IL-1β hampers glucose-stimulated insulin secretion in Cohen diabetic rat islets through mitochondrial cytochromecoxidase inhibition by nitric oxide

Abstract

induces inhibition of glucose-sensitive rats (CDs) but not Cohen diabetes-resistant rats (CDr). Coppersupplemented HSD increased activity of the copper-dependent mitochondrial respiratory chain enzyme cytochrome c oxidase (COX) and reversed hyperglycemia. This study examined the mechanism by which interleukin-1␤ modulates GSIS and the role of COX in this process. We measured COX activity, ATP content, GSIS, iNOS expression, and nitrite production with and without IL-1␤, N -nitro-L-arginine, copper, or potassium cyanide in isolated islets of CDs and CDr fed different diets. We found reduced COX activity, ATP content, and GSIS in isolated islets of CDs rats fed a regular diet. These were severely reduced following HSD and were restored to regular diet levels on copper-supplemented HSD (P Ͻ 0.01 vs. CDr islets). Potassium cyanide chemically reduced COX activity, decreasing GSIS and thus reinforcing the link between islet COX activity and GSIS. Interleukin-1␤ (2.5 U/ml) reduced GSIS and COX activity in CDs islets. Exposure to 10 U/ml interleukin-1␤ decreased GSIS and COX activity in both CDs and CDr islets, inducing a similar nitrite production. Nevertheless, the effect on GSIS was more marked in CDs islets. A significant iNOS expression was detected in CDs on the HSD diet, which was reduced by copper supplementation. N -nitro-L-arginine and copper prevented the deleterious effect of interleukin-1␤ on COX activity and GSIS. We conclude that reduced islet COX activity renders vulnerability to GSIS inhibition on low-copper HSD through two interrelated pathways: 1) by further reducing the activity of COX that is essential for ␤-cell ATP-production and insulin secretion and 2) by inducing the expression of iNOS and nitric oxide-mediated COX inhibition. We suggest that islet COX activity must be maintained above a critical threshold to sustain adequate GSIS with exposure to low-copper HSD.interleukin-1␤; pancreatic ␤-cell; copper; cytochrome c oxidase; inducible nitrix oxide synthase ELEVATED PLASMA GLUCOSE LEVELS will cause a rise in pancreatic ␤-cell ATP/ADP ratio, triggering insulin secretion by oxidative phosphorylation (OXPHOS), a process elicited by the mitochondrial respiratory chain (20, 51). Therefore, mitochondrial dysfunction could lead to impaired glucose-stimulated insulin secretion (GSIS) and an increased risk of diabetes (25,27). The mitochondrial respiratory chain, situated in the inner mitochondrial membrane, consists of five multisubunit complexes (I-V). Complex IV [cytochrome c oxidase (COX)] is the terminal electron transport chain complex that catalyzes the transfer of electrons from cytochrome c to molecular oxygen. The electrochemical proton gradient formed by complexes I, III, and IV (COX) is utilized by complex V (ATP synthase) to generate ATP (25). COX activity is regulated and inhibited by numerous molecules, including potassium cyanide (KCN) and nitric oxide (NO), which reversibly competes with oxygen at the heme copper active site (8). Studies in diabetic animal models suggest that interleuki...

Upregulation of Mitochondrial Content in Cytochrome c Oxidase Deficient Fibroblasts

“…We recently showed that islets isolated from CDs rats exhibited a consistent partial reduction in COX activity, ATP content and glucose stimulated insulin secretion, which could be recovered by feeding on a copper-sufficient diabetogenic-diet. These observations are supporting the involvement of COX in β-cell dysfunction in CDs rat islets [12]. …”

Antidiabetic Effect of Interleukin-1β Antibody Therapy Through β-Cell Protection in the Cohen Diabetes-Sensitive Rat

“…The extent of protection provided by IL-1bAb was associated with the duration of the treatment, demonstrating pronounced protection when IL-1bAb was injected every day during the 15 days of HSD feeding and a weaker effect when IL-1bAb was given during only the first 5 days of HSD feeding. As shown in our previous studies (5)(6)(7)11,14,15) and confirmed in the current study, IL1b is the sole proinflammatory cytokine expressed by macrophages infiltrating the pancreas. An expression of other proinflammatory markers such as the chemokine MCP1 or the cytokines IL-2, IL-6, TNF-a, and IFN-g could not be detected in the infiltrating macrophages.…”

“…IL-1b has been shown to reduce glucose-stimulated insulin secretion (GSIS) in isolated islets (4,5). In vivo studies of patients with T2DM and animal models have shown evidence of elevated IL-1b expression in the pancreas, in insulin target tissues, as well as in the circulation (1,3,4,6,7).…”

Chronic Exposure to Proline Causes Aminoacidotoxicity and Impaired Beta-Cell Function: StudiesIn Vitro

“…This was further validated in the present study using RT-PCR ( Figure 2I). Interestingly, WesklerZangen et al confirmed that the Cohen diabetic rat, which is a genetic model of nutritionally induced diabetes, could be linked directly to reduced OxPhos [29]. The critical regulatory role of ATP production by OxPhos is underscored by the observation that the cytochrome c oxidase (Cox) activity in islets from the transgenic MKR mouse (a dominant-negative IGF-1 receptor mutation specifically in skeletal muscle) was significantly reduced.…”