My laboratory is currently investigating the molecular mechanisms involved in the regulation of oxidative stress and inflammation signaling in two pancreatic diseases, type 1 diabetes and pancreatic cancer.

TYPE 1 DIABETES
Type 1 diabetes is a chronic (lifelong) disease that occurs when self immune cells (T cells and monocytes) that are programmed to attack and destroy bacteria and viruses, attack and destroy the beta cells of the pancreas that produce insulin. Insulin is the hormone that allows glucose to enter body cells. When insulin is absent glucose builds up in the bloodstream instead of going into the cells. Insulin-secreteing beta cells are present with other hormone-secreting cells as little clusters in the pancreas called the pancreatic islets. Accumulation of immune cells around the islets is known as insulitis or islet inflammation. In the early stages of insulitis, monocytes and T cells are attracted to the islets and produce harmful substances called cytokines and free radicals, which contribute to beta cell death. There are currently no effective therapies available for the prevention of type 1 diabetes. An improved understanding of the natural history of pre diabetes is critical for prevention of islet inflammation in type 1 diabetes.

CURRENT LAB PROJECTS ON TYPE 1 DIABETES:

1. Endogenous mechanisms for regulation of inducible nitric oxide synthase in the pancreatic islets:
Islet graft injury by cytokines released from inflammatory cells that infiltrate the transplant site is an important mechanism of early islet transplant dysfunction. The detrimental effect that cytokines impact on the metabolic function is mediated in part by upregulation of inducible nitric oxide synthase (iNOS) gene expression and increased nitric oxide (NO) production. Inhibition of NO has been shown to promote islet graft survival. However, very little is known about the endogenous factors and mechanisms in the islet microenvironment that are known to inhibit iNOS is so they can be induced to inhibit iNOS expression to control the early graft dysfunction. Our lab has recognized a novel islet protein, osteopontin (OPN), as a protective feedback regulator of cytokine-induced oxidative stress and iNOS production in the islets. We are currently working to elucidate the signaling mechanisms by which this novel factor mediates its protective effects in the islets.

2. Protection of the islets by osteopontin for islet transplantation:
Revealing the endogenous feedback mechanisms by which the pancreatic islets respond to external insults, and might offer islet protection, should provide more understanding to islet cell biology and may provide additional therapeutic strategies to improve the outcome of islet transplantation. In these studies we are testing the hypothesis that overexpression of OPN gene in the islets represents an approach for affecting cytokine-induced signal transduction to prevent or reduce activation of the cascade of downstream devastating effects after islet transplantation. We use adenoviral gene delivery system to induce OPN expression in isolated islets followed by their transplantation into a type 1 diabetes animal model.

3. Regulation of osteopontin by cytokines in insulin producing cells
We have recently identified the presence of an endogenous system for the regulation of nitric oxide (NO)-mediated oxidative stress in the islets. This regulatory system is mediated by a novel protein, osteopontin (OPN), which is expressed in the pancreatic islets. OPN improves cytokine-mediated beta cell dysfunction and reduces cytokine-induced NO production. Interestingly, OPN mRNA and protein are endogenously expressed in the pancreatic islets. Islets that lack OPN are dysfunctional and lack the optimum response to cytokines and show defective insulin release in response to glucose stimulation. The presence of OPN as a novel regulatory system suggests potential targets for modulation of the NO-dependent components of the inflammatory response. However, a better understanding of OPN regulation in the islets will help to unravel the pathophysiology of early islet graft dysfunction. Our guiding hypothesis for these studies is that OPN acts a stress-induced molecule that feedback to protect the islets and beta cells through different mechanisms. In these studies we characterize the regulation of OPN expression in insulin-producing cells by cytokines and glucose. We use OPN promoter -reporter transfection studies to identify the enhancer elements and transcription factors that mediate induced expression of OPN in beta cells. We also use deleted constructs of the OPN promoter region and by site-directed mutagenesis of the specific transcription factor(s) binding site(s) present in the OPN promoter. These studies will define a novel and as yet, poorly described cytokine/glucose-dependent signal transduction pathway that regulates OPN as an indirect endogenous NO regulatory mechanism in beta cells.

4. Osteopontin role in type 1 diabetes:
Osteopontin (OPN) is a phosphorylated acidic glycoprotein that causes chemotaxis of macrophages and downregulation of nitric oxide synthesis. OPN has been shown to be involved in the pathogenesis of autoimmune diseases. In these studies we are testing the hypothesis that that increased expression of pancreatic OPN in experimental diabetes has a protective role. To do this, we utilize different experimental models for type 1 diabetes and a novel genetically engineered OPN knock out mouse model and also adenoviral-mediated islet gene delivery.

5. The role of the pancreatic renin angiotensin system (RAS) in type 1 diabetes:
The molecular and cellular mechanisms underlying insulitis as the pathological hallmark of type 1 diabetes are poorly understood. Recent data derived from clinical trials using angiotensin I converting enzyme (ACE) inhibitors and angiotensin II type 1 receptor (AT1R) blockers indirectly suggest a role for angiotensin II (AngII) in the diabetogenic process. However, the direct role of AngII in islet inflammation is yet to be identified. The central hypothesis of this project is that AngII interacts with angiotensin receptor on islet cells to stimulate inflammation and development of insulitis by stimulating monocyte chemoattractant protein-1 (MCP-1) synthesis and other chemokines through activation of MAP kinase signaling cascade and NF-kB. Our studies will test the inhibition of AngII using the commercially available ACE inhibitors and/or AT1R blockers as a novel and promising strategy for controlling islet inflammation and prevention of the development of type 1 diabetes.

PANCREATIC CANCER
Pancreatic cancer is a devastating disease as the fourth leading cause of cancer death in the United States. The mortality rate is the highest among common cancer types. The most lethal of pancreatic cancers is called adenocarcinoma, which arises in the pancreatic ducts. Due to its aggressiveness and the inability to detect it early, the disease is often far advanced in patients by the time the diagnosis is established. There are currently no effective therapies available for the cure of pancreatic cancer. It is extremely essential to understand the changes and behavioral difference between normal and cancer cells in order to identify different targets for potential therapy.

CURRENT LAB PROJECTS ON PANCREATC CANCER:

1. Angiotensin II type 1 receptor expression in pancreatic cancer and its correlation with tumor angiogenesis and patient survival: Angiotensin II, a main effector peptide in the renin-angiotensin system, acts as a growth-promoting and angiogenic factor via type 1 angiotensin II receptors (AT1R). We have recently demonstrated that angiotensin II enhances tumor cell vascular endothelial growth factor (VEGF) secretion via AT1R in pancreatic ductal adenocarcinoma (PDA) cell lines in vitro. The aim of these studies is to determine whether AT1R expression in PDA is correlated with clinicopathological parameters, angiogenic factors, and patient survival. Results from our studies will determine the clinical potential of AT1R as a novel molecular target in strategies for PDA treatment.

2. Angiotensin II converting enzyme (ACE) inhibitors as a novel therapy for pancreatic ductal adenocarcinoma: ACE inhibitors, which block the production of angiotensin II (AngII) are commonly used for treatment of high blood pressure (hypertension). Recent studies have shown that there is a low incidence of cancer in hypertensive patients who receive ACE inhibitors. Furthermore, studies in other cancer types have shown that ACE inhibitors could be effective in controlling cancer cell division and reducing the blood supply for cancer cells. Our central hypothesis here is that local pancreatic AngII might not be properly regulated in pancreatic ductal adenocarcinoma, and that ACE inhibitors could be tested on pancreatic cancer cell lines and animal models to determine their potential as novel anticancer therapy in pancreatic adenocarcinoma.

3. Angiotensin II-vascular endothelial growth factor interaction in pancreatic cancer cells: In these studies, we are evaluating the signal transduction pathways that are involved in the induction of VEGF by AngII in pancreatic cancer cell lines. In particular, we are interested in the role of oxidative stress and the generation of reactive oxygen species in AngII-VEGF induction.

4. Regulation of VEGF by AngII in PDA cells: In these studies, we are analyzing the VEGF promoter for AngII binding sites. In addition, the role of HIF-1a in the AngII-mediated induction of VEGF is being evaluated.

5. The relationship between G-protein coupled receptors and MAP kinase pathway in AngII induced VEGF: We have recently shown that AngII induces VEGF production via an AT1R-ERK-dependent pathway. In these studies, we are examining the role of AngII as an activator of VEGFR and systematically analyzing the steps and factors involved in the pathway between AngII binding to its receptor and activation of VEGFR. Understanding the involved mechanisms will help us identify novel targets to prevent tumor metastasis and improve PDA patient survival.

6. The molecular basis of smoking as the greatest risk factor in pancreatic cancer: Several epidemiological studies have identified cigarette smoke as the number 1 risk factor in pancreatic cancer. Smokers who are able to quit smoking can reduce their risk of pancreatic cancer by nearly 50% within two years, however, their risk of developing pancreatic cancer remains higher than that of non-smokers for 10 years. Nicotine is an important component in cigarette smoke and has been shown to activate growth-promoting pathways in several cancers. However, the mechanistic bases for these findings are poorly understood in pancreatic cancer. Here, we are investigating the signaling pathways involved in the nicotine-induced molecular and cellular changes that lead to pancreatic cancer progression. In particular, we are focusing on the interactions of nicotine and osteopontin (OPN), a protein that is we found to be significantly upregulated by nicotine in pancreatic cancer cells. OPN is a secreted glycosylated protein, variably serine-phosphorylated, that binds integrins and certain CD44 variants, triggering a cascade of intracellular signaling events regulating cell motility, survival and proliferation. We are testing the hypothesis that OPN is a novel therapeutic target in the control of pancreatic cancer progression, recurrence, and metastasis, especially in the cigarette-smoking population.