Sitagliptin, an anti‐diabetic drug, inhibits the pro‐inflammatory microglia reactivity via dipeptidyl peptidase‐4 (DPP4)

Abstract

Aims/Purpose: Diabetic retinopathy is characterized by a chronic low‐grade retinal neuroinflammation triggered by diabetes and mediated, at least in part, by microglial cells. We previously showed that sitagliptin, an oral drug for type 2 diabetes, developed to inhibit dipeptidyl peptidase 4 (DPP4) and increase insulin release, can prevent retinal neuroinflammation in diabetic rat models and the LPS‐induced morphological changes of microglial cells in retinal organotypic cultures. However, the mechanisms underlying these effects are not clarified. We hypothesize that sitagliptin is able to directly inhibit microglia reactivity via Dpp4.Methods: BV‐2 microglia cell line was exposed to a non‐toxic dose of lipopolysaccharide (LPS, 0.1 μg/mL) in the presence or absence of 200 μM sitagliptin. The expression of Dpp4, iNOS, IL‐1 beta and TNF were assessed by Western Blot and/or RT‐qPCR. The BV‐2 phagocytic efficiency was assessed using fluorescent microbeads. The metabolic activity and proliferation of BV‐2 cells were assessed by resazurin assay and Edu staining, respectively. Dpp4 deletion in BV‐2 cells was generated using Crispr‐cas9 method.Results: Sitagliptin inhibited the LPS‐induced increase in protein levels of iNOS, IL‐1 beta and TNF to 39.9 ± 6.3%, 47.2 ± 8.1% and 34.0 ± 7.2%, respectively, comparing to LPS. Sitagliptin reduced the LPS‐induced increase in phagocytic efficiency by approximately 40%. Sitagliptin did not affect the metabolism and proliferation of BV‐2. BV‐2 cells express Dpp4. Dpp4 deletion does not affect the LPS‐induced phagocytosis but abrogated the effect of sitagliptin on the reduction of BV‐2 phagocytic efficiency (approx. 320% as in LPS).Conclusions: Sitagliptin exerts direct anti‐inflammatory effects on microglia, mediated by DPP4. These results suggest that sitagliptin can potentially be used in retinal pathologies characterized by microglia‐mediated neuroinflammation.Support.FCT‐Portugal: PEst UID/NEU/04539/2013, UIDB/04539/2020 and UIDP/04539/2020 and PTDC/NEU‐OSD/1113/2012. COMPETE‐FEDER.