c-Jun N-Terminal Kinase (JNK) and p38 Play Different Roles in Age-Related Purkinje Cell Death in Murine Organotypic Culture

JNK Inhibitor SP600125 Attenuates Paraquat-Induced Acute Lung Injury: an In Vivo and In Vitro Study

Acute lung injury (ALI) is a major complication soon after paraquat poisoning and rapidly progresses with high mortality. However, the specific mechanism underlying paraquat-induced ALI is still unclear. In this study, the mechanism underlying the protective effects of SP600125 on paraquat-induced ALI was investigated according to oxidative stress, inflammation, and apoptosis. The rats were randomly assigned into the control group (CON), the paraquat poisoning group (PQ), and the PQ + SP600125 group (SP). A549 cells were divided into the Con group, Pq group, and Sp group. H&E staining and detection of lung wet/dry ratio were employed to evaluate lung injury. Annexin V-PI staining was done to evaluate A549 cell apoptosis. Dihydroethidium fluorescence was used to measure reactive oxygen species (ROS) in the lungs and A549 cells. ELISA was performed to detect TNF-α and IL-6 in the supernatant of bronchoalveolar lavage fluid (BALF) and A549 cells. RT-qPCR was done to measure the messenger RNA (mRNA) expression of TNF-α and IL-6 in the lungs and A549 cells. Western blotting assay was performed to detect the protein expression of phospho-JNK, total JNK, and cleaved caspase-3. Electrophoretic mobility shift assay was employed to detect the DNA binding activities of AP-1 and P-p65. JNK inhibitor SP600125 reduced JNK phosphorylation, downregulated cleaved caspase-3 protein level, decreased AP-1 transcriptional activity and ROS level, and reduced the transcription and expression of TNF-α and IL-6, which improved ALI and cell apoptosis after paraquat poisoning. Our results indicate that JNK/AP-1 mediates ALI as well as oxidative stress and inflammation deterioration secondary to paraquat poisoning.

JNK3 involvement in nerve cell apoptosis and neurofunctional recovery after traumatic brain injury

Increasing evidence has revealed that the activation of the JNK pathway participates in apoptosis of nerve cells and neurological function recovery after traumatic brain injury. However, which genes in the JNK family are activated and their role in traumatic brain injury remain unclear. Therefore, in this study, in situ end labeling, reverse transcription-PCR and neurological function assessment were adopted to investigate the alteration of JNK1, JNK2 and JNK3 gene expression in cerebral injured rats, and their role in cell apoptosis and neurological function restoration. Results showed that JNK3 expression significantly decreased at 1 and 6 hours and 1 and 7 days post injury, but that JNK1 and JNK2 expression remained unchanged. In addition, the number of apoptotic nerve cells surrounding the injured cerebral cortex gradually reduced over time post injury. The Neurological Severity Scores gradually decreased over 1, 3, 5, 14 and 28 days post injury. These findings suggested that JNK3 expression was downregulated at early stages of brain injury, which may be associated with apoptosis of nerve cells. Downregulation of JNK3 expression may promote the recovery of neurological function following traumatic brain injury.

Enhanced survival of wild-type and Lurcher Purkinje cells in vitro following inhibition of conventional PKCs or stress-activated MAP kinase pathways

Recent studies using both dissociated and organotypic cell cultures have shown that heterozygous Lurcher (Lc/+) Purkinje cells (PCs) grown in vitro share many of the same survival and morphological characteristics as Lc/+ PCs in vivo. We have used this established tissue culture system as a valuable model for studying cell death mechanisms in a relatively simple system where neurodegeneration is induced by a constitutive cation leak mediated by the Lurcher mutation in the δ2 glutamate receptor (GluRδ2). In this study, Ca(++) imaging and immunocytochemistry studies indicate that intracellular levels of Ca(++) are chronically increased in Lc/+ PCs and the concentration and/or distribution of the conventional PKCγ isoform is altered in degenerating Lc/+ PCs. To begin to characterize the molecular mechanisms that regulate Lc/+ PC death, the contributions of conventional PKC pathways and of two MAP kinase family members, JNK and p38, were examined in slice cultures from wild-type and Lc/+ mutant mouse cerebellum. Cerebellar slice cultures from P0 pups were treated with either a conventional PKC inhibitor, a JNK inhibitor, or a p38 inhibitor either from 0 to 14 or 7 to 14 DIV. Treatment with either of the three inhibitors from 0 DIV significantly increased wild type and Lc/+ PC survival through 14 DIV, but only Lc/+ PC survival was significantly increased following treatments from 7 to 14 DIV. The results suggest that multiple PC death pathways are induced by the physical trauma of making organotypic slice cultures, naturally-occurring postnatal cell death, and the GluRδ2 (Lc) mutation.

Klf9 is necessary and sufficient for Purkinje cell survival in organotypic culture

During their phase of developmental programmed cell death (PCD), neurons depend on target-released trophic factors for survival. After this period, however, they critically change as their survival becomes target-independent. The molecular mechanisms underlying this major transition remain poorly understood. Here, we investigated, which transcription factors (TFs) might be responsible for the closure of PCD. We used Purkinje cells as a model since their PCD is restricted to the first postnatal week in the mouse cerebellum. Transcriptome analysis of Purkinje cells during or after PCD allowed the identification of Krüppel like factor 9 (Klf9) as a candidate for PCD closure, given its high increase of expression at the end of the 1st postnatal week. Klf9 function was tested in organotypic cultures, through lentiviral vector-mediated manipulation of Klf9 expression. In absence of trophic factors, the Purkinje cell survival rate is of 40%. Overexpression of Klf9 during PCD dramatically increases the Purkinje cell survival rate from 40% to 88%, whereas its down-regulation decreases it to 14%. Accordingly, in organotypic cultures of Klf9 knockout animals, Purkinje cell survival rate is reduced by half as compared to wild-type mice. Furthermore, the absence of Klf9 could be rescued by Purkinje cell trophic factors, Insulin growth factor-1 and Neurotrophin3. Altogether, our results ascribe a clear role of Klf9 in Purkinje cell survival. Thus, we propose that Klf9 might be a key molecule involved in turning off the phase of Purkinje PCD.

Profound morphological and functional changes of rodent Purkinje cells between the first and the second postnatal weeks: a metamorphosis?

Between the first and the second postnatal week, the development of rodent Purkinje cells is characterized by several profound transitions. Purkinje cells acquire their typical dendritic "espalier" tree morphology and form distal spines. During the first postnatal week, they are multi-innervated by climbing fibers and numerous collateral branches sprout from their axons, whereas from the second postnatal week, the regression of climbing fiber multi-innervation begins, and Purkinje cells become innervated by parallel fibers and inhibitory molecular layer interneurons. Furthermore, their periods of developmental cell death and ability to regenerate their axon stop and their axons become myelinated. Thus a Purkinje cell during the first postnatal week looks and functions differently from a Purkinje cell during the second postnatal week. These fundamental changes occur in parallel with a peak of circulating thyroid hormone in the mouse. All these features suggest to some extent an interesting analogy with amphibian metamorphosis.

Novel protective effect of mifepristone on detrimental GABAA receptor activity to immature Purkinje neurons

Immature Purkinje neurons are particularly vulnerable cells. They survive in cerebellar slice cultures under treatment by the synthetic steroid mifepristone (RU486) that depolarizes them at this age. The present study aims at understanding the mechanism underlying this neuroprotective effect. In the developing cerebellum, the role of γ-aminobutyric acid (GABA) in neuron survival is unknown. In 3-d-old mouse cerebellar slice cultures, we show that GABA(A) receptor activation is depolarizing and excitatory. Antagonists of GABA(A) receptors rescue Purkinje neurons, demonstrating that GABA is endogenously released in this preparation and is toxic. Mifepristone likely protects these neurons by reversing GABA(A) receptor-mediated chloride fluxes and reducing their driving force. Neuroprotection by mifepristone is dose-dependently decreased by the agonist of GABA(A) receptors muscimol and by caffeine, an agonist of internal calcium store release. Moreover, the survival induced by neomycin, an inhibitor of calcium release, is partially reversed by muscimol. The p38 mitogen-activated protein kinase (MAPK) inhibitor SB239063 also rescues Purkinje neurons. In summary, we propose that when GABA is depolarizing, mifepristone protects Purkinje neurons by shunting GABA responses and probably chloride fluxes, by inhibiting p38 MAPK activity and likely internal calcium store release. A new and nonhormonal effect of mifepristone is thus revealed.