Insect nephrocytes as a model for human podocyte ageing

Authors: Sivakumar, S., Coward, R. and Hartley, P.S.

Start date: 19 June 2017

Objectives: Mammalian podocytes exhibit age-dependent functional decline that may be associated with reduced renal function. In addition, disruption of metabolism may hasten cellular ageing and impact podocyte function in conditions such as diabetic nephropathy. Studying ageing using mammalian models is ethically, technically and temporally challenging. Alternative models are therefore attractive. Drosophila nephrocytes are large pericardial cells with slit diaphragms that are functionally and genetically analogous to human podocytes (figure 1a). In this work we examined whether Drosophila nephrocytes may be used to model podocyte ageing.

Methods: Nephrocyte ageing was analysed in Drosophila aged for 1 to 5 weeks (about late 'middle age' for a fly). Nephrocyte ageing in insulin signalling mutants was also analysed, as was the impact on ageing of silencing insulin signalling genes specifically in nephrocytes using the dKlf15-Gal4 driver. Antisera were raised to dumbfounded (duf; ortholog of the human NEPH1 protein) and used to stain nephrocytes. Endocytic function of nephrocytes was monitored using fluorescently tagged 10kDa dextran. Intracellular calcium was monitored in nephrocytes expressing the GCamp6 calcium reporter under the control of the Dorothy-Gal4 driver.

Results: Pericardial nephrocytes underwent age-dependent hypertrophy, developed abnormal calcium handling, reduced endocytic function and death. Nephrocytes were smaller and exhibited extended health-span in flies heterozygous for loss-of-function mutations in Chico (IRS1), PI3K and Thor2 (4E-BP) (figure 1b). In contrast, silencing insulin signalling genes (InR and Akt) specifically in nephrocytes, led to a premature ageing phenotype.

Conclusions: These data confirm nephrocyte ageing within Drosophila and highlight the possibility conserved ageing mechanisms relevant to mammalian podocytes. The data also indicate that disruption of insulin signalling may have both a protective and deleterious impact on cellular ageing which depend on the genetic context for loss of function. It is concluded that the Drosophila nephrocyte is an instructive and tractable model of podocyte ageing in humans.

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