Abstract P124: Role of Add3 Dysfunction in Renal Epithelial Cells in the Development of Renal Injury in Fhh Rats

Abstract

The Fawn Hooded Hypertensive Rat (FHH) is a genetic model of hypertension, in which Add3 has been identified as a candidate gene for renal injury but the mechanism is unknown. The present study examined the effects of knockdown of Add3 on rat renal epithelial (NRK) cells which are the model system for podocytes and proximal tubular cells. Knockdown of the expression of Add3 using a 27-mer Dicer-substrate RNAi (DsiRNA) decreased cell viability using an MTS assay by 50% in comparison to cells treated with vehicle or scrambled DSiRNA (Add3DsiRNA, OD 0.5±0.1; untreated cells 0.9±0.1; NC-1 0.9±0.1; n=8, P<0.001). F-actin immunostaining revealed that Add3 DSiRNA markedly disrupted the cytoskeleton, and the F-actin staining intensity/cell ratio was significantly reduced (untreated 543±47, n=552 cells; NC-1 592±39, n=566 cells; Add3DsiRNA 430±58, n=385 cells, P<0.05). The maximum mitochondrial respiratory rate was reduced in Add3 DsiRNA treated cells (untreated 444±42; NC-1 414±32; Add3 DsiRNA 275±16 pmole/min/μg, P<0.01). Proton leak was higher (untreated 42±3; NC-1 40±4; Add3 DsiRNA 63±5 pmole/min/μg, P<0.002) and oxygen consumption coupled to ATP production was decreased in Add3 DsiRNA treated cells (untreated 229±12, n=9; NC-1 200±12, n=8; Add3 DsiRNA 146±11 pmole/min/μg, n=9, P<0.001). Spare respiratory capacity, an index of cell fitness, was reduced by knockdown of Add3 (untreated 154±42, n=9: NC-1 143±32, n=8; Add3DsiRNA 33±16 pmole/min/μg, n=9, P<0.001). Non-mitochondrial oxygen consumption rate (OCR/μg protein) increased in cells treated with Add3 DsiRNA (untreated 57±7; NC-1 80±11; Add3DsiRNA 116±15 pmole/min/μg, P<0.01) suggesting a possible metabolic switch to glycolytic oxygen consumption. In conclusion, knockdown of Add3 in NRK cells disrupts the actin cytoskeleton, promotes mitochondrial dysfunction and decreases cell viability. Loss of Add3 function may contribute to proteinuria in FHH rats by altering the cytoskeleton and promoting effacement and loss of podocytes and the reuptake of filtered protein in the proximal tubule.