Parkinson’s disease (PD) is a common age-related neurodegenerative disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra region [3, 22]. While the mechanism underlying PD pathogenesis is still poorly understood [1, 4]. So far, it is believed that PD results from a complicated interplay of genetic and environmental factors affecting numerous fundamental cellular processes [8]. Moreover, epigenetic factors such as miRNAs have been shown to be important biological molecules involved in the pathogenesis of PD [11, 12]. In this study, we adopted miRNA and mRNA datasets from GEO database, conducted multiple bioinformatics methods to construct a potential miRNA-mRNA regulatory network, and identified several signaling pathways and hub genes that associate with PD development, which were verified by qRT-PCR on blood samples of PD patients and healthy donors. And an upregulation of LEPR and downregulation of miR-101-3p in PD patients compared to healthy donors were discovered.
MiRNAs have been emerging as pivotal molecules involved in PD pathogenesis. A previous study suggests that miR-425 deficiency triggers necroptosis of dopaminergic neurons, and targeting miR-425 in PD mouse model restored dysfunctional dopaminergic neurodegeneration and ameliorated behavioral deficits[23]. And miR-27a and miR-27b were thought to regulate autophagic clearance of damaged mitochondria and PINK1 gene expression which is the most common cause of autosomal recessive PD[24]. Moreover, miRNAs analyzed in our study, including miR-30e, miR-21, miR-101, miR-19a and miR-142 which were downregulated, were previously presented as regulators of PD [25, 26]. Among which, the miR-30 family was studied in multiple studies and seemed to play critical roles during PD [12, 27, 28]. Bioinformatics analysis on various patient samples of PD identified miR-30 family as the potential upstream regulators of progression rates-related biomarkers of PD [29]. Moreover, miR-30e could attenuate the levels of inflammatory cytokines, such as TNF-α, COX-2, iNOS, and ameliorates neuroinflammation in a MPTP model of PD through directly targeting Nlrp3 [30]. MiR-101-3p was previously reported to mediate lncRNA Mirt2 suppressed inflammation [31]. Our study determined the notably reduced level of miR-101-3p in PBMCs of PD patients, supported its negative regulatory role during PD. Noteworthy, the level of miR-30e-5p was decreased but not statistically significant in PD patients, which may be restricted to the small patient pool adopted in this study. A larger cohort of patients with different Hoehn and Yahr stages would be adopted in further study. Based on previous and our research, it is believed that the existence of miRNA-mRNA regulatory network in PD pathogenesis might be promising target for treatment of PD.
Traditionally, miRNAs function by regulating target genes in a post-transcriptional way and play critical roles in various biological processes. We further listed the members of these enriched functional terms, predicted their potential interacting mRNAs, obtained the overlaps with the DEGs, and then constructed a miRNA-mRNA regulatory network. It’s worth noting that 4 of the genes among the regulatory network, the IRS2, LEPR, JAK2 and PPARGC1A, were identified as the hub genes, suggesting their critical roles during PD progression. The three upregulated genes IRS2, LEPR, JAK2 participate in leptin-mediated metabolism and inflammatory regulation in PD, which is consistent with their roles in fatty acid transport and gluconeogenesis, further highlighted the important role of leptin signaling in PD progression [32, 33]. Moreover, we identified LEPR as a significantly elevated gene in PD patients, comparing with the healthy control. Protein leptin encoded by gene LEPR serves as a regulator of energy homeostasis and feeding behavior[34], having neurotrophic actions in the central nervous system development during perinatal development and into the adult[35]. Ho et al showed that leptin preserved cell survival in neuronal SH-SY5Y cells against MPP + toxicity (Parkinsonian models) by maintaining ATP levels and mitochondrial membrane potential. The upregulation of gene LEPR might indicate activated feedback protection by neurons which will be investigated in future studies with a larger PD cohort. As for downregulated gene PPARGC1A, it encodes a transcriptional co-activator, PGC-1α, which has been implicated in the pathogenesis of neurodegenerative disorders and found repressed in PD [36]. Targeting PGC-1α was proposed as a potential therapeutic method for PD [37]. Interestingly, PGC-1α was also reported to regulate the IRS2 level in hepatic metabolism [38]. In our study, the gene PPARGC1A interacted with three different MiRNAs, whose role in PD pathogenesis might be more complicated.
By functional enrichment analysis, we screened out biological signaling pathways to be closely related with PD, namely the Rab protein signaling transduction, AMPK signaling pathway and signaling by Leptin. The four hub genes IRS2, LEPR, JAK2 and PPARGC1A were mainly involved in AMPK and Leptin signaling pathways. Numerous evidence from PD models has supported the participation of AMPK in PD, via regulating cellular metabolism, enhancing autophagy, promoting mitochondrial quality control, suppressing oxidation, and alleviating inflammation [39–41]. AMPK activation was therefore regarded as a therapeutic target for PD treatment [39]. Moreover, it is proved that AMPK activation may facilitate clearance of α-synuclein and thereby promote neuronal survival to ameliorate PD [42]. Abnormal leptin signaling is also frequently observed in neurodegeneration diseases [43]. And increasing evidence has presented the role of leptin in regulating metabolic homeostasis during PD [43, 44]. Candia et al. also suggested that leptin played a key role in linking metabolic imbalance and the damage of nervous system [44]. Besides, leptin was also involved in blood pressure changes during orthostatic stress in PD patients [45]. Our research and previous evidence have indicated the interaction of miRNAs and mRNAs which build a regulatory network and function in various signaling pathways, participating in the pathogenesis of PD.
In conclusion, our research gave a comprehensive study on the role of miRNAs and mRNAs in PD, identifying the potential miRNA-mRNA regulatory network correlated with PD pathogenesis by using bioinformatics tools, and testified the finding in blood samples collected from PD patients. This work may provide novel insight into the pathogenesis and potential therapeutic target for PD.