The balance between sphingolipids and phosphoinositides as a driving factor in epithelial cell differentiation

PESCIO, LG; MOSCA, JM; FAVALE, NO; STERIN-SPEZIALE, NB

Rosario

Congreso; LIX Annual Meeting SAIB 2023; 2023

Epithelial cell differentiation starts with apicobasal polarization and asymmetric expression of the proteins and lipids of the membrane. Glycosphingolipids and phosphoinositides are key polarity lipids. The modulation of the distribution of the phosphoinositides is dependent on the location of specific kinases and phosphatases, and the distribution of these lipids within the plasma membrane changes during the process of epithelial cell polarization. In fully polarized cells, PI(4,5)P2 is enriched in the apical membrane, whereas PI(3,4,5)P3 is basolateral. The apical localization of PTEN allows the local synthesis of PI(4,5)P2 and the consequent apical recruitment of the PAR/aPKC complex, an important apical polarity complex.Glycosphingolipids are enriched at the apical membrane of epithelial cells. Previous results from our laboratory showed that glycosphingolipid synthesis is essential for MDCK cell differentiation, expressed by a mature apical membrane and primary cilium formation, in cells subjected to hypertonicity. Also, we showed that PTEN knockdown or inhibition impairs MDCK cell polarization inducing aberrant lumens at the lateral domain. In this study we used a pharmacological inhibitor of PTEN (SF1670) in addition to an inhibitor of Glucosylceramide synthase (D-PDMP). Cells treated with SF1670 + D-PDMP showed a fully polarized phenotype with apical accumulation of the apical marker gp135 and basolateral distribution of α catenin. These results suggest that the treatment with D-PDMP reverted the deleterious effect caused by the inhibition of PTEN. We hypothesized that the treatment with D-PDMP induce an accumulation of sphingomyelin, responsible for rescuing the phenotype. The lipid extraction and separation of sphingolipids by Thin Layer Chromatography showed an accumulation of sphingomyelin in SF1670 + D-PDMP treated cells in comparison with SF1670 treated cells. These results suggest that the enrichment of sphingomyelin cause by the inhibition of glucosylceramide synthase improve the apical – basal polarity. Previous studies showed a transbilayer colocalization between sphingomyelin rich domains in the outer leaflet and PI(4,5)P2 – rich domains in the inner leaflet. Based on these evidence, we propose that the accumulation of sphingomyelin induced by SF1670 + D-PDMP treatment promotes the clustering of this sphingolipid with PI(4,5)P2, allowing the recruitment of the proteins that are part of the polarity complexes. In conclusion, cell differentiation requires regulated mechanisms to correctly distribute the sphingolipids and phosphoinositides to proper localize the polarity proteins.