Activation of Cdk5/p25 and tau phosphorylation following chronic brain hypoperfusion in rats involves microRNA-195 down-regulation.

Chronic brain hypoperfusion (CBH) is a common clinical feature of Alzheimer's disease and vascular dementia, but the underlying molecular mechanism is unclear. Our previous study reported that the down-regulation of microRNA-195 (miR-195) promotes amyloidogenesis via regulation of amyloid precursor protein and ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) expression at the post-transcriptional level in CBH rats with bilateral common carotid artery occlusion (2VO). CBH owing to unilateral common carotid artery occlusion (UCCAO) increases tau phosphorylation levels at multiple phosphorylation sites in the brain, but the molecular mechanism is poorly understood. The purpose of this study was to investigate whether miR-195 could both deregulate amyloid metabolism and indirectly deregulate tau phosphorylation in CBH. We observed that 2VO leads to tau hyperphosphorylation at Ser202/Thr205, Ser262, Thr231, and Ser422 and to the conversion from cyclin-dependent kinase 5 (Cdk5)/p35 to Cdk5/p25 in rat hippocampi. Endogenous miR-195 was knocked down using over-expression of its antisense molecule (pre-AMO-miR-195) via a lentivirus (lenti-pre-AMO-miR-195); this knockdown increased the tau phosphorylation at Ser202/Thr205, Ser262, Thr231, Ser422, and the Cdk5/p25 activation, but over-expression of miR-195 using lenti-pre-miR-195 decreased the tau phosphorylation and Cdk5/p25 activation. Further in vitro studies demonstrated that miR-195 over-expression prevented tau hyperphosphorylation and Cdk5/p35 activity, which were increased by miR-195 inhibition. A dual luciferase reporter assay showed that miR-195 bound to the Cdk5r1 gene, which encodes p35 protein, in the 3'UTR and inhibited p35 expression. We concluded that tau hyperphosphorylation involves the down-regulation of miR-195, which is mediated by Cdk5/p25 activation in 2VO rats. Our findings demonstrated that down-regulation of miR-195 led to increased vulnerability via the regulation of multiple targets. Schematic diagram of miR-195 mediated Aß aggregation and tau hyperphosphorylation in chronic brain hypoperfusion (CBH). First, CBH results in the elevation of nuclear factor-κB (NF-κB), which binds with the promoter sequences of miR-195 and negatively regulates the expression of miR-195. Second, down-regulated miR-195 induces up-regulation of APP and BACE1 and leads to an increase in Aß levels. Third, some of the elevated Aß then enter the intracellular space and activate calpain, which promotes the conversion of Cdk5/p35 to Cdk5/p25 and catalyzes the degradation of IκB; IκB is an inhibitor of NF-κB, which activates NF-κB. Cdk5/p25 directly phosphorylates Tau. Fourth, down-regulated miR-195 induces an up-regulation of p35, which provides the active substrates of p25. Our findings demonstrated that the down-regulation of miR-195 plays a key role in the increased vulnerability to dementia via the regulation of multiple targets following CBH.

[Effect of adiponectin postconditioning against myocardial ischemia/reperfusion injury in rats and role of ADP/PI3K/Akt pathway in adiponectin postconditioning].

OBJECTIVE: To investigate the effects of adiponectin(ADP) postconditioning against myocardial ischemia/reperfusion injury(MIRI) in rats and role of ADP/PI3K/Akt pathway in ADP postconditioning. METHODS: SD rat was connected to ventilator by tracheal intubation under anesthesia, then left anterior descending coronary artery (LAD) was threaded between left auricle and pulmonary artery cone after exposing heart by surgery. MIRI model was induced by ligation of LAD for 30 min and the following reperfusion for 120 min. Rats were divided randomly into 5 groups (n=12):① Sham group:LAD was threaded without ligation; ② MIRI group; ③ADP group (ADP postconditioning) were subjected to intravenous injection of ADP when LAD ligation for 10 min and the ligation held for 20 min after that, then reperfusion for 120 min; ④ ADP+LY294002 group were subjected to injection of ADP and LY294002 when LAD ligation for 10 min, the other steps were the same as ADP group; ⑤ LY294002 group were subjected to injection of LY294002 when LAD ligation for 10 min, the other steps were the same as ADP group. Titers of lactate dehydrogenase(LDH) and cardiac troponin I(cTnI) in plasma were observed, expressions of PI3K, Akt, phosphorylated-Akt(p-Akt), ADP mRNA, ADPR1 mRNA and PI3k mRNA in myocardial tissue were measured. RESULTS: Compared with sham group, the levels of LDH and cTnI in MIRI group were increased (P<0.05); Compared with MIRI group, the levels of LDH and cTnI in ADP group were decreased (P<0.05); Compared with ADP group, the levels of LDH and cTnI were increased in LY294002 applying groups(P<0.05). Compared with MIRI group, the expressions of PI3K, p-Akt, ADP mRNA, ADPR1 mRNA and PI3K mRNA were increased in ADP group (P<0.05), the above mentioned 5 parameters in LY294002 applying groups were decreased(P<0.05). CONCLUSIONS: ADP postconditioning could reduce MIRI in rats, the protective effect might have relation to ADP/PI3k/Akt pathway.

MicroRNA-195 prevents dendritic degeneration and neuron death in rats following chronic brain hypoperfusion.

Impaired synaptic plasticity and neuron loss are hallmarks of Alzheimer's disease and vascular dementia. Here, we found that chronic brain hypoperfusion (CBH) by bilateral common carotid artery occlusion (2VO) decreased the total length, numbers and crossings of dendrites and caused neuron death in rat hippocampi and cortices. It also led to increase in N-terminal ß-amyloid precursor protein (N-APP) and death receptor-6 (DR6) protein levels and in the activation of caspase-3 and caspase-6. Further study showed that DR6 protein was downregulated by miR-195 overexpression, upregulated by miR-195 inhibition, and unchanged by binding-site mutation and miR-masks. Knockdown of endogenous miR-195 by lentiviral vector-mediated overexpression of its antisense molecule (lenti-pre-AMO-miR-195) decreased the total length, numbers and crossings of dendrites and neuron death, upregulated N-APP and DR6 levels, and elevated cleaved caspase-3 and caspase-6 levels. Overexpression of miR-195 using lenti-pre-miR-195 prevented these changes triggered by 2VO. We conclude that miR-195 is involved in CBH-induced dendritic degeneration and neuron death through activation of the N-APP/DR6/caspase pathway.

[Effect of ischemic preconditioning on lung injury induced by ischemia/reperfusion in the hind limbs of rats].

AIM: To study the effect of ischemic preconditioning on lung injury following ischemia/reperfusion (I/R) in the hind limbs of rats. METHODS: Wistar rats were randomly divided into four groups (n=8): control group,limbs ischemia/reperfusion (LI/R) group, ischemia preconditioning (IPC) group and L-NAME group. At the end of the experiment, blood/gas analysis and the contents of serum MDA, NO, ET and lung tissue MDA, NO, ET, MPO were measured. Meanwhile, lung index and W/D) of lung were measured. RESULTS: After the rats' hind limbs suffered ischemia/reperfusion, the level of PaO2 decreased and the values of W/D, LI, MPO of the lung issure and MDA, NO, ET of plasma and lung all increased significantly in the LI/R group; but the ratio of NO/ET decreased. Compared with LI/R group, the contents of NO and ratio of NO/ET increased but other parameters decreased in the IPC group. Compared with IPC group, the contents of NO and ratio of NO/ET decreased, but other parameters increased in the L-NAME group. CONCLUSION: The IPC can attenuate lung injury following IR in the hind limbs of rats, which may correlated with the increase of NO.