Browsing by Author "Saber, Maha"

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    Cellular players that shape evolving pathology and neurodegeneration following traumatic brain injury
    (Elsevier, 2018) Puntambekar, Shweta S.; Saber, Maha; Lamb, Bruce T.; Kokiko-Cochran, Olga N.; Medical and Molecular Genetics, School of Medicine
    Traumatic brain injury (TBI) is one of the leading causes of death and disability worldwide, and has emerged as a critical risk factor for multiple neurodegenerative diseases, particularly Alzheimer’s disease (AD). How the inflammatory cascade resulting from mechanical stress, axonal shearing and the loss of neurons and glia following initial impact in TBI, contributes to the development of AD-like disease is unclear. Neuroinflammation, characterized by blood-brain barrier (BBB) dysfunction and activation of brain-resident microglia and astrocytes, resulting in secretion of inflammatory mediators and subsequent recruitment of peripheral immune cells has been the focus of extensive research in attempts to identify drug-targets towards improving functional outcomes post TBI. While knowledge of intricate cellular interactions that shape lesion pathophysiology is incomplete, a major limitation in the field is the lack of understanding of how distinct cell types differentially alter TBI pathology. The aim of this review is to highlight functional differences between populations of bone marrow derived, infiltrating monocytes/macrophages and brain-resident microglia based on differential expression of the chemokine receptors CCR2 and CX3CR1. This review will focus on how unique subsets of mononuclear phagocytes shape TBI pathophysiology, neurotoxicity and BBB function, in a disease-stage dependent manner. Additionally, this review summarizes the role of multiple microglia and macrophage receptors, namely CCR2, CX3CR1 and Triggering Receptor Expressed on Myeloid Cells-2 (TREM2) in pathological neuroinflammation and neurodegeneration vs. recovery following TBI. TREM2 has been implicated in mediating AD-related pathology, and variants in TREM2 are particularly important due to their correlation with exacerbated neurodegeneration. Finally, this review highlights behavioral outcomes associated with microglial vs. macrophage variances, the need for novel treatment strategies that target unique subpopulations of peripheral macrophages, and the importance of development of therapeutics to modulate inflammatory functions of brain-resident microglia at specific stages of TBI.
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    Traumatic brain injury in hTau model mice: Enhanced acute macrophage response and altered long-term recovery
    (Liebert, 2017) Kokiko-Cochran, Olga N.; Saber, Maha; Puntambekar, Shweta; Bemiller, Shane; Katsumoto, Atsuko; Lee, Yu-Shang; Bhaskar, Kiran; Ransohoff, Richard M.; Lamb, Bruce T.; Department of Medical and Molecular Genetics, School of Medicine
    TBI induces widespread neuroinflammation and accumulation of microtubule associated protein tau (MAPT) - two key pathological features of tauopathies. This study sought to characterize the microglial/macrophage response to TBI in genomic-based MAPT transgenic mice in a Mapt knockout background (called hTau). Two-month-old hTau and age-matched control male and female mice received a single lateral fluid percussion TBI or sham injury. Separate groups of mice were aged to an acute (3 days post-injury [DPI]) or chronic (135 DPI) post-injury time point. As judged by tissue immunostaining for macrophage markers, microglial/macrophage response to TBI was enhanced at 3 DPI in hTau mice compared to control TBI and sham mice. However, MAPT phosphorylation increased in hTau mice regardless of injury group. Flow cytometric analysis revealed distinct populations of microglia and macrophages within all groups at 135 DPI. Unexpectedly, microglial reactivity was significantly reduced in hTau TBI mice compared to all other groups. Instead, hTau TBI mice showed a persistent macrophage response. In addition, TBI enhanced MAPT pathology in the temporal cortex and hippocampus of hTau TBI mice compared to controls 135 DPI. A battery of behavioral test revealed that TBI in hTau mice resulted in compromised use of spatial search strategies to complete a water maze task despite lack of motor or visual deficits. Collectively, these data indicate that the presence of wild-type human tau alters the microglial/macrophage response to a single TBI, induces delayed, region-specific MAPT pathology, and alters cognitive recovery; however, the causal relationship between these events remains unclear. These results highlight the potential significance of communication between MAPT and microglia/macrophages following TBI and emphasize the role of neuroinflammation in post-injury recovery.