Neuroinflammation is an important feature of cerebral ischemia. However, persistent inflammation can contribute to progressive tissue damage during the recovery phase. The bacterial lipopolysaccharide endotoxin (LPS) has been widely used as a model of systemic inflammation in mice. Intraperitoneal LPS injection to animals has been shown to produce an inflammatory signal in brain resulting in an increased production of pro-inflammatory cytokines and memory deficit. Activation of the a7 acetylcholine receptors (a7) has been shown to reduce the release of pro-inflammatory cytokines in vivo. Serum TNF-? levels were significantly higher in a7 knockout mice (a7-K0) compared to WT two hours after LPS endotoxin administration. In a traumatic brain injury model, the a7-K0 mice had significantly higher plasma levels of TNF-a, IL- 1b than WT mice at 24hr post injury. Our research group has identified a natural cembranoid, 4R, with neuroprotective properties. 4R protects against neuronal toxicity in vivo and significantly decreases infarction size in a rodent model of ischemic stroke. Our preliminary data shows that 4R treatment significantly lower serum TNF-?, IL-1b, and brain MCP-1 levels in mice after LPS-induced inflammation. Our hypothesis states that 4R treatment decreases LPS- induced neuroinflammation and improves memory function in mice by potentiation of the a7 receptor. The following specific aims are designed to test this hypothesis: 1) To investigate if 4R decreases neuroinflammation in mice and whether the effect is mediated by the a7 receptor. The effect of 4R will be examined by injecting LPS followed by 1) saline, 2) vehicle, or 3) 4R. Pro-and anti-inflammatory cytokines as well as phosphorylation of Akt, NF-kB, and CREB signaling proteins will be measured in cerebral cortex and hippocampus homogenates. 2) To examine the role of 4R and the a7 receptor in monocyte infiltration after LPS-induced inflammation. WT and a7-K0 mice will be randomly divided into 3 treatment groups: 1) LPS/saline, 2) LPS/vehicle, and LPS/4R and sacrificed at 24hrs, 72hrs, and 1 week after LPS injection. Flow cytometry analysis will be performed to calculate the average percentage of M1- M2 infiltrated monocytes over time. 3) To determine if 4R-cembranoid treatment improves memory deficits associated with LPS-induced inflammation in mice and whether the effect is a7 receptor dependent. Mice will be randomly divided into the same 3 treatment groups as in Aim 2. Memory function will be assessed using the novel object recognition test. 4R hippocampal neuroprotection will be determined by immunohistochemistry using stereological counting of NeuN-positive neurons in brain slices. The results of these studies will allow us to determine the mechanism of action of 4R to reduce inflammation and improve behavioral function in brain following LPS-induced inflammation in mice.
This study is relevant to public health because it is expected provide new information on the neuroprotective mechanism(s) of 4R treatment and its potential therapeutic importance in the treatment of neuroinflammation.
