TRPC1 Deficiency Impairs the Endothelial Progenitor Cell Function via Inhibition of Calmodulin/eNOS Pathway.

Endothelial progenitor cells (EPCs) promote angiogenesis and play a pivotal role in endothelial repair and re-endothelialization after vascular injury. Transient receptor potential-canonical1 (TRPC1) has been recently implied to play important roles on EPC function. Here, we studied the role of TRPC1 in regulating EPC function in vivo and in vitro. EPCs were cultured from TRPC1-knockout mice and their controls. In vitro, TRPC1 knockout reduced EPC functional activities, including migration and tube formation. Additionally, calmodulin (CaM)/endothelial nitric oxide synthase (eNOS) signaling activity were downregulated after TRPC1 knockout. Administration of CaM or eNOS inhibitor ameliorated TRPC1 knockout-reduced EPC migration and tube formation. In vivo Matrigel plug assay confirmed that TRPC1 knockout decreased formation of functional blood vessels of EPCs compared with wild-type EPCs. Taken together, these data suggest that TRPC1 is a critical regulator of angiogenesis.

Transient Receptor Potential-canonical 1 is Essential for Environmental Enrichment-Induced Cognitive Enhancement and Neurogenesis.

Transient receptor potential-canonical 1 (TRPC1) plays a crucial role in neuronal survival, nerve regeneration, and protects neurons from neurotoxic injury, but it is not reported whether or how TRPC1 may affect learning and memory. Here, we found that TRPC1 knockout did not significantly affect the spatial learning and memory ability when the mice were housed in standard cages (SC). Interestingly, after the mice were exposed to environmental enrichment (EE) for 4 weeks, TRPC1 knockout abolished the EE-induced spatial memory enhancement, LTP induction, and neurogenesis in hippocampal DG subset. By stereotaxic infusion of the recombinant adeno-associated viruses (rAAV)-TRPC1 into the hippocampal DG subsets bilaterally, we observed that the EE-associated neurogenesis, LTP induction and the cognitive enhancement were efficiently rescued in TRPC1 knockout mice. EE increased the phosphorylation levels of ERK, p38, and cyclic AMP response element-binding protein (CREB) in wild-type mice, whereas the activation of ERK and CREB was not seen in TRPC1 knockout mice, and the phosphorylation of p38 was same in EE-TRPC1-/- and WT-EE. Finally, EE increased TRPC1 expression and overexpression of TRPC1 increased neurogenesis and activated ERK/CREB pathway in the wild-type mice. These findings suggest that TRPC1 is indispensable for the EE-induced hippocampal neurogenesis and cognitive enhancement.

AMPK activation ameliorates Alzheimer's disease-like pathology and spatial memory impairment in a streptozotocin-induced Alzheimer's disease model in rats.

Collecting evidence has shown that type 2 diabetes mellitus is a high risk factor of late-onset Alzheimer's disease (AD); the energy metabolic dysfunction is thought to be a convergent point of the two diseases. However, the underlying mechanisms of diabetes-associated AD are still unclear. In the current study, we investigated the roles of AMPK in diabetes-related AD-like pathologic features in models of intracerebroventricular-streptozotocin (ICV-STZ) animals. Rats infused with STZ (3 mg/kg, once) were followed by injection of AICAR (AMPK activator) or vehicle via ICV. We found that the level of p-AMPK (active type of AMPK) and SIRT1 activity were decreased and the level of phosphorylated tau was increased at Ser396 and Thr231 sites in ICV-STZ rats when compared with control rats. Mitochondria from ICV-STZ rats displayed a significant decrease in mitochondrial membrane potential, complex I activity, ATP level, and superoxide dismutase activity as well as an increase of reactive oxygen species production when compared with that from control rats. Meanwhile the number of apoptotic cell confirmed by cleaved caspase-3 (active type of caspase-3) staining was also stronger in ICV-STZ rats than control rats. All pathological changes including biochemistry and cognitive function could be mitigated through rescuing AMPK activity with its specific activator (AICAR) in ICV-STZ rats. Taken together, these results suggested that AMPK activation improves AD-like pathological changes via repairing mitochondrial functions in ICV-STZ rats.

Activation of sirtuin 1 attenuates cerebral ventricular streptozotocin-induced tau hyperphosphorylation and cognitive injuries in rat hippocampi.

Patients with diabetes in the aging population are at high risk of Alzheimer's disease (AD), and reduction of sirtuin 1 (SIRT1) activity occurs simultaneously with the accumulation of hyperphosphorylated tau in the AD-affected brain. It is not clear, however, whether SIRT1 is a suitable molecular target for the treatment of AD. Here, we employed a rat model of brain insulin resistance with intracerebroventricular injection of streptozotocin (ICV-STZ; 3 mg/kg, twice with an interval of 48 h). The ICV-STZ-treated rats were administrated with resveratrol (RSV; SIRT1-specific activator) or a vehicle via intraperitoneal injection for 8 weeks (30 mg/kg, once per day). In ICV-STZ-treated rats, the levels of phosphorylated tau and phosphorylated extracellular signal-regulated kinases 1 and 2 (ERK1/2) at the hippocampi were increased significantly, whereas SIRT1 activity was decreased without change of its expression level. The capacity of spatial memory was also significantly lower in ICV-STZ-treated rats compared with age-matched control. RSV, a specific activator of SIRT1, which reversed the ICV-STZ-induced decrease in SIRT1 activity, increases in ERK1/2 phosphorylation, tau phosphorylation, and impairment of cognitive capability in rats. In conclusion, SIRT1 protects hippocampus neurons from tau hyperphosphorylation and prevents cognitive impairment induced by ICV-STZ brain insulin resistance with decreased hippocampus ERK1/2 activity.

Nmnat2 attenuates Tau phosphorylation through activation of PP2A.

The activity of protein phosptase-2A (PP2A) is significantly decreased in the brains of Alzheimer's disease (AD) patients, but the upstream effectors for regulating PP2A activity are not fully understood. Nicotinamide mononucleotide adenylyltransferase 2 (Nmnat2) is a key enzyme involved in energy metabolism and its gene expression level is reduced in AD brain specimens. Whether Nmnat2 can activate PP2A deserves to be explored. Here, we first measured the level of Nmnat2, Tyr307-phosphorylation of PP2A, and tau phosphorylation in Tg2576 mice. We observed that the mRNA and protein levels of Nmnat2 were significantly decreased with a simultaneous elevation of p-Tyr307-PP2A and tau phosphorylation in Tg2576 mice. Further studies in HEK293 cells with stable expression of human tau441 (HEK293/tau) demonstrated that simultaneous inhibition of PP2A by okadaic acid abolished the Nmnat2-induced tau dephosphorylation. Moreover, we further demonstrated that overexpression of Nmnat2 could activate PP2A with attenuation of tau phosphorylation, whereas downregulation of Nmnat2 by shRNA inhibited PP2A with tau hyperphosphorylation at multiple AD-associated sites. Our data provide the first evidence that Nmnat2 affects tau phosphorylation by regulating PP2A activity, suggesting that Nmnat2 may serve as a potential target in arresting AD-like tau pathologies.

Capsaicin ameliorates stress-induced Alzheimer's disease-like pathological and cognitive impairments in rats.

Hyperphosphorylated tau aggregated into neurofibrillary tangles is a hallmark lesion of Alzheimer's disease (AD) and is linked to synaptic and cognitive impairments. In animal models, cold water stress (CWS) can cause cognitive disorder and tau hyperphosphorylation. Capsaicin (CAP), a specific TRPV1 agonist, is neuroprotective against stress-induced impairment, but the detailed mechanisms are still elusive. Here, we investigated whether CAP mitigates CWS-induced cognitive and AD-like pathological alterations in rats. The animals were administered CAP (10 mg/kg in 0.2 ml, 0.1% ethanol) or a control (0.2 ml normal saline, 0.1% ethanol) by intragastric infusion 1 h before CWS treatment. Our results showed that CAP significantly attenuated CWS-induced spatial memory impairment and suppression of PP-DG long-term potentiation; CAP abolished CWS-induced dendritic regression and enhanced several memory-associated proteins decreased by CWS, such as synapsin I and PSD93; CAP also prevented CWS-induced tau hyperphosphorylation by abolishing inhibition of protein phosphatase 2A. Taken together, this study demonstrated that activation of TRPV1 can mitigate CWS-induced AD-like neuropathological alterations and cognitive impairment and may be a promising target for therapeutic intervention in AD.

Methylglyoxal induces tau hyperphosphorylation via promoting AGEs formation.

The hyperphosphorylated tau is a major protein component of neurofibrillary tangle, which is one of hallmarks of Alzheimer's disease (AD). While the level of methylglyoxal (MG) is significantly increased in the AD brains, the role of MG in tau phosphorylation is still not reported. Here, we found that MG could induce tau hyperphosphorylation at multiple AD-related sites in neuroblastoma 2a cells under maintaining normal cell viability. MG treatment increased the level of advanced glycation end products (AGEs) and the receptor of AGEs (RAGE). Glycogen synthesis kinase-3ß (GSK-3ß) and p38 MAPK were activated, whereas the level and activity of JNK, Erk1/2, cdk5, and PP2A were not altered after MG treatment. Simultaneous inhibition of GSK-3ß or p38 attenuated the MG-induced tau hyperphosphorylation. Aminoguanidine, a blocker of AGEs formation, could effectively reverse the MG-induced tau hyperphosphorylation. These data suggest that MG induces AD-like tau hyperphosphorylation through AGEs formation involving RAGE up-regulation and GSK-3ß activation and p38 activation is also partially involved in MG-induced tau hyperphosphorylation. Thus, targeting MG may be a promising therapeutic strategy to prevent AD-like tau hyperphosphorylation.