The long-term goal of this research is to identify the early mechanisms of pancreatic beta-cell dysfunction in development of diabetes. Evidence suggests that inflammation, mediated by at least in part by cytokines, is a key component in both type 1 diabetes (T1D) and type 2 diabetes (T2D). In T1D, the current consensus is that cytokines produced locally within the islets at very high doses by immune cells play a critical role in the destruction of pancreatic beta cells. In T2D, circulating cytokine levels are elevated early in the development of the disease due to low-grade systemic inflammation. However, circulating cytokine levels associated with low- grade systemic inflammation are ~100-1000x lower than seen within the islet during direct immune cell infiltration associated with T1D. To date, the effects of these low-level cytokines on beta-cells have not been systematically examined, particularly in models of obesity and T2D. Our preliminary data show for the first time that specific cytokine combinations, present at concentrations found in the blood of obese and diabetic individuals, are sufficient to induce excess basal intracellular free calcium, reduce endoplasmic reticulum (ER) calcium storage, and impair insulin secretion in pancreatic islets. Furthermore, these cytokine effects are more severe in islets from pre-diabetic db/db mice, a mouse model of T2D. The hypothesis for this proposal is that circulating cytokines at concentrations typical of low-grade systemic inflammation directly cause beta-cell dysfunction by disrupting intracellular calcium handling in diabetes-prone individuals. Using molecular, electrophysiological, and imaging-based approaches, we will test this hypothesis by addressing three specific aims: (I) Compare the effects of low-grade inflammation on islet calcium handling and markers of cell stress in islets from normal and diabetes-prone mice, (II) Determine the cellular sites of cytokine-induced dysfunction in beta-cells, (III) Determine the in vivo effects of low-grade inflammation in normal vs. diabetes-prone or obese mice. Collectively, these studies will elucidate novel aspects of cytokine action at concentrations present in the systemic circulation in obese and diabetic individuals. Identifying early stages in cytokine-mediated beta-cell dysfunction will open new avenues of therapeutic intervention to prevent beta-cell dysfunction in early T2D.
Diabetes is a devastating metabolic disorder affecting over 23 million Americans that is caused, at least in part, by the death of insulin-producing beta-cells in the pancreas. This proposal addresses a novel trigger of beta- cell failure caused by small increases in inflammatory agents called cytokines circulating in the blood of obese and diabetic individuals. Our findings will provide new insights into the early stages of the disease process and open up possible new directions for the treatment and/or prevention of diabetes.
|Nunemaker, Craig S; Satin, Leslie S (2014) Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH. Endocrine 47:49-63|
|Nunemaker, Craig S; Chung, H Grace; Verrilli, Gretchen M et al. (2014) Increased serum CXCL1 and CXCL5 are linked to obesity, hyperglycemia, and impaired islet function. J Endocrinol 222:267-76|
|O'Neill, Christina M; Lu, Christine; Corbin, Kathryn L et al. (2013) Circulating levels of IL-1B+IL-6 cause ER stress and dysfunction in islets from prediabetic male mice. Endocrinology 154:3077-88|
|Geisler, Jessica C; Corbin, Kathryn L; Li, Qin et al. (2013) Vesicular nucleotide transporter-mediated ATP release regulates insulin secretion. Endocrinology 154:675-84|
|Ren, Jianhua; Sherman, Arthur; Bertram, Richard et al. (2013) Slow oscillations of KATP conductance in mouse pancreatic islets provide support for electrical bursting driven by metabolic oscillations. Am J Physiol Endocrinol Metab 305:E805-17|
|Ramadan, James W; Steiner, Stephen R; O'Neill, Christina M et al. (2011) The central role of calcium in the effects of cytokines on beta-cell function: implications for type 1 and type 2 diabetes. Cell Calcium 50:481-90|