Dan Summers

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Dan Summers
Assistant Professor
PhD, University of North Carolina at Chapel Hill, 2011
Email: Phone:
(319) 467-0919
236 Biology Building East
210 East Iowa Avenue, Iowa City, IA 52242-1324
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Research Areas

Research Summary

Protein homeostasis in developing and diseased neurons

Our nervous system controls every aspect of how we perceive and react to the world around us. To accomplish this incredible task, neurons establish connections throughout the human body, extending long projections called axons that can reach over a meter in length. In isolation from the neuronal cell body, axons are highly autonomous and carry out many basic biological functions such as protein synthesis, transport, and degradation. The neurons in our body are post-mitotic so axons must survive and function for our entire lifetime. Due to this incredible burden axon degeneration is a prominent event in many neurodegenerative disorders of the peripheral and central nervous systems (See Figure 1)

To better understand neuronal function and identify new therapeutic approaches for neurodegeneration we study the neuronal pathways responsible for protein homeostasis. Defects in protein homeostasis underlie many neurological disorders including Alzheimer’s disease, Parkinson’s disease, and numerous peripheral neuropathies. We have a particular focus on axon biology to discover how this unique subcellular compartment operates and declines in aging or disease. We use a combination of biochemistry, live imaging, primary neuron, and animal models to address this problem. (See Figure 2 for an example)

How do proteostasis networks regulate axon vulnerability or resistance to disease?
Axons are specialized cellular compartments that utilize many undiscovered strategies for regulating the biogenesis and disposal of axonal proteins. These proteostasis networks have important implications for neuronal function and survival. For example, axons require a constant supply of survival proteins and must efficiently balance protein transport and synthesis with regulated protein degradation. Disturbing this balance can deplete axons of essential factors and provoke axon degeneration or enhance vulnerability to stress and dysfunction. Conversely, blocking specific protein degradation pathways can increase the abundance of these factors and promote axon survival. Therefore, we study the protein homeostasis of axon survival factors and what molecular pathways regulate this balance with the goal of boosting axon resistance to degeneration. (See Figure 3)

How does local protein translation affect axon biology and susceptibility to disease?
To circumvent transporting proteins across long distances, axons locally synthesize many proteins needed for function. Translating a protein is not a simple process and requires numerous auxiliary factors (ex. molecular chaperones) to facilitate the maturation of a new polypeptide into a functional protein. We are investigating the biogenesis of locally translated axonal proteins, how these proteins are properly folded, localized, and regulated in response to stress. We are also developing animal models to explore this question in vivo and in the context of chronic neurodegeneration.

How do stress response pathways intersect to elicit an adaptive (or maladaptive) cellular outcome?
Neurons possess multiple stress response pathways that sense changes in the external as well as internal cellular environment. The consequences of activating a stress response pathway are not always beneficial as over-stimulation can aggravate neuronal dysfunction. We are characterizing the spatial-temporal dynamics of stress response complexes (ex. MAP Kinases) in neurons and how they coordinately elicit local changes in axon compartments as well as transcriptional adaptations.

How does local environment influence neuron proteostasis?
Neurons do not exist in isolation. Rather, neurons respond to signals in their environment and interact with a variety of cells including glia and immune cells. More and more, we are coming to appreciate the powerful influence these interactions have on neuron health and function. My lab investigates how non-cell autonomous signals from supporting glia and immune cells influence neuronal proteostasis. We suspect these pathways will have important implications for neuronal function and degeneration in disease. 

Selected Images

Axon diagram
Axon proteostasis