A rapid, inexpensive high throughput screen method for neurite outgrowth

B355252 Suppresses LPS-Induced Neuroinflammation in the Mouse Brain

B355252 is a small molecular compound known for potentiating neural growth factor and protecting against neuronal cell death induced by glutamate in vitro and cerebral ischemia in vivo. However, its other biological functions remain unclear. This study aims to investigate whether B355252 suppresses neuroinflammatory responses and cell death in the brain. C57BL/6j mice were intraperitoneally injected with a single dosage of lipopolysaccharide (LPS, 1 mg/kg) to induce inflammation. B355252 (1 mg/kg) intervention was started two days prior to the LPS injection. The animal behavioral changes were assessed pre- and post-LPS injections. The animal brains were harvested at 4 and 24 h post-LPS injection, and histological, biochemical, and cytokine array outcomes were examined. Results showed that B355252 improved LPS-induced behavioral deterioration, mitigated brain tissue damage, and suppressed the activation of microglial and astrocytes. Furthermore, B355252 reduced the protein levels of key pyroptotic markers TLR4, NLRP3, and caspase-1 and inhibited the LPS-induced increases in IL-1β, IL-18, and cytokines. In conclusion, B355252 demonstrates a potent anti-neuroinflammatory effect in vivo, suggesting that its potential therapeutic value warrants further investigation.

5β-reduced neuroactive steroids as modulators of growth and viability of postnatal neurons and glia

Endogenous neurosteroids (NS) and their synthetic analogs, neuroactive steroids (NAS), are potentially useful drug-like compounds affecting the pathophysiology of miscellaneous central nervous system disorders (e.g. Alzheimer´s disease, epilepsy, depression, etc.). Additionally, NS have been shown to promote neuron viability and neurite outgrowth upon injury. The molecular, structural and physicochemical basis of the NS effect on neurons is so far not fully understood, and the development of new, biologically relevant assays is essential for their comparative analysis and for assessment of their mechanism of action. Here, we report the development of a novel, plate-based, high-content in vitro assay for screening of NS and newly synthesized, 5β-reduced NAS for the promotion of postnatal neuron survival and neurite growth using fluorescent, postnatal mixed cortical neuron cultures isolated from thy1-YFP transgenic mice. The screen allows a detailed time course analysis of different parameters, such as the number of neurons or neurite lengths of 7-day, in vitro neuron cultures. Using the screen, we identify a new NAS, compound 42, that promotes the survival and growth of postnatal neurons significantly better than several endogenous NS (dehydroepiandrosterone, progesterone, and allopregnanolone). Interestingly, we demonstrate that compound 42 also promotes the proliferation of glia (in particular oligodendrocytes) and that the glial function is critical for its neuron growth support. Computational analysis of the biological data and calculated physicochemical properties of tested NS and NAS demonstrated that their biological activity is proportional to their lipophilicity. Together, the screen proves useful for the selection of neuron-active NAS and the comparative evaluation of their biologically relevant structural and physicochemical features.

Human coculture model of astrocytes and SH-SY5Y cells to test the neurotoxicity of chemicals

In this study, we established a coculture model comprising human neuroblastoma SH-SY5Y cells and induced pluripotent stem cell-derived astrocytes, faithfully replicating the human brain environment for in vitro neurotoxicity assessment. We optimized the cell differentiation duration and cell ratios to obtain images conducive to neurite outgrowth evaluation. Subsequently, the neurotoxic effects in the coculture and monoculture of SH-SY5Y cells were confirmed using neurotoxic agents such as acrylamide (ACR) and hydrogen peroxide (H2O2). Disparities in the neurotoxic impacts of ACR and H2O2 within the coculture were mirrored in the expression of genes associated with early neuronal injury. Notably, the reduction in neurite outgrowth induced by neurotoxic agents revealed the coculture's lower sensitivity compared to monocultures. Furthermore, the coculture system exhibited distinct effects of test agents on nerve damage and manifested protective influences on nerve cells. The proposed methodology holds promise for large-scale chemical neurotoxicity screening through neurite change measurements. This in vitro coculture model, accounting for cell interactions, emerges as a valuable tool in toxicity testing, offering insights into the potential effects of chemicals within the human body.

Loss of POGZ alters neural differentiation of human embryonic stem cells

POGZ is a pogo transposable element derived protein with multiple zinc finger domains. Many de novo loss-of-function (LoF) variants of the POGZ gene are associated with autism and other neurodevelopmental disorders. However, the role of POGZ in human cortical development remains poorly understood. Here we generated multiple POGZ LoF lines in H9 human embryonic stem cells (hESCs) using CRISPR/CAS9 genome editing. These lines were then differentiated into neural structures, similar to those found in early to mid-fetal human brain, a critical developmental stage for studying disease mechanisms of neurodevelopmental disorders. We found that the loss of POGZ reduced neural stem cell proliferation in excitatory cortex-patterned neural rosettes, structures analogous to the cortical ventricular zone in human fetal brain. As a result, fewer intermediate progenitor cells and early born neurons were generated. In addition, neuronal migration from the apical center to the basal surface of neural rosettes was perturbed due to the loss of POGZ. Furthermore, cortical-like excitatory neurons derived from multiple POGZ homozygous knockout lines exhibited a more simplified dendritic architecture compared to wild type lines. Our findings demonstrate how POGZ regulates early neurodevelopment in the context of human cells, and provide further understanding of the cellular pathogenesis of neurodevelopmental disorders associated with POGZ variants.

Optimised techniques for high-throughput screening of differentiated SH-SY5Y cells and application for neurite outgrowth assays

Neuronal models are a crucial tool in neuroscientific research, helping to elucidate the molecular and cellular processes involved in disorders of the nervous system. Adapting these models to a high-throughput format enables simultaneous screening of multiple agents within a single assay. SH-SY5Y cells have been widely used as a neuronal model, yet commonly in an undifferentiated state that is not representative of mature neurons. Differentiation of the SH-SY5Y cells is a necessary step to obtain cells that express mature neuronal markers. Despite this understanding, the absence of a standardised protocol has limited the use of differentiated SH-SY5Y cells in high-throughput assay formats. Here, we describe techniques to differentiate and re-plate SH-SY5Y cells within a 96-well plate for high-throughput screening. SH-SY5Y cells seeded at an initial density of 2,500 cells/well in a 96-well plate provide sufficient space for neurites to extend, without impacting cell viability. Room temperature pre-incubation for 1 h improved the plating homogeneity within the well and the ability to analyse neurites. We then demonstrated the efficacy of our techniques by optimising it further for neurite outgrowth analysis. The presented methods achieve homogenously distributed differentiated SH-SY5Y cells, useful for researchers using these cells in high-throughput screening assays.

Novel Concept of Micro Patterned Micro Titer Plates Fabricated via UV-NIL for Automated Neuronal Cell Assay Read-Out

The UV-nanoimprint lithography(UV-NIL) fabrication of a novel network of micron-sized channels, forming an open channel microfluidic system is described. Details about the complete manufacturing process, from mastering to fabrication in small batches and in high throughput with up to 1200 micro titer plates per hour is presented. Deep insight into the evaluation of a suitable UV-curable material, mr-UVCur26SF is given, presenting cytotoxic evaluation, cell compatibility tests and finally a neuronal assay. The results indicate how the given pattern, in combination with the resist, paves the way to faster, cheaper, and more reliable drug screening.

Phenoxythiophene sulfonamide compound B355252 protects neuronal cells against glutamate-induced excitotoxicity by attenuating mitochondrial fission and the nuclear translocation of AIF

Glutamate neurotoxicity has been implicated in the initiation and progression of various neurological and neurodegenerative disorders. Therefore, it is necessary to develop therapeutics for the treatment of patients with these devastating diseases. Mitochondrial fission plays an import role in the mediation of cell death and survival. The objective of the present study was to determine whether B355252, a phenoxythiophene sulfonamide derivative, reduces glutamate-induced cell death by inhibiting mitochondrial fission and the nuclear translocation of apoptosis-inducing factor (AIF) in glutamate-challenged HT22 neuronal cells. The results revealed that glutamate treatment led to large increases in the mitochondrial levels of the major fission proteins dynamin-related protein 1 (Drp1) and mitochondrial fission 1 protein (Fis1), but only small elevations in the fusion proteins mitofusin 1 and 2 (Mfn1/2) and optic atrophy 1 (Opa1). In addition, glutamate toxicity disrupted mitochondrial reticular networks and increased the translocation of AIF to the nucleus. Pretreatment with B35525 reduced glutamate-induced cell death and prevented the increases in the protein levels of Drp1, Fis1, Mfn1/2 and Opa1 in the mitochondrial fraction. More importantly, the architecture of the mitochondria was protected and nuclear translocation of AIF was completely inhibited by B35525. These findings suggest that the regulation of mitochondrial dynamics is central to the neuroprotective properties of B355252, and presents an attractive opportunity for potential development as a therapy for neurodegenerative disorders associated with mitochondria dysfunction.

Trkb-IP3 Pathway Mediating Neuroprotection in Rat Hippocampal Neuronal Cell Culture Following Induction of Kainic Acid

Background

Following brain injury, development of hippocampal sclerosis often led to the temporal lobe epilepsy which is sometimes resistant to common anti-epileptic drugs. Cellular and molecular changes underlying epileptogenesis in animal models were studied, however, the underlying mechanisms of kainic acid (KA) mediated neuronal damage in rat hippocampal neuron cell culture alone has not been elucidated yet.

Methods

Embryonic day 18 (E-18) rat hippocampus neurons were cultured with poly-L-lysine coated glass coverslips. Following optimisation, KA (0.5 μM), a chemoconvulsant agent, was administered at three different time-points (30, 60 and 90 min) to induce seizure in rat hippocampal neuronal cell culture. We examined cell viability, neurite outgrowth density and immunoreactivity of the hippocampus neuron culture by measuring brain derived neurotrophic factor (BDNF), γ-amino butyric acid A (GABA_A) subunit α-1 (GABRA1), tyrosine receptor kinase B (TrkB), and inositol trisphosphate receptor (IP₃R/IP3) levels.

Results

The results revealed significantly decreased and increased immunoreactivity changes in TrkB (a BDNF receptor) and IP₃R, respectively, at 60 min time point.

Conclusion

The current findings suggest that TrkB and IP3 could have a neuroprotective role which could be a potential pharmacological target for anti-epilepsy drugs.

Analysis of Gene Expression and Neuronal Phenotype in Neuroscreen-1 (NS-1) Cells

Neuroscreen-1 (NS-1) a sub-clone of pheochromocytoma (PC12) cell is gaining broad acceptance as in vitro neuronal model for biochemical and phenotypic assays due to robust growth and differentiation profiles. However, the molecular characteristics of the cell remains to be documented. In this study, we performed comparative analysis for expression of neuronal marker genes in undifferentiated and nerve growth factor (NGF) differentiated NS-1 and PC12 by qPCR and immunoblot assays. We show that differentiation of NS-1 occurred under low concentrations of NGF relative to PC12. Cell growth also occurred more rapidly in NS-1. Transcriptional analysis of neuronal marker genes showed comparable expression of tyrosine receptor kinases (Ntrk1, Ntrk2, NGFR/p75NTR) and muscarinic acetylcholine (Chrm1, Chrm2, Chrm3, Chrm4) receptors in unspecialized cells. Ntrk2, adenosine receptors (Adora1, Adora2A) and choline acetyltransferase (ChAT) were altered in undifferentiated NS-1. In contrast, Ntrk1, Ntrk2, Chrm2 transcripts were vastly increased in NS-1 with NGF exposure, while Ntrk3, Adora1 and Adora2A transcripts were reduced. In differentiated PC12, Chrm4 and ChAT were markedly upregulated. Our data suggests that differences in morphological and phenotypic characteristics that distinguish NS-1 from PC12 is likely the product of altered gene expression. Furthermore, expression of neuron type genes in NS-1 support its use as an alternative model to PC12.

Screening of quorum sensing peptides for biological effects in neuronal cells

Quorum sensing peptides (QSP) are an important class of bacterial peptides which can have an effect on human host cells. These peptides are used by bacteria to communicate with each other. Some QSP are able to cross the blood-brain barrier and reach the brain parenchyma. However, nothing is known about the effects of these peptides in the brain. Therefore, 85 quorum sensing peptides were screened on six different neuronal cell lines using MTT toxicity, neurite differentiation, cytokine production and morphology as biological outcomes. This primary screening resulted in 22 peptides with effects observed on neuronal cell lines, indicating a possible role in the gut-brain axis. Four peptides (Q138, Q143, Q180 and Q212) showed induction of neurite outgrowth while two peptides (Q162 and Q208) inhibited NGF-induced neurite outgrowth in PC12 cells. Eight peptides (Q25, Q135, Q137, Q146, Q151, Q165, Q208 and Q298) induced neurite outgrowth in human SH-SY5Y neuroblastoma cells. Two peptides (Q13 and Q52) were toxic for SH-SY5Y cells and one (Q123) for BV-2 microglia cells based on the MTT assay. Six peptides had an effect on BV-2 microglia, Q180, Q184 and Q191 were able to induce IL-6 expression and Q164, Q192 and Q208 induced NO production. Finally, Q75 and Q147 treated C8D1A astrocytes demonstrated a higher fraction of round cells. Overall, these in vitro screening study results indicate for the first time possible effects of QSP on neuronal cells.

Quantitative assessment of neural outgrowth using spatial light interference microscopy

Optimal growth as well as branching of axons and dendrites is critical for the nervous system function. Neuritic length, arborization, and growth rate determine the innervation properties of neurons and define each cell’s computational capability. Thus, to investigate the nervous system function, we need to develop methods and instrumentation techniques capable of quantifying various aspects of neural network formation: neuron process extension, retraction, stability, and branching. During the last three decades, fluorescence microscopy has yielded enormous advances in our understanding of neurobiology. While fluorescent markers provide valuable specificity to imaging, photobleaching, and photoxicity often limit the duration of the investigation. Here, we used spatial light interference microscopy (SLIM) to measure quantitatively neurite outgrowth as a function of cell confluence. Because it is label-free and nondestructive, SLIM allows for long-term investigation over many hours. We found that neurons exhibit a higher growth rate of neurite length in low-confluence versus medium- and high-confluence conditions. We believe this methodology will aid investigators in performing unbiased, nondestructive analysis of morphometric neuronal parameters.

Exercise and BDNF reduce Aβ production by enhancing α-secretase processing of APP

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by aggregation of toxic forms of amyloid β peptide (Aβ). Treatment strategies have largely been focused on inhibiting the enzymes (β- and γ-secretases) that liberate Aβ from the amyloid precursor protein (APP). While evidence suggests that individuals who exercise regularly are at reduced risk for AD and studies of animal models demonstrate that running can ameliorate brain Aβ pathology and associated cognitive deficits, the underlying mechanisms are unknown. However, considerable evidence suggests that brain-derived neurotrophic factor (BDNF) mediates beneficial effects of exercise on neuroplasticity and cellular stress resistance. Here, we tested the hypothesis that BDNF promotes non-amyloidogenic APP processing. Using a transgenic mouse model of Alzheimer's disease and cultured human neural cells, we demonstrate that exercise and BDNF reduce production of toxic Aβ peptides through a mechanism involving enhanced α-secretase processing of APP. This anti-amyloidogenic APP processing involves subcellular redistribution of α-secretase and an increase in intracellular neuroprotective APP peptides capable of binding and inhibiting β-secretase. Moreover, our results suggest that BDNF's ability to promote neurite outgrowth is primarily exerted through pathways other than APP processing. Exercise and other factors that enhance BDNF signaling may therefore have both therapeutic and prophylactic value in the battle against AD. Read the Editorial Highlight for this article on page 191.

A Combined In Vitro Assay for Evaluation of Neurotrophic Activity and Cytotoxicity

Neurotrophic assays are phenotypic methods to identify molecules that stimulate differentiation of neuronal cells. Bioactive small molecules with neurotrophic actions hold great promise as therapeutic agents for the treatment of neurodegenerative diseases and neuronal injuries by virtue of their ability to stimulate neuritic outgrowth. A combined in vitro method, which measures neurotrophic activity and cytotoxicity in a single assay, has been described. This assay, performed in 96-well microplates with PC12 and Neuroscreen-1 (NS-1; a subclone of PC12) cells, is a simple tool for identification of new neurotrophic agents. Stimulation of neurite outgrowth was measured with NIS software by analysis of digital cell images as multiple parameters, namely, mean neurite length, neurite length/cell, nodes/cell, and number of neurites/cell. The assay has been standardized and validated with dose-response analysis for nerve growth factor (NGF) and mechanism-based inhibitors of NGF-induced neurite outgrowth, namely, SU6656 (an Src family kinase inhibitor) and PD98059 (a MEK inhibitor). The assay has been successfully applied for screening natural and synthetic compound libraries for cytotoxicity and neurotrophic activity. Screening of a set of harmala alkaloids identified harmine as a potential neurotrophic molecule that significantly stimulated NGF-induced neurite outgrowth in the NS-1 cells. Important advantages of this method are its simplicity and determination of cytotoxicity and neurotrophic activity in a single assay. This assay may be suitable for primary and cultured neuronal cells.

In vitro models of axon regeneration

A variety of in vitro models have been developed to understand the mechanisms underlying the regenerative failure of central nervous system (CNS) axons, and to guide pre-clinical development of regeneration-promoting therapeutics. These range from single-cell based assays that typically focus on molecular mechanisms to organotypic assays that aim to recapitulate in vivo behavior. By utilizing a combination of models, researchers can balance the speed, convenience, and mechanistic resolution of simpler models with the biological relevance of more complex models. This review will discuss a number of models that have been used to build our understanding of the molecular mechanisms of CNS axon regeneration.

The Mineralocorticoid Agonist Fludrocortisone Promotes Survival and Proliferation of Adult Hippocampal Progenitors

Glucocorticoid receptor (GR) activation has been shown to reduce adult hippocampal progenitor cell proliferation and neurogenesis. By contrast, mineralocorticoid receptor (MR) signaling is associated with neuronal survival in the dentate gyrus of the hippocampus, and impairment of hippocampal MR has been linked to pathological conditions, such as depression or neurodegenerative disorders. Here, we aimed to further clarify the protective role of MR in adult hippocampal neurons by studying the survival and proliferative effects of the highly potent MR agonist fludrocortisone (Fludro) in adult rat hippocampal progenitor cells (AHPs), along with the associated signaling mechanisms. Fludro, which upregulated MR but not GR expression, increased survival and proliferation and prevented apoptosis in AHPs cultured in growth factor-deprived medium. These effects were blunted by the MR antagonist spironolactone and by high doses of the GR agonist dexamethasone. Moreover, they involved signaling through cAMP/protein kinase A (PKA)/cAMP response element-binding protein, phosphoinositide 3-kinase (PI3K)/Akt and its downstream targets glycogen synthase kinase-3β (GSK-3β) and mammalian target of rapamycin. Furthermore, Fludro attenuated the detrimental effects of amyloid-β peptide 1-42 (Aβ1-42) on cell survival, proliferation, and apoptosis in AHPs, and increased the phosphorylation of both PI3K/Akt and GSK-3β, which was reduced by Aβ1-42. Finally, Fludro blocked Aβ1-42-induced hyperphosphorylation of Tau protein, which is a main feature of Alzheimer's disease. Overall, these results are the first to show the protective and proliferative role of Fludro in AHPs, suggesting the potential therapeutic importance of targeting MR for increasing hippocampal neurogenesis and for treating neurodegenerative diseases.

Differential intensity-dependent effects of magnetic stimulation on the longest neurites and shorter dendrites in neuroscreen-1 cells

OBJECTIVE

Magnetic stimulation (MS) is a potential treatment for neuropsychiatric disorders. This study investigates whether MS-regulated neuronal activity can translate to specific changes in neuronal arborization and thus regulate synaptic activity and function.

APPROACH

To test our hypotheses, we examined the effects of MS on neurite growth of neuroscreen-1 (NS-1) cells over the pulse frequencies of 1, 5 and 10 Hz at field intensities controlled via machine output (MO). Cells were treated with either 30% or 40% MO. Due to the nature of circular MS coils, the center region of the gridded coverslip (zone 1) received minimal (∼5%) electromagnetic current density while the remaining area (zone 2) received maximal (∼95%) current density. Plated NS-1 cells were exposed to MS twice per day for three days and then evaluated for length and number of neurites and expression of brain-derived neurotrophic factor (BDNF).

MAIN RESULTS

We show that MS dramatically affects the growth of the longest neurites (axon-like) but does not significantly affect the growth of shorter neurites (dendrite-like). Also, MS-induced changes in the longest neurite growth were most evident in zone 1, but not in zone 2. MS effects were intensity-dependent and were most evident in bolstering longest neurite outgrowth, best seen in the 10 Hz MS group. Furthermore, we found that MS-increased BDNF expression and secretion was also frequency-dependent. Taken together, our results show that MS exerts distinct effects when different frequencies and intensities are applied to the neuritic compartments (longest neurite versus shorter dendrite(s)) of NS-1 cells.

SIGNIFICANCE

These findings support the concept that MS increases BDNF expression and signaling, which sculpts longest neurite arborization and connectivity by which neuronal activity is regulated. Understanding the mechanisms underlying MS is crucial for efficiently incorporating its use into potential therapeutic strategies.

A facile method for simultaneously measuring neuronal cell viability and neurite outgrowth

Neurite outgrowth is an important morphological phenotype of neuronal cells that correlates with their function and cell health, yet there are limited methods available for measuring this phenomenon. Current approaches to measuring neurite outgrowth are laborious and time-consuming, relying largely upon immunocytochemical staining of neuronal markers (e.g., beta-III tubulin or MAP2) followed by manual or automated microscopy for image acquisition and analysis. Here we report the development of a quick and simple dual-color fluorescent dye-based staining method that allows for the simultaneous measurement of neuronal cell health and relative neurite outgrowth from the same sample. An orangered fluorescent dye that stains cell membrane surfaces is used as an indirect reporter of changes in relative neurite outgrowth due to alterations in the number or length of membrane projections emanating from neuronal cell bodies. Cell viability is assessed simultaneously via the use of a cell-permeant dye that is converted by intracellular esterase activity from a non-fluorescent substrate to a green-fluorescent product. Using Neuroscreen-1 cells (a PC-12 subclone), primary rat cortex neurons, and human induced pluripotent stem cell (iPSC)-derived neurons, we demonstrate that this multiplex assay allows for rapid visualization and unbiased, quantitative plate reader analysis of neuronal cell health and neurite outgrowth.

A high-content morphological screen identifies novel microRNAs that regulate neuroblastoma cell differentiation

Neuroblastoma, the most common extracranial solid tumor of childhood, arises from neural crest cell precursors that fail to differentiate. Inducing cell differentiation is an important therapeutic strategy for neuroblastoma. We developed a direct functional high-content screen to identify differentiation-inducing microRNAs, in order to develop microRNA-based differentiation therapy for neuroblastoma. We discovered novel microRNAs, and more strikingly, three microRNA seed families that induce neuroblastoma cell differentiation. In addition, we showed that microRNA seed families were overrepresented in the identified group of fourteen differentiation-inducing microRNAs, suggesting that microRNA seed families are functionally more important in neuroblastoma differentiation than microRNAs with unique sequences. We further investigated the differentiation-inducing function of the microRNA-506-3p/microRNA-124-3p seed family, which was the most potent inducer of differentiation. We showed that the differentiation-inducing function of microRNA-506-3p/microRNA-124-3p is mediated, at least partially, by down-regulating expression of their targets CDK4 and STAT3. We further showed that expression of miR-506-3p, but not miR-124-3p, is dramatically upregulated in differentiated neuroblastoma cells, suggesting the important role of endogenous miR-506-3p in differentiation and tumorigenesis. Overall, our functional screen on microRNAs provided the first comprehensive analysis on the involvements of microRNA species in neuroblastoma cell differentiation and identified novel differentiation-inducing microRNAs. Further investigations are certainly warranted to fully characterize the function of the identified microRNAs in order to eventually benefit neuroblastoma therapy.

Evaluation of a human neurite growth assay as specific screen for developmental neurotoxicants

Organ-specific in vitro toxicity assays are often highly sensitive, but they lack specificity. We evaluated here examples of assay features that can affect test specificity, and some general procedures are suggested on how positive hits in complex biological assays may be defined. Differentiating human LUHMES cells were used as potential model for developmental neurotoxicity testing. Forty candidate toxicants were screened, and several hits were obtained and confirmed. Although the cells had a definitive neuronal phenotype, the use of a general cell death endpoint in these cultures did not allow specific identification of neurotoxicants. As alternative approach, neurite growth was measured as an organ-specific functional endpoint. We found that neurite extension of developing LUHMES was specifically inhibited by diverse compounds such as colchicine, vincristine, narciclasine, rotenone, cycloheximide, or diquat. These compounds reduced neurite growth at concentrations that did not compromise cell viability, and neurite growth was affected more potently than the integrity of developed neurites of mature neurons. A ratio of the EC50 values of neurite growth inhibition and cell death of >4 provided a robust classifier for compounds associated with a developmental neurotoxic hazard. Screening of unspecific toxicants in the test system always yielded ratios <4. The assay identified also compounds that accelerated neurite growth, such as the rho kinase pathway modifiers blebbistatin or thiazovivin. The negative effects of colchicine or rotenone were completely inhibited by a rho kinase inhibitor. In summary, we suggest that assays using functional endpoints (neurite growth) can specifically identify and characterize (developmental) neurotoxicants.

Label-free detection of neuronal differentiation in cell populations using high-throughput live-cell imaging of PC12 cells

Detection of neuronal cell differentiation is essential to study cell fate decisions under various stimuli and/or environmental conditions. Many tools exist that quantify differentiation by neurite length measurements of single cells. However, quantification of differentiation in whole cell populations remains elusive so far. Because such populations can consist of both proliferating and differentiating cells, the task to assess the overall differentiation status is not trivial and requires a high-throughput, fully automated approach to analyze sufficient data for a statistically significant discrimination to determine cell differentiation. We address the problem of detecting differentiation in a mixed population of proliferating and differentiating cells over time by supervised classification. Using nerve growth factor induced differentiation of PC12 cells, we monitor the changes in cell morphology over days by phase-contrast live-cell imaging. For general applicability, the classification procedure starts out with many features to identify those that maximize discrimination of differentiated and undifferentiated cells and to eliminate features sensitive to systematic measurement artifacts. The resulting image analysis determines the optimal post treatment day for training and achieves a near perfect classification of differentiation, which we confirmed in technically and biologically independent as well as differently designed experiments. Our approach allows to monitor neuronal cell populations repeatedly over days without any interference. It requires only an initial calibration and training step and is thereafter capable to discriminate further experiments. In conclusion, this enables long-term, large-scale studies of cell populations with minimized costs and efforts for detecting effects of external manipulation of neuronal cell differentiation.