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Current literature finds females have improved outcomes over their male counterparts after severe traumatic brain injury (TBI), while the opposite seems to be true for mild TBI. This begs the question as to what may be driving these sex differences after TBI. Estrogen is thought to be neuroprotective in certain diseases, and its actions have been shown to influence mitochondrial function. Mitochondrial impairment is a major hallmark of TBI, and interestingly, this dysfunction has been shown to be more severe in males than females after brain injury. This suggests estrogen could be playing a role in promoting "mitoprotection" following TBI. Despite the existence of estrogen receptors in mitochondria, few studies have examined the direct role of estrogen on mitochondrial function, and no studies have explored this after TBI. We hypothesized ex vivo treatment of isolated mitochondria with 17β-estradiol (E2) would improve mitochondrial function after experimental TBI in mice. Total mitochondria from the ipsilateral (injured) and contralateral (control) cortices of male and female mice were isolated 24 h post-controlled severe cortical impact (CCI) and treated with vehicle, 2 nM E2, or 20 nM E2 immediately before measuring reactive oxygen species (ROS) production, bioenergetics, electron transport chain complex (ETC) activities, and β-oxidation of palmitoyl carnitine. Protein expression of oxidative phosphorylation (OXPHOS) complexes was also measured in these mitochondrial samples to determine whether this influenced functional outcomes with respect to sex or injury. While mitochondrial ROS production was affected by CCI in both sexes, there were other sex-specific patterns of mitochondrial injury 24 h following severe CCI. For instance, mitochondria from males were more susceptible to CCI-induced injury with respect to bioenergetics and ETC complex activities, whereas mitochondria from females showed only Complex II impairment and reduced β-oxidation after injury. Neither concentration of E2 influenced ETC complex activities themselves, but 20 nM E2 appeared to uncouple mitochondria isolated from the contralateral cortex in both sexes, as well as the injured ipsilateral cortex of females. These studies highlight the significance of measuring mitochondrial dysfunction in both sexes after TBI and also shed light on another potential neuroprotective mechanism in which E2 may attenuate mitochondrial dysfunction after TBI in vivo.

Mitochondrial function analysis is a well-established method used in preclinical and clinical investigations to assess pathophysiological changes in various disease states, including traumatic brain injury (TBI). Although there are multiple approaches to assess mitochondrial function, one common method involves respirometric assays utilizing either Clark-type oxygen electrodes or fluorescent-based Seahorse analysis (Agilent). However, these functional analysis methods are typically limited to the availability of freshly isolated tissue samples due to the compromise of the electron transport chain (ETC) upon storage, caused by freeze-thaw-mediated breakdown of mitochondrial membranes. In this study, we propose and refine a method for evaluating electron flux through the ETC, encompassing complexes I, II, and IV, in frozen homogenates or mitochondrial samples within a single well of a Seahorse plate. Initially, we demonstrate the impact of TBI on freshly isolated mitochondria using the conventional oxidative phosphorylation protocol (OxPP), followed by a comparison with ETC analysis conducted on frozen tissue samples within the context of a controlled cortical impact (CCI) model of TBI. Additionally, we explore the effects of mitochondrial isolation from fresh versus snap-frozen brain tissues and their storage at -80°C, assessing its impact on electron transport chain protocol (ETCP) activity. Our findings indicate that while both sets of samples were frozen at a single time point, mitochondria from snap-frozen tissues exhibited reduced injury effects compared to preparations from fresh tissues, which were either homogenized or isolated into mitochondria and subsequently frozen for later use. Thus, we demonstrate that the preparation of homogenates or isolated mitochondria can serve as an appropriate method for storing brain samples, allowing for later analysis of mitochondrial function, following TBI using ETCP., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Vekaria, Kalimon, Prajapati, Velmurugan and Sullivan.)

Mild traumatic brain injury (mTBI) results in impairment of brain metabolism, which is propagated by mitochondrial dysfunction in the brain. Mitochondrial dysfunction has been identified as a pathobiological therapeutic target to quell cellular dyshomeostasis. Further, therapeutic approaches targeting mitochondrial impairments, such as mild mitochondrial uncoupling, have been shown to alleviate behavioral alterations after TBI. To examine how mild mitochondrial uncoupling modulates acute mitochondrial outcomes in a military-relevant model of mTBI, we utilized repeated blast overpressure of 11 psi peak overpressure to model repeated mild blast traumatic brain injury (rmbTBI) in rats followed by assessment of mitochondrial respiration and mitochondrial-related oxidative damage at 2 days post-rmbTBI. Treatment groups were administered 8 or 80 mg/kg MP201, a prodrug of 2,4 dinitrophenol (DNP) that displays improved pharmacokinetics compared with its metabolized form. Synaptic and glia-enriched mitochondria were isolated using fractionated a mitochondrial magnetic separation technique. There was a consistent physiological response, decreased heart rate, following mbTBI among experimental groups. Although there was a lack of injury effect in mitochondrial respiration of glia-enriched mitochondria, there were impairments in mitochondrial respiration in synaptic mitochondria isolated from the prefrontal cortex (PFC) and the amygdala/entorhinal/piriform cortex (AEP) region. Impairments in synaptic mitochondrial respiration were rescued by oral 80 mg/kg MP201 treatment after rmbTBI, which may be facilitated by increases in complex II and complex IV activity. Mitochondrial oxidative damage in glia-enriched mitochondria was increased in the PFC and hippocampus after rmbTBI. MP201 treatment alleviated elevated glia-enriched mitochondrial oxidative damage following rmbTBI. However, there was a lack of injury-associated differences in oxidative damage in synaptic mitochondria. Overall, our report demonstrates that rmbTBI results in mitochondrial impairment diffusely throughout the brain and mild mitochondrial uncoupling can restore mitochondrial bioenergetics and oxidative balance.

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., Competing Interests: No competing financial interests exist., (© Olivia J. Kalimon et al., 2023; Published by Mary Ann Liebert, Inc.)

Monoamine oxidase (MAO) is an enzyme located on the outer mitochondrial membrane that metabolizes amine substrates like serotonin, norepinephrine and dopamine. MAO inhibitors (MAOIs) are frequently utilized to treat disorders such as major depression or Parkinson's disease (PD), though their effects on brain mitochondrial bioenergetics are unclear. These studies measured bioenergetic activity in mitochondria isolated from the mouse cortex in the presence of inhibitors of either MAO-A, MAO-B, or both isoforms. We found that only 10 μM clorgyline, the selective inhibitor of MAO-A and not MAO-B, increased mitochondrial oxygen consumption rate in State V(CI) respiration compared to vehicle treatment. We then assessed mitochondrial bioenergetics, reactive oxygen species (ROS) production, and Electron Transport Chain (ETC) complex function in the presence of 0, 5, 10, 20, 40, or 80 μM of clorgyline to determine if this change was dose-dependent. The results showed increased oxygen consumption rates across the majority of respiration states in mitochondria treated with 5, 10, or 20 μM with significant bioenergetic inhibition at 80 μM clorgyline. Next, we assessed mitochondrial ROS production in the presence of the same concentrations of clorgyline in two different states: high mitochondrial membrane potential (ΔΨ m ) induced by oligomycin and low ΔΨ m induced by carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP). There were no changes in ROS production in the presence of 5, 10, 20, or 40 μM clorgyline compared to vehicle after the addition of oligomycin or FCCP. There was a significant increase in mitochondrial ROS in the presence of 80 μM clorgyline after FCCP addition, as well as reduced Complex I and Complex II activities, which are consistent with inhibition of bioenergetics seen at this dose. There were no changes in Complex I, II, or IV activities in mitochondria treated with low doses of clorgyline. These studies shed light on the direct effect of MAO-A inhibition on brain mitochondrial bioenergetic function, which may be a beneficial outcome for those taking these medications., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Pioglitazone interacts through the mitochondrial protein mitoNEET to improve brain bioenergetics following traumatic brain injury. To provide broader evidence regarding the therapeutic effects of pioglitazone after traumatic brain injury, the current study is focused on immediate and delayed therapy in a model of mild brain contusion. To assess pioglitazone therapy on mitochondrial bioenergetics in cortex and hippocampus, we use a technique to isolate subpopulations of total, glia-enriched and synaptic mitochondria. Pioglitazone treatment was initially administered at either 0.25, 3, 12 or 24 h following mild controlled cortical impact. At 48 h post-injury, ipsilateral cortex and hippocampus were dissected and mitochondrial fractions were isolated. Maximal mitochondrial respiration injury-induced deficits were observed in total and synaptic fractions, and 0.25 h pioglitazone treatment following mild controlled cortical impact was able to restore respiration to sham levels. While there are no injury-induced deficits in hippocampal fractions, we do find that 3 h pioglitazone treatment after mild controlled cortical impact can significantly increase maximal mitochondrial bioenergetics compared to vehicle-treated mild controlled cortical impact group. However, delayed pioglitazone treatment initiated at either 3 or 24 h after mild brain contusion does not improve spared cortical tissue. We demonstrate that synaptic mitochondrial deficits following mild focal brain contusion can be restored with early initiation of pioglitazone treatment. Further investigation is needed to determine functional improvements with pioglitazone beyond that of overt cortical tissue sparing following mild contusion traumatic brain injury., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Guarantors of Brain.)