Tau-Induced Ca/Calmodulin-Dependent Protein Kinase-IV Activation Aggravates Nuclear Tau Hyperphosphorylation / 神经科学通报·英文版

Hyperphosphorylated tau is the major protein component of neurofibrillary tangles in the brains of patients with Alzheimer's disease (AD). However, the mechanism underlying tau hyperphosphorylation is not fully understood. Here, we demonstrated that exogenously expressed wild-type human tau40 was detectable in the phosphorylated form at multiple AD-associated sites in cytoplasmic and nuclear fractions from HEK293 cells. Among these sites, tau phosphorylated at Thr205 and Ser214 was almost exclusively found in the nuclear fraction at the conditions used in the present study. With the intracellular tau accumulation, the Ca concentration was significantly increased in both cytoplasmic and nuclear fractions. Further studies using site-specific mutagenesis and pharmacological treatment demonstrated that phosphorylation of tau at Thr205 increased nuclear Ca concentration with a simultaneous increase in the phosphorylation of Ca/calmodulin-dependent protein kinase IV (CaMKIV) at Ser196. On the other hand, phosphorylation of tau at Ser214 did not significantly change the nuclear Ca/CaMKIV signaling. Finally, expressing calmodulin-binding protein-4 that disrupts formation of the Ca/calmodulin complex abolished the okadaic acid-induced tau hyperphosphorylation in the nuclear fraction. We conclude that the intracellular accumulation of phosphorylated tau, as detected in the brains of AD patients, can trigger nuclear Ca/CaMKIV signaling, which in turn aggravates tau hyperphosphorylation. Our findings provide new insights for tauopathies: hyperphosphorylation of intracellular tau and an increased Ca concentration may induce a self-perpetuating harmful loop to promote neurodegeneration.

Protective effects of genistein on Aβ₂₅₋₃₅-induced PC12 cell injury via regulating CaM-CaMKIV signaling pathway / 中国中药杂志

Genistein is a kind of isoflavone compounds， also called phytoestrogens， with clinical effects on cardiovascular disease， cancer and postmenopausal-related gynecological diseases， and also has the potentiality in the prevention and treatment of Alzheimer's disease(AD). In this study， the protective effect of genistein on Aβ₂₅₋₃₅-induced PC12 cell injury and effect on CaM-CaMKIV signaling pathway were observed to investigate its mechanism for AD. PC12 cells were cultured and then the safe concentration of genistein and the modeling concentration and optimal time point of administration of Aβ₂₅₋₃₅ were screened by MTT assay. After being pretreated with different concentrations of genistein(25， 50， 100 μmol·L⁻¹) on PC12 cells， the AD model of PC12 cells was induced by Aβ₂₅₋₃₅. Then the survival rate of cells was detected by MTT assay; morphological change of cells was observed under the inverted microscope， and apoptosis of cells was assessed by AO/EB fluorescence staining; the neuroprotective effects of genistein on AD cell model were observed and the optimal concentration of genistein was determined. Expressions of mRNA and protein levels of CaM， CaMKK， CaMKIV and tau were detected by qRT-PCR and Western blot assay， respectively. The results showed that as compared with the blank group， the cell survival rate was decreased; the cell damage and apoptosis were increased; and the expressions of mRNA and protein levels of CaM， CaMKK， CaMKIV and tau were increased in AD model group. Genistein could significantly improve the cell survival rate， reduce the cell damage and apoptosis of AD cell model， and significantly down-regulate the expressions of mRNA and protein levels of CaM， CaMKK， CaMKIV and tau of AD cell model. These results indicated that genistein has obviously neuroprotective effect on the AD cell model induced by Aβ₂₅₋₃₅， and the mechanism may be related to the down-regulation of CaM-CaMKIV signaling pathway and Tau protein expression.

Association between gene polymorphism of calcium/calmodulin-dependent kinase 4 and efficacy of amlodipine in the treatment of hypertension in Chinese Han nationality / 中南大学学报(医学版)

OBJECTIVE@#To evaluate the association between single nucleotide polymorphisms of calcium/calmodulin-dependent kinase 4 (CAMK4) and the therapeutic effect of amlodipine in essential hypertensive patients in Chinese Han nationality.
@*METHODS@#A total of 108 mild-to-moderate essential hypertension patients in Chinese Han nationality were treated with amlodipine for 8 weeks at a dosage of 5 mg/d. Polymerase chain reaction-restriction fragment length polymorphism was performed to detect the genotypes (rs10491334). Blood pressure was measured and analyzed.
@*RESULTS@#The result of rs10491334 polymorphism of CAMK4 was consistent with Hardy-Weinberg equilibrium distribution and the frequencies of C allele and T allele were 88.89% and 11.11%, respectively. The systolic blood pressure and diastolic blood pressure before amlodipine treatment were not statistically different among different genotype carriers (P>0.05). The blood pressure was significantly reduced in all patients after amlodipine treatment (P<0.05). Systolic blood pressure was significantly decreased in patients with rs10491334 CC genotype and CT genotype compared with those patients with rs10491334 TT genotype. Total effective rates of CT and TT carriers were higher than those of the CC genotype carriers (P<0.01).
@*CONCLUSION@#The CAMK4 gene polymorphism might be associated with the efficacy of calcium channel blocker in treating mild-to-moderate essential hypertension patients.

Effects of calcium and calmodulin dependent kinase against hypoxic neuronal injury / 中国当代儿科杂志

<p><b>OBJECTIVE</b>To study the effects of calcium and calmodulin dependent kinase against hypoxic neuronal injury and its possible mechanisms.</p><p><b>METHODS</b>Embryonic cortical neurons of 17-day pregnant embryo Sprague-Dawley rats were cultured in vitro and the cultured neurons were randomly allocated into different groups that exposed to hypoxia or hypoxia +calcium channel antagonist. Nimodipine and MK-801 were used to block the L-voltage sensitive calcium channel and NMDA receptor respectively before hypoxia. The methyl thiazolyl tetrazolium (MTT) method was used to determine the cell viability. Fluo-4AM, an intracellular calcium indictor, was used to detect the changes of intracellular calcium after hypoxia. The expressions of CaMKII and CaMKIV were detected by Western blot.</p><p><b>RESULTS</b>The cell viability of the nimodipine or MK-801-treated groups was significantly higher than that of the untreated hypoxia group. The intracellular calcium level of the nimodipine-treated group decreased rapidly after hypoxia. Compared to nimodipine treatment, MK-801 treatment could inhibit hypoxia-induced calcium influx for a longer time. Nimodipine treatment decreased the CaMKII expression while MK-801 treatment decreased the CaMKIV expression.</p><p><b>CONCLUSIONS</b>Nimodipine and MK-801 protect neurons from hypoxic injury possibly by the inhibition of CaMKII and CaMKIV expressions respectively.</p>