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Abstract: FR-PO253

Active BRAF Inhibits LKB1-AMPK Signaling and Acetyl-CoA Carboxylase Phosphorylation and Increases Renal Fibrosis in a Model of Polycystic Kidney Disease

Session Information

Category: Genetic Diseases of the Kidneys

  • 1101 Genetic Diseases of the Kidneys: Cystic

Authors

  • Zhang, Yan, University of Kansas Medical Center, Kansas City, Kansas, United States
  • Daniel, Emily A., University of Kansas Medical Center, Kansas City, Kansas, United States
  • Raman, Archana, University of Kansas Medical Center, Kansas City, Kansas, United States
  • Reif, Gail, University of Kansas Medical Center, Kansas City, Kansas, United States
  • Parnell, Stephen C., University of Kansas Medical Center, Kansas City, Kansas, United States
  • Wallace, Darren P., University of Kansas Medical Center, Kansas City, Kansas, United States
Background

Dysregulated fatty acid oxidation (FAO) in renal epithelial cells contributes to fibrosis in chronic kidney disease. Evidence has shown that reprogrammed metabolism causes reduced FAO in polycystic kidney disease (PKD), and factors that enhance FAO attenuate disease progression in PKD mice. Liver kinase B1 (LKB1) is the main kinase regulating AMP-activating protein kinase (AMPK) and its downstream target acetyl-CoA carboxylase (ACC), an essential rate-limiting enzyme for FAO. Previously, we showed that BRAF, a kinase upstream of MEK-ERK signaling, is the central intermediate for cAMP-induced proliferation of PKD cells. Collecting duct (CD) expression of active BRAF (BRAFV600E, a common activating mutation) was sufficient to induce cyst formation in wildtype mice as early as 3 weeks of age, resulting in a novel model of PKD, and accelerated cystic disease in Pkd1RC/RC mice. Constitutively active BRAF in melanoma cells inhibits AMPK signaling through phosphorylation of LKB1 at Ser 428, an important inhibitory site. We hypothesize that active BRAF leads to ERK-dependent inhibition of LKB1-AMPK signaling, ACC dephosphorylation, and dysregulated FAO, contributing to renal fibrosis in PKD.

Methods

To investigate the effect of BRAF on renal fibrosis, mice expressing a conditional BRAFV600E were bred with Pkhd1-Cre mice to express active BRAF in CD (BRafCD mice). At 10 weeks, we collected BRafCD kidneys and examined renal fibrosis, macrophage accumulation, and levels of phosphorylated LKB1 (P-LKB1) and ACC (P-ACC).

Results

Expression of active BRAF caused an accumulation of immune cells, determined by staining with the macrophage marker CD68, extensive interstitial fibrosis, and increased levels of blood urea nitrogen, indicating a decline in renal function. CD expression of BRAF increased ERK phosphorylation, as expected, and phosphorylation of LKB1 at Ser 428. There were also striking decreases in ACC and P-ACC levels, which have been shown to reduce FAO, leading to increased matrix production and fibrosis.

Conclusion

In a novel model of renal cystic disease, BRAF activation of MEK-ERK caused phosphorylation of an inhibitory site on LKB1, leading to decreased AMPK phosphorylation of ACC and increased fibrosis. We propose that ACC is a potential therapeutic target to reduce fibrosis in PKD.

Funding

  • NIDDK Support