Expression of Exosome-Derived MicroRNAs miR-21 and miR-135 are Differentially Regulated Among Dental Pulp Stem Cells

Dental Pulp Stem Cells (DPSCs) are a type of mesenchymal stem cell that has the potential to differentiate into various types of cells and tissue. Previous research has demonstrated that DPSCs can be easily accessed and isolated from both permanent and deciduous teeth, such as wisdom teeth or third molars, although there is less information available about the mechanisms and factors that regulate the growth and proliferative phenotypes and responses of DPSCs. Recent studies have revealed that a type of non-coding RNA known as microRNA can modulate these characteristics among many types of stem cells, although much is still unknown about how DPSC phenotypes may be regulated by microRNAs. Due to this lack of knowledge, the primary objective of this study was to evaluate microRNA expression and determine any correlations with DPSC phenotypes, such as proliferation or growth. Six DPSC isolates were retrieved from an existing repository and cultured using an existing approved protocol. Exosomes and extracellular vesicles were extracted from each DPSC isolate, which ranged in size from 50 to 250 nm. Exosome isolation was confirmed using Western blots for CD63 and Bradford protein assays. In addition, RNA was extracted, cDNA was synthesized, and qPCR was performed, which revealed that all DPSC isolates expressed miR-124, miR-133, and miR-224. However, differential expression of miR-21 among rapid and intermediate doubling time (rDT, iDT) isolates was observed, with expression of miR-135 found only among the intermediate and slow (iDT, sDT) DPSC isolates. This study provides some of the first evidence of associations between miRNA expression and specific DPSC growth phenotypes. Further studies will be needed to confirm these results and determine the mechanisms associated with the expression of miR-21 among rapidly growing DPSCs and miR-135 expression among more slowly growing DPSCs.