Exploring the neuroprotective effects and mechanisms of pituitary adenylate cyclase-activating polypeptides in Parkinson's disease animal models

Abstract

Objective To investigate the neuroprotective effects and mechanisms of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Parkinson's Disease (PD) animal models. Methods SD rats were divided into five groups: sham-operated group (Sham group), PD group (Parkinson's modeling group), PD + PACAP_low concentration group (modeling + 5 μg / kg of PACAP intranasal administration according to body weight), PD+ PACAP_medium concentration group (modeling + 10 μg / kg of PACAP intranasal administration according to body weight), PD+ PACAP_high concentration group (modeling + 20 μg / kg of PACAP intranasal administration according to body weight). Each group included 10 animals. The four PD models were established by injecting lipopolysaccharide solution into the substantia nigra of SD rats. The Sham group was operated in the same way but injected with saline. The behavioral performance of the rats was assessed using the rotarod test. The concentration of glutamate (Glu) and the levels of α-synuclein (α-syn) in the substantia nigra were detected using ELISA. The expression levels of α-syn in the substantia nigra, as well as those of κ-light chain of nuclear factoractivated B-cells (NF- κB) and inhibitor of nuclear factor κB (IκBα) were detected using WB analysis. Quantitative Polymerase Chain Reaction (qPCR) was used to detect the mRNA expression levels of the rat nigral inflammatory factors Tumor Necrosis Factor α (TNF-α), Interleukin-1β (IL-1β), Interleukin-6 (IL-6). WB and immunofluorescence methods were used to detect the levels of nuclear transcription factor Glial Fibrillary Acidic Protein (GFAP) to observe the activation level of astrocytes, and the TUNEL method was used to detect apoptosis in nigrostriatal neurons. Results (1) Behavioral results from the rotarod test indicated that compared to the Sham group, the PD group had a shorter latency and an increased number of falls (37.20±5.27 falls /min). In comparison to the PD group, the PACAP group showed a prolonged latency and a decreased number of falls (14.50±2.32 falls/min). As the concentration of PACAP increased, the latency in the PACAP group was prolonged, and the number of falls decreased (P<0.001). (2) Indicators related to astrocyte activation showed that the expression level of GFAP and the number of apoptotic nigrostriatal neurons were significantly higher in the PD group than in the Sham group. These indicators in the PACAP group were significantly reduced with the increasing concentration of PACAP (P<0.01). (3) Neuroinflammation markers in the substantia nigra showed that compared to the Sham group, the PD group had significantly increased NF - κB content and mRNA levels of TNF - α, IL-1β, IL-6, along with a significantly decrease in IκBα content. In the PACAP group, NF-κB content and mRNA levels of TNF-α, IL-1β, IL-6 were reduced, and IκBα content was increased with rising concentration of PACAP (P<0.01). (4) Indicators of PD disease characteristics revealed that both glutamate and α - syn levels were significantly higher in the PD group compared to the sham group. These levels were significantly reduced in all three PACAP groups compared to the PD group, with a decreasing trend as the PACAP concentration increased (P<0.01), with the most pronounced effect observed in the PD + PACAP high concentration group. Conclusion PACAP exhibits neuroprotective effects in the PD model, potentially through the inhibition of astrocyte activation, thereby reducing neuroinflammation.

Keywords

• parkinson's disease
• neuroinflammation
• pituitary adenylate cyclase-activating polypeptide
• astrocytes