Histochemical Mapping of hnRNP A2/B1 in Rat Brain After Ischemia–Reperfusion Insults

Abstract

Cerebral ischemia-reperfusion (I/R) insults result in neuronal cell death, brain tissue loss, and severe neurological deficits. However, the underlying mechanism is still not fully understood. Heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 belongs to a family of RNA-binding proteins that plays a central role in pre-mRNA processing. Recent studies have revealed that hnRNP A2/B1 may be involved in the progress of I/R; therefore, the present study aimed to examine expression patterns of hnRNP A2/B1 to better understand posttranscriptional regulations in cerebral I/R insults. Focal cerebral I/R models were induced by right middle cerebral artery occlusion (MCAO) for 120 min followed by 3, 6, 12, 24, 48, and 72 hr of reperfusion in male Sprague-Dawley rats. We employed immunohistochemistry to examine expression of hnRNP A2/B1 in rat cerebral cortex (including cingulate cortex, striate cortex, temporal cortex, and piriform cortex) and hippocampus after I/R insults. Results showed that expression of hnRNP A2/B1 was significantly downregulated in cerebral cortex and hippocampus from 3 to 24 hr of reperfusion after MCAO for 120 min, but significantly upregulated at 48 hr of reperfusion. Unexpectedly, translocation of hnRNP A2/B1 from nucleus to cytoplasm and even to neurites was observed in cerebral cortex at 3 hr of reperfusion, reaching a peak at 24 hr of reperfusion, but not in hippocampus, indicating different posttranscriptional regulation patterns in different brain regions. Interestingly, translocation of hnRNP A2/B1 was only observed in cerebral cortex with MCAO but not in the opposite side, suggesting an I/R-specific expression pattern in the brain. Our data suggest that hnRNP A2/B1 participates in posttranscriptional regulation of neurons in cerebral cortex and hippocampus that suffered I/R insults, although posttranscriptional regulation is more extensive in neuronal cells of cerebral cortex than in hippocampus.

Dynamic Expression Pattern of Neuro-oncological Ventral Antigen 1 (Nova1) in the Rat Brain after Focal Cerebral Ischemia/Reperfusion Insults

“…Daoud et al (2002) also report that ischemia causes the cytoplasmic accumulation and hyperphosphylation of the splicing factor Tra2-β1, which changes alternative splicing patterns in the brain. We, similarly, showed that hnRNP A2/B1 participated in the posttranscriptional regulation of neurons in the cerebral cortex and hippocampus after suffering from I/R insults (Liu et al 2010). These reports strongly suggest that the transcriptional and posttranscriptional regulation of neurons is helpful for better understanding the mechanism of cerebral I/R insults.…”

“…In line with our observations, these data suggest that important splicing factors are activated during ischemia. Recently, our group has also demonstrated that hnRNP A2/B1 translocated from the nucleus to the cytoplasm and dendrites in the cerebral cortex from 3 to 24 hr after I/R (Liu et al 2010). Darnel et al found that Nova shuttles between the nucleus and cytoplasm and colocalizes with target RNAs in the dendrites (GIRK2 and GlyRα2) (Racca et al 2010).…”

Shutdown of Achaete-scute Homolog-1 Expression by Heterogeneous Nuclear Ribonucleoprotein (hnRNP)-A2/B1 in Hypoxia

“…Altered expression of hnRNP-A2/B1 has also been reported during lung carcinogenesis where hASH1 seems to be involved (54,55). Histochemical mapping of hnRNP-A2/B1 suggested a function in post-transcriptional regulation of neurons in the cerebral cortex and hippocampus in response to ischemia-reperfusion injury (56). Prolonged hypoxia has been reported to have a pronounced effect on cytoplasmic hnRNP-A2/B1 levels that is partially dependent on a higher mRNA turnover under hypoxic conditions (57).…”

Stress Granules and Acute Ischemic Stroke: Beyond mRNA Translation

“…Different RBPs neither have to respond in the same way nor have the same role in neuronal outcome following an ischemic insult. For example, hnRNPA2-B1 is another RBP whose immunohistochemical signal globally decreased after 3, 6, 12, and 24 h of reperfusion in a rat tMCAO model [ 30 ]. Similar to other RBPs, this reduction was also accompanied by a cortical, but not hippocampal, translocation of hnRNPA2-B1 from the nucleus to the cytoplasm during reperfusion [ 30 ].…”

“…For example, hnRNPA2-B1 is another RBP whose immunohistochemical signal globally decreased after 3, 6, 12, and 24 h of reperfusion in a rat tMCAO model [ 30 ]. Similar to other RBPs, this reduction was also accompanied by a cortical, but not hippocampal, translocation of hnRNPA2-B1 from the nucleus to the cytoplasm during reperfusion [ 30 ]. A higher level of such translocation was seen in the more severely damaged cortical areas compared with the other cortical areas observed [ 30 ].…”