Heme catabolism and heme oxygenase in neurodegenerative disease.

Heme oxygenase, the rate-limiting step in heme catabolism, appears to play an important role in a number of neurodegenerative disorders, such as Alzheimer disease. Interestingly, the spatial distribution of heme oxygenase-1 expression in diseased brain is essentially identical to that of the pathological expression of tau, suggesting a key role for both in disease progression. Like heme oxygenase, the expression, phosphorylation, and aggregation of tau are regulated through signal cascades, including the extracellular signal-regulated kinases, whose activities are modulated by oxidative stress. Therefore, the expression of tau and heme oxygenase-1 in a coordinated manner likely plays a pivotal role in the cytoprotection of neuronal cells. This places heme oxygenase at the center of disease pathogenesis and offers a novel therapeutic approach targeted at either the causes or consequences of enzyme induction.