Acute liver failure-induced hepatic encephalopathy s associated with changes in microRNA expression rofiles in cerebral cortex of the mouse [corrected]

Abstract

The mechanisms that promote brain dysfunction after acute liver failure (ALF) are not clearly understood. The small noncoding RNAs known as microRNAs (miRNAs) significantly control mRNA translation and thus normal and pathological functions in the mammalian body. To understand their significance in ALF, we currently profiled the expression of miRNAs in the cerebral cortex of mice sacrificed at coma stage following treatment with azoxymethane. Of the 470 miRNAs profiled using microarrays, 37 were significantly altered (20 up-and 17 down-regulated) in their expression in the ALF group compared to sham group. In silico analysis showed that the ALF-responsive miRNAs target on average 231 mRNAs/miRNA (range: 3 to 840 targets). Pathways analysis showed that many miRNAs altered after ALF target multiple mRNAs that are part of various biological and molecular pathways. Glutamatergic synapse, Wnt signaling, MAP-kinase signaling, axon guidance, PI3-kinase-AKT signaling, T-cell receptor signaling and ubiquitin-mediated proteolysis are the top pathways targeted by the ALF-sensitive miRNAs. At least 28 ALF-responsive miRNAs target each of the above pathways. We hypothesize that alterations in miRNAs and their down-stream mRNAs of signaling pathways might play a role in the induction and progression of neurological dysfunction observed during ALF.

Fig. 1:

The pie-chart shows the relative expression levels of miRNAs in the normal rat cerebral cortex (each value is a mean of n = 3). Of the 470 miRNAs analyzed, 268 (57%) were observed to be expressed at >200 units on a scale of 1 to 51,000 units.

Fig. 2:

Hierarchical clustering of the miRNAs altered after ALF in comparison to sham controls (n=3 microarrays/group). The figure shows the miRNAs altered in the ALF group at 3 different statistically significant levels (p<0.01, p<0.05 and p<0.10). In the ALF group 37 miRNAs were observed to be significantly altered compared to sham (20 miRNAs were up-regulated and 17 miRNAs were down-regulated). The color code in the heat maps is linear with green as the lowest and red as the highest. The miRNAs that were increased in expression were shown in green to red while the miRNAs that were decreased in expression were shown from red to green. The individual expression signal of each miRNA in each array was clustered using Euclidean distance function. The dendrograms (tree diagrams) show the grouping of miRNAs according to the order in which they were joined during the clustering. The miRNAs with most similar expression patters were placed next to each other.

Fig. 3:

Effect of ALF-responsive miRNAs on members of the Wnt signaling pathway. The genes shown in orange are targeted by multiple miRNAs, while the genes shown in yellow are targeted by at least one miRNA and the genes shown in green are not targeted by miRNAs altered after ALF.

Fig. 4:

Effect of ALF-responsive miRNAs on members of the MAP-kinase signaling pathway. The genes shown in orange are targeted by multiple miRNAs, while the genes shown in yellow are targeted by at least one miRNA and the genes shown in green are not targeted by miRNAs altered after ALF.