Akt activity in presenilin 1 wild-type and mutation transfected human SH-SY5Y neuroblastoma cells after serum deprivation and high glucose stress

Combined Scutellarin and C18H17NO6 Imperils the Survival of Glioma: Partly Associated With the Repression of PSEN1/PI3K-AKT Signaling Axis

Glioma, the most common intracranial tumor, harbors great harm. Since the treatment for it has reached the bottleneck stage, the development of new drugs becomes a trend. Therefore, we focus on the effect of scutellarin (SCU) and its combination with C₁₈H₁₇NO₆ (abbreviated as combination) on glioma and its possible mechanism in this study. Firstly, SCU and C₁₈H₁₇NO₆ both suppressed the proliferation of U251 and LN229 cells in a dose-dependent manner, and C₁₈H₁₇NO₆ augmented the inhibition effect of SCU on U251 and LN229 cells in vitro. Moreover, there was an interactive effect between them. Secondly, SCU and C₁₈H₁₇NO₆ decreased U251 cells in G2 phase and LN229 cells in G2 and S phases but increased U251 cells in S phase, respectively. Meanwhile, the combination could further reduce U251 cells in G2 phase and LN229 cells in G2 and S phases. Thirdly, SCU and C₁₈H₁₇NO₆ both induced the apoptosis of U251 and LN229. The combination further increased the apoptosis rate of both cells compared with the two drugs alone. Furthermore, SCU and C₁₈H₁₇NO₆ both inhibited the lateral and vertical migration of both cells, which was further repressed by the combination. More importantly, the effect of SCU and the combination was better than positive control-temozolomide, and the toxicity was low. Additionally, SCU and C₁₈H₁₇NO₆ could suppress the growth of glioma in vivo, and the effect of the combination was better. Finally, SCU and the combination upregulated the presenilin 1 (PSEN1) level but inactivated the phosphatidylinositol 3−kinase (PI3K)-protein kinase B (AKT) signaling in vitro and in vivo. Accordingly, we concluded that scutellarin and its combination with C₁₈H₁₇NO₆ suppressed the proliferation/growth and migration and induced the apoptosis of glioma, in which the mechanism might be associated with the repression of PSEN1/PI3K-AKT signaling axis.

Cyclin-Dependent Kinase-Like 5 (CDKL5): Possible Cellular Signalling Targets and Involvement in CDKL5 Deficiency Disorder

Cyclin-dependent kinase-like 5 (CDKL5, also known as STK9) is a serine/threonine protein kinase originally identified in 1998 during a transcriptional mapping project of the human X chromosome. Thereafter, a mutation in CDKL5 was reported in individuals with the atypical Rett syndrome, a neurodevelopmental disorder, suggesting that CDKL5 plays an important regulatory role in neuronal function. The disease associated with CDKL5 mutation has recently been recognised as CDKL5 deficiency disorder (CDD) and has been distinguished from the Rett syndrome owing to its symptomatic manifestation. Because CDKL5 mutations identified in patients with CDD cause enzymatic loss of function, CDKL5 catalytic activity is likely strongly associated with the disease. Consequently, the exploration of CDKL5 substrate characteristics and regulatory mechanisms of its catalytic activity are important for identifying therapeutic target molecules and developing new treatment. In this review, we summarise recent findings on the phosphorylation of CDKL5 substrates and the mechanisms of CDKL5 phosphorylation and dephosphorylation. We also discuss the relationship between changes in the phosphorylation signalling pathways and the Cdkl5 knockout mouse phenotype and consider future prospects for the treatment of mental and neurological disease associated with CDKL5 mutations.

Insulin-like growth factor-I mediates neuroprotection in proteasome inhibition-induced cytotoxicity in SH-SY5Y cells

The proteasome is an enzyme complex responsible for targeted intracellular proteolysis. Alterations in proteasome-mediated protein clearance have been implicated in the pathogenesis of aging, Alzheimer's disease (AD) and Parkinson's disease (PD). In such diseases, proteasome inhibition may contribute to formation of abnormal protein aggregates, which in turn activate intracellular unfolded protein responses that cause oxidative stress and apoptosis. In this study, we investigated the protective effect of Insulin-like Growth Factor-I (IGF-1) for neural SH-SY5Y cells treated with the proteasomal inhibitor, Epoxomicin. In SH-SY5Y cells, Epoxomicin treatment results in accumulation of intracellular ubiquitinated proteins and cytochrome c release from damaged mitochondria, leading to cell death, in Epoxomicin time- and dose-dependent manner. In cells treated with small amounts of IGF-1, the same dosages of Epoxomicin reduced both mitochondrial damage (cytochrome c release) and reduced caspase-3 activation and PARP cleavage, both of which are markers of apoptosis. Notably, however, IGF-1-treated SH-SY5Y cells still contained ubiquitinated protein aggregates. This result indicates that IGF-1 blocks the downstream apoptotic consequences of Epoxomicin treatment leading to decreased proteasome function. Clues as to the mechanism for this protective effect come from (a) increased AKT phosphorylation observed in IGF-1-protected cells, vs. cells exposed to Epoxomicin without IGF-1, and (b) reduction of IGF-1 protection by pretreatment of the cells with LY294002 (an inhibitor of PI3-kinase). Together these findings suggest that activation of PI3/AKT pathways by IGF-1 is involved in IGF-1 neuroprotection against apoptosis following proteasome inhibition.

Cortical development in the presenilin-1 null mutant mouse fails after splitting of the preplate and is not due to a failure of reelin-dependent signaling

Cortical development is disrupted in presenilin-1 null mutant (Psen1-/-) mice. Prior studies have commented on similarities between Psen1-/- and reeler mice. Reelin induces phosphorylation of Dab1 and activates the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Psen1 is known to modulate PI3K/Akt signaling and both known reelin receptors (apoER2 and VLDLR) are substrates for Psen1 associated gamma-secretase activity. The purpose of this study was to determine whether reelin signaling is disrupted in Psen1-/- mice. We show that, while Dab1 is hypophosphorylated late in cortical development in Psen1-/- mice, it is normally phosphorylated at earlier ages and reelin signaling is intact in Psen1-/- primary neuronal cultures. gamma-secretase activity was also not required for reelin-induced phosphorylation of Dab1. Unlike reeler mice the preplate splits in Psen1-/- brain. Thus cortical development in Psen1-/- mice fails only after splitting of the preplate and is not due to an intrinsic failure of reelin signaling.

Presenilin acts as a positive regulator of basal level activity of ERK through the Raf-MEK1 signaling pathway

Presenilins (PS) have been reported to be functionally involved in amyloid precursor protein processing, notch receptor signaling, and programmed cell death, or apoptosis. To understand the role of PS1 in the signaling events, we investigated in this study the role of PS1 in the basal level of mitogen-activated protein kinase (MAPK) pathways using PS1(-/-) mouse embryonic fibroblast (MEF) cells from PS1-null mice. Interestingly, the basal level of ERK activity, but not JNK or p38 activity, is lower in PS1(-/-) MEF cells than in PS1(+/+) MEF cells. In PS1(-/-) MEF cells, the basal activities of Raf and MEK, the upstream signaling component of ERK, are also lower than in PS1(+/+) MEF cells. Furthermore, Elk-1 transcription activity also down-regulates in PS1(-/-) MEF cells. Collectively, our data suggest that PS can modulate the basal level of ERK activity through the Raf-MEK-dependent pathway.

PS1 activates PI3K thus inhibiting GSK-3 activity and tau overphosphorylation: effects of FAD mutations

Phosphatidylinositol 3-kinase (PI3K) promotes cell survival and communication by activating its downstream effector Akt kinase. Here we show that PS1, a protein involved in familial Alzheimer's disease (FAD), promotes cell survival by activating the PI3K/Akt cell survival signaling. This function of PS1 is unaffected by gamma-secretase inhibitors. Pharmacological and genetic evidence indicates that PS1 acts upstream of Akt, at or before PI3K kinase. PS1 forms complexes with the p85 subunit of PI3K and promotes cadherin/PI3K association. Furthermore, conditions that inhibit this association prevent the PS1-induced PI3K/Akt activation, indicating that PS1 stimulates PI3K/Akt signaling by promoting cadherin/PI3K association. By activating PI3K/Akt signaling, PS1 promotes phosphorylation/inactivation of glycogen synthase kinase-3 (GSK-3), suppresses GSK-3-dependent phosphorylation of tau at residues overphosphorylated in AD and prevents apoptosis of confluent cells. PS1 FAD mutations inhibit the PS1-dependent PI3K/Akt activation, thus promoting GSK-3 activity and tau overphosphorylation at AD-related residues. Our data raise the possibility that PS1 may prevent development of AD pathology by activating the PI3K/Akt signaling pathway. In contrast, FAD mutations may promote AD pathology by inhibiting this pathway.

Insulin-like growth factor type 1 prevents hyperglycemia-induced uncoupling protein 3 down-regulation and oxidative stress

Uncoupling proteins (UCPs) have been reported to decrease the mitochondrial production of reactive oxygen species (ROS) by lowering the mitochondrial inner membrane potential (MMP). We have previously shown that UCP3 expression is positively regulated by insulin-like growth factor-1 (IGF-1). The aim of this study was to investigate the role of UCPs in IGF-1-mediated protection from hyperglycemia-induced oxidative stress and neurodegeneration. Human neuroblastoma SH-SY5Y cells were differentiated with retinoic acid for 6 days, after which exposure to 8, 30, or 60 mM glucose with or without 10 nM IGF-1 was started. After 48-72 hr, the number of neurites per cell, UCP3 protein expression, MMP, and intracellular levels of ROS and total glutathione were examined. These studies showed that glucose concentration-dependently reduced the number of neurites per cell, with a 50% reduction at 60 mM. In parallel, the UCP3 protein expression was down-regulated, and the MMP was raised 3.5-fold, compared with those in cells incubated with 8 mM glucose. Also, the ROS levels were increased, showing a twofold maximum at 60 mM glucose. This was accompanied by a twofold elevation of total glutathione levels, confirming an altered cellular redox state. IGF-1 treatment prevented the glucose-induced neurite degeneration and UCP3 down-regulation. Furthermore, the MMP and the intracellular levels of ROS and glutathione were normalized to those of control cells. These data indicate that IGF-1 may protect from hyperglycemia-induced oxidative stress and neuronal injuries by regulating MMP, possibly by the involvement of UCP3.