Renal Protection against Post Ischemia‐reperfusion Injury in Fatty Acid Amide Hydrolase Knockout Mice

Abstract

Renal fibrosis is a typical characteristic of progressive chronic kidney disease (CKD). Current treatment options to slow renal fibrosis are still very limited. Endocannabinoids known as anandamide and 2‐arachidonoylglycerol play a critical role in regulating renal physiology via cannabinoid receptors (CB1 and CB2). Fatty acid amide hydrolase (FAAH) is one of the major enzymes to metabolize endocannabinoids. Studies have shown that endocannabinoid system is present in the kidney and that CB1 and CB2 are involved in CKD. However, the role of FAAH in CKD remains unclear. The present study tested the hypothesis that FAAH pathway participates in the kidney damage in post ischemia‐reperfusion (PIR) model, which produces chronic renal injury and fibrosis, using FAAH knockout mice. Male wild type C57BL6 (WT) and Faah−/− mice were subjected to PIR by unilateral ischemia‐reperfusion and contralateral nephrectomy 10 days after ischemia‐reperfusion. Compared with WT mice, Faah−/− mice showed significantly reduced BUN (mean: 22.0 ± 1.16, 102.0± 9.50, and 61± 4.35 mg/dL in WT‐shame, WT‐PIR, and Faah−/−‐PIR mice, respectively, p<0.05) and plasma creatinine level (mean: 0.18 ± 0.02, 1.18 ± 0.06, and, 0.54± 0.05 mg/dL in WT‐shame, WT‐PIR, and Faah−/−‐PIR mice, respectively, p<0.05) in response to PIR. Western blot analysis showed that increased expression of fibrotic protein alpha‐smooth muscle actin in the kidneys were significantly reduced in Faah−/− mice, whereas remained high in WT mice under PIR (1.85‐fold versus 2.46‐fold, p<0.05). Collagen staining by Sirius Red showed the same pattern as alpha‐smooth muscle actin expression in the kidneys from different groups of mice. Histological evaluation by Periodic acid–Schiff (PAS) staining showed that Faah−/− mice exhibited less tissue damage especially in tubular structure in response to PIR compared with WT mice. These results suggest that inhibition of FAAH may preserve renal function and prevent renal fibrosis and that FAAH may serve as a target for developing novel and effective treatment for CKD. Support or Funding Information NIH grants R01DK54927, R01DK107991, R01HL145163