Meprin β deficiency associated with increased ECM protein buildup and reduced macrophage infiltration in mouse kidneys subjected to Unilateral Ureteral Obstruction (UUO)

Abstract

Meprins are zinc dependent metalloproteases that are abundantly expressed in the brush border membranes (BBM) of proximal kidney tubules. Previous studies have implicated meprins in Ischemic/Reperfusion (IR) induced acute kidney injury (AKI), and diabetic nephropathy (DN). However, the mechanisms by which meprins modulate kidney injury are not fully understood. Known meprin substrates include extracellular matrix (ECM) proteins (e.g. Collagen, Fibronectin, Laminin, and Nidogen‐1) and modulators of inflammation such as interleukin 1β (IL‐1β), IL‐6, pro‐IL‐18, monocyte chemoattractant protein‐1 (MCP‐1), and thymosin β4 – leading to release of the anti‐inflammatory peptide Ac‐SDKP. Furthermore, meprins are expressed in leukocytes (monocytes, macrophages), and play a role in leukocyte infiltration to sites of inflammation in the small intestines. Inflammation is an underlying cause of renal injury in both IR‐induced AKI and DN. The objective of the current study was to determine how meprin deficiency impacts extracellular matrix protein build up and leukocyte infiltration in unilateral ureteral obstruction (UUO)‐induced inflammation. Surgical procedures were used to ligate one ureter in twelve‐week‐old wild‐type (WT) and meprin β knockout male mice. The contralateral kidney served as the control for each mouse. At 7 days post‐UUO, the kidneys were perfused with saline to remove leukocytes present in kidney blood vessels and kidneys were harvested. Sections of the kidney tissue were snap frozen for protein extraction and some were paraffin embedded and sectioned for microscopy. For immunofluorescence F4/80, was used as a macrophage maker. The images were captured and the number of cells that stained positive for F4/80 counted. Western blot analysis was used to evaluate the levels of ECM proteins (fibronectin, laminin, and nidogen‐1) in the kidney lysates. Statistical analysis utilized 2‐way ANOVA (Graphpad Prism 7 software). Our data demonstrates increases in fibronectin protein levels in both WT and βKO kidneys subjected to UUO. However, UUO‐induced fibronectin increases were higher in βKO than in WT (p=0.0016 vs p=0.004). The baseline levels of nidogen‐1 were higher in WT mice (p=0.01) when compared to βKOs. At 7 days post‐UUO, the levels of nidogen‐1 increased significantly in the kidneys of βKO subjected to UUO (p=0.001), but not in WT kidneys. There were no significant differences in the baseline or post‐UUO levels of laminin in either genotype. Results from immunofluorescence showed that WT and meprin βKO kidneys subjected to UUO had significant increases in the number of macrophages in tubulo‐interstitial tissue when compared to control counterparts (≤0.007 and ≤0.001 respectively). Taken together, our data suggest that meprin expression/activity reduces the buildup of specific ECM proteins (fibronectin and nidogen‐1), thus reducing the fibrosis observed in inflammation. Furthermore, meprins modulate inflammation via enhanced leukocyte infiltration of (monocytes/macrophages).Support or Funding InformationNIH/National Institutes of General Medical Sciences (NIGMS) Grant #s SC3GM102049 and #SC1GM118271 to Elimelda Moige OngeriThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.