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Important role for the mammalian‐target‐of‐rapamycin (mTOR) in the collecting duct as a determinant of transporter/channel profile and function
Author(s) -
Brown Aaron L,
Lee Hwal,
Tiwari Swasti,
Li Lijun,
Ecelbarger Carolyn M.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.857.11
Subject(s) - epithelial sodium channel , medicine , endocrinology , excretion , chemistry , urine , aquaporin 2 , aldosterone , natriuresis , pi3k/akt/mtor pathway , kidney , sodium , biology , signal transduction , biochemistry , mechanical engineering , organic chemistry , water channel , engineering , inlet
mTOR, a serine‐threonine‐specific kinase, is known as a central energy integrator of a number of signaling pathways and may have a role in renal transport in the collecting duct (CD), including facilitating ENaC activation by insulin. To further elucidate the role of mTOR in the CD principal cell, we generated a CD‐principal‐cell‐select mTOR KO mouse by Cre‐lox recombination using aquaporin‐2 (AQP2) promoter to drive Cre‐recombinase. Mice were of normal appearance and body weight. Basal urine volume (24 hr) and kidney weights were not different. A benzamil‐sensitivity test showed that KO mice had significantly reduced urine chloride (Cl − ) concentrations (mM), as well as, absolute excretion of both sodium (Na + ) and Cl − (μmol/4 hours), as compared to the WT suggesting reduced ENaC activity. To further explore this finding, urine (24‐hr) was collected in male mice under normal (NS) and low‐Na+ (LS) diets (< 0.05% Na + ) over the course of a week (n = 14 mice/genotype/diet). Urine Na + concentrations under LS diet were higher in the KO on day 1, but were reduced to a similar level by the end of the week. Surprisingly, urine aldosterone excretion was slightly, but significantly, lower in the KO mice in the basal period and after 1 day LS, but rose to similar level as the WT mice by day 7. After a recovery week, mice were split into two groups and randomly assigned to receive one‐of‐the‐two diets for another week, then euthanized. Blood analyzed by iSTAT showed modest alkalosis in the KO, especially under normal Na+, i.e., slightly elevated pH, HCO 3 , base excess, and reduced pCO 2 (all significant differences). Plasma Na+ was slightly lower in the KO under NS, but not different from WT under LS. No differences in plasma K+ or Cl− were found. Western blotting conducted on cortex homogenates showed mTORKO had significantly reduced β‐ and γ‐subunits of the epithelial sodium channel (ENaC), aquaporin‐2 (AQP2), and rhesus protein family b‐glycoprotein (Rhbg) relative to WT under both dietary conditions. In the inner medulla, AQP2 was about 50% lower in the KO mice under NS, but actually 20% higher than WT under LS. We predict this may represent compensation for down‐regulation in cortical CD. Overall, these results support a central role for CD mTOR in homeostatic modeling of the CD and expression of key transport proteins. Support or Funding Information Georgetown University Department of Medicine; CTSA Georgetown/Howard; Department of Biochemistry (AB)