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). Here, SPP1 is linked to Parkinson disease.