Animal Models of Mitochondrial Diseases Associated with Nuclear Gene Mutations

Mitochondrial diseases (MDs) associated with nuclear gene mutations are part of a large group of inherited diseases caused by the suppression of energy metabolism. These diseases are of particular interest, because nuclear genes encode not only most of the structural proteins of the oxidative phosphorylation system (OXPHOS), but also all the proteins involved in the OXPHOS protein import from the cytoplasm and their assembly in mitochondria. Defects in any of these proteins can lead to functional impairment of the respiratory chain, including dysfunction of complex I that plays a central role in cellular respiration and oxidative phosphorylation, which is the most common cause of mitopathologies. Mitochondrial diseases are characterized by an early age of onset and a progressive course and affect primarily energy-consuming tissues and organs. The treatment of MDs should be initiated as soon as possible, but the diagnosis of mitopathologies is extremely difficult because of their heterogeneity and overlapping clinical features. The molecular pathogenesis of mitochondrial diseases is investigated using animal models: i.e. animals carrying mutations causing MD symptoms in humans. The use of mutant animal models opens new opportunities in the study of genes encoding mitochondrial proteins, as well as the molecular mechanisms of mitopathology development, which is necessary for improving diagnosis and developing approaches to drug therapy. In this review, we present the most recent information on mitochondrial diseases associated with nuclear gene mutations and animal models developed to investigate them.

Mitochondrion-targeted antioxidant SkQ1 prevents rapid animal death caused by highly diverse shocks

The response to stress involves the activation of pathways leading either to protection from the stress origin, eventually resulting in development of stress resistance, or activation of the rapid death of the organism. Here we hypothesize that mitochondrial reactive oxygen species (mtROS) play a key role in stress-induced programmed death of the organism, which we called "phenoptosis" in 1997. We demonstrate that the synthetic mitochondria-targeted antioxidant SkQ1 (which specifically abolishes mtROS) prevents rapid death of mice caused by four mechanistically very different shocks: (a) bacterial lipopolysaccharide (LPS) shock, (b) shock in response to intravenous mitochondrial injection, (c) cold shock, and (d) toxic shock caused by the penetrating cation C₁₂TPP. Importantly, under all these stresses mortality was associated with a strong elevation of the levels of pro-inflammatory cytokines and administration of SkQ1 was able to switch off the cytokine storms. Since the main effect of SkQ1 is the neutralization of mtROS, this study provides evidence for the role of mtROS in the activation of innate immune responses mediating stress-induced death of the organism. We propose that SkQ1 may be used clinically to support patients in critical conditions, such as septic shock, extensive trauma, cooling, and severe infection by bacteria or viruses.

Motor Activity and "Neotenic" Sleep in the Naked Mole Rat (Heterocephalus glaber) under Isolation

For the first time, continuous registration of motor activity and electroencephalogram for 40 days was carried out in four individuals of the naked mole rat (Heterocephalus glaber) in isolated conditions in the laboratory. A clear circadian rhythm of motor activity was found, with a gradual decrease during the night and an increase during the day, which remained both in the 12L/12D mode and in conditions of complete darkness. The rest states occupied, on average, about half the time of the day. There were both typical and atypical sleep periods, in which REM sleep episodes preceded NREM sleep periods. REM sleep percentage was unusually high (up to 50% of the total sleep time). During REM sleep episodes, a synchronized two-phase high-amplitude rhythm with a frequency of 12-16 Hz was recorded in the EEG. In addition, there were hard-to-identify periods of sleep, combining elements of both NREM and REM sleep. The sleep structure of naked mole rats resembles that of evolutionarily ancient species, as well as the "disorganized" sleep characteristic of the early stages of ontogenesis in altricial mammals.

Ultrastructure of Hepatocytes from Laboratory Mice Fed a Standard Dry Laboratory Animal Diet

The significant destructive changes in ultrastructure of hepatocytes from laboratory mice kept in different vivariums in Moscow and fed with dry laboratory animal diets acquired from different domestic manufacturers that were not standardized for initial products were demonstrated using electron microscopy. Furthermore, disruption in the ultrastructure of liver parenchymal cells occurred regardless of the animal status (SPF or conventional), conditions of various vivariums, as well as the feed manufacturer. At the same time, studies on ultrastructure of liver hepatocytes from mice kept in the Charles River Laboratory facilities in Germany and fed with the Altromin Spezialfutter laboratory animal diet (GmbH & Co., Germany) that was produced using quality control of ingredients did not reveal destructive changes in the internal ultrastructure of hepatocytes. However, if these mice were later fed with the food produced in local manufactures, changes in the structure of liver cells developed after 2 months. Thus, feeding with dry diet from the domestic producers of an unspecified composition causes significant changes in the ultrastructure of hepatocytes in control animals, reflecting the development of some pathological processes in the body.

Simple Recommendations for Improving Efficiency in Generating Genome-Edited Mice

The generation of transgenic model organisms (primarily mice) is an integral part of modern fundamental and applied research. Simple techniques based on the biology of these laboratory rodents can often increase efficiency when generating genome-edited mouse strains. In this study, we share our three years of experience in the optimization of mouse genome editing based on microinjection of CRISPR/Cas9 components into ca. 10,000 zygotes. We tested a number of techniques meant to improve efficiency in generating knockout mice, such as optimization of the superovulation method and choosing the optimal mouse strains to be used as zygote donors and foster mothers. The presented results might be useful to laboratories aiming to quickly and efficiently create new mouse strains with tailored genome editing.

The local repolarization heterogeneity in the murine pulmonary veins myocardium contributes to the spatial distribution of the adrenergically induced ectopic foci

An atrial tachyarrhythmias is predominantly triggered by a proarrhythmic activity originate from the pulmonary veins (PV) myocardial sleeves; sympathetic or adrenergic stimulation facilitates PV proarrhythmia. In the present study the electrophysiological inhomogeneity, spatiotemporal characteristics of the adrenergically induced ectopic firing and sympathetic nerves distribution have been investigated in a murine PV myocardium to clarify mechanisms of adrenergic PV ectopy. Electrically paced murine PV demonstrate atrial-like pattern of conduction and atrial-like action potentials (AP) with longest duration in the mouth of PV. The application of norepinephrine (NE), agonists of α- and β-adrenergic receptors (ARs) or intracardiac nerves stimulation induced spontaneous AP in a form of periodical bursts or continuous firing. NE- or ARs agonists-induced SAP originated from unifocal ectopic foci with predominant localization in the region surrounding PV mouth, but not in the distal portions of a murine PV myocardium. A higher level of catecholamine content and catecholamine fiber network density was revealed in the PV myocardial sleeves relative to LA appendage. However, no significant local variation of catecholamine content and fiber density was observed in the murine PV. In conclusion, PV mouth region appear to be a most susceptible to adrenergic proarrhythmia in mice. Intrinsic spatial heterogeneity of AP duration can be considered as a factor influencing localization of the ectopic foci in PV.

Mitochondria-Targeted Antioxidant SkQ1 (10-(6´-Plastoquinonyl)decyltriphenylphosphonium Bromide) Inhibits Mast Cell Degranulation in vivo and in vitro

The therapeutic effect of mitochondria-targeted antioxidant 10-(6´-plastoquinonyl)decyltriphenylphosphonium bromide (SkQ1) in experimental models of acute inflammation and wound repair has been shown earlier. It was suggested that the antiinflammatory activity of SkQ1 is related to its ability to suppress inflammatory activation of the vascular endothelium and neutrophil migration into tissues. Here, we demonstrated that SkQ1 inhibits activation of mast cells (MCs) followed by their degranulation and histamine release in vivo and in vitro. Intraperitoneal injections of SkQ1 in the mouse air-pouch model reduced the number of leukocytes in the air-pouch cavity and significantly decreased the histamine content in it, as well as suppressing MC degranulation in the air-pouch tissue. The direct effect of SkQ1 on MCs was studied in vitro in the rat basophilic leukemia RBL-2H3 cell line. SkQ1 inhibited induced degranulation of RBL-2H3 cells. These results suggest that mitochondrial reactive oxygen species are involved in the activation of MCs. It is known that MCs play a crucial role in regulation of vascular permeability by secreting histamine. Suppression of MC degranulation by SkQ1 might be a significant factor in the antiinflammatory activity of this mitochondria-targeted antioxidant.

Spontaneous and Experimentally Induced Pathologies in the Naked Mole Rat (Heterocephalus glaber)

The naked mole rat (Heterocephalus glaber, Rüppell, 1842) is a unique eusocial rodent with unusually long lifespan. Therefore, the study of spontaneous and experimentally induced pathologies in these animals is one of the most important tasks of gerontology. Various infections, noninfectious pathologies (including age-dependent changes), and tumors have been described in the naked mole rat. The most frequent pathologies are traumas (bite wounds), purulent and septic complications of traumatic injuries, renal tubular calcinosis, chronic progressive nephropathy, hepatic hemosiderosis, testicular interstitial cell hyperplasia, calcinosis cutis, cardiomyopathy, and dysbiosis-related infectious lesions of the digestive system. However, the summarized data on pathology (including tumor incidence) and on the causes of mortality are insufficient. There are only few publications about the results of experiments where pathologies were induced in the naked mole rat. All these problems could be subjects for promising future studies without which adequate studies on mechanisms providing the long lifespan of the naked mole rat are impossible, as well as the elucidation of causes of tumor resistance of this species.

Effects of Mitochondrial Antioxidant SkQ1 on Biochemical and Behavioral Parameters in a Parkinsonism Model in Mice

According to one hypothesis, Parkinson's disease pathogenesis is largely caused by dopamine catabolism that is catalyzed on mitochondrial membranes by monoamine oxidase. Reactive oxygen species are formed as a byproduct of these reactions, which can lead to mitochondrial damage followed by cell degeneration and death. In this study, we investigated the effects of administration of the mitochondrial antioxidant SkQ1 on biochemical, immunohistochemical, and behavioral parameters in a Parkinson-like condition caused by protoxin MPTP injections in C57BL/6 mice. SkQ1 administration increased dopamine quantity and decreased signs of sensory-motor deficiency as well as destruction of dopaminergic neurons in the substantia nigra and ventral tegmental area in mice with the Parkinson-like condition.

Comparison of the Effects of Mitochondria-Targeted Antioxidant 10-(6'-Plastoquinonyl)Decyltriphenylphosphonium Bromide (SkQ1) and a Fragment of its Molecule Dodecyltriphenylphosphonium on Carrageenan-Induced Acute Inflammation in Mouse Model of Subcuteneous Air Pouch

The effect of mitochondria-targeted antioxidant 10-(6'-plastoquinonyl) decyltriphenylphosphonium bromide (SkQ1) and its fragment dodecyltriphenylphosphonium (C12TPP), weak uncouplers of respiration and oxidative phosphorylation, was studied using a mouse model of carrageenan-induced acute inflammation in the subcutaneous air pouch. In our model, SkQ1 demonstrated a strong anti-inflammatory effect that manifested in a decrease in the absolute number of inflammatory cells, mainly neutrophils, and their relative number in parallel with an increase in macrophages and mast cell content in the inflammatory exudate. The concentration of proinflammatory cytokine IL-6 in the exudate also tended to decrease. C12TPP produced no significant effect on the inflammation process.