Ph.D. Candidate Molecular and Cell Biology Program
Abstract Text: National Capital Area TBI Symposium – 2023 Abstract
Military related TBI induced chronic astrogliosis in ferret and human influence astrocyte homeostatic protein expression
Nicholas R. Breehl, MSc2, 3, Susan C. Schwerin, PhD1,3, Mitali Chatterjee, BS7, David S. Priemer, MD5, 6, 7, Daniel P. Perl, MD5, 6, Sharon L. Juliano, PhD1,2,3.4
Department of Anatomy, Physiology and Genetics USUHS1, Molecular and Cellular Biology Program USUHS2, Center for Neuroscience and Regenerative Medicine3, Neuroscience Program USUHS4, Department of Pathology5 USUHS, The Department of Defense/Uniformed Services University Brain Tissue Repository6, Henry M Jackson Foundation for the Advancement of Military Medicine, Inc.7, Bethesda MD
In modern warfare, active-duty military members are at an increased risk of traumatic brain injuries (TBI). The injuries are widely varied, including exposure to a blast produced by a shockwave after a detonation, typically involving severe impact and/or rotation of the head. To better understand the pathological patterns of these impacts our laboratory has developed a model (multiple blast exposures and a Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA)) to better mimic these multimodal experiences. Recently, we reported chronic diffuse inflammation and astrogliosis in the brain of ferrets up to 12 weeks post-blast TBI, an important gyrencephalic animal model, with microglial marker IBA1 and reactive astrocyte marker GFAP [1]. In addition to blast-alone TBI, we have confirmed reactive chronicity continues to 6 months post-injury in the multimodal TBI model. Subsequently, we applied GFAP immunofluorescence analysis to the postmortem military prefrontal cortex (in control and blast recipient populations) and observed a similar chronic and diffuse increase in astrogliosis, as reported previously by Shively et al [2]. Both human and ferret pathologies are concentrated in subpial layers, perivascular spaces, and the white-grey-matter interface. As astrocytes are vital to maintaining homeostasis in the brain, especially through the blood-brain barrier (BBB), glymphatic system, and spatial buffering via a well-connected glial syncytium, we turned our focus on the expression patterns of aquaporin-4 (AQP-4) and connexin-43 (Conn-43). Astrocyte end-feet expressed aquaporin-4 water channel proteins help in the removal of interstitially derived waste through the glymphatic system, while also contributing to BBB integrity, surrounding of vessels with the glial limitans. Results from the ferret show a significant increase of AQP-4 at 6 months post-injury. Human samples show a similar increase in AQP-4, at levels that did not reach significance. Conn-43 gap junction proteins are expressed by astrocytes and responsible for ion and metabolite regulation ensuring the physiological function of neurons. Conn-43 in ferrets reveals a loss of strong continuous patterns at the vessel after injury but a subtle increase in interstitial space expression. An interesting observation while investigating human tissue reveals two dominant populations of astrocytes: AQP-4 (+) only and GFAP (+) only. After injury a third population increases where AQP-4 and GFAP co-label the same astrocytes. Additionally, GFAP (+) only astrocytes appear to have a dramatic change in morphology, shifting from cells with fine branches to cells lacking smooth textures. The double positive population of cells retains the fine branches seen in controls. Conn-43 staining in human control vs injury shows an increase after injury while also appearing in deeper gray matter areas rather than in subpial layer 1 seen in controls. When we co-labeled the human astrocytes with either GFAP+Conn-43 or AQP-4+Conn-43, Conn-43 augments primarily in astrocytes of the AQP4 (+) only population. These findings suggest this apparent shift in the astrocyte population may be an important functional component in understanding and defining the subsequent pathology of blast-related TBIs.
1. Schwerin, S.C., et al., Expression of GFAP and Tau Following Blast Exposure in the Cerebral Cortex of Ferrets. J Neuropathol Exp Neurol, 2021. 80(2): p. 112-128. 2. Shively, S.B., et al., Characterisation of interface astroglial scarring in the human brain after blast exposure: a post-mortem case series. The Lancet Neurology, 2016. 15(9): p. 944-953.
