Synergy Between Gαz Deficiency and GLP-1 Analog Treatment in Preserving Functional ß-Cell Mass in Experimental Diabetes.

A defining characteristic of type 1 diabetes mellitus (T1DM) pathophysiology is pancreatic ß-cell death and dysfunction, resulting in insufficient insulin secretion to properly control blood glucose levels. Treatments that promote ß-cell replication and survival, thus reversing the loss of ß-cell mass, while also preserving ß-cell function, could lead to a real cure for T1DM. The α-subunit of the heterotrimeric Gz protein, Gαz, is a tonic negative regulator of adenylate cyclase and downstream cAMP production. cAMP is one of a few identified signaling molecules that can simultaneously have a positive impact on pancreatic islet ß-cell proliferation, survival, and function. The purpose of our study was to determine whether mice lacking Gαz might be protected, at least partially, from ß-cell loss and dysfunction after streptozotocin treatment. We also aimed to determine whether Gαz might act in concert with an activator of the cAMP-stimulatory glucagon-like peptide 1 receptor, exendin-4 (Ex4). Without Ex4 treatment, Gαz-null mice still developed hyperglycemia, albeit delayed. The same finding held true for wild-type mice treated with Ex4. With Ex4 treatment, Gαz-null mice were protected from developing severe hyperglycemia. Immunohistological studies performed on pancreas sections and in vitro apoptosis, cytotoxicity, and survival assays demonstrated a clear effect of Gαz signaling on pancreatic ß-cell replication and death; ß-cell function was also improved in Gαz-null islets. These data support our hypothesis that a combination of therapies targeting both stimulatory and inhibitory pathways will be more effective than either alone at protecting, preserving, and possibly regenerating ß-cell mass and function in T1DM.

Prostaglandin E2 receptor, EP3, is induced in diabetic islets and negatively regulates glucose- and hormone-stimulated insulin secretion.

BTBR mice develop severe diabetes in response to genetically induced obesity due to a failure of the ß-cells to compensate for peripheral insulin resistance. In analyzing BTBR islet gene expression patterns, we observed that Pgter3, the gene for the prostaglandin E receptor 3 (EP3), was upregulated with diabetes. The EP3 receptor is stimulated by prostaglandin E2 (PGE2) and couples to G-proteins of the Gi subfamily to decrease intracellular cAMP, blunting glucose-stimulated insulin secretion (GSIS). Also upregulated were several genes involved in the synthesis of PGE2. We hypothesized that increased signaling through EP3 might be coincident with the development of diabetes and contribute to ß-cell dysfunction. We confirmed that the PGE2-to-EP3 signaling pathway was active in islets from confirmed diabetic BTBR mice and human cadaveric donors, with increased EP3 expression, PGE2 production, and function of EP3 agonists and antagonists to modulate cAMP production and GSIS. We also analyzed the impact of EP3 receptor activation on signaling through the glucagon-like peptide (GLP)-1 receptor. We demonstrated that EP3 agonists antagonize GLP-1 signaling, decreasing the maximal effect that GLP-1 can elicit on cAMP production and GSIS. Taken together, our results identify EP3 as a new therapeutic target for ß-cell dysfunction in T2D.

Overview of affinity tags for protein purification.

Addition of an affinity tag is a useful method for differentiating recombinant proteins expressed in bacterial and eukaryotic expression systems from the background of total cellular proteins, as well as for detecting protein-protein interactions. This overview describes the historical basis for the development of affinity tags, affinity tags that are commonly used today, how to choose an appropriate affinity tag for a particular purpose, and several recently developed affinity tag technologies that may prove useful in the near future.

Deletion of GαZ protein protects against diet-induced glucose intolerance via expansion of ß-cell mass.

Insufficient plasma insulin levels caused by deficits in both pancreatic ß-cell function and mass contribute to the pathogenesis of type 2 diabetes. This loss of insulin-producing capacity is termed ß-cell decompensation. Our work is focused on defining the role(s) of guanine nucleotide-binding protein (G protein) signaling pathways in regulating ß-cell decompensation. We have previously demonstrated that the α-subunit of the heterotrimeric G(z) protein, Gα(z), impairs insulin secretion by suppressing production of cAMP. Pancreatic islets from Gα(z)-null mice also exhibit constitutively increased cAMP production and augmented glucose-stimulated insulin secretion, suggesting that Gα(z) is a tonic inhibitor of adenylate cyclase, the enzyme responsible for the conversion of ATP to cAMP. In the present study, we show that mice genetically deficient for Gα(z) are protected from developing glucose intolerance when fed a high fat (45 kcal%) diet. In these mice, a robust increase in ß-cell proliferation is correlated with significantly increased ß-cell mass. Further, an endogenous Gα(z) signaling pathway, through circulating prostaglandin E activating the EP3 isoform of the E prostanoid receptor, appears to be up-regulated in insulin-resistant, glucose-intolerant mice. These results, along with those of our previous work, link signaling through Gα(z) to both major aspects of ß-cell decompensation: insufficient ß-cell function and mass.

Stable nitrogen and carbon isotope ratios indicate traditional and market food intake in an indigenous circumpolar population.

The transition of a society from traditional to market-based diets (termed the nutrition transition) has been associated with profound changes in culture and health. We are developing biomarkers to track the nutrition transition in the Yup'ik Eskimo population of Southwest Alaska based on naturally occurring variations in the relative abundances of carbon and nitrogen stable isotopes (δ(15)N and δ(13)C values). Here, we provide three pieces of evidence toward the validation of these biomarkers. First, we analyzed the δ(15)N and δ(13)C values of a comprehensive sample of Yup'ik foods. We found that δ(15)N values were elevated in fish and marine mammals and that δ(13)C values were elevated in market foods containing corn or sugar cane carbon. Second, we evaluated the associations between RBC δ(15)N and δ(13)C values and self-reported measures of traditional and market food intake (n = 230). RBC δ(15)N values were correlated with intake of fish and marine mammals (r = 0.52; P < 0.0001). RBC δ(13)C values were correlated with intake of market foods made from corn and sugar cane (r = 0.46; P < 0.0001) and total market food intake (r = 0.46; P < 0.0001). Finally, we assessed whether stable isotope ratios captured population-level patterns of traditional and market intake (n = 1003). Isotopic biomarkers of traditional and market intake were associated with age, community location, sex, and cultural identity. Self-report methods showed variations by age and cultural identity only. Thus, stable isotopes show potential as biomarkers for monitoring dietary change in indigenous circumpolar populations.

Sharing results from complex disease genetics studies: a community based participatory research approach.

OBJECTIVES: Dissemination of research results to communities builds capacity of the community to understand and utilize the results. The objective of this manuscript was to propose a culturally appropriate approach to disseminate complex disease genetics research findings in small Alaska Native communities. STUDY DESIGN: The Center for Alaska Native Health Research is a community-based participatory research project (CBPR) directed at understanding the interactions between genetic, nutritional and psychosocial risk factors for obesity, diabetes, and cardiovascular disease in Yup'ik Eskimos. METHODS: We have consulted with regional healthcare providers, tribal leaders, and university-, local-, and national-institutional review boards to identify potential mechanisms for sharing population-based genetics research results or progress. RESULTS: We propose a six step CBPR-approach to conducting genetics research in isolated identifiable communities. This CPBR-approach includes generating a common research question, determining community interest, recruitment, capacity building, sharing power and control, avoiding group harm, and development of culturally appropriate dissemination procedures. CONCLUSIONS: Research scientists and community members should both benefit from population-based genetics research. Although we are just beginning our discussions with regard to sharing genetics research progress and findings, we believe that it is essential move forward as co-researchers in the CBPR enterprise.