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Abstract: FR-PO969

Protein Phosphatase Mg2+/Mn2+-Dependent 1A (PPM1A) and PTEN Deregulation in Kidney Fibrosis: Novel Mechanisms and Co-Dependency of Expression

Session Information

Category: Pathology and Lab Medicine

  • 1601 Pathology and Lab Medicine: Basic

Authors

  • Tang, Jiaqi, Albany Medical College, Watervliet, New York, United States
  • Goldschmeding, Roel, University Medical Center Utrecht, Utrecht, Netherlands
  • Samarakoon, Rohan, Albany Medical College, Watervliet, New York, United States
  • Higgins, Paul J., Albany Medical College, Watervliet, New York, United States
Background

PPM1A and PTEN emerged as novel suppressors of the TGF-β1 pathway during renal disease. Loss of PPM1A and PTEN, following obstructive renal injury, promoted tubular dysfunction as evident by fibrotic factor deposition, epithelial dedifferentiation and cell cycle arrest. However, the molecular mechanism of PPM1A deregulation in renal fibrosis is unknown. We hypothesize that TGF-β1 orchestrates PPM1A loss of expression and that there is functional collaboration between PPM1A and PTEN during progressive fibrosis.

Methods

A double transgenic mouse model of conditional TGF-β1 renal tubular upregulation (created by crossing Pax8-rtTA with Tet-O-TGF-β1 mice and subsequent doxycycline administration) and the TGF-β1-driven aristolochic acid nephropathy (AAN)-induced renal fibrosis system were employed to determine the role of TGF-β1 in PPM1A deregulation. Human renal epithelial cells (HK-2) and primary kidney fibroblasts (HKFs) with stable PPM1A and PTEN expression or depletion were created to investigate the potential functional interplay among TGF-β1, PPM1A and PTEN.

Results

Renal tubular-specific upregulation of TGF-β1 resulted in tubulointerstitial loss of PPM1A expression 2-3 days post-doxycycline administration in mice. TGF-β1 dramatically attenuated PPM1A and PTEN expression in both HK-2 cells and HKFs via mechanisms involving protein degradation. TGF-β1 promotes ubiquitination of PTEN and PPM1A. A proteasomal inhibitor, MG132 rescued PTEN and PPM1A expression, even in the presence of TGF-β1, along with decreased fibrogenesis. Concurrent loss of PPM1A and PTEN expression in a mouse model of AAN further suggests crosstalk between these repressors. PPM1A stable silencing in HKFs, in fact, resulted in PTEN loss, while PTEN stable depletion decreased PPM1A expression, resulting in a fibro-proliferative response in each case. Transient expression of PPM1A, conversely, increased PTEN protein levels, while PTEN transient induction led to elevated PPM1A expression.

Conclusion

TGF-β1 promotes loss of PPM1A and PTEN expression in vitro and in vivo. We are the first to uncover the pathological functional cooperation between PPM1A and PTEN as they co-regulate each other’s relative abundance, identifying previously unknown links between TGF-β1-repressors in progressive renal injury and CKD.

Funding

  • Other NIH Support