Sex differences in mitochondrial (dys)function: Implications for neuroprotection

Sex-dependent regulation of retinal pigment epithelium and retinal function by Pgc-1α

Age-related macular degeneration (AMD) is a major cause of blindness that affects people over 60. While aging is the prominent factor in AMD, studies have reported a higher prevalence of AMD in women compared to age-matched men. Higher levels of the innate immune response's effector proteins complement factor B and factor I were also found in females compared to males in intermediate AMD. However, the mechanisms underlying these differences remain elusive. Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a key regulator of mitochondrial biogenesis and metabolic pathways. Previously, we showed that Pgc-1α repression and high-fat diet induce drastic AMD-like phenotypes in mice. Our recent data revealed that Pgc-1α repression alone can also induce retinal pigment epithelium (RPE) and retinal dysfunction in mice, and its inhibition in vitro results in lipid droplet accumulation in human RPE. Whether sex is a contributing factor in these phenotypes remains to be elucidated. Using electroretinography, we demonstrate that sex could influence RPE function during aging independent of Pgc-1α in wild-type (WT) mice. We further show that Pgc-1α repression exacerbates RPE and retinal dysfunction in females compared to aged-match male mice. Gene expression analyses revealed that Pgc-1α differentially regulates genes related to antioxidant enzymes and mitochondrial dynamics in males and females. RPE flat mounts immunolabeled with TOMM20 and DRP1 indicated a sex-dependent role for Pgc-1α in regulating mitochondrial fission. Analyses of mitochondrial network morphology suggested sex-dependent effects of Pgc-1α repression on mitochondrial dynamics. Together, our study demonstrates that inhibition of Pgc-1α induces a sex-dependent decline in RPE and retinal function in mice. These observations on the sex-dependent regulation of RPE and retinal function could offer novel insights into targeted therapeutic approaches for age-related RPE and retinal degeneration.

Phenotype and energy metabolism differ between osteoarthritic chondrocytes from male compared to female patients: Implications for sexual dimorphism in osteoarthritis development?

OBJECTIVES

The prevalence and severity of knee osteoarthritis (OA) are greater in females than males. The purpose of this study was to determine whether there is an underlying difference in the biology of OA chondrocytes between males and females.

METHODS

Chondrocytes were obtained following knee arthroplasty from male and female patients with primary OA. Phenotype marker expression, glucose and fat consumption, and rates of glycolysis and oxidative phosphorylation were compared between females and males. RNAi was used to determine the consequences of differential expression of Sry-box transcription factor 9 (SOX9) and PGC1α between males and females.

RESULTS

OA chondrocytes from male donors showed elevated ribonucleic acid (RNA) and protein levels of SOX9, elevated COL2A1 protein synthesis, higher glucose consumption, and higher usage of glycolysis compared to females. OA chondrocytes from females had higher PGC1α protein levels, higher fat consumption, and higher oxidative energy metabolism than males. Knockdown of SOX9 reduced expression of COL2A1 to a greater extent in male OA chondrocytes than females whereas knockdown of PGC1α reduced COL2A1 expression in females but not males. Expression of ACAN and the glycolytic enzyme PGK1 was also reduced in males but not females following SOX9 knockdown.

CONCLUSIONS

OA chondrocyte phenotype and energy metabolism differ between males and females. Our results indicate transcriptional control of COL2A1 differs between the two. Differences in chondrocyte biology between males and females imply the underlying mechanisms involved in OA may also differ, highlighting the need to consider sex and gender when investigating pathogenesis and potential treatments for OA.

Sex-specific loss of mitochondrial membrane integrity in the auditory brainstem of a mouse model of Fragile X syndrome

Sound sensitivity is one of the most common sensory complaints for people with autism spectrum disorders (ASDs). How and why sounds are perceived as overwhelming by affected people is unknown. To process sound information properly, the brain requires high activity and fast processing, as seen in areas like the medial nucleus of the trapezoid body (MNTB) of the auditory brainstem. Recent work has shown dysfunction in mitochondria, which are the primary source of energy in cells, in a genetic model of ASD, Fragile X syndrome (FXS). Whether mitochondrial functions are also altered in sound-processing neurons, has not been characterized yet. To address this question, we imaged the MNTB in a mouse model of FXS. We stained MNTB brain slices from wild-type and FXS mice with two mitochondrial markers, TOMM20 and PMPCB, located on the Outer Mitochondrial Membrane and in the matrix, respectively. These markers allow exploration of mitochondrial subcompartments. Our integrated imaging pipeline reveals significant sex-specific differences between genotypes. Colocalization analyses between TOMM20 and PMPCB reveal that the integrity of mitochondrial subcompartments is most disrupted in female FXS mice compared to female wildtype mice. We highlight a quantitative fluorescence microscopy pipeline to monitor mitochondrial functions in the MNTB from control or FXS mice and provide four complementary readouts. Our approach paves the way to understanding how cellular mechanisms important to sound encoding are altered in ASDs.

Mitochondrial heterogeneity and crosstalk in aging: Time for a paradigm shift?

The hallmarks of aging have been influential in guiding the biology of aging research, with more recent and growing recognition of the interdependence of these hallmarks on age-related health outcomes. However, a current challenge is personalizing aging trajectories to promote healthy aging, given the diversity of genotypes and lived experience. We suggest that incorporating heterogeneity-including intrinsic (e.g., genetic and structural) and extrinsic (e.g., environmental and exposome) factors and their interdependence of hallmarks-may move the dial. This editorial perspective will focus on one hallmark, namely mitochondrial dysfunction, to exemplify how consideration of heterogeneity and interdependence or crosstalk may reveal new perspectives and opportunities for personalizing aging research. To this end, we highlight heterogeneity within mitochondria as a model.

Sex-specific associations of kynurenic acid with neopterin in Alzheimer's disease

BACKGROUND

Sex differences in neuroinflammation could contribute to women's increased risk of Alzheimer's disease (AD), providing rationale for exploring sex-specific AD biomarkers. In AD, dysregulation of the kynurenine pathway (KP) contributes to neuroinflammation and there is some evidence of sex differences in KP metabolism. However, the sex-specific associations between KP metabolism and biomarkers of AD and neuroinflammation need to be explored further.

METHODS

Here we investigate sex differences in cerebrospinal fluid concentrations of seven KP metabolites and sex-specific associations with established AD biomarkers and neopterin, an indicator of neuroinflammation. This study included 311 patients with symptomatic AD and 105 age-matched cognitively unimpaired (CU) controls, followed for up to 5 years.

RESULTS

We found sex differences in KP metabolites in the AD group, with higher levels of most metabolites in men, while there were no sex differences in the CU group. In line with this, more KP metabolites were significantly altered in AD men compared to CU men, and there was a trend in the same direction in AD women. Furthermore, we found sex-specific associations between kynurenic acid and the kynurenic acid/quinolinic acid ratio with neopterin, but no sex differences in the associations between KP metabolites and clinical progression.

DISCUSSION

In our cohort, sex differences in KP metabolites were restricted to AD patients. Our results suggest that dysregulation of the KP due to increased inflammation could contribute to higher AD risk in women.

Male-specific behavioral and transcriptomic changes in aging C. elegans neurons

Aging is a complex biological process with sexually dimorphic aspects. Although cognitive aging of Caenorhabditis elegans hermaphrodites has been studied, less is known about cognitive decline in males. We found that cognitive aging has both sex-shared and sex-dimorphic characteristics, and we identified neuron-specific age-associated sex-differential targets. In addition to sex-shared neuronal aging genes, males differentially downregulate mitochondrial metabolic genes and upregulate GPCR genes with age, while the X chromosome exhibits increased gene expression in hermaphrodites and altered dosage compensation complex expression with age, indicating possible X chromosome dysregulation that contributes to sexual dimorphism in cognitive aging. Finally, the sex-differentially expressed gene hrg-7, an aspartic-type endopeptidase, regulates male cognitive aging but does not affect hermaphrodites' behaviors. These results suggest that males and hermaphrodites exhibit different age-related neuronal changes. This study will strengthen our understanding of sex-specific vulnerability and resilience and identify pathways to target with treatments that could benefit both sexes.

Protein restriction slows the development and progression of pathology in a mouse model of Alzheimer's disease

Dietary protein is a critical regulator of metabolic health and aging. Low protein diets are associated with healthy aging in humans, and dietary protein restriction extends the lifespan and healthspan of mice. In this study, we examined the effect of protein restriction (PR) on metabolic health and the development and progression of Alzheimer's disease (AD) in the 3xTg mouse model of AD. Here, we show that PR promotes leanness and glycemic control in 3xTg mice, specifically rescuing the glucose intolerance of 3xTg females. PR induces sex-specific alterations in circulating and brain metabolites, downregulating sphingolipid subclasses in 3xTg females. PR also reduces AD pathology and mTORC1 activity, increases autophagy, and improves the cognition of 3xTg mice. Finally, PR improves the survival of 3xTg mice. Our results suggest that PR or pharmaceutical interventions that mimic the effects of this diet may hold promise as a treatment for AD.

Differential impact of sex on regulation of skeletal muscle mitochondrial function and protein homeostasis by hypoxia-inducible factor-1α in normoxia

Hypoxia-inducible factor (HIF)-1α is continuously synthesized and degraded in normoxia. During hypoxia, HIF1α stabilization restricts cellular/mitochondrial oxygen utilization. Cellular stressors can stabilize HIF1α even during normoxia. However, less is known about HIF1α function(s) and sex-specific effects during normoxia in the basal state. Since skeletal muscle is the largest protein store in mammals and protein homeostasis has high energy demands, we determined HIF1α function at baseline during normoxia in skeletal muscle. Untargeted multiomics data analyses were followed by experimental validation in differentiated murine myotubes with loss/gain of function and skeletal muscle from mice without/with post-natal muscle-specific Hif1a deletion (Hif1amsd). Mitochondrial oxygen consumption studies using substrate, uncoupler, inhibitor, titration protocols; targeted metabolite quantification by gas chromatography-mass spectrometry; and post-mitotic senescence markers using biochemical assays were performed. Multiomics analyses showed enrichment in mitochondrial and cell cycle regulatory pathways in Hif1a deleted cells/tissue. Experimentally, mitochondrial oxidative functions and ATP content were higher with less mitochondrial free radical generation with Hif1a deletion. Deletion of Hif1a also resulted in higher concentrations of TCA cycle intermediates and HIF2α proteins in myotubes. Overall responses to Hif1amsd were similar in male and female mice, but changes in complex II function, maximum respiration, Sirt3 and HIF1β protein expression and muscle fibre diameter were sex-dependent. Adaptive responses to hypoxia are mediated by stabilization of constantly synthesized HIF1α. Despite rapid degradation, the presence of HIF1α during normoxia contributes to lower mitochondrial oxidative efficiency and greater post-mitotic senescence in skeletal muscle. In vivo responses to HIF1α in skeletal muscle were differentially impacted by sex. KEY POINTS: Hypoxia-inducible factor -1α (HIF1α), a critical transcription factor, undergoes continuous synthesis and proteolysis, enabling rapid adaptive responses to hypoxia by reducing mitochondrial oxygen consumption. In mammals, skeletal muscle is the largest protein store which is determined by a balance between protein synthesis and breakdown and is sensitive to mitochondrial oxidative function. To investigate the functional consequences of transient HIF1α expression during normoxia in the basal state, myotubes and skeletal muscle from male and female mice with HIF1α knockout were studied using complementary multiomics, biochemical and metabolite assays. HIF1α knockout altered the electron transport chain, mitochondrial oxidative function, signalling molecules for protein homeostasis, and post-mitotic senescence markers, some of which were differentially impacted by sex. The cost of rapid adaptive responses mediated by HIF1α is lower mitochondrial oxidative efficiency and post-mitotic senescence during normoxia.

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.

Bacterial muropeptides promote OXPHOS and suppress mitochondrial stress in mammals

Mitochondrial dysfunction critically contributes to many major human diseases. The impact of specific gut microbial metabolites on mitochondrial functions of animals and the underlying mechanisms remain to be uncovered. Here, we report a profound role of bacterial peptidoglycan muropeptides in promoting mitochondrial functions in multiple mammalian models. Muropeptide addition to human intestinal epithelial cells (IECs) leads to increased oxidative respiration and ATP production and decreased oxidative stress. Strikingly, muropeptide treatment recovers mitochondrial structure and functions and inhibits several pathological phenotypes of fibroblast cells derived from patients with mitochondrial disease. In mice, muropeptides accumulate in mitochondria of IECs and promote small intestinal homeostasis and nutrient absorption by modulating energy metabolism. Muropeptides directly bind to ATP synthase, stabilize the complex, and promote its enzymatic activity in vitro, supporting the hypothesis that muropeptides promote mitochondria homeostasis at least in part by acting as ATP synthase agonists. This study reveals a potential treatment for human mitochondrial diseases.

Mechanisms of sex differences in Alzheimer's disease

Alzheimer's disease (AD) and the mechanisms underlying its etiology and progression are complex and multifactorial. The higher AD risk in women may serve as a clue to better understand these complicated processes. In this review, we examine aspects of AD that demonstrate sex-dependent effects and delve into the potential biological mechanisms responsible, compiling findings from advanced technologies such as single-cell RNA sequencing, metabolomics, and multi-omics analyses. We review evidence that sex hormones and sex chromosomes interact with various disease mechanisms during aging, encompassing inflammation, metabolism, and autophagy, leading to unique characteristics in disease progression between men and women.

Estrogen's sex-specific effects on ischemic cell death and estrogen receptor mRNA expression in rat cortical organotypic explants

Estrogens, such as the biologically active 17-β estradiol (E2), regulate not only reproductive behaviors in adults, but also influence neurodevelopment and neuroprotection in both females and males. E2, contingent upon the timing and concentration of the therapy, is neuroprotective in female and male rodent models of stroke. In Vivo studies suggest that E2 may partially mediate this neuroprotection, particularly in the cortex, via ERα. In Vitro studies, utilizing a chemically induced ischemic injury in cortical explants from both sexes, suggest that ERα or ERβ signaling is needed to mediate the E2 protection. Since we know that the timing and concentration of E2 therapy may be sex-specific, we examined if E2 (1 nM) mediates neuroprotection when female and male cortical explants are separately isolated from postnatal day (PND) 3-4 rat. Changes in basal levels ERα, ERβ, and AR mRNA expression are compared across early post-natal development in the intact cortex and the corresponding days in vitro (DIV) for cortical explants. Following ischemic injury at 7 DIV, cell death and ERα, ERβ and AR mRNA expression was compared in female and male cortical explants. We provide evidence that E2-mediated protection is maintained in isolated cortical explants from females, but not male rats. In female cortical explants, the E2-mediated protection at 24 h occurs secondarily to a blunted transient increase in ERα mRNA at 12 h. These results suggest that cortical E2-mediated protection is influenced by sex and supports data to differentially treat females and males following ischemic injury.

Skeletal Muscle Energetics Explain the Sex Disparity in Mobility Impairment in the Study of Muscle, Mobility and Aging

The age-related decline in muscle mitochondrial energetics contributes to the loss of mobility in older adults. Women experience a higher prevalence of mobility impairment compared to men, but it is unknown whether sex-specific differences in muscle energetics underlie this disparity. In the Study of Muscle, Mobility and Aging (SOMMA), muscle energetics were characterized using in vivo phosphorus-31 magnetic resonance spectroscopy and high-resolution respirometry of vastus lateralis biopsies in 773 participants (56.4% women, age 70-94 years). A Short Physical Performance Battery (SPPB) score ≤8 was used to define lower-extremity mobility impairment. Muscle mitochondrial energetics were lower in women compared to men (eg, Maximal Complex I&II OXPHOS: Women = 55.06 ± 15.95; Men = 65.80 ± 19.74; p < .001) and in individuals with mobility impairment compared to those without (eg, Maximal Complex I&II OXPHOS in women: SPPB ≥ 9 = 56.59 ± 16.22; SPPB ≤ 8 = 47.37 ± 11.85; p < .001). Muscle energetics were negatively associated with age only in men (eg, Maximal ETS capacity: R = -0.15, p = .02; age/sex interaction, p = .04), resulting in muscle energetics measures that were significantly lower in women than men in the 70-79 age group but not the 80+ age group. Similarly, the odds of mobility impairment were greater in women than men only in the 70-79 age group (70-79 age group, odds ratio [OR]age-adjusted = 1.78, 95% confidence interval [CI] = 1.03, 3.08, p = .038; 80+ age group, ORage-adjusted = 1.05, 95% CI = 0.52, 2.15, p = .89). Accounting for muscle energetics attenuated up to 75% of the greater odds of mobility impairment in women. Women had lower muscle mitochondrial energetics compared to men, which largely explain their greater odds of lower-extremity mobility impairment.

Mother's Curse effects on lifespan and aging

The Mother's Curse hypothesis posits that mothers curse their sons with harmful mitochondria, because maternal mitochondrial inheritance makes selection blind to mitochondrial mutations that harm only males. As a result, mitochondrial function may be evolutionarily optimized for females. This is an attractive explanation for ubiquitous sex differences in lifespan and aging, given the prevalence of maternal mitochondrial inheritance and the established relationship between mitochondria and aging. This review outlines patterns expected under the hypothesis, and traits most likely to be affected, chiefly those that are sexually dimorphic and energy intensive. A survey of the literature shows that evidence for Mother's Curse is limited to a few taxonomic groups, with the strongest support coming from experimental crosses in Drosophila. Much of the evidence comes from studies of fertility, which is expected to be particularly vulnerable to male-harming mitochondrial mutations, but studies of lifespan and aging also show evidence of Mother's Curse effects. Despite some very compelling studies supporting the hypothesis, the evidence is quite patchy overall, with contradictory results even found for the same traits in the same taxa. Reasons for this scarcity of evidence are discussed, including nuclear compensation, factors opposing male-specific mutation load, effects of interspecific hybridization, context dependency and demographic effects. Mother's Curse effects may indeed contribute to sex differences, but the complexity of other contributing factors make Mother's Curse a poor general predictor of sex-specific lifespan and aging.

Sex differences in physiological response to increased neuronal excitability in a knockin mouse model of pediatric epilepsy

BACKGROUND

Epilepsy is a common neurological disease; however, few if any of the currently marketed antiseizure medications prevent or cure epilepsy. Discovery of pathological processes in the early stages of epileptogenesis has been challenging given the common use of preclinical models that induce seizures in physiologically normal animals. Moreover, despite known sex dimorphism in neurological diseases, females are rarely included in preclinical epilepsy models.

METHODS

We characterized sex differences in mice carrying a pathogenic knockin variant (p.N1768D) in the Scn8a gene that causes spontaneous tonic-clonic seizures (TCs) at ∼3 months of age and found that heterozygous females are more resilient than males in mortality and morbidity. To investigate the cellular mechanisms that underlie female resilience, we utilized blood-brain barrier (BBB) and hippocampal transcriptomic analyses in heterozygous mice before seizure onset (pre-TC) and in mice that experienced ∼20 TCs (post-TC).

RESULTS

In the pre-TC latent phase, both sexes exhibited leaky BBB; however, patterns of gene expression were sexually dimorphic. Females exhibited enhanced oxidative phosphorylation and protein biogenesis, while males activated gliosis and CREB signaling. After seizure onset (chronic phase), females exhibited a metabolic switch to lipid metabolism, while males exhibited increased gliosis and BBB dysfunction and a strong activation of neuroinflammatory pathways.

CONCLUSION

The results underscore the central role of oxidative stress and BBB permeability in the early stages of epileptogenesis, as well as sex dimorphism in response to increasing neuronal hyperexcitability. Our results also highlight the need to include both sexes in preclinical studies to effectively translate results of drug efficacy studies.

Neuroprotection or Sex Bias: A Protective Response to Traumatic Brain Injury in the Females

Traumatic brain injury (TBI) is a major healthcare problem and a common cause of mortality and morbidity. Clinical and preclinical research suggests sex-related differences in short- and longterm outcomes following TBI; however, males have been the main focus of TBI research. Females show a protective response against TBI. Female animals in preclinical studies and women in clinical trials have shown comparatively better outcomes against mild, moderate, or severe TBI. This reflects a favorable protective nature of the females compared to the males, primarily attributed to various protective mechanisms that provide better prognosis and recovery in the females after TBI. Understanding the sex difference in the TBI pathophysiology and the underlying mechanisms remains an elusive goal. In this review, we provide insights into various mechanisms related to the anatomical, physiological, hormonal, enzymatic, inflammatory, oxidative, genetic, or mitochondrial basis that support the protective nature of females compared to males. Furthermore, we sought to outline the evidence of multiple biomarkers that are highly potential in the investigation of TBI's prognosis, pathophysiology, and treatment and which can serve as objective measures and novel targets for individualized therapeutic interventions in TBI treatment. Implementations from this review are important for the understanding of the effect of sex on TBI outcomes and possible mechanisms behind the favorable response in females. It also emphasizes the critical need to include females as a biological variable and in sufficient numbers in future TBI studies.

Sex differences in frailty among older adults

By definition, aging is a natural, gradual and continuous process. On the other hand, frailty reflects the increase in vulnerability to stressors and shortens the time without disease (health span) while longevity refers to the length of life (lifespan). The average life expectancy has significantly increased during the last few decades. A longer lifespan has been accompanied by an increase in frailty and decreased independence in older adults, with major differences existing between men and women. For example, women tend to live longer than men but also experience higher rates of frailty and disability. Sex differences prevent optimization of lifestyle interventions and therapies to effectively prevent frailty. Sex differences in frailty and aging are rooted in a complex interplay between uncontrollable (genetic, epigenetic, physiological), and controllable factors (psychosocial and lifestyle factors). Thus, understanding the underlying causes of sex differences in frailty and aging is essential for developing personalized interventions to promote healthy aging and improve quality of life in older men and women. In this review, we have discussed the key contributors and knowledge gaps related to sex differences in aging and frailty.

Sex difference of pre- and post-natal exposure to six developmental neurotoxicants on intellectual abilities: a systematic review and meta-analysis of human studies

BACKGROUND

Early life exposure to lead, mercury, polychlorinated biphenyls (PCBs), polybromide diphenyl ethers (PBDEs), organophosphate pesticides (OPPs), and phthalates have been associated with lowered IQ in children. In some studies, these neurotoxicants impact males and females differently. We aimed to examine the sex-specific effects of exposure to developmental neurotoxicants on intelligence (IQ) in a systematic review and meta-analysis.

METHOD

We screened abstracts published in PsychINFO and PubMed before December 31st, 2021, for empirical studies of six neurotoxicants (lead, mercury, PCBs, PBDEs, OPPs, and phthalates) that (1) used an individualized biomarker; (2) measured exposure during the prenatal period or before age six; and (3) provided effect estimates on general, nonverbal, and/or verbal IQ by sex. We assessed each study for risk of bias and evaluated the certainty of the evidence using Navigation Guide. We performed separate random effect meta-analyses by sex and timing of exposure with subgroup analyses by neurotoxicant.

RESULTS

Fifty-one studies were included in the systematic review and 20 in the meta-analysis. Prenatal exposure to developmental neurotoxicants was associated with decreased general and nonverbal IQ in males, especially for lead. No significant effects were found for verbal IQ, or postnatal lead exposure and general IQ. Due to the limited number of studies, we were unable to analyze postnatal effects of any of the other neurotoxicants.

CONCLUSION

During fetal development, males may be more vulnerable than females to general and nonverbal intellectual deficits from neurotoxic exposures, especially from lead. More research is needed to examine the nuanced sex-specific effects found for postnatal exposure to toxic chemicals.

Skeletal muscle energetics explain the sex disparity in mobility impairment in the Study of Muscle, Mobility and Aging (SOMMA)

The age-related decline in muscle mitochondrial energetics contributes to the loss of mobility in older adults. Women experience a higher prevalence of mobility impairment compared to men, but it is unknown whether sex-specific differences in muscle energetics underlie this disparity. In the Study of Muscle, Mobility and Aging (SOMMA), muscle energetics were characterized using in vivo phosphorus-31 magnetic resonance spectroscopy and high-resolution respirometry of vastus lateralis biopsies in 773 participants (56.4% women, age 70-94 years). A Short Physical Performance Battery score ≤ 8 was used to define lower-extremity mobility impairment. Muscle mitochondrial energetics were lower in women compared to men (e.g. Maximal Complex I&II OXPHOS: Women=55.06 +/- 15.95; Men=65.80 +/- 19.74; p<0.001) and in individuals with mobility impairment compared to those without (e.g., Maximal Complex I&II OXPHOS in women: SPPB≥9=56.59 +/- 16.22; SPPB≤8=47.37 +/- 11.85; p<0.001). Muscle energetics were negatively associated with age only in men (e.g., Maximal ETS capacity: R=-0.15, p=0.02; age/sex interaction, p=0.04), resulting in muscle energetics measures that were significantly lower in women than men in the 70-79 age group but not the 80+ age group. Similarly, the odds of mobility impairment were greater in women than men only in the 70-79 age group (70-79 age group, OR age-adjusted =1.78, 95% CI=1.03, 3.08, p=0.038; 80+ age group, OR age-adjusted =1.05, 95% CI=0.52, 2.15, p=0.89). Accounting for muscle energetics attenuated up to 75% of the greater odds of mobility impairment in women. Women had lower muscle mitochondrial energetics compared to men, which largely explain their greater odds of lower-extremity mobility impairment.

Sex-specific lung inflammation and mitochondrial damage in a model of electronic cigarette exposure in asthma

The prevalence of electronic cigarette (EC) use among adult with asthma has continued to increase over time, in part due to the belief of being less harmful than smoking. However, the extent of their toxicity and the involved mechanisms contributing to the deleterious impact of EC exposure on patients with preexisting asthma have not been delineated. In the present project, we tested the hypothesis that EC use contributes to respiratory damage and worsening inflammation in the lungs of patients with asthma. To define the consequences of EC exposure in established asthma, we used a mouse model with/without preexisting asthma for short-term exposure to EC aerosols. C57/BL6J mice were sensitized and challenged with a DRA (dust mite, ragweed, Aspergillus fumigates, 200 µg/mL) mixture and exposed daily to EC with nicotine (2% nicotine in 30:70 propylene glycol: vegetable glycerin) or filtered air for 2 wk. The mice were evaluated at 24 h after the final EC exposure. After EC exposure in asthmatic mice, lung inflammatory cell infiltration and goblet cell hyperplasia were increased, whereas EC alone did not cause airway inflammation. Our data also show that mitochondrial DNA (mtDNA) content and a key mtDNA regulator, mitochondrial transcription factor A (TFAM), are reduced in asthmatic EC-exposed mice in a sex-dependent manner. Together, these results indicate that TFAM loss in lung epithelium following EC contributes to male-predominant sex pathological differences, including mitochondrial damage, inflammation, and remodeling in asthmatic airways.NEW & NOTEWORTHY Respiratory immunity is dysregulated in preexisting asthma, and further perturbations by EC use could exacerbate asthma severity. However, the extent of their toxicity and the involved mechanisms contributing to the deleterious impact of EC exposure on patients with preexisting asthma have not been delineated. We found that EC has unique biological impacts in lungs and potential sex differences with loss of TFAM, a key mtDNA regulator, in lung epithelial region from our animal EC study.

Mitochondrial health index correlates with plasma circulating cell-free mitochondrial DNA in bipolar disorder

Although mitochondrial dysfunction is known to play an essential role in the pathophysiology of bipolar disorder (BD), there is a glaring gap in our understanding of how mitochondrial dysfunction can modulate clinical phenotypes. An emerging paradigm suggests mitochondria play an important non-energetic role in adaptation to stress, impacting cellular resilience and acting as a source of systemic allostatic load. Known as mitochondrial allostatic load, this (phenomenon) occurs when mitochondria are unable to recalibrate and maintain cell homeostasis. This study aimed to evaluate the composite mitochondrial health index (MHI) in BD subjects and non-psychiatry controls. We will also explore whether lower MIH will be related to higher cell-free mtDNA (ccf-mtDNA) levels and poor clinical outcomes. In this study, 14 BD-I patients and 16 age- and sex-matched non-psychiatry controls were enrolled. Peripheral blood mononuclear cells (PBMCs) were used to measure the enzymatic activities of citrate synthase and complexes I, II, and IV and mtDNA copy number. Ccf-mtDNA was evaluated by qPCR in plasma. Mitochondrial quality control (MQC) proteins were evaluated by western blotting. After adjusting for confounding variables, such as age, sex, body mass index (BMI), and smoking status, patients with BD presented lower MHI compared to non-psychiatry controls, as well as higher ccf-mtDNA levels that negatively correlated with MHI. Because the MQC network is essential to maintain mitochondrial health, MHI and ccf-mtDNA were also examined in relation to several MQC-related proteins, such as Fis-1, Opa-1, and LC3. Our results showed that MHI correlated negatively with Fis-1 and positively with Opa-1 and LC3. Accordingly, ccf-mtDNA had a positive correlation with Fis-1 and a negative correlation with Opa-1 and LC3. Furthermore, we found a noteworthy inverse correlation between illness severity and MHI, with lower MHI and higher ccf-mtDNA levels in subjects with a longer illness duration, worse functional status, and higher depressive symptoms. Our findings indicate that mitochondrial allostatic load contributes to BD, suggesting mitochondria represent a potential biological intersection point that could contribute to impaired cellular resilience and increased vulnerability to stress and mood episodes. Ultimately, by linking mitochondrial dysfunction to disease progression and poor outcomes, we might be able to build a predictive marker that explains how mitochondrial function and its regulation contribute to BD development and that may eventually serve as a treatment guide for both old and new therapeutic targets.

Evaluation of heterogeneity in effect of therapeutic hypothermia by sex among infants with neonatal encephalopathy

BACKGROUND

Our objective was to examine heterogeneity in the effect of therapeutic hypothermia by sex in infants with moderate or severe neonatal encephalopathy.

METHODS

We conducted a post hoc analysis of the Induced Hypothermia trial, which included infants born at gestational ages ≥36 weeks, admitted at ≤6 postnatal hours with evidence of severe acidosis or perinatal complications and moderate or severe neonatal encephalopathy. Multivariate modified Poisson regression models were used to compare the treatment effect of whole-body hypothermia versus control, with an evaluation of interaction by sex, on the primary outcome of death or moderate or severe disability at 18-22 months of corrected age.

RESULTS

A total of 101 infants (51 male, 50 female) were randomly assigned to hypothermia treatment and 104 infants (64 male, 40 female) to control. The primary outcome occurred in 45% of the hypothermia group and 63% of the control group (RR 0.73; 95% CI 0.56, 0.94). There was no significant difference (interaction P = 0.50) in the treatment effect of hypothermia on the primary outcome between females (RR 0.79; 95% CI 0.54, 1.17) compared to males (RR 0.63; 95% CI 0.44, 0.91).

CONCLUSION

We found no evidence that sex influences the treatment effect of hypothermia in infants with moderate or severe neonatal encephalopathy.

IMPACT

Preclinical evidence suggests a differential effect in response to cooling treatment of hypoxic-ischemic injury between males and females. We found no evidence of heterogeneity in the treatment effect of whole-body hypothermia by sex in this post hoc subgroup analysis of infants with moderate or severe neonatal encephalopathy from the National Institute of Child Health and Human Development Neonatal Research Network Induced Hypothermia trial.

The mitoepigenome responds to stress, suggesting novel mito-nuclear interactions in vertebrates

The mitochondria are central in the cellular response to changing environmental conditions resulting from disease states, environmental exposures or normal physiological processes. Although the influences of environmental stressors upon the nuclear epigenome are well characterized, the existence and role of the mitochondrial epigenome remains contentious. Here, by quantifying the mitochondrial epigenomic response of pineal gland cells to circadian stress, we confirm the presence of extensive cytosine methylation within the mitochondrial genome. Furthermore, we identify distinct epigenetically plastic regions (mtDMRs) which vary in cytosinic methylation, primarily in a non CpG context, in response to stress and in a sex-specific manner. Motifs enriched in mtDMRs contain recognition sites for nuclear-derived DNA-binding factors (ATF4, HNF4A) important in the cellular metabolic stress response, which we found to be conserved across diverse vertebrate taxa. Together, these findings suggest a new layer of mito-nuclear interaction in which the nuclear metabolic stress response could alter mitochondrial transcriptional dynamics through the binding of nuclear-derived transcription factors in a methylation-dependent context.

Prospective network analysis of proinflammatory proteins, lipid markers, and depression components in midlife community women

BACKGROUND

Vulnerability theories propose that suboptimal levels of lipid markers and proinflammatory proteins predict future heightened depression. Scar models posit the reverse association. However, most studies that tested relationships between non-specific immune/endocrine markers and depression did not separate temporal inferences between people and within-person and how different immunometabolism markers related to unique depression symptoms. We thus used cross-lagged prospective network analyses (CLPN) to investigate this topic.

METHODS

Community midlife women (n = 2224) completed the Center for Epidemiologic Studies-Depression scale and provided biomarker samples across five time-points spanning 9 years. CLPN identified significant relations (edges) among components (nodes) of depression (depressed mood, somatic symptoms, interpersonal issues), lipid markers [insulin, fasting glucose, triglycerides, low-density lipoprotein-cholesterol (LDL), high-density lipoprotein-cholesterol (HDL)], and proinflammatory proteins [C-reactive protein (CRP), fibrinogen], within and across time-points. All models adjusted for age, estradiol, follicle-stimulating hormone, and menopausal status.

RESULTS

In within-person temporal networks, higher CRP and HDL predicted all three depression components (d = 0.131-2.112). Increased LDL preceded higher depressed mood and interpersonal issues (v. somatic symptoms) (d = 0.251-0.327). Elevated triglycerides predicted more somatic symptoms (v. depressed mood and interpersonal problems) (d = 0.131). More interpersonal problems forecasted elevated fibrinogen and LDL levels (d = 0.129-0.331), and stronger somatic symptoms preceded higher fibrinogen levels (d = 0.188).

CONCLUSIONS

Results supported both vulnerability and scar models. Long-term dysregulated immunometabolism systems, social disengagement, and related patterns are possible mechanistic accounts. Cognitive-behavioral therapies that optimize nutrition and physical activity may effectively target depression.

Succinate prodrugs as treatment for acute metabolic crisis during fluoroacetate intoxication in the rat

Sodium fluoroacetate (FA) is a metabolic poison that systemically inhibits the tricarboxylic acid (TCA) cycle, causing energy deficiency and ultimately multi-organ failure. It poses a significant threat to society because of its high toxicity, potential use as a chemical weapon and lack of effective antidotal therapy. In this study, we investigated cell-permeable succinate prodrugs as potential treatment for acute FA intoxication. We hypothesized that succinate prodrugs would bypass FA-induced mitochondrial dysfunction, provide metabolic support, and prevent metabolic crisis during acute FA intoxication. To test this hypothesis, rats were exposed to FA (0.75 mg/kg) and treated with the succinate prodrug candidate NV354. Treatment efficacy was evaluated based on cardiac and cerebral mitochondrial respiration, mitochondrial content, metabolic profiles and tissue pathology. In the heart, FA increased concentrations of the TCA metabolite citrate (+ 4.2-fold, p < 0.01) and lowered ATP levels (- 1.9-fold, p < 0.001), confirming the inhibition of the TCA cycle by FA. High-resolution respirometry of cardiac mitochondria further revealed an impairment of mitochondrial complex V (CV)-linked metabolism, as evident by a reduced phosphorylation system control ratio (- 41%, p < 0.05). The inhibition of CV-linked metabolism is a novel mechanism of FA cardiac toxicity, which has implications for drug development and which NV354 was unable to counteract at the given dose. In the brain, FA induced the accumulation of β-hydroxybutyrate (+ 1.4-fold, p < 0.05) and the reduction of mitochondrial complex I (CI)-linked oxidative phosphorylation (OXPHOSCI) (- 20%, p < 0.01), the latter of which was successfully alleviated by NV354. This promising effect of NV354 warrants further investigations to determine its potential neuroprotective effects.

Progranulin deficiency results in sex-dependent alterations in microglia in response to demyelination

Heterozygous mutations in the granulin (GRN) gene, resulting in the haploinsufficiency of the progranulin (PGRN) protein, is a leading cause of frontotemporal lobar degeneration (FTLD). Complete loss of the PGRN protein causes neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disorder. Polymorphisms in the GRN gene have also been associated with several other neurodegenerative diseases, including Alzheimer's disease (AD), and Parkinson's disease (PD). PGRN deficiency has been shown to cause myelination defects previously, but how PGRN regulates myelination is unknown. Here, we report that PGRN deficiency leads to a sex-dependent myelination defect with male mice showing more severe demyelination in response to cuprizone treatment. This is accompanied by exacerbated microglial proliferation and activation in the male PGRN-deficient mice. Interestingly, both male and female PGRN-deficient mice show sustained microglial activation after cuprizone removal and a defect in remyelination. Specific ablation of PGRN in microglia results in similar sex-dependent phenotypes, confirming a microglial function of PGRN. Lipid droplets accumulate in microglia specifically in male PGRN-deficient mice. RNA-seq analysis and mitochondrial function assays reveal key differences in oxidative phosphorylation in male versus female microglia under PGRN deficiency. A significant decrease in myelination and accumulation of myelin debris and lipid droplets in microglia were found in the corpus callosum regions of FTLD patients with GRN mutations. Taken together, our data support that PGRN deficiency leads to sex-dependent alterations in microglia with subsequent myelination defects.

Mitochondrial Health Index Correlates with Plasma Circulating Cell-Free Mitochondrial DNA in Bipolar Disorder

Background: Although mitochondria dysfunction is known to play an essential role in the pathophysiology of bipolar disorder (BD), there is a glaring gap in our understanding of how mitochondrial dysfunction can modulate clinical phenotypes. This study aimed to evaluate the composite mitochondrial health index (MHI) in BD subjects and non-psychiatry controls (Non-psychiatry controls). We will also explore whether lower MIH will be related to higher cell-free mtDNA (ccf-mtDNA) levels and poor clinical outcomes. Methods: Fourteen BD-I patients and 16 age- and sex-matched non-psychiatry controls were enrolled for this study. Peripheral blood mononuclear cells (PBMCs) were used to measure the enzymatic activities of citrate synthase and complexes I, II, and IV and mtDNA copy number. ccf-mtDNA was evaluated by qPCR in plasma. Mitochondrial quality control (MQC) proteins were evaluated by western blotting. Results: One-Way ANCOVA after controlling for age, sex, body mass index (BMI), and smoking status showed that patients with BD present a decrease in the MHI compared to non-psychiatry controls, and higher ccf-mtDNA levels, which was negatively correlated with MHI. Because the MQC network is essential to maintain mitochondrial health, we also evaluated the relationship between MQC-related proteins with MHI and ccf-mtDNA. Our results showed that MHI negatively correlated with Fis-1 and positively with Opa-1 and LC3. Moreover, we found a negative correlation between ccf-mtDNA, Opa-1, and LC3 and a positive correlation between cff-mtDNA and Fis-1. Finally, we found that subjects with longer illness duration, higher depressive symptom scores, and worse functional status had lower MHI and higher ccf-mtDNA. Conclusion: In summary, the present findings corroborate previous studies and provide strong support for the hypothesis that mitochondrial regulation and function are integral parts of the pathogenesis of BD.

Blood immune cells from people with HIV on antiviral regimens that contain tenofovir alafenamide (TAF) and tenofovir disoproxil fumarate (TDF) have differential metabolic signatures

BACKGROUND

Mitochondria regulate immune and organ function. It is unknown whether higher intracellular drug levels observed in peripheral blood mononuclear cells (PBMCs) treated with tenofovir alafenamide (TAF) compared to tenofovir disoproxil fumarate (TDF) may alter mitochondrial function and energy production in immune cells in HIV(+) patients.

METHODS

Cellular bioenergetics were determined in PBMCs from HIV-1(-) participants exposed to TAF versus TDF in vitro, at a comparable concentration to a clinically relevant plasma exposure. A decrease in cellular oxygen consumption rate (OCR) at baseline (basal-OCR) and under cellular stress (max-OCR) may suggest mitochondrial dysfunction. We also assessed the in vivo impact of TAF vs TDF on OCR in PBMCs from 26 people with HIV (PWH) interchanged from TDF-based to TAF-based antiretroviral therapy (ART) over a 9-month period in the setting of an open label clinical trial. The Wilcoxon and Mann Whitney tests were used for comparison of continuous variables.

RESULTS

PBMCs from HIV-1(-) participants exposed in vitro to a concentration of 0.12-3.3 μM for TAF and TDF at 2 and 24 h, reduced basal and maximal OCR compared to vehicle control. Switch studies of antivirals (TAF vs TDF) within the same PWH showed that TAF-based ART was associated with reduced OCR compared to TDF-based ART in PBMCs. We observed that TAF-treated PBMCs selectively relied more on glucose/pyruvate supply rather than fatty acid to fuel their mitochondria.

CONCLUSIONS

Compared to TDF, TAF may alter bioenergetics in immune cells from PWH in vitro and in vivo. The clinical significance in terms of the differential impact caused by TAF versus TDF on mitochondrial function and energy production in immune cells, a regulator of immune function, requires further studied in HIV, preexposure prophylaxis and hepatitis B.

Pre and postnatal exposure to 900 MHz electromagnetic fields induce inflammation and oxidative stress, and alter renin-angiotensin system components differently in male and female offsprings

AIMS

This study was designed to investigate inflammation, oxidative stress and renin-angiotensin system components in brain and kidney tissues of female and male rats prenatally and/or postnatally exposed to 900 MHz electromagnetic field (EMF). It is aimed to evaluate the biological effects of 900 MHz EMF exposure due to the increase in mobile phone use and especially the more widespread use of the GSM 900 system.

MAIN METHODS

Male and female Wistar albino offsprings were divided into four groups of control, prenatal, postnatal, and prenatal+postnatal exposed to 900 MHz EMF for 1 h/day (23 days during pregnancy for prenatal period, 40 days for postnatal period). The brain and kidney tissues were collected when they reached puberty.

KEY FINDINGS

It was found that the total oxidant status, IL-2, IL-6, and TNF-α levels increased (p < 0.001) and the total antioxidant status levels decreased (p < 0.001) in all three EMF groups comparing to controls in both male and female brain and kidney tissues. The renin- angiotensin system components such as angiotensinogen, renin, angiotensin type 1 and type 2 receptors, and MAS1-like G protein-coupled receptor expression were higher (p < 0.001) in all three EMF exposure groups comparing to controls in both male and female brain and kidney tissues. Although there are some differences of the levels of proinflammatory markers, ROS components and RAS components in brain and kidney tissues between males and females, the common result of all groups was increase in oxidative stress, inflammation markers and angiotensin system components with exposure to 900 MHz EMF.

SIGNIFICANCE

In conclusion, our study suggested that the 900 MHz EMF can activate brain and kidney renin-angiotensin system, and this activation is maybe related to inflammation and oxidative stress in both male and female offsprings.

Influence of sex, age and diabetes on brain transcriptome and proteome modifications following cerebral ischemia

Ischemic stroke is a major cause of death and disability worldwide. Translation into the clinical setting of neuroprotective agents showing promising results in pre-clinical studies has systematically failed. One possible explanation is that the animal models used to test neuroprotectants do not properly represent the population affected by stroke, as most of the pre-clinical studies are performed in healthy young male mice. Therefore, we aimed to determine if the response to cerebral ischemia differed depending on age, sex and the presence of comorbidities. Thus, we explored proteomic and transcriptomic changes triggered during the hyperacute phase of cerebral ischemia (by transient intraluminal middle cerebral artery occlusion) in the brain of: (1) young male mice, (2) young female mice, (3) aged male mice and (4) diabetic young male mice. Moreover, we compared each group's proteomic and transcriptomic changes using an integrative enrichment pathways analysis to disclose key common and exclusive altered proteins, genes and pathways in the first stages of the disease. We found 61 differentially expressed genes (DEG) in male mice, 77 in females, 699 in diabetics and 24 in aged mice. Of these, only 14 were commonly dysregulated in all groups. The enrichment pathways analysis revealed that the inflammatory response was the biological process with more DEG in all groups, followed by hemopoiesis. Our findings indicate that the response to cerebral ischemia regarding proteomic and transcriptomic changes differs depending on sex, age and comorbidities, highlighting the importance of incorporating animals with different phenotypes in future stroke research studies.

Mitochondrial transplantation against gentamicin-induced toxicity on rat renal proximal tubular cells: the higher activity of female rat mitochondria

Mitochondrial dysfunction is a fundamental mechanism leading to drug nephrotoxicity, such as gentamicin-induced nephrotoxicity. Mitochondrial therapy (mitotherapy) or exogenous mitochondria transplantation is a method that can be used to replace dysfunctional mitochondria with healthy mitochondria. This method can help in the treatment of diseases related to mitochondria. In this research, we studied the transplantation effect of freshly isolated mitochondria on the toxicity induced by gentamicin on renal proximal tubular cells (RPTCs). Furthermore, possible gender-related effects on supplying exogenous rat kidney mitochondria on gentamicin-induced RPTCs were investigated. At first, the normality and proper functioning of fresh mitochondria were assessed by measuring mitochondrial succinate dehydrogenase activity (SDH) and changes in mitochondrial membrane potential (MMP). Then, the protective effects of mitochondrial transplantation against gentamicin-induced mitochondrial toxicity were evaluated through parameters including lactate dehydrogenase (LDH) leakiness, reactive oxygen species (ROS) production, lipid peroxidation (LPO) content, reduced glutathione (GSH) level, extracellular oxidized glutathione (GSSG) level, ATP level, MMP collapse, and caspase-3 activity. According to the statistical analysis, transplanting the healthy mitochondria decreased the cytotoxicity, ROS production, MMP collapse, LPO content, GSSG levels, and caspase-3 activity caused by gentamicin in RPTCs. Also, it has caused an increase in the level of ATP and GSH in the RPTCs. Furthermore, higher preventive effects were observed for the female group. According to the current study, mitochondrial transplantation is a potent therapeutic method in xenobiotic-caused nephrotoxicity.

Porcine blood cell and brain tissue energy metabolism: Effects of "early life stress"

Background: Early Life Stress (ELS) may exert long-lasting biological effects, e.g., on PBMC energy metabolism and mitochondrial respiration. Data on its effect on brain tissue mitochondrial respiration is scarce, and it is unclear whether blood cell mitochondrial activity mirrors that of brain tissue. This study investigated blood immune cell and brain tissue mitochondrial respiratory activity in a porcine ELS model. Methods: This prospective randomized, controlled, animal investigation comprised 12 German Large White swine of either sex, which were weaned at PND (postnatal day) 28-35 (control) or PND21 (ELS). At 20-24 weeks, animals were anesthetized, mechanically ventilated and surgically instrumented. We determined serum hormone, cytokine, and "brain injury marker" levels, superoxide anion (O₂ ^•¯) formation and mitochondrial respiration in isolated immune cells and immediate post mortem frontal cortex brain tissue. Results: ELS animals presented with higher glucose levels, lower mean arterial pressure. Most determined serum factors did not differ. In male controls, TNFα and IL-10 levels were both higher than in female controls as well as, no matter the gender in ELS animals. MAP-2, GFAP, and NSE were also higher in male controls than in the other three groups. Neither PBMC routine respiration and brain tissue oxidative phosphorylation nor maximal electron transfer capacity in the uncoupled state (ETC) showed any difference between ELS and controls. There was no significant relation between brain tissue and PBMC, ETC, or brain tissue, ETC, and PBMC bioenergetic health index. Whole blood O₂ ^•¯ concentrations and PBMC O₂ ^•¯ production were comparable between groups. However, granulocyte O₂ ^•¯ production after stimulation with E. coli was lower in the ELS group, and this effect was sex-specific: increased O₂ ^•¯ production increased upon stimulation in all control animals, which was abolished in the female ELS swine. Conclusion: This study provides evidence that ELS i) may, gender-specifically, affect the immune response to general anesthesia as well as O₂ ^•¯ radical production at sexual maturity, ii) has limited effects on brain and peripheral blood immune cell mitochondrial respiratory activity, and iii) mitochondrial respiratory activity of peripheral blood immune cells and brain tissue do not correlate.

Reactive oxygen species-responsive HET0016 prodrug-loaded liposomes attenuate neuroinflammation and improve neurological deficit in a rat model of juvenile traumatic brain injury

The arachidonic acid pathway metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to ischemia/reperfusion brain injury. Inhibition of 20-HETE formation can protect the developing brain from global ischemia. In previous studies, we have found that treatment with the 20-HETE synthesis inhibitor N-hydroxy-N-4-butyl-2-methylphenylformamidine (HET0016) can protect the immature brain from traumatic brain injury (TBI), but its hydrophobic nature limits its full potential. We designed a reactive oxygen species-responsive HET0016 prodrug, which consists of a thioketal link between HET0016 and stearyl alcohol (HET-TK-SA), and used the nanoprodrug strategy to successfully synthesize liposomes HET0016 prodrug liposomes (HPLs) to facilitate the application of HET0016 in protection from TBI. HPLs demonstrated spherical shape, size of about 127.8 nm, a zeta potential of -28.8 mv, a narrow particle size distribution and good stability. Male rats at postnatal day 16-17 underwent controlled cortical impact (CCI) followed by intravenous injection with vehicle or HET0016 (1 mg/kg, 2 h post-injury, once/day for 3 days). The results of the in vivo demonstrated that HPLs has good biosafety and can pass through the blood-brain barrier. Not only that compared with HET0016, HPLs better-inhibited inflammation and improved neuronal degeneration, which further led to lesion volume reduction, upgraded behavioral task performance, and ameliorated the degree of TBI impairment. Our results demonstrated HPLs could be a new strategy for juvenile TBI therapy.

Alpha1-antitrypsin protects the immature mouse brain following hypoxic-ischemic injury

Introduction: Preterm brain injury often leads to lifelong disabilities affecting both cognitive and motor functions, and effective therapies are limited. Alpha1-antitrypsin (AAT), an endogenous inhibitor of serine proteinases with anti-inflammatory, anti-apoptotic, and cytoprotective properties, might be beneficial in treating preterm brain injury. The aim of this study was to investigate whether AAT has neuroprotective effects in a mouse preterm brain injury model. Methods: Preterm brain injury was induced on postnatal day 5, and mouse pups' right common carotid arteries were cut between two ligations followed by hypoxia induction. Brain injury was evaluated through immunohistochemistry staining and magnetic resonance imaging. Fluoro-Jade B and immunohistochemistry staining were performed to investigate the neuronal cell death and blood-brain barrier (BBB) permeability. The motor function and anxiety-like behaviors were revealed by CatWalk gait analysis and the open field test. Results: After hypoxia-ischemia (HI) insult, brain injury was alleviated by AAT treatment, and this was accompanied by reduced BBB permeability, reduced neuronal cell death and caspase-3 activation, and inhibition of microglia activation. In addition, AAT administration significantly improved HI-induced motor function deficiencies in mice. The neuroprotective effect of AAT was more pronounced in male mice. Conclusion: AAT treatment is neuroprotective against preterm brain injury in neonatal mice, and the effect is more pronounced in males.

The Effect of Donor Rat Gender in Mitochondrial Transplantation Therapy of Cisplatin-Induced Toxicity on Rat Renal Proximal Tubular Cells

Background

Cisplatin-induced nephrotoxicity has been linked to a fundamental mechanism of mitochondrial dysfunction. A treatment called mitochondrial transplantation therapy can be used to replace damaged mitochondria with healthy mitochondria. Mitochondrial-related diseases may benefit from this approach.

Objectives

We investigated the effect of mitochondrial transplantation on cisplatin-induced nephrotoxicity using freshly isolated mitochondria obtained from renal proximal tubular cells (RPTCs).

Methods

Based on our previous findings, we hypothesized that direct exposure of healthy mitochondria to cisplatin-affected RPTCs might improve cytotoxicity markers and restore mitochondrial function. Therefore, the primary objective of this study was to determine whether newly isolated mitochondrial transplantation protected RPTCs from cisplatin-induced cytotoxicity. The supply of exogenous rat kidney mitochondria to cisplatin-affected RPTCs was also a goal of this study to investigate the possibility of gender differences. After the addition of cisplatin (100 µM), rat RPTCs (106 cells/mL) were suspended in Earle's solution (pH = 7.4) at 37°C for two hours. Freshly isolated mitochondria were extracted at 4°C and diluted in 100 and 200 µg/mL mitochondrial protein.

Results

Statistical analysis revealed that transplantation of healthy mitochondria decreased ROS level, mitochondrial membrane potential (MMP) collapse, MDA level, glutathione depletion, lysosomal membrane damage, and caspase-3 activity induced by cisplatin in rat RPTCs. In addition, our results demonstrated that transplantation of female rat kidney mitochondria has higher protective activity at reducing toxicity parameters than male mitochondria.

Conclusions

The findings reaffirmed that mitochondrial transplantation is a novel, potential, and promising therapeutic strategy for xenobiotic-induced nephrotoxicity.

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.

Female and male C57BL/6J offspring exposed to maternal obesogenic diet develop altered hypothalamic energy metabolism in adulthood

Maternal obesity is exceedingly common and strongly linked to offspring obesity and metabolic disease. Hypothalamic function is critical to obesity development. Hypothalamic mechanisms causing obesity following exposure to maternal obesity have not been elucidated. Therefore, we studied a cohort of C57BL/6J dams, treated with a control or high-fat-high-sugar diet, and their adult offspring to explore potential hypothalamic mechanisms to explain the link between maternal and offspring obesity. Dams treated with obesogenic diet were heavier with mild insulin resistance, which is reflective of the most common metabolic disease in pregnancy. Adult offspring exposed to maternal obesogenic diet had no change in body weight but significant increase in fat mass, decreased glucose tolerance, decreased insulin sensitivity, elevated plasma leptin, and elevated plasma thyroid-stimulating hormone. In addition, offspring exposed to maternal obesity had decreased energy intake and activity without change in basal metabolic rate. Hypothalamic neurochemical profile and transcriptome demonstrated decreased neuronal activity and inhibition of oxidative phosphorylation. Collectively, these results indicate that maternal obesity without diabetes is associated with adiposity and decreased hypothalamic energy production in offspring. We hypothesize that altered hypothalamic function significantly contributes to obesity development. Future studies focused on neuroprotective strategies aimed to improve hypothalamic function may decrease obesity development.NEW & NOTEWORTHY Offspring exposed to maternal diet-induced obesity demonstrate a phenotype consistent with energy excess. Contrary to previous studies, the observed energy phenotype was not associated with hyperphagia or decreased basal metabolic rate but rather decreased hypothalamic neuronal activity and energy production. This was supported by neurochemical changes in the hypothalamus as well as inhibition of hypothalamic oxidative phosphorylation pathway. These results highlight the potential for neuroprotective interventions in the prevention of obesity with fetal origins.

Role of Vitamin E in Neonatal Neuroprotection: A Comprehensive Narrative Review

Vitamin E (Vit E) is an essential lipophilic antioxidant and anti-inflammatory agent that has potential as a neuroprotectant in newborn infants with brain injury. Vit E has shown promise in many in vitro studies, but success in translation to in vivo animal studies and the clinical setting has been mixed, with concern of adverse effects at high intravenous doses in preterm infants. However, a recent rise in knowledge of the beneficial effects of fat emulsions containing higher levels of Vit E, along with associated improved outcomes in some neonatal co-morbidities, has led many to reconsider Vit E administration as a potential therapeutic modality to improve neurological outcomes in the setting of neonatal brain injury. This narrative review discusses Vit E's structure, mechanism(s) of action, evidence in animal models, and association with health outcomes in neonates, including both dietary and supplemental Vit E and their bioavailability and pharmacokinetics as it relates to the brain. Lastly, long-term neurodevelopmental outcomes along with gaps in current knowledge are critiqued, which to date suggests that additional translational studies in larger animal models and assessment of safety profiles of different routes and doses of administration should be explored prior to large clinical trials. Importantly, a greater understanding of the brain region(s) and cell type(s) affected by Vit E may help to target the use of Vit E as a beneficial neuroprotective agent to specific populations or types of injury seen in newborns.

Sex specific effects of buprenorphine on behavior, astrocytic opioid receptor expression and neuroinflammation after pediatric traumatic brain injury in mice

Children who suffered traumatic brain injury (TBI) often experience acute and chronic pain, which is linked to a poor quality of life. Buprenorphine (BPN) is commonly used to treat moderate to severe persistent pain in children, however, the efficacy and safety profile of BPN in the pediatric population is still inconclusive. This study investigated the sex-specific effects of BPN on body weight, motor coordination and strength, expression of opioid receptors in the white matter astrocytes, and neuroinflammation in a mouse impact acceleration model of pediatric TBI. Male and female littermates were randomized on postnatal day 20-21(P20-21) into Sham, TBI + saline and TBI + BPN groups. Mice in the TBI + saline and TBI + BPN groups underwent TBI, while the Sham group underwent anesthesia without injury. BPN (0.075 mg/kg) was administered to the TBI + BPN mice at 30 min after injury, and then every 6-12 h for 2 days. Mice in the TBI + saline group received the same amount of saline injections. The impact of BPN on body weight, motor function, opioid receptor expression, and neuroinflammation was evaluated at 1-day (d), 3-d and 7-d post-injury. We found that 1) TBI induced significant weight loss in both males and females. BPN treatment improved weight loss at 3-d post-injury in females. 2) TBI significantly impaired motor coordination and strength. BPN improved motor coordination and strength in both males and females at 1-d and 3-d post-injury. 3) TBI significantly decreased exploration activity at 1-d post-injury in males, and at 7-d post-injury in females, while BPN improved the exploration activity in females. 4) TBI significantly increased mRNA expression of mu-opioid receptors (MOR) at 7-d post-injury in males, but decreased mRNA expression of MOR at 1-d post-injury in females. BPN normalized MOR mRNA expression at 1-d post-injury in females. 5) MOR expression in astrocytes at corpus callosum significantly increased at 7-d post-injury in male TBI group, but significantly decreased at 1-d post-injury in female TBI group. BPN normalized MOR expression in both males and females. 6) TBI significantly increased the mRNA expression of TNF-α, IL-1β, IL-6 and iNOS. BPN decreased mRNA expression of iNOS, and increased mRNA expression of TGF-β1. In conclusion, this study elucidates the sex specific effects of BPN during the acute phase after pediatric TBI, which provides the rationale to assess potential effects of BPN on chronic pathological progressions after pediatric TBI in both males and females.

Females Exhibit Better Cerebral Pressure Autoregulation, Less Mitochondrial Dysfunction, and Reduced Excitotoxicity following Severe Traumatic Brain Injury

The aim of the study was to investigate sex-related differences in intracranial pressure (ICP) dynamics, cerebral pressure autoregulation (PRx55-15), cerebral energy metabolism, and clinical outcome after severe traumatic brain injury (TBI). One-hundred sixty-nine adult TBI patients, treated at the neurointensive care (NIC) unit, at Uppsala University Hospital, 2008-2020, with ICP and cerebral microdialysis (MD) monitoring, were included. Of the 169 TBI patients, 131 (78%) were male and 38 (22%) female. Male patients were more often injured by motor vehicle accidents and less often by bicycle accidents (p < 0.05). There were otherwise no difference in age, neurological status at admission, and types of intracranial hemorrhages between the sexes. The percent of monitoring time with ICP above 20 mmHg and CPP below 60 mmHg were similar for both sexes. Males exhibited more disturbed cerebral pressure autoregulation (PRx55-15 (mean ± SD); 0.28 ± 0.18 vs. 0.17 ± 0.23, p < 0.05) day 1, worse cerebral energy metabolism (MD-lactate-/pyruvate-ratio (median (IQR)); 25 (19-31) vs. 20 (17-25), p < 0.01) and mitochondrial dysfunction (higher burden of MD-LPR > 25 and MD-pyruvate > 120 µM (median (IQR)); 13 (0-58) % vs. 3 (0-17) %, p < 0.05) day 2 to 5, increased excitotoxicity (MD-glutamate median (IQR); 9 (4-32) µM vs. 5 (3-10) µM, p < 0.05) day 2 to 5, and higher biomarker levels of cellular injury (MD-glycerol median (IQR); 103 (66-193) µM vs. 68 (49-106) µM, p < 0.01) most pronounced day 6 to 10. There was no difference in mortality or the degree of favorable outcome between the sexes. Altogether, females exhibited more favorable cerebral physiology post-TBI, particularly better mitochondrial function and reduced excitotoxicity, but this did not translate into better clinical outcome compared to males. Future studies needs to further explore potential sex differences in secondary injury mechanisms in TBI.

The role of sex and pregnancy in multiple sclerosis: what do we know and what should we do?

INTRODUCTION

Multiple sclerosis (MS) is more prevalent in women than in men. The sex of the patient, and pregnancy, are reported to be associated with the clinical features of MS. The mechanism of this is unclear.

AREAS COVERED

This review summarizes data about sex differences in MS and the role of pregnancy. Possible mechanisms for the effects of sex and pregnancy are summarized, and practical suggestions for addressing these issues are provided.

EXPERT OPINION

There is considerable interdependence of the variables that are associated with MS. Men have a worse outcome of MS, and this could be due to the same factors that lead to greater incidence of neurodegenerative disease in men. The possible role of parity on the long-term outcome of MS is of interest. Future studies that look at the mechanisms of the effects of the sex of the patient on the outcome of MS are required. However, there are some actions that can be taken without further research. We can concentrate on public health measures that address the modifiable risk factors for MS and ensure that disease is controlled in women who intend to become pregnant and use appropriate disease modifying agents during pregnancy.

Sex-Specific Catabolic Metabolism Alterations in the Critically Ill following High Dose Vitamin D

Pharmacological interventions are essential for the treatment and management of critical illness. Although women comprise a large proportion of the critically ill, sex-specific pharmacological properties are poorly described in critical care. The sex-specific effects of vitamin D₃ treatment in the critically ill are not known. Therefore, we performed a metabolomics cohort study with 1215 plasma samples from 428 patients from the VITdAL-ICU trial to study sex-specific differences in the metabolic response to critical illness following high-dose oral vitamin D₃ intervention. In women, despite the dose of vitamin D₃ being higher, pharmacokinetics demonstrated a lower extent of vitamin D₃ absorption compared to men. Metabolic response to high-dose oral vitamin D₃ is sex-specific. Sex-stratified individual metabolite associations with elevations in 25(OH)D following intervention showed female-specific positive associations in long-chain acylcarnitines and male-specific positive associations in free fatty acids. In subjects who responded to vitamin D₃ intervention, significant negative associations were observed in short-chain acylcarnitines and branched chain amino acid metabolites in women as compared to men. Acylcarnitines and branched chain amino acids are reflective of fatty acid B oxidation, and bioenergesis may represent notable metabolic signatures of the sex-specific response to vitamin D. Demonstrating sex-specific pharmacometabolomics differences following intervention is an important movement towards the understanding of personalized medicine.

Nanotherapeutics and the Brain

Brain disease remains a significant health, social, and economic burden with a high failure rate of translation of therapeutics to the clinic. Nanotherapeutics have represented a promising area of technology investment to improve drug bioavailability and delivery to the brain, with several successes for nanotherapeutic use for central nervous system disease that are currently in the clinic. However, renewed and continued research on the treatment of neurological disorders is critically needed. We explore the challenges of drug delivery to the brain and the ways in which nanotherapeutics can overcome these challenges. We provide a summary and overview of general design principles that can be applied to nanotherapeutics for uptake and penetration in the brain. We next highlight remaining questions that limit the translational potential of nanotherapeutics for application in the clinic. Lastly, we provide recommendations for ongoing preclinical research to improve the overall success of nanotherapeutics against neurological disease. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Vitamin E Decreases Cytotoxicity and Mitigates Inflammatory and Oxidative Stress Responses in a Ferret Organotypic Brain Slice Model of Neonatal Hypoxia-Ischemia

The gyrencephalic ferret brain is an excellent model in which to study hypoxia-ischemia (HI), a significant contributor to neurological injury in neonates. Vitamin E, an essential fat-soluble antioxidant, reduces oxidative stress and inflammation in both animal models and neonates. The aim of this study was to assess the effects of Vitamin E after oxygen glucose deprivation (OGD) in an organotypic ferret brain slice model of neonatal HI. We hypothesized that Vitamin E would decrease cytotoxicity, inflammation, and oxidative stress in OGD-exposed brain slices. Term-equivalent ferrets were sacrificed at postnatal (P) day 21-23 and 300µM whole hemisphere brain slices were obtained. During a 24h rest period, slices were cultured in either non-treated control conditions or with Erastin, a promotor of oxidative stress. Slices were then exposed to 2h of OGD followed by Vitamin E (25-100 IU/kg), Erastin (10µM) or Ferrostatin (1µM), an inhibitor of ferroptosis. Relative cytotoxicity was determined using an LDH assay, cell death was quantified via nuclear propidium iodide (PI) staining, oxidative stress was quantified via cellular GSH (glutathione) levels and target genes responsive to oxidative stress and inflammation were evaluated by qRT-PCR. OGD increased cytotoxicity, which was significantly reduced by treatment with Vitamin E. Vitamin E also preserved GSH after OGD and decreased amplification of certain markers of oxidative stress (CHAC1, SLC7A11) and inflammation (TNF-alpha, IL-8). Vitamin E remained protective after pretreatment with Erastin and was more protective than Ferrostatin, presumably due to its added anti-inflammatory properties. Results from the ferret whole hemisphere OGD model support the premise that Vitamin E neuroprotection is mediated by restoring GSH and acutely decreasing inflammation and oxidative stress after neonatal HI brain injury.

Dysregulation of mitochondrial dynamics, mitophagy and apoptosis in major depressive disorder: Does inflammation play a role?

Recent studies have suggested that mitochondrial dysfunction and dysregulated neuroinflammatory pathways are involved in the pathophysiology of major depressive disorder (MDD). Here, we aimed to assess the differences in markers of mitochondrial dynamics, mitophagy, general autophagy, and apoptosis in peripheral blood mononuclear cells (PBMCs) of MDD patients (n = 77) and healthy controls (HCs, n = 24). Moreover, we studied inflammation engagement as a moderator of mitochondria dysfunctions on the severity of depressive symptoms. We found increased levels of Mfn-2 (p < 0.001), short Opa-1 (S-Opa-1) (p < 0.001) and Fis-1 (p < 0.001) in MDD patients, suggesting an increase in the mitochondrial fragmentation. We also found that MDD patients had higher levels of Pink-1 (p < 0.001), p62/SQSTM1 (p < 0.001), LC3B (p = 0.002), and caspase-3 active (p = 0.001), and lower levels of parkin (p < 0.001) compared with HCs. Moreover, we showed that that MDD patients with higher CRP levels had higher levels of Mfn-2 (p = 0.001) and LC3B (p = 0.002) when compared with MDD patients with low CRP. Another notable finding was that the severity of depressive symptoms in MDD is associated with changes in protein levels in pathways related to mitochondrial dynamics and mitophagy, and can be dependent on the inflammatory status. Overall, our study demonstrated that a disruption in the mitochondrial dynamics network could initiate a cascade of abnormal changes relevant to the critical pathological changes during the course of MDD and lead to poor outcomes.

Targeting whole body metabolism and mitochondrial bioenergetics in the drug development for Alzheimer's disease

Aging is by far the most prominent risk factor for Alzheimer's disease (AD), and both aging and AD are associated with apparent metabolic alterations. As developing effective therapeutic interventions to treat AD is clearly in urgent need, the impact of modulating whole-body and intracellular metabolism in preclinical models and in human patients, on disease pathogenesis, have been explored. There is also an increasing awareness of differential risk and potential targeting strategies related to biological sex, microbiome, and circadian regulation. As a major part of intracellular metabolism, mitochondrial bioenergetics, mitochondrial quality-control mechanisms, and mitochondria-linked inflammatory responses have been considered for AD therapeutic interventions. This review summarizes and highlights these efforts.

Evaluation of Gender Differences in Response to Photobiomodulation Therapy, Including Laser Acupuncture: A Narrative Review and Implication to Precision Medicine

Background: The influence of gender is significant in the manifestation and response to many diseases and in the treatment strategy. Photobiomodulation (PBM) therapy, including laser acupuncture, is an evidence-based treatment and disease prevention modality that has shown promising efficacy for a myriad of chronic and acute diseases. Anecdotal experience and limited clinical trials suggest gender differences exist in treatment outcomes to PBM therapy. There is preliminary evidence that gender may be as important as skin color in the individual response to PBM therapy. Purpose: To conduct a literature search of publications addressing the effects of gender differences in PBM therapy, including laser acupuncture, to provide a narrative review of the findings, and to explore potential mechanisms for the influence of gender. Methods: A narrative review of the literature on gender differences in PBM applications was conducted using key words relating to PBM therapy and gender. Results: A total of 13 articles were identified. Of these articles, 11 have direct experimental investigations into the response difference in gender for PBM, including laser acupuncture. A variety of cadaver, human, and experimental studies demonstrated results that gender effects were significant in PBM outcome responses, including differences in tendon structural and mechanical outcomes, and mitochondrial gene expression. One cadaver experiment showed that gender was more important than skin tone. The physiologic mechanisms directing gender differences are explored and postulated. Conclusions: The review suggests that to address the requirements of a proficient precision medicine-based strategy, it is important for PBM therapy to consider gender in its treatment plan and dosing prescription. Further research is warranted to determine the correct dose for optimal gender treatment, including gender-specific treatment plans to improve outcomes, taking into account wavelength, energy exposure, intensity, and parameters related to the deliverance of treatment to each anatomical location.

The serotonin reuptake transporter modulates mitochondrial copy number and mitochondrial respiratory complex gene expression in the frontal cortex and cerebellum in a sexually dimorphic manner

Neuropsychiatric and neurodevelopmental disorders such as major depressive disorder (MDD) and autism spectrum disorder (ASD) are complex conditions attributed to both genetic and environmental factors. There is a growing body of evidence showing that serotonergic signaling and mitochondrial dysfunction contribute to the pathophysiology of these disorders and are linked as signaling through specific serotonin (5-HT) receptors drives mitochondrial biogenesis. The serotonin transporter (SERT) is important in these disorders as it regulates synaptic serotonin and therapeutically is the target of selective serotonin reuptake inhibitors which are a major class of anti-depressant drug. Human allelic variants of the serotonin transporter-linked polymorphic region (5-HTTLPR) such as the S/S variant, are associated with reduced SERT expression and increased susceptibility for developing neuropsychiatric disorders. Using a rat model that is haploinsufficient for SERT and displays reduced SERT expression similar to the human S/S variant, we demonstrate that reduced SERT expression modulates mitochondrial copy number and expression of respiratory chain electron transfer components in the brain. In the frontal cortex, genotype-related trends were opposing for males and females, such that reduced SERT expression led to increased expression of the Complex I subunit mt-Nd1 in males but reduced expression in females. Our findings suggest that SERT expression and serotonergic signaling have a role in regulating mitochondrial biogenesis and adenosine triphosphate (ATP) production in the brain. We speculate that the sexual dimorphism in mitochondrial abundance and gene expression contributes to the sex bias found in the incidence of neuropsychiatric disorders such as MDD and ASD.

Metabolic Sex Dimorphism of the Brain at the Gene, Cell, and Tissue Level

The palpable observation in the sex bias of disease prevalence in the CNS has fascinated scientists for several generations. Brain sex dimorphism has been visualized by imaging and analytical tools at the tissue, cellular, and molecular levels. Recent work highlighted the specificity of such sex bias in the brain and its subregions, offering a unique lens through which disease pathogenesis can be investigated. The brain is the largest consumer of energy in the body and provides a unique metabolic environment for diverse lineages of cells. Immune cells are increasingly recognized as an integral part of brain physiology, and their function depends on metabolic homeostasis. This review focuses on metabolic sex dimorphism in brain tissue, resident, and infiltrating immune cells. In this context, we highlight the relevance of recent advances in metabolomics and RNA sequencing technologies at the single cell resolution and the development of novel computational approaches.

Human-Induced Pluripotent Stem Cell-Based Models for Studying Sex-Specific Differences in Neurodegenerative Diseases

The prevalence of neurodegenerative diseases is steadily increasing worldwide, and epidemiological studies strongly suggest that many of the diseases are sex-biased. It has long been suggested that biological sex differences are crucial for neurodegenerative diseases; however, how biological sex affects disease initiation, progression, and severity is not well-understood. Sex is a critical biological variable that should be taken into account in basic research, and this review aims to highlight the utility of human-induced pluripotent stem cells (iPSC)-derived models for studying sex-specific differences in neurodegenerative diseases, with advantages and limitations. In vitro systems utilizing species-specific, renewable, and physiologically relevant cell sources can provide powerful platforms for mechanistic studies, toxicity testings, and drug discovery. Matched healthy, patient-derived, and gene-corrected human iPSCs, from both sexes, can be utilized to generate neuronal and glial cell types affected by specific neurodegenerative diseases to study sex-specific differences in two-dimensional (2D) and three-dimensional (3D) human culture systems. Such relatively simple and well-controlled systems can significantly contribute to the elucidation of molecular mechanisms underlying sex-specific differences, which can yield effective, and potentially sex-based strategies, against neurodegenerative diseases.