Traumatic brain injury (TBI) is currently a major cause of morbidity and poor quality of life in Western society, with an estimate of 2.5 million people affected per year in Europe, indicating the need for advances in TBI treatment. Within the first 24 h after TBI, several inflammatory response factors become upregulated, including the lectin galectin-3. In this study, using a controlled cortical impact (CCI) model of head injury, we show a large increase in the expression of galectin-3 in microglia and also an increase in the released form of galectin-3 in the cerebrospinal fluid (CSF) 24 h after head injury. We report that galectin-3 can bind to TLR-4, and that administration of a neutralizing antibody against galectin-3 decreases the expression of IL-1β, IL-6, TNFα and NOS2 and promotes neuroprotection in the cortical and hippocampal cell populations after head injury. Long-term analysis demonstrated a significant neuroprotection in the cortical region in the galectin-3 knockout animals in response to TBI. These results suggest that following head trauma, released galectin-3 may act as an alarmin, binding, among other proteins, to TLR-4 and promoting inflammation and neuronal loss. Taking all together, galectin-3 emerges as a clinically relevant target for TBI therapy.
Graphical Abstract Highlights d TET2 is upregulated in microglia cells upon various inflammatory stimuli d TET2 regulates TLR-4-induced type I IFN response and LPSinduced aerobic glycolysis d TET2 regulates the proinflammatory response induced by LPS in vitro and in vivo d TET2 is expressed by amyloid b plaque-associated microglia in AD brains SUMMARY Epigenomic mechanisms regulate distinct aspects of the inflammatory response in immune cells. Despite the central role for microglia in neuroinflammation and neurodegeneration, little is known about their epigenomic regulation of the inflammatory response.Here, we show that Ten-eleven translocation 2 (TET2) methylcytosine dioxygenase expression is increased in microglia upon stimulation with various inflammogens through a NF-kBdependent pathway. We found that TET2 regulates early gene transcriptional changes, leading to early metabolic alterations, as well as a later inflammatory response independently of its enzymatic activity. We further show that TET2 regulates the proinflammatory response in microglia of mice intraperitoneally injected with LPS. We observed that microglia associated with amyloid b plaques expressed TET2 in brain tissue from individuals with Alzheimer's disease (AD) and in 5xFAD mice. Collectively, our findings show that TET2 plays an important role in the microglial inflammatory response and suggest TET2 as a potential target to combat neurodegenerative brain disorders.
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