HMOX1 and Parkinson disease: Elevated expression of heme oxygenase-1 (HO-1) in human astrocytes has been reported to contribute to PD features, and is also associated with Fe3+ deposition.[37] Cristina et al found higher levels of HO-1 expression and greater alterations in iron metabolism-related proteins in microglial cells of older mice (15–18 months) compared to younger mice (3–4 months).