5-HT4 Receptor Antagonist Exacerbates Neuropathology Via Gut-brain Axis In Parkinson’s Disease Mice

Parkinson’s disease(PD)is the common degenerative disease.The principal pathophysiology of PD is the degenerative death of dopaminergic neurons in the substantia nigra pars compacta,and the reduction of dopamine(DA)neurotransmitter released in the striatum.The exact pathogenesis of PD is not clear yet,neuroinflammation and accumulation of α-synuclein may be involved in the pathogenesis of PD.The main clinical symptoms of PD are bradykinesia and rigidity.Interestingly,preceding the classic motor symptoms of PD patients usually exhibit nonmotor symptoms,such as constipation and gastroparesis.However,there is no excellent pharmacotherapy and surgical treatment in PD include pharmacotherapy and surgical treatment.The previous studies of our laboratory showed striatal 5-HT decreased as well as DA in MPTP-induced acute and subacute PD mice,suggesting serotonergic system may be involved in PD occurence and development.5-HT must combine with corresponding receptors to play its role.Among 5-HT receptors,gastrointestinal motility can be regulated by 5-HT4 R,and 5-HT4 R agonists are often used to treat constipation in clinical therapy and can relieve gastrointestinal symptoms of PD patients.However,there was no study about 5-HT4 R on the brain pathology of PD.5-HT receptors gene m RNA expression in PD model mice brain tissues were detected by RT-q PCR.The results showed that the Htr4 expression was decreased in the hypothalamus and the hippocampus.To explore the role of 5-HT4 R in PD,5-HT4 R antagonist GR 125487 was selected.In our study,8-week-old male C57BL/6J mice were received GR 125487 three days before MPTP treatment by intraperitoneal injection.The mice were administered intraperitoneal with MPTP to make MPTP model.GR 125487 was administrated for following consecutive 8 days after the MPTP treatment.Motor and non-motor symptoms were tested after the administration.Striatal neurotransmitters were detetected by HPLC,TH and JAK2/PKA/CREB expression were detected by western blot,dopaminergic neurons and glial cells were detected by IF,the level of cytokine was detected by ELISA and gut microbiota composition were detected by 16 s r RNA were performed to explore the role of5-HT4 R in MPTP-induced PD model mice.The results showed that GR 125487 increased gastrointestinal transit time and aggravated motor dysfunction and exacerbated the loss of dopaminergic neurons probably by suppressing JAK2/PKA/CREB signaling pathway in the striatum.GR 125487 administration also decreased striatal DOPAC level and TH expression.Futhermore,GR 125487 administration increased astrocytes in the SNpc and increased striatal TNF-α and IL-1β,suggesting GR 125487 promoted neuroinflammation.In addition,16 S r DNA sequencing of fecal microbiota showed that GR 125487 altered the composition of inflammation associated gut microbiota,in which the abundance of Akkermansia muciniphila and Clostridium clostridioforme was increased,whereas that of Parabacteroides distasonis and Bacteroides fragilis was decreased.Taken together,we demonstrated that GR 125487 treatment exacerbates MPTP-induced striatal neurodegenerative processes possibly via the JAK2/PKA/CREB pathway and alters gut microbiota composition.The role of 5-HT4 R in the microbiota-gut-brain axis of PD should be further explored,and 5-HT4 R may serve as a target for PD diagnosis and treatment.