Abstract
Olfactory dysfunction, one of the earliest non-motor symptoms of Parkinson disease (PD), is accompanied by abnormal deposition of SNCA/α-synuclein in the olfactory bulb (OB). The macroautophagy/autophagy-lysosome pathway (ALP) plays an important role in degrading pathological SNCA and modulating this pathway may be a promising treatment strategy. P2RX4 (purinergic receptor P2X, ligand-gated ion channel 4), a member of the purinergic receptor X family, is a key molecule regulating ALP. Piperine (PIP) is a Chinese medicine with anti-inflammatory and anti-oxidant effects. The present study investigated the neuroprotective effects of PIP on SNCA overexpression-induced PD cell and mouse models. We found that PIP oral administration (25, 50 and 100 mg/kg) for 6 weeks attenuated olfactory deficits and delayed motor deficits in Thy 1-SNCA transgenic mice overexpressing human SNCA. This was accompanied by a degradation of pathological SNCA in OB. In addition, PIP improved cell viability and promoted degradation of human SNCA in SK-N-SH cells. These protective effects were exerted via autophagy flux promotion by enhancing autophagosome-lysosome membrane fusion. Furthermore, tandem mass tag proteomics analyses showed that P2RX4 plays an important role in PIP treatment-induced activation of autophagy flux. These findings demonstrate that PIP exerts neuroprotective effects in PD models via promotion of autophagy flux and may be an effective agent for PD treatment.Abbreviations: 6-OHDA, 6-hydroxydopamine; ALP, autophagy-lysosome pathway; BafA1, bafilomycin A1; CoQ10, coenzyme Q10; DMSO: dimethyl sulfoxide; HPLC, high-performance liquid chromatography; IVE, ivermectin; LDH, lactate dehydrogenase; MAP1LC3/LC3-II, lipid-conjugated microtubule-associated protein 1 light chain 3; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; mRFP-GFP, tandem monomeric red fluorescent protein-green fluorescent protein; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; OB, olfactory bulb; P2RX4, purinergic receptor P2X, ligand-gated ion channel 4; PD, Parkinson disease; PBS: phosphate-buffered saline; PI: propidium iodide; PIP, piperine; PLG, piperlongumine; p-SNCA, SNCA phosphorylated at Ser129; Rap, rapamycin; RT-PCR: quantitative real-time PCR; SNARE, soluble N-ethylmaleimide-sensitive factor-attachment protein receptor; SNCA/α-synuclein, synuclein, alpha; STX17, syntaxin17; TG, transgenic; TH, tyrosine hydroxylase; UPS, ubiquitin-proteasome system; WT, wild-type.