PPAR δ Agonism Ameliorates Renal Fibrosis in an Alport Syndrome Mouse Model

Abstract

Key Points:

1. A peroxisome proliferator-activated receptor δ agonist, REN001, ameliorates kidney dysfunction in a mouse model of Alport syndrome.

2. REN001 suppresses glomerular injury and renal fibrosis.

3. REN001 decreases the levels of inflammation- and fibrosis-related proteins.

Background: Alport syndrome is a genetic kidney disease caused by mutation in any of the COL4A3, COL4A4, or COL4A5 genes encoding the type IV collagen α3, α4, and α5 chains. Defects of type IV collagen α3α4α5 cause glomerular basement membrane abnormalities and lead to defects in glomerular filtration and ESKD. Treatment with angiotensin-converting enzyme inhibitors (ACEis) dramatically slows disease progression but does not stop progression to renal failure. Therefore, novel therapeutic options with different modes of action from ACEis are needed. Peroxisome proliferator-activated receptor (PPAR) δ agonists have shown renoprotective effects in several acute kidney injury mouse models. In this study, we investigated the effects of a potent and selective PPARδ agonist, REN001 (formerly HPP593), in a mouse model of Alport syndrome.

Methods: We administered REN001 from the early stages to the late stages of disease by once daily intraperitoneal injections.

Results: REN001 treatment halved proteinuria at the late stages of disease in Col4a3^−/− mice. BUN levels were also decreased, and histological and molecular analyses showed that REN001 ameliorated renal inflammation and fibrosis.

Conclusions: These results indicate that REN001 slows kidney disease progression in Alport mice. REN001 has a different mechanism of action from ACEis, so we, therefore, hypothesize that combining the two treatments may show additive effects to attenuate renal injury and slow progression to renal failure.

Trial registration: ClinicalTrials.gov NCT01613118.

Graphical abstract

Figure 1

Schematic diagram of pharmacological interventions. B6129S1F1 hybrid Col4a3^−/− mice were administered by intraperitoneal injection, either vehicle (PBS) or REN001 (10 mg/kg), once a day from 6 to 17 weeks of age. Additional details about dosing are provided in the materials and methods section. Studies were initiated with 12 mice per group, as indicated.

Figure 2

REN001 administration suppressed progressive proteinuria in Alport mice. (A) Proteinuria scores were derived from urinary protein-creatinine ratios. Urine was collected at 12, 15, and 17 weeks of age. Proteinuria was significantly lower in REN001-treated Alport mice compared with vehicle-treated Alport mice at 17 weeks. (B) BUN levels were assayed at 12, 15, and 17 weeks of age. BUN was significantly lower at 12 and 17 weeks, with a similar trend at 15 weeks (although P>0.05). P values were assessed by the Dunnett test (*P<0.05, **P<0.01 versus vehicle-treated mice).

Figure 3

REN001 decreased the areas of tubular necrosis and fibrosis in Alport mice. (A) PAS and trichrome staining of kidney sections at 17 weeks of age shows reduced pathology in REN001-treated Alport mice. Scale bar: 200 μm. (B) Glomerulosclerosis scoring results indicate that REN001 treatment decreased glomerular injury. Glomerular injury scores ranged from 0 to 4: 0, no lesion; 1, mesangial expansion; 2, mesangial expansion and 25%–50% sclerosis; 3, 50%–75% sclerosis with expansion of Bowman's epithelial cells and adhesion of the glomerular tuft to Bowman's capsule; 4, 75%–100% sclerosis. (C) REN001 decreased the extent of fibrosis (nonpink areas in trichrome-stained sections) in the renal cortex of Alport mice. P values were assessed by the Student t test (***P<0.005 versus vehicle-treated mice).

Figure 4

REN001 decreased expression of proteins related to inflammation and fibrosis in Alport mice. (A) Whole kidney lysates from the indicated 17-week-old groups of mice were analyzed by immunoblotting. (B) The relative amounts of proteins were quantified. P values were assessed by the Dunnett test (*P<0.05, **P<0.01, ***P<0.005 versus vehicle-treated Alport mice).