HOXD9/APOC1 axis promotes macrophage M1 polarization to exacerbate diabetic kidney disease progression through activating NF-κB signaling pathway

BackgroundDiabetic kidney disease (DKD) is a complication caused by end-stage diabetes mellitus and usually results in glomerular podocyte injury. Exosomes are important for intercellular information exchange. However, the effect of podocyte exosomes on DKD has not been elucidated.MethodsGEO, PROMO, and GSE1009 databases were used to identify the gene APOC1 and transcription factor HOXD9. qRT-PCR, western blot, and transmission electron microscopy (TEM) were investigated to confirm APOC1 change in high glucose-treated podocytes and exosomes. Flow cytometry, immunofluorescence, qPCR, immunoblotting, wound healing, Transwell invasion assays, dual luciferase assay, and ChIP-PCR assay were performed to detect the effect of APOC1 and HOXD9 on macrophage polarization in high glucose-treated podocytes and exosomes. qRT-PCR and immunoblotting assays were employed to assess the impact of APOC1 knockdown on the M1 polarization of macrophages in response to liraglutide treatment.ResultsThe results suggested that the expression of APOC1 in human podocytes (HPC) and exosomes was elevated. High glucose-treated HPC exosomes promoted macrophage M1-type polarization, which was reversed by adding sh-APOC1. Afterward, HOXD9 was identified as a potential transcription factor for APOC1. Knockdown of HOXD9 led to macrophage M2 polarization, and overexpression of APOC1 polarized macrophage M1. In addition, enhanced p65 phosphorylation verified that HOXD9/APOC1 induced macrophage M1-type polarization by activating the NF-kappa B signaling pathway. Knocking down APOC1 enhanced the inhibitory effect of liraglutide on macrophage M1 polarization.ConclusionOur findings highlighted that HOXD9/APOC1 was a key player in causing podocyte injury in diabetic kidney disease and led to macrophage M1 polarization through the NF-kappa B signaling pathway.