Erythropoietin alleviates hyperglycaemia-associated inflammation by regulating macrophage polarization via the JAK2/STAT3 signalling pathway.

BACKGROUND

Erythropoietin (EPO), which is clinically used for renal anaemia, reportedly exerts beneficial pleiotropic effects in atherosclerosis. This aim of this study was to investigate the effects of EPO on macrophage inflammation and polarization under hyperglycaemic conditions and to identify the effects of EPO-treated macrophage supernatants (SNs) on endothelial cell (EC) function.

METHODS

Peritoneal macrophages (pMΦs) were isolated from normal, diabetic or EPO-injected mice. Pro-inflammatory factors were detected by qRT-PCR and ELISA, and macrophage phenotype markers were evaluated by flow cytometry. High glucose culture was used to mimic the hyperglycaemic microenvironment of diabetes mellitus (DM) in vitro. After exposure to various doses of stimuli, macrophage inflammation and phenotype were detected via ELISA, qRT-PCR and flow cytometry. The underlying mechanism was investigated through western blotting. To examine the communication between macrophages and ECs, ECs were cultured with the SN of macrophages treated with different stimuli, and the tube formation ability of ECs was detected using Matrigel. The VEGF, ICAM-1 and VCAM-1 protein expression levels were determined by western blotting, and the nitric oxide (NO) and endothelin-1 (ET-1) expression levels were measured with a nitric oxide indicator and by ELISA, respectively.

RESULTS

EPO treatment increased the M2 macrophage population and decreased the number of M1 macrophages. EPO decreased the secretion of pro-inflammatory factors, including TNF-α, iNOS and IL-6. The JAK2/STAT3 signalling pathway was also identified as being involved in the M1 macrophage transition. The SN of macrophages treated with EPO (SN-EPO) presented increased NO and ET-1 levels and decreased ICAM-1 and VCAM-1 levels. Tube formation assays revealed that the SN-EPO promoted the ability of ECs to form capillary-like structures in vitro. In contrast, AZD1480, a JAK2 inhibitor, abolished this SN-EPO effect.

CONCLUSION

EPO treatment alleviated the inflammatory reaction in DM mice and inhibited M1 polarization through the JAK2/STAT3 pathway. Moreover, EPO treatment promoted the tube formation ability of ECs in a VEGF-dependent manner and decreased the production of adhesion molecules, a vasodilator and a vasoconstrictor.