Biology subjects

Sullivan, P. G.

Publications and source records attributed to Sullivan, P. G..

6 recordsLinked to original sources

bioRxiv2026

Spatial, temporal and sex specific mitochondrial dynamic changes in severe controlled cortical impact mouse model of traumatic brain injury

Traumatic brain injury (TBI) triggers complex and evolving secondary cascades that disrupt mitochondrial homeostasis and contribute to progressive neurodegeneration. Although mitochondrial impairment is a well-recognized driver of post-traumatic pathology, the spatial and temporal progression of mitochondrial dysfunction, particularly in regions distal to the injury site, remains poorly defined, and potential sex-specific responses remain understudied. Here, we performed a comprehensive mitochondrial-focused analysis in a mouse model of controlled cortical impact (CCI), quantifying mtDNA copy number (mtDNA-CN), mitochondrial gene expression, and protein markers regulating biogenesis, transcription, electron transport chain integrity, and mitophagy. Mitochondrial profiles were assessed across four brain regions (cortex at 2, 4, and 6 mm from the injury epicenter, and hippocampus) at four time points (6h, 12h, 24h, and 48h) in both female and male C57BL/6J mice. While mtDNA content exhibited only modest and region-restricted reduction, particularly near the injury core, transcriptional and protein-level changes were far more pronounced and sex-divergent. Females displayed extensive early cortical gene activation followed by widespread hippocampal suppression at 48 h across mitochondrial dynamics, OXPHOS, transcriptional regulation, and biogenesis pathways, accompanied by 48h in PGC-1, TFAM, and NDUFS1. In contrast, males showed minimal transcriptional disruption but demonstrated delayed compensatory increases in TFAM, NDUFS1, and p62 protein levels, suggesting activation of mitochondrial maintenance and recovery programs. These spatially and temporally distinct responses reveal fundamental sex-specific vulnerabilities in mitochondrial regulation after TBI. Together, our findings provide a direction to an integrated mitochondrial landscape of early post-injury events and identifies critical windows and pathways that may support sex-specific therapeutic targeting to restore mitochondrial function after TBI.

neuroscience↗

bioRxiv2026

Ceramide-rich extracellular vesicles as pathogenic biomarkers in traumatic brain injury

Extracellular vesicles (EVs) contribute to the damage caused by traumatic brain injury (TBI) and can cross the blood-brain barrier (BBB). We analyzed plasma-derived EVs from human TBI patients to identify factors potentially contributing to TBI pathology. EVs were isolated using membrane affinity (ExoEasy) and size exclusion chromatography (iZone), both yielding CD9(+) and CD63(+) EVs with minimal contamination by serum albumin and apolipoprotein. Immunoblotting detected GFAP in TBI but not control EVs, indicating astrocyte-derived EVs crossing the BBB. Proteomic analysis and immunoblotting of EVs from TBI samples identified C-reactive protein and 14-3-3 proteins, which were not detected in control EVs, indicating inflammation associated with TBI. Lipidomic analysis showed ceramide enrichment in TBI EVs, validated by anti-ceramide immunoprecipitation. In a mouse closed head-controlled cortical impact model, brain EVs similarly showed elevated ceramide, confirming ceramide-rich EV release after TBI. Immunocytochemistry localized acid sphingomyelinase (ASM), a ceramide-generating enzyme, to ependymal cilia, suggesting these sites as a potential source of EVs. This was further supported by the detection of ASM in both brain- and plasma-derived EVs, along with the ciliary marker Arl13b in the brain. To assess function, we treated murine neuronal (N2a) cells with TBI EVs. Transcriptomics and STRING analyses revealed enrichment of mitochondrial-associated transcripts. Immunoblotting showed increased p53 and voltage-dependent anion channel 1 (VDAC1), which mediate ceramide-induced apoptosis. Seahorse assays showed that TBI EVs suppressed glycolysis, as indicated by reduced ECAR, while mitochondrial respiration (OCR) remained unchanged. LDH assays further indicated that TBI EVs were more neurotoxic than control EVs. Together, these findings identify ceramide-rich EVs as plasma biomarkers of TBI-induced inflammation, potential mediators of neuronal mitochondrial dysfunction, and pharmacological targets to prevent TBI-induced damage.

neuroscience↗

bioRxiv2026

Astrocytic response to traumatic brain injury to rescue neuronal mitochondrial dysfunction through mitochondrial transfer

As highly dynamic organelles, mitochondria play an essential role in neuronal survival and synaptic function. Excitotoxicity is as a critical factor that promotes mitochondrial dysfunction after traumatic brain injury (TBI). Intercellular mitochondrial transfer and exogenous mitochondrial transplantation are emerging concepts to understand mitochondrial trafficking in response to mitochondrial dysfunction; however, robust in vivo evidence remains limited on the extent of these processes in the central nervous system (CNS). There is a significant knowledge gap in our understanding of mitochondrial transfer mechanisms under both normal physiological conditions and after experimental TBI. Mouse lines expressing mitochondrial green-fluorescent dendra-2 (mtD2) and GFP (mtGFP) targeted to inner and outer mitochondrial membranes, respectively, were used to study astrocyte-specific (Aldh1l1-CreER; mtD2f/f - AmtD2 and Aldh1l1-CreER; mtGFPf/f - AmtGFP) and neuron-specific (CamK2aCre; mtD2f/f - NmtD2 and CamK2aCre; mtGFPf/f - NmtGFP) mitochondrial dynamics and bioenergetics in acute TBI and excitotoxicity. At 24 hrs following TBI, neurons in the NmtD2 mouse brain exhibited rapid and significant alterations in mitochondrial morphology, including changes in total mitochondrial volume, volume distribution, and sphericity. Synaptic neuronal (SN) mitochondria display robust deficits in mitochondrial bioenergetics and complex protein levels while non-synaptic neuronal (NSN) mitochondria show State III bioenergetics and complex proteins at control levels. These findings are accompanied by a marked increase in astrocyte-derived mitochondria (AmtGFP) transfer to neurons at 24 hrs post-injury, compared to control animals, but no increase in transfer to neuronal synapses. While TBI also altered astrocytic mitochondrial morphology in the cortex, astrocytic mitochondrial bioenergetics remained preserved. Single-cell RNA-seq analysis of astrocytes revealed significant transcriptional reprogramming following TBI, characterized by the upregulation of genes associated with mitochondrial homeostasis and the machinery for organelle trafficking. In vitro co-cultures of primary cortical astrocytes and neurons demonstrated that astrocytes can transfer mitochondria to neurons via direct contact and that NMDA-mediated excitotoxicity further enhanced this astrocyte-to-neuron mitochondrial transfer. Furthermore, astrocytic-derived extracellular vesicles containing mitochondria (EV-mito) deliver mitochondria to neurons and EV-mediated mitochondrial transfer significantly ameliorated NMDA-induced mitochondrial dysfunction in primary cortical neurons. Together, these findings show that astrocytes take on a TBI-related phenotype that facilitates dynamic changes in mitochondrial networks and mitochondrial trafficking to neurons. Astrocytic transfer of respiratory-competent mitochondria support is an intrinsic neuroprotective response to injury that supports mitochondrial function in neuronal soma, dendrites, and axons but not at the neuronal synapse. Finally, we show therapeutic potential of exogenous mitochondrial transfer, particularly via EV-mito, for treating neurological disorders associated with excitotoxicity, such as TBI.

neuroscience↗

bioRxiv2025

Active mitochondria in healthy spiny mouse fibroblasts resemble megamitochondria and remain resilient across lifespan

Although they exhibit limited regenerative ability of some tissues and organs shortly after birth or towards the end of fetal development, humans and laboratory mammals quickly transition to producing scar tissue for tissue repair. In contrast, spiny mice exhibit complex tissue regeneration as adults and provide a blueprint for how regeneration can occur throughout adulthood in mammals. Fibroblasts are key mediators of wound healing outcomes and prior work uncovered that cells from highly regenerative mammals (spiny mice and rabbits) exhibit extreme resistance to oxidative stress compared to those from non-regenerating laboratory mice and rats. Using a battery of cellular tests in primary ear pinna fibroblasts from highly regenerative and non-regenerative mammals, we find that cells from spiny mice and rabbits exhibit a baseline preference for glycolysis supporting a lower ROS-producing basal state. Uniquely, spiny mouse fibroblasts exhibit large, spherical, depolarized mitochondria similar to megamitochondria identified in pathological tissues. The megamitochondria phenotype was present across lifespan in ear pinna fibroblasts from fetal, young and old spiny mice. While rabbit, mouse and rat fibroblasts had polarized tubular mitochondrial networks typical of adult mammalian fibroblasts, isolated rabbit and spiny mice fibroblasts shared lower oxygen consumption efficiency even in the absence of a potential gradient. Taken together, our results support that a shared metabolic signature exists in stromal cells from highly regenerative mammals, although possibly driven by different mechanisms, to converge on a ROS-resistant phenotype which ultimately helps supports tissue regeneration.

cell biology↗

bioRxiv2025

Traumatic brain injury exacerbates mitochondrial dysfunction in APP/PS1 knock-in mice through time-dependent pathways

Cerebral hypometabolism occurs in both traumatic brain injury (TBI) and Alzheimers disease (AD), but whether these conditions act through distinct or overlapping mechanisms is unclear. TBI disrupts cerebral metabolism via blood-brain barrier damage, altered glucose transporter expression, calcium buffering abnormalities, and oxidative damage to metabolic enzymes. AD-related hypometabolism is linked to amyloid-{beta} (A{beta}) effects on mitochondria, including impaired respiration, oxidative stress, and altered mitophagy, fusion, and fission. We tested whether TBI-induced mitochondrial dysfunction exacerbates A{beta}-mediated impairment using a closed-head injury (CHI) model in APP/PS1 knock-in (KI) mice. Injuries were delivered at 4-5 months of age, before plaque formation and mitochondrial deficits in KI mice. Bioenergetics were measured at 1, 4, and 8 months post-injury in hippocampus and cortex using Seahorse assays on isolated mitochondria. At 1 month, genotype-by-injury interactions revealed greater dysfunction in KI mice than either condition alone, with males more vulnerable than females. At 4-8 months, amyloid-mediated effects predominated, while TBI-specific changes were no longer apparent, suggesting recovery or convergence onto shared mechanisms. These results indicate that TBI can temporarily worsen mitochondrial dysfunction in the context of early amyloidosis, with sex influencing vulnerability. Findings provide insight into the temporal relationship between TBI and amyloid-induced mitochondrial deficits and support the importance of sex as a biological variable in neurodegenerative disease progression. HighlightsTBI and APP/PS1 genotype interact to worsen early mitochondrial dysfunction. Hippocampus exhibits greater susceptibility to combined TBI and amyloid pathology. Sex-specific effects and temporal patterns underscore TBIs role in AD risk. Male mice show heightened vulnerability to TBI-induced mitochondrial dysfunction. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=71 SRC="FIGDIR/small/679790v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@198e17org.highwire.dtl.DTLVardef@1bfa6d4org.highwire.dtl.DTLVardef@161c1d0org.highwire.dtl.DTLVardef@fb4dc1_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Tau pathology reprograms glucose metabolism to support glutamatergic activity and excitatory imbalance

Alzheimers disease (AD) is not only characterized by amyloid-beta (A{beta}) and tau pathology, but also by early and progressive disruptions in metabolism. Neuronal excitability is tightly coupled with metabolic demand, and aberrant excitatory activity - observed in AD patients and models - can drive changes in metabolism. While A{beta}-related metabolic impairments are well-described, less is known about how tau pathology independently contributes to altered metabolic states and excitatory tone. Therefore, we explored how tau pathology impacted whole body and CNS metabolism in mouse models of tauopathy, including the P301S PS19 and Tau4RTg2652 mice. In both models, hyperphosphorylated tau prevents the age-related decline in whole-body metabolism by preserving glucose tolerance and mitigating shifts in fuel utilization (respiratory exchange ratio; RER), suggesting the mice are "glucose needy". Tau pathology also preserves diurnal rhythms in hippocampal interstitial fluid (ISF) glucose and lactate, likely due to increased neuronal activity during the active (dark) phase. Stable isotope-resolved metabolomics following 13C-glucose administration revealed that glucose is preferentially shunted toward glutamate synthesis--at the expense of GABA--highlighting a shift in excitatory/inhibitory balance. Interestingly, these changes were not explained by a primary deficit in synaptic mitochondria but by alterations in glycolytic flux. Adaptations were time of day dependent, where ISF glutamate rises after a glucose injection in the dark period but not the light period. This suggests increased glutamatergic activity may drive metabolic demand during the dark period when mice are more active. Together, these studies fundamentally highlight the important coupling between metabolism and excitability, which is disrupted by hyperphosphorylated tau, tau aggregation, and neurodegeneration. Understanding how tau pathology and metabolism interrelate provides a novel lens for the development of therapeutic targets in late stage AD.

neuroscience↗