Eicosanoids and the Regulation of Cardiac Glucose Transport

Abstract

Intact actin microfilaments are necessary for insulin‐regulated GLUT4 translocation from intracellular pools to the plasma membrane. Products of the lipoxygenase (LO) pathway were shown to be implicated in the regulation of actin cytoskeleton rearrangement. The aim of this study was to examine the role of these LO products for cardiac insulin signaling and glucose uptake, GLUT4 translocation, and actin‐based cytoskeleton structure. Exposure of cardiomyocytes to esculetin or NDGA, two structurally different LO inhibitors, induced a complete inhibition of insulin‐stimulated glucose uptake, whereas control cells showed a threefold stimulation by insulin. Addition of 12(S)‐HETE rendered the NDGA‐treated cells insulin‐sensitive. Early insulin signaling was not changed in cells exposed to LO inhibitors. Cell surface biotinylation of control cells showed a twofold increase of GLUT4 at the cell surface after insulin stimulation. In contrast, the LO inhibitors induced a complete inhibition of insulin‐stimulated GLUT4 translocation. Labeling of the F‐actin cytoskeleton revealed a prominent disassembly of actin fibers in cells exposed to the LO inhibitors. In conclusion, we show here that products of the LO reaction participate in the organization of the actin network in ventricular cardiomyocytes. Inhibition of LO blocks GLUT4 translocation without affecting insulin signaling events. These data suggest that products of the LO reaction participate in the regulation of glucose transport by contribution to a rearrangement of actin cytoskeletal elements.

Activation of Mitochondrial Calcium-independent Phospholipase A2γ (iPLA2γ) by Divalent Cations Mediating Arachidonate Release and Production of Downstream Eicosanoids

“…These include the regulation of ion channel kinetics (53-56), contractility (53, 57), metabolic flux, and bioenergetic efficiency (58 -60). For example, lipoxygenase inhibi- tion has been demonstrated to block insulin-mediated glucose uptake in cultured ventricular myocytes suggesting the importance of downstream lipoxygenase metabolites in insulin signaling (61). Furthermore, 12-HETE has been previously demonstrated to increase myocardial mitochondrial Ca 2ϩ content as well as mitochondrial nitric-oxide synthase activity, which led to increased apoptosis in HL-1 cardiac myocytes (51,62).…”

Altered GLUT4 Translocation in Skeletal Muscle of 12/15-Lipoxygenase Knockout Mice

“…A 12−LO isoform has been cloned from cardiac muscle [13] and 12−HETE, the product of 12/15−LO, has been found to be the main LO metabolite in ventricular cardiomyocytes [14]. Our laboratory previously demonstrated the possible involve− ment of 12−HETE in cardiac glucose transport [15,16]. We found that inhibitors of 12−LO led to a disarrangement of actin fibers in isolated rat cardiomyocytes, thus completely disturbing insulin− stimulated GLUT4 translocation and glucose uptake.…”

Calcium signaling recruits substrate transporters GLUT4 and CD36 to the sarcolemma without increasing cardiac substrate uptake

“…This method is also suitable for detecting cell surface GLUT4, notwithstanding that GLUT4 expresses only a single extracellular lysine (at position 50). Accordingly, we (22) and others (11,42) have shown that insulin stimulates the binding of sulfo-NHS-LC-biotin to GLUT4. In the present study, oligomycin, a well-established inducer of GLUT4 and CD36 translocation (32), was used as positive control to validate the suitability of the cell surface biotinylation protocol and also of the other methods to detect surface GLUT4 and CD36.…”