BDNF and Parkinson disease: Finally, the same study demonstrated that circDLGAP4/miR-134-5p axis regulates CREB signaling, as well as the transcription of CREB downstream target genes BDNF, Bcl-2 and PGC-1a, all of which are neuroprotective factors involved in many NDDs including AD and PD [218,219,220].