Abstract
Heme oxygenase-1 (HO-1), an inducible enzyme up-regulated in Alzheimer's disease, catabolises heme to biliverdin, Fe2+ and carbon monoxide (CO). CO can protect neurones from oxidative stress-induced apoptosis by inhibiting Kv2.1 channels, which mediates cellular K+ efflux as an early step in the apoptotic cascade. Since apoptosis contributes to the neuronal loss associated with amyloid β peptide (Aβ) toxicity in AD, we investigated the protective effects of HO-1 and CO against Aβ1-42 toxicity in SH-SY5Y cells, employing cells stably transfected with empty vector or expressing the cellular prion protein, PrPc, and rat primary hippocampal neurons. Aβ1-42 (containing protofibrils) caused a concentration-dependent decrease in cell viability, attributable at least in part to induction of apoptosis, with the PrPc-expressing cells showing greater susceptibility to Aβ1-42 toxicity. Pharmacological induction or genetic over-expression of HO-1 significantly ameliorated the effects of Aβ1-42. The CO-donor CORM-2 protected cells against Aβ1-42 toxicity in a concentration-dependent manner. Electrophysiological studies revealed no differences in the outward current pre- and post-Aβ1-42 treatment suggesting that K+ channel activity is unaffected in these cells. Instead, Aβ toxicity was reduced by the L-type Ca2+ channel blocker nifedipine, and by the CaMKKII inhibitor, STO-609. Aβ also activated the downstream kinase, AMP-dependent protein kinase (AMPK). CO prevented this activation of AMPK. Our findings indicate that HO-1 protects against Aβ toxicity via production of CO. Protection does not arise from inhibition of apoptosis-associated K+ efflux, but rather by inhibition of AMPK activation, which has been recently implicated in the toxic effects of Aβ. These data provide a novel, beneficial effect of CO which adds to its growing potential as a therapeutic agent.
Highlights
The axon or soma) appear intact, their health at this early stage of disease progression is not clear
To investigate any potential role of Heme oxygenases (HO)-1 and carbon monoxide (CO) in affording protection against toxicity induced by amyloid β peptide (Aβ)(1-42), we first determined their effectiveness in SHSY5Y cells either expressing the cellular prion protein (PrPc) or containing the empty vector, as PrPc is a receptor for oligomeric[38,39] and protofibrillar[40] forms of Aβ
Using MTT assays to evaluate cell viability following exposure to Aβ for 24 h, we found that the protofibrillar Aβ caused a concentration-dependent loss of viability, and that cells over-expressing PrPc were significantly more sensitive to Αβ toxicity than the cells lacking PrPc
Summary
The axon or soma) appear intact, their health at this early stage of disease progression is not clear. There is growing evidence that CO can be neuroprotective, for example against the damage of focal ischemia.[36] Our recent studies have demonstrated that CO provides protection against oxidant-induced apoptosis by selectively inhibiting Kv2.1.23,37 In the present study, we have investigated whether HO-1, or its product CO, can provide protection against Aβ-induced toxicity in the human neuroblastoma, SH-SY5Y, and in rat primary hippocampal neurones, and whether this involves regulation of K+ channels We show that both HO-1 and CO protect cells against the toxicity of protofibrillar Aβ1-42 but that protection does not arise from inhibition of apoptosis-associated K+ efflux, but rather by inhibition of AMPK activation
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