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Abstract: FR-OR021

Macrophage COX-2 Protects Against AKI via Promotion of M2 Polarization and Efferocytosis

Session Information

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Pan, Yu, Vanderbilt University Medical School, Nashville, Tennessee, United States
  • Jin, Guannan, Vanderbilt University Medical School, Nashville, Tennessee, United States
  • Chung, Sungjin, The Catholic University of Korea College of Medicine, Seoul, Korea (the Republic of)
  • Wang, Yinqiu, Vanderbilt University Medical School, Nashville, Tennessee, United States
  • Wang, Suwan, Vanderbilt University Medical School, Nashville, Tennessee, United States
  • Zhang, Ming-Zhi, Vanderbilt University Medical School, Nashville, Tennessee, United States
  • Harris, Raymond C., Vanderbilt University Medical School, Nashville, Tennessee, United States
Background



Efferocytosis, the clearance of apoptotic cells by macrophages, plays a key role in recovery from acute kidney injury (AKI) by promoting the production of anti-inflammatory cytokines. Our previous studies show that macrophage cyclooxygenase-2 (COX-2) plays an essential role in polarization and maintenance of a macrophage alternatively activated, tissue-reparative M2 phenotype. Macrophages with an M2 phenotype exhibit higher efferocytotic capacity and play a pivotal role in recovery from AKI. We examined the role of macrophage COX-2 in efferocytosis, recovery from AKI and subsequent development of fibrosis.

Methods



Wild type (COX-2f/f) or CD11b-Cre; COX-2f/f mice (male, 8 weeks, FVB background) were uninephrectomized, immediately followed by unilateral ischemia-reperfusion with 29-min renal pedicle clamping. Mice were sacrificed at different time points after AKI. Renal macrophages were isolated with a mixture of CD11b and CD11c microbeads and used for efferocytosis assay with phagocytosing fluorescent beads or apoptotic neutrophils.

Results

Compared to WT mice, CD11b-Cre; COX-2f/f mice had delayed recovery after AKI, as indicated by BUN and creatinine and had subsequent increases in renal fibrosis as indicated by Masson’s Trichrome and Sirius red staining, increased profibrotic and fibrotic components, and increased renal macrophage and lymphocyte infiltration. In WT mice, renal proinflammatory cytokines such as iNOS, TNF-α, CCL3, and IL-23α increased 6 hours after AKI, peaked at 16 hours, and returned to baseline at day 3. In CD11b-Cre; COX-2f/f mice, these cytokines increased to a greater extent and were still elevated 7 days after AKI. Two days after AKI, CD11b-Cre; COX-2f/f mice had increased proinflammatory Th1/M1 but decreased anti-inflammatory Th2/M2 cytokines, in association with decreased expression levels of components of efferocytosis, including TIM4, Axl, and Tyro3 and Gas6. Renal macrophages isolated from CD11b-Cre; COX-2f/f mice 2 days after AKI showed significantly decreased efferocytotic ability in both the fluorescent bead phagocytosis assay and the neutrophil efferocytosis assay.

Conclusion


Macrophage COX-2 protects against AKI and development of renal fibrosis after severe AKI, at least in part due to COX-2-derived PGE2-mediated macrophage M2 polarization and efferocytosis.

Funding

  • NIDDK Support