Aims/hypothesis The pro-inflammatory cytokines IL-1 and IFNγ are critical molecules in immune-mediated beta cell destruction leading to type 1 diabetes mellitus. Suppressor of cytokine signalling (SOCS)-3 inhibits the cytokinemediated destruction of insulinoma-1 cells. Here we investigate the effect of SOCS3 in primary rodent beta cells and diabetic animal models. Methods Using mice with beta cell-specific Socs3 expression and a Socs3-encoding adenovirus construct, we characterised the protective effect of SOCS3 in mouse and rat islets subjected to cytokine stimulation. In transplantation studies of NOD mice and alloxan-treated mice the survival of Socs3 transgenic islets was investigated. Results Socs3 transgenic islets showed significant resistance to cytokine-induced apoptosis and impaired insulin release. Neither glucose-stimulated insulin release, insulin content or glucose oxidation were affected by SOCS3. Rat islet cultures transduced with Socs3-adenovirus displayed reduced cytokine-induced nitric oxide and apoptosis associated with inhibition of the IL-1-induced nuclear factor-κB and mitogen-activated protein kinase (MAPK) pathways. Transplanted Socs3 transgenic islets were not protected in diabetic NOD mice, but showed a prolonged graft survival when transplanted into diabetic allogenic BALB/c mice. Conclusions/interpretation SOCS3 inhibits IL-1-induced signalling through the nuclear factor-κB and MAPK pathways and apoptosis induced by cytokines in primary beta cells. Moreover, Socs3 transgenic islets are protected in an allogenic transplantation model. SOCS3 may represent a target for pharmacological or genetic engineering in islet transplantation for treatment of type 1 diabetes mellitus.

In order to elucidate a possible relationship between b-cell function and conversion of proinsulin to insulin, isolated rat pancreatic islets were maintained in tissue culture for 1 week at various glucose concentrations (5 . 6-56 mM). Studies were also conducted on islets cultured for 48 h with interleukin-1b (IL-1b). By pulse-chase labelling and immunoprecipitation, the relative contents of newly synthesized proinsulin and insulin were determined. ELISA was used to analyse insulin and proinsulin content in medium and within islets. Using real-time PCR, the mRNA levels of proinsulin converting enzymes (PC1 and PC2) were studied. Islets cultured at 56 mM glucose had an increased proportion of newly synthesized proinsulin when compared with islets cultured at 5 . 6 mM glucose after a 90-min chase periods, however, no difference was observed after culture at 11 and 28 mM glucose. ELISA measurements revealed that culture at increased glucose concentrations as well as islet exposure to IL-1b increased proinsulin accumulation in the culture media. The mRNA expression of PC1 was increased after culture at 11 and 28 mM glucose. Treatment for 48 h with IL-1b increased the proportion of proinsulin both at 45 and 90 min when compared with control islets. These islets also displayed a decreased mRNA level of PC1 as well as PC2. Calculations of the half-time for proinsulin demonstrated a significant prolongation after treatment with IL-1b. We conclude that a sustained functional stimulation by glucose of islets is coupled to a decreased conversion of proinsulin which is also true for islets treated with IL-1b. This may contribute to the elevated levels of proinsulin found both at the onset of type 1 diabetes as well as in type 2 diabetes.

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