Cascade Signals of Papaverine Inhibiting LPS-Induced Retinal Microglial Activation

Ting Zhou,Yu Zhu

doi:10.1007/s12031-019-01289-w

Ting Zhou, Yu Zhu

Open Access

https://doi.org/10.1007/s12031-019-01289-w

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Abstract

Studies have shown that papaverine can inhibit lipopolysaccharide (LPS)-induced microglial activation. The retinal primary microglia of newborn SD rats were isolated and purified, and a LPS-induced microglia activation model was established. The protein phosphorylation level of the signaling pathway was detected by western blotting. The transcription and expression of TNF-α, IL-1β, and IL-10 were respectively detected by RT-PCR and ELISA to observe the abnormal activation of primary microglia. The cAMP inhibitor Rp-isomer, PKA inhibitor H89, and MEK inhibitor U0126 were separately added to further investigate the role of MEK/Erk in PAP inhibition of primary microglial activation and the relationship between cAMP/PKA and MEK/Erk. It was found that the level of MEK phosphorylation was upregulated after LPS stimulation, which was blocked by 10 μg/ml of papaverine.10μM U0126 significantly inhibited TNF-α and IL-1β and increased IL-10 transcription and expression in retinal microglia (P < 0.01). Both Rp-isomer and H89 upregulated the phosphorylation levels of MEK and Erk. Papaverine may inhibit inflammatory factors and promote the expression of anti-inflammatory factors through the cAMP/PKA and MEK/Erk pathway, thereby inhibiting LPS-induced activation of primary retinal microglia, and the MEK/Erk pathway may be partially regulated by cAMP/PKA, which can provide theoretical basis and experimental basis for its protection of the central nervous system.

Highlights

Papaverine is a non-selective PDE inhibitor that relaxes cardiovascular, respiratory, and gastrointestinal smooth muscles and is commonly used in cerebral thrombosis, pulmonary embolism, and arterial spasm (Zhu et al 2014; Kim et al 2014)
Our study found that papaverine inhibited the activation of primary retinal microglia by inhibiting the expression of inflammatory factors and promoting the expression of anti-inflammatory factors
To further investigate the mechanism of papaverine inhibition of microglial activation, we investigated the involvement of MEK/Erk during the activation of microglia and analyzed the relationship between cAMP/PKA and MEK/Erk signaling pathway, which could explore the mechanism of papaverine regulating the functional status of retinal microglia and provide theoretical basis and experimental basis for its protection of the central nervous system

Summary

Introduction

Papaverine is a non-selective PDE inhibitor that relaxes cardiovascular, respiratory, and gastrointestinal smooth muscles and is commonly used in cerebral thrombosis, pulmonary embolism, and arterial spasm (Zhu et al 2014; Kim et al 2014). Our study found that papaverine inhibited the activation of primary retinal microglia by inhibiting the expression of inflammatory factors and promoting the expression of anti-inflammatory factors. The downside is that chronic abnormally activated microglia release inflammatory mediators and excessively phagocytose injured neurons. Recent studies have shown that abnormally activated microglia can phagocytose active neurons under stress, which called phagocytic apoptosis (Brown and Neher 2014). TNF-α and IL-1β are cytotoxic inflammatory mediators released by microglia in early retinal injury, which initiate a series of cellular responses, including activation and migration of microglia and astrocytes (Pousset et al 1999; Milner and Campbell 2002; Tanuma et al 2006). Some studies had shown that inhibition of TNF-α and IL-1β

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