Implication of sphingolipids in epithelial-mesenchymal transition process in renal collecting ducts of aged rats

BRANDÁN, Y.R.; GUAYTIMA, E.V; PESCIO, L. G.; FAVALE, N. O.; STERIN-SPEZIALE, N.B.; MÁRQUEZ, M. G.

Salta

Congreso; LV REUNIÓN ANUAL DE LA SOCIEDAD ARGENTINA DE INVESTIGACIÓN BIOQUÍMICA Y BIOLOGÍA MOLECULAR (SAIB) y XIV PANAMERICAN ASSOCIATION OF BIOCHEMISTRY AND MOLECULAR BIOLOGY (PABMB) CONGRESS; 2019

SOCIEDAD ARGENTINA DE INVESTIGACIÓN BIOQUÍMICA Y BIOLOGÍA MOLECULAR (SAIB) y PANAMERICAN ASSOCIATION OF BIOCHEMISTRY AND MOLECULAR BIOLOGY (PABMB)

The epithelial-mesenchymal transition (EMT) is a process in which the cells lose their epithelial phenotype and acquire the characteristics of the mesenchymal cells, which includes loss of cell-cell binding. Renal function declines progressively with age, and the EMT process has been suggested as a mechanism that drives renal fibrosis, with the consequent loss of tissue functions, which occurs mainly in old age. In previous works, we demonstrated that the inhibition of sphingomyelin synthase 1, the enzyme responsible for the synthesis of sphingomyelin (SM) at the Golgi Ap level, induces a EMT process in CD cells from renal papilla of young rats (70 days-old). We also demonstrated that the EMT occurs spontaneously in renal papilla CD cells of middle-aged rats (6-8 months), denoted by an impairment of cell-cell adhesion, a high expression of the mesenchymal protein vimentin, and the de novo synthesis of α-smooth muscle actin (α-SMA), another mesenchymal biomarker. These results motivated us to study the possible implication of sphingolipids, and in particular SM content, in the occurrence of EMT in renal papilla CD cells. We analyzed the total SM content in CD cells from young, middle-aged and aged-rats (15 months) by thin layer chromatography (TLC) and densitometry. Surprisingly, although we observed an EMT in CD cells from middle-aged rats, the quantitative results showed a decrease in SM content only in CD cells isolated from renal papilla of aged rats (young vs aged-rats, p= 0.0030). Since the occurrence of the EMT process was observed in rats from 6 month old, we performed a recovery experiment using the exogenous addition of 10 μM C12-SM to primary cultured CD cells from middle-aged rats. For this purpose, we simultaneously evaluated the intercellular adhesions by α- catenin immunostaining, and the expression of the mesenchymal biomarker α-SMA. After SM exogenous aggregate, the intercellular spaces between the CD cells disappeared and α- catenin lined the lateral cell membranes, reflecting the presence of adherens junctions. Moreover, the percentage of CD cells that express α-SMA decreased (young vs middle-aged, p=0.0006). Taking into account our previous and present results, we conclude that the epithelial-mesenchymal phenotypic conversion that spontaneously occurs in CD cells during aging is reversible, and can be reverted by the exogenous addition of SM. Physiological aging refers to the set of mechanisms and processes that lead to an inexorable and gradual decrease in the level of the organism in functional capacity. Taken together, we propose that the sphingolipids metabolism play a role as a modulator of the fate of renal papilla CD cells during aging.