PROJECT SUMMARY/ABSTRACT
Each year, over 200,000 Americans suffer from global cerebral ischemia associated with cardiac arrest leading
to cognitive deficits or death. While emergency treatments of cardiac arrest focus on restoring cardiac function
and blood flow, an effective therapeutic treatment for neurodegeneration and cognitive deficits associated with
global cerebral ischemia is a crucial unmet medical need. Although the entire brain is deprived of oxygen, global
ischemia causes selective, delayed death of hippocampal CA1 pyramidal neurons, which in turn induces severe
deficits in hippocampus-dependent cognitive function. Although the mechanisms underlying the pathophysiology
of global ischemia are unclear, the long delay between insult and neuronal death is consistent with a role for
transcriptional changes. In preliminary studies, we performed RNA-seq using next generation Massively parallel
sequencing to investigate alterations of gene expression in post-ischemic hippocampal CA1 in rats. Ingenuity
Pathway Analysis (IPA) revealed that `Triggering receptor expressed in myeloid cells 1 (TREM1) signaling' and
`Neuroinflammation' are the top canonical pathways. TREM1 is an inflammatory type I membrane receptor
expressed in myeloid lineage and known to magnify the proinflammatory innate immune response. Evidence
implicates a proinflammatory role of TREM1 in inflammatory diseases, cancer, and other brain diseases,
however, the role of TREM1 in global cerebral ischemia associated with cardiac arrest remains unknown. Our
preliminary confocal imaging showed that TREM1 is activated in CD11b positive immune cells but not in neurons
or astrocytes in hippocampal CA1 after global ischemia. IPA analysis further identified BRD4 and p300 as
upstream effectors which are recently reported as epigenetic regulators of TREM1 in inflammatory related
diseases. We also validated both proteins are increased in TREM1 positive cells in post-ischemic hippocampal
CA1 and upregulated TREM1 expression was rescued by a BRD4 inhibitor. Importantly, our preliminary data
showed that TREM1 peptide inhibitors LR12 and GJ073, and BRD4 inhibitor JQ1 attenuate global ischemia-
induced neuronal death. The overall objectives of this proposal are to determine the pathological importance of
TREM1 and mechanisms of TREM1-mediated neuroinflammation in global ischemia-induced neuronal death, and
establish inhibitors of TREM1 and its upstream BRD4 as novel therapeutic agents to improve outcomes in global
ischemia. The central hypothesis is that global ischemia activates neuroinflammation by epigenetic regulation of
TREM1 in hippocampal CA1 and that inhibition of TREM1 signaling rescues neurons against global ischemic
insults. We seek to test this hypothesis as described in the following Specific Aims; Aim 1. Determine the
pathological importance of TREM1 in global cerebral ischemia. Aim 2. Determine the mechanism by which global
ischemia activates TREM1 mediated neuroinflammation. Aim 3. Evaluate the ability of TREM1 and BRD4 inhibitors
as potential therapeutic agents to rescue neurons against global ischemic insults.
