The inhibition of sphingomyelin synthase 1 activity induces collecting duct cells to lose their epithelial phenotype

Abstract

Epithelial tissue requires that cells attach to each other and to the extracellular matrix by the assembly of adherens junctions (AJ) and focal adhesions (FA) respectively. We have previously shown that, in renal papillary collecting duct (CD) cells, both AJ and FA are located in sphingomyelin (SM)-enriched plasma membrane microdomains. In the present work, we investigated the involvement of SM metabolism in the preservation of the epithelial cell phenotype and tissue organization. To this end, primary cultures of renal papillary CD cells were performed. Cultured cells preserved the fully differentiated epithelial phenotype as reflected by the presence of primary cilia. Cells were then incubated for 24h with increasing concentrations of D609, a SM synthase (SMS) inhibitor. Knock-down experiments silencing SMS 1 and 2 were also performed. By combining biochemical and immunofluorescence studies, we found experimental evidences suggesting that, in CD cells, SMS 1 activity is essential for the preservation of cell-cell adhesion structures and therefore for the maintenance of CD tissue/tubular organization. The inhibition of SMS 1 activity induced CD cells to lose their epithelial phenotype and to undergo an epithelial-mesenchymal transition (EMT) process.

Influence of sphingomyelin metabolism during epithelial–mesenchymal transition associated with aging in the renal papilla

“…Anyway, it is known that an increase in mRNA quantity does not always translate into an increase in protein. Taking into account our present and past results (Brandán et al,2018; Favale et al,2015; Márquez et al,2012), we propose that the synthesis of SM is necessary to maintain the epithelial characteristics of the CD cells and that the decrease in SM induces mesenchymalization during aging.…”

“…More recently, we demonstrated that the intracellular synthesis of SM is a requirement for the acquisition of mature AJ, necessary to preserve the tissue organization and the differentiated epithelial phenotype of MDCK cells, a cell line of dog kidney CD (Favale et al,2015). We further reported that the inhibition of SMS1, but not SMS2, altered intercellular adhesions in cultured renal papillary CD cells from young rats (Brandán et al,2018). Li et al (2007) reported that the downregulation of the two SMS isoforms alters the amount of SM exclusively in the plasma membrane raft domains of HEK 293 cells.…”

“…Thereafter, we also reported that in the mature kidney, there is a balance between the CD cells that carry out EMT and those that carry out MET, thus maintaining tissue homeostasis. For the maintenance of such EMT‐MET balance, we showed that a correct biosynthesis of SM is required because when SM biosynthesis was affected the equilibrium was preferentially towards EMT, which favored the formation of myofibroblasts (Brandán et al,2018). It is well known that when an irregular EMT occurs in the adult kidney, pathological conditions such as renal fibrosis and cancer are generated (Boutet, 2006 Kalluri & Weinberg,2009; López‐Novoa & Nieto,2009).…”

“…Afterward, by utilizing a renal cell line, we demonstrated that SM content is essential to preserve the integrity of mature AJ as well as the cell epithelial phenotype of cultured differentiated Madin‐Darby canine kidney (MDCK) cells (Favale et al, 2015). More recently, we reported that the inhibition of sphingomyelin synthase (SMS) 1, the enzyme responsible for the synthesis of SM at the Golgi Ap level, induces an EMT process in CD cells from the renal papilla of young adult rats (Brandán et al, 2018). These results motivated us to continue studying the implication of SM metabolism in the maintenance of the tissue organization of the renal papilla CD.…”

Potential therapeutic targets for atherosclerosis in sphingolipid metabolism

“…Although SMS1 deficiency in macrophages showed similar anti-atherosclerotic effects in a mice model [ 36 ], SMS1 is indeed not an appropriate therapeutic target. To date, it has been reported that SMS1 −/− mice exhibited several severe abnormalities, including defective insulin secretion [ 37 ], progressive hearing loss at a low frequency range [ 38 ], CD4 + T-cell dysfunction [ 39 ], adipocyte lipid storage dysfunction [ 40 ], male spermatogenesis defects [ 41 ], and mesenchymal transition of epithelial cells derived from the renal papillary collecting duct [ 42 ]. Disruption of SMSr in mice resulted in marginal changes in the plasma levels of sphingomyelin, ceramide, and S1P [ 43 , 44 ].…”