Abstract
Spinal cord injury (SCI) is a devastating condition resulting in loss of function below the level of injury. Inflammation after SCI promotes cell death, increases injury size, and decreases functional recovery. The inflammatory response is coordinated by many different signaling modalities including the epigenetic modification of promoters and enhancers. Bromodomain and extraterminal domain-containing proteins (BETs) are epigenetic readers that bind acetylated lysines in promoters and enhancers to promote pro-inflammatory transcription. BET inhibition suppresses inflammation in multiple animal models, including rheumatoid arthritis and sepsis. However, the role of BETs in neuroinflammation is not well understood. Using quantitative PCR, I demonstrated BET mRNA expression in primary neurons, astrocytes, oligodendrocytes, and microglia and in the spinal cord. To assess the role of BETs in neuroinflammation, I pharmacologically inhibited the binding of BETs to acetylated chromatin using the small-molecule JQ1. JQ1 significantly reduced cytokine-induced inflammatory activation of neurons, astrocytes, oligodendrocytes, and microglia in vitro. Furthermore, JQ1 treatment significantly reduced the expression of multiple cytokines after experimental SCI in mice. Because JQ1 also decreased the expression of many key chemokines, I hypothesized that BET inhibition would decrease leukocyte infiltration after SCI. Using flow cytometry, I found that JQ1 treatment significantly decreased the number of macrophages and neutrophils infiltrating the lesion site 3 days post-injury. These results suggest that BET inhibition is an effective anti-inflammatory therapeutic in acute SCI. To determine whether inflammatory inhibition acutely after SCI improved tissue sparing and functional recovery, I treated contusion-injured mice with JQ1 and assessed locomotor recovery using the Basso Mouse Scale (BMS) open field test and sensory recovery using the acetone and hotplate assays. JQ1 treatment did not significantly improve locomotor recovery or reduce lesion size, but did alleviate thermal hyperalgesia, suggesting BETs may also play a role in chronic pain. These results indicate that although BET inhibition reduces inflammation acutely after SCI, it is insufficient to promote significant tissue sparing or locomotor recovery in a mouse model of SCI. Overall, these studies demonstrate that targeting epigenetic proteins is an effective therapeutic mechanism for decreasing inflammation acutely after SCI and allows for the simultaneous inhibition of multiple inflammatory-response genes.