Replication stress in mitochondria

Novel blood and tissue-based mitochondrial D-loop mutations detected in an Iranian NAFLD patient cohort

Non-alcoholic fatty liver disease (NAFLD) is an increasingly prevalent chronic liver disease characterized by an elusive etiology. In its advanced stages, this condition can pose life-threatening implications. Mitochondrial dysfunction due to its impact on hepatic lipid homeostasis, cytokine release, ROS production, and cell death, contributes to the pathogenesis of NAFLD. Previous research reveals a direct link between NAFLD genetic predictors and mitochondrial dysfunction. The emphasis on the D-loop stems from its association with impaired mtDNA replication, underscoring its crucial role in NAFLD progression. We included 38 Iranian NAFLD patients (comprising 16 patients with non-alcoholic fatty liver [NAFL] and 22 patients with non-alcoholic steatohepatitis [NASH]), with matched blood and liver tissue samples collected from each to compare variations in the mitochondrial D-loop sequence within samples. The mitochondrial DNA (mtDNA) D-loop region was amplified using PCR, and variations were identified through sequencing. The resultant sequences were compared with the reference sequence of human mtDNA available in the MITOMAP Database for comparative analysis. In this study, 97 somatic mutations in the mtDNA D-loop region were identified in NAFLD patients. Our study revealed significant difference between the NAFLD patients and control group in 13 detected mutations (P ≤ 0.05). Novel mutations were discovered in hepatic tissues, while mutation 16220-16221ins C was found in both tissues and blood. A significant difference was found in the distribution of D310 and mt514-mt523 (CA)n repeat variations between NAFLD patients and the control group (P < 0.001). C to T and T to C transitions were the prevalent substitution among patients. Identification of the 16220-16221ins C mutation in both blood and tissue samples from NAFLD patients holds substantial promise as a potential diagnostic marker. However, further research is imperative to corroborate these findings.

An exploration of biomarkers for noise exposure: mitochondrial DNA copy number and micronucleus frequencies in Chinese workers

Few studies have been conducted that use biomarkers as early warning signals for noise-associated health hazards. To explore potentially effective biomarkers for noise-exposed populations, we recruited 218 noise-exposed male workers in China. We calculated cumulative noise exposure (CNE) through noise intensity and noise-exposed duration. When the model was fully adjusted, ln-transformed relative mitochondrial DNA copy number (mtDNAcn) decreased by 0.014 (95% confidence interval (CI): -0.026, -0.003) units with each 1 dB(A)∙year increase in CNE levels. CNE was further included in the model as a grouping variable, and the results showed a negative dose-effect relationship between relative mtDNAcn and CNE (P-trend = 0.045). However, we did not find a correlation between CNE and micronucleus (MN) frequencies. Our findings suggest that CNE in workers was associated with a decrease in relative mtDNAcn which may provide a potential biomarker for noise and for certain health risk but not with MN frequencies.

mTRIP, an Imaging Tool to Investigate Mitochondrial DNA Dynamics in Physiology and Disease at the Single-Cell Resolution

Mitochondrial physiology and metabolism are closely linked to replication and transcription of mitochondrial DNA (mtDNA). However, the characterization of mtDNA processing is poorly defined at the single-cell level. We developed mTRIP (mitochondrial Transcription and Replication Imaging Protocol), an imaging approach based on modified fluorescence in situ hybridization (FISH), which simultaneously reveals mitochondrial structures committed to mtDNA initiation of replication as well as the mitochondrial RNA (mtRNA) content at the single-cell level in human cells. Also specific RNA regions, rather than global RNA, can be tracked with mTRIP. In addition, mTRIP can be coupled to immunofluorescence for in situ protein tracking, or to MitoTracker, thereby allowing for simultaneous labeling of mtDNA, mtRNA, and proteins or mitochondria, respectively. Altogether, qualitative and quantitative alterations of the dynamics of mtDNA processing are detected by mTRIP in human cells undergoing physiological changes, as well as stress and dysfunction. mTRIP helped elucidating mtDNA processing alterations in cancer cells, and has a potential for diagnostic of mitochondrial diseases.

β-Amyloid and mitochondrial-derived peptide-c are additive predictors of adverse outcome to high-on-treatment platelet reactivity in type 2 diabetics with revascularized coronary artery disease

BACKGROUND AND AIMS

Increased β-amyloid and decreased mitochondrial-derived peptide (MOTS-c), are reported in diabetes. We investigated their additive value to high on-clopidogrel platelet reactivity (HPR) for adverse outcome in type 2 diabetics after recent revascularization.

PATIENTS AND METHODS

In 121 type II diabetics, treated with clopidogrel and aspirin, (93 males, mean age 67.2 years) we measured: (a) maximum platelet aggregation to adenosine diphosphate (ADP) by light transmission aggregometry (LTAmax), (b) malondialdehyde (MDA), as oxidative stress marker, (c) MOTS-c, (d) β-amyloid blood levels. Cardiac death and acute coronary syndromes (MACE) were recorded during 2 years of follow-up.

RESULTS

Out of 121 patients, 32 showed HPR (LTAmax > 48%,). At baseline, HPR was associated with β-amyloid > 51 pg/ml (p = 0.006) after adjusting clinical variables, HbA1c, MOTS-c, MDA and medication. During follow-up, 22 patients suffered a MACE. HPR, β-amyloid > 51 pg/ml and MOTS-c < 167 ng/ml were predictors of MACE (relative risk 3.1, 3.5 and 3.8 respectively, p < 0.05) after adjusting for confounders and medication. There was significant interaction between HPR and β-amyloid or MOTS-c for the prediction of MACE (p < 0.05). Patients with HPR and β-amyloid > 51 mg/dl or HPR and MOTS-c concentration < 167 ng/ml had a fourfold higher risk for MACE than patients without these predictors (relative risk 4.694 and 4.447 respectively p < 0.01). The above results were confirmed in an external validation cohort of 90 patients with diabetes and CAD.

CONCLUSIONS

Increased β-amyloid or low MOTS-c are additive predictors to high on-clopidogrel platelet reactivity for adverse outcome in diabetics with CAD during 2-years follow-up. Clinical Trial Registration-URL: https://www.clinicaltrials.gov. Unique identifier: NCT04027712.

Air pollution and placental mitochondrial DNA copy number: Mechanistic insights and epidemiological challenges

During embryogenesis and embryo implantation, the copy number of mtDNA is elaborately regulated to meet the cellular demand for division, growth and differentiation. With large numbers of mitochondria for energy production, placental cells possess strong endocrine functionalities and capacities for efficient signaling communication. Recently, several environmental epidemiological studies have shown an association between mitochondrial DNA copy number, adverse birth outcomes and maternal exposure to air pollution, which has shed light on the possible effect of pollutants on placental molecular events. Because the mtDNA replication is thought to be a direct drive of mtDNA change, we tried to highlight the essential factors involved in the process of mtDNA replication. Then we traced the mtDNA change in the formation of placenta during embryogenesis, and evaluated the importance of mitochondrial genome maintenance during gestation. The possible mechanism from the epidemiological and experimental studies were reviewed and summarized, and recommendations were proposed for future studies to improve the precision of the estimated difference. The issue will be well-understood if the integrated profiles, such as familial genetic tendency, maternal genetic information, identification of mitochondrial DNA copy number in each placental cell type, and total personal exposure assessment, are considered in the future study.

Broad spectrum metabolomics for detection of abnormal metabolic pathways in a mouse model for retinitis pigmentosa

Retinitis pigmentosa (RP) is a degenerative disease of the retina that affects approximately 1 million people worldwide. There are multiple genetic causes of this disease, for which, at present, there are no effective therapeutic strategies. In the present report, we utilized broad spectrum metabolomics to identify perturbations in the metabolism of the rd10 mouse, a genetic model for RP that contains a mutation in Pde6β. These data provide novel insights into mechanisms that are potentially critical for retinal degeneration. C57BL/6J and rd10 mice were raised in cyclic light followed by either light or dark adaptation at postnatal day (P) 18, an early stage in the degeneration process. Mice raised entirely in the dark until P18 were also evaluated. After euthanasia, retinas were removed and extracted for analysis by ultra-performance liquid chromatography-time of flight-mass spectrometry (UPLC-QTOF-MS). Compared to wild type mice, rd10 mice raised in cyclic light or in complete darkness demonstrate significant alterations in retinal pyrimidine and purine nucleotide metabolism, potentially disrupting deoxynucleotide pools necessary for mitochondrial DNA replication. Other metabolites that demonstrate significant increases are the Coenzyme A intermediate, 4'-phosphopantothenate, and acylcarnitines. The changes in these metabolites, identified for the first time in a model of RP, are highly likely to disrupt normal energy metabolism. High levels of nitrosoproline were also detected in rd10 retinas relative to those from wild type mice. These results suggest that nitrosative stress may be involved in retinal degeneration in this mouse model.

Mechanical forces on cellular organelles

The intracellular environment of eukaryotic cells is highly complex and compact. The limited volume of the cell, usually a few hundred femtoliters, is not only occupied by numerous complicated, diverse membranous and proteinaceous structures, these structures are also highly dynamic due to constant remodeling and trafficking events. Consequently, intracellular interactions are more than just opportunities to exchange molecules; they also involve components physically navigating around each other in a highly confined space. While the biochemical interactions between organelles have been intensely studied in the past decades, the mechanical properties of organelles and the physical interactions between them are only beginning to be unraveled. Indeed, recent studies show that intracellular organelles are, at times, under extreme mechanical strain both in widely used experimental systems as well as in vivo. In this Hypothesis, we highlight known examples of intracellular mechanical challenges in biological systems and focus on the coping mechanisms of two important organelles, the nucleus and mitochondria, for they are the best studied in this aspect. In the case of mitochondria, we propose that ER–mitochondrial contact sites at thin cell peripheries may induce mitochondrial fission by mechanically constricting mitochondrial tubules. We also briefly discuss the mechano-responsiveness of other organelles and interesting directions for future research.