Background-The importance of free radical homeostasis and apoptosis in normal and diseased hearts and their interrelationships are poorly defined. We tested whether reactive oxygen species can trigger apoptosis in cardiomyocytes, and we explored the underlying pathways. Methods and

Different reactive oxygen species exert distinct effects on VSMCs, with O2- inducing proliferation and H2O2 causing apoptosis. Thus, reactive oxygen species might participate in atherosclerosis, restenosis, and hypertension in a dual manner by stimulating proliferation and triggering apoptosis of VSMCs.

After mild ischemic insults, many neurons undergo delayed neuronal death. Aberrant activation of the cell cycle machinery is thought to contribute to apoptosis in various conditions including ischemia. We demonstrate that loss of endogenous cyclin-dependent kinase (Cdk) inhibitor p16INK4a is an early and reliable indicator of delayed neuronal death in striatal neurons after mild cerebral ischemia in vivo. Loss of p27 Kip1 , another Cdk inhibitor, precedes cell death in neocortical neurons subjected to oxygen-glucose deprivation in vitro. The loss of Cdk inhibitors is followed by upregulation of cyclin D1, activation of Cdk2, and subsequent cytoskeletal disintegration. Most neurons undergo cell death before entering S-phase, albeit a small number (ϳ1%) do progress to the S-phase before their death. Treatment with Cdk inhibitors significantly reduces cell death in vitro. These results show that alteration of cell cycle regulatory mechanisms is a prelude to delayed neuronal death in focal cerebral ischemia and that pharmacological interventions aimed at neuroprotection may be usefully directed at cell cycle regulatory mechanisms.

p27(Kip1) (p27) blocks cell proliferation through the inhibition of cyclin-dependent kinase-2 (Cdk2). Despite its robust expression in the heart, little is known about both the function and regulation of p27 in this and other nonproliferative tissues, in which the expression of its main target, cyclin E-Cdk2, is known to be very low. Here we show that angiotensin II, a major cardiac growth factor, induces the proteasomal degradation of p27 through protein kinase CK2-alpha'-dependent phosphorylation. Conversely, unphosphorylated p27 potently inhibits CK2-alpha'. Thus, the p27-CK2-alpha' interaction is regulated by hypertrophic signaling events and represents a regulatory feedback loop in differentiated cardiomyocytes analogous to, but distinct from, the feedback loop arising from the interaction of p27 with Cdk2 that controls cell proliferation. Our data show that extracellular growth factor signaling regulates p27 stability in postmitotic cells, and that inactivation of p27 by CK2-alpha' is crucial for agonist- and stress-induced cardiac hypertrophic growth.

Apoptosis of vascular smooth muscle cell (VSMC) plays an important role in the genesis of atherosclerosis and restenosis. In order to investigate the role of reactive oxygen species in the induction of VSMC apoptosis, rat VSMCs were treated with glucose oxidase/glucose (GO/G) or diethylmaleate (DEM). The results showed that GO/G and DEM led to VSMC death. Administration of catalase, superoxide dismutase and deferoxamine revealed that H 2 0 2 was the major reactive oxygen species causing cell death, and H 2 0 2 0 exerted its effect by formation of hydroxyl radical ('OH). GO/G-and DEM-induced VSMC death occurred by apoptosis characterized by "DNA ladders", condensation of nuclei, positive to in situ nick-end labeling and increases in histone-associated DNA fragmentation. This study suggests that H 2 0 2 and its derived form 'OH might be related to apoptosis of VSMC in atherosclerosis and restenosis.