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Abstract: FR-OR07

Hepatocyte Nuclear Factor 4 Alpha 2 Is a Novel Osteoblast Transcription Factor That Plays a Role in CKD-MBD

Session Information

Category: Bone and Mineral Metabolism

  • 401 Bone and Mineral Metabolism: Basic

Authors

  • Martinez-Calle, Marta, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Courbon, Guillaume, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Hunt-Tobey, Bridget, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Spindler, Jadeah Jeannine, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Wang, Xueyan, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • dos Reis, Luciene, Hospital das Clinicas da Faculdade de Medicina de Botucatu, Botucatu, São Paulo, Brazil
  • Martins, Carolina Steller wagner, Hospital das Clinicas da Faculdade de Medicina de Botucatu, Botucatu, São Paulo, Brazil
  • Moyses, Rosa M.A., Hospital das Clinicas da Faculdade de Medicina de Botucatu, Botucatu, São Paulo, Brazil
  • Martin, Aline, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • David, Valentin, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
Background

Renal osteodystrophy (ROD) is a poorly understood disorder of bone metabolism that affects virtually all patients with chronic kidney disease (CKD), and is associated with adverse clinical outcomes including fractures, cardiovascular events and death. Using RNA (RNAseq) and Chromatin Immunoprecipitation (ChIPseq) sequencing approaches and complementary mouse models, we aimed to identify novel bone-derived factors that contribute to the onset and progression of ROD.

Methods

We first performed RNAseq in bone biopsies isolated from patients and mice with and without CKD and identified hepatocyte nuclear factor (HNF) 4 alpha as one of the top regulated genes with reduced expression in CKD. Next, we generated mice harboring a conditional deletion of Hnf4a in osteoblasts and osteocytes (Hnf4αOc-cKO) and studied their bone phenotype at 6 and 12 weeks of age. In parallel, we characterized the transcriptome and HNF4a cistrome of MC3T3 and osteoblast cultures lacking (Hnf4αKO) or overexpressing Hnf4α (Hnf4αTg). Finally, we evaluated the impact of restoring osteoblastic Hnf4a expression in mice with CKD.

Results

Osteoblast deletion of Hnf4α resulted in impaired osteogenesis in cells and mice. Hnf4αOc-cKO mice showed reduced bone formation and increased bone resorption, resulting in a ~50% loss of trabecular bone volume at 12 weeks of age compared to wild-type (WT) littermates. In addition, osteoblast cultures isolated from Hnf4αOc-cKO mice showed altered differentiation and mineralization compared to WT cells. In sharp contrast, Hnf4αTg cells showed increased expression of osteoblastic markers, such as Runx2, Sp7 (Osterix) and Bglap (Osteocalcin), and ChIPseq analysis demonstrated that HNF4α is a master regulator of osteogenic genes. As a consequence, osteoblast specific overexpression of Hnf4α in mice with CKD delayed the onset of ROD and resulted in a 2-fold increase in trabecular bone volume and ~40% reduction of cortical porosity compared to CKD mice.

Conclusion

Our results establish the direct role of HNF4α in the regulation of osteogenesis, suggest that osseous HNF4α deficiency contributes to the pathogenesis of ROD and propose a novel mechanism to explain intrinsic bone defects in patients with CKD.

Funding

  • NIDDK Support