Neonatal DEX exposure leads to hyperanxious and depressive-like behaviors as well as a persistent reduction of BDNF expression in developmental stages

An Interaction between Brain-Derived Neurotrophic Factor and Stress-Related Glucocorticoids in the Pathophysiology of Alzheimer's Disease

Both the brain-derived neurotrophic factor (BDNF) and glucocorticoids (GCs) play multiple roles in various aspects of neurons, including cell survival and synaptic function. BDNF and its receptor TrkB are extensively expressed in neurons of the central nervous system (CNS), and the contribution of the BDNF/TrkB system to neuronal function is evident; thus, its downregulation has been considered to be involved in the pathogenesis of Alzheimer's disease (AD). GCs, stress-related molecules, and glucocorticoid receptors (GRs) are also considered to be associated with AD in addition to mental disorders such as depression. Importantly, a growing body of evidence suggests a close relationship between BDNF/TrkB-mediated signaling and the GCs/GR system in the CNS. Here, we introduce the current studies on the interaction between the neurotrophic system and stress in CNS neurons and discuss their involvement in the pathophysiology of AD.

Sprouty4 at the crossroads of Trk neurotrophin receptor signaling suppression by glucocorticoids

Glucocorticoids (GC) affect neuronal plasticity, development and function of the nervous system by inhibiting neurotrophin-induced Trk signaling. It has been established that pretreatment with dexamethasone (DEX) restricts Neurotrophin-induced neurite outgrowth by inhibiting Trk-dependent activation of Ras-Erk1/2 signaling pathways. However, the precise molecular mechanism through which DEX interferes with neurotrophin signaling and Trk-mediated neurite outgrowth has not been clearly defined yet. Here, we observed that in PC12 cells DEX treatment promotes the transcription of Sprouty4, a regulatory molecule that is part of a negative feedback module that specifically abrogates Ras to Erk1/2 signaling in response to NGF. In line with this, either knockdown of Sprouty4 or overexpression of a dominant negative form of Sprouty4 (Y53A), rescue the inhibition of NGF/TrkA-promoted neurite outgrowth and Erk1/2 phosphorylation induced by DEX. Likewise, treatment of hippocampal neurons with DEX induces the expression of Sprouty4 and its knockdown abrogates the inhibitory effect of DEX on primary neurite formation, dendrite branching and Erk1/2 activation induced by BDNF. Thus, these results suggest that the induction of Sprouty4 mRNA by DEX translates into a significant inhibition of Trk to Erk1/2 signaling pathway. Together, these findings bring new insights into the crosstalk between DEX and neurotrophin signaling and demonstrate that Sprouty4 mediates the inhibitory effects of DEX on neurotrophin function.

Multimodal Magnetic Resonance and Fluorescence Imaging of the Induced Pluripotent Stem Cell Transplantation in the Brain

Abstract

The understanding of the engrafted cell behaviors such as the survival, growth and distribution is the prerequisite to optimize cell therapy, and a multimodal imaging at both anatomical and molecular levels is designed to achieve this goal. We constructed a lentiviral vector carrying genes of ferritin heavy chain 1 (FTH1), near-infrared fluorescent protein (iRFP) and enhanced green fluorescent protein (egfp), and established the induced pluripotent stem cells (iPSCs) culture stably expressing these three reporter genes. These iPSCs showed green and near-infrared fluorescence as well as the iron uptake capacity in vitro. After transplanted the labeled iPSCs into the rat brain, the engrafted cells could be in vivo imaged using magnetic resonance imaging (MRI) and near-infrared fluorescent imaging (NIF) up to 60 days at the anatomical level. Moreover, these cells could be detected using EGFP immunostaining and Prussian blue stain at the cellular level. The developed approach provides a novel tool to study behaviors of the transplanted cells in a multimodal way, which will be valuable for the effectiveness and safety evaluation of cell therapy.

[Effect of dexamethasone on the expression of Dynein heavy chain and Dynactin in the cytoplasm of fetal rat cerebral cortical neurons cultured in vitro]

OBJECTIVE

To study the effect of dexamethasone (DEX) on the expression of Dynein heavy chain (DHC) and Dynactin in the cytoplasm of fetal rat cerebral cortical neurons cultured in vitro.

METHODS

Primary cerebral cortical neurons of fetal rats were cultured in vitro and were used to establish a cellular model of DEX intervention. According to the final concentration of DEX, the neurons were divided into three groups:control (without DEX), 0.1 μmol/L DEX, and 1.0 μmol/L DEX. On days 1, 3, and 7 after intervention, the quantitative PCR was used to observe the effect of DEX on the mRNA expression of DHC and Dynactin. The Western blot was used to observe the effect of DEX on the protein expression of DHC and Dynactin.

RESULTS

There was no significant difference in the mRNA expression levels of DHC and Dynactin among the three groups at all time points (P > 0.05). On day 7 after DEX intervention, the protein expression of DHC in the 1.0 μmol/L DEX group gradually increased and reached the peak over time, which was significantly higher than that in the control and 0.1 μmol/L DEX groups (P < 0.05). The control and 0.1 μmol/L DEX groups had a significant increase in the protein expression of Dynactin from day 1 to days 3 and 7 after DEX intervention (P < 0.05). The control group had a significant increase in the protein expression of Dynactin from day 3 to day 7 after intervention (P < 0.05), while the 0.1 μmol/L DEX group had a significant reduction in the protein expression of Dynactin from day 3 to day 7 after intervention (P < 0.05). On days 3 and 7 after DEX intervention, the 0.1 μmol/L DEX and 1.0 μmol/L DEX groups had a significantly lower protein expression level of Dynactin in the cerebral cortical neurons than the control group (P < 0.05). On day 7 after DEX intervention, the 1.0 μmol/L DEX group had a significantly lower protein expression level of Dynactin than the 0.1 μmol/L DEX group (P < 0.05).

CONCLUSIONS

DEX affects the protein expression of DHC and Dynactin in the fetal rat cerebral cortical neurons cultured in vitro, possibly in a concentration- and time-dependent manner.