Macrophage depletion ameliorates glycerol-induced acute kidney injury in mice.

BACKGROUND: This study was conducted to elucidate the role of renal macrophages in the development of acute kidney injury (AKI) in a glycerol (Gly)-induced rhabdomyolysis mouse model. METHODS: The experimental model of rhabdomyolysis requires injecting 50% Gly (10 ml/kg) intramuscularly into mice. Control mice were injected into the tail vein with the liposomal vehicle. Liposome-encapsulated clodronate (LEC)-only mice were injected with LEC. Gly-only mice were injected with Gly into a hind limb. LEC+Gly-treated mice were injected intravenously with 100 µl of LEC 24 h prior to Gly injection. Mice were sacrificed 24 h after Gly injection. RESULTS: Gly injection increased the serum creatinine level, and induced tubular damage. Renal CD45(+)CD11b(+)Ly6c(+) or CD45(+)CD11b(+)Ly6c(+)F4/80(+) macrophages were decreased by pretreatment with LEC in both normal and injured kidneys. Macrophage depletion prevented Gly-induced apoptotic death of tubular epithelial cells by decreasing caspase-9, ERK and p53, while increasing Bcl-2 expression. Expression of the inflammatory mediators NF-κB, MCP-1, ICAM-1, iNOS and COX-2 were also decreased with LEC pretreatment of mice injected with Gly. CONCLUSION: These results support the hypothesis that depletion of macrophages prevents renal dysfunction by abrogating apoptosis and attenuating inflammation during AKI.

AdipoR2 is transcriptionally regulated by ER stress-inducible ATF3 in HepG2 human hepatocyte cells.

Adiponectin acts as an insulin-sensitizing adipokine that protects against obesity-linked metabolic disease, which is generally associated with endoplasmic reticulum (ER) stress. The physiological effects of adiponectin on energy metabolism in the liver are mediated by its receptors. We found that the hepatic expression of adiponectin receptor 2 (AdipoR2) was lower, but the expression of markers of the ER stress pathway, 78 kDa glucose-regulated protein (GRP78) and activating transcription factor 3 (ATF3), was higher in the liver of ob/ob mice compared with control mice. To investigate the regulation of AdipoR2 by ER stress, we added thapsigargin, an ER stress inducer, to a human hepatocyte cell line, HepG2. Addition of the ER stress inducer increased the levels of GRP78 and ATF3, and decreased that of AdipoR2, whereas addition of a chemical chaperone, 4-phenyl butyric acid (PBA), could reverse them. Up- or down-regulation of ATF3 modulated the AdipoR2 protein levels and AdipoR2 promoter activities. Reporter gene assays using a series of 5'-deleted AdipoR2 promoter constructs revealed the location of the repressor element responding to ER stress and ATF3. In addition, using electrophoretic mobility shift and chromatin immunoprecipitation assays, we identified a region between nucleotides -94 and -86 of the AdipoR2 promoter that functions as a putative ATF3-binding site in vitro and in vivo. Thus, our findings suggest that the ER stress-induced decrease in both protein and RNA of AdipoR2 results from a concomitant increase in expression of ATF3, which may play a role in the development of obesity-induced insulin resistance and related ER stress in hepatocytes.