The growth factor multimodality on treating human dental mesenchymal stem cells: a systematic review

The systematic review utilized The databases Web of Science core collection and PubMed databases due to their high quality and abundance of relevant articles. The reviewers searched the Web of Science core collection database using the following terms: “dental mesenchymal stem cell*” OR “periodontal ligament stem cell*” OR “dental follicle stem cell*” OR “stem cell from human exfoliated deciduous teeth” OR “dental pulp stem cell*” OR “stem cells of the apical papilla” OR “gingival mesenchymal stem cell*” AND “Receptors, Growth Factor”. At the same time, the PubMed database was used to perform “Majr” of “Receptors, Growth Factor”. Nearly 10 years of English works of literature from 2014 to 2023 were screened. Moreover, the final selection was made on the 15th of July 2023.

The study included experimental articles that provided information on the effects of GFs during the application of human dental MSCs. The following literature was excluded: nonhuman, no open access, reviews, retracted, unspecified, meeting, and other topics (studies that do not treat with GFs, genetic, plasmidor adenoviruses treated, impact factors < 2.5). After screening the full text of the eligible articles, only papers focusing on the effects of GFs during the application of human dental MSCs were included. The reviewers independently studied the screening records and read the full text of each article to identify potentially qualified and relevant studies. This method allowed for the analysis of the content of a manuscript that meets the requirements. Only the literature that fulfilled the inclusion criteria was selected for this review.

The reviewers independently collected outcomes related to two aspects - single GF and multiple GFs. Firstly, the assessment of publication year and types of dental MSCs was completed. The unique parameters and information about the authors’ names, studies, GFs, dental MSCs, receptors, mechanisms, and effects were further extracted to evaluate the efficacy outcomes.

In this systematic review, 3847 records were initially obtained through database searching from the Web of Science core collection, and 20 records from PubMed were included. After excluding 2886 manuscripts due to duplication, non-human content, lack of open access, reviews, untraceable sources, unspecified content, and meetings, only 19 records remained for screening. After reviewing the titles and abstracts of 962 articles, 830 were excluded because they did not cover GFs. The full text of the remaining 132 articles was analyzed, and 56 were selected for their focus on the effects of GFs for treating human dental MSCs. Out of those 56 articles, 32 focused on a single growth factor while 24 focused on multiple growth factors. A flow chart illustrating this process is presented in Fig. 1.

For this systematic review, a total of 56 studies were selected. Human dental MSCs have garnered increasing attention from scholars due to their unique advantages in the field of regenerative medicine. This has made it a focal point for future research. According to the review, 47% of the articles were about DPSC, while 34% covered PDLSC, SHED, SCAP, and GMSC to a lesser extent. However, there were no studies on DFSC. This indicates that DPSC and PDLSC have the most promising applications in human dental MSCs. Over the past decade, research on GFs treatment of human dental MSCs has shown a gradual increase, with only two papers meeting the subject requirement in 2014, but increasing to ten in 2020 (Fig. 2).

This review covers 32 literary works using human dental MSCs with single GF treatment. The research mainly examines the therapeutic effects of different GFs on dental MSCs. However, there are only a few studies on the corresponding body or specific mechanism. The literature commonly uses pathway inhibitors to validate receptors and mechanisms. Table 1 presents detailed information about growth factors (GFs), cell types, receptors, pathways, and effects.

In this review, 24 pieces of literature focus on the effects of different GFs on human dental MSCs. The combination of multiple GFs is more complex when compared to the treatment of just one GF. The previous studies mainly focused on the efficacy of dental MSCs combined with GFs and rarely investigated the corresponding receptors or pathways. Table 2 provides detailed information on GFs, cell types, receptors, pathways, and their effects.

How GFs work is not straightforward. Although different GFs can affect dental MSCs using the same signaling pathway, a single GF can also use several signaling pathways to influence dental MSCs. As per the data gathered so far, various GFs affecting specific receptors or signaling pathways on dental MSCs are illustrated in Fig. 3.

Different GFs have varying effects on dental MSCs. FGF-2 treatment increases the proportion of Stro-1 + /CD146 + progenitor cells in SHED and improves vascularization differentiation efficiency more than hypoxia [24]. Similarly, treating DPSC with BDNF using the traditional SH-SY5Y sequential method can lead to more noticeable neuron-like characteristics [44]. These results suggest that supplementing with GFs can be a potential therapy for regenerating human dental MSCs in the pulp, blood vessels, and nerves. The effects of GFs may vary depending on the concentration used. J Qian et al. [28] discovered that the ability of DPSC to undergo osteogenic differentiation increased after 1 week of bFGF pretreatment. Although the effectiveness of bFGF is not diminished by passage, the osteogenic impact is reduced after 2 weeks of preconditioning, which is consistent with the findings of Casiano Del Angel-Mosqueda et al. [31].

A single GF can have multiple biological roles. The effect of bFGF on DPSC is not limited to osteogenesis but also helps to up-regulate the TRPC1 channel, which prevents apoptosis. Continuous treatment of Stem Cells from SHED with bFGF plays a vital role in regulating Pi/PPi metabolism and maintaining stem cell properties [28‐30]. GFs can also have the same impact on dental MSCs. For instance, NGF and EGF both have osteogenic effects, and BMP2 and FGF9 are also capable of inhibiting osteogenic differentiation. This could provide the basis for the combined application of GFs [23, 31, 38, 47].

When comparing single GF treatment to combined GF treatment, it can have either a synergistic or antagonistic effect. The combination of IGF-1 and VEGF works through the AKT pathway to stimulate DPSC growth. FGF-2 can work with TGF-β1 to stimulate PDLSC differentiation but antagonize BMP-induced differentiation [48, 50]. The use of multiple GFs has proven to be a better alternative to traditional stem cell culture medium. EGF, bFGF, and BDNF in a medium can stimulate dopaminergic neuron formation [58, 59]. DPSC can induce Schwann-like cells using PDGF-aa, bFGF, NRG, TGF-β3, BMP-2/-6/-7, and IGF-1 [56, 57]. PDLSC, on the other hand, can differentiate into corneal cells using bFGF-2, TGF-β3, and SP. Lastly, an EHFM medium is the best option for the long-term expansion of PDLSC [53, 55].

Different human platelet derivatives contain natural GFs with various effects. PRP enhances cell viability in PDLSC while PL has higher activity of GFs and fewer side effects [64, 65, 68‐70]. AFC is also a safe alternative to serum with a high content of GFs [60]. In i-PRF, yellow i-PRF stimulates osteogenic differentiation earlier, but red i-PRF is more suitable for bone regeneration [61]. However, GFs in vivo have limitations, improving their delivery systems can extend their stability and lifespan [75]. Hydrogel materials and modified gels enable tissue engineering with GFs like FGF, BMP, VEGF, and TGF-β [21, 25, 51, 66, 71]. Mineral trioxide aggregate (MTA), root BP Plus, and doxycycline (DOX) play an auxiliary role in the interaction process [35, 40, 67].

The mechanism by which GFs act on human dental MSCs is complex but critical. The receptors related to the TGF-β1 signal, such as TGF-βRIs (ALK1, ALK3, ALK5), TGF-βRII, β glycan, and endothelial glycoproteins, are detectable in SHED. Type I and II receptors within SHED enhance collagen synthesis, and TGF-β1 further affects SHED through differentially regulating ALK5/Smad2/3, TAK1, p38, and MEK/ERK pathways [18]. At a molecular level, TGF-β1 promotes the activity of β-galactosidase and the expression of p16 and p21 in PDLSC, leading to cellular senescence due to excessive ROS generation [17]. As for DPSC, researchers believe that BMP2, VEGF-a, GDNF, and BDNF mediate cell proliferation, migration, and differentiation through specific receptors [38, 41, 43, 46]. These findings suggest that GFs initiate biological processes by activating particular receptors in dental MSCs.

It is important to acknowledge certain limitations in this study. The search strategy only considered literature from the last decade, which means that not all available literature was included. Additionally, the included research mainly focused on basic research of cells or the primary animal model used in mice, which increases the risk of bias and confounding. This article mainly discusses dental MSCs, types of GFs, and specific uses in regenerative medicine, while ignoring the following aspects: (1) age, sex, and viability of human dental MSC donors; (2) number of animal experiments and duration of intervention, and (3) statistical methods used. Dental MSCs show great promise in regenerative medicine. However, the literature does not clarify the mechanism of interaction between different GFs in detail. Potential biases in the data may have further affected the systematic analysis. Due to the lack of a clinical database, a meta-analysis was not performed.

Therefore, to strengthen the conclusion, future improvements can be made in the following areas. First, conducting additional research that includes experiments and data from a broader range of species such as pigs, dogs, or humans is necessary. Second, it is important to consider the potential for publication, ensuring an adequate description of the mechanisms governing interaction between different growth factors in human dental MSCs. More consistent use of statistical methods, age, sex, and viability of human dental MSC donors, along with inhibition of experimental intervention can lead to higher-quality articles.