In situ autolysis of mouse brain: ultrastructure of mitochondria and the function of oxidative phosphorylation and mitochondrial DNA

Unique prenatal manifestations of biallelic NDUFAF5 variants: expansion of phenotype

OBJECTIVE

Mitochondrial complex-I deficiency, nuclear type 16, is a rare autosomal recessive disorder caused by biallelic pathogenic variants in NDUFAF5 (C20orf7) (OMIM 618238). The aim of this study was to describe a severe early prenatal manifestation of this disorder, which was previously considered to occur only postnatally.

METHODS

This was a multicenter retrospective case series including five fetuses from three non-related families, which shared common sonographic abnormalities, including brain cysts, corpus callosal malformations, non-immune hydrops fetalis and growth restriction. Genetic evaluation included chromosomal microarray analysis and exome sequencing. Two fetuses from the same family were also available for pathology examination, including electron microscopy.

RESULTS

Chromosomal microarray analysis revealed no chromosomal abnormality in any of the tested cases. Trio exome sequencing demonstrated that three affected fetuses from three unrelated families were compound heterozygous or homozygous for likely pathogenic variants in NDUFAF5. No other causative variants were detected. The association between NDUFAF5 variants and fetal malformations was further confirmed by segregation analysis. Histological evaluation of fetal tissues and electron microscopy of the skeletal muscle, liver, proximal tubules and heart demonstrated changes that resembled postmortem findings in patients with mitochondrial depletion disorders as well as previously undescribed findings.

CONCLUSIONS

Mitochondrial complex-I deficiency and specifically biallelic mutations in NDUFAF5 have a role in abnormal fetal development, presenting with severe congenital malformations. Mitochondrial complex-I disorders should be considered in the differential diagnosis of corpus callosal malformations and brain cysts, especially when associated with extracranial abnormalities, such as fetal growth restriction and non-immune hydrops fetalis. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Alveolar Mitochondrial Quality Control During Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a leading cause of respiratory failure and death in patients in the intensive care unit. Experimentally, acute lung injury resolution depends on the repair of mitochondrial oxidant damage by the mitochondrial quality control (MQC) pathways, mitochondrial biogenesis, and mitophagy, but nothing is known about this in the human lung. In a case-control autopsy study, we compared the lungs of subjects dying of ARDS (n = 8; cases) and age-/gender-matched subjects dying of nonpulmonary causes (n = 7; controls). Slides were examined by light microscopy and immunofluorescence confocal microscopy, randomly probing for co-localization of citrate synthase with markers of oxidant stress, mitochondrial DNA damage, mitophagy, and mitochondrial biogenesis. ARDS lungs showed diffuse alveolar damage with edema, hyaline membranes, and neutrophils. Compared with controls, a high degree of mitochondrial oxidant damage was seen in type 2 epithelial (AT2) cells and alveolar macrophages by 8-hydroxydeoxyguanosine and malondialdehyde co-staining with citrate synthase. In ARDS, antioxidant protein heme oxygenase-1 and DNA repair enzyme N-glycosylase/DNA lyase (Ogg1) were found in alveolar macrophages but not in AT2 cells. Moreover, MAP1 light chain-3 (LC3) and serine/threonine-protein kinase (Pink1) staining were absent in AT2 cells, suggesting a mitophagy failure. Nuclear respiratory factor-1 staining was missing in the alveolar region, suggesting impaired mitochondrial biogenesis. Widespread hyperproliferation of AT2 cells in ARDS could suggest defective differentiation into type 1 cells. ARDS lungs show profuse mitochondrial oxidant DNA damage but little evidence of MQC activity in AT2 epithelium. Because these pathways are important for acute lung injury resolution, our findings support MQC as a novel pharmacologic target for ARDS resolution.

Liver Pathology in Mitochondrial Complex I Deficiency from Bi-Allelic Mutations in NDUFS2: A Report of Findings at Autopsy

Background: Mitochondriopathies are a heterogeneous group of genetic disorders with a wide array of symptomatology, organ system involvement, and inheritance patterns. Neonatal presentation can be fatal with neuromuscular dysfunction, lactic acidosis and hepatic failure. Historic literature has numerous phenotypic illustrations; however, genotypic correlation is limited. With improved testing methods, genotype-phenotype correlation is now increasingly feasible as demonstrated herein. Case Report: We present liver pathology findings in an infant who expired with a diagnostic suspicion of a mitochondrial disorder. Postmortem hepatocyte hypereosinophilia with microvesicular steatosis associated with ultrastructural findings of mitochondrial hyperplasia supported a mitochondriopathy. Genetic testing eventually confirmed mitochondrial complex I deficiency from bi-allelic mutations in NDUFS2. Conclusions: Morphologic attributes can assist in diagnosis of mitochondriopathies before specific genetic testing results are available. This case also highlights that diagnostic information can be gained from ultrastructural examination of postmortem liver tissue.

DNA barcoding in mammals

DNA barcoding provides an operational framework for mammalian taxonomic identification and cryptic species discovery. Focused effort to build a reference library of genetic data has resulted in the assembly of over 35 K mammalian cytochrome c oxidase subunit I sequences and outlined the scope of mammal-related barcoding projects. Based on the above experience, this chapter recounts three typical methodological pathways involved in mammalian barcoding: routine methods aimed at assembling the reference sequence library from high quality samples, express approaches used to attain cheap and fast taxonomic identifications for applied purposes, and forensic techniques employed when dealing with degraded material. Most of the methods described are applicable to a range of vertebrate taxa outside Mammalia.

Mitochondrial respiratory chain in brain homogenates: activities in different brain areas in patients with Alzheimer's disease

BACKGROUND AND AIMS

The potential influence of impaired oxidative metabolism in the modulation of manifestations in sporadic Alzheimer's disease (AD) has attracted much attention in the last 50 years. Unfortunately, many clinical and experimental results aiming at proving this hypothesis are still controversial. The aim was to study the enzymatic activities of respiratory chain (RC) complexes I through V in three brain areas of a group of patients with definite AD, and to compare the results with a group of normal brains. We simultaneously assessed the lipid peroxidation of the samples as a measure of free radical damage.

METHODS

The specific activity of the individual complexes of the RC was measured spectrophotometrically, and the loss of cis-parinaric acid fluorescence was used to determine the chemical process of lipid peroxidation.

RESULTS

We were not able to detect differences in any of the analyzed RC enzymatic activities, or in the level of lipid peroxidation between patients with AD and controls. Instead, differences were found in the number of mitochondria and in the intrinsic enzymatic activities of complexes III and IV in various brain areas.

CONCLUSIONS

Spectrophotometric enzymatic analyses of respiratory complexes in brain homogenates do not support the primary contribution of mitochondrial RC dysfunction in the pathogenesis of AD.

Long-term postmortem survival of mitochondrial genomes in mouse synaptosomes and their rescue in a mitochondrial DNA-less mouse cell line

Mitochondrial DNA (mtDNA) transfer was carried out from postmortem mouse tissues to mouse mtDNA-less (rho0) cells to determine how long it takes for autolysis of mtDNA after death and whether mtDNA in postmortem tissues can recover its function in rho0 cells. The results showed that mtDNA was stable in postmitotic tissues stored at 4 degreesC. Moreover, mtDNA in postmortem brain tissues stored for up to 1 month still retained functional properties, causing complete recovery of mitochondrial respiratory function, when it was transferred to rho0 cells. These observations suggest that mtDNA in brain tissue can survive for 1 month after death and can start replication and gene expression in rho0 cells without showing any functional defects. This procedure might be applied to human autopsy brain tissues for examination of the influence of accumulated somatic mutations in mtDNA from aged subjects.

Clinicopathological features of MERRF

Clinical features of MERRF are varied in terms of patterns and severity of symptoms at the early stage. The age of onset differs even in the same family. Occasionally, ragged-red fibers are not found upon the muscle biopsy. Pathological features in some patients are very mild in comparison with their clinical symptoms; genetic analysis is needed for diagnosis. Unique clinical features in members of three families with MERRF are reported.