Protein Aggregation and Proteasome Dysfunction After Brain Ischemia

Abstract

Background and Purpose-Protein unfolding and aggregation are dominant early pathogenic events in neurons after brain ischemia. This study used a transient cerebral ischemia model to investigate whether overproduction of unfolded proteins after brain ischemia is a consequence of proteasome dysfunction. Methods-Proteasome peptidase activity and proteasome subcellular redistribution and assembly were studied by peptidase activity assay, Western blot analysis, and size-exclusion chromatography. Results-Proteasome peptidase activity, as determined with the peptide substrate succinyl-LLVY-7-amino-4-methylcoumarin, was moderately decreased, and the 26S proteasome was disassembled during the early period of reperfusion after transient brain ischemia. Furthermore, the proteasome subunits, particularly the 19S components, were deposited into the protein aggregate-containing fraction after an episode of transient cerebral ischemia. Conclusions-These results clearly demonstrate that after an episode of brain ischemia, proteasomes are disassembled and aggregated and thus fail to function normally. Deposition of proteasomes into protein aggregates may also indicate that proteasomes attempt to degrade ubiquitin-conjugated proteins (ubiproteins) overproduced after brain ischemia. However, ubiproteins are too numerous to be degraded and trap some of the proteasomes into their aggregates after brain ischemia. (Stroke. 2007;38:3230-3236.)

rAAV8-733-Mediated Gene Transfer of CHIP/Stub-1 Prevents Hippocampal Neuronal Death in Experimental Brain Ischemia

“…10 It has been suggested that irreversible aggregation of translational complex components, chaperones, and protein folding enzymes following brain ischemia lead to inhibition of translation and subsequent neuron death. 26 Consistent with this view, we detected augmented levels of ubiquitinated proteins after either OGD followed by 24 hr of reperfusion or GBI followed by 3 hr of reperfusion, particularly among high molecular weight protein bands in western blots. This is corrected upon rAAV8-733-CHIP treatment in the hippocampus, thus suggesting that increased E3 ligase activity promoted by CHIP overexpression is sufficient to decrease protein ubiquitination and neuronal degeneration in ischemic conditions.…”

Role of the ubiquitin–proteasome system in brain ischemia: Friend or foe?

“…Transient cerebral ischemia is associated with an inflammatory response and a rapid and excessive production of various misfolded proteins due to oxidative stress and other mechanisms (Ge et al, 2007. Overproduction of damaged proteins following ischemia is reflected in a pronounced increase of conjugation of targeted proteins with ubiquitin (Hayashi et al, 1992).…”

“…In fact, translational complex components are irreversibly clumped into large abnormal protein aggregates after transient brain ischemia (Liu et al, 2005) or focal brain ischemia (Zhang et al, 2006a), suggesting that the irreversible inhibition of translation in neurons destined to die after ischemia is caused by irreversible aggregation of translational complex components, chaperones and protein folding enzymes. Moreover, proteasomes, particularly the 19S RP, are also sequestered into these protein aggregates in post-ischemic brains (Ge et al, 2007). Furthermore, cytoplasmic ubiquitin-containing aggregates and stress granules are clustered together in CA1 neurons at day 2-3 of reperfusion following global forebrain ischemia and may contribute to sustained translation arrest and CA1 pyramidal neuron vulnerability .…”

Role of mitochondrial function in the protective effects of ischaemic postconditioning on ischaemia/reperfusion cerebral damage

“…1 Animal experiments have demonstrated that many factors are involved in the pathological course of cerebral damage caused by ischaemia and reperfusion, such as endoplasmic reticulum stress and protein aggregation. 2,3 Antioxidants have been shown to have therapeutic effects on ischaemia/reperfusion brain injury, suggesting that oxidative stress has an active role in modulating neuronal destiny. [4][5][6] In addition, other neurological disorders (including neurodegenerative diseases and traumatic brain injury) are related to oxidative stress.…”

“…[17][18][19][20][21] This protection is not only associated with inhibition of inflammation and apoptosis, 22,23 but also with attenuation of oxidative stress. 3,24 The aim of the present study was to use a rat model of ischaemia/ reperfusion injury to evaluate the effects of ischaemic postconditioning on mitochondrial ROS production, in order to determine whether its inhibitory effects on oxidative stress are mediated via the mitochondrial pathway, since the golgi apparatus is also a source of ROS. 25 …”