L-mimosine and hypoxia enhance angiopoietin-like 4 production involving hypoxia-inducible factor-1alpha: Insights from monolayer and spheroid cultures of dental pulp-derived cells and tooth slice cultures

Objective: Angiopoietin-like 4 (Angptl4) is an angiogenesis modulating signaling factor and as such involved in blood vessel formation but also in hard tissue resorption. Here we hypothesized that the hypoxia mimetic agent L-mimosine (L-MIM) and hypoxia stimulate the production of Angptl4 in the dental pulp. Material and methods: Monolayer and spheroid cultures of primary human dental pulp-derived cells (DPC) were treated with L-MIM or hypoxia. Furthermore, tooth slice cultures were performed. The production of Angptl4 was assessed at mRNA and protein levels using reverse transcription qPCR and immunoassays, respectively. To assess the involvement of hypoxia inducible factor (HIF)-l alpha (HIF-isignaling, inhibitor studies with echinomycin and Western Blot analysis for HIF-1 alpha were performed in DPC monolayer cultures.(HIF-1 Results: L-MIM and hypoxia increased production of Angptl4 at mRNA and protein levels in monolayer cultures of DPC. The increase of Angptl4 was paralleled by an increase of HIF-l alpha and inhibited by echinomycin. Angptl4 protein levels were also elevated in spheroid cultures. In tooth slice cultures, the pulp tissue expressed and released Angptl4 under normoxic and hypoxic conditions and in the presence of L-MIM. There was a trend for an increase in Angptl4 mRNA levels and a trend for a decrease in the protein levels of the supernatants. Conclusions: Our results suggest that the hypoxia mimetic agent L-MIM and hypoxia can increase Angptl4 production in DPC involving HIF-l alpha However, the increase in the cell culture supernatants does not translate in an increased release in tooth slice organ cultures.