Phosphatidylinositol 3-kinase signaling determines kidney size
Jian-Kang Chen, … , Eric G. Neilson, Raymond C. Harris
Jian-Kang Chen, … , Eric G. Neilson, Raymond C. Harris
Published May 18, 2015
Citation Information: J Clin Invest. 2015;125(6):2429-2444. https://doi.org/10.1172/JCI78945.
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Research Article Nephrology

Phosphatidylinositol 3-kinase signaling determines kidney size

Abstract

Kidney size adaptively increases as mammals grow and in response to the loss of 1 kidney. It is not clear how kidneys size themselves or if the processes that adapt kidney mass to lean body mass also mediate renal hypertrophy following unilateral nephrectomy (UNX). Here, we demonstrated that mice harboring a proximal tubule–specific deletion of Pten (PtenptKO) have greatly enlarged kidneys as the result of persistent activation of the class I PI3K/mTORC2/AKT pathway and an increase of the antiproliferative signals p21Cip1/WAF and p27Kip1. Administration of rapamycin to PtenptKO mice diminished hypertrophy. Proximal tubule–specific deletion of Egfr in PtenptKO mice also attenuated class I PI3K/mTORC2/AKT signaling and reduced the size of enlarged kidneys. In PtenptKO mice, UNX further increased mTORC1 activation and hypertrophy in the remaining kidney; however, mTORC2-dependent AKT phosphorylation did not increase further in the remaining kidney of PtenptKO mice, nor was it induced in the remaining kidney of WT mice. After UNX, renal blood flow and amino acid delivery to the remaining kidney rose abruptly, followed by increased amino acid content and activation of a class III PI3K/mTORC1/S6K1 pathway. Thus, our findings demonstrate context-dependent roles for EGFR-modulated class I PI3K/mTORC2/AKT signaling in the normal adaptation of kidney size and PTEN-independent, nutrient-dependent class III PI3K/mTORC1/S6K1 signaling in the compensatory enlargement of the remaining kidney following UNX.

Authors

Jian-Kang Chen, Kojiro Nagai, Jianchun Chen, David Plieth, Masayo Hino, Jinxian Xu, Feng Sha, T. Alp Ikizler, C. Chad Quarles, David W. Threadgill, Eric G. Neilson, Raymond C. Harris

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Figure 12

Knockdown of class III PI3K activity inhibits mTOR translocation to lysosomal membranes and activation in cultured renal proximal tubule epithelial cells.

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Knockdown of class III PI3K activity inhibits mTOR translocation to lyso...
(A–C) Mouse MCT cells transfected with either scrambled control siRNA or class III PI3K–specific siRNA and made quiescent before treatment with 1× amino acids, 100 nM insulin, or vehicle (saline) alone for 30 minutes. Cell lysates were subjected to immunoblotting (A and B) and class III PI3K activity assays (C, top), along with confirmation of the levels of immunoprecipitated class III PI3K (C, bottom) by immunoblotting following immunoprecipitation with anti–class III PI3K antibodies. (D and E) MCT cells were transfected with scrambled control siRNA (D) or siRNA specific for mouse class III PI3K (E). Cells were made quiescent 48 hours after transfection as detailed in Methods and then restimulated with vehicle control (–AA) or 1× amino acids (+AA) for 10 minutes. Cells were then processed for coimmunofluorescence staining to detect endogenous mTOR (green) and the lysosomal membrane marker LAMP1 (red), along with DAPI to highlight nuclei (blue), and imaged by confocal microscopy. The mTOR and LAMP1 localization pattern was exhibited by 90% to 100% of the cells. Shown are representative images from at least 3 independent cell culture experiments with similar results. Scale bar: 5 μm.