Mitochondrial regulation during male germ cell development.

Mitochondria tailor their morphology to execute their specialized functions in different cell types and/or different environments. During spermatogenesis, mitochondria undergo continuous morphological and distributional changes with germ cell development. Deficiencies in these processes lead to mitochondrial dysfunction and abnormal spermatogenesis, thereby causing male infertility. In recent years, mitochondria have attracted considerable attention because of their unique role in the regulation of piRNA biogenesis in male germ cells. In this review, we describe the varied characters of mitochondria and focus on key mitochondrial factors that play pivotal roles in the regulation of spermatogenesis, from primordial germ cells to spermatozoa, especially concerning metabolic shift, stemness and reprogramming, mitochondrial transformation and rearrangement, and mitochondrial defects in human sperm. Further, we discuss the molecular mechanisms underlying these processes.

Mice harboring the FXN I151F pathological point mutation present decreased frataxin levels, a Friedreich ataxia-like phenotype, and mitochondrial alterations.

Friedreich Ataxia (FA) is a rare neuro-cardiodegenerative disease caused by mutations in the frataxin (FXN) gene. The most prevalent mutation is a GAA expansion in the first intron of the gene causing decreased frataxin expression. Some patients present the GAA expansion in one allele and a missense mutation in the other allele. One of these mutations, FXNI154F, was reported to result in decreased content of mature frataxin and increased presence of an insoluble intermediate proteoform in cellular models. By introducing this mutation into the murine Fxn gene (I151F, equivalent to human I154F) we have now analyzed the consequences of this pathological point mutation in vivo. We have observed that FXNI151F homozygous mice present low frataxin levels in all tissues, with no evidence of insoluble proteoforms. Moreover, they display neurological deficits resembling those observed in FA patients. Biochemical analysis of heart, cerebrum and cerebellum have revealed decreased content of components from OXPHOS complexes I and II, decreased aconitase activity, and alterations in antioxidant defenses. These mitochondrial alterations are more marked in the nervous system than in heart, precede the appearance of neurological symptoms, and are similar to those observed in other FA models. We conclude that the primary pathological mechanism underlying the I151F mutation is frataxin deficiency, like in patients carrying GAA expansions. Therefore, patients carrying the I154F mutation would benefit from frataxin replacement therapies. Furthermore, our results also show that the FXNI151F mouse is an excellent tool for analyzing tissue-specific consequences of frataxin deficiency and for testing new therapies.

Role of IL-33 receptor (ST2) deletion in diaphragm contractile and mitochondrial function in the Sugen5416/hypoxia model of pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature that leads to right ventricular failure. Skeletal muscle maladaptations limit physical activity and may contribute to disease progression. The role of alarmin/inflammatory signaling in PAH respiratory muscle dysfunction is unknown. We hypothesized that diaphragm mitochondrial and contractile functions are impaired in SU5416/hypoxia-induced pulmonary hypertension due to increased systemic IL-33 signaling. We induced pulmonary hypertension in adult C57Bl/6 J (WT) and ST2 (IL1RL1) gene ablated mice by SU5416/hypoxia (SuHx). We measured diaphragm fiber mitochondrial respiration, inflammatory markers, and contractile function ex vivo. SuHx reduced coupled and uncoupled permeabilized myofiber respiration by ∼40 %. During coupled respiration with complex I substrates, ST2-/- attenuated SuHx inhibition of mitochondrial respiration (genotype × treatment interaction F[1,67] = 3.3, p = 0.07, η2 = 0.04). Flux control ratio and coupling efficiency were not affected by SuHx or genotype. A higher substrate control ratio for succinate was observed in SuHx fibers and attenuated in ST2-/- fibers (F[1,67] = 5.3, p < 0.05, η2 = 0.07). Diaphragm TNFα, but not IL-33 or NFkB, was increased in SuHx vs. DMSO in both genotypes (F[1,43] = 4.7, p < 0.05, η2 = 0.1). Diaphragm force-frequency relationships were right-shifted in SuHx vs. WT (F[3,440] = 8.4, p < 0.05, η2 = 0.0025). There was no effect of ST2-/- on the force-frequency relationship. Force decay during a fatigue protocol at 100 Hz, but not at 40 Hz, was attenuated by SuHx vs. DMSO in both genotypes (F[1,41] = 5.6, p < 0.05, η2 = 0.11). SuHx mice exhibit a modest compensation in diaphragm contractility and mitochondrial dysfunction during coupled respiration; the latter partially regulated through ST2 signaling.

Association Between Hyperlactatemia, Perfusional Parameters, and Lymphocyte Mitochondrial Dysfunction in Septic Shock Patients.

INTRODUCTION: In septic shock, mitochondrial dysfunction, and hypoperfusion are the main triggers of multi-organ failure. Little is known about the crosstalk between mitochondrial dysfunction and hemodynamic alterations, especially in the post-resuscitation phase. Here, we assess whether hypoperfusion and lactate levels are associated with oxygen consumption linked to mitochondrial bioenergetic activity in lymphocytes of patients admitted with septic shock. PATIENTS AND METHODS: Prospective cohort study in patients with septic shock defined as the requirement of vasopressors to maintain a mean arterial pressure 65 mm Hg after initial fluid administration. Basal mitochondrial and Complex I respiration was measured to evaluate mitochondrial activity. Both variables and capillary refill time were compared with arterial lactate post-fluid resuscitation. We also compared mitochondrial activity measurements between patients with and without hypoperfusion status. RESULTS: A total of 90 patients were included in analysis. The median arterial lactate at the time of septic shock diagnosis was 2.0 mmol/Dl (IQR 1.3-3.0). Baseline respiration at the time of septic shock diagnosis was correlated with lactate (Spearman -0.388, 95% CI -0.4893 to -0.1021; P = 0.003), as well as Complex I respiration (Spearman -0.403, 95% CI -0.567 to -0.208; P < 0.001). Patients with hypoperfusion status had no difference in basal respiration when compared with patients who did not have hypoperfusion status (P = 0.22) nor in Complex I respiration (P = 0.09). CONCLUSION: Changes in lymphocytic mitochondrial metabolism are associated with post-resuscitation arterial lactate in septic shock; however, they are not associated with the presence of a hypoperfusional status. In this scenario, it is therefore suggested that systemic perfusion and mitochondrial metabolism have different courses.

Mitochondrial dysfunction governs immunometabolism in leukocytes of patients with acute-on-chronic liver failure.

BACKGROUND & AIMS: Patients with acute-on-chronic liver failure (ACLF) present a systemic hyperinflammatory response associated with increased circulating levels of small-molecule metabolites. To investigate whether these alterations reflect inadequate cell energy output, we assessed mitochondrial morphology and central metabolic pathways with emphasis on the tricarboxylic acid (TCA) cycle in peripheral leukocytes from patients with acutely decompensated (AD) cirrhosis, with and without ACLF. METHODS: The study included samples from patients with AD cirrhosis (108 without and 128 with ACLF) and 41 healthy individuals. Leukocyte mitochondrial ultrastructure was visualized by transmission electron microscopy and cytosolic and mitochondrial metabolic fluxes were determined by assessing NADH/FADH2 production from various substrates. Plasma GDF15 and FGF21 were determined by Luminex and acylcarnitines by LC-MS/MS. Gene expression was analyzed by RNA-sequencing and PCR-based glucose metabolism profiler array. RESULTS: Mitochondrial ultrastructure in patients with advanced cirrhosis was distinguished by cristae rarefication and swelling. The number of mitochondria per leukocyte was higher in patients, accompanied by a reduction in their size. Increased FGF21 and C6:0- and C8:0-carnitine predicted mortality whereas GDF15 strongly correlated with a gene set signature related to leukocyte activation. Metabolic flux analyses revealed increased energy production in mononuclear leukocytes from patients with preferential involvement of extra-mitochondrial pathways, supported by upregulated expression of genes encoding enzymes of the glycolytic and pentose phosphate pathways. In patients with ACLF, mitochondrial function analysis uncovered break-points in the TCA cycle at the isocitrate dehydrogenase and succinate dehydrogenase level, which were bridged by anaplerotic reactions involving glutaminolysis and nucleoside metabolism. CONCLUSIONS: Our findings provide evidence at the cellular, organelle and biochemical levels that severe mitochondrial dysfunction governs immunometabolism in leukocytes from patients with AD cirrhosis and ACLF. LAY SUMMARY: Patients at advanced stages of liver disease have dismal prognosis due to vital organ failures and the lack of treatment options. In this study, we report that the functioning of mitochondria, which are known as the cell powerhouse, is severely impaired in leukocytes of these patients, probably as a consequence of intense inflammation. Mitochondrial dysfunction is therefore a hallmark of advanced liver disease.

Mitochondrial Oxidative Stress-A Causative Factor and Therapeutic Target in Many Diseases.

The excessive formation of reactive oxygen species (ROS) and impairment of defensive antioxidant systems leads to a condition known as oxidative stress. The main source of free radicals responsible for oxidative stress is mitochondrial respiration. The deleterious effects of ROS on cellular biomolecules, including DNA, is a well-known phenomenon that can disrupt mitochondrial function and contribute to cellular damage and death, and the subsequent development of various disease processes. In this review, we summarize the most important findings that implicated mitochondrial oxidative stress in a wide variety of pathologies from Alzheimer disease (AD) to autoimmune type 1 diabetes. This review also discusses attempts to affect oxidative stress as a therapeutic avenue.

Baicalein resensitizes tamoxifen-resistant breast cancer cells by reducing aerobic glycolysis and reversing mitochondrial dysfunction via inhibition of hypoxia-inducible factor-1α.

Drug resistance is a major hurdle for the effectiveness of tamoxifen (TAM) to provide clinical benefit. Therefore, it is essential to identify a sensitizer that could be used to improve TAM efficacy in treating TAM-resistant breast cancer. Here, we investigated the ability of baicalein to reverse TAM resistance. We found that baicalein increased the efficacy of TAM in inhibiting proliferation and inducing apoptosis of TAM-resistant cells. It also enhanced the TAM-induced growth reduction of resistant cells from NOD/SCID mouse mammary fat pads, without causing obvious systemic toxicity. Analyses using the CellMiner tool and the Kaplan-Meier plotter database showed that HIF-1α expression was inversely correlated with TAM therapeutic response in NCI-60 cancer cells and breast cancer patients. HIF-1α expression was increased in TAM-resistant cells due to an increase in mRNA levels and reduced ubiquitin-mediated degradation. Baicalein reduced HIF-1α expression by promoting its interaction with PHD2 and pVHL, thus facilitating ubiquitin ligase-mediated proteasomal degradation and thereby suppressing the nuclear translocation, binding to the hypoxia-response element, and transcriptional activity of HIF-1α. As a result, baicalein downregulated aerobic glycolysis by restricting glucose uptake, lactate production, ATP generation, lactate/pyruvate ratio and expression of HIF-1α-targeted glycolytic genes, thereby enhancing the antiproliferative efficacy of TAM. Furthermore, baicalein interfered with HIF-1α inhibition of mitochondrial biosynthesis, which increased mitochondrial DNA content and mitochondrial numbers, restored the generation of reactive oxygen species in mitochondria, and thus enhanced the TAM-induced mitochondrial apoptotic pathway. The HIF-1α stabilizer dimethyloxallyl glycine prevented the baicalein-induced downregulation of glycolysis and mitochondrial biosynthesis and reduced the effects of baicalein on reversing TAM resistance. Our results indicate that baicalein is a promising candidate to help overcome TAM resistance by sensitizing resistant cells to TAM-induced growth inhibition and apoptosis. The mechanism underlying the effects of baicalein consists of inhibition of HIF-1α-mediated aerobic glycolysis and mitochondrial dysfunction.

Novel understanding on genetic mechanisms of enteric neuropathies leading to severe gut dysmotility.

The enteric nervous system (ENS) is the third division of the autonomic autonomic nervous system and the largest collection of neurons outside the central nervous system (CNS). The ENS has been referred to as "the brain in the gut" or "the second brain of the human body" because of its highly integrated neural circuits controlling a vast repertoire of gut functions, including absorption/secretion, splanchnic blood vessels, some immunological aspects, intestinal epithelial barrier, and gastrointestinal (GI) motility. The latter function is the result of the ENS fine-tuning over smooth musculature, along with the contribution of other key cells, such as enteric glia (astrocyte like cells supporting and contributing to neuronal activity), interstitial cells of Cajal (the pacemaker cells of the GI tract involved in neuromuscular transmission), and enteroendocrine cells (releasing bioactive substances, which affect gut physiology). Any noxa insult perturbing the ENS complexity may determine a neuropathy with variable degree of neuro-muscular dysfunction. In this review, we aim to cover the most recent update on genetic mechanisms leading to enteric neuropathies ranging from Hirschsprung's disease (characterized by lack of any enteric neurons in the gut wall) up to more generalized form of dysmotility such as chronic intestinal pseudo-obstruction (CIPO) with a significant reduction of enteric neurons. In this line, we will discuss the role of the RAD21 mutation, which we have demonstrated in a family whose affected members exhibited severe gut dysmotility. Other genes contributing to gut motility abnormalities will also be presented. In conclusion, the knowledge on the molecular mechanisms involved in enteric neuropathy may unveil strategies to better manage patients with neurogenic gut dysmotility and pave the way to targeted therapies.

Expanding the phenotypic spectrum of BCS1L-related mitochondrial disease.

OBJECTIVE: To delineate the full phenotypic spectrum of BCS1L-related disease, provide better understanding of the genotype-phenotype correlations and identify reliable prognostic disease markers. METHODS: We performed a retrospective multinational cohort study of previously unpublished patients followed in 15 centres from 10 countries. Patients with confirmed biallelic pathogenic BCS1L variants were considered eligible. Clinical, laboratory, neuroimaging and genetic data were analysed. Patients were stratified into different groups based on the age of disease onset, whether homozygous or compound heterozygous for the c.232A>G (p.Ser78Gly) variant, and those with other pathogenic BCS1L variants. RESULTS: Thirty-three patients were included. We found that growth failure, lactic acidosis, tubulopathy, hepatopathy and early death were more frequent in those with disease onset within the first month of life. In those with onset after 1 month, neurological features including movement disorders and seizures were more frequent. Novel phenotypes, particularly involving movement disorder, were identified in this group. The presence of the c.232A>G (p.Ser78Gly) variant was associated with significantly worse survival and exclusively found in those with disease onset within the first month of life, whilst other pathogenic BCS1L variants were more frequent in those with later symptom onset. INTERPRETATION: The phenotypic spectrum of BCS1L-related disease comprises a continuum of clinical features rather than a set of separate syndromic clinical identities. Age of onset defines BCS1L-related disease clinically and early presentation is associated with poor prognosis. Genotype correlates with phenotype in the presence of the c.232A>G (p.Ser78Gly) variant.

Coenzyme Q10 a mitochondrial restorer for various brain disorders.

Coenzyme Q10 (ubiquinone or CoQ10) is a lipid molecule that acts as an electron mobile carrier of the electron transport chain and also contains antioxidant properties. Supplementation of CoQ10 has been very useful to treat mitochondrial diseases. CoQ10 along with its synthetic analogue, idebenone, is used largely to treat various neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic lateral sclerosis, and Friedreich's ataxia and additional brain disease condition like autism, multiple sclerosis, epilepsy, depression, and bipolar disorder, which are related to mitochondrial impairment. In this article, we have reviewed numerous physiological functions of CoQ10 and the rationale for its use in clinical practice in different brain disorders.

Variants in the MIPEP gene presenting with complex neurological phenotype without cardiomyopathy, impair OXPHOS protein maturation and lead to a reduced OXPHOS abundance in patient cells.

Most mitochondrial proteins are synthesized in the cytosol and targeted to mitochondria via N-terminal mitochondrial targeting signals (MTS) that are proteolytically removed upon import. Sometimes, MTS removal is followed by a cleavage of an octapeptide by the mitochondrial intermediate peptidase (MIP), encoded by the MIPEP gene. Previously, MIPEP variants were linked to four cases of multisystemic disorder presenting with cardiomyopathy, developmental delay, hypotonia and infantile lethality. We report here a patient carrying compound heterozygous MIPEP variants-one was not previously linked to mitochondrial disease-who did not have cardiomyopathy and who is alive at the age of 20 years. This patient had developmental delay, global hypotonia, mild optic neuropathy and mild ataxia. Functional characterization of patient fibroblasts and HEK293FT cells carrying MIPEP hypomorphic alleles demonstrated that deficient MIP activity was linked to impaired post-import processing of subunits from four of the five OXPHOS complexes and decreased abundance and activity of some of these complexes in human cells possibly underlying the development of mitochondrial disease. Thus, our work expands the genetic and clinical spectrum of MIPEP-linked disease and establishes MIP as an important regulator of OXPHOS biogenesis and function in human cells.

Hypotonia-cystinuria 2p21 deletion syndrome: Intrafamilial variability of clinical expression.

Two siblings presented similarly with congenital hypotonia, lactic acidosis, and failure to thrive. Later in childhood, the brother developed cystinuria and nephrolithiasis whereas the older sister suffered from cystinuria and chronic neurobehavioral disturbances. Biopsied muscle studies demonstrated deficient cytochrome c oxidase activities consistent with a mitochondrial disease. Whole exome sequencing (WES), however, revealed a homozygous 2p21 deletion involving two contiquous genes, SLC3A1 (deletion of exons 2-10) and PREPL (deletion of exons 2-14). The molecular findings were consistent with the hypotonia-cystinuria 2p21 deletion syndrome, presenting similarly in infancy with mitochondrial dysfunction but diverging later in childhood and displaying intrafamilial phenotypic variability.

Development and characterization of a mouse model for Acad9 deficiency.

Acyl CoA Dehydrogenase 9 (ACAD9) is a member of the family of flavoenzymes that catalyze the dehydrogenation of acyl-CoAs to 2,3 enoyl-CoAs in mitochondrial fatty acid oxidation (FAO). Inborn errors of metabolism of all family members, including ACAD9, have been described in humans, and represent significant causes of morbidity and mortality particularly in children. ACAD9 deficiency leads to a combined defect in fatty acid oxidation and oxidative phosphorylation (OXPHOS) due to a dual role in the pathways. In addition to its function in mitochondrial FAO, ACAD9 has a second function as one of 14 factors responsible for assembly of complex I of the electron transport chain (ETC). Considerable controversy remains over the relative role of these two functions in normal physiology and the disparate clinical findings described in patients with ACAD9 deficiency. To better understand the normal function of ACAD9 and the pathophysiology of its deficiency, several knock out mouse models were developed. Homozygous total body knock out appeared to be lethal as no ACAD9 animals were obtained. Cre-lox technology was then used to generate tissue-specific deletion of the gene. Cardiac-specific ACAD9 deficient animals had severe neonatal cardiomyopathy and died by 17 days of age. They had severe mitochondrial dysfunction in vitro. Muscle-specific mutants were viable but exhibited muscle weakness. Additional studies of heart muscle from the cardiac specific deficient animals were used to examine the evolutionarily conserved signaling Intermediate in toll pathway (ECSIT) protein, a known binding partner of ACAD9 in the electron chain complex I assembly pathway. As expected, ECSIT levels were significantly reduced in the absence of ACAD9 protein, consistent with the demonstrated impairment of the complex I assembly. The various ACAD9 deficient animals should serve as useful models for development of novel therapeutics for this disorder.

Identification and characterization of novel compound variants in SLC25A26 associated with combined oxidative phosphorylation deficiency 28.

BACKGROUND: Combined oxidative phosphorylation deficiency 28 (COXPD28) is associated with mitochondrial dysfunction caused by mutations in SLC25A26, the gene which encodes the mitochondrial S-adenosylmethionine carrier (SAMC) that responsible for the transport of S-adenosylmethionine (SAM) into the mitochondria. OBJECTIVE: To identify and characterize pathogenic variants of SLC25A26 in a Chinese pedigree, provide a basis for clinical diagnosis and genetic counseling. METHODS: We conducted a systematic analysis of the clinical characteristics of a female with COXPD28. Whole-exome and mitochondrial genome sequencing was applied for the genetic analysis, together with bioinformatic analysis of predicted consequences of the identified variant. A homotrimer model was built to visualize the affected region and predict possible outcomes of this mutation. Then a literature review was performed by online searching all cases reported with COXPD28. RESULTS: The novel compound heterozygous SLC25A26 variants (c.34G > C, p.A12P; c.197C > A; p.A66E) were identified in a Chinese patient with COXPD28. These two variants are located in the transmembrane region 1 and transmembrane region 2, respectively. As a member of the mitochondrial carrier family, the transmembrane region of SAMC is highly conserved. The variants were predicted to be pathogenic by in silico analysis and lead to a change in the protein structure of SAMC. And the change of the SAMC structure may lead to insufficient methylation and cause disease by affecting the SAM transport. CONCLUSIONS: The variants in this region probably resulted in a variable loss of mitochondrial SAMC transport function and cause the COXPD28. This study that further refine genotype-phenotype associations can provide disease prognosis with a basis and families with reproductive planning options.

Allele-specific mitochondrial stress induced by Multiple Mitochondrial Dysfunctions Syndrome 1 pathogenic mutations modeled in Caenorhabditis elegans.

Multiple Mitochondrial Dysfunctions Syndrome 1 (MMDS1) is a rare, autosomal recessive disorder caused by mutations in the NFU1 gene. NFU1 is responsible for delivery of iron-sulfur clusters (ISCs) to recipient proteins which require these metallic cofactors for their function. Pathogenic variants of NFU1 lead to dysfunction of its target proteins within mitochondria. To date, 20 NFU1 variants have been reported and the unique contributions of each variant to MMDS1 pathogenesis is unknown. Given that over half of MMDS1 individuals are compound heterozygous for different NFU1 variants, it is valuable to investigate individual variants in an isogenic background. In order to understand the shared and unique phenotypes of NFU1 variants, we used CRISPR/Cas9 gene editing to recreate exact patient variants of NFU1 in the orthologous gene, nfu-1 (formerly lpd-8), in C. elegans. Five mutant C. elegans alleles focused on the presumptive iron-sulfur cluster interaction domain were generated and analyzed for mitochondrial phenotypes including respiratory dysfunction and oxidative stress. Phenotypes were variable between the mutant nfu-1 alleles and generally presented as an allelic series indicating that not all variants have lost complete function. Furthermore, reactive iron within mitochondria was evident in some, but not all, nfu-1 mutants indicating that iron dyshomeostasis may contribute to disease pathogenesis in some MMDS1 individuals.

Mitochondrial disease in adults: recent advances and future promise.

Mitochondrial diseases are some of the most common inherited neurometabolic disorders, and major progress has been made in our understanding, diagnosis, and treatment of these conditions in the past 5 years. Development of national mitochondrial disease cohorts and international collaborations has changed our knowledge of the spectrum of clinical phenotypes and natural history of mitochondrial diseases. Advances in high-throughput sequencing technologies have altered the diagnostic algorithm for mitochondrial diseases by increasingly using a genetics-first approach, with more than 350 disease-causing genes identified to date. While the current management strategy for mitochondrial disease focuses on surveillance for multisystem involvement and effective symptomatic treatment, new endeavours are underway to find better treatments, including repurposing current drugs, use of novel small molecules, and gene therapies. Developments made in reproductive technology offer women the opportunity to prevent transmission of DNA-related mitochondrial disease to their children.

Mitochondrial function in development and disease.

Mitochondria are organelles with vital functions in almost all eukaryotic cells. Often described as the cellular 'powerhouses' due to their essential role in aerobic oxidative phosphorylation, mitochondria perform many other essential functions beyond energy production. As signaling organelles, mitochondria communicate with the nucleus and other organelles to help maintain cellular homeostasis, allow cellular adaptation to diverse stresses, and help steer cell fate decisions during development. Mitochondria have taken center stage in the research of normal and pathological processes, including normal tissue homeostasis and metabolism, neurodegeneration, immunity and infectious diseases. The central role that mitochondria assume within cells is evidenced by the broad impact of mitochondrial diseases, caused by defects in either mitochondrial or nuclear genes encoding for mitochondrial proteins, on different organ systems. In this Review, we will provide the reader with a foundation of the mitochondrial 'hardware', the mitochondrion itself, with its specific dynamics, quality control mechanisms and cross-organelle communication, including its roles as a driver of an innate immune response, all with a focus on development, disease and aging. We will further discuss how mitochondrial DNA is inherited, how its mutation affects cell and organismal fitness, and current therapeutic approaches for mitochondrial diseases in both model organisms and humans.