Responses to the additional glucose with its indicated final concentration are shown for: (A, B) Respiratory elevations (glucose); ANOVA: *FCCP prevented TBHPm increases, which then reached values <0
Responses to the additional glucose with its indicated final concentration are shown for: (A, B) Respiratory elevations (glucose); ANOVA: *FCCP prevented TBHPm increases, which then reached values <0.1 (data not shown). eminent physiological redox signaling, the impairment of which results in the lack of antilipotoxic defense and contributes to chronic lipotoxicity. 23, 958C972. Introduction A significant antioxidant role in pancreatic -cells (1, 2, 9, 13, 23, 28, 29, 31, 42, 45, 48, 54) or -cells (3) is usually provided by TFRC mitochondrial uncoupling protein-2 (UCP2). This was evidenced for UCP2 KO mice of three highly congenic strain backgrounds, all of which exhibit oxidative stress (decreased ratios of reduced-to-oxidized glutathione in blood or tissues), elevated levels of antioxidant enzymes, and increased nitrotyrosine content in their islets (42). Pancreatic -cells from UCP2 KO mice showed chronically higher reactive oxygen species (ROS) when compared with wild-type mice (29). Mice with selective knockout of UCP2 in pancreatic -cells exhibited increased glucose-induced inner mitochondrial membrane (IMM) potential (m) and elevated intracellular ROS (48). Development Fatty acid (FA)Cstimulated and redox-stimulated insulin releases have not been fully comprehended as well as acute lipotoxicity, instantly decreasing insulin secretion in pancreatic -cells. We describe a opinions antioxidant mechanism based on redox signaling initiated by FA -oxidation, and promoted plus amplified by mitochondrial phospholipase iPLA2. Not only the antioxidant synergy of iPLA2 with mitochondrial UCP2 is usually demonstrated, but also the iPLA2 role in the amplifying mechanism, since further free FAs cleaved by iPLA2 serve as messengers for G-proteinCcoupled receptor 40 (GPR40). Consequently, the iPLA2/UCP2 synergy regulates glucose-stimulated, redox-, and FA-stimulated insulin release in pancreatic Amisulpride -cells. Superoxide formation is an inevitable side reaction at Complex I and III of mitochondrial respiratory chain (24) and in 2-oxoacid dehydrogenases (41, 46). Mitochondrial superoxide formation increases with an increasing substrate (NADH) weight, represented by increasing glucose in pancreatic -cells (10). Similarly, in numerous situations of local or global electron transfer retardation within the respiratory chain, superoxide production is usually specifically elevated. This serves for redox signaling, for example, during initiation of hypoxic gene expression remodeling (27). Mitochondrial H+ pumping is usually tightly coupled to the H+ backflow Amisulpride the ATP synthase. Since any uncoupling of this accelerates electron transfer within the respiratory chain (and hence respiration), the superoxide formation is usually attenuated by mitochondrial uncoupling. This represents the key mechanism exerted by UCP2, although it slightly attenuates ATP synthesis. In pancreatic -cells, the increase in oxidative phosphorylation (OXPHOS) substantiates the canonical mechanism of glucose sensing. The increasing ATP/ADP ratio at higher glucose initiates the glucose-stimulated insulin secretion (GSIS) (5, 26, 47). By shifting ROS Amisulpride homeostasis, UCP2 may participate in redox signaling in -cells (31, 48), which may be easily transmitted due to the low capacity of redox buffers (23). H2O2-responsive gene expression is usually manifested for both major differentiation factors of -cells, PDX-1 and MafA (47). Impaired antioxidant defense leading to chronic oxidative stress may Amisulpride impact insulin secretion machinery that is finely Amisulpride tuned for optimum GSIS in -cells, as acknowledged in type 2 diabetes patients (16, 39, 40) and rodent diabetic models (30, 33). ROS may further accelerate diabetic development by promoting apoptosis, thus decreasing -cell mass (51). Consequently, oxidative stress serves as a mediator of -cell remission. The function of UCP1 (12) and recombinant UCP2 (6, 7, 20, 53) is essentially dependent on its anionic transport substrates, nonesterified fatty acids (FAs) (6, 7, 18, 20, 53). However, FAs augment GSIS in -cells, when uncovered for hours (8, 15, 19), but chronically excessive saturated FAs suppress insulin secretion (32, 43, 52), the phenomenon termed lipotoxicity (15, 19). As a simplifying plan, UCP2 might counteract acute lipotoxicity arising from oxidative stress due to the incoming FAs. Nevertheless, its role should be further clarified. The role of phospholipases A2 (PLA2) (21, 22, 25, 34, 35, 38) residing in (such as iPLA2) (34) or recruited to mitochondria of pancreatic -cells should also be explained in relation to their activation. PLA2 may amplify lipotoxicity, but in concert with UCP2 a hypothetical synergic antioxidant activity may prevail, such as with mitochondrial iPLA2 in heart (25) and lung tissues (21). Both iPLA2 and iPLA2 belong to the group VI of PLA2s (38) ascribed to the cytosolic Ca2+-impartial iPLA2s. They are also termed patatin-like phospholipase domain-containing lipases (PNPLAs), which, besides the release of unsaturated FAs by cleaving the still exhibited a substantial respiration of 23.66.3?pmol O2s?110?6 cells (exhibited virtually unchanged respiration of J0O2=25.36.3?pmol O2s?110?6cells (did not switch respiration (J0O2=24.27.4?pmol O2s?110?6 cells; or or or glucose for 16?h. Subsequently, 250?TBHP was added to cells assayed in this medium. The producing respiration elevation responses TBHPJO2 are plotted final glucose concentration (glucose). bongkrekic acid was present during the assay. (C, D) Glucose-dependent m decrease: TBHP-induced decreases.