Advanced glycation end products (AGEs) activates its receptor, RAGE, resulting in a skewing of macrophage (Mϕ) polarity toward inflammatory phenotype (M1) and an impairment of the insulin signaling (IS) in adipose tissue. IS also regulates axonal transport (AT) in the peripheral nervous system. Although impaired IS and AT are assumed to be pathophysiology of diabetic polyneuropathy (DPN), the implication of Mϕ induced inflammation with RAGE activation in those factors is not fully understood. To this end, we generated bone marrow specific RAGE deficient mice to investigate the influence of RAGE signaling in Mϕ on the development of DPN. Bone marrow cells from C57BL/6 mice (W) or RAGE deficient mice (R) were transplanted into irradiated W (BMW and BMR). After 8 weeks of diabetes (D) induced by streptozotocin, nerve conduction velocities were delayed in BMWD compared to BMW, while those of BMRD were comparable to BMR. An increased infiltration of M1 was observed in the sciatic nerve (SN) in BMWD. Western blotting (WB) showed a lower phosphorylation of AKT in response to insulin in SN of BMWD, which suggested impaired IS, while it was maintained in BMRD. Retrograde AT (RAT) was evaluated with Fluoro-gold (FG) transportation from hindlimb-footpad to the dorsal root ganglion (DRG). Immunofluorescence revealed a lower positivity of FG in DRG of BMWD which suggested a deficit of RAT, while it was maintained in BMRD. Neuronal cells isolated from mice DRG were cocultured with a Mϕ cell line RAW264, which was polarized into M1 by AGEs. Intra-axonal vesicles were labeled fluorescently. Subsequently, AT was visualized by time-lapse imaging. The ratio and the velocity of RAT was decreased in the axon of the neurons cocultured with M1 compared with naïve Mϕ.
In summary, our data suggested that the activation of RAGE signaling skewed Mϕ polarity toward M1, impairing IS and RAT through inflammation, which might trigger and develop DPN.
S. Osonoi: None. H. Mizukami: None. K. Kudo: None. Y. Yamamoto: None.
Japan Society for the Promotion of Science (18K16220)