Introduction: Inhibitors of dipeptidyl peptidase-IV (DPP-IV), which decrease the degradation of glucose-lowering GLP-1(7-36) to the metabolically inactive GLP-1(9-36), are current new treatment options for patients with type 2 diabetes mellitus, a high-risk population for cardiovascular disease. However, the effects of the metabolite GLP-1(9-36) on atherosclerosis are unknown. Thus, the present study examined the effect of GLP-1(9-36) on chemokine-induced CD4-positive lymphocyte migration as one of the early and critical steps in atherogenesis.
Methods and results: Stimulation of isolated human CD4-positive lymphocytes with SDF-1 led to a 3.4 fold (p<0.001; n = 7) increase in cell migration. Pretreatment of cells with GLP-1(9-36) reduced this effect in a concentration-dependent manner by 41% to a 2.0 fold induction at 10 nmol/L GLP-1(9-36) (p<0.001 compared to SDF-1-treated cells, n = 7). Similar effects were obtained when RANTES was used as a chemokine to induce cell migration. The action of GLP-1(9-36) on CD4-positive lymphocyte migration was mediated through an early inhibition of chemokine-induced PI-3 kinase activity. Downstream in the PI-3 kinase signaling pathway, GLP-1(9-36) inhibited SDF-1-induced phosphorylation of MLC and cofilin and decreased f-actin formation as well as ICAM3 translocation as shown by Western blotting, flow cytometry and immunohistochemistry, respectively. However, the effect of GLP-1(9-36) on PI-3 kinase signaling was not associated with increased intracellular levels of cAMP. Furthermore, experiments with siRNA demonstrated that the inhibitory effect of GLP-1(9-36) on SDF-1-induced ICAM3-translocation was preserved in human CD4-positive lymphocytes lacking the GLP-1 receptor, suggesting signaling independent of the known GLP-1 receptor.
Conclusion: Thus, GLP-1(9-36) inhibits chemokine-induced CD4-positive lymphocyte migration by inhibition of the PI3-kinase pathway independent of cAMP and GLP-1 receptor signaling. Further studies are needed to assess whether such effects may be clinically relevant for patients with type 2 diabetes treated with DPP-IV inhibitors.