Manuscript title: unravelling the neuroprotective role of miR-27a-3p in the MAPK pathway in Parkinson's disease.

Parkinson's disease (PD) is a multifaceted neurodegenerative disorder characterized by dopaminergic neuron loss and the presence of Lewy bodies. Beyond its hallmark motor symptoms, PD involves significant neuroinflammation and immune dysfunction, driven by dysregulated signalling pathways such as the Mitogen-Activated Protein Kinase (MAPK) pathway. This study investigates the therapeutic potential of hsa-miR-27a-3p in modulating these pathways, with a focus on its interaction with MKK7, a key MAPK component. Bioinformatics and experimental analyses, using miRNA-mRNA interactions and construct a protein-protein interaction (PPI) network, confirm that hsa-miR-27a-3p directly binds to the 3' untranslated region (3'UTR) of MKK7, reducing its expression. Overexpression of hsa-miR-27a-3p improves cell viability, mitigates morphological changes, and reduces neurotoxicity in SH-SY5Y (human neuroblastoma cell line for experimental validation) cells exposed to MPP +, a PD neurotoxin. The study further demonstrates that hsa-miR-27a-3p modulates apoptotic pathways by increasing anti-apoptotic BCL2 while downregulating pro-apoptotic BAX and P53, as assessed through Western blot analysis of protein expression in SH-SY5Y cells transfected with miR-27a-3p mimic or negative control, followed by quantification of protein levels. Additionally, hsa-miR-27a-3p suppresses neuroinflammatory responses by significantly reducing TNF-α and IL1β levels. Western blot analysis reveals that hsa-miR-27a-3p inhibits phosphorylation of MKK7 and other MAPK pathway components, such as JNK and p38, highlighting its role in attenuating neuroinflammation and oxidative stress. These findings establish a negative correlation between hsa-miR-27a-3p expression and key neurodegenerative processes, suggesting its potential as a therapeutic target. This study provides comprehensive insights into the neuroprotective mechanisms of hsa-miR-27a-3p, paving the way for innovative interventions in PD management.