Adipo-IR and the one-step hyperinsulinemic-euglycemic clamp technique using a palmitate tracer are good predictors of a gold standard measure of adipose tissue insulin sensitivity. However, age and physical fitness systematically affect the predictive values. Although Adipo-IR is suitable for larger population studies, the multistep pancreatic clamp technique is probably needed for mechanistic studies of adipose tissue insulin action.

The current standard of care for head and neck cancer includes surgical resection of the tumor followed by targeted head and neck radiation. This radiotherapy results in a multitude of negative side effects in adjacent normal tissues. Autophagy is a cellular mechanism that could be targeted to ameliorate these side effects based on its role in cellular homeostasis. In this study, we utilized Atg5f/f;Aqp5-Cre mice which harbor a conditional knockout of Atg5, in salivary acinar cells. These autophagy-deficient mice display increased radiosensitivity. Treatment of wild-type mice with radiation did not robustly induce autophagy following radiotherapy, however, using a model of preserved salivary gland function by IGF-1-treatment prior to irradiation, we demonstrate increased autophagosome formation 6–8 hours following radiation. Additionally, administration of IGF-1 to Atg5f/f;Aqp5-Cre mice did not preserve physiological function. Thus, autophagy appears to play a beneficial role in salivary glands following radiation and pharmacological induction of autophagy could alleviate the negative side effects associated with therapy for head and neck cancer.

Autophagy is a catabolic pathway utilized to maintain a balance among the synthesis, degradation, and recycling of cellular components, thereby playing a role in cell growth, development, and homeostasis. Previous studies revealed that a conditional knockout of essential member(s) of autophagy in a variety of tissues causes changes in structure and function of these tissues. Acinar cell-specific expression of knocked-in Cre recombinase through control of aquaporin 5 (Aqp5) promoter/enhancer (Aqp5-Cre) allows us to specifically inactivate Atg5, a protein necessary for autophagy, in salivary acinar cells of Atg5 f/f ;Aqp5-Cre mice. There was no difference in apoptotic or proliferation levels in salivary glands of Atg5/Cre mice from each genotype. However, H&E staining and electron microscopy studies revealed modestly enlarged acinar cells and accumulated secretory granules in salivary glands of Atg5 f/f ;Aqp5-Cre mice. Salivary flow rates and amylase contents of Atg5/Cre mice indicated that acinar-specific inactivation of ATG5 did not alter carbachol-evoked saliva and amylase secretion. Conversely, autophagy intersected with salivary morphological and secretory manifestations induced by isoproterenol administration. These results identified a role for autophagy as a homeostasis control in salivary glands. Collectively, Atg5 f/f ;Aqp5-Cre mice would be a useful tool to enhance our understanding of autophagy in adaptive responses following targeted head and neck radiation or Sjögren syndrome.

The standard of care for head and neck cancer typically includes surgical resection of the tumor followed by targeted head and neck radiation. However depending on tumor location and stage, some cases may not require surgical resection while others may be treated with chemoradiation. Unfortunately, these radiation treatments cause chronic negative side effects for patients. These side effects are associated with damage to surrounding normal salivary gland tissue and include xerostomia, changes in taste and malnutrition. The underlying mechanisms of chronic radiation-induced salivary gland dysfunction are unknown, however, in rodent models persistently elevated proliferation is correlated with reduced stimulated salivary flow. The rapalogue, CCI-779, has been used in other cell systems to induce autophagy and reduce proliferation, therefore the aim of this study was to determine if CCI-779 could be utilized to ameliorate chronic radiation-induced salivary gland dysfunction. Four to six week old Atg5f/f; Aqp5-Cre, Atg5+/+; Aqp5-Cre and FVB mice were treated with targeted head and neck radiation. FVB mice were treated with CCI-779, chloroquine, or DMSO post-radiation. Stimulated salivary flow rates were determined and parotid and submandibular salivary gland tissues were collected for analyses. Mice with a defect in autophagy, via a conditional knockout of Atg5 in the salivary glands, display increased compensatory proliferation in the acinar cell compartment and hypertrophy at 24-72 hours following radiation. FVB mice treated with post-therapy CCI-779 have significant improvements in salivary gland physiology as determined by stimulated salivary flow rates, proliferation indices and amylase production and secretion. Consequently, post-radiation use of CCI-779 allows for improvement of salivary gland function and reestablishment of glandular homeostasis. As CCI-779 is already FDA approved for other uses, it could have a secondary use to alleviate the chronic side effects in head and neck cancer patients who have completed anti-tumor therapy.