Spatial-temporal patterns of reactive oxygen species release from microglia and synaptic impairment

• Applicant: Dr. Stefan Wendt
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 396567251

Excessive production of reactive oxygen species (ROS) is associated with neurodegenerative diseases such as Alzheimer’s disease (AD) and is known to contribute to synaptic dysfunction and neuronal death. Microglial cells, the resident macrophages of the brain, highly express NADPH oxidase that produces superoxide and ROS as part of their immune function. Extensive Abeta production and its accumulation (termed “Abeta plaques”) are hallmarks of AD. It was recently shown that gradual ROS increase around Abeta plaques precedes neuronal death but little is known about the precise roles for microglia, critical signaling pathways, leading to the temporal patterns of ROS generation and accumulation in neurons. Recently, the MacVicar group has shown that activation of microglial cells can alter synaptic activity by inducing Long-term depression (LTD) via ROS production after stimulation of Complement receptor 3 (CR3) under hypoxic conditions with lipopolysaccharides (LPS). Preliminary data indicate that this effect is mimicked by the application of oligomeric Abeta. I hypothesize that the binding of Abeta to CR3 will induce similar NADPH oxidase activation and subsequent ROS release thereby leading to LTD in nearby synapses. Furthermore I propose that ROS increases are temporally correlated with reduced synaptic activity. The first objective is to establish stable expression of genetic ROS indicators in neurons using adeno-associated viruses (AAV’s) for plasmid delivery. These fluorescent ROS sensors will allow real-time imaging of ROS during Abeta application and hypoxia in brain slices and in vivo. They are suitable for quantitative measurements and allow comparisons between different conditions which are difficult to achieve with synthetic ROS sensors. Next, pharmacological tools as well as knock out transgenic mice (e.g. CR3 -/-) will be used to determine the receptors, cellular pathways and roles for microglia in eliciting ROS increases leading to synaptic impairments. In mouse models of AD, such as the 5xFAD mouse, chronic synaptic dysfunctions are known hallmarks at late stages of amyloidosis and include suppressed synaptic activity in the hippocampus. The complement system is known to be involved in the pathogenesis of these mice. I hypothesize that elevated Abeta acts on microglial CR3 leading to induce ROS production which results in LTD in these mice. Most recently the drug simvastatin was identified to antagonize CR3 and it is used in clinical trials for early treatments of AD patients. Identifying microglial ROS production after CR3 stimulation as a cause of synaptic impairments will encourage further development of effective CR3 antagonist to suppress excessive microglial ROS production and its consequences in AD.

• DFG Programme: Research Fellowships
• International Connection: Canada
• Host: Professor Brian MacVicar, Ph.D.