Zuoping Xie

Acute impairment of mitochondrial trafficking by beta-amyloid peptides in hippocampal neurons.

Defects in axonal transport are often associated with a wide variety of neurological diseases including Alzheimers disease (AD). β-Amyloid (Aβ) is a major component of neuritic plaques associated with pathological conditions of AD brains. Here, we report that a brief exposure of cultured hippocampal neurons to Aβ molecules resulted in rapid and severe impairment of mitochondrial transport without inducing apparent cell death and significant morphological changes. Such acute inhibition of mitochondrial transport was not associated with a disruption of mitochondria potential nor involved aberrant cytoskeletal changes. Aβ also did not elicit significant Ca2+ signaling to affect mitochondrial trafficking. However, stimulation of protein kinase A (PKA) by forskolin, cAMP analogs, or neuropeptides effectively alleviated the impairment. We also show that Aβ inhibited mitochondrial transport by acting through glycogen synthase kinase 3β (GSK3β). Given that mitochondria are crucial organelles for many cellular functions and survival, our findings thus identify an important acute action of Aβ molecules on nerve cells that could potentially contribute to various abnormalities of neuronal functions under AD conditions. Manipulation of GSK3β and PKA activities may represent a key approach for preventing and alleviating Aβ cytotoxicity and AD pathological conditions.

Stromal cell derived factor-1 acutely promotes neural progenitor cell proliferation in vitro by a mechanism involving the ERK1/2 and PI-3K signal pathways☆

Stromal cell derived factor‐1 (SDF‐1), a member of the chemotactic cytokine family, has attracted attention in recent years. It participates in diverse processes such as the regulation of neuronal migration and activation of CD4+ T cells; it is also a co‐receptor for human immunodeficiency virus‐1 (HIV‐1). Here, we show that the proliferation of neural progenitor cells dissociated from rat cortex and cultured in vitro with basic fibroblast growth factor (bFGF) is stimulated by SDF‐1. PD98059 and wortmannin, which are, respectively, specific inhibitors of the extracellular regulated kinase1/2 (ERK1/2) and phosphatidylinositol‐3 kinase (PI‐3K) signal pathways, markedly attenuate this stimulation of proliferation. These findings indicate that SDF‐1 acutely promotes the proliferation of NPCs in vitro involving the ERK1/2 and PI‐3 kinase pathways, suggesting that it plays a basic role in the development of neural progenitors.

Deoxyschisandrin modulates synchronized Ca2+ oscillations and spontaneous synaptic transmission of cultured hippocampal neurons

AbstractAim:Deoxyschisandrin is one of the most effective composites of Schisandra chinensis, a famous Chinese medicine widely used as an antistress, anti-aging, and neurological performance-improving herb. In this study, we examined its specific mechanisms of action on cultured hippocampal neurons.Methods:Hippocampal neurons, primarily cultured for 9–11 d in vitro, were used for this study. DS were dissolved in DMSO and applied to calcium imaging and whole-cell patch clamp.Results:The application of 3 mg/L DS decreased the frequency of spontaneous and synchronous oscillations of intracellular Ca2+ to 72%±2% (mean±SEM), and the spontaneous inhibitory postsynaptic currents to 60%±3% (mean±SEM). The inhibitory concentraton 50% (IC50) for the effect of DS on calcium oscillations was 3.8 mg/L. DS also depressed the high voltage-gated Ca2+ channel and the voltage-gated Na+ channel currents at the same time point. It had no effect, however, on voltage-gated K+ and spontaneous excitatory postsynaptic currents.Conclusion:DS inhibited the spontaneous and synchronous oscillations of intracellular Ca2+ through the depression of influx of extracellular calcium and the initiation of action potential. By repressing the spontaneous neurotransmitter release, DS modulated the neuronal network activities.

Effects of insulin-like growth factor 1 on synaptic excitability in cultured rat hippocampal neurons

Insulin-like growth factor 1 (IGF-1) has important functions in the brain, including metabolic, neurotrophic, neuromodulatory and neuroendocrine actions, and it also prevents beta amyloid-induced death of hippocampal neurons. However, its functions in the synaptic excitability remain uncertain. Here we investigated the effects of IGF-1 on synaptic excitability in cultured rat hippocampal neurons using whole-cell patch clamp recordings. Incubation the hippocampal neurons with different concentrations of IGF-1 for 24 h or 30 min significantly increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs), but had no effect on the frequency of miniature EPSCs (mEPSCs) and spontaneous inhibitory postsynaptic currents (sIPSCs). The mean amplitudes, rise, and decay kinetics of sEPSCs, mEPSCs, and sIPSCs were not significantly affected by IGF-1, indicating that IGF-1 increased the probability of neurotransmitter release but did not modulate postsynaptic receptors. The effects of IGF-1 were mediated by mitogen-activated protein kinase (MAPK). IGF-1 activated the ERK1/2 signaling pathway in cultured hippocampal neurons, and the inhibitor PD98059 blocked the enhancement of sEPSCs induced by IGF-1. These results demonstrated the regulatory function of IGF-1 on synaptic excitability in hippocampal neurons and its underlying signaling mechanism.

In vivo insulin deficiency as a potential etiology for demyelinating disease

Demyelinating disease is pathologically characterized by the death of mature oligodendrocytes that normally synthesize myelin to perform insulating functions. Moreover, demyelinating disease also results in the failure of remyelination process in which oligodendrocyte progenitor cells reactivate and differentiate into new oligodendrocytes. Thus, this disease reflects decreased nerve conduction velocity and eventually dysfunction of the nervous system. A notable fact in the clinic is that demyelination is one of the most common diabetes-induced complications, implying that demyelinating disease may be relevant to insulin deficiency in vivo. However, the explicit pathological relationship between demyelination and diabetes remains unclear. Mainstream theories posit that demyelinating disease is an autoimmune disease arising from abnormal immunological reactions, but this perspective is limited when applied to the clinic. Olig1 is a vital transcription factor involved in oligodendrogenesis and is essential for the survival and maturation of oligodendrocyte progenitor cells. Furthermore, Olig1 is required for the onset of remyelination in adults. In the present study, we serendipitously found by means of protein immunoblot that the expression of nuclear Olig1 was inhibited when mouse oligodendrocyte progenitor cells were cultured in the absence of insulin. Combining this finding with the clinical relevance of demyelination and diabetes, we hypothesize that in vivo insulin deficiency impairs the reactivation and differentiation of oligodendrocyte progenitor cells through downregulation of nuclear Olig1 expression and therefore hinders the remyelination, which is an important process required for functional recovery in demyelinating disease. This hypothesis implies that in vivo insulin deficiency may be a novel etiological cause of demyelinating disease and thus contribute to improved the clinical therapies for remyelination repair. We suggest that sustaining normal insulin levels and stable nuclear Olig1 expression in vivo can be new therapeutic targets for remyelination repair and diabetic neuropathy. In addition, with respect to the clinical transplantation of oligodendrocyte progenitor cells for remyelination repair, supplementing cell suspensions that are to be transplanted with appropriate doses of insulin potentially may facilitate adaptation of the transplanted progenitor cells to the heterogeneous and pathological environment in vivo and eventually improve the efficacy of the cellular transplantation.

Acute effect of β amyloid on synchronized spontaneous Ca2+ oscillations in cultured hippocampal networks

The effects of β amyloid (Aβ) on cytoplasmic Ca2+ ([Ca2+]c) have been studied extensively, but the current literature on this aspect is confusing. We reported that 20 μM Aβ25–35 significantly inhibited the synchronized spontaneous cytoplasmic Ca2+ transients immediately after application, whereas it had little effect on the baseline [Ca2+]c concentration in neurons. Aβ1–42 had a similar effect on the Ca2+ transients as Aβ25–35, while it increased baseline [Ca2+]c concentration gradually. However, Aβ1–40 had little effect on either Ca2+ transients or baseline [Ca2+]c. Such differential effects of Aβ on Ca2+ signals might explain, at least partially, the confusing observations from the previous studies and provide important therapeutic implications for preventing or reversing early neuron damage in Alzheimers disease.

Calcium near the release site is essential for basal ACh release in Xenopus

Extracellular calcium is essential for neurotransmitter release, but the detailed mechanism by which Ca2+ regulates basal synaptic release has not yet been fully explored. In this study, calcium imaging and the whole‐cell patch‐clamp technique were used to investigate the role of Ca2+ in basal acetylcholine (ACh) release in the Xenopus neuromuscular junction and in isolated myocytes exogenously loaded with ACh. Carried out in normal and Ca2+‐free extracellular solution, the results indicate that Ca2+ near the release site is essential for basal neurotransmitter release.

Astragaloside IV inhibits spontaneous synaptic transmission and synchronized Ca2+ oscillations on hippocampal neurons.

AbstractAim:To investigate the changes in the spontaneous neuronal excitability induced by astragaloside IV (AGS-IV) in the cultured hippocampal network.Methods:Hippocampal neurons in culture for 9-11 d were used for this study. The spontaneous synaptic activities of these hippocampal neurons were examined by Ca2+ imaging and whole-cell patch-clamp techniques. In total, 40 mg/L AGS-IV dissolved in DMSO and 2 mL/L DMSO were applied to the neurons under a microscope while the experiments were taking place.Results:AGS-IV inhibited the frequencies of synchronized spontaneous Ca2+ oscillations to 59.39%±3.25% (mean±SEM), the spontaneous postsynaptic currents to 43.78%±7.72% (mean±SEM), and the spontaneous excitatory postsynaptic currents to 49.25%±7.06% (mean±SEM) of those of the control periods, respectively, at 16 min after the AGS-IV applications. AGS-IV also decreased the peak values of the voltage-gated K+ and Na+ channel currents at that time point.Conclusion:These results indicate that AGS-IV suppresses the spontaneous neuronal excitabilities effectively. Such a modulation of neuronal activity could represent new evidence for AGS-IV as a neuroprotector.

Effects of insulin‐like growth factor‐1 on okadaic acid‐induced apoptosis in SH‐SY5Y cells

The effects of insulin‐like growth factor‐1 (IGF‐1) on the cytotoxicity and apoptosis induced by okadaic acid (OA) in SH‐SY5Y cells were investigated. Cell viability was measured using the MTT (3‐(4,5‐dimethylthiazolyl‐2)‐2,‐5‐diphenyltetrazolium bromide) assay. Early and late apoptosis/necrosis were analyzed by flow cytometry using Annexin V and propidium iodide (PI) double‐staining. Caspase‐3 activation was detected by Western blot analysis. Preincubation with IGF‐1 for 24 h prevented cytotoxicity induced by 40 nM OA given for 24 h, and the MTT value significantly increased. Incubation with 20 nM OA for 24 h caused a marked increase in the percentage of early apoptotic and late apoptotic/necrotic cells, which was not dependent on the activation of caspase‐3. OA‐induced apoptosis was significantly decreased by pretreatment with 10 ng/ml of IGF‐1 for 24 h. The results supported the hypothesis that IGF‐1 may be useful in the treatment of Alzheimers disease.

Effects of insulin-like growth factor 1 on voltage-gated ion channels in cultured rat hippocampal neurons

Insulin-like growth factor 1 (IGF-1) has important functions in the brain, including metabolic, neurotrophic, neuromodulatory, and neuroendocrine actions, and it is also prevents amyloid beta-induced death of hippocampal neurons. However, its functions on the voltage-gated ion channels in hippocampus remain uncertain. In the present study, we investigated the effects of IGF-1 on voltage-gated potassium, sodium, and calcium channels in the cultured rat hippocampal neurons using the whole-cell patch clamp recordings. Following incubation with different doses of IGF-1 for 24 h, a block of the peak transient A-type K+ currents amplitude (IC50: 4.425 ng/ml, Hill coefficient: 0.621) was observed. In addition, after the application of IGF-1, the amplitude of high-voltage activated Ca2+ currents significantly increased but activation kinetics did not significantly alter (V1/2: -33.45 +/- 1.32 mV, k = 6.16 +/- 1.05) compared to control conditions (V1/2: -33.19 +/- 2.28 mV, k = 7.26 +/- 1.71). However, the amplitude of Na+, K+, and low-voltage activated Ca2+ currents was not affected by the application of IGF-1. These data suggest that IGF-1 inhibits transient A-type K+ currents and enhances high-voltage-activated Ca2+ currents, but has no effects on Na+ and low-voltage-activated Ca2+ currents.