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Kidney Week

Abstract: PO0423

Evidence for a Critical Role of ARNT Homodimerization in Renal Regeneration and Attenuation of Fibrosis

Session Information

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Zeisberg, Michael, Georg-August-Universitat Gottingen, Gottingen, Niedersachsen, Germany
  • Tampe, Bjoern, Georg-August-Universitat Gottingen, Gottingen, Niedersachsen, Germany
Background

Based on the organ-spanning effectiveness of ischemic preconditioning we hypothesized that underlying mechanisms could be utilized to aid the kidney in realizing its endogenous regenerative capacity and to circumvent kidney fibrosis.
Previous studies implied that ARNT, also known as HIF1beta, plays an important role independent of HIF1alpha in ischemic preconditioning.
Here we aimed to explore the mechanisms underlying the reno-protective activity of ARNT and to exploit these mechanisitc insights for novel therapeutic strategies.

Methods

ARNT homodimerization in vivo and in vitro was studied by mass spectrometry, immunoprecipitation, proximity ligation assays, native gel analysis and the use of mutant ARNT variants.
Control of ARNT expression was studies by use of qRT PCR, immunoblot and promoter assays.
To study impact of ARNT homodimerization in vivo we utilzed mure models of UU and CCl4-induced liver fibrosis.

Results

We provide evidence that transcriptional induction of ARNT by administration of FK506 or Tacrolimus enhances renal regeneration and attenuates fibrosis in mice. This effect is not realized when ARNT is targeted by administration of in vivo morpholinos.
We demonstrate that the protective effect of ARNT is only realized when it forms homodimers.
ARNT homodimers acts as transcription factor on ALK3 and the protective effect of ARNT homodimers is not realized when ALK3 is lacking.
We identify that ARNT dimerization decision to form homodimers is controlled by phosphorylation of a critical serine 77 amino acid.
ARNT Ser77 phosphorylation is controlled by PP2A. The PP2A inhibitor LB100 enhances Ser77 phosphorylation, ARNT homodimer formation and attenuates fibrosis in the kidney.
Combination of GPI1046 (to induce ARNT transcription) and LB100 (to enhance ARNT homodimers) has additive effect to protect against fibrosis in kidney and liver.

Conclusion

Increased intracellular ARNT levels through enhanced transcription and augmented homodimerization through phosphorylation of ARNT Ser77 are pre-requisites to realize the reno-protective activity of ARNT. Utilization of this dual mechanism through combination therapy has potential to protect the kidney.