HGF and Parkinson disease: On the other hand, the liver produces hepatocyte growth factor (HGF), which has been shown to increase the growth of nigrostriatal dopaminergic axonal terminals; promote the growth and differentiation of neuronal stem cells; reduce dopaminergic neuron loss in the SN of PD animals; and exert anti-inflammatory and antioxidant effects by modulating microglia, TNF-α, and extracellular signal-regulated kinase 1/2 (ERK1/2) [98].