Inducible R138Q Podocin Knock-in Mouse Model

We have recently developed an inducible podocin KO mouse model (Nphs2Flox/-, Cre+). In these mice, albuminuria occurs within one to two weeks following tamoxifen injection, progressing within 4 weeks to massive non-selective proteinuria and renal failure, in parallel with the development of FSGS and tubulo-interstitial lesions. This model will permit for the first time to study the effects of the most common human podocin mutation in vivo, and is a unique tool to assess the efficacy of pharmacological approaches to attenuate proteinuria and prevent progressive nephron degeneration.

We will first characterize the phenotype emerging from induction of the podocin defect in different phases of postnatal life. Once the spontaneous disease evolution after induction of the podocin defect has been delineated, several interventional protocols will be applied:

By virtue of their antiproteinuric, anti-inflammatory and antifibrotic properties, antagonists of the renin-angiotensin system [(ACE inhibitors (ACEi) and angiotensin type-1 receptor blockers (ARB)] have a renoprotective potential in chronic progressive nephropathies, especially if these involve glomerular proteinuria. High dose ACEi and ARBs, alone and in combination, slow down renal failure progression both in human nephropathies and in rodent disease models. However, the efficacy of RAS blockade in genetically defined nephrotic syndrome is as yet unclear.
Groups of young adult animals will be be treated after tamoxifen administration, either with the most efficacious RAS blockade available (high-dose ACEI+ARB, ramipril 10 mg/kg/d + valsartan 50 mg/kg/d) or placebo. The course of weight and proteinuria will be monitored over 4 weeks and animal survival, final glomerular filtration rate and detailed histopathological status (glomerulosclerosis, tubulointerstitial changes) assessed at the end of the treatment period. Besides this preventive approach, the potential efficacy of the treatment in reversing established glomerulosclerosis will also be assessed by a delayed treatment protocol starting at the time point where fixed histopathological lesions can be expected.

In the second part of the project we will use the animal model to test the potential in vivo antiproteinuric efficacy of small molecules with trafficking modifying properties. A range of doses of 4-phenyl-butyrate and TMAO will be administered provided we can establish their efficacy in the cellular model.

Finally, the experience of these experiments will be used to develop an in vivo system to test and benchmark the efficacy of novel candidate compounds emerging from the high-throughput in vitro screening project.