Nathan Garnham

Identifying signaling responses governing synapse growth and function in aging neurons: defining responses to different cellular sources of oxidative stress

Aging results from the cumulative cellular damage incurred during lifetime. Reactive oxygen species (ROS) are a recognised source of damage during aging. High metabolic demand and terminal developmental state in neurons renders neural tissue vulnerable to ROS. How neurons, and in particular synapses, respond to ROS during ageing remains unclear. At low levels, ROS can act as a signal, promoting learning and memory processes potentially through the conserved Jun-kinase (JNK)/AP-1 signaling cascade. Recent work from the Sweeney lab (Milton et al., 2011, PNAS) has identified ROS as an upstream activator of JNK/AP-1 activation and synaptic growth in the Drosophila neuromuscular synapse, with pathological levels of ROS leading to overgrowth and functional failure. We observe that mitochondrial or cytoplasmic sources of ROS lead to differential signaling activation where cytoplasmic ROS activates Fos, and mitochondrial ROS activates Fos and Jun to drive synapse growth. We will use the genetic toolbox of Drosophila to define upstream signaling from JNK, and a targeted expression of a transgenic Tandem-Affinity-Purification tagged versions of Fos and Jun (followed by mass spectrometry) to identify the phosphorylation code that allows homo- or heterodimerisation of these factors. Our findings will be confirmed by the introduction of mutant genes by homologous recombination bearing appropriate phospho-mimetic and non-phosphorylatable mutations. This work will define the JNK pathway outputs regulating synapse growth and function in response to pathological levels of ROS from different cellular sources during the ageing process.

My name is Nathan Garnham, and I am currently in the second year of my PhD. I obtained a First degree in Genetics from the University of York and started my PhD with Sean Sweeney and David Ashford the following year.