Hunchback activates Bicoid in post-mitotic Pair1 neurons to regulate synapse number

The proper formation and function of neural circuits is crucial for cognition, sensation, and behavior. Neural circuits are highly-specific, and this specificity is dependent on neurons developing key features of their individual identities: morphology, anatomical location, molecular expression and biophysiological properties. Previous research has demonstrated that a neurons identity is, in part, generated by the temporal transcription window the neuron is born in, and the homeodomain transcription factors expressed in the mature neuron. However, whether temporal transcription factors and homeodomain transcription factors regulate neural circuit formation, maintenance and function remains unknown. Here, we utilize a well-characterized neural circuit in the Drosophila larvae, the Pair1 neuron. We determined that in the Pair1 neuron, the temporal transcription factor Hunchback activates the homeodomain transcription factor Bicoid (Bcd). Both Hunchback and Bcd are expressed in Pair1 throughout larval development. Interestingly, Hunchback and Bcd were not required in Pair1 for neurotransmitter identity or axonal morphology, but were required for synapse density. We found that these transcription factors were functioning post-mitotically in Pair1 to regulate synapse density. Additionally, knocking down Hunchback and Bcd in Pair1 neurons disrupted the behavioral output of the circuit. We utilized the genetic tool TransTango to determine that Hunchback function in Pair1 is to repress forming synapses with erroneous neurons. To our knowledge, these data are the first to show Hunchback activating Bcd expression, as well as the first to demonstrate a role for Hunchback and Bcd post-mitotically.

Gongjin-Dan Enhances Neurite Outgrowth of Cortical Neuron by Ameliorating H2O2-Induced Oxidative Damage via Sirtuin1 Signaling Pathway

Gongjin-dan (GJD) is a multiherbal formula produced from 10 medicinal herbs and has been traditonally used as an oriental medicine to treat cardiovascular diseases, alcoholic hepatitis, mild dementia, and anemia. Additionally, increasing evidence suggests that GJD exerts neuroprotective effects by suppressing inflammation and oxidative stress-induced events to prevent neurological diseases. However, the mechanism by which GJD prevents oxidative stress-induced neuronal injury in a mature neuron remains unknown. Here, we examined the preventive effect and mechanism of GJD on primary cortical neurons exposed to hydrogen peroxide (H2O2). In the neuroprotection signaling pathway, Sirtuin1 is involved in neuroprotective action as a therapeutic target for neurological diseases. After pre-treatment with GJD at three concentrations (10, 25, and 50 µg/mL) and stimulation by H2O2 (30 µM) for 24 h, the influence of GJD on Sirtuin1 activation was assessed using immunocytochemistry, real-time PCR, western blotting, and flow cytometry. GJD effectively ameliorated H2O2-induced neuronal death against oxidative damage through Sirtuin1 activation. In addition, GJD-induced Sirtuin1 activation accelerated elongation of new axons and formation of synapses via increased expression of nerve growth factor and brain-derived neurotrophic factor, as well as regeneration-related genes. Thus, GJD shows potential for preventing neurological diseases via Sirtuin1 activation.

STAT3 Involved in Cellular Vulnerability to Isoflurane

STAT3 signaling is crucial during neural spontaneous death period, a restricted developmental time window in which the neonatal brain is vulnerable to isoflurane. Here, we designed experiments to assess whether isoflurane target STAT3 to deliver its cytotoxicity. Mice at postnatal day 7 or 21, primary cortical neurons cultured for 5 or 14 days and human neuroglioma U251 cells were treated with isoflurane. A plasmid containing human wild-type STAT3, STAT3 anti-sense oligonucleotide, STAT3 specific inhibitor STA21, proteasome inhibitor MG-132 and calcineurin inhibitor FK506 were utilized to evaluate the influence of STAT3 levels on isoflurane-induced cytotoxicity. In the present study, an upregulation of STAT3 parallel with a decline in calcineurin activity as well as a decrease in the ability of isoflurane to trigger calcineurin activity and neuroapoptosis were observed in more mature neuron or brain. STAT3 survival pathway was impaired after isoflurane exposure in U251 cells and exerted a prominent effect. STAT3 disruption exaggerated isoflurane-induced oxidative injury and apoptosis, whereas, STAT3 overexpression exhibited notable cellular protection. The blockage of calcineurin activity ameliorated neural apoptosis, dendritic spine impairment and cognitive dysfunction induced by isoflurane. Overall, these results indicated that specific regulation of STAT3 was closely related with the cellular vulnerability to isoflurane.

The Impact of Differentiation on Cytotoxicity and Insulin Sensitivity in Streptozotocin Treated SH-SY5Y Cells

Recently neuronal insulin resistance was suggested playing a role in Alzheimer’s disease. Streptozotocin (STZ) is commonly used to induce impairment in insulin metabolism. In our previous work on undifferentiated SH-SY5Y cells the compound exerted cytotoxicity without altering insulin sensitivity. Nevertheless, differentiation of the cells to a more mature neuron-like phenotype may considerably affect the significance of insulin signaling and its sensitivity to STZ. We aimed at studying the influence of STZ treatment on insulin signaling in SH-SY5Y cells differentiated by retinoic acid (RA). Cytotoxicity of STZ or low serum (LS) condition and protective effect of insulin were compared in RA differentiated SH-SY5Y cells. The effect of insulin and an incretin analogue, exendin-4 on insulin signaling was also examined by assessing glycogen synthase kinase-3 (GSK-3) phosphorylation. STZ was found less cytotoxic in the differentiated cells compared to our previous results in undifferentiated SH-SY5Y cells. The cytoprotective concentration of insulin was similar in the STZ and LS groups. However, the right-shifted concentration–response curve of insulin induced GSK-3 phosphorylation in STZ-treated differentiated cells is suggestive of the development of insulin resistance that was further confirmed by the insulin potentiating effect of exendin-4. Differentiation reduced the sensitivity of SH-SY5Y cells for the non-specific cytotoxicity of STZ and enhanced the relative significance of development of insulin resistance. The differentiated cells thus serve as a better model for studying the role of insulin signaling in neuronal survival. However, direct cytotoxicity of STZ also contributes to the cell death.

Axonal TAU sorting requires the C-terminus of TAU but is independent of ANKG and TRIM46 enrichment at the AIS

Somatodendritic missorting of the axonal protein TAU is a hallmark of Alzheimer’s disease and related tauopathies. Cultured rodent primary neurons and iPSC-derived neurons are used for studying mechanisms of neuronal polarity, including TAU trafficking. However, these models are expensive, time-consuming and/or require the sacrification of animals. In this study, we evaluated four differentiation procedures to generate mature neuron cultures from human SH-SY5Y neuroblastoma cells, in comparison to mouse primary neurons, and tested their TAU sorting capacity. We show that SH-SY5Y-derived neurons, differentiated with sequential RA/BDNF treatment, are suitable for investigating axonal TAU sorting. These human neurons show pronounced neuronal polarity, axodendritic outgrowth, expression of the neuronal maturation markers TAU and MAP2, and, importantly, efficient axonal sorting of endogenous and transfected human wild type TAU, similar to primary neurons. We demonstrate that axonal TAU enrichment requires the presence of the C-terminal half, as a C-terminus-lacking construct (N-term-TAUHA) is not axonally enriched in both neuronal cell models. Moreover, SH-SY5Y-derived neurons do not show formation of a classical axon initial segment (AIS), indicated by the lack of Ankyrin G (ANKG) and tripartite motif-containing protein 46 (TRIM46) at the proximal axon, which suggests that successful axonal TAU sorting is independent of classical AIS formation. Taken together, our results suggest i) that SH-SY5Y-derived neurons are a valuable human neuronal cell model for studying TAU sorting, which is readily accessible at low cost and without animal need, and that ii) the mechanisms of axonal TAU targeting require the TAU C-terminal half but are independent of ANKG or TRIM46 enrichment at the proximal axon.

Ginsenoside Compound K Induces Adult Hippocampal Proliferation and Survival of Newly Generated Cells in Young and Elderly Mice

Cognitive impairment can be associated with reduced adult hippocampal neurogenesis, and it may contribute to age-associated neurodegenerative diseases such as Alzheimer’s (AD). Compound K (CK) is produced from the protopanaxadiol (PPD)-type ginsenosides Rb1, Rb2, and Rc by intestinal microbial conversion. Although CK has been reported as an inducing effector for neuroprotection and improved cognition in hippocampus, its effect on adult neurogenesis has not been explored yet. Here, we investigated the effect of CK on hippocampal neurogenesis in both young (2 months) and elderly (24 months) mice. CK treatment increased the number of cells co-labeled with 5-ethynyl-2′-deoxyuridine (EdU) and proliferating cell nuclear antigen (PCNA); also, Ki67, specific markers for progenitor cells, was more expressed, thus enhancing the generation of new cells and progenitor cells in the dentate gyrus of both young and elderly mice. Moreover, CK treatment increased the number of cells co-labeled with EdU and NeuN, a specific marker for mature neuron in the dentate gyrus, suggesting that newly generated cells survived and differentiated into mature neurons at both ages. These findings demonstrate that CK increases adult hippocampal neurogenesis, which may be beneficial against neurodegenerative disorders such as AD.

C3orf70 Is Involved in Neural and Neurobehavioral Development

Neurogenesis is the process by which undifferentiated progenitor cells develop into mature and functional neurons. Defects in neurogenesis are associated with neurodevelopmental and neuropsychiatric disorders; therefore, elucidating the molecular mechanisms underlying neurogenesis can advance our understanding of the pathophysiology of these disorders and facilitate the discovery of novel therapeutic targets. In this study, we performed a comparative transcriptomic analysis to identify common targets of the proneural transcription factors Neurog1/2 and Ascl1 during neurogenesis of human and mouse stem cells. We successfully identified C3orf70 as a novel common target gene of Neurog1/2 and Ascl1 during neurogenesis. Using in situ hybridization, we demonstrated that c3orf70a and c3orf70b, two orthologs of C3orf70, were expressed in the midbrain and hindbrain of zebrafish larvae. We generated c3orf70 knockout zebrafish using CRISPR/Cas9 technology and demonstrated that loss of c3orf70 resulted in significantly decreased expression of the mature neuron markers elavl3 and eno2. We also found that expression of irx3b, a zebrafish ortholog of IRX3 and a midbrain/hindbrain marker, was significantly reduced in c3orf70 knockout zebrafish. Finally, we demonstrated that neurobehaviors related to circadian rhythm and altered light–dark conditions were significantly impaired in c3orf70 knockout zebrafish. These results suggest that C3orf70 is involved in neural and neurobehavioral development and that defects in C3orf70 may be associated with midbrain/hindbrain-related neurodevelopmental and neuropsychiatric disorders.

Analysis of Synapses in Cerebral Organoids

Cerebral organoids are an emerging cutting-edge technology to model human brain development and neurodevelopmental disorders, for which mouse models exhibit significant limitations. In the human brain, synaptic connections define neural circuits, and synaptic deficits account for various neurodevelopmental disorders. Thus, harnessing the full power of cerebral organoids for human brain modeling requires the ability to visualize and analyze synapses in cerebral organoids. Previously, we devised an optimized method to generate human cerebral organoids, and showed that optimal organoids express mature-neuron markers, including synaptic proteins and neurotransmitter receptors and transporters. Here, we give evidence for synaptogenesis in cerebral organoids, via microscopical visualization of synapses. We also describe multiple approaches to quantitatively analyze synapses in cerebral organoids. Collectively, our work provides sufficient evidence for the possibility of modeling synaptogenesis and synaptic disorders in cerebral organoids, and may help advance the use of cerebral organoids in molecular neuroscience and studies of neurodevelopmental disorders such as autism.

Regulatory mechanisms for the axonal localization of tau in neurons

Tau is a microtubule (MT)-associated protein, which precisely localizes to the axon of a mature neuron. Although it has been widely used as an axonal marker, the mechanisms for its axonal localization have been elusive. This might be largely due to the lack of an experimental system, as exogenously expressed tau, such as GFP-tau, mis-localizes to the soma and dendrites. In this study, we found that the expression of endogenous tau and its axonal localization in cultured rat hippocampal neurons mainly occur during early neuronal development and are coupled. By mimicking this early expression, we demonstrate that exogenously expressed human tau can be properly localized to the axon, thereby providing the first experimental model to study the mechanisms of tau localization. Using this model, we obtained surprising findings that the axonal localization of tau did not require the MT-binding domain nor correlate with the MT-binding ability. Instead, we identified a transport mechanism mediated by the proline-rich region 2 (PRR2), which contains a number of important phosphorylation sites. Mimicking phosphorylation and dephosphorylation in PRR2 disrupts the axonal localization, suggesting that it is regulated by the phosphorylation state of PRR2. These results shed new lights on the mechanism for the axonal localization of tau and indicate a link between the hyperphosphorylation and mis-localization of tau observed in tauopathies.Significance statementIn this paper, we present a first experimental system, in which expressed tau is properly localized to the axon, and which can therefore be used to study the mechanisms of tau localization and mis-localization. Using this system, we provide evidence that the microtubule binding domain of tau nor stable binding of tau to microtubules is not necessary for its axonal localization. Instead, we identified the proline-rich region and its phosphorylation-state dictate the localization of tau in neurons. These results provide a novel foundation to consider how axonal tau mis-localize to the soma and dendrites during early pathogenesis of Alzheimer’s disease.