Detection of calcium transients in embryonic stem cells and their differentiated progeny

Calcium signaling in human pluripotent stem cells

Human pluripotent stem cells provide new tools for developmental and pharmacological studies as well as for regenerative medicine applications. Calcium homeostasis and ligand-dependent calcium signaling are key components of major cellular responses, including cell proliferation, differentiation or apoptosis. Interestingly, these phenomena have not been characterized in detail as yet in pluripotent human cell sates. Here we review the methods applicable for studying both short- and long-term calcium responses, focusing on the expression of fluorescent calcium indicator proteins and imaging methods as applied in pluripotent human stem cells. We discuss the potential regulatory pathways involving calcium responses in hPS cells and compare these to the implicated pathways in mouse PS cells. A recent development in the stem cell field is the recognition of so called "naïve" states, resembling the earliest potential forms of stem cells during development, as well as the "fuzzy" stem cells, which may be alternative forms of pluripotent cell types, therefore we also discuss the potential role of calcium homeostasis in these PS cell types.

Characterization of calcium signals in human embryonic stem cells and in their differentiated offspring by a stably integrated calcium indicator protein

Intracellular calcium signaling pathways play a major role in cellular responses such as proliferation, differentiation and apoptosis. Human embryonic stem cells (hESC) provide new possibilities to explore the development and differentiation of various cell types of the human body. Intracellular calcium responses to various ligands and the calcium signaling pathways, however, have not been thoroughly studied in embryonic stem cells and in their differentiated progenies. In our previous work we demonstrated that the use of the fluorescent calcium indicator Fluo-4 with confocal microscopy allows sensitive and reliable measurements of calcium modulation in human embryonic stem cells and stem-cell derived cardiomyocytes. Here we developed a human embryonic stem cell line stably expressing a genetically encoded Ca(2+) indicator (GCaMP2) using a transposon-based gene delivery system. We found that the differentiation properties were fully preserved in the GCaMP2-expressing hESC lines and Ca imaging could be performed without the need of toxic dye-loading of the cells. In undifferentiated hES cells the calcium signals induced by various ligands, ATP, LPA, trypsin or angiotensin II were comparable to those in Fluo-4 loaded cells. In accordance with previous findings, no calcium signal was evoked by thrombin, histamine or GABA. Cardiomyocyte colonies differentiated from hES-GCaMP2 cells could be recognized by spontaneous contractions and Ca(2+) oscillations. GCaMP2-expressing neural cells were identified based on their morphological and immuno-staining properties and Ca signals were characterized on those cells. Characteristics of both the spontaneous and ligand-induced Ca(2+) signals, as well as their pharmacological modification could be successfully examined in these model cells by fluorescence imaging.

A voltage-sensitive dye-based assay for the identification of differentiated neurons derived from embryonic neural stem cell cultures

BACKGROUND

Pluripotent and multipotent stem cells hold great therapeutical promise for the replacement of degenerated tissue in neurological diseases. To fulfill that promise we have to understand the mechanisms underlying the differentiation of multipotent cells into specific types of neurons. Embryonic stem cell (ESC) and embryonic neural stem cell (NSC) cultures provide a valuable tool to study the processes of neural differentiation, which can be assessed using immunohistochemistry, gene expression, Ca(2+)-imaging or electrophysiology. However, indirect methods such as protein and gene analysis cannot provide direct evidence of neuronal functionality. In contrast, direct methods such as electrophysiological techniques are well suited to produce direct evidence of neural functionality but are limited to the study of a few cells on a culture plate.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we describe a novel method for the detection of action potential-capable neurons differentiated from embryonic NSC cultures using fast voltage-sensitive dyes (VSD). We found that the use of extracellularly applied VSD resulted in a more detailed labeling of cellular processes compared to calcium indicators. In addition, VSD changes in fluorescence translated precisely to action potential kinetics as assessed by the injection of simulated slow and fast sodium currents using the dynamic clamp technique. We further demonstrate the use of a finite element model of the NSC culture cover slip for optimizing electrical stimulation parameters.

CONCLUSIONS/SIGNIFICANCE

Our method allows for a repeatable fast and accurate stimulation of neurons derived from stem cell cultures to assess their differentiation state, which is capable of monitoring large amounts of cells without harming the overall culture.

Developmental cues and persistent neurogenic potential within an in vitro neural niche

Background

Neurogenesis, the production of neural cell-types from neural stem cells (NSCs), occurs during development as well as within select regions of the adult brain. NSCs in the adult subependymal zone (SEZ) exist in a well-categorized niche microenvironment established by surrounding cells and their molecular products. The components of this niche maintain the NSCs and their definitive properties, including the ability to self-renew and multipotency (neuronal and glial differentiation).

Results

We describe a model in vitro NSC niche, derived from embryonic stem cells, that produces many of the cells and products of the developing subventricular zone (SVZ) and adult SEZ NSC niche. We demonstrate a possible role for apoptosis and for components of the extracellular matrix in the maintenance of the NSC population within our niche cultures. We characterize expression of genes relevant to NSC self-renewal and the process of neurogenesis and compare these findings to gene expression produced by an established neural-induction protocol employing retinoic acid.

Conclusions

The in vitro NSC niche shows an identity that is distinct from the neurally induced embryonic cells that were used to derive it. Molecular and cellular components found in our in vitro NSC niche include NSCs, neural progeny, and ECM components and their receptors. Establishment of the in vitro NSC niche occurs in conjunction with apoptosis. Applications of this culture system range from studies of signaling events fundamental to niche formation and maintenance as well as development of unique NSC transplant platforms to treat disease or injury.