MMP9 and hyperlipidemia: First, neurons become hyperactive in response to neurotoxic factors, hyperglycemia and hyperlipidemia, after which they release slow-acting microglial activators, such as matrix metalloproteinase-9 (MMP-9), ATP, and chemokines, mainly monocyte chemoattractant protein-1 (MCP-1, also known as chemokine CCL2), and CX3CL1 (fractalkine).