Effects of Pkd1 Deficiency on the Response to Endoplasmic Reticulum Stress Induced by Tunicamycin

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Background: Most cases of autosomal dominant polycystic kidney disease are caused by a germline variant in PKD1, the gene that encodes polycystin-1 (PC1). Pkd1 deficiency has been shown to increase susceptibility to kidney ischemia/reperfusion. Proper functional levels of PC1 depend on its appropriate processing in the endoplasmic reticulum (ER). In response to a cellular insult, different pathways are activated to protect the cell during transient stress or to induce apoptosis under persistent stress. Previous studies have investigated how modulation of ER stress (ERS) can influence cystic disease progression but not the potential effect of Pkd1 deficiency on response to ERS induction. Methods: We employed an in vitro model comprising Pkd1+/+, Pkd1+/-, and Pkd1-/- kidney tubular epithelial cells to assess this relationship. These cells were exposed to the ERS inducer tunicamycin (TUN) at 1ug/mL and ER protein expression was analyzed by western blot. Results: Pkd1+/- cells exhibited higher baseline expression of GRP78 than Pkd1+/+ cells, while Pkd1-/- cells showed an intermediary profile [Pkd1+/+: 1.00±0.16 vs Pkd1+/-: 1.62±0.32 vs Pkd1-/-: 1.29±0.24 fold change (FC); n=4; P=0.02]. On the other hand, Pkd1+/+ cells showed a numerically more intense activation of the IRE1α/XBP1s pathway than the other cells in response to TUN [XBP1s expression; 6-h exposure - Pkd1+/+: control 0.86 (0.69-1.03) vs TUN 2.99 (2.42-3.54) FC; Pkd1+/-: control 1.25±0.09 vs TUN 1.77±0.44 FC; Pkd1-/-: 0.75±0.12 vs TUN 1.45±0.22 FC; n=4; comparisons statistically significant]. Pkd1-/- cells, in turn, showed a numerically greater CHOP elevation after treatment with TUN compared to the other cell lines (6-h exposure; Pkd1+/+: control 1.14±0.08 vs TUN 1.76±0.15 FC; Pkd1+/-: control 0.87±0.14 vs TUN 2.23±0.16 FC; Pkd1-/-: control 1.08±0.11 vs TUN 2.61±0.39 FC; n=4; comparisons statistically significant). TUN did not determine significant changes in cleaved caspase-3 levels in the 3 cell lines. Conclusion: Our data suggest that Pkd1 deficiency may hinder the adaptive response to TUN-induced ERS, favoring cell death, affecting the response to ERS. Our findings may have also provided key information on the mechanism of PC1 protection against kidney insults. Funding: Government Support – Non-U.S.

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