Proper salivary gland function is critical for oral health. Radiation therapy for head and neck cancer often causes notable side effects that impact normal salivary gland function, most commonly xerostomia. Current therapies are unable to permanently restore salivary function, which remains a major therapeutic challenge. The long-term goal of our research is to elucidate the molecular and cellular mechanisms, in particular the signaling networks, involved in salivary gland homeostatic control and regeneration. One of the homeostatic control mechanisms, autophagy, is a constitutive cellular catabolic degradation process whereby cellular proteins and organelles are engulfed, digested through the lysosomal machinery and recycled. The autophagy-related 5 gene, Atg5, has been established as an indispensable player in autophagy. Our preliminary data suggest that acute hypoxic stress utilizes the JNK1/Beclin 1-dependent pathway to induce autophagy, providing transient protection against hypoxic stress-elicited cell death in salivary cells. Moreover, we generated Aqp5-Cre transgenic mice, in which the Cre recombinase was targeted to express in salivary acinar cells by being knocked in the exon 1 of Aquaporin-5 (Aqp5) gene, as Aqp5 protein is preferentially expressed in salivary acinar cells. Utilizing this knowledge and these tools, we propose to investigate the role of autophagy in governing homeostatic control, regeneration and adaptive responses following stress or injury of various types and/or severity to salivary acinar cells. Our central hypotheses are: 1) Loss-of-Atg5-function impairs the ability of salivary acinar cells to maintain homeostatic control against stress (Aim 1), 2) Autophagy plays a transient cytoprotective role during injury (Aim 2), and 3) Crosstalk among autophagic, apoptotic and necrotic pathways decides the fate of stressed or injured salivary acinar cells (Aim 3). We postulate that autophagy protects salivary glands from stress and pathologic insults by promoting acinar cell survival and regeneration as a stress adaptation response. Our objective will be pursued through the following means: (1) Characterize mice with salivary acinar-targeted Atg5 inactivation from crossing Aqp5-Cre mice with Atg5f/f mice, representing a unique source on which our experimental plan is based, (2) Determine the contribution of autophagy to homeostatic control using a chronic isoproterenol- injection model and to salivary acinar cell death and regeneration using a submandibular ductal ligation/de- ligation model, respectively, and (3) Investigate crosstalk of autophagy with other cell death pathways in underlying salivary adaptive responses. These studies will greatly improve our understanding of salivary gland homeostatic control and/or regeneration in a deleterious environment. In addition, they will provide a unique opportunity to evaluate the feasibility of autophagy-targeted therapies to ameliorate or restore salivary gland (dys)function following injury in human.
Autophagy is a biological process, associated with cell death, which has important implications in normal physiology and many pathological conditions, including acute and chronic disease states and a myriad of cancers. Understanding how these autophagic processes modulate adaptation to cellular stress is essential for developing effective therapeutics to target diseased salivary tissues, as well as tissue engineering of salivary glands for tissue replacement. The proposed studies will not only open the field of salivary research, but will also assist in developing a strategy to prevent the loss of salivary gland function resulting from disease or cell death in head and neck cancer patients undergoing radiation therapy.
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