Inflammation, insulin resistance (IR) , and deficit of retrograde axonal transport (RAT) are implicated in the pathogenesis of diabetic polyneuropathy (DPN) . Pro-inflammatory macrophage (M1) skewed by diabetic insults causes IR in adipose tissue. The activation of Advanced Glycation End products (AGEs) - Receptor for AGEs (RAGE) signaling is involved in the macrophage polarization into M1, while its contribution to the deficit of RAT in DPN is still unclear. In this study, we investigated the implication of M1-related inflammation to RAT deficit in sensory neurons. We evaluated the activation of macrophage cell line RAW 264.7 (RAW) and neurons isolated from dorsal root ganglia (DRG) of C57BL/6 mice stimulated by 200 μg/ml of AGE. A DRG neurons-RAW co-culture system was established by seeding RAW onto DRG neurons. After 12h co-culturing, we added AGE to the co-culture and stimulated RAW. A DRG neuronal mono-culture was treated with 500 nM of insulin receptor antagonist (BMS-754807) , and 20 ng/ml of TNF-α with/without 50 nM JNK inhibitor (SP600125) . Axonal transport was visualized by Lysotracker and captured by time-lapse microscopy. The movements were quantified on kymographs generated from 100 μm axonal segments. AGE induced the M1 phenotype in RAW with elevated expressions of iNOS and TNF-α mRNA, while no effects on DRG neuron were identified. In the co-culture, the frequency of RAT (RAT%) was significantly reduced when RAW was stimulated by AGE compared to naive RAW (p < 0.001) . In the mono-culture, RAT% was significantly reduced when neurons were treated with BMS-7548 and TNFα (vs. control, both p < 0.001) . TNFα stimulation also increased the phosphorylation of JNK in the axons, a major target of TNFα, which was confirmed by immunofluorescence. The reduction of RAT% by TNFα was rescued by SP600125.
In summary, RAT could be impaired by TNF-α and IR, which suggests inflammation induced by M1 in SN can attenuate RAT, which contributes to the DPN pathology.
S.Osonoi: None. H.Mizukami: None. S.Ogasawara: None. K.Kudoh: None. M.Daimon: None. S.Yagihashi: None.
Japan Society for the Promotion of Science (18K16220)