Modulating GRP75 to restore calcium homeostasis: a novel neuroprotective strategy of CRSE6# in Parkinson’s disease models

Introduction Parkinson’s disease (PD) is characterized by dopaminergic neuron loss and α-synuclein (α-syn) aggregation, with no available disease-modifying treatments. Endoplasmic reticulum (ER) stress and consequent mitochondrial calcium overload via the IP3R-GRP75-VDAC1 axis are key pathogenic mechanisms. Objectives This study aimed to evaluate the neuroprotective effects of Citri Reticulatae Semen extract (CRSE6 # ) in PD models and elucidate its underlying molecular mechanisms, focusing on calcium signaling regulation. Methods The chemical consistency of CRSE6 # was confirmed through multiple batch fingerprinting. In vitro, rotenone-induced PC-12 and SH-SY5Y cells were treated with CRSE6 # . In vivo, A53T-αSyn-Tg mice received oral CRSE6 # for 8 weeks. Behavioral tests, histology, and molecular analyses were performed. Liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis of serum samples for the identification of bioactive components. RNA sequencing and Gene Set Enrichment Analysis (GSEA) were conducted. The role of GRP75 was validated via stereotaxic injection of sh HSPA9 (GRP75 knockdown) in mouse brain. Results CRSE6 # reduced cell apoptosis, restored mitochondrial membrane potential, and attenuated reactive oxygen species production in vitro. In mice, it improved motor deficits and spatial memory, reduced α-syn aggregation, and suppressed neuroinflammation. Serum pharmacochemical analysis identified 186 absorbed components, including eight compounds with high confidence: kaempferol, hesperidin, narirutin, ferulic acid, senegenin, secoisolariciresinol, 2′,5,6-trimethoxyflavone, and 5-O-demethylnobiletin. Mechanistically, CRSE6 # suppressed ER stress and disrupted the IP3R-GRP75-VDAC1 complex, alleviating mitochondrial calcium overload. RNA sequencing and gene interference experiments further suggested that GRP75 is a potential target regulated by CRSE6 # in calcium signaling pathways: knocking down GRP75 mimics its protective effect, while overexpressing GRP75 blocks its therapeutic efficacy. Conclusion These findings suggest that CRSE6 # may exert neuroprotective effects in PD models by modulating calcium homeostasis via GRP75. Serum pharmacochemical analysis further identified eight candidate compounds, which may be associated with its biological activity. Collectively, these results reveal a novel function of CRSE6 # as a regulator of GRP75-mediated MAM calcium signaling, highlighting its potential as a natural neuroprotective agent for further preclinical investigation.