Fig 2: Protein expression of CaSR and claudin-14 in a calcium oxalate environment. (A) Protein expression of CaSR and claudin-14 in NRK-52E cells. The data are presented as the mean ± standard deviation of three independent experiments. *p < 0.05 vs the control group. Statistical analyses were performed by two-tailed unpaired t-tests. (B) Immunohistochemical distribution of CaSR and claudin-14 protein expression in the rat kidney after 4 weeks of ethylene glycol treatment. The left column comprises representative images showing the expression of CaSR and claudin-14 in 0-week-old rats, and the right column comprises representative images showing the expression of CaSR and claudin-14 in 4-week-old rats. COM, calcium oxalate monohydrate; CaSR, calcium-sensing receptor.

Fig 3: CaSR regulates STAT3 phosphorylation levels through PKA. (A) Protein expression of the p-PKA substrate and intracellular cAMP level in NRK-52E cells specifically activated with R568 or inhibited with NPS2134 for CaSR. (B) Protein expression of p-STAT3 and claudin-14 in NRK-52E cells specifically activated with 8-Bromca-cAMP or H 89 2HCl inhibited by NPS2134 for PKA. The data are presented as the mean ± standard deviation of three independent experiments. *p < 0.05 vs the control group; **p < 0.01 vs.; △ p < 0.05 vs the COM group (the second band); △△ p < 0.01 vs the COM group. The control group. Statistical analyses were performed by one-way analysis of variance. COM, calcium oxalate monohydrate; CaSR, calcium-sensing receptor; STAT3, signal transducer and activator of transcription 3; PKA, protein kinase (A).

Fig 4: STAT3 is a transcription factor involved in CaSR regulation of claudin-14. (A) NRK-52E cells were induced with COM (0, 33.5, 67 or 134 μg/cm2 of cells) for 6 h, after which p-STAT3 protein expression was examined by Western blotting. (B) Luciferase activity of NRK-52E cells specifically activated with IL-6 or inhibited with STAT3-IN-1. (C) The protein expression of p-STAT3 and claudin-14 in NRK-52E cells specifically activated with R568 or inhibited with NPS2134. (D) Protein expression of CaSR and claudin-14 in NRK-52E cells specifically activated with IL-6 or inhibited with STAT3-IN-1. The data are presented as the mean ± standard deviation of three independent experiments. *p < 0.05 vs the control group; **p < 0.01 vs the control group; △ p < 0.05 vs the COM group (the second band); △△ p < 0.01 vs the COM group. Statistical analyses were performed by one-way analysis of variance. COM, calcium oxalate monohydrate; CaSR, calcium sensing receptor; STAT3, signal transducer and activator of transcription 3.