Altered proinsulin conversion in rat pancreatic islets exposed long-term to various glucose concentrations or interleukin-1β

Abstract

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.

Inhibition of Gamma-Secretase Activity Promotes Differentiation of Embryonic Pancreatic Precursor Cells into Functional Islet-like Clusters in Poly(Ethylene Glycol) Hydrogel Culture

“…40 Our cultures compare favorably to the freshly isolated islets, as day 14 insulin per DNA values were 4.6 and 4.1 when exposed to 7 or 14 days of gammasecretase inhibitor, respectively. These results were confirmed by proinsulin measurements consistent with known proinsulin to insulin ratios, 29 making it highly unlikely that these measurements were a result of insulin uptake from the medium. Additionally, pancreatic precursor cell clusters encapsulated in a PEGCol hydrogel culture platform and exposed to gamma-secretase inhibitor were glucose responsive by day 7 (GSIR *3.3), and maintained their glucose responsiveness for an additional 7 days in culture (GSIR *3).…”

“…Proinsulin: insulin ratios for clustered cells in PEGCol hydrogel cultures ranged between 1:26 and 1:32, comparable to previously published values for adult rat islets. 29 Functional differentiation. Released C-peptide concentrations were measured in low-and high-glucose media and glucose-stimulated insulin release (GSIR) values were calculated.…”

IL-1 antagonism reduces hyperglycemia and tissue inflammation in the type 2 diabetic GK rat

“…Our data do support a functional role of IL-1 inhibition with respect to insulin processing in the ␤ cell. Studies have documented that IL-1␤ downregulates PC1 and PC2 expression, impairing insulin processing, either alone or in combination with other cytokines such as IL-6 and TNF␣ (34)(35)(36)(37). IL-1Ra reduced the local production of IL-1␤, IL-6, and TNF␣, likely explaining the improved insulin processing seen in our treated GK rats.…”

The pharmacological study of hypoglycemic properties of the recombinant antagonist interleukin-1 receptor

“…ІЛ-1 також гальмує секре-цію інсуліну, що викликає при-гнічення утилізації глюкози тка-нинами і депресію глікогеноутво-рення. Таким чином, інсуліноре-зистентність, посилення глюко-неогенезу і пригнічення утилі-зації глюкози, зрештою, призво-дять до розвитку гіперглікемії та до порушення толерантності до глюкози [2,6,11,13,15,16].…”