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Method Article
This protocol describes an endothelial differentiation technique for cardiac progenitor cells. It particularly focuses on how serum concentration and cell-seeding density affect the endothelial differentiation potential.
Cardiac progenitor cells (CPCs) may have therapeutic potential for cardiac regeneration after injury. In the adult mammalian heart, intrinsic CPCs are extremely scarce, but expanded CPCs could be useful for cell therapy. A prerequisite for their use is their ability to differentiate in a controlled manner into the various cardiac lineages using defined and efficient protocols. In addition, upon in vitro expansion, CPCs isolated from patients or preclinical disease models may offer fruitful research tools for the investigation of disease mechanisms.
Current studies use different markers to identify CPCs. However, not all of them are expressed in humans, which limits the translational impact of some preclinical studies. Differentiation protocols that are applicable irrespective of the isolation technique and marker expression will allow for the standardized expansion and priming of CPCs for cell therapy purpose. Here we describe that the priming of CPCs under a low fetal bovine serum (FBS) concentration and low cell density conditions facilitates the endothelial differentiation of CPCs. Using two different subpopulations of mouse and rat CPCs, we show that laminin is a more suitable substrate than fibronectin for this purpose under the following protocol: after culturing for 2 - 3 days in medium including supplements that maintain multipotency and with 3.5% FBS, CPCs are seeded on laminin at <60% confluence and cultured in supplement-free medium with low concentrations of FBS (0.1%) for 20 - 24 hours before differentiation in endothelial differentiation medium. Because CPCs are a heterogeneous population, serum concentrations and incubation times may need to be adjusted depending on the properties of the respective CPC subpopulation. Considering this, the technique can be applied to other types of CPCs as well and provides a useful method to investigate the potential and mechanisms of differentiation and how they are affected by disease when using CPCs isolated from respective disease models.
Recent studies support the existence of resident cardiac progenitor cells (CPCs) in the adult mammalian heart1,2,3, and CPCs could be a useful source for cell therapy after cardiac injury4,5. In addition, expanded CPCs may provide a fruitful model for drug screening and the investigation of disease mechanisms when isolated from patients with rare cardiomyopathies, or from respective disease models6,7.
CPCs isolated from the adult heart possess stem/progenitor cell characteristics1,2,3,8 as they are multipotent, clonogenic, and have the capacity for self-renewal. However, there are many different (sub)populations of CPCs exhibiting different surface marker profiles, including, for instance, c-kit, Sca-1, and others, or retrieved by different isolation techniques (Table 1). Several culture and differentiation protocols have been established1,2,8,9,10,11,12,13,14,15,16,17,18. These protocols vary mostly with respect to the growth factor and serum content, which are adjusted according to the purpose of the culturing and which can lead to differences in results and outcomes, including differentiation efficiency.
Marker-based Isolation Techniques:
CPCs can be isolated based on a specific surface marker expression1,2,8,9,10,11,12,13,14,15,16,17,18. Previous studies suggest that c-kit and Sca-1 may be the best markers to isolate resident CPCs1,11,14,19,20. Because none of these markers is truly specific for CPCs, combinations of different markers are usually applied. For example, whereas CPCs express low levels of c-kit21, c-kit is also expressed by other cell types, including mast cells22, endothelial cells23, and hematopoietic stem/progenitor cells24. An additional problem is the fact that not all markers are expressed across all species. This is the case for Sca-1, which expresses in mouse but not in human25. Therefore, using protocols that are independent of isolation markers may be advantageous in view of clinical trials and studies using human samples.
Marker-independent Isolation Techniques:
There are several major techniques of CPC isolation, which are primarily independent of surface marker expression, but which can be refined by the consecutive selection of specific marker-positive subfractions as needed (see also Table 1). (1) The side population (SP) technique has originally been characterized in a primitive population of hematopoietic stem cells based on the ability to efflux the DNA dye Hoechst 3334226 by ATP-binding cassette (ABC) transporters27. Cardiac SP cells have been isolated by different groups and reported to express a variety of markers with some minor differences between reports2,8,13,14. (2) Colony-forming unit fibroblast cells (CFU-Fs) have originally been defined based on a mesenchymal stromal cell (MSC)-like phenotype. Isolated MSCs are cultured on dishes to induce colony formation. Such colony-forming MSC-like CFU-Fs can be isolated from the adult heart and are capable to differentiate into cardiac lineages15. (3) Cardiosphere-derived cells (CDC) are single cells derived from clusters of cells grown from tissue biopsies or explants28,29,30,31. It was recently shown that mostly the CD105+/CD90-/c-kit- cell fraction exhibits cardiomyogenic and regenerative potential32.
Here, using SP-CPCs isolated from mice, we provide a protocol for the efficient induction of endothelial lineage based on a previous study in rat CPCs and mouse SP-CPCs33. The protocol contains specific adaptations to the culture and expansion technique with respect to the cell density, the serum content of the medium, and the substrate. It can be applied not only to mouse SP-CPCs but to different types of CPCs for the purpose to induce a fate switch from an amplifying to an endothelial-committed CPC, be it in view of transplantation of these cells or their use for mechanistic in vitro studies.
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The use of mice for cell isolation purpose was in accordance with the Guide for the Care and Use of Laboratory Animals and with the Swiss Animal Protection Law and was approved by the Swiss Cantonal Authorities.
NOTE: The isolation of Sca-1+/CD31- SP-CPCs from the mouse heart was essentially done as previously described34 with some modifications. For the materials and reagents used, see Table of Materials. For all experiments, cardiac SP-CPCs isolated from mice were amplified, passaged, and used in a cell line-like manner. Passages 7 - 20 were used for this study.
1. Tissue Preparation
NOTE: All experiments using mice must be carried out according to the guidelines and regulations. This protocol uses four mice. Culture plates that are 100 mm in diameter are described as P100 and culture plates that are 60 mm in diameter are described as P60 for the following parts of the protocol.
2. Digestion
3. Filtration
4. Sorting of Cardiac SP Cells by Flow Cytometry
NOTE: Verapamil inhibits Hoechst efflux by blocking multidrug resistance (MDR) ABC transporter activity. Hoechst 33342 is a DNA-binding dye that can be used in living cells to detect the cell cycle as it correlates with the DNA content. Hoechst-33342-extruding cells appear in the Hoechst low part of both emission channels (450 nm, Hoechst blue; 650 nm, Hoechst red), that is, aside of the Hoechst-retaining “main population”, giving them their name “side population”. SP cells are enriched in cells with progenitor properties and show a high expression of multidrug-resistant ABC transporters (such as MDR1 and ABCG2). Hoechst 33342 is written as Hoechst for the following parts of the protocol. It is important to protect light-sensitive materials for ideal results.
5. Primary Culture of Isolated SP-CPCs
NOTE: Three different types of media were used in this protocol. They are referred to as Medium 1 (according to Noseda et al.)8, Medium 2, and Medium 3 and are described in the Table of Materials regarding their composition.
6. Expansion and Differentiation of SP-CPCs
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Mouse SP-CPC Isolation:
In this study, we used mouse CPCs isolated according to the SP phenotype, whereas results from rat CPCs are modified and added from a previous report with permission (Figure 8)33.
Cell Proliferation Under High and Low Cell Densities and with Different Serum Concentrations:
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Advantages of this Protocol:
This protocol provides an endothelial differentiation technique of CPCs. We found that a low serum concentration and low cell density could improve the efficiency of endothelial differentiation, whereby LN proved to be a more suitable substrate than FN under these conditions. We used two distinct types of CPCs: rat CPCs, which were used in a cell line-like manner, and mouse SP-CPCs, which were isolated and expanded. Notably, the protocol was applicable to both types o...
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The authors have nothing to disclose.
The authors thank Vera Lorenz for her helpful support during the experiments and the staff from the Flow Cytometry Facility from the Department of Biomedicine (DBM), University and University Hospital Basel. This work was supported by the Stay-on track program from the University of Basel (to Michika Mochizuki). Gabriela M. Kuster is supported by a grant from the Swiss National Science Foundation (grant number 310030_156953).
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Name | Company | Catalog Number | Comments |
Culture medium | |||
Iscove's Modified Dulbecco's Medium (IMDM) | ThermoFisher | #12440 | |
Dulbecco's Modified Eagle's Medium (DMEM)/Nutrient Mixture F12 Ham | Merck | #D8437 | |
Penicillin-Streptomycin (P/S) | ThermoFisher | #15140122 | |
Fetal Bovine Serum (FBS) | Hyclone | #SH30071 | 3.5% (0.1% for lineage induction) |
L-Glutamine | ThermoFisher | #25030 | Final concentration 2 mM |
Glutathione | Merck | #G6013 | |
Recombinant Human Epidermal Growth Factor (EGF) | Peprotech | #AF-100-15 | |
Recombinant Basic Fibroblast Growth Factor (FGF) | Peprotech | #AF-100-18B | |
B27 Supplement | ThermoFisher | #17504044 | |
Cardiotrophin 1 | Peprotech | #250-25 | |
Thrombin | Diagontech AG, Switzerland | #100-125 | |
Hanks' Balanced Salt Solution (HBSS) CaCl2(-), MgCl2(-) | ThermoFisher | #14170 | |
0.05 % Trypsin-EDTA | ThermoFisher | #25300 | |
T75 Flask | Sarstedt | #83.3911 | |
Endothelial differentiation | |||
Endothelial Cell Growth Medium (EGM)-2 BulletKit | Lonza | #CC-3162 | |
Ham's F-12K (Kaighn's) Medium | ThermoFisher | #21127 | |
Laminin | Merck | #L2020 | |
Fibronectin | Merck | #F4759 | Dilute in ddH2O |
6 Well Plate | Falcon | #353046 | |
Formaldehyde Solution | Merck | #F1635 | Diluite 1:10 in PBS (3.7% final concentration) |
Triton X-100 | Merck | #93420 | 0.1% in ddH2O |
Normal Goat Serum (10%) | ThermoFisher | #50062Z | |
Anti-von Willebrand Factor antibody | Abcam | #ab6994 | 1:100 in 10% goat serum |
Goat anti-Rabbit IgG, Alexa Fluor 546 | ThermoFisher | #A11010 | 1:500 in 10% goat serum |
4',6-diamidino-2-phenylindole, dihydrochloride (DAPI) | ThermoFisher | #62247 | 1:500 in ddH2O |
SlowFade Antifade Kit | ThermoFisher | #S2828 | |
BX63 widefield microscope | Olympus | ||
Tube formation | |||
96 Well Plate | Falcon | #353072 | |
5 ml Round Bottom Tube with Strainer Cap | Falcon | #352235 | |
Matrigel Growth Factor Reduced | Corning | #354230 | |
IX50 widefield microscope | Olympus | ||
Sca-1+/CD31- cardiac side population isolation34 | |||
Reagents | |||
Pentobarbital Natrium 50 mg/ml ad usum vet. | in house hospital pharmacy | #9077862 | Working solution: 200 mg/kg |
Phosphate Buffered Saline (PBS) CaCl2(-), MgCl2(-) | ThermoFisher | #20012 | |
Hanks' Balanced Salt Solution (HBSS) CaCl2(-), MgCl2(-), phenol red (-) | ThermoFisher | #14175 | Prepare HBSS 500 mL + 2% FBS for quenching Collagenase B activity |
Dulbecco's Modified Eagle's Medium (DMEM) 1g/L of D-Glucose, L-Glutamine, Pyruvate | ThermoFisher | #331885 | Prepare DMEM + 10% FBS + 25 mM HEPES+ P/S for Hoechst stanining |
Penicillin-Streptomycin (P/S) | ThermoFisher | #15140122 | |
HEPES 1 M | ThermoFisher | #15630080 | Final concentration 25 mM |
Fetal Bovine Serum (FBS) | Hyclone | #SH30071 | |
RBC LysisBuffer (10X) | BioLegend | #420301/100mL | Dilute to 1X in ddH2O and filter through a 0.2 µm filter |
Collagenase B | Merck | #11088807001 | Final concentration 1 mg/mL in HBSS, filtered through a 0.2 µm filter |
bisBenzimide H33342 Trihydrochloride (Hoechst) | Merck | #B2261 | Prepare 1 mg/mL in ddH2O |
Verapamil-hydrochloride | Merck | #V4629 | Final concentration 83.3 µM |
APC Rat Anti-Mouse CD31 | BD Biosciences | #551262 | 0.25 µg/107cells |
FITC Rat Anti-Mouse Ly-6A/E (Sca-1) | BD Biosciences | #557405 | 0.6 µg/107cells |
7-Aminoactinomycin D (7-ADD) | ThermoFisher | #A1310 | 0.15 µg/106cells |
APC rat IgG2a k Isotype Control | BD Biosciences | #553932 | 0.25 µg/107cells |
FITC Rat IgG2a k Isotype Control | BD Biosciences | #554688 | 0.6 µg/107cells |
Material | |||
Needles 27G | Terumo | #NN-2719R | |
Needles 18G | Terumo | #NN-1838S | |
Single Use Syringes 1 mL sterile | CODAN | #62.1640 | |
Transferpipette 3.5 mL | Sarstedt | #86.1171.001 | |
Cell Strainer 40 µm blue | BD Biosciences | #352340 | |
Cell Strainer 100 µm yellow | BD Biosciences | #352360 | |
Lumox Dish 50 | Sarstedt | #94.6077.305 | |
Culture Dishes P100 | Corning | #353003 | |
Culture Dishes P60 | Corning | #353004 | |
Mouse | |||
Line | Age | Breeding | |
C57BL/6NRj / male | 12 weeks | in house | |
Product Name | Company | Catalogue No. | |
Reagents | |||
Iscove's Modified Dulbecco's Medium (IMDM) | ThermoFisher | #12440 | |
Dulbecco's Modified Eagle's Medium (DMEM)/Nutrient Mixture F12 Ham | Merck | #D8437 | |
Penicillin-Streptomycin (P/S) | ThermoFisher | #15140122 | |
Fetal Bovine Serum (FBS) | Hyclone | #SH30071 | |
L-Glutamine | ThermoFisher | #25030 | |
Glutathione | Merck | #G6013 | |
B27 Supplement | ThermoFisher | #17504044 | |
Recombinant Human Epidermal Growth Factor (EGF) | Peprotech | #AF-100-15 | |
Recombinant Basic Fibroblast Growth Factor (FGF) | Peprotech | #AF-100-18B | |
Cardiotrophin 1 | Peprotech | #250-25 | |
Thrombin | Diagontech AG, Switzerland | #100-125 | |
Endothelial Cell Growth Medium (EGM)-2 BulletKit | Lonza | #CC-3162 | |
Overview of medium compositions. Some of this infomation is identical with the one provided above, but sorted according to the composition of Media 1-3. | |||
Product Name | Medium 18 | Medium 2 | Medium 3 |
Reagents | Culture | Lineage induction | Endothelial diff. |
Iscove's Modified Dulbecco's Medium (IMDM) | 35% | 35% | |
Dulbecco's Modified Eagle's Medium (DMEM)/Nutrient Mixture F12 Ham | 65% | 65% | |
Penicillin-Streptomycin (P/S) | 1% | 1% | |
Fetal Bovine Serum (FBS) | 3.5% | ≤0.1% | |
L-Glutamine | 2 mM | 2 mM | |
Glutathione | 0.2 nM | 0.2 nM | |
B27 Supplement | 1.3% | ||
Recombinant Human Epidermal Growth Factor (EGF) | 6.5 ng/mL | ||
Recombinant Basic Fibroblast Growth Factor (FGF) | 13 ng/mL | ||
Cardiotrophin 1 | 0.65 ng/mL | ||
Thrombin | 0.0005 U/mL | All necessary components included in the kit | |
Endothelial Cell Growth Medium (EGM)-2 BulletKit | All necessary components included in the kit |
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