Primary Culture of Dental Pulp Stem Cells

Summary

This article provides a stepwise guide to establish a primary culture of dental pulps stem cells using the explant culture method and characterization of these cells based on ICSCRT guidelines. The cells isolated by this protocol can be considered as mesenchymal stem cells for further applications.

Abstract

The human dental pulp represents a promising multipotent stem cell reservoir with pre-eminent regenerative competence that can be harvested from an extracted tooth. The neural crest-derived ecto-mesenchymal origin of dental pulp stem cells (DPSCs) bestows a high degree of plasticity that owes to its multifaceted benefits in tissue repair and regeneration. There are various practical ways of harvesting, maintaining, and proliferating adult stem cells being investigated for their use in regenerative medicine. In this work, we demonstrate the establishment of a primary mesenchymal stem cell culture from dental tissue by the explant culture method. The isolated cells were spindle-shaped and adhered to the plastic surface of the culture plate. The phenotypic characterization of these stem cells showed positive expression of the international society of cell therapy (ISCT)-recommended cell surface markers for MSC, such as CD90, CD73, and CD105. Further, negligible expression of hematopoietic (CD45) and endothelial markers (CD34), and less than 2% expression of HLA-DR markers, confirmed the homogeneity and purity of the DPSC cultures. We further illustrated their multipotency based on differentiation to adipogenic, osteogenic, and chondrogenic lineages. We also induced these cells to differentiate into hepatic-like and neuronal-like cells by adding corresponding stimulation media. This optimized protocol will aid in the cultivation of a highly expandable population of mesenchymal stem cells to be utilized in the laboratory or for preclinical studies. Similar protocols can be incorporated into clinical setups for practicing DPSC-based treatments.

Introduction

Adult stem cells have transpired into a powerful therapeutic tool for cell-directed treatments and therapies due to their plasticity, paracrine mechanisms, and immunomodulatory properties^1,2,3. The encouraging data from stem cell-based preclinical studies have inspired researchers to work for the bench to-bedside translation. The type of stem cells used for stem cell therapy plays a significant role in successful outcomes. In preclinical and clinical studies, the most widely reported source for mesenchymal stem cells (MSCs) remain bone marrow^4,5. However, major drawbacks to using bone marrow-derived stem cells (BMSCs) include their rare population, highly invasive procedures for isolation, and their limited ability to expand. Therefore, alternative sources of MSCs are being explored. In this regard, dental tissues, with their ease of accessibility, enormous plasticity, high regenerative potential, and high proliferative ability, have now been deemed as a rich and potential alternative source of stem cells^6,7,8,9,10.

Dental pulp stem cells (DPSCs) were the first type of dental stem cells to be isolated and characterized by Gronthos in 2000¹¹. DPSCs have grabbed the attention for tissue engineering applications because of their high proliferation rate, significant differentiation potential, ease of accessibility with effortless culturing, and, most importantly, their ability to be obtained from a discarded tooth without any ethical concern¹². The limitations posed by other stem cell sources, such as BMSCs and adipose-derived stem cells (ADSCs), in their isolation and inadequate self-renewal capacities are circumvented by DPSCs¹³. Human DPSCs can be obtained from human primary teeth, permanent teeth, wisdom teeth, exfoliated deciduous teeth (SHEDs), and apical papillae. Moreover, DPSCs can also be isolated from supernumerary teeth, which are generally discarded¹⁴. DPSCs express neural crest-associated markers and have the potential to differentiate into neuronal cells both in vitro and in vivo¹⁵. In addition to their neurogenic potential, DPSCs can differentiate into other cell lineages, such as osteogenic, chondrogenic, adipogenic, hepatic, and myogenic, when given specific differentiation conditions¹³. Thus, these multipotent cells hold great potential for cell-based therapy and can be employed for the regeneration of various tissues. Studies have also reported the potential role of DPSCs in the reconstruction of the cornea¹⁶, repair of myocardial infarction¹⁷, and their potential therapeutic role in diseases like limb ischemia¹⁸, Alzheimer's ¹⁹, Parkinson's ²⁰, and aging²¹. Therefore, dental tissue-derived stem cells can be used not only for dental regeneration, but also for the repair and regeneration of non-dental organs like eyes¹⁶, hearts¹⁷, livers²², bones²³ etc.

There are two particular methods for the isolation of an MSC population from pulp tissue - enzymatic digestion and explant culture^24,25. Successful establishment of primary cultures without any significant difference in the quantity and properties of DPSCs have been reported by both these methods²⁶. In this study, we have focused on the isolation of DPSCs by the explant method²⁷, since this method generates DPSCs without contamination of hematopoietic and endothelial cells, as compared to enzymatic digestion which can result in fibroblast contamination²⁸.

Protocol

All the procedures described in the study have been approved by the Institute Ethics Committee (IEC# 9195/PG-12 ITRG/2571-72) of PGIMER, Chandigarh. All the cell culture related experiments need to be performed in a Class II biological safety cabinet (BSC) following aseptic technique. Dental pulp was obtained from healthy teeth of three (F/14, M/14, and M/20) patients undergoing third molar extractions for orthodontic reasons. Before the sample collection, written informed consent was obtained from the patient/guardian i…

Representative Results

Here, we describe how researchers can establish a pure culture of DPSCs via the explant method6,7,8,9,10 and induce them toward multiple lineages to establish the purity of culture for downstream applications. We established a primary culture of DPSCs from the small tissue of pulp extracted from the third molar tooth of pat…

Discussion

Stem cells have pinned the hopes of curing numerous diseases, owing to their plasticity, robustness, immunomodulatory properties, paracrine mechanisms, and homing efficiencies. Dental pulp tissue is considered the most potent and valuable source of stem cells, with eminent plasticity and a regenerative capability. Here, we demonstrate the isolation of DPSCs, utilizing the widely adopted explant culture method, in which the cells migrate from pieces of pulp tissue or explants to grow into a homogenous cell culture that mo…

Materials

6 well cell culture plate	Costar	3516	For cell culture
Alcian blue stain	EZstain chondrocyte staining kit, HiMedia	CCK029
alizarin red S stain	Sigma-Aldrich	TMS-008	Osteogenic stain
Antibiotic cocktail	Himedia	A002-5X50ML	To prevent culture contamination
Ascorbic Acid	Himedia	TC094-25G	Chondrogenic induction
B27 supplement	Gibco	17504044	For neural induction
bFGF ( basic Fibroblast Growth Factor)	Gibco	PHG0024	For neural induction
CD 105	BD-Pharmingen	560839
CD 35	Biolegend	343604
CD 45	Biolegend	304006
CD 73	Biolegend	344016
CD 90	Biolegend	328107	Characterization
cetyl pyridinium chloride (CPC)	Sigma-Aldrich	1104006	For Alizarin Red extraction
Dexamethasone 21-phosphate disodium	Sigma-Aldrich	D1159-100MG
Dulbecco's Phosphate Buffered Saline	Himedia	TS1006-5L	For washing purpose
EGF (Epidermal Growth Factor)	Gibco	PHG0311	For hepatic and neural  induction
EVOS LED microscope	Invitrogen		For  fluorescence imaging
EZ stain Chondrocyte staining kit	Himedia	CCK029-1KT	Chondro stain Kit
FACS Canto flow cytometer	BD Biosciences		For cell characterization
Fetal Bovine Serum	Gibco	16000044	For primary culture
Fetal Bovine Serum	Sigma-Aldrich	F2442	For cell culture
G5 supplement	Gibco	17503012	For neural induction
HGF( Hepatocyte Growth Factor)	Sigma-Aldrich	H1404	For hepatic Induction
HLA-DR	Biolegend	307605
Human TGF-β3	Peprotech	#100-36E-10U
Insulin-Transferrin-Selenous acid premix	Sigma-Aldrich	I3146	For hepatic Induction
ITS premix	Corning	354350
LDL Uptake Assay kit	Abcam	ab133127	For hepatic characterization
Low glucose DMEM	Gibco	11885-084	For hepatic induction
MAP2 antibody	Sigma-Aldrich	M4403	For neural characterization
N2 supplement	Gibco	17502048	For neural induction
Neural Basal Media	Gibco	21103049	For neural induction
NFM antibody	Sigma-Aldrich	N4142	For neural characterization
Nikon Elipse TS100 microscope	Nikon		For  fluorescence imaging
Oil Red O	Sigma-Aldrich	01391-250Ml	Adipogenic stain
Oncostatin M	R&D Systems	295-OM-010/CF	For hepatic Induction
Petridish	Tarson	460090-90MM	For tissue cutting
Potassium phosphate monobasic	Sigma-Aldrich	15655-100G	Osteogenic induction
Propan-2-ol	Thermo Fisher	Q13827	For Oil Red O extraction
Sodium pyruvate solution	Sigma life sciences	S8636-100ML
Trypsin-EDTA	Sigma-Aldrich	T4049	For cell passaging
Whatman filter paper	merck	WHA1001325	filter paper
α- Minimum Essential Media (α-MEM)	Sigma-Aldrich	M0643-10X 1L	Media for primary culture
β-glycerophosphate disodium salt hydrate	Sigma-Aldrich	G9422-50G