MAP2K4 and Parkinson disease: The astrocyte-derived exosomal miR-200a-3p was found to attenuate apoptotic cell death in MPP+-treated PD cell models and glutamate-treated hippocampal neuron cultures through downregulation of the mitogen-activated protein kinase kinase 4 (MKK4), which is an important upstream kinase in the c-Jun N-terminal kinase cell death pathway [78].