Fontaine progeroid syndrome with neonatal mitochondrial disease

In Reply to “The Spectrum of Renal Abnormalities in Mitochondrial Disorders Is Broad”

Mitochondrial diseases are among the most common metabolic disorders caused by mitochondrial dysfunction. Analyzing mitochondrial respiratory chain enzyme activity is essential for diagnosis. However, clinical laboratories often rely on mitochondria isolated from muscle biopsies or cultured skin fibroblasts, which may be unacceptable for some pediatric patients. This highlights the need for improved blood-based diagnostic methods. This paper describes spectrophotometric assays to evaluate mitochondrial respiratory chain enzyme activity in peripheral blood monocytes. Sample preparation methods and assays for respiratory complexes I-IV and the mitochondrial matrix enzyme citrate synthase are detailed. The assays were validated via samples from a panel of 28 healthy children and validated in patients with combined and isolated mitochondrial oxidative phosphorylation system (OXPHOS) deficiency. The citrate synthase-normalized activities were 0.23 ± 0.08 for complex I, 0.22 ± 0.081 for complex II, 0.16 ± 0.07 for complex III, and 0.22 ± 0.07 for complex IV. All patients with mitochondrial disease exhibited the expected reductions in respiratory complex activity. We established a method to analyze the respiratory complex activities via blood samples. The normal enzymatic activity ranges were established from healthy Chinese pediatric populations. We also validated the assay via samples from patients with mitochondrial disease. By establishing the first pediatric-specific reference ranges for mitochondrial respiratory chain complex activities in a Chinese population and validating this minimally invasive blood-based assay in patients with mitochondrial disease, our study enabled earlier detection, precise monitoring, and personalized management of mitochondrial disorders while avoiding the need for invasive tissue biopsies.

Pathogenic mitochondrial DNA heteroplasmy has mainly been assessed with bulk sequencing in individuals with mitochondrial disease. However, the distribution of heteroplasmy at the single-cell level in skin fibroblasts obtained from individuals, together with detailed clinical and biochemical information, remains to be investigated. We used the mitochondrial DNA single-cell assay for the transposase-accessible chromatin sequencing method. Skin fibroblasts were obtained from six individuals with mitochondrial disease and pathogenic m.3243A>G variants of differing severity. Different distributions of heteroplasmy at the single-cell level were identified in skin fibroblasts from all six individuals. Four individuals with different outcomes showed similar averaged heteroplasmy rates with normal mitochondrial respiratory chain enzyme activity, while the distribution of single-cell heteroplasmy patterns differed among the individuals. This study showed different heteroplasmy distribution patterns at the single-cell level in individuals with the m.3243A>G variant, who had a similar averaged heteroplasmy rates with normal mitochondrial respiratory chain enzyme activity. Whether such different heteroplasmy distribution patterns explain the different clinical outcomes should be assessed further in future studies. Measuring heteroplasmy of pathogenic mitochondrial DNA variants at the single-cell level could be important in individuals with mitochondrial disease.

Combined oxidative phosphorylation (OXPHOS) deficiency 44 (COXPD44; MIM# 618855) is caused by biallelic pathogenic variants in FAS-activated serine-threonine kinase domain 2 (FASTKD2) (MIM# 612322). COXPD44 is characterized by variable clinical features-developmental delay, chronic epileptic encephalopathy, seizure disorder/status epilepticus and cerebellar ataxia. We ascertained one sibwith episodic acute encephalomyopathy triggered by acute gastroenteritis and associated with haematological abnormalities, rhabdomyolysis leading to acute kidney injury, hypotensive shock leading to early death and a similarly affected sib with early death. Both siblings were normal neurologically in between the acute episodes. Whole exome sequencing (WES) was performed in the elder sibling. Mitochondrial respiratory chain enzyme activity assaywas performed in fibroblast cells and muscle tissue of the elder sibling. Also, Adenosine triphosphate (ATP) determination assay was done in fibroblast cells of the elder sibling. WES revealed compound heterozygous missense likely pathogenic variants in FASTKD2. Mitochondrial respiratory chain enzyme activity in muscle tissue showed reduced complex IV activity and ATP determination assay showed a reduction of ATP in skin fibroblasts. Herein, we report two siblings with novel clinical phenotype associated with COXPD44. Our report further validates the biallelic variants in FASTKD2 associated with the variable phenotypes and mitochondrial OXPHOS defect.

Objective To investigate the clinical features of the non-syndromic mitochondrial disease in children which were identified by mitochondrial respiratory chain enzyme complex activity assay. Methods From March 2010 to April 2011, seven children who were diagnosed as non-syndromic mitochondrial disease were included into this study. The enzyme activity of respiratory chain enzyme complexes (Ⅰ-Ⅳ) and ATP synthase (complex Ⅴ) in peripheral blood leukocytes of 7 children were determined. All the children whose routine screening of mitochondrial genes were negative. Children's clinical data were retrospectively analyzed. Results ①There were intelligence backwards after infection in 5 cases, combined seizures in 4 cases, paralysis in 6 cases; deafness, ataxia in 2 cases, combining anterior pituitary hypofunction/episodes of hypoglycemia in 1 case; myodynamia and hypomyotonia in 7 cases. The findings of brain MRI were abnormal in 6 cases, the findings of electroencephalogram (EEG) were abnormal in 5 cases and abnormal findings of electromyography (EMG) in 3 cases. Blood lactate increased slightly in 3 cases, the level of myocardial enzyme were abnormal in 2 cases. ②Conventional mitochondrial genes screening was negative. ③ 4 childen had isolated complex defects: complex Ⅱ deficiency (2 cases), complex deficiency of Ⅰ or Ⅳ (1 case, respectively); 3 cases were found to have combined deficiencies: 2 cases had combined deficiencies of complex Ⅰ and Ⅲ, 1 case had combined deficiencies of complex Ⅱ and V. Conclusions Mitochondrial respiratory chain enzyme deficiency in children may present non-specific neurological symptoms, the clinical features were extensive involvement of multi-system, and regular screening of mitochondrial gene was negative, the mitochondrial respiratory chain enzyme activity assay of peripheral leukocyte may help to identify the non-syndromic mitochondrial disease. Key words: mitochondrial respiratory chain enzyme deficiency; respiratory chain enzyme complex activity; child

De novo frameshift variant in MT-ND1 causes a mitochondrial complex I deficiency associated with MELAS syndrome

Linezolid is an oxazolidinone antibiotic that is increasingly used to treat drug-resistant, gram-positive pathogens. The mechanism of action is inhibition of bacterial protein synthesis. Optic and/or peripheral neuropathy and lactic acidosis are reported side effects, but the underlying pathophysiological mechanism has not been unravelled. We studied mitochondrial ultrastructure, mitochondrial respiratory chain enzyme activity, and mitochondrial DNA (mtDNA) in muscle, liver, and kidney samples obtained from a patient who developed optic neuropathy, encephalopathy, skeletal myopathy, lactic acidosis, and renal failure after prolonged use of linezolid. In addition, we evaluated mtDNA, respiratory chain enzyme activity, and protein amount in muscle and liver samples obtained from experimental animals that received linezolid or placebo. In the patient, mitochondrial respiratory chain enzyme activity was decreased in affected tissues, without ultrastructural mitochondrial abnormalities and without mutations or depletion of mtDNA. In the experimental animals, linezolid induced a dose- and time-dependent decrease of the activity of respiratory chain complexes containing mtDNA-encoded subunits and a decreased amount of protein of these complexes, whereas the amount of mtDNA was normal. These results provide direct evidence that linezolid inhibits mitochondrial protein synthesis with potentially severe clinical consequences. Prolonged courses of linezolid should be avoided if alternative treatment options are available.

Association of mitochondrial function with feed efficiency in rainbow trout: Diets and family effects

To study the mitochondrial respiratory chain enzyme activities in patients with idiopathic dilated cardiomyopathy (IDC). Mitochondrial respiratory chain enzyme activities were assessed spectrophotometrically in left ventricular tissue of 17 patients with IDC undergoing cardiac transplantation, as well as in two groups of controls: a group of six patients suffering from ischemic dilated cardiomyopathy (IC) also undergoing cardiac transplantation, and a group of 17 organ donors considered normal from a cardiac point of view. Cytochrome b gene from three IDC patients whose complex III activity was particularly low and from three controls was also sequenced. We found that complex III enzymatic activity was lower not only in IDC but also in IC patients when compared with normal controls. When analysing cytochrome b gene we only found neutral polymorphisms previously described. In view of such results, we believe that the decrease of respiratory chain complex III activity found in some cases of IDC is a secondary phenomenon, and not due to a primary mitochondrial disease.

Genetic variation in feed consumption, growth, nutrient utilization efficiency and mitochondrial function within a farmed population of channel catfish (Ictalurus punctatus)

17β-estradiol rescues the damage of thiazolidinedione on chicken Sertoli cell proliferation via adiponectin

We reported previously that complete spinal cord transection (SCT) results in depression of mitochondrial respiratory chain enzyme activity that triggers apoptosis via sequential activations of apoptosis-inducing factor (AIF)- and caspase-dependent cascades in the injured spinal cord. This study tested the hypothesis that nitric oxide (NO) and superoxide anion (O(2)(.-)) serve as the interposing signals between SCT and impaired mitochondrial respiratory functions. Adult Sprague-Dawley rats manifested a significant increase in NO or O(2)(.-) level in the injured spinal cord during the first 3 days after SCT. The augmented O(2)(.-) production, along with concomitant reduction in mitochondrial respiratory chain enzyme activity or ATP level, nuclear translocation of AIF, cytosolic release of cytochrome c, and DNA fragmentation were reversed by osmotic minipump infusion of a NO trapping agent, carboxy-PTIO, or a superoxide dismutase mimetic, tempol, into the epicenter of the transected spinal cord. Intriguingly, carboxy-PTIO significantly suppressed upregulation of poly(ADP-ribose) polymerase-1 (PARP-1) in the nucleus, attenuated nuclear translocation of AIF, inhibited mitochondrial translocation of Bax and antagonized mitochondrial release of cytochrome c; whereas tempol only inhibited the later two cellular events after SCT. We conclude that overproduction of NO and O(2)(.-) in the injured spinal cord promulgates mitochondrial dysfunction and triggers AIF- and caspase-dependent apoptotic signaling cascades via differential upregulation of nuclear PARP-1 and mitochondrial translocation of Bax.

Laboratory data interpretation for the assessment of complex biological systems remains a great challenge, as occurs in mitochondrial function research studies. The classical biochemical data interpretation of patients versus reference values may be insufficient, and in fact the current classifications of mitochondrial patients are still done on basis of probability criteria. We have developed and applied a mathematic agglomerative algorithm to search for correlations among the different biochemical variables of the mitochondrial respiratory chain in order to identify populations displaying correlation coefficients >0.95. We demonstrated that coenzyme Q10 may be a better biomarker of mitochondrial respiratory chain enzyme activities than the citrate synthase activity. Furthermore, the application of this algorithm may be useful to re-classify mitochondrial patients or to explore associations among other biochemical variables from different biological systems.

Prolonged fluoride exposure induces spatial-memory deficit and hippocampal dysfunction by inhibiting small heat shock protein 22 in mice

Correlation Between Mitochondrial DNA 4977-bp Deletion and Respiratory Chain Enzyme Activities in Aging Human Skeletal Muscles