A novel serum-free medium for the isolation, expansion and maintenance of stemness and tissue-specific markers of primary human periodontal ligament cells.

Purpose: Periodontal ligament (PDL) cell cultures are classically maintained in serum-containing media. However, unwanted side-effects of these conditions on cellular and molecular characteristics demand a serum-free alternative. Even though these limitations are well known and efforts for the development of adequate serum-free alternatives have been made, these approaches for replacement remained unsuccessful so far. This study aimed at developing a well-defined, serum-free formulation supporting both isolation from tissue samples and efficient expansion of PDL cells. Here, of particular focus was the perpetuation of tissue-characteristic markers detectable in primary tissues and of stemness features.

Basic Procedures: Primary PDL cell cultures from generally healthy human donors (n = 3) were maintained in basal media N2B27 and E6 together with different concentrations of growth and attachment factors. Cell proliferation was recorded via microscopy and WST assay. Gene expression of RUNX2, Periostin, ALP, CD73, CD90, CD105, CD45, SOX10 and SOX2 was compared to primary PDL explants via qRT-PCR. Immunocytochemistry was performed for anti-CD105, SSEA-3, CD271, HNK1. Serum-containing sDMEM medium served as control.

Main Findings: N2B27 medium substituted with 25 ng/mL EGF, 25 ng/mL IGF1, 0.5 mg/mL Fetuin plus gelatine coating (designated N2B27-PDLsf) emerged as potent serum-free formulation ensuring adequate culture isolation and expansion. Here, PDL primary tissue signature markers RUNX2 and Periostin remained stable in N2B27-PDLsf compared to controls (229.0-fold ±101.0 and 83.2-fold ±9.6 increase). Additionally, stemness markers ALP and CD105 were significantly upregulated on transcriptional, and CD105 and SOX2 on protein level.

Principal Conclusions: This investigation identified a novel serum-free medium for the isolation, and expansion of primary human PDL cells with constantly high proliferation rates. Here, purity and stemness properties are maintained. Thus, N2B27-PDLsf represents a valid replacement for serum-containing media in PDL cultures.