TH and Parkinson disease: Further study showed that the arginine-glycine-aspartic acid (RGD)-containing domain of OPN, could protect tyrosine hydroxylase (TH)-positive cells against toxic insult induced by MPP+ and LPS, indicating that this peptide fragment of OPN may be necessary for the survival of TH cells and have neuroprotective properties relevant to Parkinson’s disease (Iczkiewicz et al., 2010).