Bidirectional Relationship between the BDNF Gene and miRNA: Implications for PD Pathogenesis

Parkinson's disease (PD) is a neurological degenerative condition that primarily affects older people. Although reduced motor skills, stiffness, dyslexia, and other motor symptoms predominate in PD, the nonmotor symptoms, such as cognitive impairment, also play an important part in the PD-affected brain. Studies have reported that the brain-derived neurotrophic factor (BDNF) has a pivotal role in monitoring the nonmotor symptoms of PD. The receptor of BDNF, which is tropomyosin-related kinase (BDNF/TrkB), is prominently dispersed in the substantia nigra region, where the presence of dopaminergic (DAergic) neurons is dense. This shows that the BDNF/TrkB receptor promotes the maintenance, protection, and plasticity of neurons in the brain. Studies have reported that the expression of BDNF/TrkB is found to be downregulated, which significantly elevates the impairments related to cognition. Reports also suggest that miRNAs belong to the class of long noncoding RNA (LncRNAs) and have a critical role in the development and maintenance of neurons, especially dopaminergic neurons (DAergic neurons). Interestingly, it is found that LncRNA BDNF-AS also causes PD pathogenesis by regulating the neurotrophin signaling pathway associated with BDNF and its miRNA targets. This evidence suggests that BDNF could have a dual role in PD, which is a protector as well as a modulator for DAergic neurons in the PD brain. Therefore, in this review, we depict the important roles of the BDNF gene, its receptors, and LncRNA BDNF-AS in causing PD pathogenesis. Also, we suggest how miRNA targets could act as a potential remedy for PD.