The adipose-derived secretory factor adiponectin promotes an increase in ceramide catabolism, which is dependent on adiponectin receptors 1 and 2. The receptor-associated ceramidase activity promotes ceramide degradation and generation of sphingosine 1-phosphate (S1P), offering b-cells protection from caspase-8- dependent pro-apoptotic insults. The simple 2-step conversion of ceramide to S1P and starkly opposing roles of the two lipids on cell survival and proliferation has led us and others to postulate the existence of a cellular rheostat governed by these two lipids. As adiponectin promotes improvements in whole body metabolism, it remains unclear whether the local actions of adiponectin within the b-cell elicit these protective effects, or if improvements in the circulaing metabolic milieu mediate these protective responses. Understanding this protective mechanism is critical for developing strategies to maintain healthy populations of b-cells in individuals. I hypothesize that adiponectin receptors promote b-cell survival and proliferation by governing the ceramide:S1P ratio. Here, I will evaluate the effects of b-cell-specific overexpression of adiponectin receptors or acid ceramidase (a presumed positive control) on the maintenance of functional b-cell mass. Moreover, I will examine the contributions of S1P-mediated protective effects on b-cell survival in mice lacking S1P receptors (1, 2 or 3) or mice overexpressing the S1P degrading enzyme S1P lyase. To do that, I will take advantage of the "PANIC-ATTAC" transgenic mouse, which offers inducible, titratable, b-cell specific apoptosis. Since I functionaly inactivate the b-cells through mild apoptosis as opposed to necrosis, I reduce the pro-inflammatory component of b-cell death, and thus b-cell mass can be reconstituted upon cessation of dimerizer treatment. Collectively, I will be able to evaluate the effects of adiponectin, adiponectin receptors, acid ceramidase, and S1P on: a) the adiponectin-mediated anti-apoptotic actions in the b-cell, and b) adiponectin's ability to enhance the regenerative potential of functional b-cell mass. I will also determine if b-cell-specific overexpression of adiponectin receptor 1, adiponectin receptor 2, or acid ceramidase (AC) is sufficient to maintain functional islet mass using the ob/ob mouse as a model of diabetic b-cell failure. These studies will hopefully suggest novel therapeutic avenues for the treatment and prevention of diabetes by promoting b-cell functionality, and by promoting regenerative processes within the b-cell population.

Public Health Relevance

Understanding the protective mechanisms by which adiponectin maintains functional b-cell mass is critical for developing strategies to maintain healthy populations of b-cells in individuals. These studies may suggest novel therapies for the treatment and prevention of diabetes by promoting functional b-cell mass, and potential regenerative processes within the b-cell. Moreover, they will enhance the general understanding of factors governing cell survival and proliferation, which has implications for a diverse array of diseases and treatment modalities influenced by cell death.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Career Transition Award (K99)
Project #
5K99DK094973-02
Application #
8460928
Study Section
Diabetes, Endocrinology and Metabolic Diseases B Subcommittee (DDK)
Program Officer
Appel, Michael C
Project Start
2012-05-01
Project End
2014-03-31
Budget Start
2013-04-01
Budget End
2014-03-31
Support Year
2
Fiscal Year
2013
Total Cost
$87,978
Indirect Cost
$6,517
Name
University of Texas Sw Medical Center Dallas
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
800771545
City
Dallas
State
TX
Country
United States
Zip Code
75390
Tao, Caroline; Sifuentes, Angelica; Holland, William L (2014) Regulation of glucose and lipid homeostasis by adiponectin: effects on hepatocytes, pancreatic ? cells and adipocytes. Best Pract Res Clin Endocrinol Metab 28:43-58
Sun, Kai; Park, Jiyoung; Gupta, Olga T et al. (2014) Endotrophin triggers adipose tissue fibrosis and metabolic dysfunction. Nat Commun 5:3485
Unger, Roger H; Scherer, Philipp E; Holland, William L (2013) Dichotomous roles of leptin and adiponectin as enforcers against lipotoxicity during feast and famine. Mol Biol Cell 24:3011-5
Holland, William L; Adams, Andrew C; Brozinick, Joseph T et al. (2013) An FGF21-adiponectin-ceramide axis controls energy expenditure and insulin action in mice. Cell Metab 17:790-7