Gene expressions of ubiquitin and hsp70 following focal ischaemia in rat brain

The 4-Celled Tetrabaena socialis Nuclear Genome Reveals the Essential Components for Genetic Control of Cell Number at the Origin of Multicellularity in the Volvocine Lineage

Multicellularity is the premier example of a major evolutionary transition in individuality and was a foundational event in the evolution of macroscopic biodiversity. The volvocine chlorophyte lineage is well suited for studying this process. Extant members span unicellular, simple colonial, and obligate multicellular taxa with germ-soma differentiation. Here, we report the nuclear genome sequence of one of the most morphologically simple organisms in this lineage-the 4-celled colonial Tetrabaena socialis and compare this to the three other complete volvocine nuclear genomes. Using conservative estimates of gene family expansions a minimal set of expanded gene families was identified that associate with the origin of multicellularity. These families are rich in genes related to developmental processes. A subset of these families is lineage specific, which suggests that at a genomic level the evolution of multicellularity also includes lineage-specific molecular developments. Multiple points of evidence associate modifications to the ubiquitin proteasomal pathway (UPP) with the beginning of coloniality. Genes undergoing positive or accelerating selection in the multicellular volvocines were found to be enriched in components of the UPP and gene families gained at the origin of multicellularity include components of the UPP. A defining feature of colonial/multicellular life cycles is the genetic control of cell number. The genomic data presented here, which includes diversification of cell cycle genes and modifications to the UPP, align the genetic components with the evolution of this trait.

Differential regulation of Nedd4 ubiquitin ligases and their adaptor protein Ndfip1 in a rat model of ischemic stroke

Ubiquitin-modification of proteins by E3 ubiquitin ligases is an important post-translational mechanism implicated in neuronal survival and injury following cerebral ischemia. However, of the 500 or so E3s thought to be present in mammalian cells, very few specific E3s have been identified and associated with brain ischemia. Here, we demonstrate endogenous induction of HECT-type E3 ligases of the Nedd4 family and their adaptor Nedd4-family interacting protein 1 (Ndfip1) following transient focal cerebral ischemia in rats. Ndfip1 is upregulated in surviving cortical neurons and its neuroprotective activity is correlated with Nedd4-2 upregulation, but not two other Nedd4 family members examined (Nedd4-1 and Itch). Immunoprecipitation assays confirmed biochemical binding of Ndfip1 with Nedd4-2 in the brain, with or without ischemic stroke, indicating their endogenous interaction. While Ndfip1 and Itch have been previously shown to interact outside of the nervous system, ischemic induction of Itch in the present study was associated with cellular survival independent of Ndfip1. Together, these findings demonstrate specific and differential regulation of Nedd4 family E3 ligases under ischemic conditions, and identify two E3 ligases and their adaptor that potentially regulate ubiquitination in ischemic stroke to provide neuroprotection.

Ischemic preconditioning prevents protein aggregation after transient cerebral ischemia

Transient cerebral ischemia leads to protein aggregation mainly in neurons destined to undergo delayed neuronal death after ischemia. This study utilized a rat transient cerebral ischemia model to investigate whether ischemic preconditioning is able to alleviate neuronal protein aggregation, thereby protecting neurons from ischemic neuronal damage. Ischemic preconditioning was introduced by a sublethal 3 min period of ischemia followed by 48 h of recovery. Brains from rats with either ischemic preconditioning or sham-surgery were then subjected to a subsequent 7 min period of ischemia followed by 30 min, 4, 24, 48 and 72 h of reperfusion. Protein aggregation and neuronal death were studied by electron and confocal microscopy, as well as by biochemical analyses. Seven minutes of cerebral ischemia alone induced severe protein aggregation after 4 h of reperfusion mainly in CA1 neurons destined to undergo delayed neuronal death (which took place after 72 h of reperfusion). Ischemic preconditioning reduced significantly protein aggregation and virtually eliminated neuronal death in CA1 neurons. Biochemical analyses revealed that ischemic preconditioning decreased accumulation of ubiquitin-conjugated proteins (ubi-proteins) and reduced free ubiquitin depletion after brain ischemia. Furthermore, ischemic preconditioning also reduced redistribution of heat shock cognate protein 70 and Hdj1 from cytosolic fraction to protein aggregate-containing fraction after brain ischemia. These results suggest that ischemic preconditioning decreases protein aggregation after brain ischemia.

Ubiquitin-proteasome system and proteasome inhibition: new strategies in stroke therapy

BACKGROUND AND PURPOSE

Proteasomes are large multicatalytic proteinase complexes that are found in the cytosol and in the nucleus of eukaryotic cells with a central role in cellular protein turnover. The ubiquitin-proteasome system (UPS) has a central role in the selective degradation of intracellular proteins. Among the key proteins whose levels are modulated by the proteasome are those involved in the control of inflammatory processes, cell cycle regulation, and gene expression. There are now overwhelming data suggesting that the UPS contributes to cerebral ischemic injury.

SUMMARY OF REVIEW

Proteasome inhibition is a potential treatment option for stroke. Thus far, proof of principle has been obtained from studies in several animal models of cerebral ischemia. Treatment with proteasome inhibitors reduces effectively neuronal and astrocytic degeneration, cortical infarct volume, infarct neutrophil infiltration, and NF-kappaB immunoreactivity with an extension of the neuroprotective effect at least 6 hours after ischemic insult. However, it is clear that the UPS represents a central pathway for the processing and metabolism of multiple proteins with critical roles in cellular function. To avoid eliciting significant side effects associated with complete inhibition of the proteasome and the possible immunosuppressive effects from persistent suppression of NF-kappaB activation, it is critical that we understand how to partially and temporally attenuate proteasome function to elicit the desired therapeutic effect before any large-scale use in humans.

CONCLUSIONS

This review highlights the most recent advances in our knowledge on UPS, as well as the early experience of using proteasome inhibition strategies to treat acute stroke.

Protein aggregation after focal brain ischemia and reperfusion

Two hours of transient focal brain ischemia causes acute neuronal death in the striatal core region and a somewhat more delayed type of neuronal death in neocortex. The objective of the current study was to investigate protein aggregation and neuronal death after focal brain ischemia in rats. Brain ischemia was induced by 2 hours of middle cerebral artery occlusion. Protein aggregation was analyzed by electron microscopy, laser-scanning confocal microscopy, and Western blotting. Two hours of focal brain ischemia induced protein aggregation in ischemic neocortical neurons at 1 hour of reperfusion, and protein aggregation persisted until neuronal death at 24 hours of reperfusion. Protein aggregates were found in the neuronal soma, dendrites, and axons, and they were associated with intracellular membranous structures during the postischemic phase. High-resolution confocal microscopy showed that clumped protein aggregates surrounding nuclei and along dendrites were formed after brain ischemia. On Western blots, ubiquitinated proteins (ubi-proteins) were dramatically increased in neocortical tissues in the postischemic phase. The ubi-proteins were Triton-insoluble, indicating that they might be irreversibly aggregated. The formation of ubi-protein aggregates after ischemia correlated well with the observed decrease in free ubiquitin and neuronal death. The authors concluded that proteins are severely damaged and aggregated in neurons after focal ischemia. The authors propose that protein damage or aggregation may contribute to ischemic neuronal death.

Induction by synaptic zinc of heat shock protein-70 in hippocampus after kainate seizures

Following seizures, heat shock protein (HSP)-70 is induced in various brain regions. Since zinc that can induce HSP-70 in various cell systems is enriched in certain glutamatergic terminals and translocates to postsynaptic neurons with seizures, we examined the possibility that HSP-70 induction in the epileptic brain is mediated by synaptic zinc. Adult rats were injected intraperitoneally with kainate to induce seizures. Seizures were halted 3 h after the kainate administration by the injection of phenytoin. Staining of brain sections with zinc-specific fluorescent dye TFL at 24 h after the kainate injection revealed a one-to-one correlation between dense TFL fluorescence and acidophilic neuronal degeneration in the hippocampus. Subsequent staining with anti-HSP-70 antibody, however, revealed that more numerous neurons than degenerating neurons exhibited HSP-70 immunoreactivity. Most of the HSP-70(+) neurons were not stained with acid fuchsin but exhibited mild zinc fluorescence in the cytoplasm. Intraventricular injection of CaEDTA attenuated neuronal death as well as the HSP-70 induction in a dose-dependent manner. Supporting the specificity of zinc rather than calcium as the inducer of HSP-70 in neurons, exposure to zinc but not to a calcium ionophore or excitotoxins increased expression of HSP-70 mRNA and protein in cultured cortical neurons. The present results suggest that not only selective neuronal death, but also HSP-70 induction in neurons after seizures, is mediated by the translocation of endogenous synaptic zinc.