Sex Differences in Mitochondrial Function Following a Controlled Cortical Impact Traumatic Brain Injury in Rodents

An antioxidant and anti-ER stress combination therapy elevates phosphorylation of α-Syn at serine 129 and alleviates post-TBI PD-like pathology in a sex-specific manner in mice

Clinical studies have shown that traumatic brain injury (TBI) increases the onset of Parkinson's disease (PD) in later life by >50%. Oxidative stress, endoplasmic reticulum (ER) stress, and inflammation are the major drivers of both TBI and PD pathologies. We presently evaluated if curtailing oxidative stress and ER stress concomitantly using a combination of apocynin and tert-butylhydroquinone and salubrinal during the acute stage after TBI in mice reduces the severity of late-onset PD-like pathology. The effect of multiple low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on post-TBI neurodegeneration was also evaluated. The combo therapy elevated the level of phosphorylation at serine 129 (pS129) of α-Syn in the pericontusional cortex of male mice at 72 h post-TBI. Motor and cognitive deficits induced by TBI lasted at least 3 months and the combo therapy curtailed these deficits in both sexes. At 3 months post-TBI, male mice given combo therapy exhibited significantly lesser α-Syn aggregates in the SN and higher TH+ cells in the SNpc, compared to vehicle control. However, the aggregate number was not significantly different between groups of female mice. Moreover, TBI-induced loss of TH+ cells was negligible in female mice irrespective of treatment. The MPTP treatment aggravated PD-like pathology in male mice but had a negligible effect on the loss of TH+ cells in female mice. Thus, the present study indicates that mitigation of TBI-induced oxidative stress and ER stress at the acute stage could potentially reduce the risk of post-TBI PD-like pathology at least in male mice, plausibly by elevating pS129-α-Syn level.

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.

Experimental traumatic brain injury increases epichaperome formation

Under normal conditions, heat shock proteins work in unison through dynamic protein interactions collectively referred to as the "chaperome." Recent work revealed that during cellular stress, the functional interactions of the chaperome are modified to form the "epichaperome," which results in improper protein folding, degradation, aggregation, and transport. This study is the first to investigate this novel mechanism of protein dishomeostasis in traumatic brain injury (TBI). Male and female adult, Sprague-Dawley rats received a lateral controlled cortical impact (CCI) and the ipsilateral hippocampus was collected 24 h 1, 2, and 4 weeks after injury. The epichaperome complex was visualized by measuring HSP90, HSC70 and HOP expression in native-PAGE and normalized to monomeric protein expression. A two-way ANOVA examined the effect of injury and sex at each time-point. Native HSP90, HSC70 and HOP protein expression showed a significant effect of injury effect across all time-points. Additionally, HSC70 and HOP showed significant sex effects at 24 h and 4 weeks. Altogether, controlled cortical impact significantly increased formation of the epichaperome across all proteins measured. Further investigation of this pathological mechanism can lead to a greater understanding of the link between TBI and increased risk of neurodegenerative disease and targeting the epichaperome for therapeutics.

Characterizing Sex Differences in Mitochondrial Dysfunction After Severe Traumatic Brain Injury in Mice

Traumatic brain injury (TBI) is caused by an impact or penetrating injury to the head resulting in abnormal brain function. Mitochondrial dysfunction is an important hallmark of TBI and has been thoroughly studied in male rodent models of brain injury, but relatively little is known about these outcomes in females. These studies were designed to examine sex as a biological variable for mitochondria-related outcomes after the severe controlled cortical impact (CCI) mouse model of TBI. Synaptic and non-synaptic mitochondria were isolated from the sham- or CCI-injured cortex as well as the hippocampus ipsilateral to the craniotomy 3, 12, 24, or 48 h post-surgery, and then bioenergetics were measured. Subtle variations were observed in the timeline of mitochondrial dysfunction between sexes. Non-synaptic cortical mitochondria from injured females showed early impairment at 12 h post-CCI compared to mitochondria from injured males at 24 h post-CCI. Contrastingly, in the synaptic fraction, mitochondria from injured males showed early impairment at 12 h post-CCI, whereas mitochondria from injured females showed impairment at 24 h post-CCI. Based on bioenergetic impairments at 24 h post-CCI, synaptic and non-synaptic mitochondrial calcium loading was also measured at this time point. Consistent with bioenergetic data at 24 h, non-synaptic mitochondria from injured males had increased calcium loading compared to uninjured control, but this effect was not observed in females. Finally, histological assessment of cortical tissue sparing in each sex was measured at 7 days post-injury. There was a lack of sex-based differences in cortical tissue sparing after severe CCI. Overall, there were some subtle sex differences in mitochondrial outcomes after CCI, but these findings were not statistically significant. This study highlights the importance of utilizing both sexes when measuring mitochondrial function after severe CCI.

Acute effects of single and repeated mild traumatic brain injury on levels of neurometabolites, lipids, and mitochondrial function in male rats

Introduction

Mild traumatic brain injuries (mTBIs) are the most common form of acquired brain injury. Symptoms of mTBI are thought to be associated with a neuropathological cascade, potentially involving the dysregulation of neurometabolites, lipids, and mitochondrial bioenergetics. Such alterations may play a role in the period of enhanced vulnerability that occurs after mTBI, such that a second mTBI will exacerbate neuropathology. However, it is unclear whether mTBI-induced alterations in neurometabolites and lipids that are involved in energy metabolism and other important cellular functions are exacerbated by repeat mTBI, and if such alterations are associated with mitochondrial dysfunction.

Methods

In this experiment, using a well-established awake-closed head injury (ACHI) paradigm to model mTBI, male rats were subjected to a single injury, or five injuries delivered 1 day apart, and injuries were confirmed with a beam-walk task and a video observation protocol. Abundance of several neurometabolites was evaluated 24 h post-final injury in the ipsilateral and contralateral hippocampus using in vivo proton magnetic resonance spectroscopy (1H-MRS), and mitochondrial bioenergetics were evaluated 30 h post-final injury, or at 24 h in place of 1H-MRS, in the rostral half of the ipsilateral hippocampus. Lipidomic evaluations were conducted in the ipsilateral hippocampus and cortex.

Results

We found that behavioral deficits in the beam task persisted 1- and 4 h after the final injury in rats that received repetitive mTBIs, and this was paralleled by an increase and decrease in hippocampal glutamine and glucose, respectively, whereas a single mTBI had no effect on sensorimotor and metabolic measurements. No group differences were observed in lipid levels and mitochondrial bioenergetics in the hippocampus, although some lipids were altered in the cortex after repeated mTBI.

Discussion

The decrease in performance in sensorimotor tests and the presence of more neurometabolic and lipidomic abnormalities, after repeated but not singular mTBI, indicates that multiple concussions in short succession can have cumulative effects. Further preclinical research efforts are required to understand the underlying mechanisms that drive these alterations to establish biomarkers and inform treatment strategies to improve patient outcomes.

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.

Sex-based differences of antioxidant enzyme nanoparticle effects following traumatic brain injury

Following traumatic brain injury (TBI), reactive oxygen species (ROS) are released in excess, causing oxidative stress, carbonyl stress, and cell death, which induce the additional release of ROS. The limited accumulation and retention of small molecule antioxidants commonly used in clinical trials likely limit the target engagement and therapeutic effect in reducing secondary injury. Small molecule drugs also need to be administered every several hours to maintain bioavailability in the brain. Therefore, there is a need for a burst and sustained release system with high accumulation and retention in the injured brain. Here, we utilized Pro-NP™ with a size of 200 nm, which was designed to have a burst and sustained release of encapsulated antioxidants, Cu/Zn superoxide dismutase (SOD1) and catalase (CAT), to scavenge ROS for >24 h post-injection. Here, we utilized a controlled cortical impact (CCI) mouse model of TBI and found the accumulation of Pro-NP™ in the brain lesion was highest when injected immediately after injury, with a reduction in the accumulation with delayed administration of 1 h or more post-injury. Pro-NP™ treatment with 9000 U/kg SOD1 and 9800 U/kg CAT gave the highest reduction in ROS in both male and female mice. We found that Pro-NP™ treatment was effective in reducing carbonyl stress and necrosis at 1 d post-injury in the contralateral hemisphere in male mice, which showed a similar trend to untreated female mice. Although we found that male and female mice similarly benefit from Pro-NP™ treatment in reducing ROS levels 4 h post-injury, Pro-NP™ treatment did not significantly affect markers of post-traumatic oxidative stress in female CCI mice as compared to male CCI mice. These findings of protection by Pro-NP™ in male mice did not extend to 7 d post-injury, which suggests subsequent treatments with Pro-NP™ may be needed to afford protection into the chronic phase of injury. Overall, these different treatment effects of Pro-NP™ between male and female mice suggest important sex-based differences in response to antioxidant nanoparticle delivery and that there may exist a maximal benefit from local antioxidant activity in injured brain.

APOE in the bullseye of neurodegenerative diseases: impact of the APOE genotype in Alzheimer’s disease pathology and brain diseases

ApoE is the major lipid and cholesterol carrier in the CNS. There are three major human polymorphisms, apoE2, apoE3, and apoE4, and the genetic expression of APOE4 is one of the most influential risk factors for the development of late-onset Alzheimer's disease (AD). Neuroinflammation has become the third hallmark of AD, together with Amyloid-β plaques and neurofibrillary tangles of hyperphosphorylated aggregated tau protein. This review aims to broadly and extensively describe the differential aspects concerning apoE. Starting from the evolution of apoE to how APOE's single-nucleotide polymorphisms affect its structure, function, and involvement during health and disease. This review reflects on how APOE's polymorphisms impact critical aspects of AD pathology, such as the neuroinflammatory response, particularly the effect of APOE on astrocytic and microglial function and microglial dynamics, synaptic function, amyloid-β load, tau pathology, autophagy, and cell–cell communication. We discuss influential factors affecting AD pathology combined with the APOE genotype, such as sex, age, diet, physical exercise, current therapies and clinical trials in the AD field. The impact of the APOE genotype in other neurodegenerative diseases characterized by overt inflammation, e.g., alpha- synucleinopathies and Parkinson's disease, traumatic brain injury, stroke, amyotrophic lateral sclerosis, and multiple sclerosis, is also addressed. Therefore, this review gathers the most relevant findings related to the APOE genotype up to date and its implications on AD and CNS pathologies to provide a deeper understanding of the knowledge in the APOE field.

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.

N-Acetyl-Aspartyl-Glutamate in Brain Health and Disease

N-acetyl-aspartyl-glutamate (NAAG) is the most abundant dipeptide in the brain, where it acts as a neuromodulator of glutamatergic synapses by activating presynaptic metabotropic glutamate receptor 3 (mGluR3). Recent data suggest that NAAG is selectively localized to postsynaptic dendrites in glutamatergic synapses and that it works as a retrograde neurotransmitter. NAAG is released in response to glutamate and provides the postsynaptic neuron with a feedback mechanisms to inhibit excessive glutamate signaling. A key regulator of synaptically available NAAG is rapid degradation by the extracellular enzyme glutamate carboxypeptidase II (GCPII). Increasing endogenous NAAG—for instance by inhibiting GCPII—is a promising treatment option for many brain disorders where glutamatergic excitotoxicity plays a role. The main effect of NAAG occurs through increased mGluR3 activation and thereby reduced glutamate release. In the present review, we summarize the transmitter role of NAAG and discuss the involvement of NAAG in normal brain physiology. We further present the suggested roles of NAAG in various neurological and psychiatric diseases and discuss the therapeutic potential of strategies aiming to enhance NAAG levels.