Heme oxygenase-1 and neurodegeneration: expanding frontiers of engagement.

The heme oxygenases (HOs), responsible for the degradation of heme to biliverdin/bilirubin, free iron and CO, have been heavily implicated in mammalian CNS aging and disease. In normal brain, the expression of HO-2 is constitutive, abundant and fairly ubiquitous, whereas HO-1 mRNA and protein are confined to small populations of scattered neurons and neuroglia. In contradistinction to HO-2, the ho-1 gene (Hmox1) is exquisitely sensitive to induction by a wide range of pro-oxidant and other stressors.