Transmembrane Protein 14A protects glomerular filtration barrier integrity 113 6 TMEM14A is primarily expressed by podocytes in the kidney TMEM14A mRNA expression was investigated - in both whole kidney tissue and purified glomeruli and compared to immortalized podocytes, HEK, and HUVEK cells. It revealed that TMEM14A is expressed by podocytes and endothelial cells. Moreover, its expression is higher in purified glomeruli than in whole kidney. mRNA expression was highest in differentiated podocytes (Figure 3A). Immunohistochemistry results from the previous experiments show that TMEM14A is also expressed in distal tubular cells (images 1C – K). Figure 3. TMEM14A is primarily expressed by podocytes In vitro experiments of relative TMEM14A mRNA expression show expression relative to GAPDH expression when comparing mRNA extracts from whole kidney, purified glomeruli, human umbilical vein endothelial cells (Huvec), human embryonic kidney (HEK), and finally podocytes. Expression in podocytes, HEK and Huvec was significantly higher than in whole kidney (p < 0.001 for all groups) and then purified glomeruli (p < 0.001 for podocytes and HEK, p < 0.05 for Huvec). Podocyte expression was highest of all cells and significantly so compared to Huvec (p < 0.05). Mean and SD shown. ANOVA with Tukey’s post hoc analysis was used. Glomerular TMEM14A protein expression is increased in proteinuric disease To establish whether TMEM14A also plays a role in the development of proteinuria in human disease, glomerular TMEM14A protein expression was examined in human kidney biopsies from patients with IgA nephropathy (IgAN), lupus nephritis (LN), minimal change disease (MCD), or diabetic nephropathy (DN). Here, we found that TMEM14A protein expression is significantly increased in IgAN, LN and MCD (p < 0.0001) but not in DN (Figure 4). No correlation was found between the level of proteinuria and the score in TMEM14A positivity (r = 0.09).
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