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Cellular and subcellular localization of peripheral benzodiazepine receptors after trimethyltin neurotoxicity
1Department of Environmental Health Sciences, Johns Hopkins University, School of Hygiene and Public Health, Baltimore, Maryland 21205, USA.
Abstract:
The peripheral benzodiazepine receptor (PBR) is currently used as a marker of inflammation and gliosis following brain injury. Previous reports suggest that elevated PBR levels in injured brain tissue are specific to activated microglia and infiltrating macrophages. We have produced hippocampal lesions using the neurotoxicant trimethyltin (TMT) to examine the cellular and subcellular nature of the PBR response. Degenerating, argyrophilic pyramidal neurons were observed in the hippocampus at 2 and 14 days after TMT exposure. Reactive microglia were also evident at both times with a maximal response observed at 14 days, subsiding by 6 weeks. Astrocytosis was observed at 14 days and 6 weeks, but not 2 days, after TMT administration, suggesting that the onset of the astroglia response is delayed, but more persistent, compared with microgliosis. Morphological evidence from [3H]PK11195 microautoradiography and PBR immunohistochemistry indicates that both astrocytes and microglia are capable of expressing high levels of PBR after injury. This was confirmed by double labeling of either Griffonia simplicifolia isolectin B4, a microglial-specific marker, or glial fibrillary acidic protein, an astrocyte-specific protein with PBR fluorescence immunohistochemistry. These results demonstrate that PBR expression is increased after brain injury in both activated microglia and astrocytes. Our findings also provide the first evidence for in situ nuclear localization of PBR in glial cells.
Insights
Peripheral benzodiazepine receptor (PBR) is found in both activated microglia and astrocytes following brain injury, challenging previous assumptions of its specificity to microglia. This study reveals PBR
Area of Science:
- Neuroscience
- Neuroinflammation
- Cellular Biology
Background:
- Peripheral benzodiazepine receptor (PBR) is a known marker for inflammation and gliosis in brain injury.
- Previous research indicated PBR expression is specific to activated microglia and macrophages in injured brain tissue.
Purpose of the Study:
- To investigate the cellular and subcellular distribution of PBR in the hippocampus following neurotoxic injury.
- To determine if astrocytes, in addition to microglia, express PBR after brain injury.
Main Methods:
- Hippocampal lesions were induced using the neurotoxicant trimethyltin (TMT).
- Cellular responses were assessed using silver staining for neuronal degeneration, immunohistochemistry for glial markers (microglia and astrocytes), and PBR fluorescence.
- [3H]PK11195 microautoradiography was employed to visualize PBR.
- Double labeling techniques were used to co-localize PBR with microglial and astrocyte markers.
Main Results:
- TMT exposure caused neuronal degeneration, microgliosis, and astrocytosis in the hippocampus.
- Both microglia and astrocytes were found to express high levels of PBR following TMT-induced injury.
- PBR expression was confirmed in both cell types using double labeling with specific markers.
- The study provides the first evidence of in situ nuclear localization of PBR within glial cells.
Conclusions:
- Peripheral benzodiazepine receptor (PBR) expression is not exclusive to microglia and macrophages but is also significantly upregulated in astrocytes after brain injury.
- These findings expand our understanding of PBR's role in neuroinflammation and suggest it is a marker for both microglial and astroglial activation.
- The discovery of nuclear PBR localization in glial cells opens new avenues for research into its intracellular functions.