FGF21 is a biomarker for mitochondrial translation and mtDNA maintenance disorders

The myokine FGF21 associates with enhanced survival in ALS and mitigates stress-induced cytotoxicity

Amyotrophic lateral sclerosis (ALS) is an age-related and fatal neurodegenerative disease characterized by progressive muscle weakness. There is marked heterogeneity in clinical presentation, progression, and pathophysiology with only modest treatments to slow disease progression. Molecular markers that provide insight into this heterogeneity are crucial for clinical management and identification of new therapeutic targets. In a prior muscle miRNA sequencing investigation, we identified altered FGF pathways in ALS muscle, leading us to investigate FGF21. We analyzed human ALS muscle biopsy samples and found a large increase in FGF21 expression with localization to atrophic myofibers and surrounding endomysium. A concomitant increase in FGF21 was detected in ALS spinal cords which correlated with muscle levels. FGF21 was increased in the SOD1G93A mouse beginning in presymptomatic stages. In parallel, there was dysregulation of the co-receptor, β-Klotho. Plasma FGF21 levels were increased and high levels correlated with slower disease progression, prolonged survival, and increased body mass index. In NSC-34 motor neurons and C2C12 muscle cells expressing SOD1G93A or exposed to oxidative stress, ectopic FGF21 mitigated loss of cell viability. In summary, FGF21 is a novel biomarker in ALS that correlates with slower disease progression and exerts trophic effects under conditions of cellular stress.

Long-term persistence of mitochondrial dysfunctions after viral infections and antiviral therapies: A review of mechanisms involved

Mitochondria are vital for most cells' functions. Viruses hijack mitochondria machinery for misappropriation of energy supply or to bypass defense mechanisms. Many of these mitochondrial dysfunctions persist after recovery from treated or untreated viral infections, particularly when mitochondrial DNA is permanently damaged. Quantitative defects and structural rearrangements of mitochondrial DNA accumulate in post-mitotic tissues as recently reported long after SARS-CoV-2 or HIV infection, or following antiviral therapy. These observations are consistent with the "hit-and-run" concept proposed decades ago to explain viro-induced cell transformation and it could apply to delayed post-viral onsets of symptoms and advocate for complementary supportive care. Thus, according to this concept, following exposure to viruses or antiviral agents, mitochondrial damage could evolve into an autonomous clinical condition. It also establishes a pathogenic link between communicable and non-communicable chronic diseases.

FGF21 agonists: An emerging therapeutic for metabolic dysfunction-associated steatohepatitis and beyond

The worldwide epidemics of obesity, hypertriglyceridemia, dyslipidaemia, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease (MASLD)/metabolic dysfunction-associated steatohepatitis (MASH) represent a major economic burden on healthcare systems. Patients with at-risk MASH, defined as MASH with moderate or significant fibrosis, are at higher risk of comorbidity/mortality, with a significant risk of cardiovascular diseases and/or major adverse liver outcomes. Despite a high unmet medical need, there is only one drug approved for MASH. Several drug candidates have reached the phase III development stage and could lead to several potential conditional drug approvals in the coming years. Within the armamentarium of future treatment options, FGF21 analogues hold an interesting position thanks to their pleiotropic effects in addition to their significant effect on both MASH resolution and fibrosis improvement. In this review, we summarise preclinical and clinical data from FGF21 analogues for MASH and explore additional potential therapeutic indications.

Activity Prediction Modeling Based on a Combination of Growth Differentiation Factor 15 and Serum Biomarker Levels in Dermatomyositis and Polymyositis

AIMS

Growth differentiation factor 15 (GDF15) plays an important role in multiple inflammatory disorders. We aimed to analyze serum GDF15 levels in adult patients with idiopathic inflammatory myopathies (IIMs).

METHODS

Serum GDF15 levels were measured in 179 adult patients with IIMs and 76 healthy controls (HCs). The association between GDF15 levels and disease variables was analyzed using Spearman's rank correlation. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the discriminatory ability of GDF15 and the GDF15-to-lymphocyte ratio (GLR). Machine learning methods were applied to build predictive models.

RESULTS

GDF15 levels and GLR were significantly elevated in patients with adult IIMs than in HCs. Compared with patients in remission, both GDF15 and GLR were significantly higher in myositis patients in an active phase. GDF15 levels correlated positively with myositis disease activity indices and negatively correlated with lymphocyte and platelet counts. ROC curve analysis revealed that GDF15 levels and GLR outperformed muscle enzymes and distinguished well between patients with active disease and those in remission. Furthermore, even in the normal muscle enzyme group, GDF15 levels and GLR were also well-distinguished between patients with active disease and those in remission. Using machine learning, a logistic regression model of GDF15 combined with creatine kinase and lymphocyte count was constructed and had a reliable predictive value for disease activity.

CONCLUSIONS

GDF15, particularly GLR, was significantly correlated with disease activity in adult patients with IIMs. They could serve as useful biochemical markers for evaluating disease activity, monitoring disease progression, and guiding treatment in adult patients with IIMs.

Unraveling cysteine deficiency-associated rapid weight loss

Forty percent of the US population and 1 in 6 individuals worldwide are obese, and the incidence of this disease is surging globally1,2. Various dietary interventions, including carbohydrate and fat restriction, and more recently amino acid restriction, have been explored to combat this epidemic3-6. We sought to investigate the impact of removing individual amino acids on the weight profiles of mice. Compared to essential amino acid restriction, induction of conditional cysteine restriction resulted in the most dramatic weight loss, amounting to 20% within 3 days and 30% within one week, which was readily reversed. This weight loss occurred despite the presence of substantial cysteine reserves stored in glutathione (GSH) across various tissues7. Further analysis demonstrated that the weight reduction primarily stemmed from an increase in the utilization of fat mass, while locomotion, circadian rhythm and histological appearance of multiple other tissues remained largely unaffected. Cysteine deficiency activated the integrated stress response (ISR) and NRF2-mediated oxidative stress response (OSR), which amplify each other, leading to the induction of GDF15 and FGF21, hormones associated with increased lipolysis, energy homeostasis and food aversion8-10. We additionally observed rapid tissue coenzyme A (CoA) depletion, resulting in energetically inefficient anaerobic glycolysis and TCA cycle, with sustained urinary excretion of pyruvate, orotate, citrate, α-ketoglutarate, nitrogen rich compounds and amino acids. In summary, our investigation highlights that cysteine restriction, by depleting GSH and CoA, exerts a maximal impact on weight loss, metabolism, and stress signaling compared to other amino acid restrictions. These findings may pave the way for innovative strategies for addressing a range of metabolic diseases and the growing obesity crisis.

BACH1 inhibits senescence, obesity, and short lifespan by ferroptotic FGF21 secretion

Ferroptosis is a type of regulated cell death characterized by iron-dependent lipid peroxidation. A model cell system is constructed to induce ferroptosis by re-expressing the transcription factor BACH1, a potent ferroptosis inducer, in immortalized mouse embryonic fibroblasts (iMEFs). The transfer of the culture supernatant from ferroptotic iMEFs activates the proliferation of hepatoma cells and other fibroblasts and suppresses cellular senescence-like features. The BACH1-dependent secretion of the longevity factor FGF21 is increased in ferroptotic iMEFs. The anti-senescent effects of the culture supernatant from these iMEFs are abrogated by Fgf21 knockout. BACH1 activates the transcription of Fgf21 by promoting ferroptotic stress and increases FGF21 protein expression by suppressing its autophagic degradation through transcriptional Sqstm1 and Lamp2 repression. The BACH1-induced ferroptotic FGF21 secretion suppresses obesity in high-fat diet-fed mice and the short lifespan of progeria mice. The inhibition of these aging-related phenotypes can be physiologically significant regarding ferroptosis.

Multiomics analysis reveals serine catabolism as a potential therapeutic target for MELAS

Mitochondrial disease is a devastating genetic disorder, with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) and m.3243A>G being the most common phenotype and genotype, respectively. The treatment for MELAS patients is still less effective. Here, we performed transcriptomic and proteomic analysis in muscle tissue of MELAS patients, and discovered that the expression of molecules involved in serine catabolism were significantly upregulated, and serine hydroxymethyltransferase 2 (SHMT2) increased significantly in both the mRNA and protein levels. The SHMT2 protein level was also increased in myoblasts with m.3243A>G mutation, which was transdifferentiated from patients derived fibroblasts, accompanying with the decreased nicotinamide adenine dinucleotide (NAD+)/reduced NAD+ (NADH) ratio and cell viability. After treating with SHMT2 inhibitor (SHIN1), the NAD+/NADH ratio and cell viability in MELAS myoblasts increased significantly. Taken together, our study indicates that enhanced serine catabolism plays an important role in the pathogenesis of MELAS and that SHIN1 can be a potential small molecule for the treatment of this disease.

Exclusion of sulfide:quinone oxidoreductase from mitochondria causes Leigh-like disease in mice by impairing sulfide metabolism

Leigh syndrome is the most common inherited mitochondrial disease in children and is often fatal within the first few years of life. In 2020, mutations in the gene encoding sulfide:quinone oxidoreductase (SQOR), a mitochondrial protein, were identified as a cause of Leigh syndrome. Here, we report that mice with a mutation in the gene encoding SQOR (SqorΔN/ΔN mice), which prevented SQOR from entering mitochondria, had clinical and pathological manifestations of Leigh syndrome. SqorΔN/ΔN mice had increased blood lactate levels that were associated with markedly decreased complex IV activity and increased hydrogen sulfide (H2S) levels. Because H2S is produced by both gut microbiota and host tissue, we tested whether metronidazole (a broad-spectrum antibiotic) or a sulfur-restricted diet rescues SqorΔN/ΔN mice from developing Leigh syndrome. Daily treatment with metronidazole alleviated increased H2S levels, normalized complex IV activity and blood lactate levels, and prolonged the survival of SqorΔN/ΔN mice. Similarly, a sulfur-restricted diet normalized blood lactate levels and inhibited the development of Leigh syndrome. Taken together, these observations suggest that mitochondrial SQOR is essential to prevent systemic accumulation of H2S. Metronidazole administration and a sulfur-restricted diet may be therapeutic approaches to treatment of patients with Leigh syndrome caused by mutations in SQOR.

The STRAT-PARK cohort: A personalized initiative to stratify Parkinson's disease

The STRAT-PARK initiative aims to provide a platform for stratifying Parkinson's disease (PD) into biological subtypes, using a bottom-up, multidisciplinary biomarker-based and data-driven approach. PD is a heterogeneous entity, exhibiting high interindividual clinicopathological variability. This diversity suggests that PD may encompass multiple distinct biological entities, each driven by different molecular mechanisms. Molecular stratification and identification of disease subtypes is therefore a key priority for understanding and treating PD. STRAT-PARK is a multi-center longitudinal cohort aiming to recruit a total of 2000 individuals with PD and neurologically healthy controls from Norway and Canada, for the purpose of identifying molecular disease subtypes. Clinical assessment is performed annually, whereas biosampling, imaging, and digital and neurophysiological phenotyping occur every second year. The unique feature of STRAT-PARK is the diversity of collected biological material, including muscle biopsies and platelets, tissues particularly useful for mitochondrial biomarker research. Recruitment rate is ∼150 participants per year. By March 2023, 252 participants were included, comprising 204 cases and 48 controls. STRAT-PARK is a powerful stratification initiative anticipated to become a global research resource, contributing to personalized care in PD.

Pathophysiological roles of the serum acylcarnitine level and acylcarnitine/free carnitine ratio in patients with cardiovascular diseases

Introduction

L-carnitine exerts protective effects, such as maintaining mitochondrial functions and decreasing reactive oxygen species, while acylcarnitine (AC) is linked to the development of heart failure and atherosclerosis.

Hypothesis

Serum carnitines play important pathophysiological roles in cardiovascular diseases.

Methods

Pre-operative biochemical data were obtained from 117 patients (71 men, average age 69.9 years) who underwent surgery for cardiovascular diseases. Measurements included pre-operative biochemical data including estimated glomerular filtration rate (eGFR), physical functions, skeletal muscle mass index (SMI) measured by bioelectrical impedance analysis, anterior thigh muscle thickness (MTh) measured by ultrasound, and routine echocardiography. Carnitine components were measured with the enzyme cycling method. Muscle wasting was diagnosed based on the Asian Working Group for Sarcopenia criteria.

Results

Plasma brain natriuretic peptide (BNP) level was correlated with serum free carnitine (FC) and AC level, and the acylcarnitine/free carnitine ratio (AC/FC). AC/FC was elevated with stage of chronic kidney disease. In multivariate analysis, log (eGFR) and log (BNP) were extracted as independent factors to define log (serum AC) (eGFR: β = 0.258, p = 0.008; BNP: β = 0.273, p = 0.011), even if corrected for age, sex and body mass index. AC/FC was negatively correlated with hand-grip strength (r = -0.387, p = 0.006), SMI (r = -0.314, p = 0.012), and anterior thigh MTh (r = -0.340, p = 0.014) in men.

Conclusions

A significant association between serum AC level and AC/FC, and chronic kidney disease and heart failure exists in patients with cardiovascular diseases who have undergone cardiovascular surgery. Skeletal muscle loss and muscle wasting are also linked to the elevation of serum AC level and AC/FC.

Mitochondrial DNA competition: starving out the mutant genome

High levels of pathogenic mitochondrial DNA (mtDNA) variants lead to severe genetic diseases, and the accumulation of such mutants may also contribute to common disorders. Thus, selecting against these mutants is a major goal in mitochondrial medicine. Although mutant mtDNA can drift randomly, mounting evidence indicates that active forces play a role in the selection for and against mtDNA variants. The underlying mechanisms are beginning to be clarified, and recent studies suggest that metabolic cues, including fuel availability, contribute to shaping mtDNA heteroplasmy. In the context of pathological mtDNAs, remodeling of nutrient metabolism supports mitochondria with deleterious mtDNAs and enables them to outcompete functional variants owing to a replicative advantage. The elevated nutrient requirement represents a mutant Achilles' heel because small molecules that restrict nutrient consumption or interfere with nutrient sensing can purge cells of deleterious mtDNAs and restore mitochondrial respiration. These advances herald the dawn of a new era of small-molecule therapies to counteract pathological mtDNAs.

Association between gut health and gut microbiota in a polluted environment

Animals host complex bacterial communities in their gastrointestinal tracts, with which they share a mutualistic interaction. The numerous effects these interactions grant to the host include regulation of the immune system, defense against pathogen invasion, digestion of otherwise undigestible foodstuffs, and impacts on host behaviour. Exposure to stressors, such as environmental pollution, parasites, and/or predators, can alter the composition of the gut microbiome, potentially affecting host-microbiome interactions that can be manifest in the host as, for example, metabolic dysfunction or inflammation. However, whether a change in gut microbiota in wild animals associates with a change in host condition is seldom examined. Thus, we quantified whether wild bank voles inhabiting a polluted environment, areas where there are environmental radionuclides, exhibited a change in gut microbiota (using 16S amplicon sequencing) and concomitant change in host health using a combined approach of transcriptomics, histological staining analyses of colon tissue, and quantification of short-chain fatty acids in faeces and blood. Concomitant with a change in gut microbiota in animals inhabiting contaminated areas, we found evidence of poor gut health in the host, such as hypotrophy of goblet cells and likely weakened mucus layer and related changes in Clca1 and Agr2 gene expression, but no visible inflammation in colon tissue. Through this case study we show that inhabiting a polluted environment can have wide reaching effects on the gut health of affected animals, and that gut health and other host health parameters should be examined together with gut microbiota in ecotoxicological studies.

DELE1 promotes translation-associated homeostasis, growth, and survival in mitochondrial myopathy

Mitochondrial dysfunction causes devastating disorders, including mitochondrial myopathy. Here, we identified that diverse mitochondrial myopathy models elicit a protective mitochondrial integrated stress response (mt-ISR), mediated by OMA1-DELE1 signaling. The response was similar following disruptions in mtDNA maintenance, from knockout of Tfam, and mitochondrial protein unfolding, from disease-causing mutations in CHCHD10 (G58R and S59L). The preponderance of the response was directed at upregulating pathways for aminoacyl-tRNA biosynthesis, the intermediates for protein synthesis, and was similar in heart and skeletal muscle but more limited in brown adipose challenged with cold stress. Strikingly, models with early DELE1 mt-ISR activation failed to grow and survive to adulthood in the absence of Dele1, accounting for some but not all of OMA1's protection. Notably, the DELE1 mt-ISR did not slow net protein synthesis in stressed striated muscle, but instead prevented loss of translation-associated proteostasis in muscle fibers. Together our findings identify that the DELE1 mt-ISR mediates a stereotyped response to diverse forms of mitochondrial stress and is particularly critical for maintaining growth and survival in early-onset mitochondrial myopathy.

Mitochondrial dysfunction affects hepatic immune and metabolic remodeling in patients with hepatitis B virus-related acute-on-chronic liver failure

BACKGROUND

Immune dysregulation and metabolic derangement have been recognized as key factors that contribute to the progression of hepatitis B virus (HBV)-related acute-on-chronic liver failure (ACLF). However, the mechanisms underlying immune and metabolic derangement in patients with advanced HBV-ACLF are unclear.

AIM

To identify the bioenergetic alterations in the liver of patients with HBV-ACLF causing hepatic immune dysregulation and metabolic disorders.

METHODS

Liver samples were collected from 16 healthy donors (HDs) and 17 advanced HBV-ACLF patients who were eligible for liver transplantation. The mitochondrial ultrastructure, metabolic characteristics, and immune microenvironment of the liver were assessed. More focus was given to organic acid metabolism as well as the function and subpopulations of macrophages in patients with HBV-ACLF.

RESULTS

Compared with HDs, there was extensive hepatocyte necrosis, immune cell infiltration, and ductular reaction in patients with ACLF. In patients, the liver suffered severe hypoxia, as evidenced by increased expression of hypoxia-inducible factor-1α. Swollen mitochondria and cristae were observed in the liver of patients. The number, length, width, and area of mitochondria were adaptively increased in hepatocytes. Targeted metabolomics analysis revealed that mitochondrial oxidative phosphorylation decreased, while anaerobic glycolysis was enhanced in patients with HBV-ACLF. These findings suggested that, to a greater extent, hepa-tocytes used the extra-mitochondrial glycolytic pathway as an energy source. Patients with HBV-ACLF had elevated levels of chemokine C-C motif ligand 2 in the liver homogenate, which stimulates peripheral monocyte infiltration into the liver. Characterization and functional analysis of macrophage subsets revealed that patients with ACLF had a high abundance of CD68+ HLA-DR+ macrophages and elevated levels of both interleukin-1β and transforming growth factor-β1 in their livers. The abundance of CD206+ CD163+ macrophages and expression of interleukin-10 decreased. The correlation analysis revealed that hepatic organic acid metabolites were closely associated with macrophage-derived cytokines/chemokines.

CONCLUSION

The results indicated that bioenergetic alteration driven by hypoxia and mitochondrial dysfunction affects hepatic immune and metabolic remodeling, leading to advanced HBV-ACLF. These findings highlight a new therapeutic target for improving the treatment of HBV-ACLF.

Biomarkers of mitochondrial disorders

Mitochondrial diseases encompass a heterogeneous group of disorders with a wide range of clinical manifestations, most classically resulting in neurological, muscular, and metabolic abnormalities, but having the potential to affect any organ system. Over the years, substantial progress has been made in identifying and characterizing various biomarkers associated with mitochondrial diseases. This review summarizes the current knowledge of mitochondrial biomarkers based on a literature review and discusses the evidence behind their use in clinical practice. A total of 13 biomarkers were thoroughly reviewed including lactate, pyruvate, lactate:pyruvate ratio, creatine kinase, creatine, amino acid profiles, glutathione, malondialdehyde, GDF-15, FGF-21, gelsolin, neurofilament light-chain, and circulating cell-free mtDNA. Most biomarkers had mixed findings depending on the study, especially when considering their utility for specific mitochondrial diseases versus mitochondrial conditions in general. However, in large biomarker comparison studies, GDF-15 followed by FGF-21, seem to have the greatest value though they are still not perfect. As such, additional studies are needed, especially in light of newer biomarkers that have not yet been thoroughly investigated. Understanding the landscape of biomarkers in mitochondrial diseases is crucial for advancing early detection, improving patient management, and developing targeted therapies.

Challenges and opportunities to bridge translational to clinical research for personalized mitochondrial medicine

Mitochondrial disorders are a group of rare and heterogeneous genetic diseases characterized by dysfunctional mitochondria leading to deficient adenosine triphosphate synthesis and chronic energy deficit in patients. The majority of these patients exhibit a wide range of phenotypic manifestations targeting several organ systems, making their clinical diagnosis and management challenging. Bridging translational to clinical research is crucial for improving the early diagnosis and prognosis of these intractable mitochondrial disorders and for discovering novel therapeutic drug candidates and modalities. This review provides the current state of clinical testing in mitochondrial disorders, discusses the challenges and opportunities for converting basic discoveries into clinical settings, explores the most suited patient-centric approaches to harness the extraordinary heterogeneity among patients affected by the same primary mitochondrial disorder, and describes the current outlook of clinical trials.

Protein biomarkers GDF15 and FGF21 to differentiate mitochondrial hepatopathies from other pediatric liver diseases

BACKGROUND

Mitochondrial hepatopathies (MHs) are primary mitochondrial genetic disorders that can present as childhood liver disease. No recognized biomarkers discriminate MH from other childhood liver diseases. The protein biomarkers growth differentiation factor 15 (GDF15) and fibroblast growth factor 21 (FGF21) differentiate mitochondrial myopathies from other myopathies. We evaluated these biomarkers to determine if they discriminate MH from other liver diseases in children.

METHODS

Serum biomarkers were measured in 36 children with MH (17 had a genetic diagnosis); 38 each with biliary atresia, α1-antitrypsin deficiency, and Alagille syndrome; 20 with NASH; and 186 controls.

RESULTS

GDF15 levels compared to controls were mildly elevated in patients with α1-antitrypsin deficiency, Alagille syndrome, and biliary atresia-young subgroup, but markedly elevated in MH (p<0.001). FGF21 levels were mildly elevated in NASH and markedly elevated in MH (p<0.001). Both biomarkers were higher in patients with MH with a known genetic cause but were similar in acute and chronic presentations. Both markers had a strong performance to identify MH with a molecular diagnosis with the AUC for GDF15 0.93±0.04 and for FGF21 0.90±0.06. Simultaneous elevation of both markers >98th percentile of controls identified genetically confirmed MH with a sensitivity of 88% and specificity of 96%. In MH, independent predictors of survival without requiring liver transplantation were international normalized ratio and either GDF15 or FGF21 levels, with levels <2000 ng/L predicting survival without liver transplantation (p<0.01).

CONCLUSIONS

GDF15 and FGF21 are significantly higher in children with MH compared to other childhood liver diseases and controls and, when combined, were predictive of MH and had prognostic implications.

Fibroblast Growth Factor 21: A Fascinating Perspective on the Regulation of Muscle Metabolism

Fibroblast growth factor 21 (FGF21) plays a vital role in normal eukaryotic organism development and homeostatic metabolism under the influence of internal and external factors such as endogenous hormone changes and exogenous stimuli. Over the last few decades, comprehensive studies have revealed the key role of FGF21 in regulating many fundamental metabolic pathways, including the muscle stress response, insulin signaling transmission, and muscle development. By coordinating these metabolic pathways, FGF21 is thought to contribute to acclimating to a stressful environment and the subsequent recovery of cell and tissue homeostasis. With the emphasis on FGF21, we extensively reviewed the research findings on the production and regulation of FGF21 and its role in muscle metabolism. We also emphasize how the FGF21 metabolic networks mediate mitochondrial dysfunction, glycogen consumption, and myogenic development and investigate prospective directions for the functional exploitation of FGF21 and its downstream effectors, such as the mammalian target of rapamycin (mTOR).

Red Flags in Primary Mitochondrial Diseases: What Should We Recognize?

Primary mitochondrial diseases (PMDs) are complex group of metabolic disorders caused by genetically determined impairment of the mitochondrial oxidative phosphorylation (OXPHOS). The unique features of mitochondrial genetics and the pivotal role of mitochondria in cell biology explain the phenotypical heterogeneity of primary mitochondrial diseases and the resulting diagnostic challenges that follow. Some peculiar features ("red flags") may indicate a primary mitochondrial disease, helping the physician to orient in this diagnostic maze. In this narrative review, we aimed to outline the features of the most common mitochondrial red flags offering a general overview on the topic that could help physicians to untangle mitochondrial medicine complexity.

Interactions of mitochondrial and skeletal muscle biology in mitochondrial myopathy

Mitochondrial dysfunction in skeletal muscle fibres occurs with both healthy aging and a range of neuromuscular diseases. The impact of mitochondrial dysfunction in skeletal muscle and the way muscle fibres adapt to this dysfunction is important to understand disease mechanisms and to develop therapeutic interventions. Furthermore, interactions between mitochondrial dysfunction and skeletal muscle biology, in mitochondrial myopathy, likely have important implications for normal muscle function and physiology. In this review, we will try to give an overview of what is known to date about these interactions including metabolic remodelling, mitochondrial morphology, mitochondrial turnover, cellular processes and muscle cell structure and function. Each of these topics is at a different stage of understanding, with some being well researched and understood, and others in their infancy. Furthermore, some of what we know comes from disease models. Whilst some findings are confirmed in humans, where this is not yet the case, we must be cautious in interpreting findings in the context of human muscle and disease. Here, our goal is to discuss what is known, highlight what is unknown and give a perspective on the future direction of research in this area.

Mitohormesis

Perturbation of mitochondrial function can trigger a host of cellular responses that seek to restore cellular metabolism, cytosolic proteostasis, and redox homeostasis. In some cases, these responses persist even after the stress is relieved, leaving the cell or tissue in a less vulnerable state. This process-termed mitohormesis-is increasingly viewed as an important aspect of normal physiology and a critical modulator of various disease processes. Here, we review aspects of mitochondrial stress signaling that, among other things, can rewire the cell's metabolism, activate the integrated stress response, and alter cytosolic quality-control pathways. We also discuss how these pathways are implicated in various disease states from pathogen challenge to chemotherapeutic resistance and how their therapeutic manipulation can lead to new strategies for a host of chronic conditions including aging itself.

Temporal dynamics of muscle mitochondrial uncoupling-induced integrated stress response and ferroptosis defense

Mitochondria play multifaceted roles in cellular function, and impairments across domains of mitochondrial biology are known to promote cellular integrated stress response (ISR) pathways as well as systemic metabolic adaptations. However, the temporal dynamics of specific mitochondrial ISR related to physiological variations in tissue-specific energy demands remains unknown. Here, we conducted a comprehensive 24-hour muscle and plasma profiling of male and female mice with ectopic mitochondrial respiratory uncoupling in skeletal muscle (mUcp1-transgenic, TG). TG mice are characterized by increased muscle ISR, elevated oxidative stress defense, and increased secretion of FGF21 and GDF15 as ISR-induced myokines. We observed a temporal signature of both cell-autonomous and systemic ISR in the context of endocrine myokine signaling and cellular redox balance, but not of ferroptotic signature which was also increased in TG muscle. We show a progressive increase of muscle ISR on transcriptional level during the active phase (night time), with a subsequent peak in circulating FGF21 and GDF15 in the early resting phase. Moreover, we found highest levels of muscle oxidative defense (GPX and NQO1 activity) between the late active to early resting phase, which could aim to counteract excessive iron-dependent lipid peroxidation and ferroptosis in muscle of TG mice. These findings highlight the temporal dynamics of cell-autonomous and endocrine ISR signaling under skeletal muscle mitochondrial uncoupling, emphasizing the importance of considering such dissociation in translational strategies and sample collection for diagnostic biomarker analysis.

Effectors Enabling Adaptation to Mitochondrial Complex I Loss in Hürthle Cell Carcinoma

Oncocytic (Hürthle cell) carcinoma of the thyroid (HCC) is genetically characterized by complex I mitochondrial DNA mutations and widespread chromosomal losses. Here, we utilize RNA sequencing and metabolomics to identify candidate molecular effectors activated by these genetic drivers. We find glutathione biosynthesis, amino acid metabolism, mitochondrial unfolded protein response, and lipid peroxide scavenging to be increased in HCC. A CRISPR-Cas9 knockout screen in a new HCC model reveals which pathways are key for fitness, and highlights loss of GPX4, a defense against lipid peroxides and ferroptosis, as a strong liability. Rescuing complex I redox activity with the yeast NADH dehydrogenase (NDI1) in HCC cells diminishes ferroptosis sensitivity, while inhibiting complex I in normal thyroid cells augments ferroptosis induction. Our work demonstrates unmitigated lipid peroxide stress to be an HCC vulnerability that is mechanistically coupled to the genetic loss of mitochondrial complex I activity.

SIGNIFICANCE

HCC harbors abundant mitochondria, mitochondrial DNA mutations, and chromosomal losses. Using a CRISPR-Cas9 screen inspired by transcriptomic and metabolomic profiling, we identify molecular effectors essential for cell fitness. We uncover lipid peroxide stress as a vulnerability coupled to mitochondrial complex I loss in HCC. See related article by Frank et al., p. 1884. This article is highlighted in the In This Issue feature, p. 1749.

Exerkines and redox homeostasis

Exercise physiology has gained increasing interest due to its wide effects to promote health. Recent years have seen a growth in this research field also due to the finding of several circulating factors that mediate the effects of exercise. These factors, termed exerkines, are metabolites, growth factors, and cytokines secreted by main metabolic organs during exercise to regulate exercise systemic and tissue-specific effects. The metabolic effects of exerkines have been broadly explored and entail a promising target to modulate beneficial effects of exercise in health and disease. However, exerkines also have broad effects to modulate redox signaling and homeostasis in several cellular processes to improve stress response. Since redox biology is central to exercise physiology, this review summarizes current evidence for the cross-talk between redox biology and exerkines actions. The role of exerkines in redox biology entails a response to oxidative stress-induced pathological cues to improve health outcomes and to modulate exercise adaptations that integrate redox signaling.

Biomarkers to predict disease progression and therapeutic response in isolated methylmalonic acidemia

Methylmalonic Acidemia (MMA) is a heterogenous group of inborn errors of metabolism caused by a defect in the methylmalonyl-CoA mutase (MMUT) enzyme or the synthesis and transport of its cofactor, 5'-deoxy-adenosylcobalamin. It is characterized by life-threatening episodes of ketoacidosis, chronic kidney disease, and other multiorgan complications. Liver transplantation can improve patient stability and survival and thus provides clinical and biochemical benchmarks for the development of hepatocyte-targeted genomic therapies. Data are presented from a US natural history protocol that evaluated subjects with different types of MMA including mut-type (N = 91), cblB-type (15), and cblA-type MMA (17), as well as from an Italian cohort of mut-type (N = 19) and cblB-type MMA (N = 2) subjects, including data before and after organ transplantation in both cohorts. Canonical metabolic markers, such as serum methylmalonic acid and propionylcarnitine, are variable and affected by dietary intake and renal function. We have therefore explored the use of the 1-13 C-propionate oxidation breath test (POBT) to measure metabolic capacity and the changes in circulating proteins to assess mitochondrial dysfunction (fibroblast growth factor 21 [FGF21] and growth differentiation factor 15 [GDF15]) and kidney injury (lipocalin-2 [LCN2]). Biomarker concentrations are higher in patients with the severe mut0 -type and cblB-type MMA, correlate with a decreased POBT, and show a significant response postliver transplant. Additional circulating and imaging markers to assess disease burden are necessary to monitor disease progression. A combination of biomarkers reflecting disease severity and multisystem involvement will be needed to help stratify patients for clinical trials and assess the efficacy of new therapies for MMA.

Exploring the correlation between serum fibroblast growth factor-21 levels and Sarcopenia: a systematic review and meta-analysis

BACKGROUND

Fibroblast growth factor 21 (FGF-21) plays an important role in the growth and metabolism of skeletal muscle cells. This study aims to systemically review the evidence regarding the relationship between FGF-21 levels and Sarcopenia, as well as the related influential factors.

METHODS

This review was conducted according to the PRISMA guidelines. We comprehensively searched PubMed, EMBASE, the Web of Science, Scopus, and Chinese Databases (CNKI, Wan Fang, VIP, and CBM) up to 1 May 2023. 3 investigators performed independent literature screening and data extraction of the included literature, and two investigators performed an independent quality assessment of case-control studies using the Joanna Briggs Institute (JBI) tool. Data analysis was performed using Review Manager 5.4 software. For continuous various outcomes, mean difference (MD) or standard mean difference (SMD) with 95% confidence intervals (CIs) was applied for assessment by fixed-effect or random-effect model analysis. The heterogeneity test was performed by the Q-statistic and quantified using I², and publication bias was evaluated using a funnel plot.

RESULTS

Five studies with a total of 625 cases were included in the review. Meta-analysis showed lower BMI in the sarcopenia group [MD= -2.88 (95% CI, -3. 49, -2.27); P < 0.00001; I² = 0%], significantly reduced grip strength in the sarcopenia group compared to the non-sarcopenia group [MD = -7.32(95% CI, -10.42,-4.23); P < 0.00001; I² = 93%]. No statistically significant differences in serum FGF21 levels were found when comparing the two groups of subjects [SMD = 0.31(95% CI, -0.42, 1.04); P = 0.41; I² = 94%], and no strong correlation was found between the onset of sarcopenia and serum FGF21 levels.

CONCLUSION

The diagnosis of sarcopenia is followed by a more significant decrease in muscle mass and strength, but there is a lack of strong evidence to support a direct relationship between elevated organismal FGF21 and sarcopenia, and it is not convincing to use FGF21 as a biological or diagnostic marker for sarcopenia. The currently used diagnostic criteria for sarcopenia and setting of cut-off values for each evaluation parameter no longer seem to match clinical practice.

Clinical spectrum and genetic causes of mitochondrial hepatopathy phenotype in children

BACKGROUND

Alterations in both mitochondrial DNA (mtDNA) and nuclear DNA genes affect mitochondria function, causing a range of liver-based conditions termed mitochondrial hepatopathies (MH), which are subcategorized as mtDNA depletion, RNA translation, mtDNA deletion, and enzymatic disorders. We aim to enhance the understanding of pathogenesis and natural history of MH.

METHODS

We analyzed data from patients with MH phenotypes to identify genetic causes, characterize the spectrum of clinical presentation, and determine outcomes.

RESULTS

Three enrollment phenotypes, that is, acute liver failure (ALF, n = 37), chronic liver disease (Chronic, n = 40), and post-liver transplant (n = 9), were analyzed. Patients with ALF were younger [median 0.8 y (range, 0.0, 9.4) vs 3.4 y (0.2, 18.6), p < 0.001] with fewer neurodevelopmental delays (40.0% vs 81.3%, p < 0.001) versus Chronic. Comprehensive testing was performed more often in Chronic than ALF (90.0% vs 43.2%); however, etiology was identified more often in ALF (81.3% vs 61.1%) with mtDNA depletion being most common (ALF: 77% vs Chronic: 41%). Of the sequenced cohort (n = 60), 63% had an identified mitochondrial disorder. Cluster analysis identified a subset without an underlying genetic etiology, despite comprehensive testing. Liver transplant-free survival was 40% at 2 years (ALF vs Chronic, 16% vs 65%, p < 0.001). Eighteen (21%) underwent transplantation. With 33 patient-years of follow-up after the transplant, 3 deaths were reported.

CONCLUSIONS

Differences between ALF and Chronic MH phenotypes included age at diagnosis, systemic involvement, transplant-free survival, and genetic etiology, underscoring the need for ultra-rapid sequencing in the appropriate clinical setting. Cluster analysis revealed a group meeting enrollment criteria but without an identified genetic or enzymatic diagnosis, highlighting the need to identify other etiologies.

Interplay of skeletal muscle and adipose tissue: sarcopenic obesity

Sarcopenic obesity is becoming a global health concern, owing to the rising older population, causing cardiometabolic morbidity and mortality. Loss of muscle exceeding normal age-related changes has been revealed to be associated with obesity, aggravating each other through complex interactions. Physiological regeneration and proliferation of muscle tissue are achieved through harmonious processes of regulated inflammation, autophagy, muscle satellite cell proliferation, and signaling molecule function. Adipokines and myokines are signaling molecules from adipose tissue and muscle, respectively, that exert autocrine, paracrine, and endocrine effects on fat and muscle tissues. These signaling molecules interact with each other to regulate metabolic homeostasis. However, excessive adiposity creates pro-inflammatory conditions, leading to metabolic disorders and the disorganization of systemic homeostasis. Therefore, obesity impedes muscle tissue regeneration and induces the loss of muscle mass and function. Numerous studies have attempted to demonstrate the pathophysiological interaction between sarcopenia and obesity, but the interwoven matrix of the relationship between myokines and adipokines has made it difficult for researchers to understand them. This review briefly describes updated information about the crosstalk between muscle and adipose tissue.

Methodologies in Mitochondrial Testing: Diagnosing a Primary Mitochondrial Respiratory Chain Disorder

BACKGROUND

Mitochondria are cytosolic organelles within most eukaryotic cells. Mitochondria generate the majority of cellular energy in the form of adenosine triphosphate (ATP) through oxidative phosphorylation (OxPhos). Pathogenic variants in mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) lead to defects in OxPhos and physiological malfunctions (Nat Rev Dis Primer 2016;2:16080.). Patients with primary mitochondrial disorders (PMD) experience heterogeneous symptoms, typically in multiple organ systems, depending on the tissues affected by mitochondrial dysfunction. Because of this heterogeneity, clinical diagnosis is challenging (Annu Rev Genomics Hum Genet 2017;18:257-75.). Laboratory diagnosis of mitochondrial disease depends on a multipronged analysis that can include biochemical, histopathologic, and genetic testing. Each of these modalities has complementary strengths and limitations in diagnostic utility.

CONTENT

The primary focus of this review is on diagnosis and testing strategies for primary mitochondrial diseases. We review tissue samples utilized for testing, metabolic signatures, histologic findings, and molecular testing approaches. We conclude with future perspectives on mitochondrial testing.

SUMMARY

This review offers an overview of the current biochemical, histologic, and genetic approaches available for mitochondrial testing. For each we review their diagnostic utility including complementary strengths and weaknesses. We identify gaps in current testing and possible future avenues for test development.

Non-pharmacological management options for MAFLD: a practical guide

Lifestyle changes should be the main basis for any treatment for metabolic dysfunction-associated fatty liver disease (MAFLD), aiming to increase energy expenditure, reduce energy intake and improve the quality of nutrients consumed. As it is a multifactorial disease, approaches such as physical exercise, a better dietary pattern, and possible pharmacological intervention are shown to be more efficient when used simultaneously to the detriment of their applications. The main treatment for MAFLD is a lifestyle change consisting of diet, activity, exercise, and weight loss. The variables for training prescription such as type of physical exercise (aerobic or strength training), the weekly frequency, and the intensity most indicated for the treatment of MAFLD remain uncertain, that is, the recommendations must be adapted to the clinical conditions comorbidities, and preferences of each subject in a way individual. This review addresses recent management options for MAFLD including diet, nutrients, gut microbiota, and physical exercise.

Luteolin Protects Against Obese Sarcopenia in Mice with High-Fat Diet-Induced Obesity by Ameliorating Inflammation and Protein Degradation in Muscles

SCOPE

Although sarcopenia is mainly caused by aging, sarcopenia due to obesity has become an emerging issue given the increase in obesity among people of various ages. There are studies on obesity or sarcopenia, our understanding of obesity-mediated sarcopenia is insufficient. Luteolin (LU) has exhibited antiobesity effects, but no studies have investigated the LU effects on antisarcopenia. This study therefore investigated the effects of LU on obese sarcopenia in mice with high-fat diet (HFD)-induced obesity.

METHODS AND RESULTS

To evaluate its inhibitory efficacy against obese sarcopenia, 5-week-old mice are fed an HFD supplemented with LU for 20 weeks. LU exerts suppressive effects on obesity, inflammation, and protein degradation in the HFD-fed obese mice. It also inhibits lipid infiltration into the muscle and decreases p38 activity and the mRNA expression of inflammatory factors, including TNF-α, Tlr2, Tlr4, MCP1, and MMP2, in the muscle. The suppression of muscle inflammation by LU leads to the inhibition of myostatin, FoxO, atrogin, and MuRF expression. These effects of LU affect inhibition of protein degradation and improvement of muscle function.

CONCLUSION

Here, it demonstrates that LU's antiobesity and antiinflammatory functionality affect inhibition of muscle protein degradation, and consequently, these interactions by LU exerts a protective effect against obese sarcopenia.

Blood biomarkers of mitochondrial disease-One for all or all for one?

The mitochondrial disease group consists of different disorders with unprecedented variability of clinical manifestations and tissue-specific symptoms. Their tissue-specific stress responses vary depending on the patients' age and type of dysfunction. These responses include secretion of metabolically active signal molecules to systemic circulation. Such signals-metabolites or metabokines-can be also utilized as biomarkers. During the past 10 years, metabolite and metabokine biomarkers have been described for mitochondrial disease diagnosis and follow-up, to complement the conventional blood biomarkers lactate, pyruvate and alanine. These new tools include metabokines FGF21 and GDF15; cofactors (NAD-forms); sets of metabolites (multibiomarkers) and the full metabolome. FGF21 and GDF15 are messengers of mitochondrial integrated stress response that together outperform the conventional biomarkers in specificity and sensitivity for muscle-manifesting mitochondrial diseases. Metabolite or metabolomic imbalance (e.g., NAD+ deficiency) is a secondary consequence to the primary cause in some diseases, but relevant as a biomarker and a potential indicator of therapy targets. For therapy trials, the optimal biomarker set needs to be tailored to match the disease of interest. The new biomarkers have increased the value of blood samples in mitochondrial disease diagnosis and follow-up, enabling prioritization of patients to different diagnostic paths and having crucial roles in follow-up of therapy effect.

Currently available therapies in mitochondrial disease

Mitochondrial diseases are a heterogeneous group of multisystem disorders caused by impaired mitochondrial function. These disorders occur at any age and involve any tissue, typically affecting organs highly dependent on aerobic metabolism. Diagnosis and management are extremely difficult due to various underlying genetic defects and a wide range of clinical symptoms. Preventive care and active surveillance are strategies to try to reduce morbidity and mortality by timely treatment of organ-specific complications. More specific interventional therapies are in early phases of development and no effective treatment or cure currently exists. A variety of dietary supplements have been utilized based on biological logic. For several reasons, few randomized controlled trials have been completed to assess the efficacy of these supplements. The majority of the literature on supplement efficacy represents case reports, retrospective analyses and open-label studies. We briefly review selected supplements that have some degree of clinical research support. In mitochondrial diseases, potential triggers of metabolic decompensation or medications that are potentially toxic to mitochondrial function should be avoided. We shortly summarize current recommendations on safe medication in mitochondrial diseases. Finally, we focus on the frequent and debilitating symptoms of exercise intolerance and fatigue and their management including physical training strategies.

Genetics of mitochondrial diseases: Current approaches for the molecular diagnosis

Mitochondrial diseases are a genetically and phenotypically variable set of monogenic disorders. The main characteristic of mitochondrial diseases is a defective oxidative phosphorylation. Both nuclear and mitochondrial DNA encode the approximately 1500 mitochondrial proteins. Since identification of the first mitochondrial disease gene in 1988 a total of 425 genes have been associated with mitochondrial diseases. Mitochondrial dysfunctions can be caused both by pathogenic variants in the mitochondrial DNA or the nuclear DNA. Hence, besides maternal inheritance, mitochondrial diseases can follow all modes of Mendelian inheritance. The maternal inheritance and tissue specificity distinguish molecular diagnostics of mitochondrial disorders from other rare disorders. With the advances made in the next-generation sequencing technology, whole exome sequencing and even whole-genome sequencing are now the established methods of choice for molecular diagnostics of mitochondrial diseases. They reach a diagnostic rate of more than 50% in clinically suspected mitochondrial disease patients. Moreover, next-generation sequencing is delivering a constantly growing number of novel mitochondrial disease genes. This chapter reviews mitochondrial and nuclear causes of mitochondrial diseases, molecular diagnostic methodologies, and their current challenges and perspectives.

Predictors of weight loss in patients with obesity treated with a Very Low-Calorie Ketogenic Diet

Introduction

The Very Low-Calorie Ketogenic Diet (VLCKD) has emerged as a safe and effective intervention for the management of metabolic disease. Studies examining weight loss predictors are scarce and none has investigated such factors upon VLCKD treatment. Among the molecules involved in energy homeostasis and, more specifically, in metabolic changes induced by ketogenic diets, Fibroblast Growth Factor 21 (FGF21) is a hepatokine with physiology that is still unclear.

Methods

We evaluated the impact of a VLCKD on weight loss and metabolic parameters and assessed weight loss predictors, including FGF21. VLCKD is a severely restricted diet (<800 Kcal/die), characterized by a very low carbohydrate intake (<50 g/day), 1.2-1.5 g protein/kg of ideal body weight and 15-30 g of fat/day. We treated 34 patients with obesity with a VLCKD for 45 days. Anthropometric parameters, body composition, and blood and urine chemistry were measured before and after treatment.

Results

We found a significant improvement in body weight and composition and most metabolic parameters. Circulating FGF21 decreased significantly after the VLCKD [194.0 (137.6-284.6) to 167.8 (90.9-281.5) p < 0.001] and greater weight loss was predicted by lower baseline FGF21 (Beta = -0.410; p = 0.012), male sex (Beta = 0.472; p = 0.011), and central obesity (Beta = 0.481; p = 0.005).

Discussion

VLCKD is a safe and effective treatment for obesity and obesity related metabolic derangements. Men with central obesity and lower circulating FGF21 may benefit more than others in terms of weight loss obtained following this diet. Further studies investigating whether this is specific to this diet or to any caloric restriction are warranted.

OxPhos defects cause hypermetabolism and reduce lifespan in cells and in patients with mitochondrial diseases

Patients with primary mitochondrial oxidative phosphorylation (OxPhos) defects present with fatigue and multi-system disorders, are often lean, and die prematurely, but the mechanistic basis for this clinical picture remains unclear. By integrating data from 17 cohorts of patients with mitochondrial diseases (n = 690) we find evidence that these disorders increase resting energy expenditure, a state termed hypermetabolism. We examine this phenomenon longitudinally in patient-derived fibroblasts from multiple donors. Genetically or pharmacologically disrupting OxPhos approximately doubles cellular energy expenditure. This cell-autonomous state of hypermetabolism occurs despite near-normal OxPhos coupling efficiency, excluding uncoupling as a general mechanism. Instead, hypermetabolism is associated with mitochondrial DNA instability, activation of the integrated stress response (ISR), and increased extracellular secretion of age-related cytokines and metabokines including GDF15. In parallel, OxPhos defects accelerate telomere erosion and epigenetic aging per cell division, consistent with evidence that excess energy expenditure accelerates biological aging. To explore potential mechanisms for these effects, we generate a longitudinal RNASeq and DNA methylation resource dataset, which reveals conserved, energetically demanding, genome-wide recalibrations. Taken together, these findings highlight the need to understand how OxPhos defects influence the energetic cost of living, and the link between hypermetabolism and aging in cells and patients with mitochondrial diseases.

Mitochondrial dysfunction reactivates α-fetoprotein expression that drives copper-dependent immunosuppression in mitochondrial disease models

Signaling circuits crucial to systemic physiology are widespread, yet uncovering their molecular underpinnings remains a barrier to understanding the etiology of many metabolic disorders. Here, we identified a copper-linked signaling circuit activated by disruption of mitochondrial function in the murine liver or heart that resulted in atrophy of the spleen and thymus and caused a peripheral white blood cell deficiency. We demonstrated that the leukopenia was caused by α-fetoprotein, which required copper and the cell surface receptor CCR5 to promote white blood cell death. We further showed that α-fetoprotein expression was upregulated in several cell types upon inhibition of oxidative phosphorylation. Collectively, our data argue that α-fetoprotein may be secreted by bioenergetically stressed tissue to suppress the immune system, an effect that may explain the recurrent or chronic infections that are observed in a subset of mitochondrial diseases or in other disorders with secondary mitochondrial dysfunction.

Clinical Reasoning: A Teenage Girl With Progressive Hyperkinetic Movements, Seizures, and Encephalopathy

The "epilepsy-dyskinesia" spectrum is increasingly recognized in neurogenetic and neurometabolic conditions. It can be challenging to diagnose because of clinical and genetic heterogeneity, atypical or nonspecific presentations, and the rarity of each diagnostic entity. This is further complicated by the lack of sensitive or specific biomarkers for most nonenzymatic neurometabolic conditions. Nevertheless, clinical awareness and timely diagnosis are paramount to facilitate appropriate prognostication, counseling, and management.This report describes a case of a teenage girl who had presented at 14 months with a protracted illness manifesting as gastrointestinal upset and associated motor and cognitive regression. A choreoathetoid movement disorder, truncal ataxia, and microcephaly evolved after the acute phase. Neurometabolic and inflammatory investigations, EEG, brain MRI, muscle biopsy (including respiratory chain enzyme studies), and targeted genetic testing were unremarkable. A second distinct regression phase ensued at 14 years consisting of encephalopathy, multifocal motor seizures, absent deep tendon reflexes and worsening movements, gut dysmotility, and dysphagia. Video EEGs showed an evolving developmental and epileptic encephalopathy with multifocal seizures and nonepileptic movements. MRI of the brain revealed evolving and fluctuating patchy bihemispheric cortical changes, cerebellar atrophy with signal change, mild generalized brain volume loss, and abnormal lactate on MR spectroscopy. The article discusses the differential diagnostic approach and management options for patients presenting with neurologic regression, encephalopathy, seizures, and hyperkinetic movements. It also emphasizes the utility of next-generation sequencing in providing a rapid, efficient, cost-effective way of determining the underlying etiology of complex neurologic presentations.

Fibroblast growth factor 21 is expressed and secreted from skeletal muscle following electrical stimulation via extracellular ATP activation of the PI3K/Akt/mTOR signaling pathway

Fibroblast growth factor 21 (FGF21) is a hormone involved in the regulation of lipid, glucose, and energy metabolism. Although it is released mainly from the liver, in recent years it has been shown that it is a "myokine", synthesized in skeletal muscles after exercise and stress conditions through an Akt-dependent pathway and secreted for mediating autocrine and endocrine roles. To date, the molecular mechanism for the pathophysiological regulation of FGF21 production in skeletal muscle is not totally understood. We have previously demonstrated that muscle membrane depolarization controls gene expression through extracellular ATP (eATP) signaling, by a mechanism defined as "Excitation-Transcription coupling". eATP signaling regulates the expression and secretion of interleukin 6, a well-defined myokine, and activates the Akt/mTOR signaling pathway. This work aimed to study the effect of electrical stimulation in the regulation of both production and secretion of skeletal muscle FGF21, through eATP signaling and PI3K/Akt pathway. Our results show that electrical stimulation increases both mRNA and protein (intracellular and secreted) levels of FGF21, dependent on an extracellular ATP signaling mechanism in skeletal muscle. Using pharmacological inhibitors, we demonstrated that FGF21 production and secretion from muscle requires the activation of the P2YR/PI3K/Akt/mTOR signaling pathway. These results confirm skeletal muscle as a source of FGF21 in physiological conditions and unveil a new molecular mechanism for regulating FGF21 production in this tissue. Our results will allow to identify new molecular targets to understand the regulation of FGF21 both in physiological and pathological conditions, such as exercise, aging, insulin resistance, and Duchenne muscular dystrophy, all characterized by an alteration in both FGF21 levels and ATP signaling components. These data reinforce that eATP signaling is a relevant mechanism for myokine expression in skeletal muscle.

Prevalence of Sarcopenic Obesity in Various Comorbidities, Diagnostic Markers, and Therapeutic Approaches: A Review

The coexistence of sarcopenia and obesity characterizes sarcopenic obesity. In this condition, there is an imbalance between lean and fat mass amounts. It is a prevalent issue that is gaining prevalence among the elderly population. To evaluate the condition, allied health professionals may employ non-invasive diagnostic techniques, such as gait speed, skeletal muscle mass, and muscle strength. Nevertheless, early diagnosis and treatment of pathology are essential for preventing debilitating effects and providing the highest quality of care. This article reviews the prevalence of sarcopenic obesity in numerous medical conditions, such as cancer, arthritis, postoperative cases, diabetes mellitus, obesity, and metabolic syndrome. In addition, this paper aims to examine the available evidence regarding the prevalence of sarcopenic obesity in other conditions along with their diagnostic markers and therapeutic approaches.

Gene therapy for primary mitochondrial diseases: experimental advances and clinical challenges

The variable clinical and biochemical manifestations of primary mitochondrial diseases (PMDs), and the complexity of mitochondrial genetics, have proven to be a substantial barrier to the development of effective disease-modifying therapies. Encouraging data from gene therapy trials in patients with Leber hereditary optic neuropathy and advances in DNA editing techniques have raised expectations that successful clinical transition of genetic therapies for PMDs is feasible. However, obstacles to the clinical application of genetic therapies in PMDs remain; the development of innovative, safe and effective genome editing technologies and vectors will be crucial to their future success and clinical approval. In this Perspective, we review progress towards the genetic treatment of nuclear and mitochondrial DNA-related PMDs. We discuss advances in mitochondrial DNA editing technologies alongside the unique challenges to targeting mitochondrial genomes. Last, we consider ongoing trials and regulatory requirements.

Mitochondrial signal transduction

The analogy of mitochondria as powerhouses has expired. Mitochondria are living, dynamic, maternally inherited, energy-transforming, biosynthetic, and signaling organelles that actively transduce biological information. We argue that mitochondria are the processor of the cell, and together with the nucleus and other organelles they constitute the mitochondrial information processing system (MIPS). In a three-step process, mitochondria (1) sense and respond to both endogenous and environmental inputs through morphological and functional remodeling; (2) integrate information through dynamic, network-based physical interactions and diffusion mechanisms; and (3) produce output signals that tune the functions of other organelles and systemically regulate physiology. This input-to-output transformation allows mitochondria to transduce metabolic, biochemical, neuroendocrine, and other local or systemic signals that enhance organismal adaptation. An explicit focus on mitochondrial signal transduction emphasizes the role of communication in mitochondrial biology. This framework also opens new avenues to understand how mitochondria mediate inter-organ processes underlying human health.

Hepatic FGF21: Its Emerging Role in Inter-Organ Crosstalk and Cancers

Fibroblast growth factor (FGF) 21 is one of the FGF members with special endocrine properties. In the last twenty years, it has attracted intense research and development for its physiological functions that respond to dietary manipulation, pharmacological benefits of improving the macronutrient metabolism, and clinical values as a biomarker of various human diseases. Generally, FGF21 can be produced by major metabolic organs, but only the subgroup from the liver shows canonical endocrine properties, which emphasizes the special value of delineating the unique secretory and functional characteristics of hepatic FGF21. There has been a growth in literature to address the extra-hepatic activities of FGF21, and many striking findings have therefore been published. Yet, they are fragmented and scattered, and controversies are raised from divergent findings. For this reason, there is a need for a systematic and critical evaluation of current research in this aspect. In this review, we focus on the current knowledge about the molecular biology of endocrine FGF21, especially present details on the regulation of circulating levels of FGF21. We also emphasize its emerging roles in inter-organ crosstalk and cancer development.

Nicotinamide riboside kinase 1 protects against diet and age-induced pancreatic β-cell failure

OBJECTIVE

Disturbances in NAD⁺ metabolism have been described as a hallmark for multiple metabolic and age-related diseases, including type 2 diabetes. While alterations in pancreatic β-cell function are critical determinants of whole-body glucose homeostasis, the role of NAD⁺ metabolism in the endocrine pancreas remains poorly explored. Here, we aimed to evaluate the role of nicotinamide riboside (NR) metabolism in maintaining NAD⁺ levels and pancreatic β-cell function in pathophysiological conditions.

METHODS

Whole body and pancreatic β-cell-specific NRK1 knockout (KO) mice were metabolically phenotyped in situations of high-fat feeding and aging. We also analyzed pancreatic β-cell function, β-cell mass and gene expression.

RESULTS

We first demonstrate that NRK1, the essential enzyme for the utilization of NR, is abundantly expressed in pancreatic β-cells. While NR treatment did not alter glucose-stimulated insulin secretion in pancreatic islets from young healthy mice, NRK1 knockout mice displayed glucose intolerance and compromised β-cells response to a glucose challenge upon high-fat feeding or aging. Interestingly, β cell dysfunction stemmed from the functional failure of other organs, such as liver and kidney, and the associated changes in circulating peptides and hormones, as mice lacking NRK1 exclusively in β-cells did not show altered glucose homeostasis.

CONCLUSIONS

This work unveils a new physiological role for NR metabolism in the maintenance of glucose tolerance and pancreatic β-cell function in high-fat feeding or aging conditions.

Mitochondrial Hepatopathy

Mitochondrial hepatopathies are a subset of mitochondrial diseases defined by primary dysfunction of hepatocyte mitochondria leading to a phenotype of hepatocyte cell injury, steatosis, or liver failure. Increasingly, the diagnosis is established by new sequencing approaches that combine analysis of both nuclear DNA and mitochondrial DNA and allow for timely diagnosis in most patients. Despite advances in diagnostics, for most affected children their disorders are relentlessly progressive, and result in substantial morbidity and mortality. Treatment remains mainly supportive; however, novel therapeutics and a more definitive role for liver transplantation hold promise for affected children.

The Biochemical Assessment of Mitochondrial Respiratory Chain Disorders

Mitochondrial respiratory chain (MRC) disorders are a complex group of diseases whose diagnosis requires a multidisciplinary approach in which the biochemical investigations play an important role. Initial investigations include metabolite analysis in both blood and urine and the measurement of lactate, pyruvate and amino acid levels, as well as urine organic acids. Recently, hormone-like cytokines, such as fibroblast growth factor-21 (FGF-21), have also been used as a means of assessing evidence of MRC dysfunction, although work is still required to confirm their diagnostic utility and reliability. The assessment of evidence of oxidative stress may also be an important parameter to consider in the diagnosis of MRC function in view of its association with mitochondrial dysfunction. At present, due to the lack of reliable biomarkers available for assessing evidence of MRC dysfunction, the spectrophotometric determination of MRC enzyme activities in skeletal muscle or tissue from the disease-presenting organ is considered the ‘Gold Standard’ biochemical method to provide evidence of MRC dysfunction. The purpose of this review is to outline a number of biochemical methods that may provide diagnostic evidence of MRC dysfunction in patients.

Research priorities for mitochondrial disorders: Current landscape and patient and professional views

Primary mitochondrial disorders encompass a wide range of clinical presentations and a spectrum of severity. They currently lack effective disease-modifying therapies and have a high mortality and morbidity rate. It is therefore essential to know that competitively funded research designed by academics meets the core needs of people with mitochondrial disorders and their clinicians. Priority setting partnerships are an established collaborative methodology that brings patients, carers and families, charity representatives and clinicians together to try to establish the most pressing and unanswered research priorities for a particular disease. We developed a web-based questionnaire, requesting all patients affected by primary mitochondrial disease, their carers and clinicians to pose their research questions. This yielded 709 questions from 147 participants. These were grouped into overarching themes including basic biology, causation, health services, clinical management, social impacts, prognosis, prevention, symptoms, treatment and psychological impact. Following the removal of "answered questions", the process resulted in a list of 42 discrete, answerable questions. This was further refined by web-based ranking by the community to 24 questions. These were debated at a face-to-face workshop attended by a diverse range of patients, carers, charity representatives and clinicians to create a definitive "Top 10 of unanswered research questions for primary mitochondrial disorders". These Top 10 questions related to understanding biological processes, including triggers of disease onset, mechanisms underlying progression and reasons for differential symptoms between individuals with identical genetic mutations; new treatments; biomarker discovery; psychological support and optimal management of stroke-like episodes and fatigue.

Leukocyte cytokine responses in adult patients with mitochondrial DNA defects

Patients with oxidative phosphorylation (OxPhos) defects causing mitochondrial diseases appear particularly vulnerable to infections. Although OxPhos defects modulate cytokine production in vitro and in animal models, little is known about how circulating leukocytes of patients with inherited mitochondrial DNA (mtDNA) defects respond to acute immune challenges. In a small cohort of healthy controls (n = 21) and patients (n = 12) with either the m.3243A > G mutation or single, large-scale mtDNA deletions, we examined (i) cytokine responses (IL-6, TNF-α, IL-1β) in response to acute lipopolysaccharide (LPS) exposure and (ii) sensitivity to the immunosuppressive effects of glucocorticoid signaling (dexamethasone) on cytokine production. In dose-response experiments to determine the half-maximal effective LPS concentration (EC₅₀), relative to controls, leukocytes from patients with mtDNA deletions showed 74-79% lower responses for IL-6 and IL-1β (p_IL-6 = 0.031, p_IL-1β = 0.009). Moreover, whole blood from patients with mtDNA deletions (p_IL-6 = 0.006), but not patients with the m.3243A > G mutation, showed greater sensitivity to the immunosuppressive effects of dexamethasone. Together, these ex vivo data provide preliminary evidence that some systemic OxPhos defects may compromise immune cytokine responses and increase the sensitivity to immune cytokine suppression by glucocorticoids. Further work in larger cohorts is needed to define the nature of immune dysregulation in patients with mitochondrial disease, and their potential implications for disease phenotypes. KEY MESSAGES: Little is known about leukocyte cytokine responses in patients with mitochondrial diseases. Leukocytes of patients with mtDNA deletions show blunted LPS sensitivity and cytokine responses. Leukocytes of patients with mtDNA deletions are more sensitive to glucocorticoid-mediated IL-6 suppression. Work in larger cohorts is needed to delineate potential immune alterations in mitochondrial diseases.