Mitochondrial diseases

tRNA modifications: greasing the wheels of translation and beyond

Transfer RNA (tRNA) is one of the most abundant RNA types in cells, acting as an adaptor to bridge the genetic information in mRNAs with the amino acid sequence in proteins. Both tRNAs and small fragments processed from them play many nonconventional roles in addition to translation. tRNA molecules undergo various types of chemical modifications to ensure the accuracy and efficiency of translation and regulate their diverse functions beyond translation. In this review, we discuss the biogenesis and molecular mechanisms of tRNA modifications, including major tRNA modifications, writer enzymes, and their dynamic regulation. We also summarize the state-of-the-art technologies for measuring tRNA modification, with a particular focus on 2'-O-methylation (Nm), and discuss their limitations and remaining challenges. Finally, we highlight recent discoveries linking dysregulation of tRNA modifications with genetic diseases.

A lipid droplet-targeted probe for imaging of lipid metabolism disorders during mitochondrial myopathy

Lipid metabolism is closely related to various biological processes in cells. The accumulation of Lipid droplets (LDs) is a typical manifestation of certain metabolic diseases, such as mitochondrial myopathy, which shows a significant increase in LDs. The accumulation of LDs can exacerbate the progression of disease, and lysosomes selectively degrade LDs to cope with this phenomenon. Visualizing lipid metabolism disorders and the interaction between LDs and other organelles is of great significance for the diagnosis and understanding of various physiological processes within cells in diseases. In this work, we synthesized two novel LD fluorescent probes and screened the best PDM, which exhibited stable fluorescence performance and strong photobleaching resistance in complex environments. The dynamics of intracellular LDs were tracked using PDM, and abnormal lipid metabolism within mitochondrial myopathy cells was visualized. This provides new tools and perspectives for studying LD dynamics and diagnosing mitochondrial myopathy.

Elucidating the mechanisms of Shenwu Capsule in improving the cognitive decline in aging based on the UPLC-Q-TOF-MS, network pharmacology, and experimental validation

Given the growing incidence of dementia-related disorders in the aging population, identifying effective treatments for age-related cognitive decline (ARCD) is crucial. Shenwu Capsule (SWC), shown to have therapeutic efficacy in phase III clinical trials for senile dementia, has unclear mechanisms and active ingredients. Aged mice were administered SWC orally for three months, and behavioral tests, including the Morris water maze, Y maze, and novel object recognition, assessed learning and memory. Neuronal damage was evaluated using histopathology, and the levels of Aβ and phosphorylated tau proteins were measured. UPLC-Q-TOF-MS identified 11 components of SWC capable of crossing the blood-brain barrier (BBB), and network pharmacology was employed to explore their potential mechanisms. Through various detection methods, including transmission electron microscopy, Western blotting, qRT-PCR, ELISA, and immunofluorescence, six key targets (AKT1, TNF, TP53, SRC, EGFR, BCL2) were elucidated. GO and KEGG pathway analyses revealed that the PI3K/Akt signaling pathway plays a crucial role in the pharmacological effects of SWC. SWC was found to suppress neuronal apoptosis by activating the PI3K/Akt/Bcl-2 signaling pathway, as demonstrated by changes in mRNA and protein levels. Histological analysis further showed that SWC treatment restored mitochondrial morphology in the hippocampus of aged mice. Molecular docking simulations confirmed strong binding affinities between the active components and key targets. Psoralidin, a component with strong molecular docking potential, was shown in vitro to activate the PI3K/Akt/Bcl-2 pathway, reduce ROS, decrease apoptosis, improve mitochondrial morphology, and stabilize mitochondrial membrane potential. These protective effects were blocked by the PI3K inhibitor LY294002. Overall, SWC ameliorates ARCD through modulation of the PI3K/Akt/Bcl-2 signaling pathway, with psoralidin identified as a potential active ingredient.

The Warburg effect: The hacked mitochondrial-nuclear communication in cancer

Mitochondrial-nuclear communication is vital for maintaining cellular homeostasis. This communication begins with mitochondria sensing environmental cues and transmitting signals to the nucleus through the retrograde cascade, involving metabolic signals such as substrates for epigenetic modifications, ATP and AMP levels, calcium flux, etc. These signals inform the nucleus about the cell's metabolic state, remodel epigenome and regulate gene expression, and modulate mitochondrial function and dynamics through the anterograde feedback cascade to control cell fate and physiology. Disruption of this communication can lead to cellular dysfunction and disease progression, particularly in cancer. The Warburg effect is the metabolic hallmark of cancer, characterized by disruption of mitochondrial respiration and increased lactate generation from glycolysis. This metabolic reprogramming rewires retrograde signaling, leading to epigenetic changes and dedifferentiation, further reprogramming mitochondrial function and promoting carcinogenesis. Understanding these processes and their link to tumorigenesis is crucial for uncovering tumorigenesis mechanisms. Therapeutic strategies targeting these disrupted pathways, including metabolic and epigenetic components, provide promising avenues for cancer treatment.

Mitochondrial Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating multisystem disorder of unclear etiology that affects many individuals worldwide. One of its hallmark symptoms is prolonged fatigue following exertion, a feature also observed in long COVID, suggesting an underlying dysfunction in energy production in both conditions. Here, mitochondrial dysfunction and its potential pathogenetic role in these disorders are reviewed.

Advances in Management of Mitochondrial Myopathies

Mitochondria, the energy factories of human organisms, can be the cause of a variety of genetic disorders called mitochondrial myopathies. Mitochondrial diseases arise from genetic alterations in either mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) and can manifest with great heterogeneity, leading to multiorgan dysfunction. The purpose of this article is to concisely review the pathophysiology, genetics and main clinical features of mitochondrial myopathies, focusing mainly on the treatment and management of these disorders. Currently, a particular treatment for mitochondrial myopathies does not exist, while the available guidelines concerning management are based on experts' opinions. The therapeutic options currently applied largely aim at symptom relief and amelioration of patients' quality of life. The most commonly used regimens involve the administration of vitamins and cofactors, although hard evidence regarding their true benefit for patients is still lacking. Recent studies have demonstrated promising results for elamipretide; however, phase III clinical trials are still ongoing. Regarding patient management, a multidisciplinary approach with the collaboration of different specialties is required. Further clinical trials for the already applied treatment options, as well as on novel experimental therapies, are of utmost importance in order to improve patients' outcomes.

Disruption of Mitochondrial Quality Control in Inherited Metabolic Disorders

Inherited metabolic disorders (IMDs) are genetic disorders often characterized by the accumulation of toxic metabolites in patient tissues and bodily fluids. Although the pathophysiologic effect of these metabolites and their direct effect on cellular function is not yet established for many of these disorders, animal and cellular studies have shown that mitochondrial bioenergetic dysfunction with impairment of citric acid cycle activity and respiratory chain, along with secondary damage induced by oxidative stress are prominent in some. Mitochondrial quality control, requiring the coordination of multiple mechanisms such as mitochondrial biogenesis, dynamics, and mitophagy, is responsible for the correction of such defects. For inborn errors of enzymes located in the mitochondria, secondary abnormalities in quality control this organelle could play a role in their pathophysiology. This review summarizes preclinical data (animal models and patient-derived cells) on mitochondrial quality control disturbances in selected IMDs.

Assessment of the respiratory chain enzyme activity in peripheral blood monocytes for the noninvasive diagnostics of mitochondrial disease

BACKGROUND

Mitochondrial diseases are among the most common metabolic disorders caused by mitochondrial dysfunction. Analyzing mitochondrial respiratory chain enzyme activity is essential for diagnosis. However, clinical laboratories often rely on mitochondria isolated from muscle biopsies or cultured skin fibroblasts, which may be unacceptable for some pediatric patients. This highlights the need for improved blood-based diagnostic methods.

METHODS

This paper describes spectrophotometric assays to evaluate mitochondrial respiratory chain enzyme activity in peripheral blood monocytes. Sample preparation methods and assays for respiratory complexes I-IV and the mitochondrial matrix enzyme citrate synthase are detailed. The assays were validated via samples from a panel of 28 healthy children and validated in patients with combined and isolated mitochondrial oxidative phosphorylation system (OXPHOS) deficiency.

RESULTS

The citrate synthase-normalized activities were 0.23 ± 0.08 for complex I, 0.22 ± 0.081 for complex II, 0.16 ± 0.07 for complex III, and 0.22 ± 0.07 for complex IV. All patients with mitochondrial disease exhibited the expected reductions in respiratory complex activity.

CONCLUSIONS

We established a method to analyze the respiratory complex activities via blood samples. The normal enzymatic activity ranges were established from healthy Chinese pediatric populations. We also validated the assay via samples from patients with mitochondrial disease. By establishing the first pediatric-specific reference ranges for mitochondrial respiratory chain complex activities in a Chinese population and validating this minimally invasive blood-based assay in patients with mitochondrial disease, our study enabled earlier detection, precise monitoring, and personalized management of mitochondrial disorders while avoiding the need for invasive tissue biopsies.

Mitochondrial Distribution and Osteocyte Mechanosensitivity

PURPOSE OF REVIEW

Mechanical loading of bone is an important physical stimulus for bone tissue remodeling and adaptation. It is transmitted from the extracellular matrix all the way to the osteocyte nucleus via the extracellular matrix-integrin-cytoskeleton-nucleus system. Mitochondria are integral in sensing of mechanical loads to allow the cell to adapt to its environment. This review provides a background of mitochondrial distribution in osteocytes especially during mechanical loading, discussing the importance of mitochondrial distribution in osteocyte mechanosensitivity and mechanotransduction.

RECENT FINDINGS

Mitochondria throughout the osteocyte are highly dynamic and provide essential metabolic and signal functions to regulate osteocyte morphology and function. They undergo the processes of fission and fusion accompanied by mitochondrial DNA distribution. The mitochondrial network structure and function in osteocytes can be regulated by mechanical loading. Interestingly, mitochondria can be transmitted by osteocytes into adjacent cells to communicate with them via tunneling nanotubes, migrasomes, and blebbisomes, causing changes in cell morphology and/or function. Mitochondrial distribution in or out osteocytes can be rearranged by physical and (bio)chemical signals via fission and fusion, as well as tunneling nanotubes, migrasomes, and blebbisomes. Mechanical loading-induced changes in mitochondria may drive signaling pathways of cell function in aging and diseases. More insights into interactions between neighbouring osteocytes and between osteocytes and other cell types would facilitate the development of new strategies to apply mitochondrial therapy for bone-related diseases.

Untargeted proteomics enables ultra-rapid variant prioritisation in mitochondrial and other rare diseases

BACKGROUND

Only half of individuals with suspected rare diseases receive a genetic diagnosis following genomic testing. A genetic diagnosis allows access to appropriate care, restores reproductive confidence and reduces the number of potentially unnecessary interventions. A major barrier is the lack of disease agnostic functional tests suitable for implementation in routine diagnostics that can provide evidence supporting pathogenicity of novel variants, especially those refractory to RNA sequencing.

METHODS

Focusing on mitochondrial disease, we describe an untargeted mass-spectrometry based proteomics pipeline that can quantify proteins encoded by > 50% of Mendelian disease genes and > 80% of known mitochondrial disease genes in clinically relevant sample types, including peripheral blood mononuclear cells (PBMCs). In total we profiled > 90 individuals including undiagnosed individuals suspected of mitochondrial disease and a supporting cohort of disease controls harbouring pathogenic variants in nuclear and mitochondrial genes. Proteomics data were benchmarked against pathology accredited respiratory chain enzymology to assess the performance of proteomics as a functional test. Proteomics testing was subsequently applied to individuals with suspected mitochondrial disease, including a critically ill infant with a view toward rapid interpretation of variants identified in ultra-rapid genome sequencing.

RESULTS

Proteomics testing provided evidence to support variant pathogenicity in 83% of individuals in a cohort with confirmed mitochondrial disease, outperforming clinical respiratory chain enzymology. Freely available bioinformatic tools and criteria developed for this study ( https://rdms.app/ ) allow mitochondrial dysfunction to be identified in proteomics data with high confidence. Application of proteomics to undiagnosed individuals led to 6 additional diagnoses, including a mitochondrial phenocopy disorder, highlighting the disease agnostic nature of proteomics. Use of PBMCs as a sample type allowed rapid return of proteomics data supporting pathogenicity of novel variants identified through ultra-rapid genome sequencing in as little as 54 h.

CONCLUSIONS

This study provides a framework to support the integration of a single untargeted proteomics test into routine diagnostic practice for the diagnosis of mitochondrial and potentially other rare genetic disorders in clinically actionable timelines, offering a paradigm shift for the functional validation of genetic variants.

SMIM20 promotes complex IV biogenesis and Ca2+ signaling in mice heart

Mitochondria are key to cellular energetics, metabolism, and signaling. Their dysfunction is linked to devastating diseases, including mitochondrial disorders, diabetes, neurodegenerative diseases, cardiac disorders, and cancer. Here, we present a knockout mouse model lacking the complex IV assembly factor SMIM20/MITRAC7. SMIM20-/- mice display cardiac pathology with reduced heart weight and cardiac output. Heart mitochondria present with reduced levels of complex IV associated with increased complex I activity, have altered fatty acid oxidation, and display elevated levels of ROS production. Interestingly, mutant mouse ventricular myocytes show unphysiological Ca2+ handling, which can be attributed to the increase in mitochondrial ROS production. Our study presents an example of a tissue-specific phenotype in the context of OXPHOS dysfunction. Moreover, our data suggest a link between complex IV dysfunction and Ca2+ handling at the endoplasmic reticulum through ROS signaling.

Caspase-11 drives macrophage hyperinflammation in models of Polg-related mitochondrial disease

Mitochondrial diseases (MtD) represent a significant public health challenge due to their heterogenous clinical presentation, often severe and progressive symptoms, and lack of effective therapies. Environmental exposures, such bacterial and viral infection, can further compromise mitochondrial function and exacerbate the progression of MtD. However, the underlying immune alterations that enhance immunopathology in MtD remain unclear. Here we employ in vitro and in vivo approaches to clarify the molecular and cellular basis for innate immune hyperactivity in models of polymerase gamma (Polg)-related MtD. We reveal that type I interferon (IFN-I)-mediated upregulation of caspase-11 and guanylate-binding proteins (GBP) increase macrophage sensing of the opportunistic microbe Pseudomonas aeruginosa (PA) in Polg mutant mice. Furthermore, we show that excessive cytokine secretion and activation of pyroptotic cell death pathways contribute to lung inflammation and morbidity after infection with PA. Our work provides a mechanistic framework for understanding innate immune dysregulation in MtD and reveals potential targets for limiting infection- and inflammation-related complications in Polg-related MtD.

Unexpected Discovery of a Novel Triphenylphosphonium Alkylalcohol That Triggers Cancer Cell Death via Mitophagy and Ferroptosis

Mitochondria-targeted delivery is a promising strategy in anticancer drug development. Triphenylphosphine cation (TPP+) is the most widely used mitochondrial-targeting carrier due to the elevated mitochondrial membrane potential (MMP) in cancer cells. Here, we report the serendipitous discovery of a mitochondrial-targeting carrier, compound 23, which exhibited potent anticancer activity (IC50 = 70 nM, HCC827) with minimal toxicity to normal cells. Compound 23 selectively accumulates in cancer cell mitochondria, induces MMP depolarization, and activates mitophagy via PINK1-Parkin pathway. It also disruptes mitochondrial functions, elevates ROS levels, and inhibits the xCT-GSH-GPX4 axis, leading to lipid peroxidation and ferroptotic cell death. In vivo, 23 significantly suppressed the growth of HCC827 xenograft tumors at 10 mg/kg. These findings support compound 23 as a highly selective and effective mitochondrial-targeting anticancer agent for further investigation.

De novo serine biosynthesis is protective in mitochondrial disease

The importance of serine as a metabolic regulator is well known for tumors and is also gaining attention in degenerative diseases. Recent data indicate that de novo serine biosynthesis is an integral component of the metabolic response to mitochondrial disease, but the roles of the response have remained unknown. Here, we report that glucose-driven de novo serine biosynthesis maintains metabolic homeostasis in energetic stress. Pharmacological inhibition of the rate-limiting enzyme, phosphoglycerate dehydrogenase (PHGDH), aggravated mitochondrial muscle disease, suppressed oxidative phosphorylation and mitochondrial translation, altered whole-cell lipid profiles, and enhanced the mitochondrial integrated stress response (ISRmt) in vivo in skeletal muscle and in cultured cells. Our evidence indicates that de novo serine biosynthesis is essential to maintain mitochondrial respiration, redox balance, and cellular lipid homeostasis in skeletal muscle with mitochondrial dysfunction. Our evidence implies that interventions activating de novo serine synthesis may protect against mitochondrial failure in skeletal muscle.

AARS2 ameliorates myocardial ischemia via fine-tuning PKM2-mediated metabolism

AARS2, an alanyl-tRNA synthase, is essential for protein translation, but its function in mouse hearts is not fully addressed. Here, we found that cardiomyocyte-specific deletion of mouse AARS2 exhibited evident cardiomyopathy with impaired cardiac function, notable cardiac fibrosis, and cardiomyocyte apoptosis. Cardiomyocyte-specific AARS2 overexpression in mice improved cardiac function and reduced cardiac fibrosis after myocardial infarction (MI), without affecting cardiomyocyte proliferation and coronary angiogenesis. Mechanistically, AARS2 overexpression suppressed cardiomyocyte apoptosis and mitochondrial reactive oxide species production, and changed cellular metabolism from oxidative phosphorylation toward glycolysis in cardiomyocytes, thus leading to cardiomyocyte survival from ischemia and hypoxia stress. Ribo-Seq revealed that Aars2 overexpression increased pyruvate kinase M2 (PKM2) protein translation and the ratio of PKM2 dimers to tetramers that promote glycolysis. Additionally, PKM2 activator TEPP-46 reversed cardiomyocyte apoptosis and cardiac fibrosis caused by AARS2 deficiency. Thus, this study demonstrates that AARS2 plays an essential role in protecting cardiomyocytes from ischemic pressure via fine-tuning PKM2-mediated energy metabolism, and presents a novel cardiac protective AARS2-PKM2 signaling during the pathogenesis of MI.

Further delineation of defects in MRPS2 causing human OXPHOS deficiency and early developmental abnormalities in zebrafish

Mitochondrial ribosomal protein-small 2 (MRPS2) encodes a vital structural protein essential for assembling mitoribosomal small subunit and thus mitochondrial translation. Any defect in mitochondrial translation impacts OXPHOS activity and cellular respiration. Defects in MRPS2 have been implicated recently in four families with combined oxidative phosphorylation deficiency-36 (MIM# 617950). We herein describe two individuals from two unrelated families with variable phenotypes of acute onset severe metabolic decompensation and symptomatic hypoglycemia. Exome sequencing identified bi-allelic variants in MRPS2 (NM_016034.5) in the affected individuals: P1: c.490 G > A p.(Glu164Lys); and P2: c.413 G > A p.(Arg138His). Further evaluation of the variant c.490 G > A p.(Glu164Lys) in patient-derived skin fibroblasts revealed decreased expression of MRPS2 transcript and protein levels of MRPS2 along with expression of complex I and IV proteins. Proteomics analysis revealed decreased expression of small subunit proteins and increased expression of large subunit proteins. Also, reduced complex I and IV enzyme activities, mitochondrial respiration (OCR), and altered mitochondrial morphology on confocal imaging were observed. Additionally, mrps2 knockout zebrafish larvae demonstrated an abnormal developmental phenotype and reduced Complex IV activity. With these findings, we identify additional families with variants in MRPS2, illustrating the variable clinical spectrum and validate the pathogenicity of defects in MRPS2 through in-vitro and in-vivo assays.

Nifuroxazide rescues the deleterious effects due to CHCHD10-associated MICOS defects in disease models

The identification of a point mutation (p.Ser59Leu) in the CHCHD10 gene was the first genetic evidence that mitochondrial dysfunction can trigger motor neuron disease. Since then, we have shown that this mutation leads to the disorganization of the MItochondrial contact site and Cristae Organizing System (MICOS) complex that maintains the mitochondrial cristae structure. Here, we generated yeast mutant strains mimicking MICOS instability and used them to test the ability of more than 1600 compounds from two repurposed libraries to rescue the growth defect of those cells. Among the hits identified, we selected nifuroxazide, a broad-spectrum antibacterial molecule. We show that nifuroxazide rescues mitochondrial network fragmentation and cristae abnormalities in CHCHD10S59L/+ patient fibroblasts. This molecule also decreases caspase-dependent death of human CHCHD10S59L/+ induced pluripotent stem cell-derived motor neurons. Its benefits involve KIF5B-mediated mitochondrial transport enhancement, evidenced by increased axonal movement and syntaphilin degradation in patient-derived motor neurons. Our findings strengthen the MICOS-mitochondrial transport connection. Nifuroxazide and analogues emerge as potential therapeutics for MICOS-related disorders like motor neuron disease. Its impact on syntaphilin hints at broader neurological disorder applicability for nifuroxazide.

In vitro modelling of the neuropathophysiological features of mitochondrial epilepsy

Epilepsy is a common and severe neurological manifestation of primary mitochondrial disease, affecting approximately 60 % of paediatric patients and 20 % of adult patients. Many of the mitochondrial epilepsies, particularly those presenting in childhood, are refractory to anti-epileptic treatment. Moreover, these conditions are typically characterised by severe neurodegeneration and closely associated with neurological decline and premature death. Indeed, there persists an urgent need to delineate the mechanisms underpinning mitochondrial epilepsy in order to develop effective treatments. In this review, we provide an overview of currently available in vitro models of the mitochondrial epilepsies. Such models offer opportunities to characterise early disease pathophysiology and interrogate novel mitochondrial-targeting and anti-epileptic treatments, with an overall aim to modulate seizure associated pathology and activity for the mitochondrial epilepsies. We discuss the use of acute cortical and subcortical brain slice preparations, obtained from both neurosurgical patients and rodents, for modelling the common neuropathophysiological features of mitochondrial epilepsy. We also review the use of induced pluripotent stem cell derived neural and glial culture models, and the development of three-dimensional cerebral organoids, generated from fibroblasts obtained from patients with primary mitochondrial disease. Human-derived, disease-relevant in vitro model systems which recapitulate the complexity and pathological features observed in patient brain tissues are crucial to help bridge the gap between animal models and patients living with mitochondrial epilepsy.

The most bothersome symptoms in neuromuscular diseases: the ERN EURO NMD Survey

BACKGROUND

Neuromuscular diseases (NMDs) comprise a range of genetic and acquired rare disorders that affect motor neurons, peripheral nerves, neuromuscular junctions and skeletal muscles, leading to significant impairments such as muscle weakness and fatigue resulting in functional limitations. This study aims to investigate the prevalence and severity of disease-related symptoms in adult patients with NMDs registered in the European Reference Network (ERN) EURO-NMD. A cross-sectional electronic survey was conducted with 1,253 participants who reported the severity of 28 symptoms, which were scored using multi-criteria decision analysis (MCDA).

RESULTS

The results identified muscle fatigue, weakness and impaired physical function/activity as the most severe and prevalent symptoms in all NMD groups, followed by coordination and/or balance problems, muscle stiffness, mental fatigue, and pain. Notably, the analysis highlighted differences in symptom severity between disease subtypes and underlined the need for standardised patient-reported outcome measures (PROMs) to address the broad heterogeneity of NMDs.

CONCLUSIONS

The findings stress the critical importance of capturing patient perspectives to guide clinical care, research priorities and therapeutic development. This work argues for the development of uniform PROMs to better assess disease impact, natural history and treatment efficacy, contributing to improved patient-centred care across diverse NMD populations.

Spectrum of clinical neuroimaging in mitochondrial disorders: a neuroanatomical approach

Mitochondrial disorders are a highly heterogeneous group of genetic diseases that impact pathways associated with the structure and function of the mitochondrion. Clinical presentations of mitochondrial disorders include a wide range of onset, progression, and spectrum of neurological symptoms - ranging from episodic, focal neurological deficits to gradual onset of developmental delays, sensorineural hearing loss, visual impairment, or ataxia. This variability provides clinicians with a diagnostic challenge in identifying suspicion of a mitochondrial disorder and prioritizing specific mitochondrial disorders within their differential. While next-generation sequencing of both the nuclear and mitochondrial genomes has aided identification of mitochondrial disorders, testing results are typically not available for weeks to months, and CSF and biochemical studies indicating possible mitochondrial disorder, such as elevated lactate, are nonspecific in differentiating between mitochondrial disorders and other neurogenetic diseases. Neuroimaging can serve as an early tool to help identify specific mitochondrial disorders; however, there are additional variability and overlap between disorders and other non-mitochondrial diseases. This review provides a framework in narrowing the mitochondrial differential by neuroanatomical localization on neuroimaging studies. We will highlight established neuroimaging patterns associated with mitochondrial disorders, review the role of MRS, and discuss the alternative non-mitochondrial etiologies associated with these findings.

Profiling mitochondrial DNA variant segregation during human preimplantation development: a prerequisite to preimplantation genetic testing for mitochondrial DNA-related disorders

STUDY QUESTION

Is preimplantation genetic testing for mitochondrial DNA (mtDNA) disorders (PGT-mt) feasible at early compaction and blastocyst stages?

SUMMARY ANSWER

Pathogenic mtDNA variants segregate evenly among cell types and various lineages of a given embryo during preimplantation development, supporting the relevance of genetic analyses performed on Day 4 blastomere and on Day 5 or 6 trophectoderm (TE) samples.

WHAT IS KNOWN ALREADY

PGT-mt is validated at cleavage stage (Day 3 of development). However, its feasibility at later stages is questionable, as little is known regarding the segregation of pathogenic mtDNA variants during preimplantation development. Since mtDNA replication is silenced until the blastocyst stage (Day 5 or 6), uneven mtDNA segregation between preimplantation embryo cellular lineages known as a 'bottleneck' effect, cannot be excluded, posing a challenge for PGT-mt.

STUDY DESIGN, SIZE, DURATION

We analyzed 112 'mito' embryos carrying pathogenic mtDNA variants and 28 control embryos with mtDNA polymorphism. Heteroplasmy levels were assessed in single cells of the TE, in different parts of blastocysts (inner cell mass and TE), and at three time points of development, namely cleavage (Day 3), early compaction (Day 4), and blastocyst stages (Day 5 or 6).

PARTICIPANTS/MATERIALS, SETTING, METHODS

As part of clinical PGT, a blastomere biopsy was performed at cleavage or early compaction stages (Day 3 or 4) on 112 'mito' and 21/28 control embryos. Further analysis was carried out at Day 5 or 6 on 51 embryos deemed unsuitable for uterine transfer and donated to research. Heteroplasmy levels were determined by semi-quantitative PCR amplification of (i) the mtDNA pathogenic variants with additional enzymatic digestion or (ii) the mtDNA polymorphic hypervariable region 2.

MAIN RESULTS AND THE ROLE OF CHANCE

Here, we first show that mtDNA variants segregate evenly among blastomeres during early compaction (Day 4), supporting the feasibility of PGT-mt at this stage. We also found that mtDNA ratios remain stable between cleavage and blastocyst stages. Yet, the substantial variation of heteroplasmy levels occurring among single TE cells in 1/8 embryos suggests that PGT is only feasible when at least 5-10 cells are collected by standard TE biopsy.

LIMITATIONS, REASONS FOR CAUTION

This study sheds light on mtDNA segregation in human preimplantation embryo development. Its limitation lies in the scarcity of the material and the small number of embryos carrying a specific pathogenic mtDNA variant. Furthermore, the study of single cells from TE was performed on control embryos only.

WIDER IMPLICATIONS OF THE FINDINGS

By supporting the relevance of blastocyst biopsy in the context of PGT for pathogenic mtDNA variants, this study contributes to the general trend of postponing the biopsy to later stages of embryonic development. However, particular attention should be paid to the number of TE cells tested. Due to the potential variation of mutant load during in utero development, a control amniocentesis for evolutive pregnancies following the transfer of heteroplasmic embryos is still recommended.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by 'Association Française contre les Myopathies/AFM Téléthon' (22112, 24317, 28525); and EUR G.E.N.E. (No. ANR-17-EURE-0013). The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Thiosulphate sulfurtransferase: Biological roles and therapeutic potential

Mitochondria are central to eukaryotic cell function, driving energy production, intermediary metabolism, and cellular homeostasis. Dysregulation of mitochondrial function often results in oxidative stress, a hallmark of numerous diseases, underscoring the critical need for maintaining mitochondrial integrity. Among mitochondrial enzymes, thiosulfate sulfurtransferase (TST) has emerged as a key regulator of sulfur metabolism, redox balance, and Fe-S protein maintenance. Beyond its well-known role in cyanide detoxification, TST facilitates hydrogen sulfide (H2S) metabolism by catalyzing the transfer of sulfur from persulfides (R-SSH) to thiosulfate (S2O32-), promoting H2S oxidation and preventing its toxic accumulation. Additionally, TST contributes to the thiol-dependent antioxidant system by regulating reactive sulfur species and sustaining mitochondrial functionality through its role in sulfide-driven bioenergetics. This review highlights the biochemical and therapeutic significance of TST in mitochondrial and cellular health, emphasizing its protective roles in diseases associated with oxidative stress and mitochondrial dysfunction. Dysregulation of TST has been implicated in diverse pathologies, including specific metabolic disorders, neurological diseases, cardiovascular conditions, kidney dysfunction, inflammatory bowel disease, and cancer. These associations underline TST's potential as a biomarker and therapeutic target. Therapeutic strategies to activate the TST pathway are explored, with a focus on sodium thiosulfate (STS), novel small molecule (Hit 2), and recombinant hTST protein. STS, an FDA-approved compound, has demonstrated antioxidant and anti-inflammatory effects across multiple preclinical models, mitigating oxidative damage and improving mitochondrial integrity. A slow-release oral formulation of STS is under development, offering promise for expanding its clinical applications. Small molecule activators like Hit 2 and hTST protein have shown efficacy in enhancing mitochondrial respiration and reducing oxidative stress, though both reagents need further in vitro and in vivo investigations. Despite promising advancements, TST-based therapies remain underexplored. Future research should focus on leveraging TST's interplay with pathways like NRF2 signaling, investigating its broader protective roles in cellular health, and developing targeted interventions. Enhancing TST activity represents an innovative therapeutic approach for addressing mitochondrial dysfunction, oxidative stress, and their associated pathologies, offering new hope for the treatment of diseases associated with mitochondrial dysfunction.

Nanozymes in biomedicine: Unraveling trends, research foci, and future trajectories via bibliometric insights (from 2007 to 2024)

Nanozymes, a new generation of artificial enzymes, have attracted significant attention in biomedical applications due to their multifunctional properties, multi-enzyme mimicking abilities, cost-effectiveness, and high stability. Leveraging these diverse catalytic activities, an increasing number of nanozyme-based therapeutic strategies have been developed for the treatment of various diseases. Despite substantial research efforts, a significant gap remains in comprehensive studies examining the progression, key areas, current trends, and future directions in this field. This study provides a comprehensive overview of nanozyme applications in biomedical research over the past 17 years, utilizing data from the Web of Science Core Collection, covering the period from January 1, 2007, to October 8, 2024. Advanced bibliometric and visualization tools were employed to facilitate a comprehensive analysis. The results highlight China's dominant role in this field, accounting for 76.83 % of total publications, significantly influencing the evolution of research in this area. Key contributions were made by institutions such as the Chinese Academy of Sciences, the University of Chinese Academy of Sciences, and the University of Science and Technology of China, with Qu Xiaogang as the leading author. The journal ACS Applied Materials & Interfaces has become the most prolific publisher in this field. Keyword analysis indicates that since 2022, research hotspots in this field have increasingly focused on areas such as photothermal therapy, chemodynamic therapy, and ferroptosis. Challenges such as obstacles to clinical translation, limitations in recyclability, and insufficient targeting ability were addressed. The potential applications of emerging interdisciplinary technologies, such as artificial intelligence, machine learning, and organoids, in advancing nanozyme development were explored. This study offers a data-driven roadmap for researchers to navigate the evolving landscape of nanozyme innovation, emphasizing interdisciplinary collaboration in impactful biomedical applications.

Metabolic rewiring caused by mitochondrial dysfunction promotes mTORC1-dependent skeletal aging

Decline of mitochondrial respiratory chain (mtRC) capacity is a hallmark of mitochondrial diseases. Patients with mtRC dysfunction often present reduced skeletal growth as a sign of premature cartilage degeneration and aging, but how metabolic adaptations contribute to this phenotype is poorly understood. Here we show that, in mice with impaired mtRC in cartilage, reductive/reverse TCA cycle segments are activated to produce metabolite-derived amino acids and stimulate biosynthesis processes by mechanistic target of rapamycin complex 1 (mTORC1) activation during a period of massive skeletal growth and biomass production. However, chronic hyperactivation of mTORC1 suppresses autophagy-mediated organelle recycling and disturbs extracellular matrix secretion to trigger chondrocytes death, which is ameliorated by targeting the reductive metabolism. These findings explain how a primarily beneficial metabolic adaptation response required to counterbalance the loss of mtRC function, eventually translates into profound cell death and cartilage tissue degeneration. The knowledge of these dysregulated key nutrient signaling pathways can be used to target skeletal aging in mitochondrial disease.

Lymphopoiesis is attenuated upon hepatocyte-specific deletion of the cytochrome c oxidase assembly factor Sco1

Mutations that negatively impact mitochondrial function are highly prevalent in humans and lead to disorders with a wide spectrum of disease phenotypes, including deficiencies in immune cell development and/or function. Previous analyses of mice with a hepatocyte-specific cytochrome c oxidase (COX) deficiency revealed an unexpected peripheral blood leukopenia associated with splenic and thymic atrophy. Here, we use mice with a hepatocyte-specific deletion of the COX assembly factor Sco1 to show that metabolic defects extrinsic to the hematopoietic compartment lead to a pan-lymphopenia represented by severe losses in both B and T cells. We further demonstrate that immune defects in these mice are associated with the loss of bone marrow lymphoid progenitors common to both lineages and early signs of autoantibody-mediated autoimmunity. Our findings collectively identify hepatocyte dysfunction as a potential instigator of immunodeficiency in patients with congenital mitochondrial defects who suffer from chronic or recurrent infections.

Mitochondria-organelle crosstalk in establishing compartmentalized metabolic homeostasis

Mitochondria serve as central hubs in cellular metabolism by sensing, integrating, and responding to metabolic demands. This integrative function is achieved through inter-organellar communication, involving the exchange of metabolites, lipids, and signaling molecules. The functional diversity of metabolite exchange and pathway interactions is enabled by compartmentalization within organelle membranes. Membrane contact sites (MCSs) are critical for facilitating mitochondria-organelle communication, creating specialized microdomains that enhance the efficiency of metabolite and lipid exchange. MCS dynamics, regulated by tethering proteins, adapt to changing cellular conditions. Dysregulation of mitochondrial-organelle interactions at MCSs is increasingly recognized as a contributing factor in the pathogenesis of multiple diseases. Emerging technologies, such as advanced microscopy, biosensors, chemical-biology tools, and functional genomics, are revolutionizing our understanding of inter-organellar communication. These approaches provide novel insights into the role of these interactions in both normal cellular physiology and disease states. This review will highlight the roles of metabolite transporters, lipid-transfer proteins, and mitochondria-organelle interfaces in the coordination of metabolism and transport.

Mitochondrial DNA variant detection in over 6,500 rare disease families by the systematic analysis of exome and genome sequencing data resolves undiagnosed cases

Variants in the mitochondrial genome (mtDNA) cause a diverse collection of mitochondrial diseases and have extensive phenotypic overlap with Mendelian diseases encoded on the nuclear genome. The mtDNA is not always specifically evaluated in patients with suspected Mendelian disease, resulting in overlooked diagnostic variants. Here, we analyzed a cohort of 6,660 rare disease families (5,625 genetically undiagnosed [84%]) from the Genomics Research to Elucidate the Genetics of Rare diseases (GREGoR) Consortium, as well as other rare disease cohorts. Using dedicated pipelines to address the technical challenges posed by the mtDNA-circular genome, variant heteroplasmy, and nuclear misalignment-we called single nucleotide variants, small insertions/deletions, and large mtDNA deletions from exome and/or genome sequencing data, in addition to RNA sequencing data when available. Diagnostic mtDNA variants were identified in 10 previously genetically undiagnosed families (1 large deletion, 8 reported pathogenic variants, and 1 previously unreported likely pathogenic variant), as well as candidate diagnostic variants in a further 11 undiagnosed families. In one additional undiagnosed proband, detection of >900 heteroplasmic variants provided functional evidence of pathogenicity to a de novo variant in the nuclear gene POLG (DNA polymerase gamma), responsible for mtDNA replication and repair. Overall, mtDNA variant calling from data generated by exome and genome sequencing-primarily for nuclear variant analysis-resulted in a genetic diagnosis for 0.2% of undiagnosed families affected by a broad range of rare diseases, as well as the identification of additional promising candidates in 0.2%.

Mitochondria in focus: From structure and function to their role in human diseases. A review

Mitochondria, double-membraned organelles within all eukaryotic cells, are essential for the proper functioning of the human organism. The frequently used phrase "powerhouses of the cell" fails to adequately capture their multifaceted roles. In addition to producing energy in the form of adenosine triphosphate through oxidative phosphorylation, mitochondria are also involved in apoptosis (programmed cell death), calcium regulation, and signaling through reactive oxygen species. Recent research suggests that they can communicate with one another and influence cellular processes. Impaired mitochondrial function on the one hand, can have widespread and profound effects on cellular and organismal health, contributing to various diseases and age-related conditions. Regular exercise on the other hand, promotes mitochondrial health by enhancing their volume, density, and functionality. Although research has made significant progress in the last few decades, mainly through the use of modern technologies, there is still a need to intensify research efforts in this field. Exploring new approaches to enhance mitochondrial health could potentially impact longevity. In this review, we focus on mitochondrial research and discoveries, examine the structure and diverse roles of mitochondria in the human body, explore their influence on energy metabolism and cellular signaling and emphasize their importance in maintaining overall health.

Impairment of Muscle Function Causes Pupal Lethality in Flies Expressing the Mitochondrial Alternative Oxidase

The mitochondrial alternative oxidase (AOX) from the tunicate Ciona intestinalis has been explored as a potential therapeutic enzyme for human mitochondrial diseases, yet its systemic effects remain poorly understood. Here, we investigate the metabolic and physiological consequences of AOX expression during the development of Drosophila cultured under dietary stress. We show that the combination of strong, ubiquitous AOX expression and a low-nutrient condition leads to pupal lethality and severe defects in larval musculature, characterized by actin aggregation and muscle shortening. These structural abnormalities correlate with a decrease in larval biomass and motility. Interestingly, the muscle defects and the motility impairments vary in severity among individuals, predicting survival rates at the pupal stage. AOX expression in specific tissues (muscle, nervous system or fat body) does not individually recapitulate the lethal phenotype observed with ubiquitous expressions of the enzyme, indicating a complex metabolic imbalance. Metabolomic analysis revealed that the low-nutrient diet and AOX expression have opposite effects on most metabolites analyzed, especially in the levels of amino acids. Notably, supplementation of the low-nutrient diet with the essential amino acids methionine and/or tryptophan partially rescues pupal viability, body size, muscle morphology, and locomotion, whereas supplementation with proline and/or glutamate does not, highlighting a specific perturbation in amino acid metabolism rather than general bioenergetic depletion. These findings demonstrate that AOX expression disrupts metabolic homeostasis, with developmental and physiological consequences that must be considered when evaluating AOX for therapeutic applications.

N7-methylguanosine tRNA modification promotes gastric cancer progression by activating SDHAF4-dependent mitochondrial oxidative phosphorylation

N7-methylguanosine (m7G) tRNA modification is closely implicated in tumor occurrence and development. However, the precise function and molecular mechanisms of m7G tRNA modification in gastric cancer (GC) remain unclear. In this study, we evaluated the expression and function of methyltransferase-like 1 (METTL1) and WD repeat domain 4 (WDR4) in GC and elucidated the mechanisms underlying the role of METTL1/WDR4-mediated m7G tRNA modifications in promoting GC progression. Upregulation of m7G methyltransferase complex proteins, METTL1 and WDR4, in GC tissues significantly correlates with poor patient prognosis. Functionally, METTL1 and WDR4 facilitate GC progression in vitro and in vivo. Mechanistically, METTL1 knockdown reduces the expression of m7G-modified tRNAs and attenuates the translation of oncogenes enriched in pathways associated with oxidative phosphorylation. Furthermore, METTL1 strengthens mitochondrial electron transport chain complex II (ETC II) activity by promoting succinate dehydrogenase assembly factor 4 (SDHAF4) translation, thereby accelerating GC metabolism and progression. Forced expression of SDHAF4 and chemical modulators of ETC II could reverse the effects of METTL1 on mouse GC. Collectively, our findings delineate the oncogenic role and molecular mechanisms of METTL1/WDR4-mediated m7G tRNA modifications in GC progression, suggesting METTL1/WDR4 and its downstream signaling axis as potential therapeutic targets for GC.

Polyamine metabolism is dysregulated in COXFA4-related mitochondrial disease

Most of the chemical energy that organisms rely on to support cellular function is generated through oxidative phosphorylation, a metabolic pathway in which electron donors NADH and FADH are oxidized through a series of successive steps to generate adenosine triphosphate. These redox reactions are orchestrated by a series of five protein complexes that sit within the mitochondrial membrane. Deficiency of cytochrome c oxidase, the fourth of these complexes, is a recognized cause of mitochondrial disease. COXFA4 encodes one of the protein subunits of cytochrome c oxidase, and variants in COXFA4 have recently been reported in individuals with a range of symptoms. These symptoms can include feeding difficulties, poor growth, cardiomyopathy, Leigh or Leigh-like disease, and neurodevelopmental delay, although these symptoms vary widely between individuals. However, a mechanistic understanding of the connection between COXFA4 loss and these varied disease manifestations is lacking. Using animal modeling in Xenopus, we explored the ramifications of coxfa4 loss of function on the early developing heart. We then conducted a hypothesis naive analysis of cellular gene expression in the context of COXFA4 deletion and discovered a downstream deficiency in the ornithine decarboxylase pathway. Small-molecule-based modulation of the ornithine decarboxylase pathway in our model modified the extent of disease, including improvement of cardiac function. Our findings point to a mechanism by which COXFA4 dysfunction leads to tissue-specific disease.

Small molecules restore mutant mitochondrial DNA polymerase activity

Mammalian mitochondrial DNA (mtDNA) is replicated by DNA polymerase γ (POLγ), a heterotrimeric complex consisting of a catalytic POLγA subunit and two accessory POLγB subunits1. More than 300 mutations in POLG, the gene encoding the catalytic subunit, have been linked to severe, progressive conditions with high rates of morbidity and mortality, for which no treatment exists2. Here we report on the discovery and characterization of PZL-A, a first-in-class small-molecule activator of mtDNA synthesis that is capable of restoring function to the most common mutant variants of POLγ. PZL-A binds to an allosteric site at the interface between the catalytic POLγA subunit and the proximal POLγB subunit, a region that is unaffected by nearly all disease-causing mutations. The compound restores wild-type-like activity to mutant forms of POLγ in vitro and activates mtDNA synthesis in cells from paediatric patients with lethal POLG disease, thereby enhancing biogenesis of the oxidative phosphorylation machinery and cellular respiration. Our work demonstrates that a small molecule can restore function to mutant DNA polymerases, offering a promising avenue for treating POLG disorders and other severe conditions linked to depletion of mtDNA.

Atf3 controls transitioning in female mitochondrial cardiomyopathy as identified by spatial and single-cell transcriptomics

Oxidative phosphorylation defects result in now intractable mitochondrial diseases (MD) with cardiac involvement markedly affecting prognosis. The mechanisms underlying the transition from compensation to dysfunction in response to metabolic deficiency remain unclear. Here, we used spatially resolved transcriptomics and single-nucleus RNA sequencing (snRNA-seq) on the heart of a patient with mitochondrial cardiomyopathy (MCM), combined with an MCM mouse model with cardiac-specific Ndufs6 knockdown (FS6KD). Cardiomyocytes demonstrated the most heterogeneous expression landscape among cell types caused by metabolic perturbation, and pseudotime trajectory analysis revealed dynamic cellular states transitioning from compensation to severe compromise. This progression coincided with the transient up-regulation of a transcription factor, ATF3. Genetic ablation of Atf3 in FS6KD corroborated its pivotal role, effectively delaying cardiomyopathy progression in a female-specific manner. Our findings highlight a fate-determining role of ATF3 in female MCM progression and that the latest transcriptomic analysis will help decipher the mechanisms underlying MD progression.

iPSC models of mitochondrial diseases

Mitochondrial diseases are historically difficult to study. They cause multi-systemic defects with prevalent impairment of hard-to-access tissues such as the brain and the heart. Furthermore, they suffer from a paucity of conventional model systems, especially because of the challenges associated with mitochondrial DNA (mtDNA) engineering. Consequently, most mitochondrial diseases are currently untreatable. Human induced pluripotent stem cells (iPSCs) represent a promising approach for developing human model systems and assessing therapeutic avenues in a patient- and tissue-specific context. iPSCs are being increasingly used to investigate mitochondrial diseases, either for dissecting mutation-specific defects within two-dimensional (2D) or three-dimensional (3D) progenies or for unveiling the impact of potential treatment options. Here, we review how iPSC-derived 2D cells and 3D organoid models have been applied to the study of mitochondrial diseases caused by either nuclear or mtDNA defects. We anticipate that the field of iPSC-driven modeling of mitochondrial diseases will continue to grow, likely leading to the development of innovative platforms for treatment discovery and toxicity that could benefit the patient community suffering from these debilitating disorders with highly unmet medical needs.

SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype

Leigh syndrome, a severe neurological disorder is commonly caused by homozygous or bi-allelic pathogenic variants in the SURF1 gene. SURF1 deficiency leads to dysfunction of Cytochrome C Oxidase (COX) activity, which is crucial for mitochondrial oxidative phosphorylation. Understanding COX activity's correlation with disease severity is essential for developing SURF1 Leigh Syndrome biomarkers. This study assesses the disease burden in SURF1 Leigh Syndrome and evaluates COX activity as a treatment biomarker. We reviewed records and questionnaires from 17 individuals, classifying them into phenotypic and genotypic groups. We compared COX activity assays in patient fibroblasts to age-matched controls, clinical data, and neuroimaging findings. Patient COX activity was at most 50% of controls, averaging 32% (p < 0.001). Common clinical features included brainstem abnormalities (93.3%), motor regression (92.3%), bi-allelic heterozygous SURF1 variants (88.2%), and delayed growth/development (35.7%). Homozygous and heterozygous nonsense/frameshift variants showed more severe phenotypes (p = 0.008) and more MRI abnormalities (p = 0.005). Significant COX activity reduction is linked to SURF1 Leigh Syndrome, with genotype influencing disease severity. Clinical and neuroimaging correlations show potential for prognostic indicators. This study lays the groundwork for future research and clinical application of COX activity as a SURF1 Leigh Syndrome biomarker.

Developmental mitochondrial complex I activity determines lifespan

Aberrant mitochondrial function has been associated with an increasingly large number of human disease states. Observations from in vivo models where mitochondrial function is altered suggest that maladaptations to mitochondrial dysfunction may underpin disease pathology. We hypothesized that the severity of this maladaptation could be shaped by the plasticity of the system when mitochondrial dysfunction manifests. To investigate this, we have used inducible fly models of mitochondrial complex I (CI) dysfunction to reduce mitochondrial function at two stages of the fly lifecycle, from early development and adult eclosion. Here, we show that in early life (developmental) mitochondrial dysfunction results in severe reductions in survival and stress resistance in adulthood, while flies where mitochondrial function is perturbed from adulthood, are long-lived and stress resistant despite having up to a 75% reduction in CI activity. After excluding developmental defects as a cause, we went on to molecularly characterize these two populations of mitochondrially compromised flies, short- and long-lived. We find that our short-lived flies have unique transcriptomic, proteomic and metabolomic responses, which overlap significantly in discrete models of CI dysfunction. Our data demonstrate that early mitochondrial dysfunction via CI depletion elicits a maladaptive response, which severely reduces survival, while CI depletion from adulthood is insufficient to reduce survival and stress resistance.

Self-Referenced Probe Enables Quantified Monitoring Mitochondrial Membrane Potential by Colocalization Coefficients

Mitochondria are dynamic organelles that have a variety of physiological states. Mitochondrial membrane potential (MMP) maintains mitochondrial physiological activities and reflects cellular health and viability. Thus, it is essential to dynamically monitor changes in MMP for understanding mitochondria-related biological processes. However, in situ, synchronous and quantitative tracking of MMP dynamic processes remains a great challenge. In this work, we designed and synthesized a fluorescent probe CBTH that undergoes spirocyclization in response to pH and emits a two-color fluorescence. Relying on the electrostatic interaction with MMP, CBTH is able to dual-color target mitochondria in cells with normal MMP. During the reduction of MMP, the fluorescence signal of the red channel (λex = 543 nm) gradually migrated to the nucleus, while one from the green channel (λex = 405 nm) stayed in the mitochondria. Thus, taking the green channel as an internal reference, the probe can detect changes in MMP through the colocalization coefficient fluctuations between the two fluorescent channels. In cellular experiments, CLC exhibited reversibly detecting ability and a direct proportional relationship to MMP. Overall, this work provides a novel strategy to quantitatively detect MMP. Moreover, a detailed explanation of the design principle and response mechanism of CBTH has been provided for the creation of this kind of probe.

Genome-Related Mechanisms Contributing to Differences in Alzheimer's Disease Incidence Between White and Black Older US Adults

In this manuscript, we leverage a modified GWAS algorithm adapted for use with multidimensional Cox models and data from the Health and Retirement Study to explore how genetic variation influences the size of the disparity in Alzheimer's disease (AD) incidence between older Black and White US adults. We identified four loci that were associated with higher AD incidence levels in older Black adults: (1) rs11077034 (hazard ratio (HR), 4.98) from the RBFOX1 gene; (2) rs7144494 (HR, 1.68) from the HISLA gene; (3) rs7660552 (HR, 3.07) from the SLC25A4 gene; and (4) rs12599485 (HR, 3.181) from the NIP30 gene. The RBFOX1, HISLA, SLC25A4, and NIP30 genes are known to be associated with AD (RBFOX1, NIP30) directly, and also influence the risk of AD risk-related morbidities such as hypertension (RBFOX1, SLC25A4), depression (SLC25A4), and certain cancers (HISLA, SLC25A4). A likely disparity-generating mechanism may lie in endocytosis and abnormal tissue growing mechanisms, depending on inherited gene mutations and the structure of proxies as well as gene-environment interactions with other risk factors such as lifestyle, education level, and access to adequate medical services.

Perceived association of mood and symptom severity in adults with mitochondrial diseases

Individuals with genetic mitochondrial diseases suffer from multisystem symptoms that vary in severity and over time, but the factors influencing disease manifestations are poorly understood. Based upon i) patient and family reports that stressful life events trigger or exacerbate symptoms, ii) biologically plausible pathways whereby psychological states and stress hormones influence mitochondrial energy transformation capacity, and iii) epidemiological literature linking traumatic/stressful life events and multiple neurologic disorders, we hypothesized that mitochondrial disease symptom severity may in part vary with daily mood. To examine patients' perception around potential psycho-biological mechanisms known to operate in other chronic illnesses, we administered the Stress, Health and Emotion Survey (SHES) to 70 adults with self-reported mitochondrial diseases. Participants rated how severe each of their symptom(s) was over the past year, separately for either 'good' (happy, calm) or 'bad' (stress, sad) emotional days. On average, patients reported that most symptoms were better on "good" emotional days (p < 0.0001) and worse on "bad" emotional days (p < 0.0001). Of the 29 symptoms assessed, 27 were associated with daily mood (p < 0.01). Some but not all symptoms were reported to be less or more severe on good and bad days, respectively, including fatigue, exercise intolerance, brain fog, and fine motor coordination (ps < 0.0001). These associative results suggest that on average individuals living with mitochondrial diseases perceive a connection between their mood and symptoms severity. These preliminary findings constitute an initial step towards developing more comprehensive models to understand the psychobiological factors that influence the course of mitochondrial diseases.

Small-molecule hypoxia therapy in mitochondrial disease

In this issue of Cell, Blume et al. provide compelling rationale for pursuing pharmacologic optimization of a small-molecule "HypoxyStat," which left-shifts the oxyhemoglobin dissociation curve in red blood cells in an attempt to induce an effective and sustained reduction of chronic tissue hyperoxia in primary mitochondrial disease (PMD) and was well-tolerated and effective for both pre-symptomatic and advanced disease treatment to extend survival and improve neurologic outcomes in a mouse model of Leigh syndrome spectrum.

Mitochondrial DNA Pathogenic Variants in Ophthalmic Diseases: A Review

Mitochondria are vital organelles responsible for ATP production and metabolic regulation, essential for energy-intensive cells such as retinal ganglion cells. Dysfunction in mitochondrial oxidative phosphorylation or mitochondrial DNA (mtDNA) pathogenic variants can disrupt ATP synthesis, cause oxidative stress, and lead to cell death. This has profound implications for tissues such as the retina, optic nerve, and retinal pigment epithelium, which are dependent on robust mitochondrial function. In this review, we provide a comprehensive compilation of pathogenic variants in the mtDNA associated with various ophthalmic diseases, including Leber's hereditary optic neuropathy, chronic progressive external ophthalmoplegia, Leigh syndrome, mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes, among others. We highlight the genetic variants implicated in these conditions, their pathogenic roles, and the phenotypic consequences of mitochondrial dysfunction in ocular tissues. In addition to well-established mutations, we also discuss the emerging evidence of the role of mtDNA's variants in complex multifactorial diseases, such as non-arteritic anterior ischemic optic neuropathy, primary open-angle glaucoma, and age-related macular degeneration. The review aims to serve as a valuable resource for clinicians and researchers, providing a detailed overview of mtDNA pathogenic variants and their clinical significance in the context of mitochondrial-related eye diseases.

Biallelic FDXR mutations induce ferroptosis in a rare mitochondrial disease with ataxia

Biallelic mutations in the FDXR are known to cause rare mitochondrial diseases. However, the underlying pathogenic mechanisms remain elusive. This study investigated a patient affected by optic atrophy, ataxia, and peripheral neuropathy resulting from compound heterozygous mutations in FDXR. Structural abnormalities in mitochondria were observed in muscle and nerve tissues. Lymphoblastic cell lines (LCLs) and muscle samples from the patient exhibited signs of mitochondrial dysfunction, iron overload, oxidative stress, and lipid peroxidation. Dysregulation of the glutathione peroxidase-4 was noted in the LCLs. Furthermore, treatment with deferoxamine, N-acetyl-cysteine, and ferrostatin-1 effectively alleviated oxidative stress and cell death. Cortical neurons demonstrate that FDXR deficiency impacts the morphogenesis of neurites. Collectively, these findings suggest that ferroptosis plays a significant role in the pathogenesis of FDXR-associated diseases. Additionally, idebenone appeared to have protective effects against various cellular injuries induced by FDXR mutations, providing novel insights and therapeutic approaches for the treatment of FDXR-associated diseases.

Phase 2b program with sonlicromanol in patients with mitochondrial disease due to m.3243A>G mutation

Mitochondrial disease incorporates a group of rare conditions with no approved treatment to date, except for Leber hereditary optic neuropathy. Therapeutic options to alleviate the symptoms of mitochondrial disease are urgently needed. Sonlicromanol is a promising candidate, as it positively alters the key metabolic and inflammatory pathways associated with mitochondrial disease. Sonlicromanol is a reductive and oxidative distress modulator, selectively inhibiting microsomal prostaglandin E1 synthase activity. This phase 2b program, aimed at evaluating sonlicromanol in adults with m.3243A>G mutation and primary mitochondrial disease, consisted of a randomized controlled (RCT) study (dose-selection) followed by a 52-week open-label extension study (EXT, long-term tolerability, safety and efficacy of sonlicromanol). Patients were randomized (1:1:1) to receive 100 or 50 mg sonlicromanol or placebo twice daily (bid) for 28 days with a ≥2-week wash-out period between treatments. Patients who completed the RCT study entered the EXT study, wherein they received 100 mg sonlicromanol bid. Overall, 27 patients were randomized (24 RCT patients completed all periods). Fifteen patients entered the EXT, and 12 patients were included in the EXT analysis set. All patients reported good tolerability and favourable safety, with pharmacokinetic results comparable to the earlier phase 2a study. The RCT primary end point [change from placebo in the attentional domain of the cognition score (visual identification; Cogstate IDN)] did not reach statistical significance. Using a categorization of the subject's period baseline a treatment effect over placebo was observed if their baseline was more affected (P = 0.0338). Using this approach, there were signals of improvements over placebo in at least one dose in the Beck Depression Inventory (BDI, P = 0.0143), Cognitive Failure Questionnaire (P = 0.0113) and the depression subscale of the Hospital Anxiety and Depression Scale (P = 0.0256). Statistically and/or clinically meaningful improvements were observed in the patient- and clinician-reported outcome measures at the end of the EXT study [Test of Attentional Performance (TAP) with alarm, P = 0.0102; TAP without alarm, P = 0.0047; BDI somatic, P = 0.0261; BDI total, P = 0.0563; SF12 physical component score, P = 0.0008]. Seven of nine domains of RAND-Short Form-36-like SF-36 pain improved (P = 0.0105). Other promising results were observed in the Neuro-Quality of Life Short Form-Fatigue Scale (P = 0.0036), mini-Balance Evaluation Systems test (P = 0.0009), McGill Pain Questionnaire (P = 0.0105), EuroQol EQ-5D-5L-Visual Analog Scale (P = 0.0213) and EQ-5D-5L-Index (P = 0.0173). Most patients showed improvement in the Five Times Sit-To-Stand Test. Sonlicromanol was well-tolerated and demonstrated a favourable benefit/risk ratio for up to 1 year. Sonlicromanol was efficacious in patients when affected at baseline, as seen across a variety of clinically relevant domains. Long-term treatment showed more pronounced changes from baseline.

A non-hydrolysable peptidomimetic for mitochondrial targeting

Peptidomimetics, molecules that mimic the activity of natural peptides with improved stability or bioavailability, have emerged as interesting materials with applications in biomedicine. In this study, we describe a hybrid γ,γ-peptidomimetic that efficiently aims at mitochondria, a key therapeutic target associated with several disorders, in living cells. Peptide backbones with a component of cationic and hydrophobic amino acids have been shown to preferentially target mitochondria due to their high negative membrane potential and hydrophobic character of the membranous invaginations of these key organelles. We here exploit the advantageous bioorthogonal properties of a peptidomimetic scaffold that consists of an alternation of (1S,3R)-3-amino-2,2-dimethylcyclobutane-1-carboxylic acid and an Nα-functionalised cis-γ-amino-L-proline derivative. This peptidomimetic exhibited excellent membrane translocation efficiency, mitochondrial targeting ability, and biocompatibility. Mitochondrial targeting was confirmed to be dependent on the electrochemical potential generated by the electron transport chain. The presence of non-natural amino acids rendered the compound exceptionally stable in the presence of proteases, maintaining its integrity and functionality for targeting the organelle even after 1 week of incubation in serum. This stability, coupled with its targeting abilities and the low cytosolic/endosomal residual signal, facilitated the tracking of relevant mitochondrial dynamics, including fission events and intracellular movement. Additionally, this peptidomimetic scaffold allowed the sustained and precise mitochondrial targeting of a pH sensitive ratiometric probe, 5(6)-carboxy-SNARF-1, which enabled mitochondrial pH monitoring. In summary, our study introduces a biomimetic peptide with exceptional mitochondria-targeting properties, ensuring stability in biological media and offering insights into crucial mitochondrial processes.

Advancements in PROTAC-based therapies for neurodegenerative diseases

Neurodegenerative diseases are characterized by impairments in movement and cognitive functions. These disorders are frequently associated with the accumulation of misfolded protein aggregates, which present significant challenges for treatment with conventional small-molecule inhibitors. While FDA-approved amyloid-beta-directed antibodies, such as Lecanemab, have recently shown clinical success in modifying disease progression, there are currently no treatments capable of curing neurodegenerative diseases. Emerging technologies like proteolysis-targeting chimeras (PROTACs) offer additional promise by targeting disease-causing proteins for degradation, potentially opening new therapeutic avenues. Recent experiments have demonstrated that PROTACs can specifically target and degrade pathogenic proteins associated with neurodegenerative diseases, thereby offering potential therapeutic avenues. This review discusses the latest advances in employing PROTACs for treating neurodegenerative diseases and delves into the associated challenges and opportunities. Our goal is to provide researchers in drug development with new insights on creating novel PROTACs for therapeutic applications.

Novel pathogenic mtDNA variants in Chinese children with neurological mitochondrial disorders

OBJECTIVE

Pathogenic variations in the mitochondrial genome are tightly linked to neurological mitochondrial disorders in children. However, the mutation spectrum of mitochondrial DNA (mtDNA) in the Chinese population remains incomplete. Therefore, the primary objective of our study was to comprehensively characterize pathogenic mtDNA variants in Chinese children with mitochondrial disorders at clinical, molecular, and functional levels.

METHODS

Between February 2019 and September 2023, we analyzed pathogenic mtDNA variants in a cohort of over 600 Chinese children suspected of having mitochondrial disorders. Whole-exome sequencing (WES) and whole-mtDNA sequencing were performed on the cohort.

RESULTS

We identified 54 pathogenic or likely pathogenic mtDNA variants in 227 Chinese children with neurological mitochondrial disorders. Among the eight novel heteroplasmic variants detected in seven patients, in silico analyses suggested likely pathogenic features. Functional analyses using either primary fibroblasts or cybrid cells carrying different mutant loads of mtDNA variants showed impaired mitochondrial respiration, ATP generation, and mitochondrial membrane potential in five of the eight novel variants, including m.4275G>A, m.10407G>A, m.5828G>A, m.3457G>A, and m.13112T>C. The m.8427T>C variant was identified as a rare polymorphism because, despite being located at MT-ATP8, it does not affect both the assembly and activity of mitochondrial complex V in cells carrying homoplasmic m.8427T>C variation. Transcriptome profiling further confirmed the pathogenic contributions of these five variants by altering mitochondrial pathways.

CONCLUSION

In summary, we revisited the mtDNA mutation spectrum in Chinese children with mitochondrial disorders, and identified five novel pathogenic mtDNA variants with functional verification that are related to neurological mitochondrial disorders in children.

Evolution, genetic diversity, and health

Human genetic diversity in today's world has been shaped by evolutionary history, demographic shifts and environmental exposures, influencing complex traits, disease susceptibility and drug responses. Capturing this diversity is essential for advancing precision medicine and promoting equitable healthcare. Despite the great progress achieved with initiatives such as the human Pangenome and large biobanks that aim for a better representation of human diversity, important challenges remain. In this Perspective, we discuss the importance of diversity in clinical genomics through an evolutionary lens. We highlight progress and challenges and outline key clinical applications of diverse genetic data. We argue that diversifying both datasets and methodologies-integrating ancestral and environmental factors-is crucial for fully understanding the genetic basis of human health and disease.

Role and mechanism of seaweed polysaccharides in regulating mitochondrial dysfunction: A review

Seaweed polysaccharides are naturally occurring macromolecules in seaweeds with a variety of health benefits. Their multiple health benefits are attributed to their regulatory effects on mitochondrial function. However, the relationship between the source of seaweed polysaccharides, polysaccharide properties, and mitochondrial dysfunction has not been comprehensively reviewed. This review summarizes the sources of seaweed polysaccharides, effects of polysaccharide properties (including molecular weight, monosaccharide composition, chemical structure, and functional groups) on regulating mitochondrial function, as well as their main potential regulatory mechanisms (including mitochondrial respiratory chain, mitochondrial membrane structural integrity, mitochondrial DNA, mitochondrial dynamic, mitochondrial autophagy, and mitochondrial Ca2+ homeostasis), with the aim to provide a theoretical reference to promote further research on the development and application of seaweed polysaccharides.

Increased Rate of Unique Mitochondrial DNA Deletion Breakpoints in Young Adults With Early-Life Stress

Background

Mounting evidence suggests that mitochondria respond to psychosocial stress. Recent studies suggest mitochondrial DNA (mtDNA) deletions may be increased in some psychiatric disorders, but no studies have examined early-life stress (ELS) and mtDNA deletions. In this study, we assessed mtDNA deletions in peripheral blood mononuclear cells of medically healthy young adults with and without ELS.

Methods

Participants (n = 181; 69% female), ages 18 to 40 years, were recruited from the community. Participants with ELS (n = 108) had moderate to severe childhood maltreatment; 83 also had parental loss, and 59 had psychiatric disorders. Participants in the control group (n = 73) had no maltreatment, parental loss, or psychiatric disorders. Standardized interviews and self-report measures assessed demographic variables, stress, and mental health. mtDNA from peripheral blood mononuclear cells was amplified via long-range polymerase chain reaction; mtDNA deletions were quantified via Seq-Well, next-generation sequencing, and the Splice-Break pipeline. Linear regression models were used to assess relationships of mtDNA deletion metrics with ELS, adult stressors, psychiatric disorders, and demographics.

Results

Participants with ELS had significantly greater rates of unique mtDNA deletion breakpoints per 10,000 coverage than participants without ELS (p < .001), correcting for age, sex, and sequencing depth. Cumulative mtDNA deletion read percentage was not significantly different between groups. Psychiatric disorders and adult stressors were associated with greater unique mtDNA deletion breakpoints (ps < .05) but did not account for associations of ELS with mtDNA deletions.

Conclusions

The increased number of unique mtDNA deletion breakpoints in participants with ELS suggests that mitochondrial genomes undergo observable alterations in the context of early stress. Future studies will examine mtDNA deletions with metabolic health measures.