The identities of insulin signaling pathway are affected by overexpression of Tau and its phosphorylation form.

Introduction: Hyperphosphorylated Tau formed neurofibrillary tangles was one of the major neuropathological hallmarks of Alzheimer's disease (AD). Dysfunctional insulin signaling in brain is involved in AD. However, the effect of Tau pathology on brain insulin resistance remains unclear. This study explored the effects of overexpressing wild-type Tau (WTau) or Tau with pseudo-phosphorylation at AT8 residues (PTau) on the insulin signaling pathway (ISP). Methods: 293T cells or SY5Y cells overexpressing WTau or PTau were treated with or without insulin. The elements in ISP or the regulators of IPS were analyzed by immunoblotting, immunofluorescent staining and co-immunoprecipitation. Akt inhibitor MK2206 was used for evaluating the insulin signaling to downstream of mTOR in Tau overexpressing cells. The effects of anti-aging drug lonafarnib on ISP in WTau or PTau cells were also analyzed with immunoblotting. Considering lonafarnib is an inhibitor of FTase, the states of Rhes, one of FTase substrate in WTau or PTau cells were analyzed by drug affinity responsive target stability (DARTS) assay and the cellular thermal shift assay (CETSA). Results: WTau or PTau overexpression in cells upregulated basal activity of elements in ISP in general. However, overexpression of WTau or PTau suppressed the ISP signaling transmission responses induced by insulin simulation, appearing relative higher response of IRS-1 phosphorylation at tyrosine 612 (IRS-1 p612) in upstream IPS, but a lower phosphorylation response of downstream IPS including mTOR, and its targets 4EPB1 and S6. This dysregulation of insulin evoked signaling transmission was more obvious in PTau cells. Suppressing Akt with MK2206 could compromise the levels of p-S6 and p-mTOR in WTau or PTau cells. Moreover, the changes of phosphatases detected in WTau and PTau cells may be related to ISP dysfunction. In addition, the effects of lonafarnib on the ISP in SY5Y cells with WTau and PTau overexpression were tested, which showed that lonafarnib treatment resulted in reducing the active levels of ISP elements in PTau cells but not in WTau cells. The differential effects are probably due to Tau phosphorylation modulating lonafarnib-induced alterations in Rhes, as revealed by DARTS assay. Conclusion and discussion: Overexpression of Tau or Tau with pseudo-phosphorylation at AT8 residues could cause an upregulation of the basal/tonic ISP, but a suppression of insulin induced the phasic activation of ISP. This dysfunction of ISP was more obvious in cells overexpressing pseudo-phosphorylated Tau. These results implied that the dysfunction of ISP caused by Tau overexpression might impair the physiological fluctuation of neuronal functions in AD. The different effects of lonafarnib on ISP between WTau and PTau cells, indicating that Tau phosphorylation mediates an additional effect on ISP. This study provided a potential linkage of abnormal expression and phosphorylation of Tau to the ISP dysfunction in AD.

Interaction between extracellular ATP5A1 and LPS alleviates LPS-induced neuroinflammation in mice.

Neuroinflammation is one of the main causes of Alzheimer's disease (AD). The presence of Lipopolysaccharide (LPS) in senile plaques (SP) of AD suggests that it plays a role in AD pathogenesis. ATP5A1 (F1F0-ATP synthase F1 α subunit) is abundant in SP. Further, the protein has recently been found to have an anti-infection role in zebrafish embryos. In the present study, we observed that LPS levels were higher in the brains of APP/PS1 mice than in control mice, and LPS co-localised with ATP5A1 in amyloid plaques. The interaction of recombinant ATP5A1(rATP5A1) and LPS was evidenced by cellular thermal shift assay and enzyme-linked immunosorbent assay-based binding assay in vitro. Neuroinflammation in the brain of a mouse model was induced by intracerebroventricular injection of LPS. The addition of rATP5A1 relieved LPS-induced reduction of spontaneous locomotor ability, depressive-like behaviour, and working memory impairment. Furthermore, rATP5A1 suppressed the activation of astrocytes and microglia, IL-1ß accumulation, and tau phosphorylation induced by LPS. Taken together, findings suggest that ATP5A1 is involved in the regulation of LPS-mediated neuroinflammation in AD.

Mechanism of Lycium barbarum polysaccharides on primary cultured rat hippocampal neurons.

Lycium barbarum polysaccharides (LBP) have been reported to have a wide range of beneficial effects including neuroprotection, anti-aging and anticancer. However, the anti-inflammation mechanism of LBP on primary cultured rat hippocampal neurons injured by oxygen-glucose deprivation/reperfusion (OGD/RP) is incompletely understood. We investigate the neuroprotective effects of LBP on neonatal rat primary cultured hippocampal neurons injured by OGD/RP with different approaches: MTT assay was used to detect cell viability, lactate dehydrogenase leakage was used to detect neuronal damage, formation of reactive oxygen species was determined by using fluorescent probe DCFH-DA. Hoechst 33,342 staining and TUNEL staining were used to determine the cell apoptosis. JC-1 was used to evaluate loss of mitochondrial membrane potential (MMP). The fluorescence intensity of [Ca2+]i in hippocampal neurons was determined by laser scanning confocal microscopy. The expression of various apoptotic markers such as TLR4, IκB, IL-6 and NF-κB were investigated by RT-PCR and western blot analysis. Results from each approach demonstrated that LBP increased the cell abilities and decreased the cell morphologic impairment. Furthermore, LBP increased MMP but inhibited [Ca2+]i elevation and significantly suppressed overexpression of NF-κB, IL-6 TLR4 and increased IκB expression.

Protective effects of aloperine on neonatal rat primary cultured hippocampal neurons injured by oxygen-glucose deprivation and reperfusion.

Aloperine (ALO), one of the alkaloids isolated from Sophora alopecuroides L., is traditionally used for various diseases including neuronal disorders. This study investigated the protective effects of ALO on neonatal rat primary-cultured hippocampal neurons injured by oxygen-glucose deprivation and reperfusion (OGD/RP). Treatment with ALO (25, 50, and 100 mg/l) attenuated neuronal damage (p < 0.01), with evidence of increased cell viability (p < 0.01) and decreased cell morphologic impairment. Furthermore, ALO increased mitochondrial membrane potential (p < 0.01), but inhibited intracellular-free calcium [Ca(2+)] i (p  < 0.01) elevation in a dose-dependent manner at OGD/RP. ALO also reduced the intracellular reactive oxygen species and malondialdehyde production and enhanced the antioxidant enzymatic activities of catalase, superoxide dismutase, glutathione peroxidase and the total antioxidant capacity. The results suggested that ALO has significant neuroprotective effects that can be attributed to anti-oxidative stress.

Neuroprotective effects of oxysophocarpine on neonatal rat primary cultured hippocampal neurons injured by oxygen-glucose deprivation and reperfusion.

CONTEXT: Oxysophocarpine (OSC), a quinolizidine alkaloid extracted from leguminous plants of the genus Robinia, is traditionally used for various diseases including neuronal disorders. OBJECTIVE: This study investigated the protective effects of OSC on neonatal rat primary-cultured hippocampal neurons were injured by oxygen-glucose deprivation and reperfusion (OGD/RP). MATERIALS AND METHODS: Cultured hippocampal neurons were exposed to OGD for 2 h followed by a 24 h RP. OSC (1, 2, and 5 µmol/L) and nimodipine (Nim) (12 µmol/L) were added to the culture after OGD but before RP. The cultures of the control group were not exposed to OGD/RP. MTT and LDH assay were used to evaluate the protective effects of OSC. The concentration of intracellular-free calcium [Ca(2+)]i and mitochondrial membrane potential (MMP) were determined to evaluate the degree of neuronal damage. Morphologic changes of neurons following OGD/RP were observed with a microscope. The expression of caspase-3 and caspase-12 mRNA was examined by real-time quantitative PCR. RESULTS: The IC50 of OSC was found to be 100 µmol/L. Treatment with OSC (1, 2, and 5 µmol/L) attenuated neuronal damage (p < 0.001), with evidence of increased cell viability (p < 0.001) and decreased cell morphologic impairment. Furthermore, OSC increased MMP (p < 0.001), but it inhibited [Ca(2+)]i (p < 0.001) elevation in a dose-dependent manner at OGD/RP. OSC (5 µmol/L) also decreased the expression of caspase-3 (p < 0.05) and caspase-12 (p < 0.05). DISCUSSION AND CONCLUSION: The results suggested that OSC has significant neuroprotective effects that can be attributed to inhibiting endoplasmic reticulum (ER) stress-induced apoptosis.