Mechanisms of Thrombin-Induced Expression of Matrix Metalloproteinase-9 in Rat Brain Astrocytes

Neuroinflammation is a hallmark of all major CNS neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson’s disease (PD). The elevated expression of various inflammatory proteins such as matrix metalloproteinases (MMPs) in experimental and clinical neurodegenerative disease, and intervention studies in experimental animals suggest that these factors contribute to neuronal injury. Several studies have demonstrated that thrombin exerts physiological and pathological functions in the CNS. The involvement of thrombin and its receptors in the development of neurodegenerative processes may be mediated through up-regulation of several inflammatory genes such as matrix metalloproteinases (MMPs), in particular MMP-9. Recently, oxidative stress due to generation of ROS (e.g. mitochondrial dysfunction and NADPH oxidase activation) may be involved in brain injury and inflammation. ROS can also be sensed by the cells and trigger intracellular signaling cascades potentiating chronic inflammation. Interplay between ROS and MMP-9 induced by thrombin leading to neurodegeneration remains largely unknown. Moreover, we have demonstrated that IL-1may act as a pro-inflammatory factor and induces expression of MMP-9 assocaited with the change of BBB function in various brain injuries and neuroinflammation. Therefore, we hypothesize that thrombin-initiated neurodegeneration is mediated by the generation of ROS and the induction of MMP-9 proteins in brain cells (i.e. glial cells and neuronal cells). To test this hypothesis, this proposal will investigate the molecular mechanisms underlying thrombin induced MMP-9expression in astrocytes, including (1) to evaluate whether MMP-9 expression induced by thrombin, (2) to characterize the role of ROS in MMP-9 expression induced by thrombin, (3) to determine whether G-protein coupled PAR receptors, PLC, PKC, Ca2+, and CaMKII were involved in thrombin-induced MMP-9 expression, (4) to determine whether activation of MAPKs (e.g. ERK, p38 MAPK, and JNK) by thrombin leading to MMP-9 expression, (5) to differentiate whether alternative pathways (RTK and PI3K/Akt transactivation) involved in MMP-9 expression induced by thrombin, (6) to characterize the roles of various transcription factors and coactivators in MMP-9 expression induced by thrombin, (7) to determine whether Jak/STAT involved in thrombin-induced MMP-9 expression, and (8) to evaluate the roles of upregulated MMP-9 on astrocytic or neuronal physiological and pathological functions in vitro and in vivo studies. These experiments should provide new insights into the mechanisms involved in neuroinflammation and neurodegeneration. Increased understanding of these mechanisms underlying up-regulation of MMP-9 genes will create opportunities for the development of therapeutic strategies in neurodegenerative diseases.

Project ID:PC10109-0155
External Project ID:NSC101-2320-B182-039-MY3