FAT/CD36Contributes To Renal Injury Under Inflammatory Stress

Objectives: Inflammatory stress was induced by subcutaneous caseininjection in C57BL/6J mice and fatty acid transporter/CD36knockout(FAT/CD36KO) mice in vivo, and by adding tumor necrosis factor-α(TNF-α) or interleukin-6(IL-6) to human kidney mesangial cells (HMCs)and human proximal tubular cell (HK2) in vitro. The aim of present studyis to investigate the relationship between fatty acid transporter/CD36(FAT/CD36) and renal injury under inflammatory stress.Methods: Eight-week-old male C57BL/6J and FAT/CD36knockout(FAT/CD36KO) mice were fed with a high fat diet or subcutaneous injectionof0.5ml10%casein every other day. Mice were killed after14weeks.Blood and urine samples were taken for cytokines and lipid assays, and thetissue samples were collected for further detection. HMCs and HK2cells inthe presence of palmitic acid (PA) or subjected to inflammatory stress byTNF-α or IL-6in vitro. FAT/CD36was knocked down by transfection withFAT/CD36small interfering RNA (siRNA) or overexpressed by transfectionwith FAT/CD36cDNA (FAT/CD36OE) in HMCs and HK2cells. SerumTNF-α and serum amyloid A (SAA) protein were measured by enzyme-linked immunosorbent assay (ELISA) kits. Real-time polymerasechain reaction (RT-PCR) and Western blotting to investigate the effects ofinflammatory cytokines on expressions of FAT/CD36in vitro and in vivo.Triglyceride (TG) and free fatty acid (FFA) in the kidneys and cells weremeasured by enzyme assay and ELISA kit, respectively. The mRNAexpressions of endoplasmic reticulum stress, and fibrosis were detected byRT-PCR in vitro and in vivo.Results: Serum SAA and TNF-α levels were increased after caseininjection in C57BL/6J mice (P<0.05). Inflammation up-regulated theprotein and gene expression of FAT/CD36(P<0.05) and lipid accumulationin inflamed kidneys and cells. The data of real-time PCR showed that themRNA expressions of endoplasmic reticulum stress signs and fibrotic genesin tissues and cells were increasd under inflammatory stress (P<0.05).Western blotting and RT-PCR showed that knock out FAT/CD36decreasedinflammatory cytokines mRNA and protein expression in the kidney (P<0.01). Knocking down FAT/CD36prevented from lipid accumulation,endoplasmic reticulum stress, oxidative stress and fibrosis in inflamedkidneys and cells. Whereas FAT/CD36OE enhanced lipid accumulation,endoplasmic reticulum stress, oxidative stress and fibrosis in cells.Conclusion: Inflammatory stress increased the expressions ofFAT/CD36and exacerbated renal lipid accumulation, oxidative stress andfibrosis in vitro and in vivo. FAT/CD36deficiency significantly improved renal dysfunction caused by inflammation. FAT/CD36plays an importantrole in renal injury under inflammatory stress.