Cyclin G1 induces maladaptive proximal tubule cell dedifferentiation and renal fibrosis through CDK5 activation
Kensei Taguchi, … , Samir M. Parikh, Craig R. Brooks
Kensei Taguchi, … , Samir M. Parikh, Craig R. Brooks
Published December 1, 2022
Citation Information: J Clin Invest. 2022;132(23):e158096. https://doi.org/10.1172/JCI158096.
View: Text | PDF
Research Article Nephrology

Cyclin G1 induces maladaptive proximal tubule cell dedifferentiation and renal fibrosis through CDK5 activation

Abstract

Acute kidney injury (AKI) occurs in approximately 13% of hospitalized patients and predisposes patients to chronic kidney disease (CKD) through the AKI-to-CKD transition. Studies from our laboratory and others have demonstrated that maladaptive repair of proximal tubule cells (PTCs), including induction of dedifferentiation, G2/M cell cycle arrest, senescence, and profibrotic cytokine secretion, is a key process promoting AKI-to-CKD transition, kidney fibrosis, and CKD progression. The molecular mechanisms governing maladaptive repair and the relative contribution of dedifferentiation, G2/M arrest, and senescence to CKD remain to be resolved. We identified cyclin G1 (CG1) as a factor upregulated in chronically injured and maladaptively repaired PTCs. We demonstrated that global deletion of CG1 inhibits G2/M arrest and fibrosis. Pharmacological induction of G2/M arrest in CG1-knockout mice, however, did not fully reverse the antifibrotic phenotype. Knockout of CG1 did not alter dedifferentiation and proliferation in the adaptive repair response following AKI. Instead, CG1 specifically promoted the prolonged dedifferentiation of kidney tubule epithelial cells observed in CKD. Mechanistically, CG1 promotes dedifferentiation through activation of cyclin-dependent kinase 5 (CDK5). Deletion of CDK5 in kidney tubule cells did not prevent G2/M arrest but did inhibit dedifferentiation and fibrosis. Thus, CG1 and CDK5 represent a unique pathway that regulates maladaptive, but not adaptive, dedifferentiation, suggesting they could be therapeutic targets for CKD.

Authors

Kensei Taguchi, Bertha C. Elias, Sho Sugahara, Snehal Sant, Benjamin S. Freedman, Sushrut S. Waikar, Ambra Pozzi, Roy Zent, Raymond C. Harris, Samir M. Parikh, Craig R. Brooks

×

Figure 5

CG1 binds to and activates CDK5 in PTCs.

Options: View larger image (or click on image) Download as PowerPoint
CG1 binds to and activates CDK5 in PTCs. (A) Representative images of p-...
(A) Representative images of p-CDK5–labeled kidneys from day 42 WT PBS, CG1-KO PBS, WT AA, and CG1-KO AA. Scale bar: 50 μm. (B) Western blot analysis of p-CDK5 in AA-treated WT and CG1-KO kidneys and quantitative analysis in WT AA (n = 5) and CG1-KO AA (n = 5). (C) Real-time PCR analysis of CDK5 and p35 following PBS or AA treatment (PBS, n = 3; AA, n = 8). (D and E) Representative images and quantification of p-CDK5 in WT and CG1-KO primary PTCs treated with PBS or AA (5 μg/mL) for 7 days. Scale bars: 50 μm. n = 5 in each group. HM, high magnification. (F) Representative images of p-CDK5 in hCG1-overexpressing HEK293T cells. Scale bars: 20 μm. (G) Representative Western blots of CG1-Myc and CDK5 in whole-cell extract (WCE) of Myc-CG1–overexpressing HEK293T and immunoprecipitation by Myc. (H) Western blot analysis of E-cadherin, CG1, and total CDK5 in LLC-PK1 cells transfected with human CG1 (hCG1) and/or hCDK5 for 48 hours. (I) Representative images of E-cadherin in AA-treated LLC-PK1 cells transfected with DN-CDK5 or empty vector (EV). Scale bar: 20 μm. (J) Representative Western blot analysis of CTGF in LLC-PK1 cells treated with/without AA (2.5 μg/mL) and PBS, roscovitine, or RO5454291 from Glixx labs (GLX). (K) Western blot analysis of CTGF in WT and CG1-KO primary PTCs treated with AA (5 μg/mL) for 7 days with/without CDK5 inhibitors roscovitine (8 μM) and GLX (50 μM). (L and M) Representative phase-contrast images and quantification of cell size in human CG1–overexpressing (hCCNG1-overexpressing) LLC-PK1 cells with/without roscovitine. Scale bar: 20 μm. n = 25 in each. Data are presented as the mean ± SD. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001 by unpaired, 2-tailed Student’s t test (B) or 1-way ANOVA with Tukey’s post hoc test (C, E, J, K, and M).