CaMKII and Kalirin, a Rac1-GEF, regulate Akt phosphorylation involved in contraction-induced glucose uptake in skeletal muscle cells.

Rac1 plays an important role in contraction-stimulated muscle glucose uptake, but the mechanism is not fully elucidated. We previously identified Rac1-dependent activation of Akt played a partial role in contraction-stimulated GLUT4 translocation to the cell surface of C2C12 myotubes. Recognizing that contraction activates CaMKII in muscle and CaMKII is known to regulate Rac1 activity in other systems, here we investigated the relationship between CaMKII, Akt and contraction-stimulated glucose uptake. Expression of a constitutively-active mutant of CaMKIIδ stimulated Akt phosphorylation that was inhibited by Rac1 inhibitor II. C2C12 myotubes were contracted by electrical pulse stimulation (EPS). We observed the CaMKII inhibitor, KN-93 and CaMKIIδ siRNA-mediated knockdown, reduced EPS-induced Akt phosphorylation in C2C12 myotubes. ITX3, an inhibitor of the Rac-GTPase Kalirin and Kalirin siRNA-mediated knockdown reduced EPS-stimulated Akt phosphorylation in myotubes. In addition, the Akt inhibitor MK2206 partly reduced EPS-stimulated glucose uptake without simultaneously affecting CaMKII phosphorylation and Kalirin protein abundance. Our findings demonstrate EPS leads to Akt activation through a CaMKII-Kalirin-Rac1 signaling pathway and partly regulates contraction-stimulated glucose uptake in muscle cells.

Hypoxic adipocytes induce macrophages to release inflammatory cytokines that render skeletal muscle cells insulin resistant.

Adipose tissue hypoxia occurs early in obesity and is associated with increased tissue macrophages and systemic inflammation that impacts muscle insulin responsiveness. We investigated how hypoxia interacted with adipocyte-macrophage crosstalk and inflammatory cytokine release, using co-culture and conditioned media (CM). Murine primary adipocytes from lean or obese mice were cultured under normoxic (21% O2) or hypoxic (1% O2) conditions. RAW264.7 macrophages were incubated under normoxic or hypoxic conditions with or without adipocyte conditioned media. Macrophage and adipocyte-macrophage co-culture CM were also collected. We found hypoxia did not elicit direct cytokine release from macrophages. However, adipocyte CM or adipocyte co-culture, synergistically stimulated TNFα and MCP-1 release from macrophages that was not further impacted by hypoxia. Exposure of muscle cells to elevated cytokines led to reduced insulin and muscle stress/inflammatory signaling. We conclude hypoxia or obesity induces release of inflammatory TNFα and MCP-1 from mice primary adipocytes but the two environmental conditions do not synergize to worsen macrophage signal transduction or insulin responsiveness.

MiR-495 regulates macrophage M1/M2 polarization and insulin resistance in high-fat diet-fed mice via targeting FTO.

MicroRNA 495 (miR-495) has been discovered to be involved in the metabolism and immune response in human body. The purpose of this study was to investigate the effect of miR-495 on macrophage M1/M2 polarization and insulin resistance in type 2 diabetes (T2D). A T2D mouse model was established by feeding C57BL/6 mice with a high-fat diet (HFD). The expressions of M1/M2 polarization markers and miR-495 in peritoneal macrophages were determined by qRT-PCR or Western blot. Mouse insulin tolerance test (ITT) and glucose tolerance test (GTT) were performed, and the targeted binding effect between miR-495, fat mass, and obesity-associated gene (FTO) was verified by double luciferase gene reporter assay. The body weight, blood glucose content, and miR-495 expression in macrophages of the HFD group were remarkably higher than those of the normal diet (ND) group. Besides, miR-495 induced the transformation of macrophages into M1-type pro-inflammatory macrophages and enhanced the insulin resistance of T2D mice. More importantly, FTO was proved to be a direct target gene of miR-495 and silencing FTO could induce the transformation of macrophages into M1-type pro-inflammatory macrophages. These results demonstrated that miR-495 could promote the transformation of macrophages into M1-type pro-inflammatory macrophages by inhibiting the expression of its target gene FTO, and aggravate the insulin resistance and adipose tissue inflammation in T2D mice, which provided a certain theoretical basis for the targeted treatment of T2D.

PKC and Rab13 mediate Ca2+ signal-regulated GLUT4 traffic.

Exercise/muscle contraction increases cell surface glucose transporter 4 (GLUT4), leading to glucose uptake to regulate blood glucose level. Elevating cytosolic Ca2+ mediates this effect, but the detailed mechanism is not clear yet. We used calcium ionophore ionomycin to raise intracellular cytosolic Ca2+ level to explore the underlying mechanism. We showed that in L6 myoblast muscle cells stably expressing GLUT4myc, ionomycin increased cell surface GLUT4myc levels and the phosphorylation of AS160, TBC1D1. siPKCα and siPKCθ but not siPKCδ and siPKCε inhibited the ionomycin-increased cell surface GLUT4myc level. siPKCα, siPKCθ inhibited the phosphorylation of AS160 and TBC1D1 induced by ionomycin. siPKCα and siPKCθ prevented ionomycin-inhibited endocytosis of GLUT4myc. siPKCθ, but not siPKCα inhibited ionomycin-stimulated exocytosis of GLUT4myc. siRab13 but not siRab8a, siRab10 and siRab14 inhibited the exocytosis of GLUT4myc promoted by ionomycin. In summary, ionomycin-promoted exocytosis of GLUT4 is partly reversed by siPKCθ, whereas ionomycin-inhibited endocytosis of GLUT4 requires both siPKCα and siPKCθ. PKCα and PKCθ contribute to ionomycin-induced phosphorylation of AS160 and TBC1D1. Rab13 is required for ionomycin-regulated GLUT4 exocytosis.

Preparation and characterization of an imprinted monolith by atom transfer radical polymerization assisted by crowding agents.

A method based on reverse atom transfer radical polymerization (R-ATRP) and molecular crowding has been used for design and synthesis of monolithic molecularly imprinted polymers (MIPs) capable of recognizing ibuprofen (IBU). 4-Vinylpyridine (4-VP) was used as the functional monomer, and ethylene glycol dimethacrylate (EDMA) was the crosslinking monomer. Azobisisobutyronitrile (AIBN)-CuCl(2)-N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA) was used as the initiating system. Compared with conventional radical polymerization-based IBU-MIPs, the imprinting effects of the obtained IBU-MIPs was enhanced, suggesting the merit of combination of reverse ATRP and molecular crowding. In addition, it was found that the polymerization time of the molecularly imprinted monolithic column, the amount of template, the degree of crosslinking, and the composition of mobile phase greatly affected retention of the template and the performance of molecular recognition.