Neurogenesis Using P19 Embryonal Carcinoma Cells

Summary

The P19 mouse embryonic carcinoma cell line (P19 cell line) is widely used for studying the molecular mechanism of neurogenesis with great simplification compared to in vivo analysis. Here, we present a protocol for retinoic acid-induced neurogenesis in the P19 cell line.

Abstract

The P19 cell line derived from a mouse embryo-derived teratocarcinoma has the ability to differentiate into the three germ layers. In the presence of retinoic acid (RA), the suspension cultured P19 cell line is induced to differentiate into neurons. This phenomenon is extensively investigated as a neurogenesis model in vitro. Therefore, the P19 cell line is very useful for molecular and cellular studies associated with neurogenesis. However, protocols for neuronal differentiation of P19 cell line described in the literature are very complex. The method developed in this study are simple and will play a part in elucidating the molecular mechanisms in neurodevelopmental abnormalities and neurodegenerative diseases.

Introduction

During embryonal development, a single cell layer is transformed into three separate germ layers^1,2,3. To increase the research possibilities of phenomena occurring in vivo, generation of three-dimensional aggregates (embryonic bodies) have been developed as a convenient model. Cellular aggregates formed in this way can be exposed to various conditions causing cell differentiation, which reflect development of the embryo^4,5. The P19 murine embryonic carcinoma cell line (P19 cell line) is commonly used as a cellular model for neurogenesis studies in vitro^6,7,8. The P19 cell line exhibits typical pluripotent stem cell features and can differentiate into neurons in the presence of retinoic acid (RA) during cell aggregation followed by neurite outgrowth under adherent conditions. Moreover, the undifferentiated P19 cell line is also capable of forming muscle- and cardiomyocyte-like cells under the influence of dimethyl sulfoxide (DMSO)^9,10,11,12.

Many methods^13,14,15,16 have been reported for neuronal differentiation, but the methodology is sometimes complicated and not easy to grasp by only reading the descriptions. For example, protocols sometimes require a combination of Dulbecco's Modified Eagle Medium (DMEM) medium supplemented with a mixture of calf serum (CS) and fetal bovine serum (FBS)¹³. Moreover, media used for neuronal development are often composed of Neurobasal and B27 supplements^13,14,15,16. As such, existing methods contain complexity in their preparation and our goal here is to simplify the protocols. In this study, we demonstrated that DMEM with FBS can be utilized for maintaining the P19 cell line (DMEM + 10% FBS) as well as for neuronal development (DMEM + 5% FBS + RA). This simplified method for neurogenesis using the P19 cell line allows us to study the molecular mechanism of how neurons are developed. Moreover, research on neurodegenerative diseases such as Alzheimer's disease is also conducted using P19 cell line^17,18, and we believe that the method developed in this study will play a part in elucidating the molecular mechanisms in neurodevelopmental abnormalities and neurodegenerative diseases.

Protocol

1. Culture Maintenance

1. Culture the P19 cell line in Maintenance Medium (Dulbecco's modified Eagle's medium with 4,500 mg/L of glucose supplemented with 10% FBS, 100 units/mL penicillin and 100 units/mL streptomycin). Incubate at 37 °C and 5% CO₂.

2. Sub-culturing Cells

1. When cells reach approximately 80% confluence, remove the spent medium from the cell culture flasks (surface area 25 cm²).
2. Wash the cells with 2 mL of phosphate buffered saline (PBS) free of calcium and magnesium.
3. Add 1 mL of 0.25% trypsin-EDTA (ethylenediaminetetraacetic acid) onto the cell monolayer.
4. Put the flask in the CO₂ incubator (37 °C and 5% CO₂) for 2-3 min.
5. Assess the cell attachment to the flask surface. Ensure that all of the cells are detached and floating in the medium.
6. Add 9 mL of Maintenance Medium to stop the enzymatic activity of trypsin.
7. Resuspend the cells in Maintenance Medium.
8. Transfer cells to a 15 mL tube and centrifuge for 5 min at 200 x g and room temperature (RT).
9. Discard the supernatant and add 10 mL of fresh Maintenance Medium into the 15 mL tube.
10. Use the cell suspension to determine the cell number using a cell counter according to manufacturer's instructions.
11. Seed cells at 2 x 10⁴ cells/cm2 in a new 25 cm² flask.
12. Add the Maintenance Medium up to 10 mL.
13. Put the flask with cells in the CO₂ incubator (37 °C and 5% CO₂) for 2-3 days.

3. Trypsin Digestion

1. Aspirate Maintenance Medium from the cell flask. Wash the cells once with 2 mL of calcium and magnesium-free PBS.
2. Add 1 mL of 0.25% trypsin-EDTA.
3. Put the flask with cells into the CO₂ incubator at 37 °C for 2-3 min.
4. Use 1 mL pipette to dissociate the cells by pipetting cells ten times.
5. Neutralize trypsin by adding 9 mL of Differentiation Medium (Dulbecco's modified Eagle's medium with 4500 mg/L of glucose supplemented with 5% FBS, 100 units/mL penicillin and 100 units/mL streptomycin) without RA to the cells.
6. Transfer cells to a 15 mL tube and centrifuge for 5 min at 200 x g and RT.
7. Discard the supernatant and add 1 mL of Differentiation Medium without retinoic acid (RA). Resuspend the cell pellet.
8. Use the cell suspension to determine the cell number using a cell counter according to manufacturer's instruction.

4. Aggregate Generation

1. Add 5 µL of RA (1 mM stock dissolved in 99.8% ethanol, stored at -20 °C) to the 10 mL of Differentiation Medium and mix well (final concentration of 0.5 µM RA).
   NOTE: RA is light sensitive. Low concentration of EtOH does not affect cell differentiation^19,20,21.
2. Add 10 mL of Differentiation Medium (with RA) to the 100 mm non-treated culture dish (dedicated to suspension culture).
3. Seed the 1 x 10⁶ cells in the 100 mm dish (Dish surface area 56.5 cm²).
4. Put the flask with cells into the incubator at 37 °C and 5% CO₂ for 2 days in order to promote aggregates formation.
5. After 2 days, exchange the Differentiation Medium. Aspirate medium containing aggregates using a 10 mL pipette and transfer to a 15 mL tube at RT.
6. Allow the aggregates to settle by gravity for 1.5 min at RT.
7. Discard the supernatant.
8. Add a fresh 10 mL of Differentiation Medium with 0.5 µM RA using a 10 mL serological pipette.
   CAUTION: Do not pipette the cell aggregates up and down.
9. Seed the aggregates into new 100 mm non-treated culture dish (dedicated to suspension culture).
10. Place the plate in the incubator (at 37 °C and 5% CO₂) for 2 days.

5. Aggregates Dissociation

1. Aspirate the cell aggregates using a 10 mL pipette.
2. Transfer the aggregates to a 15 mL tube. Allow the cell aggregates to settle by gravity for 1.5 min.
3. Remove the supernatant.
4. Wash the aggregates with DMEM alone (serum- and antibiotic- free).
5. Allow the cell aggregates to settle by gravity sedimentation for 1.5 min at RT.
6. Aspirate the supernatant and add 2 mL of trypsin-EDTA (0.25%).
7. Place the cell aggregates into a water bath (37 °C) for 10 min. Agitate the aggregates gently every 2 min by tapping with a hand.
8. Stop the trypsinization process by adding 4 mL of Maintenance Medium.
9. Pipette aggregates up and down 20 times using 1 mL pipette.
10. Centrifuge cells for 5 min at 200 x g and RT.
11. Remove the supernatant and resuspend the cell pellet in 5 mL of Maintenance Medium.
12. Determine the cell number with a cell counter.

6. Plating Cells

1. Add 3 mL per well of Maintenance Medium to a 6-well plate.
2. Seed cells in the 6-well culture plate at a density of 0.5 x 10⁶/well.
3. Incubate at 37 °C with 5% CO₂ concentration.
4. Seed the cells on cover glass in 6 well culture plate and perform immunostaining with anti-MAP2 antibody (20% confluence). Use 6-well plate to isolate RNA and perform RT-PCR for Map2, NeuN, Oct4, Nanog, and Gapdh (20% confluence).

Results

The simplified scheme of protocol for neurogenesis induction in P19 cell line is presented in Figure 1. In order to define the character of the P19 cell line in an undifferentiated state and during neurogenesis, the RT-PCR (reverse transcription-polymerase chain reaction) method was used. The undifferentiated P19 cell line expressed the pluripotency genes such as organic cation/carnitine transporter4 (Oct4) and Nanog homeobox (Nanog). Neurog...

Discussion

Here, we describe a simple protocol for neurogenesis using the P19 cell line. Although many reports have been published in this regard, a detailed methodology for neurogenesis induction using P19 cell line remains unclear. Moreover, we utilized a simple high glucose (4,500 mg/L) DMEM medium with 10% FBS for the entire experiment. This allowed us to perform the neurogenic experiment in a user-friendly manner and expand the usage of this method for the future.

The most critical points within thi...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
6x DNA Loading Dye	EURx	E0260-01
Agarose	Sigma- Aldrich	A9539
cDNA synthesis kit	EURx	E0801-02
DAPI (4′,6-Diamidine-2′-phenylindole dihydrochloride)	Sigma- Aldrich	10236276001	Working concentration: 1 μg/mL
DMEM high glucose (4.5 g/L) with L-glutamine	Lonza	BE12-604Q
Ethanol 99.8%	Chempur	CHEM*613964202
Fetal Bovine Serum (FBS)	EURx	E5050-03
MAP2 antibody	Thermo Fisher Scientific	PA517646	Dilution 1:100
PCR reaction kit	EURx	E0411-03
Penicillin/Streptomycin 10K/10K	Lonza	DE17-602E
Phosphate Buffered Saline (PBS), 1x concentrated without Ca2+, Mg2+	Lonza	BE17- 517Q
Retinoic acid	Sigma- Aldrich	R2625-50MG	dissolved in 99.8% ethanol; store in -20 °C up to 6 months
Secondary Antibody (Alexa Fluor 488)	Thermo Fisher Scientific	A11034	Dilution 1:500
Skim milk	Sigma- Aldrich	1153630500
TBE Buffer	Thermo Fisher Scientific	B52
Triton-X 100	Sigma- Aldrich	T8787-100ML
Trypsin 0.25% - EDTA in HBSS, without  Ca2+, Mg2+,with Phenol Red	biosera	LM-T1720/500
Cell Culture Plastics
1 mL Serological Pipettes	Profilab	515.01
10 mL Serological Pipettes	Profilab	515.10
100 mm dish dedicated for suspension culture	Corning	C351029
15 mL centrifuge tubes	Sigma- Aldrich	CLS430791-500EA
5 mL Serological Pipettes	Profilab	515.05
6-well plate	Corning	CLS3516
Cell culture flasks, surface area 25 cm2	Sigma- Aldrich	CLS430639-200EA