Lon protease preferentially degrades oxidized mitochondrial aconitase by an ATP-stimulated mechanism

Dual targeting of the mitochondrial Lon peptidase 1 and the chymotrypsin-like proteasome activity as a potential therapeutic strategy in malignant astrocytoma models

Malignant astrocytomas are aggressive primary brain tumors characterized by extensive hypoxia-induced, mitochondria-dependent changes such as altered respiration, increased chymotrypsin-like (CT-L) proteasome activity, decreased apoptosis, drug resistance, stemness, and increased invasiveness. Mitochondrial Lon Peptidase 1 (LonP1) overexpression and increased CT-L proteasome activity are biomarkers of an aggressive high-grade phenotype and found to be associated with recurrence and poor patient survival. In preclinical models, small molecule agents targeting either LonP1 or the proteasome CT-L activity have anti-astrocytoma activity. Here, we present evidence that the dual inhibition of LonP1 and CT-L proteasome activity effectively induces ROS production, leading to apoptosis in malignant astrocytoma established cell lines and patient-derived glioma stem cell-like cultures. We also evaluated a novel small molecule, BT317, derived from the coumarinic compound 4 (CC4) using structure-activity modeling, which we found to inhibit both LonP1 and CT-L proteasome activity. Using gain- and loss-of-function genetic models, we discovered that LonP1 is both necessary and sufficient to drive BT317 drug sensitivity in established and patient-derived glioma stem-like cells by generating ROS and inducing apoptosis. In vitro, BT317 had activity as a single agent but, more importantly, enhanced synergy with the standard of care commonly used chemotherapeutic temozolomide (TMZ). In an orthotopic xenograft astrocytoma model, BT317 crossed the blood-brain barrier, showed selective activity at the tumor site, and demonstrated therapeutic efficacy as a single agent and combined with TMZ. BT317 defines an emerging class of LonP1 and CT-L inhibitors that exhibited promising anti-tumor activity and could be a potential candidate for malignant astrocytoma therapeutics. SIMPLE SUMMARY: Malignant astrocytoma patients have poor clinical outcomes, and novel treatments are needed to limit tumor recurrence and improve their overall survival. These tumors have a malignant phenotype mediated by altered mitochondrial metabolism, abnormal protein processing, and adaptation to hypoxia. We have previously published that astrocytomas are especially vulnerable to proteasome inhibitors as well as to inhibitors of the mitochondrial Lon Peptidase 1 (LonP1), but the effect of combining the two strategies has not been reported. Here, we present evidence that the dual inhibition of LonP1 and Chymotrypsin-like (CT-L) proteasome activity effectively induces cellular reactive oxygen species (ROS) production, leading to apoptosis in malignant astrocytoma established cell lines and patient-derived glioma stem cell-like cultures. We developed BT317, a small molecule dual inhibitor, which crosses the blood-brain barrier and shows strong synergy with the standard of care, temozolomide (TMZ), in the astrocytoma cell lines independent of their isocitrate dehydrogenase (IDH) profile and in an orthotopic glioma murine model. This preclinical study demonstrated the potential of dual LonP1 and CT-L proteasome inhibition as a novel therapeutic strategy for malignant astrocytoma and provides insight for future clinical translational studies alone or in combination with other chemotherapies.

The mitochondrial LONP1 protease: molecular targets and role in pathophysiology

Lon peptidase 1 (LONP1), a member of the AAA + family, is essential for maintaining mitochondrial function. Recent studies have revealed that LONP1 serves as a multifunctional enzyme, acting not only as a protease but also as a molecular chaperone, interacting with mitochondrial DNA (mtDNA), and playing roles in mitochondrial dynamics, oxidative stress, cellular respiration, and energy metabolism. LONP1 is evolutionarily highly conserved, and mutations or dysfunctions in LONP1 can lead to diseases. There is growing evidence linking LONP1 to various human diseases, such as tumors, neurodegenerative diseases, and heart diseases. This review discusses the discovery, molecular structure, subcellular localization, tissue distribution, and mitochondrial function of LONP1. Furthermore, it summarizes the associations between LONP1 and tumors, neurodegenerative diseases, and heart diseases, exploring its role in different diseases and potential molecular mechanisms. It also analyzes the regulatory effects of related inhibitors and agonists on LONP1. Considering the pleiotropic effects of LONP1, the study of LONP1 is crucial to understanding the relevant pathophysiological processes and developing strategies to modulate and control these related diseases.

Mitochondrial quality control in cardiomyocytes: safeguarding the heart against disease and ageing

Mitochondria are multifunctional organelles that are important for many different cellular processes, including energy production and biosynthesis of fatty acids, haem and iron-sulfur clusters. Mitochondrial dysfunction leads to a disruption in these processes, the generation of excessive reactive oxygen species, and the activation of inflammatory and cell death pathways. The consequences of mitochondrial dysfunction are particularly harmful in energy-demanding organs such as the heart. Loss of terminally differentiated cardiomyocytes leads to cardiac remodelling and a reduced ability to sustain contraction. Therefore, cardiomyocytes rely on multilayered mitochondrial quality control mechanisms to maintain a healthy population of mitochondria. Mitochondrial chaperones protect against protein misfolding and aggregation, and resident proteases eliminate damaged proteins through proteolysis. Irreparably damaged mitochondria can also be degraded through mitochondrial autophagy (mitophagy) or ejected from cells inside vesicles. The accumulation of dysfunctional mitochondria in cardiomyocytes is a hallmark of ageing and cardiovascular disease. This accumulation is driven by impaired mitochondrial quality control mechanisms and contributes to the development of heart failure. Therefore, there is a strong interest in developing therapies that directly target mitochondrial quality control in cardiomyocytes. In this Review, we discuss the current knowledge of the mechanisms involved in regulating mitochondrial quality in cardiomyocytes, how these pathways are altered with age and in disease, and the therapeutic potential of targeting mitochondrial quality control pathways in cardiovascular disease.

Mitochondrial dynamics and quality control regulate proteostasis in neuronal ischemia-reperfusion

Mitochondrial damage and dysfunction are hallmarks of neuronal injury during cerebral ischemia-reperfusion (I/R). Critical mitochondrial functions including energy production and cell signaling are perturbed during I/R, often exacerbating damage and contributing to secondary injury. The integrity of the mitochondrial proteome is essential for efficient function. Mitochondrial proteostasis is mediated by the cooperative forces of mitophagy and intramitochondrial proteolysis. The aim of this study was to elucidate the patterns of mitochondrial protein dynamics and their key regulators during an in vitro model of neuronal I/R injury. Utilizing the MitoTimer reporter, we quantified mitochondrial protein oxidation and turnover during I/R injury, highlighting a key point at 2 h reoxygenation for aged/oxidized protein turnover. This turnover was found to be mediated by both LONP1-dependent proteolysis and PRKN/parkin-dependent mitophagy. Additionally, the proteostatic response of neuronal mitochondria is influenced by both mitochondrial fusion and fission machinery. Our findings highlight the involvement of both mitophagy and intramitochondrial proteolysis in the response to I/R injury.Abbreviations: cKO: conditional knockout; CLPP: caseinolytic mitochondrial matrix peptidase proteolytic subunit; DIV: days in vitro; DNM1L/DRP1: dynamin 1 like; ETC: electron transport chain; hR: hours after reoxygenation; I/R: ischemia-reperfusion; LONP1: lon peptidase 1, mitochondrial; mtUPR: mitochondrial unfolded protein response; OGD: oxygen glucose deprivation; OGD/R: oxygen glucose deprivation and reoxygenation; OPA1: OPA1 mitochondrial dynamin like GTPase; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; ROI: region of interest; WT: wild-type.

Lon protease 1-mediated metabolic reprogramming promotes the progression of prostate cancer

Lon protease 1 (LONP1) is an ATP-dependent protease located in the mitochondrial matrix and plays a crucial role in regulating mitochondrial proteostasis, metabolism, and cellular stress responses et al. Aberrant LONP1 expression has been found in the progression of various tumors; however, the role and molecular mechanisms of LONP1 in prostate cancer (PCa) remain poorly understood. Here we show that overexpression of LONP1 is closely related to adverse clinic pathological features and poor prognosis in PCa patients. Mechanistically, the findings reveal that LONP1 is implicated in modulating the metabolic switch from oxidative phosphorylation (OXPHOS) to aerobic glycolysis, thereby promoting tumor proliferation, invasion, and metastasis both in vitro and in vivo. Meanwhile, we prove that LONP1 as a protease directly targets mitochondrial pyruvate carrier 1 (MPC1), a key metabolic protein in the process of glycolysis, and enhances its degradation, which in turn suppresses tricarboxylic acid (TCA) cycle and ultimately promotes the progression of PCa. Furthermore, using PCa in cancer-prone mice homozygous for a prostate-targeted conditional Pten knockout and Lonp1 knockin, we integrate transcriptomic and proteomic analyses of prostate tumors, upon which reveals that Lonp1 overexpression results in a significant downregulation of NADH: ubiquinone oxidoreductase activity, consequently impeding the electron transfer process and mitochondrial ATP synthesis, associated with metastasis of PCa. Collectively, our results highlight that metabolic reprogramming induced by LONP1 in PCa is closely coupled with disease progression, suggesting that targeting the LONP1-mediated cascade in the mitochondrial may provide therapeutic potential for PCa disease.

The mitochondrial DNAJC co-chaperone TCAIM reduces α-ketoglutarate dehydrogenase protein levels to regulate metabolism

Mitochondrial heat shock proteins and co-chaperones play crucial roles in maintaining proteostasis by regulating unfolded proteins, usually without specific target preferences. In this study, we identify a DNAJC-type co-chaperone: T cell activation inhibitor, mitochondria (TCAIM), and demonstrate its specific binding to α-ketoglutarate dehydrogenase (OGDH), a key rate-limiting enzyme in mitochondrial metabolism. This interaction suppresses OGDH function and subsequently reduces carbohydrate catabolism in both cultured cells and murine models. Using cryoelectron microscopy (cryo-EM), we resolve the human OGDH-TCAIM complex and reveal that TCAIM binds to OGDH without altering its apo structure. Most importantly, we discover that TCAIM facilitates the reduction of functional OGDH through its interaction, which depends on HSPA9 and LONP1. Our findings unveil a role of the mitochondrial proteostasis system in regulating a critical metabolic enzyme and introduce a previously unrecognized post-translational regulatory mechanism.

Genetic Markers of Postmortem Brain Iron

Brain iron (Fe) dyshomeostasis is implicated in neurodegenerative diseases. Genome-wide association studies (GWAS) have identified plausible loci correlated with peripheral levels of Fe. Systemic organs and the brain share several Fe regulatory proteins but there likely exist different homeostatic pathways. We performed the first GWAS of inductively coupled plasma mass spectrometry measures of postmortem brain Fe from 635 Rush Memory and Aging Project (MAP) participants. Sixteen single nucleotide polymorphisms (SNPs) associated with Fe in at least one of four brain regions were measured (p < 5 × 10-8). Promising SNPs (p < 5 × 10-6) were followed up for replication in published GWAS of blood, spleen, and brain imaging Fe traits and mapped to candidate genes for targeted cortical transcriptomic and epigenetic analysis of postmortem Fe in MAP. Results for SNPs previously associated with other Fe traits were also examined. Ninety-eight SNPs associated with postmortem brain Fe were at least nominally (p < 0.05) associated with one or more related Fe traits. Most novel loci identified had no direct links to Fe regulatory pathways but rather endoplasmic reticulum-Golgi trafficking (SORL1, SORCS2, MARCH1, CLTC), heparan sulfate (HS3ST4, HS3ST1), and coenzyme A (SLC5A6, PANK3); supported by nearest gene function and omic analyses. We replicated (p < 0.05) several previously published Fe loci mapping to candidate genes in cellular and systemic Fe regulation. Finally, novel loci (BMAL, COQ5, SLC25A11) and replication of prior loci (PINK1, PPIF, LONP1) lend support to the role of circadian rhythms and mitochondria function in Fe regulation more generally. In summary, we provide support for novel loci linked to pathways that may have greater relevance to brain Fe accumulation; some of which are implicated in neurodegeneration. However, replication of a subset of prior loci for blood Fe suggests that genetic determinants or biological pathways underlying Fe accumulation in the brain are not completely distinct from those of Fe circulating in the periphery.

The interconnective role of the UPS and autophagy in the quality control of cancer mitochondria

Uncontrollable cancer cell growth is characterized by the maintenance of cellular homeostasis through the continuous accumulation of misfolded proteins and damaged organelles. This review delineates the roles of two complementary and synergistic degradation systems, the ubiquitin-proteasome system (UPS) and the autophagy-lysosome system, in the degradation of misfolded proteins and damaged organelles for intracellular recycling. We emphasize the interconnected decision-making processes of degradation systems in maintaining cellular homeostasis, such as the biophysical state of substrates, receptor oligomerization potentials (e.g., p62), and compartmentalization capacities (e.g., membrane structures). Mitochondria, the cellular hubs for respiration and metabolism, are implicated in tumorigenesis. In the subsequent sections, we thoroughly examine the mechanisms of mitochondrial quality control (MQC) in preserving mitochondrial homeostasis in human cells. Notably, we explored the relationships between mitochondrial dynamics (fusion and fission) and various MQC processes-including the UPS, mitochondrial proteases, and mitophagy-in the context of mitochondrial repair and degradation pathways. Finally, we assessed the potential of targeting MQC (including UPS, mitochondrial molecular chaperones, mitochondrial proteases, mitochondrial dynamics, mitophagy and mitochondrial biogenesis) as cancer therapeutic strategies. Understanding the mechanisms underlying mitochondrial homeostasis may offer novel insights for future cancer therapies.

Impact of ageing and disuse on neuromuscular junction and mitochondrial function and morphology: Current evidence and controversies

Inactivity and ageing can have a detrimental impact on skeletal muscle and the neuromuscular junction (NMJ). Decreased physical activity results in muscle atrophy, impaired mitochondrial function, and NMJ instability. Ageing is associated with a progressive decrease in muscle mass, deterioration of mitochondrial function in the motor axon terminals and in myofibres, NMJ instability and loss of motor units. Focusing on the impact of inactivity and ageing, this review examines the consequences on NMJ stability and the role of mitochondrial dysfunction, delving into their complex relationship with ageing and disuse. Evidence suggests that mitochondrial dysfunction can be a pathogenic driver for NMJ alterations, with studies revealing the role of mitochondrial defects in motor neuron degeneration and NMJ instability. Two perspectives behind NMJ instability are discussed: one is that mitochondrial dysfunction in skeletal muscle triggers NMJ deterioration, the other envisages dysfunction of motor terminal mitochondria as a primary contributor to NMJ instability. While evidence from these studies supports both perspectives on the relationship between NMJ dysfunction and mitochondrial impairment, gaps persist in the understanding of how mitochondrial dysfunction can cause NMJ deterioration. Further research, both in humans and in animal models, is essential for unravelling the mechanisms and potential interventions for age- and inactivity-related neuromuscular and mitochondrial alterations.

Mitochondrial proteases modulate mitochondrial stress signalling and cellular homeostasis in health and disease

Maintenance of mitochondrial homeostasis requires a plethora of coordinated quality control and adaptations' mechanisms in which mitochondrial proteases play a key role. Their activation or loss of function reverberate beyond local mitochondrial biochemical and metabolic remodelling into coordinated cellular pathways and stress responses that feedback onto the mitochondrial functionality and adaptability. Mitochondrial proteolysis modulates molecular and organellar quality control, metabolic adaptations, lipid homeostasis and regulates transcriptional stress responses. Defective mitochondrial proteolysis results in disease conditions most notably, mitochondrial diseases, neurodegeneration and cancer. Here, it will be discussed how mitochondrial proteases and mitochondria stress signalling impact cellular homeostasis and determine the cellular decision to survive or die, how these processes may impact disease etiopathology, and how modulation of proteolysis may offer novel therapeutic strategies.

The Interplay between von Hippel-Lindau Tumor Suppressor Gene, Lon Protease, ROS Accumulation, and Inflammation in Clear Cell Renal Cell Carcinoma

This study explores the role of the von Hippel-Lindau (VHL) tumor suppressor gene and Lon protease in the development of clear cell renal carcinoma (ccRCC) through mechanisms involving inflammation and reactive oxygen species (ROS) accumulation in kidney cells. By examining the impact of VHL on the early stages of kidney cancer development, this research highlights the contributions of inflammation and ROS, as well as the involvement of Lon protease. The findings reveal increased Lon expression and ROS levels in VHL-knockdown HK-2 cells, along with elevated phospho-c-Jun N-terminal kinase (JNK) levels, emphasizing the complex interplay between VHL, Lon protease, inflammation, and ROS in kidney cell models. These insights point to potential therapeutic pathways for ccRCC.

Context-dependent roles of mitochondrial LONP1 in orchestrating the balance between airway progenitor versus progeny cells

While all eukaryotic cells are dependent on mitochondria for function, in a complex tissue, which cell type and which cell behavior are more sensitive to mitochondrial deficiency remain unpredictable. Here, we show that in the mouse airway, compromising mitochondrial function by inactivating mitochondrial protease gene Lonp1 led to reduced progenitor proliferation and differentiation during development, apoptosis of terminally differentiated ciliated cells and their replacement by basal progenitors and goblet cells during homeostasis, and failed airway progenitor migration into damaged alveoli following influenza infection. ATF4 and the integrated stress response (ISR) pathway are elevated and responsible for the airway phenotypes. Such context-dependent sensitivities are predicted by the selective expression of Bok, which is required for ISR activation. Reduced LONP1 expression is found in chronic obstructive pulmonary disease (COPD) airways with squamous metaplasia. These findings illustrate a cellular energy landscape whereby compromised mitochondrial function could favor the emergence of pathological cell types.

Mitochondrial Aconitase and Its Contribution to the Pathogenesis of Neurodegenerative Diseases

This survey reviews modern ideas on the structure and functions of mitochondrial and cytosolic aconitase isoenzymes in eukaryotes. Cumulative experimental evidence about mitochondrial aconitases (Aco2) as one of the main targets of reactive oxygen and nitrogen species is generalized. The important role of Aco2 in maintenance of homeostasis of the intracellular iron pool and maintenance of the mitochondrial DNA is discussed. The role of Aco2 in the pathogenesis of some neurodegenerative diseases is highlighted. Inactivation or dysfunction of Aco2 as well as mutations found in the ACO2 gene appear to be significant factors in the development and promotion of various types of neurodegenerative diseases. A restoration of efficient mitochondrial functioning as a source of energy for the cell by targeting Aco2 seems to be one of the promising therapeutic directions to minimize progressive neurodegenerative disorders.

Proteolytic control of FixT by the Lon protease impacts FixLJ signaling in Caulobacter crescentus

Responding to changes in oxygen levels is critical for aerobic microbes. In Caulobacter crescentus, low oxygen is sensed by the FixL-FixJ two-component system which induces multiple genes, including those involved in heme biosynthesis, to accommodate microaerobic conditions. The FixLJ inhibitor FixT is also induced under low oxygen conditions and is degraded by the Lon protease when the oxygen levels are sufficient, which together provides negative feedback proposed to adjust FixLJ signaling thresholds during changing conditions. Here, we address whether degradation of FixT by the Lon protease contributes to phenotypic defects associated with loss of Lon. We find that ∆lon strains are deficient in FixLJ-dependent heme biosynthesis, consistent with elevated FixT levels as deletion of fixT suppresses this defect. Transcriptomics validate this result as, along with heme biosynthesis, there is diminished expression of many FixL-activated genes in ∆lon. However, stabilization of FixT in ∆lon strains does not contribute to restoring any known Lon-related fitness defect, such as cell morphology defects or stress sensitivity. In fact, cells lacking both FixT and Lon are compromised in viability during growth in standard aerobic conditions. Our work highlights the complexity of protease-dependent regulation of transcription factors and explains the molecular basis of defective heme accumulation in Lon-deficient Caulobacter.

IMPORTANCE

The Lon protease shapes protein quality control, signaling pathways, and stress responses in many bacteria species. Loss of Lon often results in multiple phenotypic consequences. In this work, we found a connection between the Lon protease and deficiencies in heme accumulation that then led to our finding of a global change in gene expression due in part to degradation of a regulator of the hypoxic response. However, loss of degradation of this regulator did not explain other phenotypes associated with Lon deficiencies demonstrating the complex and multiple pathways that this highly conserved protease can impact.

Structural and mechanistic studies on human LONP1 redefine the hand-over-hand translocation mechanism

AAA+ enzymes use energy from ATP hydrolysis to remodel diverse cellular targets. Structures of substrate-bound AAA+ complexes suggest that these enzymes employ a conserved hand-over-hand mechanism to thread substrates through their central pore. However, the fundamental aspects of the mechanisms governing motor function and substrate processing within specific AAA+ families remain unresolved. We used cryo-electron microscopy to structurally interrogate reaction intermediates from in vitro biochemical assays to inform the underlying regulatory mechanisms of the human mitochondrial AAA+ protease, LONP1. Our results demonstrate that substrate binding allosterically regulates proteolytic activity, and that LONP1 can adopt a configuration conducive to substrate translocation even when the ATPases are bound to ADP. These results challenge the conventional understanding of the hand-over-hand translocation mechanism, giving rise to an alternative model that aligns more closely with biochemical and biophysical data on related enzymes like ClpX, ClpA, the 26S proteasome, and Lon protease.

Artemisinins ameliorate polycystic ovarian syndrome by mediating LONP1-CYP11A1 interaction

Polycystic ovary syndrome (PCOS), a prevalent reproductive disorder in women of reproductive age, features androgen excess, ovulatory dysfunction, and polycystic ovaries. Despite its high prevalence, specific pharmacologic intervention for PCOS is challenging. In this study, we identified artemisinins as anti-PCOS agents. Our finding demonstrated the efficacy of artemisinin derivatives in alleviating PCOS symptoms in both rodent models and human patients, curbing hyperandrogenemia through suppression of ovarian androgen synthesis. Artemisinins promoted cytochrome P450 family 11 subfamily A member 1 (CYP11A1) protein degradation to block androgen overproduction. Mechanistically, artemisinins directly targeted lon peptidase 1 (LONP1), enhanced LONP1-CYP11A1 interaction, and facilitated LONP1-catalyzed CYP11A1 degradation. Overexpression of LONP1 replicated the androgen-lowering effect of artemisinins. Our data suggest that artemisinin application is a promising approach for treating PCOS and highlight the crucial role of the LONP1-CYP11A1 interaction in controlling hyperandrogenism and PCOS occurrence.

Impact of Mitochondrial Architecture, Function, Redox Homeostasis, and Quality Control on Organismic Aging: Lessons from a Fungal Model System

Significance: Mitochondria are eukaryotic organelles with various essential functions. They are both the source and the targets of reactive oxygen species (ROS). Different branches of a mitochondrial quality control system (mQCS), such as ROS balancing, degradation of damaged proteins, or whole mitochondria, can mitigate the adverse effects of ROS stress. However, the capacity of mQCS is limited. Overwhelming this capacity leads to dysfunctions and aging. Strategies to interfere into mitochondria-dependent human aging with the aim to increase the healthy period of life, the health span, rely on the precise knowledge of mitochondrial functions. Experimental models such as Podospora anserina, a filamentous fungus with a clear mitochondrial aging etiology, proved to be instrumental to reach this goal. Recent Advances: Investigations of the P. anserina mQCS revealed that it is constituted by a complex network of different branches. Moreover, mitochondrial architecture and lipid homeostasis emerged to affect aging. Critical Issues: The regulation of the mQCS is only incompletely understood. Details about the involved signaling molecules and interacting pathways remain to be elucidated. Moreover, most of the currently generated experimental data were generated in well-controlled experiments that do not reflect the constantly changing natural life conditions and bear the danger to miss relevant aspects leading to incorrect conclusions. Future Directions: In P. anserina, the precise impact of redox signaling as well as of molecular damaging for aging remains to be defined. Moreover, natural fluctuation of environmental conditions needs to be considered to generate a realistic picture of aging mechanisms as they developed during evolution.

WITHDRAWN: Dual targeting of mitochondrial Lon peptidase 1 and chymotrypsin-like protease by small molecule BT317, as potential therapeutics in malignant astrocytomas

The authors have withdrawn their manuscript owing to massive revision and data validation. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

Mitochondrial function and reactive oxygen species production during human sperm capacitation: Unraveling key players

Sperm capacitation is a critical process for male fertility. It involves a series of biochemical and physiological changes that occur in the female reproductive tract, rendering the sperm competent for successful fertilization. The precise mechanisms and, specifically, the role of mitochondria, in sperm capacitation remain incompletely understood. Previously, we revealed that in mouse sperm mitochondrial activity (e.g., oxygen consumption, membrane potential, ATP/ADP exchange, and mitochondrial Ca2+ ) increases during capacitation. Herein, we studied mitochondrial function by high-resolution respirometry (HRR) and reactive oxygen species production in capacitated (CAP) and non-capacitated (NC) human spermatozoa. We found that in capacitated sperm from normozoospermic donors, the respiratory control ratio increased by 36%, accompanied by a double oxygen consumption rate (OCR) in the presence of antimycin A. Extracellular hydrogen peroxide (H2 O2 ) detection was three times higher in CAP than in NC sperm cells. To confirm that H2 O2 production depends on mitochondrial superoxide (O 2 · - $$ {\mathrm{O}}_2^{\cdotp -} $$ ) formation, we evaluated mitochondrial aconitase (ACO2) amount, activity, and role in the metabolic flux from the sperm tricarboxylic acid cycle. We estimated that CAP cells produce, on average by individual, (59 ± 22)% moreO 2 · - $$ {\mathrm{O}}_2^{\cdotp -} $$ in the steady-state compared to NC cells. Finally, we analyzed two targets of oxidative stress: lipid peroxidation by western blot against 4-hydroxynonenal and succinate dehydrogenase (SDH) activity by HRR. We did not observe modifications in lipoperoxidation nor the activity of SDH, suggesting that during capacitation, the increase in mitochondrial H2 O2 production does not damage sperm and it is necessary for the normal CAP process.

Proteasome localization and activity in pig brain and in vivo small molecule screening for activators

Introduction

Loss of proteasome function, proteinopathy, and proteotoxicity may cause neurodegeneration across the human lifespan in several forms of brain injury and disease. Drugs that activate brain proteasomes in vivo could thus have a broad therapeutic impact in neurology.

Methods

Using pigs, a clinically relevant large animal with a functionally compartmental gyrencephalic cerebral cortex, we evaluated the localization and biochemical activity of brain proteasomes and tested the ability of small molecules to activate brain proteasomes.

Results

By Western blotting, proteasome protein subunit PSMB5 and PSMA3 levels were similar in different pig brain regions. Immunohistochemistry for PSMB5 showed localization in the cytoplasm (diffuse and particulate) and nucleus (cytoplasm < nucleus). Some PSMB5 immunoreactivity was colocalized with mitochondrial (voltage-gated anion channel and cyclophilin D) and cell death (Aven) proteins in the neuronal soma and neuropil in the neocortex of pig and human brains. In the nucleus, PSMB5 immunoreactivity was diffuse, particulate, and clustered, including perinucleolar decorations. By fluorogenic assay, proteasome chymotrypsin-like activities (CTL) in crude tissue soluble fractions were generally similar within eight different pig brain regions. Proteasome CTL activity in the hippocampus was correlated with activity in nasal mucosa biopsies. In pilot analyses of subcellular fractions of pig cerebral cortex, proteasome CTL activity was highest in the cytosol and then ~50% lower in nuclear fractions; ~15-20% of total CTL activity was in pure mitochondrial fractions. With in-gel activity assay, 26S-singly and -doubly capped proteasomes were the dominant forms in the pig cerebral cortex. With a novel in situ histochemical activity assay, MG132-inhibitable proteasome CTL activity was localized to the neuropil, as a mosaic, and to cell bodies, nuclei, and centrosome-like perinuclear satellites. In piglets treated intravenously with pyrazolone derivative and chlorpromazine over 24 h, brain proteasome CTL activity was modestly increased.

Discussion

This study shows that the proteasome in the pig brain has relative regional uniformity, prominent nuclear and perinuclear presence with catalytic activity, a mitochondrial association with activity, 26S-single cap dominance, and indications from small molecule systemic administration of pyrazolone derivative and chlorpromazine that brain proteasome function appears safely activable.

Mieap forms membrane-less organelles involved in cardiolipin metabolism

Biomolecular condensates (BCs) are formed by proteins with intrinsically disordered regions (IDRs) via liquid-liquid phase separation. Mieap/Spata18, a p53-inducible protein, participates in suppression of colorectal tumors by promoting mitochondrial quality control. However, the regulatory mechanism involved remains unclear. Here, we report that Mieap is an IDR-containing protein that drives formation of BCs involved in cardiolipin metabolism. Mieap BCs specifically phase separate the mitochondrial phospholipid, cardiolipin. Mieap directly binds to cardiolipin in vitro. Lipidomic analysis of cardiolipin suggests that Mieap promotes enzymatic reactions in cardiolipin biosynthesis and remodeling. Accordingly, four cardiolipin biosynthetic enzymes, TAMM41, PGS1, PTPMT1, and CRLS1 and two remodeling enzymes, PLA2G6 and TAZ, are phase-separated by Mieap BCs. Mieap-deficient cells exhibit altered crista structure, leading to decreased respiration activity and ATP production in mitochondria. These results suggest that Mieap may form membrane-less organelles to compartmentalize and facilitate cardiolipin metabolism, thus potentially contributing to mitochondrial quality control.

Proteolytic control of FixT by the Lon protease impacts FixLJ signaling in Caulobacter crescentus

Responding to changes in oxygen levels is critical for aerobic microbes. In Caulobacter crescentus, low oxygen is sensed by the FixL-FixJ two-component system which induces multiple genes, including heme biosynthesis, to accommodate microaerobic conditions. The FixLJ inhibitor FixT is also induced under low oxygen conditions and is degraded by the Lon protease, which together provides negative feedback proposed to adjust FixLJ signaling thresholds during changing conditions. Here, we address if the degradation of FixT by the Lon protease contributes to phenotypic defects associated with loss of Lon. We find that ∆lon strains are deficient in FixLJ-dependent heme biosynthesis, consistent with elevated FixT levels as deletion of fixT suppresses this defect. Transcriptomics validate this result as there is diminished expression of many FixLJ-activated genes in ∆lon. However, no physiological changes in response to microaerobic conditions occurred upon loss of Lon, suggesting that FixT dynamics are not a major contributor to fitness in oxygen limiting conditions. Similarly, stabilization of FixT in ∆lon strains does not contribute to any known Lon-related fitness defect, such as cell morphology defects or stress sensitivity. In fact, cells lacking both FixT and Lon are compromised in viability during adaptation to long term aerobic growth. Our work highlights the complexity of protease-dependent regulation of transcription factors and explains the molecular basis of defective heme accumulation in Lon-deficient Caulobacter.

The protease Lon prolongs insect lifespan by responding to reactive oxygen species and degrading mitochondrial transcription factor A

Diapause is a widespread adaptation of insects that enables them to survive during unfavorable seasons and is characterized by suppressed metabolism and increased lifespan. Previous works have demonstrated that high levels of reactive oxygen species (ROS) and hypoxia-inducible factor-1α (HIF-1α) in the pupal brain of the moth Helicoverpa armigera induce diapause and extend lifespan by downregulating mitochondrial transcription factor A (TFAM). However, the molecular mechanisms of ROS-HIF-1α regulating metabolic activity to extend lifespan are still poorly understood. Here, we show that the mitochondrial abundance in diapause-type pupal brains is markedly lower than that in their nondiapause-type pupae, suggesting that ROS-HIF-1α signaling negatively regulates the number of mitochondria. The protease Lon, a major mitochondrial matrix protease, can respond to ROS signals. It is activated by transcription factor HIF-1α, which specifically binds the LON promoter to promote its expression. A high level of LON mediates the degradation of TFAM, which is a crucial factor in regulating mitochondrial abundance and metabolic activity. We believe this is the first report that a previously unrecognized regulatory pathway, ROS-HIF-1α-LON-TFAM, reduces mitochondrial activity to induce diapause, extending insect lifespan.

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.

Mitochondrial AAA+ proteases

Mitochondria are multifunctional organelles that play a central role in a wide range of life-sustaining tasks in eukaryotic cells, including adenosine triphosphate (ATP) production, calcium storage and coenzyme generation pathways such as iron-sulfur cluster biosynthesis. The wide range of mitochondrial functions is carried out by a diverse array of proteins comprising approximately 1500 proteins or polypeptides. Degradation of these proteins is mainly performed by four AAA+ proteases localized in mitochondria. These AAA+ proteases play a quality control role in degrading damaged or misfolded proteins and perform various other functions. This chapter describes previously identified roles for these AAA+ proteases that are localized in the mitochondria of animal cells.

CLPX regulates mitochondrial fatty acid β-oxidation in liver cells

Mitochondrial fatty acid oxidation (β-oxidation) is an essential metabolic process for energy production in eukaryotic cells, but the regulatory mechanisms of this pathway are largely unknown. In the present study, we found that several enzymes involved in β-oxidation are associated with CLPX, the AAA+ unfoldase that is a component of the mitochondrial matrix protease ClpXP. The suppression of CLPX expression increased β-oxidation activity in the HepG2 cell line and in primary human hepatocytes without glucagon treatment. However, the protein levels of enzymes involved in β-oxidation did not significantly increase in CLPX-deleted HepG2 cells (CLPX-KO cells). Coimmunoprecipitation experiments revealed that the protein level in the immunoprecipitates of each antibody changed after the treatment of WT cells with glucagon, and a part of these changes was also observed in the comparison of WT and CLPX-KO cells without glucagon treatment. Although the exogenous expression of WT or ATP-hydrolysis mutant CLPX suppressed β-oxidation activity in CLPX-KO cells, glucagon treatment induced β-oxidation activity only in CLPX-KO cells expressing WT CLPX. These results suggest that the dissociation of CLPX from its target proteins is essential for the induction of β-oxidation in HepG2 cells. Moreover, specific phosphorylation of AMP-activated protein kinase and a decrease in the expression of acetyl-CoA carboxylase 2 were observed in CLPX-KO cells, suggesting that CLPX might participate in the regulation of the cytosolic signaling pathway for β-oxidation. The mechanism for AMP-activated protein kinase phosphorylation remains elusive; however, our results uncovered the hitherto unknown role of CLPX in mitochondrial β-oxidation in human liver cells.

Control of mitochondrial integrity influences oocyte quality during reproductive aging

Reduced quality in oocytes from women of advanced maternal age (AMA) is associated with dysfunctional mitochondria. The objective of this study was to investigate the mechanisms controlling mitochondrial quality during maternal aging in mouse and human oocytes. We first evaluated the expression of proteins involved in the mitochondrial unfolded protein response (UPRmt) and mitophagy in in vivo matured metaphase II (MII) oocytes collected from young and aged mice. Expression of UPRmt proteins, HSPD1 and LONP1, and mitophagy proteins, total-PRKN and phosphorylated-PRKN, was significantly decreased in aged compared to young oocytes. Treatment of aged oocytes during in vitro maturation with the mitochondrially targeted antioxidant mitoquinone (MQ) specifically restored total-PRKN and phosphorylated-PRKN expression to levels seen in young oocytes. We next investigated whether maturing young oocytes under a high-oxygen environment would mimic the effects observed in oocytes from aged females. Phosphorylated-PRKN expression in oxidatively stressed young oocytes was reduced compared to that in oocytes matured under normal oxygen levels, and the mitochondrial DNA (mtDNA) copy number was increased. Treating oxidatively challenged young oocytes with MQ restored the phosphorylated-PRKN expression and mtDNA copy numbers. Treatment of oxidatively challenged oocytes with MQ also increased the co-localization of mitochondria and lysosomes, suggesting increased mitophagy. These data correlated with the developmental potential of the oocytes, as blastocyst development and hatching of oxidatively stressed oocytes were reduced, while treatment with MQ resulted in a significant increase in blastocyst development and hatching, and in the percentage of inner cell mass. Consistent with our results in mice, MII oocytes from women of AMA exhibited a significant decrease in phosphorylated-PKRN and total-PRKN compared to those of young women. Our findings suggest that the protein machinery to control the health of the mitochondria via UPRmt and mitophagy may be compromised in oocytes from aged females, which may result in inefficient clearance of dysfunctional mitochondria and reduced oocyte quality.

Metabolic Regulation of Copper Toxicity during Marine Mussel Embryogenesis

The development of new tools for assessing the health of cultured shellfish larvae is crucial for aquaculture industries to develop and refine hatchery methodologies. We established a large-volume ecotoxicology/health stressor trial, exposing mussel (Perna canaliculus) embryos to copper in the presence of ethylenediaminetetraacetic acid (EDTA). GC/MS-based metabolomics was applied to identify potential biomarkers for monitoring embryonic/larval health and to characterise mechanisms of metal toxicity. Cellular viability, developmental abnormalities, larval behaviour, mortality, and a targeted analysis of proteins involved in the regulation of reactive oxygen species were simultaneously evaluated to provide a complementary framework for interpretative purposes and authenticate the metabolomics data. Trace metal analysis and speciation modelling verified EDTA as an effective copper chelator. Toxicity thresholds for P. canaliculus were low, with 10% developmental abnormalities in D-stage larvae being recorded upon exposure to 1.10 μg·L-1 bioavailable copper for 66 h. Sublethal levels of bioavailable copper (0.04 and 1.10 μg·L-1) caused coordinated fluctuations in metabolite profiles, which were dependent on development stage, treatment level, and exposure duration. Larvae appeared to successfully employ various mechanisms involving the biosynthesis of antioxidants and a restructuring of energy-related metabolism to alleviate the toxic effects of copper on cells and developing tissues. These results suggest that regulation of trace metal-induced toxicity is tightly linked with metabolism during the early ontogenic development of marine mussels. Lethal-level bioavailable copper (50.3 μg·L-1) caused severe metabolic dysregulation after 3 h of exposure, which worsened with time, substantially delayed embryonic development, induced critical oxidative damage, initiated the apoptotic pathway, and resulted in cell/organism death shortly after 18 h of exposure. Metabolite profiling is a useful approach to (1) assess the health status of marine invertebrate embryos and larvae, (2) detect early warning biomarkers for trace metal contamination, and (3) identify novel regulatory mechanisms of copper-induced toxicity.

LonP1 Links Mitochondria-ER Interaction to Regulate Heart Function

Interorganelle contacts and communications are increasingly recognized to play a vital role in cellular function and homeostasis. In particular, the mitochondria-endoplasmic reticulum (ER) membrane contact site (MAM) is known to regulate ion and lipid transfer, as well as signaling and organelle dynamics. However, the regulatory mechanisms of MAM formation and their function are still elusive. Here, we identify mitochondrial Lon protease (LonP1), a highly conserved mitochondrial matrix protease, as a new MAM tethering protein. The removal of LonP1 substantially reduces MAM formation and causes mitochondrial fragmentation. Furthermore, deletion of LonP1 in the cardiomyocytes of mouse heart impairs MAM integrity and mitochondrial fusion and activates the unfolded protein response within the ER (UPR^ER). Consequently, cardiac-specific LonP1 deficiency causes aberrant metabolic reprogramming and pathological heart remodeling. These findings demonstrate that LonP1 is a novel MAM-localized protein orchestrating MAM integrity, mitochondrial dynamics, and UPR^ER, offering exciting new insights into the potential therapeutic strategy for heart failure.

Proteolytic rewiring of mitochondria by LONP1 directs cell identity switching of adipocytes

Mitochondrial proteases are emerging as key regulators of mitochondrial plasticity and acting as both protein quality surveillance and regulatory enzymes by performing highly regulated proteolytic reactions. However, it remains unclear whether the regulated mitochondrial proteolysis is mechanistically linked to cell identity switching. Here we report that cold-responsive mitochondrial proteolysis is a prerequisite for white-to-beige adipocyte cell fate programming during adipocyte thermogenic remodelling. Thermogenic stimulation selectively promotes mitochondrial proteostasis in mature white adipocytes via the mitochondrial protease LONP1. Disruption of LONP1-dependent proteolysis substantially impairs cold- or β3 adrenergic agonist-induced white-to-beige identity switching of mature adipocytes. Mechanistically, LONP1 selectively degrades succinate dehydrogenase complex iron sulfur subunit B and ensures adequate intracellular succinate levels. This alters the histone methylation status on thermogenic genes and thereby enables adipocyte cell fate programming. Finally, augmented LONP1 expression raises succinate levels and corrects ageing-related impairments in white-to-beige adipocyte conversion and adipocyte thermogenic capacity. Together, these findings reveal that LONP1 links proteolytic surveillance to mitochondrial metabolic rewiring and directs cell identity conversion during adipocyte thermogenic remodelling.

Molecular Determinants of Mitochondrial Shape and Function and Their Role in Glaucoma

Significance: Cells depend on well-functioning mitochondria for essential processes such as energy production, redox signaling, coordination of metabolic pathways, and cofactor biosynthesis. Mitochondrial dysfunction, metabolic decline, and protein stress have been implicated in the etiology of multiple late-onset diseases, including various ataxias, diabetes, sarcopenia, neuromuscular disorders, and neurodegenerative diseases such as parkinsonism, amyotrophic lateral sclerosis, and glaucoma. Recent Advances: New evidence supports that increased energy metabolism protects neuron function during aging. Key energy metabolic enzymes, however, are susceptible to oxidative damage making it imperative that the mitochondrial proteome is protected. More than 40 different enzymes have been identified as important factors for guarding mitochondrial health and maintaining a dynamic pool of mitochondria. Critical Issues: Understanding shared mechanisms of age-related disorders of neurodegenerative diseases such as glaucoma, Alzheimer's disease, and Parkinson's disease is important for developing new therapies. Functional mitochondrial shape and dynamics rely on complex interactions between mitochondrial proteases and membrane proteins. Identifying the sequence of molecular events that lead to mitochondrial dysfunction and metabolic stress is a major challenge. Future Directions: A critical need exists for new strategies that reduce mitochondrial protein stress and promote mitochondrial dynamics in age-related neurological disorders. Discovering how mitochondria-associated degradation is related to proteostatic mechanisms in mitochondrial compartments may reveal new opportunities for therapeutic interventions. Also, little is known about how protein and membrane contacts in the inner and outer mitochondrial membrane are regulated, even though they are pivotal for mitochondrial architecture. Future work will need to delineate the molecular details of these processes.

Sex differences in antioxidant defence and the regulation of redox homeostasis in physiology and pathology

Reactive oxygen species (ROS) is a term that defines a group of unstable compounds derived from exogenous sources or endogenous metabolism. Under physiological conditions, low levels of ROS play a key role in the regulation of signal transduction- or transcription-mediated cellular responses. In contrast, excessive and uncontrolled loading of ROS results in a pathological state known as oxidative stress (OS), a leading contributor to aging and a pivotal factor for the onset and progression of many disorders. Evolution has endowed cells with an antioxidant system involved in stabilizing ROS levels to a specific threshold, preserving ROS-induced signalling function and limiting negative side effects. In mammals, a great deal of evidence indicates that females defence against ROS is more proficient than males, determining a longer lifespan and lower incidence of most chronic diseases. In this review, we will summarize the most recent sex-related differences in the regulation of redox homeostasis. We will highlight the peculiar aspects of the antioxidant defence in sex-biased diseases whose onset or progression is driven by OS, and we will discuss the molecular, genetic, and evolutionary determinants of female proficiency to cope with ROS.

Time-Related Evidence of Intestinal Oxidative Stress in Obstructive Jaundice-Induced Rats

INTRODUCTION

Obstructive jaundice is known to affect intestinal permeability and facilitate bacterial translocation through related mechanisms. This study was conducted to evaluate the alterations concerning blood biochemistry and levels of several markers of oxidative stress (OS) in blood and intestinal mucosa caused by obstructive jaundice and how these fluctuate over time, in order to further explore the possibility of intervening in the OS path in future experiments.

METHODS

A total of 54 albino Wistar rats were randomly divided into three groups (control, sham operated, and bile duct ligation) and sacrificed at specific time intervals (12 h and 2, 7, and 14 days). The intestinal barrier function was evaluated by measuring endotoxin levels in portal, aortic, and peripheral blood. Also, basic biochemical parameters were simultaneously measured in peripheral blood. Tissue samples collected from the terminal ileum were homogenized for determining the OS markers, lipid peroxidation, and protein-free radical-induced oxidation.

RESULTS

We designed this experiment to examine the alterations in enteric mucosa primarily in relation to OS in a period of 14 days. During this time period, we investigated in specific time intervals not only OS fluctuations but also other liver function parameters, as well as CRP and endotoxin levels. The alterations were monitored in relation to time after bile duct ligation.

CONCLUSION

Bile duct ligation in rats causes OS versus post-ligation time progression of the common bile duct. OS was increased by ∼50% compared to control/sham and peaked at 7 days and at least up to 14 days post-ligation. This phenomenon was accompanied with a deranging of liver function after ligation, as anticipated, but not in all measured parameters; biochemical and endotoxin levels followed the same pattern.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.

Redox sensitive human mitochondrial aconitase and its interaction with frataxin: In vitro and in silico studies confirm that it takes two to tango

Mitochondrial aconitase (ACO2) has been postulated as a redox sensor in the tricarboxylic acid cycle. Its high sensitivity towards reactive oxygen and nitrogen species is due to its particularly labile [4Fe-4S]²⁺ prosthetic group which yields an inactive [3Fe-4S]⁺ cluster upon oxidation. Moreover, ACO2 was found as a main oxidant target during aging and in pathologies where mitochondrial dysfunction is implied. Herein, we report the expression and characterization of recombinant human ACO2 and its interaction with frataxin (FXN), a protein that participates in the de novo biosynthesis of Fe-S clusters. A high yield of pure ACO2 (≥99%, 22 ± 2 U/mg) was obtained and kinetic parameters for citrate, isocitrate, and cis-aconitate were determined. Superoxide, carbonate radical, peroxynitrite, and hydrogen peroxide reacted with ACO2 with second-order rate constants of 10⁸, 10⁸, 10⁵, and 10² M^-1 s^-1, respectively. Temperature-induced unfolding assessed by tryptophan fluorescence of ACO2 resulted in apparent melting temperatures of 51.1 ± 0.5 and 43.6 ± 0.2 °C for [4Fe-4S]²⁺ and [3Fe-4S]⁺ states of ACO2, sustaining lower thermal stability upon cluster oxidation. Differences in protein dynamics produced by the Fe-S cluster redox state were addressed by molecular dynamics simulations. Reactivation of [3Fe-4S]⁺-ACO2 by FXN was verified by activation assays and direct iron-dependent interaction was confirmed by protein-protein interaction ELISA and fluorescence spectroscopic assays. Multimer modeling and protein-protein docking predicted an ACO2-FXN complex where the metal ion binding region of FXN approaches the [3Fe-4S]⁺ cluster, supporting that FXN is a partner for reactivation of ACO2 upon oxidative cluster inactivation.

LONP1 targets HMGCS2 to protect mitochondrial function and attenuate chronic kidney disease

Mitochondria comprise the central metabolic hub of cells and their imbalance plays a pathogenic role in chronic kidney disease (CKD). Here, we studied Lon protease 1 (LONP1), a major mitochondrial protease, as its role in CKD pathogenesis is unclear. LONP1 expression was decreased in human patients and mice with CKD, and tubular-specific Lonp1 overexpression mitigated renal injury and mitochondrial dysfunction in two different models of CKD, but these outcomes were aggravated by Lonp1 deletion. These results were confirmed in renal tubular epithelial cells in vitro. Mechanistically, LONP1 downregulation caused mitochondrial accumulation of the LONP1 substrate, 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), which disrupted mitochondrial function and further accelerated CKD progression. Finally, computer-aided virtual screening was performed, which identified a novel LONP1 activator. Pharmacologically, the LONP1 activator attenuated renal fibrosis and mitochondrial dysfunction. Collectively, these results imply that LONP1 is a promising therapeutic target for treating CKD.

Pharmacological Progress of Mitophagy Regulation

With the advancement in novel drug discovery, biologically active compounds are considered pharmacological tools to understand complex biological mechanisms and the identification of potent therapeutic agents. Mitochondria boast a central role in different integral biological processes and mitochondrial dysfunction is associated with multiple pathologies. It is, therefore, prudent to target mitochondrial quality control mechanisms by using pharmacological approaches. However, there is a scarcity of biologically active molecules, which can interact with mitochondria directly. Currently, the chemical compounds used to induce mitophagy include oligomycin and antimycin A for impaired respiration and acute dissipation of mitochondrial membrane potential by using CCCP/FCCP, the mitochondrial uncouplers. These chemical probes alter the homeostasis of the mitochondria and limit our understanding of the energy regulatory mechanisms. Efforts are underway to find molecules that can bring about selective removal of defective mitochondria without compromising normal mitochondrial respiration. In this report, we have tried to summarize and status of the recently reported modulators of mitophagy.

Glyoxalase I activity affects Arabidopsis sensitivity to ammonium nutrition

Elevated methylglyoxal levels contribute to ammonium-induced growth disorders in Arabidopsis thaliana. Methylglyoxal detoxification pathway limitation, mainly the glyoxalase I activity, leads to enhanced sensitivity of plants to ammonium nutrition. Ammonium applied to plants as the exclusive source of nitrogen often triggers multiple phenotypic effects, with severe growth inhibition being the most prominent symptom. Glycolytic flux increase, leading to overproduction of its toxic by-product methylglyoxal (MG), is one of the major metabolic consequences of long-term ammonium nutrition. This study aimed to evaluate the influence of MG metabolism on ammonium-dependent growth restriction in Arabidopsis thaliana plants. As the level of MG in plant cells is maintained by the glyoxalase (GLX) system, we analyzed MG-related metabolism in plants with a dysfunctional glyoxalase pathway. We report that MG detoxification, based on glutathione-dependent glyoxalases, is crucial for plants exposed to ammonium nutrition, and its essential role in ammonium sensitivity relays on glyoxalase I (GLXI) activity. Our results indicated that the accumulation of MG-derived advanced glycation end products significantly contributes to the incidence of ammonium toxicity symptoms. Using A. thaliana frostbite1 as a model plant that overcomes growth repression on ammonium, we have shown that its resistance to enhanced MG levels is based on increased GLXI activity and tolerance to elevated MG-derived advanced glycation end-product (MAGE) levels. Furthermore, our results show that glyoxalase pathway activity strongly affects cellular antioxidative systems. Under stress conditions, the disruption of the MG detoxification pathway limits the functioning of antioxidant defense. However, under optimal growth conditions, a defect in the MG detoxification route results in the activation of antioxidative systems.

Nrf2 and Oxidative Stress: A General Overview of Mechanisms and Implications in Human Disease

Organisms are continually exposed to exogenous and endogenous sources of reactive oxygen species (ROS) and other oxidants that have both beneficial and deleterious effects on the cell. ROS have important roles in a wide range of physiological processes; however, high ROS levels are associated with oxidative stress and disease progression. Oxidative stress has been implicated in nearly all major human diseases, from neurogenerative diseases and neuropsychiatric disorders to cardiovascular disease, diabetes, and cancer. Antioxidant defence systems have evolved as a means of protection against oxidative stress, with the transcription factor Nrf2 as the key regulator. Nrf2 is responsible for regulating an extensive panel of antioxidant enzymes involved in the detoxification and elimination of oxidative stress and has been extensively studied in the disease contexts. This review aims to provide the reader with a general overview of oxidative stress and Nrf2, including basic mechanisms of Nrf2 activation and regulation, and implications in various major human diseases.

Understanding the Role of Yeast Yme1 in Mitochondrial Function Using Biochemical and Proteomics Analyses

Mitochondrial i-AAA proteinase Yme1 is a multifunctional protein that plays important roles in maintaining mitochondrial protein homeostasis and regulating biogenesis and function of mitochondrial proteins. However, due to the complex interplay of mitochondria and the multifunctional nature of Yme1, how Yme1 affects mitochondrial function and protein homeostasis is still poorly understood. In this study, we investigated how YME1 deletion affects yeast Saccharomyces cerevisiae growth, chronological life span, mitochondrial protein homeostasis and function, with a focus on the mitochondrial oxidative phosphorylation (OXPHOS) complexes. Our results show that whilst the YME1 deleted cells grow poorly under respiratory conditions, they grow similar to wild-type yeast under fermentative conditions. However, the chronological life span is impaired, indicating that Yme1 plays a key role in longevity. Using highly enriched mitochondrial extract and proteomic analysis, we show that the abundances of many mitochondrial proteins are altered by YME1 deletion. Several components of the respiratory chain complexes II, III, IV and V were significantly decreased, suggesting that Yme1 plays an important role in maintaining the level and function of complexes II-V. This result was confirmed using blue native-PAGE and in-solution-based enzyme activity assays. Taken together, this study shows that Yme1 plays an important role in the chronological life span and mitochondrial protein homeostasis and has deciphered its function in maintaining the activity of mitochondrial OXPHOS complexes.

AAA+ proteases: the first line of defense against mitochondrial damage

Mitochondria play essential cellular roles in Adenosine triphosphate (ATP) synthesis, calcium homeostasis, and metabolism, but these vital processes have potentially deadly side effects. The production of the reactive oxygen species (ROS) and the aggregation of misfolded mitochondrial proteins can lead to severe mitochondrial damage and even cell death. The accumulation of mitochondrial damage is strongly implicated in aging and several incurable diseases, including neurodegenerative disorders and cancer. To oppose this, metazoans utilize a variety of quality control strategies, including the degradation of the damaged mitochondrial proteins by the mitochondrial-resident proteases of the ATPase Associated with the diverse cellular Activities (AAA+) family. This mini-review focuses on the quality control mediated by the mitochondrial-resident proteases of the AAA+ family used to combat the accumulation of damaged mitochondria and on how the failure of this mitochondrial quality control contributes to diseases.

Roles of LonP1 in Oral-Maxillofacial Developmental Defects and Tumors: A Novel Insight

Recent studies have indicated a central role for LonP1 in mitochondrial function. Its physiological functions include proteolysis, acting as a molecular chaperone, binding mitochondrial DNA, and being involved in cellular respiration, cellular metabolism, and oxidative stress. Given its vital role in energy metabolism, LonP1 has been suggested to be associated with multi-system neoplasms and developmental disorders. In this study, we investigated the roles, possible mechanisms of action, and therapeutic roles of LonP1 in oral and maxillofacial tumor development. LonP1 was highly expressed in oral-maxillofacial cancers and regulated their development through a sig-naling network. LonP1 may therefore be a promising anticancer therapy target. Mutations in LONP1 have been found to be involved in the etiology of cerebral, ocular, dental, auricular, and skeletal syndrome (CODAS). Only patients carrying specific LONP1 mutations have certain dental abnormalities (delayed eruption and abnormal morphology). LonP1 is therefore a novel factor in the development of oral and maxillofacial tumors. Greater research should therefore be conducted on the diagnosis and therapy of LonP1-related diseases to further define LonP1-associated oral phenotypes and their underlying molecular mechanisms.

Mitochondrial matrix proteases: quality control and beyond

To ensure correct function, mitochondria have developed several mechanisms of protein quality control (QC). Protein homeostasis highly relies on chaperones and proteases to maintain proper folding and remove damaged proteins that might otherwise form cell-toxic aggregates. Besides quality control, mitochondrial proteases modulate and regulate many essential functions, such as trafficking, processing and activation of mitochondrial proteins, mitochondrial dynamics, mitophagy and apoptosis. Therefore, the impaired function of mitochondrial proteases is associated with various pathological conditions, including cancer, metabolic syndromes and neurodegenerative disorders. This review recapitulates and discusses the emerging roles of two major proteases of the mitochondrial matrix, LON and ClpXP. Although commonly acknowledge for their protein quality control role, recent advances have uncovered several highly regulated processes controlled by the LON and ClpXP connected to mitochondrial gene expression and respiratory chain function maintenance. Furthermore, both proteases have been lately recognized as potent targets for anticancer therapies, and we summarize those findings.

Mitochondrial proteostasis stress in muscle drives a long-range protective response to alleviate dietary obesity independently of ATF4

Mitochondrial quality in skeletal muscle is crucial for maintaining energy homeostasis during metabolic stresses. However, how muscle mitochondrial quality is controlled and its physiological impacts remain unclear. Here, we demonstrate that mitoprotease LONP1 is essential for preserving muscle mitochondrial proteostasis and systemic metabolic homeostasis. Skeletal muscle-specific deletion of Lon protease homolog, mitochondrial (LONP1) impaired mitochondrial protein turnover, leading to muscle mitochondrial proteostasis stress. A benefit of this adaptive response was the complete resistance to diet-induced obesity. These favorable metabolic phenotypes were recapitulated in mice overexpressing LONP1 substrate ΔOTC in muscle mitochondria. Mechanistically, mitochondrial proteostasis imbalance elicits an unfolded protein response (UPR^mt) in muscle that acts distally to modulate adipose tissue and liver metabolism. Unexpectedly, contrary to its previously proposed role, ATF4 is dispensable for the long-range protective response of skeletal muscle. Thus, these findings reveal a pivotal role of LONP1-dependent mitochondrial proteostasis in directing muscle UPR^mt to regulate systemic metabolism.

Antagonistic effects of mitochondrial matrix and intermembrane space proteases on yeast aging

Background

In many organisms, aging is characterized by a loss of mitochondrial homeostasis. Multiple factors such as respiratory metabolism, mitochondrial fusion/fission, or mitophagy have been linked to cell longevity, but the exact impact of each one on the aging process is still unclear.

Results

Using the deletion mutant collection of the fission yeast Schizosaccharomyces pombe, we have developed a genome-wide screening for mutants with altered chronological lifespan. We have identified four mutants associated with proteolysis at the mitochondria that exhibit opposite effects on longevity. The analysis of the respiratory activity of these mutants revealed a positive correlation between increased respiration rate and prolonged lifespan. We also found that the phenotype of the long-lived protease mutants could not be explained by impaired mitochondrial fusion/fission activities, but it was dependent on mitophagy induction. The anti-aging role of mitophagy was supported by the effect of a mutant defective in degradation of mitochondria, which shortened lifespan of the long-lived mutants.

Conclusions

Our characterization of the mitochondrial protease mutants demonstrates that mitophagy sustains the lifespan extension of long-lived mutants displaying a higher respiration potential.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01352-w.

Evidence for mitochondrial Lonp1 expression in the nucleus

The coordinated communication between the mitochondria and nucleus is essential for cellular activities. Nonetheless, the pathways involved in this crosstalk are scarcely understood. The protease Lonp1 was previously believed to be exclusively located in the mitochondria, with an important role in mitochondrial morphology, mtDNA maintenance, and cellular metabolism, in both normal and neoplastic cells. However, we recently detected Lonp1 in the nuclear, where as much as 22% of all cellular Lonp1 can be found. Nuclear localization is detectable under all conditions, but the amount is dependent on a response to heat shock (HS). Lonp1 in the nucleus interacts with heat shock factor 1 (HSF1) and modulates the HS response. These findings reveal a novel extramitochondrial function for Lonp1 in response to stress.

Posttranslational regulation of mitochondrial frataxin and identification of compounds that increase frataxin levels in Friedreich's ataxia

Friedreich's ataxia (FRDA) is a degenerative disease caused by a decrease in the mitochondrial protein frataxin (Fxn), which is involved in iron-sulfur cluster (ISC) synthesis. Diminutions in Fxn result in decreased ISC synthesis, increased mitochondrial iron accumulation, and impaired mitochondrial function. Here, we show that conditions that result in increased mitochondrial reactive oxygen species in yeast or mammalian cell culture give rise to increased turnover of Fxn but not of other ISC synthesis proteins. We demonstrate that the mitochondrial Lon protease is involved in Fxn degradation and that iron export through the mitochondrial metal transporter Mmt1 protects yeast Fxn from degradation. We also determined that when FRDA fibroblasts were grown in media containing elevated iron, mitochondrial reactive oxygen species increased and Fxn decreased compared to WT fibroblasts. Furthermore, we screened a library of FDA-approved compounds and identified 38 compounds that increased yeast Fxn levels, including the azole bifonazole, antiparasitic fipronil, antitumor compound dibenzoylmethane, antihypertensive 4-hydroxychalcone, and a nonspecific anion channel inhibitor 4,4-diisothiocyanostilbene-2,2-sulfonic acid. We show that top hits 4-hydroxychalcone and dibenzoylmethane increased mRNA levels of transcription factor nuclear factor erythroid 2-related factor 2 in FRDA patient-derived fibroblasts, as well as downstream antioxidant targets thioredoxin, glutathione reductase, and superoxide dismutase 2. Taken together, these findings reveal that FRDA progression may be in part due to oxidant-mediated decreases in Fxn and that some approved compounds may be effective in increasing mitochondrial Fxn in FRDA, delaying disease progression.

Targeting Mitochondrial Proteases for Therapy of Acute Myeloid Leukemia

Targeting cancer metabolism has emerged as an attractive approach to improve therapeutic regimens in acute myeloid leukemia (AML). Mitochondrial proteases are closely related to cancer metabolism, but their biological functions have not been well characterized in AML. According to different catogory, we comprehensively reviewed the role of mitochondrial proteases in AML. This review highlights some 'powerful' mitochondrial protease targets, including their biological function, chemical modulators, and applicative prospect in AML.

Insights Into Mitochondrial Dynamics in Chlamydial Infection

Mitochondria are intracellular organelles that are instrumental in the creation of energy, metabolism, apoptosis, and intrinsic immunity. Mitochondria exhibit an extraordinarily high degree of flexibility, and are constantly undergoing dynamic fusion and fission changes. Chlamydia is an intracellular bacterium that causes serious health problems in both humans and animals. Due to a deficiency of multiple metabolic enzymes, these pathogenic bacteria are highly dependent on their eukaryotic host cells, resulting in a close link between Chlamydia infection and host cell mitochondria. Indeed, Chlamydia increase mitochondrial fusion by inhibiting the activation of dynein-related protein 1 (DRP1), which can regulate host cell metabolism for extra energy. Additionally, Chlamydia can inhibit mitochondrial fission by blocking DRP1 oligomerization, preventing host cell apoptosis. These mechanisms are critical for maintaining a favorable environment for reproduction and growth of Chlamydia. This review discusses the molecular mechanisms of mitochondrial fusion and fission, as well as the mechanisms by which Chlamydia infection alters the mitochondrial dynamics and the prospects of limiting chlamydial development by altering mitochondrial dynamics.