Osteopontin Protects the Islets and β-Cells from Interleukin-1 β-Mediated Cytotoxicity through Negative Feedback Regulation of Nitric Oxide

Abstract

Osteopontin (OPN), a phosphorylated glycoprotein that binds to an integrin-binding motif, has been shown to regulate nitric oxide (NO) production via inhibition of induced NO synthase (iNOS) synthesis. In the transplanted islets, iNOS and toxic amounts of NO are produced as a result of islets infiltration with inflammatory cells and production of proinflammatory cytokines. Here, we demonstrate that addition of OPN before IL-1beta in freshly isolated rat islets improved their glucose stimulated insulin secretion dose-dependently and inhibited IL-1beta-induced NO production in an arginine-glycine-aspartate-dependent manner. Transient transfection of OPN gene in RINm5F beta-cells fully prevented the toxic effect of IL-1beta at concentrations that reduced the viability by 50% over 3 d. OPN prevention of IL-1beta-induced toxicity was accompanied by inhibited transcription of iNOS by 80%, resulting in 50% decreased formation of the toxic NO. In OPN-transfected cells, the IL-1beta-induced nuclear factor-kappaB activity was significantly reduced. Islets exposed to IL-1beta revealed a naturally occurring early up-regulated OPN transcription. OPN promoter activity was increased in the presence of IL-1beta, IL-1beta-induced NO, and an inducer of NO synthesis. These data suggest the presence of a cross talk between the IL-1beta and OPN pathways and a unique trans-regulatory mechanism in which IL-1beta-induced NO synthesis feedback regulates itself through up-regulation of OPN gene transcription. Our data also suggest that influencing OPN expression represents an approach for affecting cytokine-induced signal transduction to prevent or reduce activation of the cascade of downstream devastating effects after islet transplantation.

Osteopontin: Role in immune regulation and stress responses

“…Wei and colleagues (Wei et al, 2003) demonstrated that HU causes a dramatic reduction in the number of mouse splenocytes and thymocytes; the reduction in lymphocyte number resulting from stress is corticosteroid-dependent and apparently due to the induction of apoptosis. OPN has been found to inhibit apoptosis in various situations Arafat et al, 2007;Hur et al, 2007). It has previously been reported that OPN is necessary for the HU-induced remodeling of bone Yoshitake et al, 1999).…”

Osteopontin regulates hindlimb-unloading-induced lymphoid organ atrophy and weight loss by modulating corticosteroid production

“…Wei et al (24) demonstrated that HU caused a dramatic reduction in the number of mouse splenocytes and thymocytes; the reduction in lymphocyte number resulting from stress was corticosteroid-dependent and apparently caused by the induction of apoptosis. OPN has been found to inhibit apoptosis in various situations (1,13,14). It has previously been reported that OPN is necessary for the HU-induced remodeling of bone (1,25).…”

“…It is classified as a T helper-1 (Th1) cytokine because it enhances production of the Th1 cytokines IFN-␥ and IL-12 and inhibits production of the T helper-2 (Th2) cytokine IL-10 (5, 6). Although it is a proinflammatory cytokine associated with autoimmune diseases, the Th1 inflammatory response, B cell function, and natural killer T cell function, it also has antiinflammatory functions, such as inhibiting the induction of inducible nitric oxide synthase and inhibiting the production of Th2 cytokines (7)(8)(9)(10)(11)(12)(13)(14). Its up-regulation is also a hallmark for many major pathological disorders, such as cardiovascular disease, cancer, and lung disease (12,15).…”

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

“…Conversely, LPS in the presence of NO induced transcription of the Opn gene, suggesting a negative function of osteopontin to limit inflammatory production of NO (67). A similar negative feedback role was found for limiting NO production in rat pancreatic islets and RINm5F b cells (6).…”

“…Together these findings suggest several reasons for possible resistance to Ang II-mediated vasoconstriction in arteries from Thbs1 -/-and Cd47 -/-mice, a hypothesis waiting to be tested. 6. TSP1 in aging.…”