Vps34 Deficiency Reveals the Importance of Endocytosis for Podocyte Homeostasis

Abstract

The molecular mechanisms that maintain podocytes and consequently, the integrity of the glomerular filtration barrier are incompletely understood. Here, we show that the class III phosphoinositide 3-kinase vacuolar protein sorting 34 (Vps34) plays a central role in modulating endocytic pathways, maintaining podocyte homeostasis. In mice, podocyte-specific conditional knockout of Vps34 led to early proteinuria, glomerular scarring, and death within 3-9 weeks of age. Vps34-deficient podocytes exhibited substantial vacuolization and foot process effacement. Although the formation of autophagosomes and autophagic flux were impaired, comparisons between podocyte-specific Vps34-deficient mice, autophagy-deficient mice, and doubly deficient mice suggested that defective autophagy was not primarily responsible for the severe phenotype caused by the loss of Vps34. In fact, Rab5-positive endosomal compartments, endocytosis, and fluid-phase uptake were severely disrupted in Vps34-deficient podocytes. Vps34 deficiency in nephrocytes, the podocyte-like cells of Drosophila melanogaster, resulted in a block between Rab5-and Rab7-positive endosomal compartments. In summary, these data identify Vps34 as a major regulator of endolysosomal pathways in podocytes and underline the fundamental roles of endocytosis and fluid-phase uptake for the maintenance of the glomerular filtration barrier.

TOM1 is a PI5P effector involved in the regulation of endosomal maturation

“…PI3P was reported to affect receptor sorting, through its interaction with the ESCRT-0 Hrs protein, but not bulk transport (Petiot et al, 2003). However, in podocytes from the phosphatidylinositol 3-kinase Vps34-invalidated mice, both receptor-mediated endocytosis and fluidphase uptake are compromised at the level of Rab5 and EEA1-positive early endosomes (Bechtel et al, 2013). It is interesting to note that, in our model, contrary to a loss of PI3P, a strong increase in PI5P leads to the blockade.…”

Differential regulatory functions of three classes of phosphatidylinositol and phosphoinositide 3-kinases in autophagy

“…167,168 However, studies from several Pik3c3 knockout animal models suggest that PtdIns3P generation and autophagic function rely predominantly on PIK3C3 activity. 111,169,170 The question of whether class III PtdIns3K is the exclusive kinase responsible for PtdIns3P generation during autophagy remained unsolved until a recent study by Devereaux et al revealed an alternative source of PtdIns3P in Pik3c3 knockout MEFs. 171 In Pik3c3 KO MEFs, it is surprising that PtdIns3P is still detectable using a higher affinity PtdIns3P probe and the PtdIns3P-binding protein WIPI1, and autophagosomes are still observed under starvation conditions; class II PI3K was confirmed as another contributor to the PtdIns3P pool during autophagy, and depletion of class II PI3K further decreases autophagic flux, which is inhibited by Pik3c3 deletion.…”

Cathepsin D in Podocytes Is Important in the Pathogenesis of Proteinuria and CKD

“…17,18 In addition, recent studies have reported that podocytes exert a higher level of autophagy under basal conditions and that autophagy significantly contributes to maintaining the functional integrity of podocytes. [19][20][21][22][23][24] Considering the importance of CD in neuronal autophagy and the resemblance between neurons and podocytes, we hypothesized that it is of particular importance to elucidate the role of CD in podocytes. In this study, we investigated the effects of CD deficiency on podocyte structure and function using podocytespecific, CD-deficient mice.…”