IL-3 induces expression of lymphatic markers Prox-1 and podoplanin in human endothelial cells

Factors determining lymphatic differentiation in the adult organism are not yet well characterized. We have made the observation that mixed primary cultures of dermal blood endothelial cells (BEC) and lymphatic endothelial cells (LEC) grown under standard conditions change expression of markers during subculture: After passage 6, they uniformly express LEC-specific markers Prox-1 and podoplanin. Using sorted cells, we show that LEC but not BEC constitutively express IL-3, which regulates Prox-1 and podoplanin expression in LEC. The addition of IL-3 to the medium of BEC cultures induces Prox-1 and podoplanin. Blocking IL-3 activity in LEC cultures results in a loss of Prox-1 and podoplanin expression. In conclusion, endogenous IL-3 is required to maintain the LEC phenotype in culture, and the addition of IL-3 to BEC appears to induce transdifferentiation of BEC into LEC.