With the discovery of endothelial progenitor cells (EPCs) in the late 1990s, a paradigm shift in the concept of neoangiogenesis occurred. The identification of circulating EPCs in peripheral blood marked the beginning of a new era with enormous potential in the rapidly transforming regenerative field. Overwhelmed with the revelation, researchers across the globe focused on isolating, defining, and interpreting the role of EPCs in various physiological and pathological conditions. Consequently, controversies emerged regarding the isolation techniques and classification of EPCs. Nevertheless, the potential of using EPCs in tissue engineering as an angiogenic source has been extensively explored. Concomitantly, the impact of EPCs on various diseases, such as diabetes, cancer, and cardiovascular diseases, has been studied. Within the limitations of the current knowledge, this review attempts to delineate the concept of EPCs in a sequential manner from the speculative history to a definitive presence (origin, sources of EPCs, isolation, and identification) and significance of these EPCs. Additionally, this review is aimed at serving as a guide for investigators, identifying potential research gaps, and summarizing our current and future prospects regarding EPCs.

Stem cell–based therapeutics is a promising strategy in dental pulp regeneration. However, low cell viability after transplantation in vivo due to the ischemic microenvironment is still a critical challenge for future clinical application. With the aim of improving postimplantation cell survival and pulp tissue regeneration, stem cells from human exfoliated deciduous teeth (SHED) were preconditioned to a hypoxic condition by hypoxia-inducible factor 1α (HIF-1α) stabilization via knockdown of prolyl hydroxylase domain-containing protein 2 (PHD2) using lentiviral short hairpin RNA. HIF-1α–stabilized SHED were encapsulated in PuraMatrix hydrogel, injected into root canals of human tooth fragments, and implanted in the subcutaneous space of immunodeficient mice. After 28 d, enhanced dental pulp–like tissue formation was observed with a significantly higher level of vascularization, which could be attributed to both endothelial differentiation of SHED and recruitment of host blood vessels. Furthermore, dentin-like tissue formation in vivo and accelerated odontogenic/osteogenic differentiation both in vivo and in vitro were observed. At 7 d postimplantation, significantly less DNA damage and higher Ki67 expression were detected in the HIF-1α–stabilized SHED group compared with the control SHED. Accordingly, cell viability assay and staining for Ki67 and apoptotic cells in vitro showed that HIF-1α stabilization could decrease cell apoptosis and enhance cell survival significantly. We demonstrated that PI3K/AKT pathway activation had resulted in low caspase 3 expression in HIF-1α–stabilized SHED in hypoxic conditions. Furthermore, we found that HIF-1α–induced cell survival could also be attributed to the upregulated expression of PDK1, HK2, and Glut1, which contributes to the maintenance of reactive oxygen species homeostasis and metabolic adaptation in hypoxia. In addition, we identified Smad7 as 1 of the top 3 upregulated genes through RNA sequencing in HIF-1α–stabilized SHED and demonstrated its essential role in HK2 and Glut1 upregulation. Taken together, HIF-1α stabilization enhances cell survival of SHED through modulating various target genes and potential signaling pathways, as well as odontogenic tissue formation during dental pulp regeneration, which could benefit stem cell–based therapy in general.

Objectives Recently, a new strategy has been developed to directly reprogram one cell type towards another targeted cell type using small molecule compounds. Human fibroblasts have been chemically reprogrammed into neuronal cells, Schwann cells and cardiomyocyte-like cells by different small molecule combinations. This study aimed to explore whether stem cells from apical papilla (SCAP) could be reprogrammed into endothelial cells (ECs) using the same strategy. Materials and methods The expression level of endothelial-specific genes and proteins after chemical induction of SCAP was assessed by RT-PCR, western blotting, flow cytometry and immunofluorescence. The in vitro functions of SCAP-derived chemical-induced endothelial cells (SCAP-ECs) were evaluated by tube-like structure formation assay, acetylated low-density lipoprotein (ac-LDL) uptake and NO secretion detection. The proliferation and the migration ability of SCAP-ECs were evaluated by CCK-8 and Transwell assay. LPS stimulation was used to mimic the inflammatory environment in demonstrating the ability of SCAP-ECs to express adhesion molecules. The in vivo Matrigel plug angiogenesis assay was performed to assess the function of SCAP-ECs in generating vascular structures using the immune-deficient mouse model. Results SCAP-ECs expressed upregulated endothelial-specific genes and proteins; displayed endothelial transcriptional networks; exhibited the ability to form functional tubular-like structures, uptake ac-LDL and secrete NO in vitro; and contributed to generate blood vessels in vivo. The SCAP-ECs could also express adhesion molecules in the pro-inflammatory environment and have a similar migration and proliferation ability as HUVECs. Conclusions Our study demonstrates that the set of small molecules and growth factors could significantly promote endothelial transdifferentiation of SCAP, which provides a promising candidate cell source for vascular engineering and treatment of ischemic diseases.

BackgroundHuman periodontal ligament stem cells (hPDLSCs) have been shown to be a reliable source of mesenchymal stem cells (MSCs). On the other hand, rabbits have been commonly used in preclinical trials for musculoskeletal research. However, there is a lack of sufficient data on using rabbit periodontal ligament stem cells (rPDLSCs) for regenerative dentistry. This study, for the first time, comprehensively compared rPDLSCs against hPDLSCs in terms of clonogenicity, growth potential, multi-differential capacity and surface antigens.MethodsPeriodontal ligament (PDL) was obtained from the rabbit and human teeth. rPDL and hPDL cells were isolated from PDL using enzymatic digestion method. After culturing for 2 weeks, the cells were first analyzed microscopically. STRO-1+CD146+ PDLSCs were then sorted from PDL cells by fluorescence-activated cell sorting (FACS) followed by examination of CD34, CD45, CD90, vimentin and desmin markers. The cells were also evaluated by immunohistocytochemical and multi-differentiation potential tests. The clonogenicity and growth of PDL cells were analyzed by Independent T test and 2-way repeated measures ANOVA respectively.ResultsrPDL cells were broader and less elongated as compared to hPDL cells. STRO-1+CD146+ hPDLSCs were isolated from hPDL cells but not from the rPDL cells. Therefore, heterogeneous population of rabbit and human PDL cells were subsequently used for latter comparative studies. FACS analysis and immunohistocytochemistry revealed that rPDL cells were partially positive for STRO-1 as compared to hPDL cells. Furthermore, both rPDL cells and hPDL cells were positive for CD146, CD90, vimentin, and desmin, while negative for CD34 and CD45. No difference in clonogenicity between rPDL and hPDL cells was found (p > 0.05). The proliferative potential of rPDL cells displayed significantly slower growth as compared to hPDL cells (p < 0.05). Osteogenic, adipogenic, and chondrogenic differentiation potential was comparatively less in rPDL cells than that of hPDL cells, but the neurogenic differential potential was similar.ConclusionAlthough rPDL cells manifested variable differences in expression of stem cell markers and multi-differential potential as compared to hPDL cells, they demonstrated the attributes of stemness. Further studies are also required to validate if the regenerative potential of rPDL cells is similar to rPDLSCs.

Curcumin has been used in traditional medicine forages. The present study aimed to develop a curcumin-based hydrogel system and assess its antimicrobial potential and wound healing (WH) activity on an invitro and in silico basis. A topical hydrogel was prepared using chitosan, PVA, and Curcumin in varied ratios, and hydrogels were evaluated for physicochemical properties. The hydrogel showed antimicrobial activity against both gram-positive and gram-negative microorganisms. In silico studies showed good binding energy scores and significant interaction of curcumin components with key residues of inflammatory proteins that help in WH activity. Dissolution studies showed sustained release of curcumin. Overall, the results indicated wound healing potential of chitosan–PVA–curcumin hydrogel films. Further in vivo experiments are needed to evaluate the clinical efficacy of such films for wound healing.