Aldehyde-induced modifications of the microtubular system in 3T3 fibroblasts

The lipid peroxidation product 4-hydroxynonenal inhibits neurite outgrowth, disrupts neuronal microtubules, and modifies cellular tubulin

Oxidative stress is believed to be an important factor in the development of age-related neurodegenerative diseases such as Alzheimer's disease (AD). The CNS is enriched in polyunsaturated fatty acids and is therefore particularly vulnerable to lipid peroxidation. Indeed, accumulation of lipid peroxidation products has been demonstrated in affected regions in brains of AD patients. Another feature of AD is a change in neuronal microtubule organization. A possible causal relationship between lipid peroxidation products and changes in neuronal cell motility and cytoskeleton has not been investigated. We show here that 4-hydroxy-2(E)-nonenal (HNE), a major product of lipid peroxidation, inhibits neurite outgrowth and disrupts microtubules in Neuro 2A cells. The effect of HNE on microtubules was rapid, being observed after incubation times as short as 15 min. HNE can react with target proteins by forming either Michael adducts or pyrrole adducts. 4-Oxononanal, an HNE analogue that can form only pyrrole adducts but not Michael adducts, had no effect on the microtubules. This suggests that the HNE-induced disruption of microtubules occurs via Michael addition. We also show that cellular tubulin is one of the major proteins modified by HNE and that the HNE adduction to tubulin occurs via Michael addition. Inhibition of neurite outgrowth, disruption of microtubules, and tubulin modification were observed at pathologically relevant HNE concentrations and were not accompanied by cytotoxicity. Our results show that these are proximal effects of HNE that may contribute to cytoskeletal alterations that occur in AD.

Cytoskeletal alterations in cultured cardiomyocytes following exposure to the lipid peroxidation product, 4-hydroxynonenal

Damage to the cardiac myocyte sarcolemma following any of several pathological insults such as ischemia (anoxia) alone or followed by reperfusion (reoxygenation), is most apparent as progressive sarcolemmal blebbing, an event attributed by many investigators to a disruption in the underlying cytoskeletal scaffolding. Scanning electron microscopic observation of tissue cultured rat neonatal cardiomyocytes indicates that exposure of these cells to the toxic aldehyde 4-hydroxynonenal (4-HNE), a free radical-induced, lipid peroxidation product, results in the appearance of sarcolemmal blebs, whose ultimate rupture leads to cell death. Indirect immunofluorescent localization of a number of cytoskeletal components following exposure to 4-HNE reveals damage to several, but not all, key cytoskeletal elements, most notably microtubules, vinculin-containing costameres, and intermediate filaments. The exact mechanism underlying the selective disruption of these proteins cannot be ascertained at this time. Colocalization of actin indicated that whereas elements of the cytoskeleton were disrupted by increasing length of exposure to 4-HNE, neither the striated appearance of the myofibrils nor the lateral register of neighboring myofibrils was altered. Monitoring systolic and diastolic levels of intracellular calcium ([Ca2+]i) indicated that increases in [Ca2+]i occurred after considerable cytoskeletal changes had already taken place, suggesting that damage to the cytoskeleton, at least in early phases of exposure to 4-HNE, does not involve Ca(2+)-dependent proteases. However, 4-HNE-induced cytoskeletal alterations coincide with the appearance of, and therefore suggest linkage to, sarcolemmal blebs in cardiac myocytes. Although free radicals produced by reperfusion or reoxygenation of ischemic tissue have been implicated in cellular damage, these studies represent the first evidence linking cardiomyocyte sarcolemmal damage to cytoskeletal disruption produced by a free radical product.