Limits...
The Lowe syndrome protein OCRL1 is required for endocytosis in the zebrafish pronephric tubule.

Oltrabella F, Pietka G, Ramirez IB, Mironov A, Starborg T, Drummond IA, Hinchliffe KA, Lowe M - PLoS Genet. (2015)

Bottom Line: This coincides with a reduction in levels of the scavenger receptor megalin and its accumulation in endocytic compartments, consistent with reduced recycling within the endocytic pathway.We also observe reduced numbers of early endocytic compartments and enlarged vacuolar endosomes in the sub-apical region of pronephric cells.Catalytic activity of OCRL1 is required for renal tubular endocytosis and the endocytic defect can be rescued by suppression of PIP5K.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.

ABSTRACT
Lowe syndrome and Dent-2 disease are caused by mutation of the inositol 5-phosphatase OCRL1. Despite our increased understanding of the cellular functions of OCRL1, the underlying basis for the renal tubulopathy seen in both human disorders, of which a hallmark is low molecular weight proteinuria, is currently unknown. Here, we show that deficiency in OCRL1 causes a defect in endocytosis in the zebrafish pronephric tubule, a model for the mammalian renal tubule. This coincides with a reduction in levels of the scavenger receptor megalin and its accumulation in endocytic compartments, consistent with reduced recycling within the endocytic pathway. We also observe reduced numbers of early endocytic compartments and enlarged vacuolar endosomes in the sub-apical region of pronephric cells. Cell polarity within the pronephric tubule is unaffected in mutant embryos. The OCRL1-deficient embryos exhibit a mild ciliogenesis defect, but this cannot account for the observed impairment of endocytosis. Catalytic activity of OCRL1 is required for renal tubular endocytosis and the endocytic defect can be rescued by suppression of PIP5K. These results indicate for the first time that OCRL1 is required for endocytic trafficking in vivo, and strongly support the hypothesis that endocytic defects are responsible for the renal tubulopathy in Lowe syndrome and Dent-2 disease. Moreover, our results reveal PIP5K as a potential therapeutic target for Lowe syndrome and Dent-2 disease.

No MeSH data available.


Related in: MedlinePlus

Reduced endosomal staining in OCRL1 deficient pronephros.A-C. Confocal transverse sections of the zebrafish proximal pronephric tubule of 72 hpf wild-type (WT) and ocrl-/- mutant embryos labelled with antibodies to EEA1 or endofin (A), or to GFP (B and C) to detect expressed GFP-Rab11 (B) or GFP-Rab7 (C). White dashed lines indicate the outline of pronephric tubules. Scale bars represent 10 μm.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4383555&req=5

pgen.1005058.g003: Reduced endosomal staining in OCRL1 deficient pronephros.A-C. Confocal transverse sections of the zebrafish proximal pronephric tubule of 72 hpf wild-type (WT) and ocrl-/- mutant embryos labelled with antibodies to EEA1 or endofin (A), or to GFP (B and C) to detect expressed GFP-Rab11 (B) or GFP-Rab7 (C). White dashed lines indicate the outline of pronephric tubules. Scale bars represent 10 μm.

Mentions: It has previously been shown in both mouse and zebrafish that loss of megalin results in a profound reduction in abundance of endocytic compartments in the renal proximal tubule, likely due to reduced flux of material through the endocytic pathway [33,40,41]. We therefore performed fluorescence microscopy to visualise endocytic compartments in the proximal tubular cells of ocrl-/- embryos, which have reduced endocytosis and lower megalin abundance in comparison to controls (Figs. 1 and 2). Early endosomes, labelled with antibodies to EEA1 or endofin, were abundant in the apical pole in control embryos (Fig. 3A). Although the distribution of EEA1 and endofin in ocrl-/- embryos was similar to controls, the labelling intensity was weaker (Fig. 3A). This was also true for Rab11, which marks recycling endosomes (Fig. 3B), while late endosomes, labelled with GFP-Rab7, were not obviously affected (Fig. 3C).


The Lowe syndrome protein OCRL1 is required for endocytosis in the zebrafish pronephric tubule.

Oltrabella F, Pietka G, Ramirez IB, Mironov A, Starborg T, Drummond IA, Hinchliffe KA, Lowe M - PLoS Genet. (2015)

Reduced endosomal staining in OCRL1 deficient pronephros.A-C. Confocal transverse sections of the zebrafish proximal pronephric tubule of 72 hpf wild-type (WT) and ocrl-/- mutant embryos labelled with antibodies to EEA1 or endofin (A), or to GFP (B and C) to detect expressed GFP-Rab11 (B) or GFP-Rab7 (C). White dashed lines indicate the outline of pronephric tubules. Scale bars represent 10 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4383555&req=5

pgen.1005058.g003: Reduced endosomal staining in OCRL1 deficient pronephros.A-C. Confocal transverse sections of the zebrafish proximal pronephric tubule of 72 hpf wild-type (WT) and ocrl-/- mutant embryos labelled with antibodies to EEA1 or endofin (A), or to GFP (B and C) to detect expressed GFP-Rab11 (B) or GFP-Rab7 (C). White dashed lines indicate the outline of pronephric tubules. Scale bars represent 10 μm.
Mentions: It has previously been shown in both mouse and zebrafish that loss of megalin results in a profound reduction in abundance of endocytic compartments in the renal proximal tubule, likely due to reduced flux of material through the endocytic pathway [33,40,41]. We therefore performed fluorescence microscopy to visualise endocytic compartments in the proximal tubular cells of ocrl-/- embryos, which have reduced endocytosis and lower megalin abundance in comparison to controls (Figs. 1 and 2). Early endosomes, labelled with antibodies to EEA1 or endofin, were abundant in the apical pole in control embryos (Fig. 3A). Although the distribution of EEA1 and endofin in ocrl-/- embryos was similar to controls, the labelling intensity was weaker (Fig. 3A). This was also true for Rab11, which marks recycling endosomes (Fig. 3B), while late endosomes, labelled with GFP-Rab7, were not obviously affected (Fig. 3C).

Bottom Line: This coincides with a reduction in levels of the scavenger receptor megalin and its accumulation in endocytic compartments, consistent with reduced recycling within the endocytic pathway.We also observe reduced numbers of early endocytic compartments and enlarged vacuolar endosomes in the sub-apical region of pronephric cells.Catalytic activity of OCRL1 is required for renal tubular endocytosis and the endocytic defect can be rescued by suppression of PIP5K.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.

ABSTRACT
Lowe syndrome and Dent-2 disease are caused by mutation of the inositol 5-phosphatase OCRL1. Despite our increased understanding of the cellular functions of OCRL1, the underlying basis for the renal tubulopathy seen in both human disorders, of which a hallmark is low molecular weight proteinuria, is currently unknown. Here, we show that deficiency in OCRL1 causes a defect in endocytosis in the zebrafish pronephric tubule, a model for the mammalian renal tubule. This coincides with a reduction in levels of the scavenger receptor megalin and its accumulation in endocytic compartments, consistent with reduced recycling within the endocytic pathway. We also observe reduced numbers of early endocytic compartments and enlarged vacuolar endosomes in the sub-apical region of pronephric cells. Cell polarity within the pronephric tubule is unaffected in mutant embryos. The OCRL1-deficient embryos exhibit a mild ciliogenesis defect, but this cannot account for the observed impairment of endocytosis. Catalytic activity of OCRL1 is required for renal tubular endocytosis and the endocytic defect can be rescued by suppression of PIP5K. These results indicate for the first time that OCRL1 is required for endocytic trafficking in vivo, and strongly support the hypothesis that endocytic defects are responsible for the renal tubulopathy in Lowe syndrome and Dent-2 disease. Moreover, our results reveal PIP5K as a potential therapeutic target for Lowe syndrome and Dent-2 disease.

No MeSH data available.


Related in: MedlinePlus