mTOR-Dependent Autophagy Regulates Slit Diaphragm Density in Podocyte-like Drosophila Nephrocytes

Abstract

Both mTOR signaling and autophagy are important modulators of podocyte homeostasis, regeneration, and aging and have been implicated in glomerular diseases. However, the mechanistic role of these pathways for the glomerular filtration barrier remains poorly understood. We used Drosophila nephrocytes as an established podocyte model and found that inhibition of mTOR signaling resulted in increased spacing between slit diaphragms. Gain-of-function of mTOR signaling did not affect spacing, suggesting that additional cues limit the maximal slit diaphragm density. Interestingly, both activation and inhibition of mTOR signaling led to decreased nephrocyte function, indicating that a fine balance of signaling activity is needed for proper function. Furthermore, mTOR positively controlled cell size, survival, and the extent of the subcortical actin network. We also showed that basal autophagy in nephrocytes is required for survival and limits the expression of the sns (nephrin) but does not directly affect slit diaphragm formation or endocytic activity. However, using a genetic rescue approach, we demonstrated that excessive, mTOR-dependent autophagy is primarily responsible for slit diaphragm misspacing. In conclusion, we established this invertebrate podocyte model for mechanistic studies on the role of mTOR signaling and autophagy, and we discovered a direct mTOR/autophagy-dependent regulation of the slit diaphragm architecture.

A protective role forDrosophilaFilamin in nephrocytes via Yorkie mediated hypertrophy

“…Therefore, we cannot exclude the possibility that TOR and Yorkie pathways act independently of Cheerio. Of note, our findings regarding cell size control mediated via TOR (activation and repression) are in line with recent findings by Spitz et al (2022) .…”

The Wolbachia WalE1 effector alters Drosophila endocytosis

“…Uptake of dextran was imaged (shown in green) and quantified (boxplot panel) across the time course [0 (on ice), 15, and 30 minutes (warming to room temperature)]. Anti-HRP staining (shown below the dextran channel) was used to identify garland cell plasma membranes and to corroborate update of dextran [ 49 , 50 , 54 , 55 ]. We observed a significant effect of genotype (Glm, poisson model, χ 2 = 839123511, df = 1, p < 0.001).…”

Oxidative Stress Contributes to Slit Diaphragm Defects Caused by Disruption of Endocytosis

“…We and others have previously demonstrated that ZO-1 specifically localizes to the slit diaphragm in fly nephrocytes, and its mislocalization from the cell surface is a reliable indicator of slit diaphragm disruption. 12 , 41 , 42 , 43 …”