Angiocrine Factors in Salivary Gland Regeneration

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Abstract: Salivary hypofunction, or reduced saliva flow, is a common condition resulting from the autoimmune disease Sjögren’s Syndrome, radiation therapy for treatment of head and neck cancer, and side effects of medications. Salivary hypofunction can lead to difficulties with nutritional, dental, and psychological health, leading to a decreased quality of life. Current treatment options are only palliative and new regenerative therapies are needed. Regeneration is the growth, renewal, or restoration of tissue following injury or damage. Regenerative ability varies among organisms, with mammalian regeneration being largely limited. To study regeneration of the submandibular salivary gland we will employ a ductal ligation model in which the gland atrophies following a two-week ligation, resulting in a decrease in gland weight due to acinar cell death and loss of secretory granules. After clip removal, or deligation, the submandibular salivary gland regenerates, increasing in gland weight, due to acinar cell proliferation and restoration of secretory granules. Most studies using the ductal ligation model have focused on the role of the acinar cells due to their importance in producing saliva; however, endothelial cells that line the interior surface of blood vessels are critical for regeneration of other organs. Although endothelial cell dysfunction has been linked to a subset of Sjögren’s Syndrome patients as well as patients receiving radiation therapy as a treatment for head and neck cancer, how endothelial cells contribute to salivary gland function and repair capacity is not understood. Endothelial cells play critical roles in organ development, homeostasis, and regeneration through the secretion of paracrine factors, including growth factors, morphogens, extracellular matrix components, and chemokines that act on epithelial cells, which are collectively referred to as angiocrine factors. Angiocrine factor signaling has been shown to be organ-specific, to vary during times of regeneration, and to change over the time course of regeneration. However, angiocrine factors produced by the submandibular salivary gland during homeostasis and regeneration have not been defined. Using the ductal ligation model, I will profile angiocrine factors produced by endothelial cells after three and six days of deligation in comparison to two weeks of ligation relative to surgical control glands. RNA-seq will be used to identify the angiocrine factor targets that are produced by actively regenerating salivary endothelial cells. Microarray analysis of epithelial cells after three and six days deligation will be used to identify potential changes in angiocrine factor receptor expression. Knockdown and overexpression lentiviral constructs will be used ex vivo to determine the contribution of these putative angiocrine factors in salivary gland organoids and to identify possible mechanisms of action. Defining the mechanism of action of the angiocrine factors during regeneration will allow for a better understanding of possible means for future functional restoration of the salivary gland. This training program will also prepare me for a career in research and teaching as a professor.