NR4A2 and Parkinson disease: On the other hand, it has also been known that down-regulated Nurr1 expression contributed to neuronal degeneration, and that restoration of Nurr1 expression could decrease apoptotic neuronal death in the substantia nigra of the MPTP (1- methyl-4- phenyl-1,2,3,6- tetrahydropyridine)-induced Parkinson’s disease mouse model (28).