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Pearson A, Koprivica M, Eisenbaum M, Ortiz C, Browning M, Vincennie T, Tinsley C, Mullan M, Crawford F, Ojo J. PPARγ activation ameliorates cognitive impairment and chronic microglial activation in the aftermath of r-mTBI. J Neuroinflammation 2024; 21:194. [PMID: 39097742 PMCID: PMC11297749 DOI: 10.1186/s12974-024-03173-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2024] [Accepted: 07/12/2024] [Indexed: 08/05/2024] Open
Abstract
Chronic neuroinflammation and microglial activation are key mediators of the secondary injury cascades and cognitive impairment that follow exposure to repetitive mild traumatic brain injury (r-mTBI). Peroxisome proliferator-activated receptor-γ (PPARγ) is expressed on microglia and brain resident myeloid cell types and their signaling plays a major anti-inflammatory role in modulating microglial responses. At chronic timepoints following injury, constitutive PPARγ signaling is thought to be dysregulated, thus releasing the inhibitory brakes on chronically activated microglia. Increasing evidence suggests that thiazolidinediones (TZDs), a class of compounds approved from the treatment of diabetes mellitus, effectively reduce neuroinflammation and chronic microglial activation by activating the peroxisome proliferator-activated receptor-γ (PPARγ). The present study used a closed-head r-mTBI model to investigate the influence of the TZD Pioglitazone on cognitive function and neuroinflammation in the aftermath of r-mTBI exposure. We revealed that Pioglitazone treatment attenuated spatial learning and memory impairments at 6 months post-injury and reduced the expression of reactive microglia and astrocyte markers in the cortex, hippocampus, and corpus callosum. We then examined whether Pioglitazone treatment altered inflammatory signaling mechanisms in isolated microglia and confirmed downregulation of proinflammatory transcription factors and cytokine levels. To further investigate microglial-specific mechanisms underlying PPARγ-mediated neuroprotection, we generated a novel tamoxifen-inducible microglial-specific PPARγ overexpression mouse line and examined its influence on microglial phenotype following injury. Using RNA sequencing, we revealed that PPARγ overexpression ameliorates microglial activation, promotes the activation of pathways associated with wound healing and tissue repair (such as: IL10, IL4 and NGF pathways), and inhibits the adoption of a disease-associated microglia-like (DAM-like) phenotype. This study provides insight into the role of PPARγ as a critical regulator of the neuroinflammatory cascade that follows r-mTBI in mice and demonstrates that the use of PPARγ agonists such as Pioglitazone and newer generation TZDs hold strong therapeutic potential to prevent the chronic neurodegenerative sequelae of r-mTBI.
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Affiliation(s)
- Andrew Pearson
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA.
- The Open University, Walton Hall, Kents Hill, Milton Keynes, MK7 6AA, UK.
| | - Milica Koprivica
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
| | - Max Eisenbaum
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
- The Open University, Walton Hall, Kents Hill, Milton Keynes, MK7 6AA, UK
| | - Camila Ortiz
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
- The Open University, Walton Hall, Kents Hill, Milton Keynes, MK7 6AA, UK
| | | | - Tessa Vincennie
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
| | - Cooper Tinsley
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
| | - Michael Mullan
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
| | - Fiona Crawford
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
- The Open University, Walton Hall, Kents Hill, Milton Keynes, MK7 6AA, UK
- James A. Haley Veterans' Hospital, 13000 Bruce B Downs Blvd, Tampa, FL, 33612, USA
| | - Joseph Ojo
- The Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL, 34243, USA
- The Open University, Walton Hall, Kents Hill, Milton Keynes, MK7 6AA, UK
- James A. Haley Veterans' Hospital, 13000 Bruce B Downs Blvd, Tampa, FL, 33612, USA
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Ortiz C, Pearson A, McCartan R, Roche S, Carothers N, Browning M, Perez S, He B, Ginsberg SD, Mullan M, Mufson EJ, Crawford F, Ojo J. Overexpression of pathogenic tau in astrocytes causes a reduction in AQP4 and GLT1, an immunosuppressed phenotype and unique transcriptional responses to repetitive mild TBI without appreciable changes in tauopathy. J Neuroinflammation 2024; 21:130. [PMID: 38750510 PMCID: PMC11096096 DOI: 10.1186/s12974-024-03117-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2024] [Accepted: 04/30/2024] [Indexed: 05/18/2024] Open
Abstract
Epidemiological studies have unveiled a robust link between exposure to repetitive mild traumatic brain injury (r-mTBI) and elevated susceptibility to develop neurodegenerative disorders, notably chronic traumatic encephalopathy (CTE). The pathogenic lesion in CTE cases is characterized by the accumulation of hyperphosphorylated tau in neurons around small cerebral blood vessels which can be accompanied by astrocytes that contain phosphorylated tau, the latter termed tau astrogliopathy. However, the contribution of tau astrogliopathy to the pathobiology and functional consequences of r-mTBI/CTE or whether it is merely a consequence of aging remains unclear. We addressed these pivotal questions by utilizing a mouse model harboring tau-bearing astrocytes, GFAPP301L mice, subjected to our r-mTBI paradigm. Despite the fact that r-mTBI did not exacerbate tau astrogliopathy or general tauopathy, it increased phosphorylated tau in the area underneath the impact site. Additionally, gene ontology analysis of tau-bearing astrocytes following r-mTBI revealed profound alterations in key biological processes including immunological and mitochondrial bioenergetics. Moreover, gene array analysis of microdissected astrocytes accrued from stage IV CTE human brains revealed an immunosuppressed astroglial phenotype similar to tau-bearing astrocytes in the GFAPP301L model. Additionally, hippocampal reduction of proteins involved in water transport (AQP4) and glutamate homeostasis (GLT1) was found in the mouse model of tau astrogliopathy. Collectively, these findings reveal the importance of understanding tau astrogliopathy and its role in astroglial pathobiology under normal circumstances and following r-mTBI. The identified mechanisms using this GFAPP301L model may suggest targets for therapeutic interventions in r-mTBI pathogenesis in the context of CTE.
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Affiliation(s)
- Camila Ortiz
- The Roskamp Institute, Sarasota, FL, USA.
- The Open University, Milton Keynes, UK.
| | - Andrew Pearson
- The Roskamp Institute, Sarasota, FL, USA
- The Open University, Milton Keynes, UK
| | | | | | | | | | | | - Bin He
- Barrow Neurological Institute, Phoenix, AZ, USA
| | - Stephen D Ginsberg
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA
- Departments of Psychiatry, Neuroscience and Physiology, and NYU Neuroscience Institute, New York University Grossman School of Medicine, New York, NY, USA
| | | | | | - Fiona Crawford
- The Roskamp Institute, Sarasota, FL, USA
- The Open University, Milton Keynes, UK
- James A. Haley Veterans Hospital, Tampa, FL, USA
| | - Joseph Ojo
- The Roskamp Institute, Sarasota, FL, USA
- The Open University, Milton Keynes, UK
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Eisenbaum M, Pearson A, Ortiz C, Koprivica M, Cembran A, Mullan M, Crawford F, Ojo J, Bachmeier C. Repetitive head trauma and apoE4 induce chronic cerebrovascular alterations that impair tau elimination from the brain. Exp Neurol 2024; 374:114702. [PMID: 38301863 PMCID: PMC10922621 DOI: 10.1016/j.expneurol.2024.114702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Accepted: 01/25/2024] [Indexed: 02/03/2024]
Abstract
Repetitive mild traumatic brain injuries (r-mTBI) sustained in the military or contact sports have been associated with the accumulation of extracellular tau in the brain, which may contribute to the pathogenesis of neurodegenerative tauopathies. The expression of the apolipoprotein E4 (apoE4) isoform has been associated with higher levels of tau in the brain, and worse clinical outcomes after r-mTBI, though the influence of apoE genotype on extracellular tau dynamics in the brain is poorly understood. We recently demonstrated that extracellular tau can be eliminated across blood-brain barrier (BBB), which is progressively impaired following r-mTBI. The current studies investigated the influence of repetitive mild TBI (r-mTBI) and apoE genotype on the elimination of extracellular solutes from the brain. Following intracortical injection of biotin-labeled tau into humanized apoE-Tr mice, the levels of exogenous tau residing in the brain of apoE4 mice were elevated compared to other isoforms, indicating reduced tau elimination. Additionally, we found exposure to r-mTBI increased tau residence in apoE2 mice, similar to our observations in E2FAD animals. Each of these findings may be the result of diminished tau efflux via LRP1 at the BBB, as LRP1 inhibition significantly reduced tau uptake in endothelial cells and decreased tau transit across an in vitro model of the BBB (basolateral-to-apical). Notably, we showed that injury and apoE status, (particularly apoE4) resulted in chronic alterations in BBB integrity, pericyte coverage, and AQP4 polarization. These aberrations coincided with an atypical reactive astrocytic gene signature indicative of diminished CSF-ISF exchange. Our work found that CSF movement was reduced in the chronic phase following r-mTBI (>18 months post injury) across all apoE genotypes. In summary, we show that apoE genotype strongly influences cerebrovascular homeostasis, which can lead to age-dependent deficiencies in the elimination of toxic proteins from the brain, like tau, particularly in the aftermath of head trauma.
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Affiliation(s)
| | | | | | | | | | | | - Fiona Crawford
- The Roskamp Institute, Sarasota, FL, USA; James A. Haley Veterans' Hospital, Tampa, FL, USA
| | - Joseph Ojo
- The Roskamp Institute, Sarasota, FL, USA
| | - Corbin Bachmeier
- The Roskamp Institute, Sarasota, FL, USA; Bay Pines VA Healthcare System, Bay Pines, FL, USA
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Browning JL, Wilson KA, Shandra O, Wei X, Mahmutovic D, Maharathi B, Robel S, VandeVord PJ, Olsen ML. Applying Proteomics and Computational Approaches to Identify Novel Targets in Blast-Associated Post-Traumatic Epilepsy. Int J Mol Sci 2024; 25:2880. [PMID: 38474127 DOI: 10.3390/ijms25052880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Revised: 02/20/2024] [Accepted: 02/22/2024] [Indexed: 03/14/2024] Open
Abstract
Traumatic brain injury (TBI) can lead to post-traumatic epilepsy (PTE). Blast TBI (bTBI) found in Veterans presents with several complications, including cognitive and behavioral disturbances and PTE; however, the underlying mechanisms that drive the long-term sequelae are not well understood. Using an unbiased proteomics approach in a mouse model of repeated bTBI (rbTBI), this study addresses this gap in the knowledge. After rbTBI, mice were monitored using continuous, uninterrupted video-EEG for up to four months. Following this period, we collected cortex and hippocampus tissues from three groups of mice: those with post-traumatic epilepsy (PTE+), those without epilepsy (PTE-), and the control group (sham). Hundreds of differentially expressed proteins were identified in the cortex and hippocampus of PTE+ and PTE- relative to sham. Focusing on protein pathways unique to PTE+, pathways related to mitochondrial function, post-translational modifications, and transport were disrupted. Computational metabolic modeling using dysregulated protein expression predicted mitochondrial proton pump dysregulation, suggesting electron transport chain dysregulation in the epileptic tissue relative to PTE-. Finally, data mining enabled the identification of several novel and previously validated TBI and epilepsy biomarkers in our data set, many of which were found to already be targeted by drugs in various phases of clinical testing. These findings highlight novel proteins and protein pathways that may drive the chronic PTE sequelae following rbTBI.
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Affiliation(s)
- Jack L Browning
- School of Neuroscience, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
- Genetics, Bioinformatics and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Kelsey A Wilson
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Oleksii Shandra
- Department of Biomedical Engineering, Florida International University, Miami, FL 33174, USA
| | - Xiaoran Wei
- Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Dzenis Mahmutovic
- Department of Cell Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Biswajit Maharathi
- Neurology & Rehabilitation, University of Illinois, Chicago, IL 60612, USA
| | - Stefanie Robel
- Department of Cell Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Pamela J VandeVord
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
- Salem Veteran Affairs Medical Center, Salem, VA 24153, USA
| | - Michelle L Olsen
- School of Neuroscience, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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