Chapter 6 114 Figure 4. Glomerular TMEM14A expression is increased in human proteinuric renal diseases (A) Glomerular TMEM14A protein expression was examined in human kidney biopsies from patients with diabetic nephropathy (DN), lupus nephritis (LN), IgA nephropathy (IgAN), minimal change disease (MCD), and healthy controls. Compared to controls, TMEM14A protein expression is significantly more extensive in IgAN, LN, and MCD, but not in DN. (B – F) Representative images of glomeruli stained for TMEM14A in healthy controls (B), diabetic nephropathy (C), lupus nephritis (D), IgA nephropathy (E), and minimal change disease (F). Slides were stained with goat anti-TMEM14A antibody and immunoreactivity was assessed by diaminobenzidine. This results in a brown colour which then indicates TMEM14A localization. Counterstaining with haematoxylin results in blue-purple colouring of cell nuclei. Boxes in A show the range of values between the lower and upper quartile, the whiskers show 5th to 95th percentile, triangles show values lying outside the 5th to 95th percentile, the line in the box shows the median, and ‘+’ indicates the mean. The scale bar in B applies to B through F and indicates 50µm. * = p < 0.001. ANOVA with Tukey’s post hoc analysis was used. Discussion TMEM14A is a relatively unknown protein that is identified to be essential in maintaining GFB integrity. In spontaneously proteinuric rats, we show that glomerular Tmem14a mRNA and protein expression is relatively diminished, especially before onset of proteinuria. Also, knocking down tmem14a mRNA translation in zebrafish results in proteinuria. In vitro experiments reveal that TMEM14A is primarily expressed by podocytes. Lastly, we show that glomerular TMEM14A protein expression is increased in various proteinuric renal diseases, but not in diabetic nephropathy. Overall, these results imply that TMEM14A is an important factor in the development of proteinuria. Based on the results in this study, we postulate that its role in GFB integrity appears to be a protective one. First, a lack of sufficient Tmem14a expression in spontaneously proteinuric rats before onset of proteinuria supports this notion. Furthermore, direct inhibition of tmem14a mRNA translation resulted in proteinuria in the zebrafish model.
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