Temporal and spatial changes in reactive astrogliosis examined by 18F-THK5351 positron emission tomography in a patient with severe traumatic brain injury

Background The positron emission tomography (PET) radioligand 18F-THK5351 is now used to evaluate monoamine oxidase B expression in the reactive astrogliosis seen in various central nervous diseases. Traumatic brain injury (TBI) is known to induce reactive astrogliosis in the lesion site. This is a first report to examine the spatial and temporal changes in reactive astrogliosis as evaluated by 18F-THK5351 after a severe TBI. Case presentation A 27-year-old man suffering from a severe TBI with multiple brain contusions was examined using 18F-THK5351 PET/CT in the subacute and chronic phases after the injury. The first PET scan, performed 46 days after the TBI, showed intense uptake of 18F-THK5351 in and around the brain contusions. The second PET scan, performed 271 days after the TBI, showed reduced uptake of 18F-THK5351 at the original sites of the brain contusions and increased uptakes in the white matter surrounding the contusions and the corpus callosum. The patient exhibited sustained improvement of neuropsychological impairment between the two PET examinations and remarkable recovery from the severe TBI. Conclusions There were evident temporal and spatial changes in 18F-THK5351 uptake in the traumatized brain between the two PET examinations. These changes may have been related to the remarkable neurological recovery in this patient. The degree and distribution of reactive astrogliosis detected by 18F-THK5351 PET may be useful in assessing pathophysiology and predicting prognosis in TBI patients.

Astrocyte Role in Temporal Lobe Epilepsy and Development of Mossy Fiber Sprouting

Epilepsy affects approximately 50 million people worldwide, with 60% of adult epilepsies presenting an onset of focal origin. The most common focal epilepsy is temporal lobe epilepsy (TLE). The role of astrocytes in the presentation and development of TLE has been increasingly studied and discussed within the literature. The most common histopathological diagnosis of TLE is hippocampal sclerosis. Hippocampal sclerosis is characterized by neuronal cell loss within the Cornu ammonis and reactive astrogliosis. In some cases, mossy fiber sprouting may be observed. Mossy fiber sprouting has been controversial in its contribution to epileptogenesis in TLE patients, and the mechanisms surrounding the phenomenon have yet to be elucidated. Several studies have reported that mossy fiber sprouting has an almost certain co-existence with reactive astrogliosis within the hippocampus under epileptic conditions. Astrocytes are known to play an important role in the survival and axonal outgrowth of central and peripheral nervous system neurons, pointing to a potential role of astrocytes in TLE and associated cellular alterations. Herein, we review the recent developments surrounding the role of astrocytes in the pathogenic process of TLE and mossy fiber sprouting, with a focus on proposed signaling pathways and cellular mechanisms, histological observations, and clinical correlations in human patients.

ChK1 Activation Induces Reactive Astrogliosis Through CIP2A/PP2A/STAT3 Pathway In Alzheimer's Disease

Background: In Alzheimer’s disease (AD), activation of astrocyte participates in the development of neurodegenerative diseases through neuroinflammation and disturbs glia-neuron interaction. Cancerous Inhibitor of PP2A (CIP2A) is an endogenous PP2A inhibitor. CIP2A upregulation specifically in astrocytes causes reactive astrogliosis, synaptic degeneration and cognitive deficits. However, the underlying mechanism of CIP2A upregulation remains unclear. Methods: In 3xTg-AD mice, we determined ChK1 was activated and related to DNA damage upregulating CIP2A by WB. We transfected EGFP-ChK1 plasmid into HEK293-T cell to determine ChK1 induces CIP2A upregulation and PP2A inhibition. We incubated Aβ and infected GFAP-ChK1-LV into primary astrocytes to confirm the signaling pathway in astrocytes and astrogliosis in AD. GFAP-ChK1-AAV was injected into C57/BL6 mice to induce specific expression of target protein in astrocytes. ChK1 inhibitor (SB) was performed to reverse the ChK1 activity. Outcomes were assessed using molecular (immunofluorescent staining, Western Blot and Golgi staining) measures to estimate symptomatic pathology and behavioral (NORT, OLT, MWM and FCT) measures to assess cognitive function. For most experiments, subjects were randomly assigned to experimental groups, and data were collected under blinded experimental conditions.Results: We demonstrated that DNA damage related Checkpoint kinase 1 (ChK1) was activated in 3xTg-AD mice. ChK1-mediated CIP2A overexpression drove inhibition of PP2A and activated STAT3, then led to reactive astrogliosis and neurodegeneration in vitro. Infection of mouse brain with GFAP-ChK1-AAV induced AD-like cognitive deficits and exacerbated AD pathologies in vivo. In conclusion, we showed that ChK1 activation induced reactive astrogliosis, degeneration of neurons and deterioration of AD through CIP2A-PP2A-STAT3 pathway, and inhibiting ChK1 might be a potential therapeutic approach for AD treatment.Conclusions: These results suggest that ChK1 is upregulated in 3xTg-AD mice, ChK1-mediated CIP2A overexpression drives inhibition of PP2A and activates STAT3, then leads to reactive astrogliosis, neurodegeneration and AD-like cognitive deficits in vitro and in vivo.

Tamoxifen Application Is Associated with Transiently Increased Loss of Hippocampal Neurons Following Virus Infection

Tamoxifen is frequently used in murine knockout systems with CreER/LoxP. Besides possible neuroprotective effects, tamoxifen is described as having a negative impact on adult neurogenesis. The present study investigated the effect of a high-dose tamoxifen application on Theiler’s murine encephalomyelitis virus (TMEV)-induced hippocampal damage. Two weeks after TMEV infection, 42% of the untreated TMEV-infected mice were affected by marked inflammation with neuronal loss, whereas 58% exhibited minor inflammation without neuronal loss. Irrespective of the presence of neuronal loss, untreated mice lacked TMEV antigen expression within the hippocampus at 14 days post-infection (dpi). Interestingly, tamoxifen application 0, 2 and 4, or 5, 7 and 9 dpi decelerated virus elimination and markedly increased neuronal loss to 94%, associated with increased reactive astrogliosis at 14 dpi. T cell infiltration, microgliosis and expression of water channels were similar within the inflammatory lesions, regardless of tamoxifen application. Applied at 0, 2 and 4 dpi, tamoxifen had a negative impact on the number of doublecortin (DCX)-positive cells within the dentate gyrus (DG) at 14 dpi, without a long-lasting effect on neuronal loss at 147 dpi. Thus, tamoxifen application during a TMEV infection is associated with transiently increased neuronal loss in the hippocampus, increased reactive astrogliosis and decreased neurogenesis in the DG.