse

Wolfram syndrome (WFS) is a rare autosomal recessive disorder characterized by diabetes mellitus and insipidus, progressive optic atrophy and sensorineural deafness. An increased incidence of psychiatric disorders has also been reported in WFS patients. There are two subtypes of WFS. Type 1 (WFS1) is caused by mutations in the WFS1 gene and type 2 (WFS2) results from mutations in the CISD2 gene. Existing Wfs1 knockout mice exhibit many WFS1 cardinal symptoms including diabetic nephropathy, metabolic disruptions and optic atrophy. Far fewer studies have examined loss of Cisd2 function in mice. We identified B6.DDY-Cisd2^m1Lmt, a mouse model with a spontaneous mutation in the Cisd2 gene. B6.DDY-Cisd2^m1Lmt mice were initially identified based on the presence of audible sonic vocalizations as well as decreased body size and weight compared to unaffected wildtype littermates. Although Wfs1 knockout mice have been characterized for numerous behavioral phenotypes, similar studies have been lacking for Cisd2 mutant mice. We tested B6.DDY-Cisd2^m1Lmt mice in a battery of behavioral assays that model phenotypes related to neurological and psychiatric disorders including anxiety, sensorimotor gating, stress response, social interaction and learning and memory. B6.DDY-Cisd2^m1Lmt mice displayed hypoactivity across several behavioral tests, exhibited increased stress response and had deficits in spatial learning and memory and sensorimotor gating compared to wildtype littermates. Our data indicate that the B6.DDY-Cisd2^m1Lmt mouse strain is a useful model to investigate potential mechanisms underlying the neurological and psychiatric symptoms observed in WFS.

The NFκB Antagonist CDGSH Iron-Sulfur Domain 2 Is a Promising Target for the Treatment of Neurodegenerative Diseases

Proinflammatory response and mitochondrial dysfunction are related to the pathogenesis of neurodegenerative diseases (NDs). Nuclear factor κB (NFκB) activation has been shown to exaggerate proinflammation and mitochondrial dysfunction, which underlies NDs. CDGSH iron-sulfur domain 2 (CISD2) has been shown to be associated with peroxisome proliferator-activated receptor-β (PPAR-β) to compete for NFκB and antagonize the two aforementioned NFκB-provoked pathogeneses. Therefore, CISD2-based strategies hold promise in the treatment of NDs. CISD2 protein belongs to the human NEET protein family and is encoded by the CISD2 gene (located at 4q24 in humans). In CISD2, the [2Fe-2S] cluster, through coordinates of 3-cysteine-1-histidine on the CDGSH domain, acts as a homeostasis regulator under environmental stress through the transfer of electrons or iron-sulfur clusters. Here, we have summarized the features of CISD2 in genetics and clinics, briefly outlined the role of CISD2 as a key physiological regulator, and presented modalities to increase CISD2 activity, including biomedical engineering or pharmacological management. Strategies to increase CISD2 activity can be beneficial for the prevention of inflammation and mitochondrial dysfunction, and thus, they can be applied in the management of NDs.

A Simplified Method for the Histochemical Detection of Iron in Paraffin Sections: Intracellular Iron Deposits in Central Nervous System Tissue

Although all cells contain iron, most histochemical methods fail to reveal the presence of iron within many cells of the central nervous system (CNS), particularly neurons. Previously, a sensitive method was developed that limited the extraction of iron in paraffin sections, and this method revealed staining within neurons. However, the staining was often too robust making it difficult to discern discrete intracellular structures. In 1970, a study incorporated acetone in an iron histochemical procedure to facilitate the demarcation of staining features. In the present study, both acetone and limits to iron extraction were included in a simplified staining procedure. This procedure was applied to paraffin sections of CNS tissue from CISD2 deficient and littermate control mice. Discrete nuclear and cytoplasmic staining features were detected in all mice. Although widely present in neurons, punctate cytoplasmic staining was particularly prominent in large neurons within the hindbrain. Evaluation of extended depth of focus images, from serial focal planes, revealed numerous stained cytoplasmic structures. Additionally, the simplified staining procedure was applied to paraffin sections from Alzheimer’s disease and control cases. Despite suboptimal processing conditions compared to mouse tissue, discrete staining of cytoplasmic structures was revealed in some neurons, although many other neurons had nondescript staining features. In addition, initial findings revealed iron deposited within some vessels from patients with Alzheimer’s disease. In summary, since paraffin sections are commonly used for histological preparations, this simplified histochemical procedure could facilitate the study of iron in various CNS conditions by revealing staining details often missed by other procedures.

CISD2 maintains cellular homeostasis

CDGSH Iron Sulfur Domain 2 (CISD2) is the causative gene for the disease Wolfram syndrome 2 (WFS2; MIM 604928), which is an autosomal recessive disorder showing metabolic and neurodegenerative manifestations. CISD2 protein can be localized on the endoplasmic reticulum (ER), outer mitochondrial membrane (OMM) and mitochondria-associated membrane (MAM). CISD2 plays a crucial role in the regulation of cytosolic Ca²⁺ homeostasis, ER integrity and mitochondrial function. Here we summarize the most updated publications and discuss the central role of CISD2 in maintaining cellular homeostasis. This review mainly focuses on the following topics. Firstly, that CISD2 has been recognized as a prolongevity gene and the level of CISD2 is a key determinant of lifespan and healthspan. In mice, Cisd2 deficiency shortens lifespan and accelerates aging. Conversely, a persistently high level of Cisd2 promotes longevity. Intriguingly, exercise stimulates Cisd2 gene expression and thus, the beneficial effects offered by exercise may be partly related to Cisd2 activation. Secondly, that Cisd2 is down-regulated in a variety of tissues and organs during natural aging. Three potential mechanisms that may mediate the age-dependent decrease of Cisd2, via regulating at different levels of gene expression, are discussed. Thirdly, the relationship between CISD2 and cell survival, as well as the potential mechanisms underlying the cell death control, are discussed. Finally we discuss that, in cancers, CISD2 may functions as a double-edged sword, either suppressing or promoting cancer development. This review highlights the importance of the CISD2 in aging and age-related diseases and identifies the urgent need for the translation of available genetic evidence into pharmaceutic interventions in order to alleviate age-related disorders and extend a healthy lifespan in humans.

A central role of the endoplasmic reticulum in the cell emerges from its functional contact sites with multiple organelles

Early eukaryotic cells emerged from the compartmentalization of metabolic processes into specific organelles through the development of an endomembrane system (ES), a precursor of the endoplasmic reticulum (ER), which was essential for their survival. Recently, substantial evidence emerged on how organelles communicate among themselves and with the plasma membrane (PM) through contact sites (CSs). From these studies, the ER-the largest single structure in eukaryotic cells-emerges as a central player communicating with all organelles to coordinate cell functions and respond to external stimuli to maintain cellular homeostasis. Herein we review the functional insights into the ER-CSs with other organelles in a physiological perspective. We hypothesize that, in addition to the primitive role by the ES in the appearance of proto-eukaryotes, its successor-the ER-emerges as the key coordinator of inter-organelle/PM communication. The ER thus appears to be the 'maestro' driving eukaryotic cell evolution by incorporating new functions/organelles, while remaining the real coordinator overarching cellular functions and orchestrating them with the external milieu.

Chemical targeting of NEET proteins reveals their function in mitochondrial morphodynamics

Several human pathologies including neurological, cardiac, infectious, cancerous, and metabolic diseases have been associated with altered mitochondria morphodynamics. Here, we identify a small organic molecule, which we named Mito-C. Mito-C is targeted to mitochondria and rapidly provokes mitochondrial network fragmentation. Biochemical analyses reveal that Mito-C is a member of a new class of heterocyclic compounds that target the NEET protein family, previously reported to regulate mitochondrial iron and ROS homeostasis. One of the NEET proteins, NAF-1, is identified as an important regulator of mitochondria morphodynamics that facilitates recruitment of DRP1 to the ER-mitochondria interface. Consistent with the observation that certain viruses modulate mitochondrial morphogenesis as a necessary part of their replication cycle, Mito-C counteracts dengue virus-induced mitochondrial network hyperfusion and represses viral replication. The newly identified chemical class including Mito-C is of therapeutic relevance for pathologies where altered mitochondria dynamics is part of disease etiology and NEET proteins are highlighted as important therapeutic targets in anti-viral research.

MERCs. The Novel Assistant to Neurotransmission?

In neuroscience, much attention is paid to intercellular interactions, in particular, to synapses. However, many researchers do not pay due attention to the contribution of intracellular contacts to the work of intercellular interactions. Nevertheless, along with synapses, intracellular contacts also have complex organization and a tremendous number of regulatory elements. Mitochondria-endoplasmic reticulum contacts (MERCs) are a specific site of interaction between the two organelles; they provide a basis for a large number of cellular functions, such as calcium homeostasis, lipid metabolism, autophagy, and apoptosis. Despite the presence of these contacts in various parts of neurons and glial cells, it is yet not known whether they fulfill the same functions. There are still many unsolved questions about the work of these intracellular contacts, and one of the most important among them is if MERCs, with their broad implication into synaptic events, can be considered the assistant to neurotransmission?

Function of WFS1 and WFS2 in the Central Nervous System: Implications for Wolfram Syndrome and Alzheimer's disease

L.P. Li, L. Venkataraman, S. Chen, and H.J. Fu. Function of WFS1 and WFS2 in the Central Nervous System: Implications for Wolfram Syndrome and Alzheimer's Disease. NEUROSCI BIOBEHAV REVXXX-XXX,2020.-Wolfram syndrome (WS) is a rare monogenetic spectrum disorder characterized by insulin-dependent juvenile-onset diabetes mellitus, diabetes insipidus, optic nerve atrophy, hearing loss, progressive neurodegeneration, and a wide spectrum of psychiatric manifestations. Most WS patients belong to Wolfram Syndrome type 1 (WS1) caused by mutations in the Wolfram Syndrome 1 (WFS1/Wolframin) gene, while a small fraction of patients belongs to Wolfram Syndrome type 2 (WS2) caused by pathogenic variants in the CDGSH Iron Sulfur Domain 2 (CISD2/WFS2) gene. Although currently there is no treatment for this life-threatening disease, the molecular mechanisms underlying the pathogenesis of WS have been proposed. Interestingly, Alzheimer's disease (AD), an age-dependent neurodegenerative disease, shares some common mechanisms with WS. In this review, we focus on the function of WFS1 and WFS2 in the central nervous system as well as their implications in WS and AD. We also propose three future directions for elucidating the role of WFS1 and WFS2 in WS and AD.

Exploring the FMN binding site in the mitochondrial outer membrane protein mitoNEET

MitoNEET is a mitochondrial outer membrane protein that hosts a redox active [2Fe-2S] cluster in the C-terminal cytosolic domain. Increasing evidence has shown that mitoNEET has an essential role in regulating energy metabolism in human cells. Previously, we reported that the [2Fe-2S] clusters in mitoNEET can be reduced by the reduced flavin mononucleotide (FMNH₂) and oxidized by oxygen or ubiquinone-2, suggesting that mitoNEET may act as a novel redox enzyme catalyzing electron transfer from FMNH₂ to oxygen or ubiquinone. Here, we explore the FMN binding site in mitoNEET by using FMN analogs and find that lumiflavin, like FMN, at nanomolar concentrations can mediate the redox transition of the mitoNEET [2Fe-2S] clusters in the presence of flavin reductase and NADH (100 μM) under aerobic conditions. The electron paramagnetic resonance (EPR) measurements show that both FMN and lumiflavin can dramatically change the EPR spectrum of the reduced mitoNEET [2Fe-2S] clusters and form a covalently bound complex with mitoNEET under blue light exposure, suggesting that FMN/lumiflavin has specific interactions with the [2Fe-2S] clusters in mitoNEET. In contrast, lumichrome, another FMN analog, fails to mediate the redox transition of the mitoNEET [2Fe-2S] clusters and has no effect on the EPR spectrum of the reduced mitoNEET [2Fe-2S] clusters under blue light exposure. Instead, lumichrome can effectively inhibit the FMNH₂-mediated reduction of the mitoNEET [2Fe-2S] clusters, indicating that lumichrome may act as a potential inhibitor to block the electron transfer activity of mitoNEET.

The balancing act of NEET proteins: Iron, ROS, calcium and metabolism

NEET proteins belong to a highly conserved group of [2Fe-2S] proteins found across all kingdoms of life. Due to their unique [2Fe2S] cluster structure, they play a key role in the regulation of many different redox and oxidation processes. In eukaryotes, NEET proteins are localized to the mitochondria, endoplasmic reticulum (ER) and the mitochondrial-associated membranes connecting these organelles (MAM), and are involved in the control of multiple processes, ranging from autophagy and apoptosis to ferroptosis, oxidative stress, cell proliferation, redox control and iron and iron‑sulfur homeostasis. Through their different functions and interactions with key proteins such as VDAC and Bcl-2, NEET proteins coordinate different mitochondrial, MAM, ER and cytosolic processes and functions and regulate major signaling molecules such as calcium and reactive oxygen species. Owing to their central role in cells, NEET proteins are associated with numerous human maladies including cancer, metabolic diseases, diabetes, obesity, and neurodegenerative diseases. In recent years, a new and exciting role for NEET proteins was uncovered, i.e., the regulation of mitochondrial dynamics and morphology. This new role places NEET proteins at the forefront of studies into cancer and different metabolic diseases, both associated with the regulation of mitochondrial dynamics. Here we review recent studies focused on the evolution, biological role, and structure of NEET proteins, as well as discuss different studies conducted on NEET proteins function using transgenic organisms. We further discuss the different strategies used in the development of drugs that target NEET proteins, and link these with the different roles of NEET proteins in cells.

Effects of lifelong exercise on age-related body composition, oxidative stress, inflammatory cytokines, and skeletal muscle proteome in rats

PURPOSE

This study aims to evaluate whether regular lifelong exercise has effects on age-related inflammatory cytokines, oxidative stress, and the skeletal muscle proteome.

METHODS

Four groups of adult-aged (8-month-old) female Sprague Dawley rats were used: rats for which training was initiated at either 8 (8 M-MICT, moderate-intensity continuous training) or 18 months (18 M-MICT) and sedentary rats aged either 26 (26 M-SED) or 8 months (8M-SED), who served as aging and adult sedentary controls, respectively. Aged skeletal muscles were subjected to proteomic and Kyoto Encyclopedia of Genes and Genomes (KEGG) and immunoblotting analyses.

RESULTS

Age-related loss of physical performance and anti-inflammatory steroid levels were lowest in the 8 M-MICT group, while the anti-oxidative activities remained unchanged compared to 18 M-MICT rats. The proteomic analysis demonstrated an amelioration of age-related changes to muscle contraction, focal adhesion signaling, mitochondrial function, apoptosis and regeneration, anti-oxidation, and protein processing in the endoplasmic reticulum in the 8 M-MICT. Additionally, neurotrophin (BDNF) and AKT/FOXO signaling pathways were upregulated in 8 M-MICT rats compared to 26 M-SED.

CONCLUSION

8 M-MICT exhibited greater beneficial effects in ameliorating age-related inflammation and physical performance loss, compared to 18 M-MICT. The amelioration is potentially related to the upregulation of autophagy activities via BDNF/AKT signaling.

Cisd2: a promising new target in Alzheimer's disease†

The CISD2 gene encodes the CDGSH iron-sulfur domain-containing protein 2. Cisd2 is involved in mammalian lifespan control, the unfolded protein response, Ca²⁺ buffering, and autophagy regulation. It has been demonstrated previously that Cisd2 deficiency causes an accelerated ageing phenotype characterised by the accumulation of damaged mitochondria, while Cisd2 overexpression leads to mitochondrial protection against typical age-associated alterations. Accumulating data suggest that neuronal amyloid-beta (Aβ) deposition, Ca²⁺ dysregulation, impairment of autophagic flux, and accumulation of damaged organelles including mitochondria play an important role in Alzheimer's disease (AD) pathogenesis. In a recent issue of The Journal of Pathology, Yi-Fan Chen and collaborators put together all these experimental observations and demonstrated that Cisd2 overexpression attenuates AD pathogenesis by guaranteeing mitochondrial quality and synaptic functions. The authors report convincing evidence to highlight the role of Cisd2 in Aβ-mediated mitochondrial damage and, interestingly, this neuroprotection could be dependent on other molecular mechanisms beyond the canonical and previously described roles of Cisd2. Collectively, these data open up new avenues in neuroprotection and highlight Cisd2 as a promising new target in AD. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Injectable Hydrogel-Based Nanocomposites for Cardiovascular Diseases

Cardiovascular diseases (CVDs), including a series of pathological disorders, severely affect millions of people all over the world. To address this issue, several potential therapies have been developed for treating CVDs, including injectable hydrogels as a minimally invasive method. However, the utilization of injectable hydrogel is a bit restricted recently owing to some limitations, such as transporting the therapeutic agent more accurately to the target site and prolonging their retention locally. This review focuses on the advances in injectable hydrogels for CVD, detailing the types of injectable hydrogels (natural or synthetic), especially that complexed with stem cells, cytokines, nano-chemical particles, exosomes, genetic material including DNA or RNA, etc. Moreover, we summarized the mainly prominent mechanism, based on which injectable hydrogel present excellent treating effect of cardiovascular repair. All in all, it is hopefully that injectable hydrogel-based nanocomposites would be a potential candidate through cardiac repair in CVDs treatment.

Calcium mishandling in absence of primary mitochondrial dysfunction drives cellular pathology in Wolfram Syndrome

Wolfram syndrome (WS) is a recessive multisystem disorder defined by the association of diabetes mellitus and optic atrophy, reminiscent of mitochondrial diseases. The role played by mitochondria remains elusive, with contradictory results on the occurrence of mitochondrial dysfunction. We evaluated 13 recessive WS patients by deep clinical phenotyping, including optical coherence tomography (OCT), serum lactic acid at rest and after standardized exercise, brain Magnetic Resonance Imaging, and brain and muscle Magnetic Resonance Spectroscopy (MRS). Finally, we investigated mitochondrial bioenergetics, network morphology, and calcium handling in patient-derived fibroblasts. Our results do not support a primary mitochondrial dysfunction in WS patients, as suggested by MRS studies, OCT pattern of retinal nerve fiber layer loss, and, in fibroblasts, by mitochondrial bioenergetics and network morphology results. However, we clearly found calcium mishandling between endoplasmic reticulum (ER) and mitochondria, which, under specific metabolic conditions of increased energy requirements and in selected tissue or cell types, may turn into a secondary mitochondrial dysfunction. Critically, we showed that Wolframin (WFS1) protein is enriched at mitochondrial-associated ER membranes and that in patient-derived fibroblasts WFS1 protein is completely absent. These findings support a loss-of-function pathogenic mechanism for missense mutations in WFS1, ultimately leading to defective calcium influx within mitochondria.

Cisd2 is essential to delaying cardiac aging and to maintaining heart functions

CDGSH iron-sulfur domain-containing protein 2 (Cisd2) is pivotal to mitochondrial integrity and intracellular Ca2+ homeostasis. In the heart of Cisd2 knockout mice, Cisd2 deficiency causes intercalated disc defects and leads to degeneration of the mitochondria and sarcomeres, thereby impairing its electromechanical functioning. Furthermore, Cisd2 deficiency disrupts Ca2+ homeostasis via dysregulation of sarco/endoplasmic reticulum Ca2+-ATPase (Serca2a) activity, resulting in an increased level of basal cytosolic Ca2+ and mitochondrial Ca2+ overload in cardiomyocytes. Most strikingly, in Cisd2 transgenic mice, a persistently high level of Cisd2 is sufficient to delay cardiac aging and attenuate age-related structural defects and functional decline. In addition, it results in a younger cardiac transcriptome pattern during old age. Our findings indicate that Cisd2 plays an essential role in cardiac aging and in the heart's electromechanical functioning. They highlight Cisd2 as a novel drug target when developing therapies to delay cardiac aging and ameliorate age-related cardiac dysfunction.

Light-induced release of nitric oxide from the nitric oxide-bound CDGSH-type [2Fe-2S] clusters in mitochondrial protein Miner2

Human mitochondrial matrix protein Miner2 hosts two [2Fe-2S] clusters via two CDGSH (Cys-Asp-Gly-Ser-His) motifs. Unlike other iron-sulfur clusters in proteins, the reduced CDGSH-type [2Fe-2S] clusters in Miner2 are able to bind nitric oxide (NO) and form stable NO-bound [2Fe-2S] clusters without disruption of the clusters. Here we report that the NO-bound Miner2 [2Fe-2S] clusters can quickly release NO upon the visible light excitation. The UV-visible and Electron Paramagnetic Resonance (EPR) measurements show that the NO-bound Miner2 [2Fe-2S] clusters are converted to the reduced Miner2 [2Fe-2S] clusters upon the light excitation under anaerobic conditions, suggesting that NO binding in the reduced Miner2 [2Fe-2S] clusters is reversible. Additional studies reveal that binding of NO effectively inhibits the redox transition of the Miner2 [2Fe-2S] clusters, indicating that NO may modulate the physiological activity of Miner2 in mitochondria by directly binding to the CDGSH-type [2Fe-2S] clusters in the protein.

NEET Proteins: A New Link Between Iron Metabolism, Reactive Oxygen Species, and Cancer

SIGNIFICANCE

Cancer cells accumulate high levels of iron and reactive oxygen species (ROS) to promote their high metabolic activity and proliferation rate. However, high levels of iron and ROS can also lead to enhanced oxidative stress and the activation of cell death pathways such as apoptosis and ferroptosis. This has led to the proposal that different drugs that target iron and/or ROS metabolism could be used as anticancer drugs. However, due to the complex role iron and ROS play in cells, the majority of these drugs yielded mixed results, highlighting a critical need to identify new players in the regulation of iron and ROS homeostasis in cancer cells. Recent Advances: NEET proteins belong to a newly discovered class of iron-sulfur proteins (2Fe-2S) required for the regulation of iron and ROS homeostasis in cells. Recent studies revealed that the NEET proteins NAF-1 (CISD2) and mitoNEET (CISD1) play a critical role in promoting the proliferation of cancer cells, supporting tumor growth and metastasis. Moreover, the function of NEET proteins in cancer cells was found to be dependent of the degree of lability of their 2Fe-2S clusters.

CRITICAL ISSUES

NEET proteins could represent a key regulatory link between the maintenance of high iron and ROS in cancer cells, the activation of cell death and survival pathways, and cellular proliferation.

FUTURE DIRECTIONS

Because the function of NEET proteins depends on the lability of their clusters, drugs that target the 2Fe2S clusters of NEET proteins could be used as promising anticancer drugs.

Binding of thiazolidinediones to the endoplasmic reticulum protein nutrient-deprivation autophagy factor-1

Nutrient-deprivation autophagy factor-1 (NAF-1, miner1; gene cisd2) is part of the [2Fe-2S]-containing protein family which includes mitoNEET (gene cisd1) and MiNT (miner2; gene cisd3). These proteins are redox active and are thought to play an important role in cellular energy homeostasis with NAF-1 playing a critical role in calcium regulation and aging. To date, no studies have investigated potential ligand interaction with NAF-1. Here we show that the thiazolidinediones pioglitazone and rosiglitazone along with the mitoNEET ligand, NL-1, bind to NAF-1 with low micromolar affinities. Further, we show that overexpression of NAF-1 in hepatocellular carcinoma (HepG2) cells reduces inhibition of mitochondrial respiration by pioglitazone. Our findings support the need for further efforts of the rational design of selective NAF-1 ligands.