There is a fundamental gap in understanding how the islets of Langerhans function in vivo, either in the native environment in the pancreas or after transplantation to treat type 1 diabetes. Most studies on islet function have been performed in vitro, and as a consequence little is known about the role of innervation on islet hormone secretion. The long-term goal of our research is to understand the cell biology of islets of Langerhans within the regulatory networks that exist in the living organism. The objective of this particular application is to determine the role sensory innervation plays in islet biology using ne technological platforms allowing in situ and in vivo imaging of islets. For in vivo imaging, islets are transplanted into the anterior chamber of the eye, and their function is recorded locally and systemically after manipulation of the eye's neural input. The central hypothesis is that sensory axons detect molecules released during islet activity and in response release substances that modulate islet function. In the proposed mechanism, sensory axons are localized between endocrine cells, resident macrophages, and vascular cells and are therefore positioned optimally to screen the extracellular space for changes in the chemical composition. When activated by local signals, sensory axons release neuropeptides that dampen endocrine activity, alter vascular function, and keep resident macrophages quiescent, thus promoting tissue homeostasis. The rationale for the proposed research is that the results will contribute a missing, fundamental element to basic knowledge, without which islet biology cannot be understood. The proposed research is therefore relevant to the mission of the NIH that pertains to the pursuit of fundamental knowledge about the nature and behavior of living systems. Guided by strong preliminary data, this hypothesis will be tested by pursuing three specific aims: 1) The innervation patterns of sensory axons in mouse and human pancreatic islets; 2) The functional role of sensory axons innervating the pancreatic islet; and 3) The role of sensory axons in islet biology and glucose homeostasis in vivo. Under the first aim, the sensory innervation patterns of islets and the neurotransmitter receptor profiles of the innervated islet cell types will be systematically examined in mouse and human islets using immunohistochemistry and physiological recordings. Under the second aim, the response profiles of sensory axons innervating the islet and their effects on islet cells will be studied usng pancreas tissue slices from mice expressing functional reporters in sensory axons or islet cells. Under the third aim, local responses in the islet and regulation of glucose homeostasis by intraocular islet grafts will be challenged by activating, blocking or ablating sensory input. The proposed work is innovative because it capitalizes on new technological platforms that allows for the first time in situ and in vivo functional imaging of sensory axons innervating the pancreatic islet. The proposed research is significant because it is expected to advance and expand current models of the regulation of glucose homeostasis by pancreatic islets. Ultimately, such knowledge has the potential to impact the way diabetes is treated.
The proposed work will demonstrate the role of innervation for pancreatic islet function. It takes advantage of a new technological platform developed by our group allowing for the first time imaging of innervated islets in a living organism. As a major expected outcome we will obtain a comprehensive picture of the influence islet innervation has on islet biology, which will have a strong impact on current models of islet regulation of glucose homeostasis.
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