Heme oxygenase-1: role in brain aging and neurodegeneration

The mechanisms responsible for excessive iron deposition and mitochondrial insufficiency in the aging and degenerating nervous system remain poorly understood. Heme oxygenase-1 (HO-1) is a 32kDa stress protein that degrades heme to biliverdin, free iron and carbon monoxide. Our laboratory has shown that cysteamine, dopamine, beta-amyloid, IL-1beta and TNF-alpha up-regulate HO-1 followed by mitochondrial sequestration of non-transferrin-derived 55Fe in cultured rat astroglia. In these cells and in rat astroglia transfected with the human HO-1 gene, mitochondrial iron trapping is abrogated by the HO-1 inhibitors, tin-mesoporphyrin and dexamethasone. We determined that HO-1 immunoreactivity is enhanced greatly in neurons and astrocytes of the hippocampus and cerebral cortex of Alzheimer subjects and co-localizes to senile plaques and neurofibrillary tangles (NFT). HO-1 staining is also augmented in astrocytes and decorates neuronal Lewy bodies in the Parkinson nigra. Collectively, our findings suggest that HO-1 over-expression contributes to the pathological iron deposition and mitochondrial damage documented in these aging-related neurodegenerative disorders. We recently observed that, paradoxically, HO-1 mRNA levels are markedly suppressed in peripheral lymphocytes of patients with early sporadic Alzheimer disease and may thus provide a useful biological marker of this condition.