Hydroxynonenal-generated crosslinking fluorophore accumulation in Alzheimer disease reveals a dichotomy of protein turnover

Abstract

Lipid peroxidation generates reactive aldehydes, most notably hydroxynonenal (HNE), which covalently bind amino acid residue side chains leading to protein inactivation and insolubility. Specific adducts of lipid peroxidation have been demonstrated in intimate association with the pathological lesions of Alzheimer disease (AD), suggesting that oxidative stress is a major component of AD pathogenesis. Some HNE-protein products result in protein crosslinking through a fluorescent compound similar to lipofuscin, linking lipid peroxidation and the lipofuscin accumulation that commonly occurs in post-mitotic cells such as neurons. In this study, brain tissue from AD and control patients was examined by immunocytochemistry and immunoelectron microscopy for evidence of HNE-crosslinking modifications of the type that should accumulate in the lipofuscin pathway. Strong labeling of granulovacuolar degeneration (GVD) and Hirano bodies was noted but lipofuscin did not contain this specific HNE-fluorophore. These findings directly implicate lipid crosslinking peroxidation products as accumulating not in the lesions or the lipofuscin pathways, but instead in a distinct pathway, GVD, that accumulates cytosolic proteins.

Biomarkers of lipid peroxidation in Alzheimer disease (AD): an update

“…In addition, the HNE lysine-derived pyrrole adducts (Fig 2B) were strongly, but not exclusively, associated with neurofibrillary tangle (NFT)-bearing neurons in LAD subjects (Montine et al 1997a; Montine et al 1997b; Sayre et al 1997). More recently, fluorophoric HNE modifications localized to neuronal cytoplasm, corresponding to grandovacular degeneration, were significantly elevated in the HIP of LAD subjects compared to age-matched NC subjects (Zhu et al 2012). HNE adduct colocalization with non-perivascular senile plaques was relatively weak (Sayre et al 1997) and reported in only a fraction of AD subjects (Ando et al 1998).…”

Neuronal failure in Alzheimer’s disease: a view through the oxidative stress looking-glass

“…Some of the free radicals thus generated escape; rather than appropriately transporting their electron to the next molecule in the cascade, they abandon the inner membrane of the mitochondria and impose alterations on other macromolecules within the cell. These alterations are often detrimental: DNA/RNA oxidation may yield fragmentation and deficiencies in repair machinery 32, 33 ; oxidative modification of enzymes and metabolic signaling proteins may lead to metabolic impairments 34 ; and protein cross-linkages and impaired proteolysis network resulting from oxidative modification may render proteins insoluble and prone to aggregate abnormally 35–37 .…”

Neurofilaments are the major neuronal target of hydroxynonenal-mediated protein cross-links

“…The best-studied reactive carbonyl is hydroxynonenal (HNE) [8] and one of its defined products is a fluorescent cross-link (HNE-fluorophore) between two lysines [12]. In AD, antibodies specific to HNE-fluorophore show its accumulation in the degradation pathway and granulovacuolar degeneration (GVD) in vulnerable neurons [13]. Additionally, HNE cross-links are seen in axons of AD and controls, as well as non-cross-linking HNE modifications [14].…”