Global Gene Expression Profile of the Hippocampus in a Rat Model of Vascular Dementia

Electroacupuncture inhibits hippocampal neuronal apoptosis and improves cognitive dysfunction in mice with vascular dementia via the JNK signaling pathway

BACKGROUND

Electroacupuncture (EA) has been shown to reduce cognitive impairment in vascular dementia (VaD) patients. However, the mechanism of action remains unknown.

OBJECTIVE

The c-Jun N-terminal kinase (JNK) signaling pathway plays an important role in apoptosis. Herein, we focused on whether EA can inhibit apoptosis and alleviate cognitive impairment by regulating the JNK signaling pathway using a mouse model of VaD induced by modified bilateral common carotid artery occlusion (BCCAo).

METHODS

In experiment I, 60 mice were randomly divided into a Sham group, BCCAo group, BCCAo + EA group, BCCAo + Sham-EA group, BCCAo + SP group (receiving the selective JNK inhibitor SP600125) and BCCAo + SP + EA group. Morris water maze tests, TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining and flow cytometry were used to evaluate the effect of the EA intervention on VaD. In experiment II, 30 mice were randomly divided into a Sham group, BCCAo group, BCCAo + EA group, BCCAo + SP group and BCCAo + SP + EA group. Western blotting and real-time reverse transcription polymerase chain reaction were used to detect protein and mRNA expression of key factors in the JNK signaling pathway in the hippocampus.

RESULTS

EA, SP600125 and EA + SP600125 significantly inhibited hippocampal apoptosis and improved cognitive impairment in VaD model mice. There were no significant differences between the BCCAo group and the BCCAo + Sham-EA group. EA, EA + SP600125 and SP600125 inhibited the phosphorylation of JNK and caspase-3. EA and EA + SP600125 promoted protein and mRNA expression of B-cell lymphoma 2 (Bcl-2) in the hippocampus of VaD mice and inhibited protein and mRNA expression of activator protein (AP)-1, p53 and Bax.

CONCLUSION

EA can reverse cognitive deficits and inhibit hippocampal neuronal apoptosis in VaD model mice, at least partially through inhibition of the JNK signaling pathway and regulation of apoptosis signals.

Involvement of Endothelin-1, H2S and Nrf2 in Beneficial Effects of Remote Ischemic Preconditioning in Global Cerebral Ischemia-Induced Vascular Dementia in Mice

The present study explored the role of endothelin-1, H2S, and Nrf2 in remote preconditioning (RIPC)-induced beneficial effects in ischemia-reperfusion (I/R)-induced vascular dementia. Mice were subjected to 20 min of global ischemia by occluding both carotid arteries to develop vascular dementia, which was assessed using Morris water maze test on 7th day. RIPC was given by subjecting hind limb to four cycles of ischemia (5 min) and reperfusion (5 min) and it significantly restored I/R-induced locomotor impairment, neurological severity score, cerebral infarction, apoptosis markers along with deficits in learning and memory. Biochemically, there was increase in the plasma levels of endothelin-1 along with increase in the brain levels of H2S and its biosynthetic enzymes viz., cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CLS). There was also an increase in the expression of Nrf2 and glutathione reductase in the brain in response to RIPC. Pretreatment with bosentan (dual blocker of ETA and ETB receptors), amino-oxyacetic acid (CBS synthase inhibitor), and DL-propargylglycine (CLS inhibitor) significantly attenuated RIPC-mediated beneficial effects and biochemical alterations. The effects of bosentan on behavioral and biochemical parameters were more significant than individual treatments with CBS or CLS inhibitors. Moreover, CBS and CLS inhibitors did not alter the endothelin-1 levels possibly suggesting that endothelin-1 may act as upstream mediator of H2S. It is concluded that RIPC may stimulate the release endothelin-1, which may activate CBS and CLS to increase the levels of H2S and latter may increase the expression of Nrf2 to decrease oxidative stress and prevent vascular dementia.

Effect of Endogenous Arginine-Vasopressin Arising from the Paraventricular Nucleus on Learning and Memory Functions in Vascular Dementia Model Rats

The hippocampus is a key structure for encoding and processing memory and for spatial orientation, which are among the cognitive functions most sensitive to cerebral ischemia, hypoxia, and vascular dementia (VD). Since hippocampal formation is one of the principle forebrain targets for arginine-vasopressin (AVP) innervations arising in the hypothalamic paraventricular nucleus (PVN), we explored the contributions of AVP to VD pathogenesis. To this end, we randomly assigned pathogen-free, male Wistar rats to one of seven groups in a VD model and tested AVP treatment effects on spatial learning and memory using the Morris water maze. We also measured the superoxide dismutase (SOD) activity and malondialdehyde (MDA) concentration in brain samples and monitored the expression of AVP-positive neurons in the hippocampus by immunohistochemistry. The VD model with repeated cerebral ischemia-reperfusion injury evoked impairment of cognitive function and reduced cerebral concentrations of the antioxidation markers. Lesioning the rat PVN showed a similar effect on learning and memory and reduced antioxidation markers in the brain tissue. However, AVP injection into the PVN improved cognitive performance in VD rats, while enhancing/rectifying the changes in antioxidation markers. We conclude that our VD model may decrease AVP secretion in the PVN and subsequently reduce antioxidant capacity in the hippocampus, leading to impaired cognitive function.

Global gene expression profile of cerebral ischemia-reperfusion injury in rat MCAO model

It is well-established that reperfusion following cerebral ischemic injury gives rise to secondary injury accompanied by structural and functional damage. However, it remains unclear how global genes changes in cerebral ischemia-reperfusion injury (IRI). This study investigated global gene expression in the hippocampi of Wistar rats following transient cerebral IRI using an RNA-sequencing strategy. The results revealed ≥2-fold up-regulation of 156 genes and ≥2-fold down-regulation of 26 genes at 24 h post-reperfusion. Fifteen differentially expressed genes were selected to confirm the RNA-sequencing results. Gene expression levels were dynamic, with the peak expression level of each gene occurring at different time points post-reperfusion. Gene Ontology (GO) analysis classified the differentially expressed genes as mainly involved in inflammation, stress and immune response, glucose metabolism, proapoptosis, antiapoptosis, and biological processes. KEGG pathway analysis suggested that IRI activated different signaling pathways, including focal adhesion, regulation of actin cytoskeleton, cytokine-cytokine receptor interaction, MAPK signaling, and Jak-STAT signaling. This study describes global gene expression profiles in the hippocampi of Wistar rats using the middle cerebral artery occlusion (MCAO) model. These findings provide new insights into the molecular pathogenesis of IRI and potential drug targets for the prevention and treatment of IRI in the future.