Cilia deficient renal tubule cells are primed for injury with mitochondrial defects and aberrant tryptophan metabolism

The exocyst and Ift88 are necessary for primary ciliogenesis. Overexpression of Exoc5 (OE), a central exocyst component, resulted in longer cilia and enhanced injury recovery. Mitochondria are involved in acute kidney injury (AKI). To investigate cilia and mitochondria, basal respiration and mitochondrial maximal and spare respiratory capacity were measured in: Exoc5 OE, Exoc5 knockdown (KD), Exoc5 ciliary targeting sequence mutant (CTS-mut), control MDCK, Ift88 knockout (KO), and Ift88 rescue cells. In Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells, these parameters were decreased. In Exoc5 OE and Ift88 rescue cells they were increased. Reactive oxygen species were higher in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells compared to Exoc5 OE, control, and Ift88 rescue cells. By EM, mitochondria appeared abnormal in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells. A metabolomics screen of control, Exoc5 KD, Exoc5 CTS-mut, Exoc5 OE, Ift88 KO, and Ift88 rescue cells showed a marked increase in tryptophan levels in Exoc5 CTS-mut (113-fold) and Exoc5 KD (58-fold) compared to control cells. A 21% increase was seen in Ift88 KO compared to rescue cells. In Exoc5 OE compared to control cells tryptophan was decreased 59%. To determine effects of ciliary loss on AKI, we generated proximal tubule-specific Exoc5 and Ift88 KO mice. These mice had loss of primary cilia, decreased mitochondrial ATP synthase, and increased tryptophan in proximal tubules with greater injury following ischemia reperfusion. These data indicate that cilia deficient renal tubule cells are primed for injury with mitochondrial defects in tryptophan metabolism.