NADH-linked mitochondrial respiration in the developing mouse brain is sex-, age- and tissue-dependent

Sex-specific decline in prefrontal cortex mitochondrial bioenergetics in aging baboons correlates with walking speed

Mitochondria play a crucial role in brain aging due to their involvement in bioenergetics, neuroinflammation and brain steroid synthesis. Mitochondrial dysfunction is linked to age-related neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. We investigated changes in the activities of the electron transport chain (ETC) complexes in normally aging baboon brains and determined how these changes relate to donor sex, morning cortisol levels, and walking speed. Using a novel approach, we assessed mitochondrial bioenergetics from frozen prefrontal cortex (PFC) tissues from a large cohort (60 individuals) of well-characterized aging baboons (6.6-22.8 years, approximately equivalent to 26.4-91.2 human years). Aging was associated with a decline in mitochondrial ETC complexes in the PFC, which was more pronounced when activities were normalized for citrate synthase activity, suggesting that the decline in respiration is predominantly driven by changes in the specific activity of individual complexes rather than changes in mitochondrial number. Moreover, when donor sex was used as a covariate, we found that mitochondrial respiration was preserved with age in females, whereas males showed significant loss of ETC activity with age. Males had higher activities of each individual ETC complex and greater lactate dehydrogenase activity relative to females. Circulating cortisol levels correlated only with complex II-linked respiration in males. We also observed a robust positive predictive relationship between walking speed and respiration linked to complexes I, III, and IV in males but not in females. This data reveals a previously unknown link between aging and bioenergetics across multiple tissues linking frailty and bioenergetic function. This study highlights a potential molecular mechanism for sexual dimorphism in brain resilience and suggests that in males changes in PFC bioenergetics contribute to reduced motor function with age.

Effects of methylphenidate on mitochondrial dynamics and bioenergetics in the prefrontal cortex of juvenile rats are sex-dependent

Methylphenidate (MPH) is a central nervous system stimulant drug and a first order prescription in the treatment of Attention Deficit Hyperactivity Disorder (ADHD). Although MPH biochemistry in neurodevelopment is not completely understood, studies showed it alters energy metabolism in rat brains. ADHD prevalence during neurodevelopment is related to males and the investigation has been mainly done in these subjects, therefore, little is known about MPH action in females and, consequently, about sexual dimorphism. In the present study we evaluated markers of mitochondrial dynamics (DRP1 and MFN2, fission and fusion, respectively), biogenesis (mtTFA) and bioenergetics (respiratory chain complexes) in prefrontal cortex of male and female juvenile rats submitted to exposure to MPH to better understand MPH effect during postnatal neurodevelopment. ATP and oxidative stress levels were also evaluated. Wistar rats received intraperitoneal injection of MPH (2.0 mg/kg) or control (saline), once a day, from 15th to 45th day of age. Results showed that MPH increased DRP1 and decreased MFN2, as well as increased mtTFA in prefrontal cortex of male rats. In female, MPH decreased NRF1 and increased Parkin, which are mitochondrial regulatory proteins. Respiratory chain complexes (complex I, SDH, complexes III and IV), ATP production and oxidative stress parameters were altered and shown to be sex-dependent. Taken together, results suggest that chronic MPH exposure at an early age in healthy animals changes mitochondrial dynamics, biogenesis and bioenergetics differently depending on the sex of the subjects.

Lack of detectable sex differences in the mitochondrial function of Caenorhabditis elegans

BACKGROUND

Sex differences in mitochondrial function have been reported in multiple tissue and cell types. Additionally, sex-variable responses to stressors including environmental pollutants and drugs that cause mitochondrial toxicity have been observed. The mechanisms that establish these differences are thought to include hormonal modulation, epigenetic regulation, double dosing of X-linked genes, and the maternal inheritance of mtDNA. Understanding the drivers of sex differences in mitochondrial function and being able to model them in vitro is important for identifying toxic compounds with sex-variable effects. Additionally, understanding how sex differences in mitochondrial function compare across species may permit insight into the drivers of these differences, which is important for basic biology research. This study explored whether Caenorhabditis elegans, a model organism commonly used to study stress biology and toxicology, exhibits sex differences in mitochondrial function and toxicant susceptibility. To assess sex differences in mitochondrial function, we utilized four male enriched populations (N2 wild-type male enriched, fog-2(q71), him-5(e1490), and him-8(e1498)). We performed whole worm respirometry and determined whole worm ATP levels and mtDNA copy number. To probe whether sex differences manifest only after stress and inform the growing use of C. elegans as a mitochondrial health and toxicologic model, we also assessed susceptibility to a classic mitochondrial toxicant, rotenone.

RESULTS

We detected few to no large differences in mitochondrial function between C. elegans sexes. Though we saw no sex differences in vulnerability to rotenone, we did observe sex differences in the uptake of this lipophilic compound, which may be of interest to those utilizing C. elegans as a model organism for toxicologic studies. Additionally, we observed altered non-mitochondrial respiration in two him strains, which may be of interest to other researchers utilizing these strains.

CONCLUSIONS

Basal mitochondrial parameters in male and hermaphrodite C. elegans are similar, at least at the whole-organism level, as is toxicity associated with a mitochondrial Complex I inhibitor, rotenone. Our data highlights the limitation of using C. elegans as a model to study sex-variable mitochondrial function and toxicological responses.

Sex-specific DNA methylation and associations with in utero tobacco smoke exposure at nuclear-encoded mitochondrial genes

Sex-linked differences in mitochondrial ATP production, enzyme activities, and reactive oxygen species generation have been reported in multiple tissue and cell types. While the effects of reproductive hormones underlie many of these differences, regulation of sexually dimorphic mitochondrial function has not been fully characterized. We hypothesized that sex-specific DNA methylation contributes to sex-specific expression of nuclear genes that influence mitochondrial function. Herein, we analysed DNA methylation data specifically focused on nuclear-encoded mitochondrial genes in 191 males and 190 females. We found 596 differentially methylated sites (DMSs) (FDR p < 0.05), corresponding to 324 genes, with at least a 1% difference in methylation between sexes. To investigate the potential functional significance, we utilized gene expression microarray data. Of the 324 genes containing DMSs, 17 showed differences in gene expression by sex. Particularly striking was that ATP5G2, encoding subunit C of ATP synthase, contains seven DMSs and exhibits a sex difference in expression (p = 0.04). Finally, we also found that alterations in DNA methylation associated with in utero tobacco smoke exposure were sex-specific in these nuclear-encoded mitochondrial genes. Interestingly, the level of sex differences in DNA methylation at nuclear-encoded mitochondrial genes and the level of methylation changes associated with smoke exposure were less prominent than that of other genes. This suggests more conservative regulation of DNA methylation at these nuclear-encoded mitochondrial genes as compared to others. Overall, our findings suggest that sex-specific DNA methylation may help establish sex differences in expression and function and that sex-specific alterations in DNA methylation in response to exposures could contribute to sex-variable toxicological responses.

Sex differences in the mouse photothrombotic stroke model investigated with X-ray fluorescence microscopy and Fourier transform infrared spectroscopic imaging

Stroke is a leading cause of death and disability around the world. To date, the majority of pre-clinical research has been performed using male lab animals and results are commonly generalized to both sexes. In clinical stoke cases females have a higher incidence of ischemic stroke and poorer outcomes, compared to males. Best practices for improving translatability of findings for stroke, encourage the use of both sexes in studies. Since estrogen and progesterone have recognized neuroprotective effects, it is important to compare the size, severity and biochemical composition of the brain tissue following stroke in female and male animal models. In this study a photothrombotic focal stroke was induced in male and female mice. Vaginal secretions were collected twice daily to track the stage of estrous. Mice were euthanized at 24 h post-stroke. Histological staining, Fourier transform infrared imaging and X-ray fluorescence imaging were performed to better define the size and metabolic markers in the infarct core and surrounding penumbra. Our results show while the female mice had a significantly lower body mass than males, the cross-sectional area of the brain and the size of infarct and penumbra were not significantly different between the groups. In addition to the general expected sex-linked differences of altered NADH levels between males and females, estrus females had significantly elevated glycogen in the penumbra compared with males and total phosphorus levels were noted to be higher in the penumbra of estrus females. Elevated glycogen reserves in the tissue bordering the infarct core in females may present alternatives for improved functional recovery in females in the early post-stroke phase.

Characterizing region-specific glucose metabolic profile of the rodent brain using Seahorse XFe96 analyzer

The brain is highly complex with diverse structural characteristics in accordance with specific functions. Accordingly, differences in regional function, cellular compositions, and active metabolic pathways may link to differences in glucose metabolism at different brain regions. In the current study, we optimized an acute biopsy punching method and characterized region-specific glucose metabolism of rat and mouse brain by a Seahorse XFe96 analyzer. We demonstrated that 0.5 mm diameter tissue punches from 180-µm thick brain sections allow metabolic measurements of anatomically defined brain structures using Seahorse XFe96 analyzer. Our result indicated that the cerebellum displays a more quiescent phenotype of glucose metabolism than cerebral cortex, basal ganglia, and hippocampus. In addition, the cerebellum has higher AMPK activation than other brain regions evidenced by the expression of pAMPK, upstream pLKB1, and downstream pACC. Furthermore, rodent brain has relatively low mitochondrial oxidative phosphorylation efficiency with up to 30% of respiration linked to proton leak. In summary, our study discovered region-specific glucose metabolic profile and relative high proton leak coupled respiration in the brain. Our study warrants future research on spatial mapping of the brain glucose metabolism in physiological and pathological conditions and exploring the mechanisms and significance of mitochondrial uncoupling in the brain.

Role of Bioactive Compounds in the Regulation of Mitochondrial Dysfunctions in Brain and Age-Related Neurodegenerative Diseases

Mitochondria are multifunctional organelles that participate in a wide range of metabolic processes, including energy production and biomolecule synthesis. The morphology and distribution of intracellular mitochondria change dynamically, reflecting a cell’s metabolic activity. Oxidative stress is defined as a mismatch between the body’s ability to neutralise and eliminate reactive oxygen and nitrogen species (ROS and RNS). A determination of mitochondria failure in increasing oxidative stress, as well as its implications in neurodegenerative illnesses and apoptosis, is a significant developmental process of focus in this review. The neuroprotective effects of bioactive compounds linked to neuronal regulation, as well as related neuronal development abnormalities, will be investigated. In conclusion, the study of secondary components and the use of mitochondrial features in the analysis of various neurodevelopmental diseases has enabled the development of a new class of mitochondrial-targeted pharmaceuticals capable of alleviating neurodegenerative disease states and enabling longevity and healthy ageing for the vast majority of people.

Transcriptomic Regulations Underlying Pair-bond Formation and Maintenance in the Socially Monogamous Male and Female Prairie Vole

BACKGROUND

The ability to form enduring social bonds is characteristic of human nature, and impairments in social affiliation are central features of severe neuropsychiatric disorders including autism spectrum disorder and schizophrenia. Owing to its ability to form long-term pair-bonds, the socially monogamous prairie vole has emerged as an excellent model to study the neurobiology of social attachment. Despite the enduring nature of the bond, however, surprisingly few genes have been implicated in the pair-bonding process in either sex.

METHODS

Male and female prairie voles (Microtus ochrogaster) were cohabitated with an opposite-sex partner for 24 hours or 3 weeks, and transcriptomic regulations in the nucleus accumbens were measured by RNA sequencing.

RESULTS

We found sex-specific response patterns despite similar behavioral indicators of pair-bond establishment. Indeed, 24 hours of cohabitation with an opposite-sex partner induced widespread transcriptomic changes that remained sustained to some extent in females after 3 weeks but returned to baseline before a second set of regulations in males. This led to a highly sexually biased nucleus accumbens transcriptome at 3 weeks related to processes such as neurotransmission, protein turnover, and DNA transcription. In particular, we found sex-specific alterations of mitochondrial dynamics following cohabitation, with a shift toward fission in males.

CONCLUSIONS

In addition to identifying the genes, networks, and pathways involved in the pair-bonding process in the nucleus accumbens, our work illustrates the vast extent of sex differences in the molecular mechanisms underlying pair-bonding in prairie voles and paves the way to further our understanding of the complex social bonding process.

Toxicity of silver nanoparticles (AgNPs) in the model ciliate Paramecium multimicronucleatum: Molecular mechanisms of activation are dose- and particle size-dependent

Current understanding of toxicity mechanisms of nanoparticles is still far from comprehensive, partly because of the neglect of control factors such as the dependence of mechanism activation on the exposure dosage and particle size. To reveal molecular mechanisms of silver nanoparticle (AgNP) toxicity, the model ciliate Paramecium multimicronucleatum was exposed for 12 h to different concentrations of AgNPs with particle size of 20 nm (0.08, 0.12, and 0.30 mg/l) and 40 nm (0.08 and 0.30 mg/l). Transcriptomes of the tested ciliates were then analyzed based on dendrograms of gene expression, Gene Ontology (GO) terms, KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, and up- and down-regulated genes. Results showed that: (1) toxicity mechanisms of AgNP revealed by analyses of GO and KEEG were significantly involved in the metabolic pathways of nutrients and the biosynthesis of macromolecules; (2) the top five up-regulated genes were mainly related to biological oxidation, biosynthesis, and oxidative stress, while top five down-regulated genes were mainly related to glycolysis; (3) activated mechanisms varied both in quantity and in type with dosages and particle sizes of AgNPs; (4) AgNP-treatments with different exposure dosages and particle sizes can produce the same toxicity in terms of 12 h-EC₅₀, but the underlying molecular mechanisms differed significantly. In brief, this study provides insights into the molecular mechanisms of AgNP toxicity through transcriptome analyses and confirmed their dependence of activation on the exposure dosage and particle size of AgNPs.

Fetal Cardiac Lipid Sensing Triggers an Early and Sex-related Metabolic Energy Switch in Intrauterine Growth Restriction

CONTEXT

Intrauterine growth restriction (IUGR) is an immediate outcome of an adverse womb environment, exposing newborns to developing cardiometabolic disorders later in life.

OBJECTIVE

This study investigates the cardiac metabolic consequences and underlying mechanism of energy expenditure in developing fetuses under conditions of IUGR.

METHODS

Using an animal model of IUGR characterized by uteroplacental vascular insufficiency, mitochondrial function, gene profiling, lipidomic analysis, and transcriptional assay were determined in fetal cardiac tissue and cardiomyocytes.

RESULTS

IUGR fetuses exhibited an upregulation of key genes associated with fatty acid breakdown and β-oxidation (Acadvl, Acadl, Acaa2), and mitochondrial carnitine shuttle (Cpt1a, Cpt2), instigating a metabolic gene reprogramming in the heart. Induction of Ech1, Acox1, Acox3, Acsl1, and Pex11a indicated a coordinated interplay with peroxisomal β-oxidation and biogenesis mainly observed in females, suggesting sexual dimorphism in peroxisomal activation. Concurring with the sex-related changes, mitochondrial respiration rates were stronger in IUGR female fetal cardiomyocytes, accounting for enhanced adenosine 5'-triphosphate production. Mitochondrial biogenesis was induced in fetal hearts with elevated expression of Ppargc1a transcript specifically in IUGR females. Lipidomic analysis identified the accumulation of arachidonic, eicosapentaenoic, and docosapentaenoic polyunsaturated long-chain fatty acids (LCFAs) in IUGR fetal hearts, which leads to nuclear receptor peroxisome proliferator-activated receptor α (PPARα) transcriptional activation in cardiomyocytes. Also, the enrichment of H3K27ac chromatin marks to PPARα-responsive metabolic genes in IUGR fetal hearts outlines an epigenetic control in the early metabolic energy switch.

CONCLUSION

This study describes a premature and sex-related remodeling of cardiac metabolism in response to an unfavorable intrauterine environment, with specific LCFAs that may serve as predictive effectors leading to IUGR.

S-Palmitoylation of Synaptic Proteins as a Novel Mechanism Underlying Sex-Dependent Differences in Neuronal Plasticity

Although sex differences in the brain are prevalent, the knowledge about mechanisms underlying sex-related effects on normal and pathological brain functioning is rather poor. It is known that female and male brains differ in size and connectivity. Moreover, those differences are related to neuronal morphology, synaptic plasticity, and molecular signaling pathways. Among different processes assuring proper synapse functions are posttranslational modifications, and among them, S-palmitoylation (S-PALM) emerges as a crucial mechanism regulating synaptic integrity. Protein S-PALM is governed by a family of palmitoyl acyltransferases, also known as DHHC proteins. Here we focused on the sex-related functional importance of DHHC7 acyltransferase because of its S-PALM action over different synaptic proteins as well as sex steroid receptors. Using the mass spectrometry-based PANIMoni method, we identified sex-dependent differences in the S-PALM of synaptic proteins potentially involved in the regulation of membrane excitability and synaptic transmission as well as in the signaling of proteins involved in the structural plasticity of dendritic spines. To determine a mechanistic source for obtained sex-dependent changes in protein S-PALM, we analyzed synaptoneurosomes isolated from DHHC7-/- (DHHC7KO) female and male mice. Our data showed sex-dependent action of DHHC7 acyltransferase. Furthermore, we revealed that different S-PALM proteins control the same biological processes in male and female synapses.

Mice and Rats Display Different Ventilatory, Hematological, and Metabolic Features of Acclimatization to Hypoxia

Phylogeographic studies showed that house mice (Mus musculus) originated in the Himalayan region, while common rats (Rattus rattus and Rattus norvegicus) come from the lowlands of China and India. Accordingly, it has been proposed that its origins gave mice, but not rats, the ability to invade ecological niches at high altitudes (pre-adaptation). This proposal is strongly supported by the fact that house mice are distributed throughout the world, while common rats are practically absent above 2,500 m. Considering that the ability of mammals to colonize high-altitude environments (>2,500 m) is limited by their capability to tolerate reduced oxygen availability, in this work, we hypothesize that divergences in the ventilatory, hematological, and metabolic phenotypes of mice and rats establish during the process of acclimatization to hypoxia (Hx). To test this hypothesis male FVB mice and Sprague-Dawley (SD) rats were exposed to Hx (12% O₂) for 0 h (normoxic controls), 6 h, 1, 7, and 21 days. We assessed changes in ventilatory [minute ventilation (V_E), respiratory frequency (f_R), and tidal volume (V_T)], hematological (hematocrit and hemoglobin concentration), and metabolic [whole-body O₂ consumption (VO₂) and CO₂ production (VCO₂), and liver mitochondrial oxygen consumption rate (OCR) parameters]. Compared to rats, results in mice show increased ventilatory, metabolic, and mitochondrial response. In contrast, rats showed quicker and higher hematological response than mice and only minor ventilatory and metabolic adjustments. Our findings may explain, at least in part, why mice, but not rats, were able to colonize high-altitude habitats.

Age-related sex differences in the expression of important disease-linked mitochondrial proteins in mice

The prevalence and progression of many illnesses, such as neurodegenerative and cardiovascular diseases, obesity, and cancer, vary between women and men, often in an age-dependent manner. A joint hallmark of these diseases is some type of mitochondrial dysfunction. While several mitochondrial proteins are known to be regulated by sex hormones, the levels of those proteins have not been systematically analyzed with regard to sex and age, and studies that consider sex and/or age differences in the protein expression are very rare. In this study, we compared the expression patterns of physiologically important mitochondrial proteins in female and male C57BL/6N mice of age cohorts frequently used in experiments. We found that sex-related differences in the expression of uncoupling proteins 1 and 3 (UCP1 and UCP3) occur in an age-dependent manner. The sex-specific expression of UCP1 and UCP3 in brown adipose tissue (BAT) was inversely correlated with differences in body weight. Expression of UCP4 in the brain, Complex I in the spleen, and Complex II in the brain and BAT was least affected by the sex of the mouse. We further demonstrated that there are serious limitations in using VDAC1 and actin as markers in western blot analyses, due to their sex- and age-specific fluctuations. Our results confirm that sex and age are important parameters and should be taken into account by researchers who examine the mechanistic aspects of diseases. HIGHLIGHTS: I.The levels of UCP1 and UCP3 protein expression differ between females and males in an age-dependent manner.II.Pre-pubertal expression of almost all proteins tested in this study does not depend on the sex of the mouse.III.Expression of VDAC1 and actin, which are often used as loading control proteins in western blot analysis, is tissue-specifically influenced by sex and age.