Agnieszka Podraza-Farhanieh - Functions and novel roles of three proteins in relation to insulin signaling and secretion

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Functions and novel roles of three proteins in relation to insulin signaling and secretion

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Diabetes mellitus is a group of disorders characterized by disrupted glucose homeostasis. Globally, it is among the most widespread diseases, currently affecting more than 500 million people worldwide.

The pathogenesis of diabetes is associated with insufficient insulin production and characterized by raised blood glucose levels. The response to these elevated levels includes the pancreatic β-cells’ insulin secretion, which is regulated by various factors. The purpose of the thesis project was to gain an understanding the functions of three proteins and describe their novel roles in regulating of insulin signaling and secretion.

The model organism in my study is a nematode, C. elegans, a roundworm (*). This is a model widely used in fundamental research, since it conserves the pathways, which are highly homologous between humans and nematodes. By using this model system, I was able to better understand how the proteins of interest regulate insulin secretion, says Agnieszka Podraza-Farhanieh. She has a bachelor’s degree in biotechnology from the University of Agriculture in Krakow, Poland and a master’s degree in biomedicine from the University of Skövde.

Figure 1: In humans, insulin is expressed and secreted by the pancreatic beta cells in response to elevated glucose levels. In the model organism used in this study, insulin is expressed and secreted by the neuroendocrine cells. The levels of secreted insulin are measured in the scavenger cells that pick up the secreted peptide. The process of insulin signaling and insulin secretion is highly conserved between humans and C. elegans.

How ENPL-1, ASNA-1, and SMN-1 control insulin signaling and insulin secretion
The main objective of the thesis was to understand how three proteins (ENPL-1, ASNA-1 and SMN-1) control insulin signaling and insulin secretion.

ENPL-1 is a protein that has many roles in maintaining cellular homeostasis.
We found that ENPL-1 is the positive regulator of insulin secretion. Loss of enpl-1 resulted in reduced insulin signaling and inhibited insulin secretion. We also discovered the mechanism of ENPL-1 function and showed that ENPL-1 binds to proinsulin and is essential for proinsulin processing to create mature, active insulin.

The second study focused on the role of ASNA-1.
Our analysis showed that protein is sensitive to changes in oxidative stress levels. Based on these findings, we were able to separate the clinically relevant functions of ASNA-1 and show that the oxidized form of protein is responsible for insulin secretion. In following up this project, we discovered the interaction between oxidized ASNA-1 and ENPL-1. We found that this interaction requires proinsulin and that the presence of ASNA-1 in Golgi compartments of the cell is probably necessary for retrograde transport.

Figure 2, above: We separated ASNA-1 functions based on its redox state. Oxidized ASNA-1 interacts with ENPL-1 in the Golgi apparatus of the neuroendocrine cells. This interaction requires the presence of insulin and is essential for insulin secretion. In the intestines, reduced ASNA-1 interacts with ER receptor, WRB-1. This interaction is essential for insertion of tail-anchored proteins into the endoplasmic reticulum and for detoxification of the anticancer drug cisplatin.

The last project was aimed at understanding the role of SMN-1, a protein whose deletion leads to the development of spinal muscular atrophy.
We showed that loss of smn-1 results in neuropeptide secretion defects and leads to changes in the localization of the insulin, from the neuroendocrine cells to non-neuronal cells. In summary, by using genetic and molecular analyses in C. elegans, we identified and characterized the mechanisms of novel genetic factors that contribute to a better understanding of insulin secretion processes.

MORE FACTS

• C. elegans is a roundworm that exists in two forms: as self-fertilizing hermaphrodites and as males. They are characterized by a short generation cycle, lasting approximately 3.5 days and involving an embryonic stage, four larval stages, and an adult stage.