Increased aquaporin expression and urine concentration in epidermal growth factor (EGF) knockout mice

Water homeostasis is a critical kidney function, but the mechanism is complex and involves several signaling pathways. The canonical pathway involves the action of vasopressin (VP) on its receptor (V2R), resulting in increased cAMP, protein kinase A activation, and changes in the phosphorylation state of AQP2. This leads to aquaporin-2 (AQP2) membrane accumulation in principal cells, increased collecting duct (CD) water permeability, and urine concentration. We and others previously reported that epidermal growth factor (EGF) inhibits VP-induced CD water permeability, and inhibits AQP2 phosphorylation, and that the EGFR inhibitor Erlotinib mimics the effect of VP on AQP2 trafficking and water permeability in mice. To examine the role of EGF in greater depth, we studied urine concentrating ability and AQP2 expression using a mouse model that lacks EGF (EGF -/- mice). 12-week-old mice were acclimated to metabolic cages. Knockout mice of both genders weighed 15% less than WT littermates and had smaller kidneys. 24-hour urine collection showed that the knockout mice produced less urine than the wild-type mice, and their urine was significantly more concentrated. Similar results were observed with urine collected directly from the bladder, where the urine of male (2532 ± 400 mOsm/kg; n = 23) and female (2666 ± 430; n=21) knockout mice was markedly more hypertonic than the wild-type mice (1824 ± 480; n=21 and 1681 ± 467; n=16, respectively). Serum osmolarity was slightly, but not significantly, higher in EGF -/- mice than in wild type mice in males (330 vs 327 mOsm/kg) and (325 vs 320 mOsm/kg). Western blot analysis was performed on total kidney lysates to study the effect of EGF depletion on proteins regulating water and salt reabsorption. EGF KO mice had significantly increased expression of AQP2 compared to wild-type (144 % ± 34 vs 100 % ± 25, n=18, p<0.001). Expression of Na/K-ATPase increased in the knockout mice, while no significant change in expression of the sodium chloride cotransporter (NCC) was observed. Interestingly, there was a significant reduction of the V-ATPase B1 subunit (associated with intercalated cells) in knockout mice compared to wild-type. Finally, we implanted osmotic minipumps delivering EGF or control solution into the male EGF KO mice. After three days, there was an increase in urine volume from 0.92 ± 0.46 to 1.35 ± 0.54 ml/ml that did not quite reach significance due to variability among animals (n=10, p=0.07) whereas there was a marked and significant reduction of urine osmolarity in the same mice from 4472 ± 1014 to 2887 ± 606 mOsm/kg (n=10, p<0.001). These results show that EGF plays an important role in moderating the VP-induced regulation of water reabsorption and that its absence results in increased expression of AQP2 water channels and increased urine concentration, likely resulting from the unopposed action of VP on water channel expression. This work was supported by the National Institutes of Health (NIH) grant DK096586, DK057521 and DK043351. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.