Gq signaling causes glomerular injury by activating TRPC6
Liming Wang, … , Michelle P. Winn, Robert F. Spurney
Liming Wang, … , Michelle P. Winn, Robert F. Spurney
Published April 6, 2015
Citation Information: J Clin Invest. 2015;125(5):1913-1926. https://doi.org/10.1172/JCI76767.
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Research Article Nephrology

Gq signaling causes glomerular injury by activating TRPC6

Abstract

Familial forms of focal segmental glomerulosclerosis (FSGS) have been linked to gain-of-function mutations in the gene encoding the transient receptor potential channel C6 (TRPC6). GPCRs coupled to Gq signaling activate TRPC6, suggesting that Gq-dependent TRPC6 activation underlies glomerular diseases. Here, we developed a murine model in which a constitutively active Gq α subunit (GqQ209L, referred to herein as GqQ>L) is specifically expressed in podocytes and examined the effects of this mutation in response to puromycin aminonucleoside (PAN) nephrosis. We found that compared with control animals, animals expressing GqQ>L exhibited robust albuminuria, structural features of FSGS, and reduced numbers of glomerular podocytes. Gq activation stimulated calcineurin (CN) activity, resulting in CN-dependent upregulation of TRPC6 in murine kidneys. Deletion of TRPC6 in GqQ>L-expressing mice prevented FSGS development and inhibited both tubular damage and podocyte loss induced by PAN nephrosis. Similarly, administration of the CN inhibitor FK506 reduced proteinuria and tubular injury but had more modest effects on glomerular pathology and podocyte numbers in animals with constitutive Gq activation. Moreover, these Gq-dependent effects on podocyte injury were generalizable to diabetic kidney disease, as expression of GqQ>L promoted albuminuria, mesangial expansion, and increased glomerular basement membrane width in diabetic mice. Together, these results suggest that targeting Gq/TRPC6 signaling may have therapeutic benefits for the treatment of glomerular diseases.

Authors

Liming Wang, Grant Jirka, Paul B. Rosenberg, Anne F. Buckley, Jose A. Gomez, Timothy A. Fields, Michelle P. Winn, Robert F. Spurney

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Figure 6

Effect of CN inhibition on PAN nephrosis in GqQ>L mice.

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Effect of CN inhibition on PAN nephrosis in GqQ>L mice. (A) FK506 inh...
(A) FK506 inhibited albuminuria induced by PAN in GqQ>L mice. (B and C) The development of FSGS was similar in GqQ>L mice treated with either vehicle or FK506. Scale bars: 10 μm. (D and E) FK506 significantly inhibited tubule dilation and casts. Scale bars: 40 μm. (F and G) FK506 significantly preserved SYN expression. (H) PAN nephrosis significantly reduced podocyte numbers in GqQ>L mice treated with vehicle compared with those in an untreated non-Tg control group. FK506 caused a modest and nonsignificant increase in podocyte numbers. (I) FK506 tended to reduce expression of the CN-responsive genes Trpc6 and Rcan1. (J) The increase in Cox2 mRNA caused by induction of GqQ>L (Figure 4I) was not affected by FK506. For the albuminuria studies, 16 vehicle-treated mice and 21 mice treated with FK506 were used. Sixteen vehicle-treated mice and 8 mice treated with FK506 were used for the histologic studies. For the immunoblot studies, 4 vehicle-treated mice and 4 mice treated with FK506 were used. To assess podocyte numbers, 11 untreated controls, 13 GqQ>L mice treated with vehicle, and 8 GqQ>L mice treated with FK506 were used. For qRT-PCR, mRNA samples from 14 vehicle-treated mice and 7 mice treated with FK506 were used. *P < 0.05, †P < 0.025, or ‡P < 0.01 versus the indicated groups using Fisher’s exact test for histologic data, a 2-tailed t test for albuminuria and immunoblotting data, and ANOVA, followed by Bonferroni’s post-hoc analysis, for the other studies.