Abrogation of lectin-like oxidized LDL receptor-1 attenuates acute myocardial ischemia-induced renal dysfunction by modulating systemic and local inflammation

Abstract

It is assumed that acute myocardial infarction affects renal function. To study the mechanism, we used mice following permanent ligation of their left coronary artery that results in extensive myocardial infarction. Soon after ligation, there was a marked rise in circulating pro-inflammatory cytokines and malondialdehyde (thiobarbituric acid-positive evidence of lipid peroxidation). Renal function had significantly declined by the third day in association with mild fibrosis, and swelling of glomeruli and tubules. There was a significant increase in the expression of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), interelukin-1β, vascular cell adhesion molecule-1, and thiobarbituric acid-reactive substances in the kidney. Renal function showed some recovery by Day 21; however, there was progressive fibrosis of the kidneys. LOX-1 knockout mice had significantly diminished increases in systemic and renal pro-inflammatory cytokines, malondialdehyde, structural alterations, and decline in renal function than the wild-type mice following ligation of the left coronary artery. Cardiac function and survival rates were also significantly better in the LOX-1 knockout mice than in the wild-type mice. Hence, severe myocardial ischemia results in renal dysfunction and histological abnormalities suggestive of acute renal injury. Thus, LOX-1 is a key modulator among multiple mechanisms underlying renal dysfunction following extensive myocardial infarction.

Figure 1. Representative M-mode echocardiography tracings and summary data

Shown are the data on ejection fraction, left ventricular (LV) anterior wall systolic thickness, and LV internal diameter in end-diastole in the wild-type (WT) and low-density lipoprotein receptor-1 (LOX-1) knockout (KO) group at Days 3 and 21 (3 weeks) after total left coronary artery (LCA) ligation. Note that the changes were less pronounced in the LOX-1 KO mice subjected to the same duration of ischemia (P < 0.05 vs. WT). Data, shown as mean ± s.d., are based on measurements from six mice in each group. LVIDd, left ventricular internal diameter in diastole; LVIDs, left ventricular internal diameter in systole. *P < 0.05 vs. corresponding sham ischemia group; ^‡P < 0.05 vs. WT group.

Figure 2. Renal function and blood pressure following left coronary artery (LCA) occlusion measured as glomerular filtration rate (GFR), serum blood urea nitrogen (BUN), and creatinine

Note that the blood pressure was similar in wild-type (WT) and lipoprotein receptor-1 (LOX-1) knockout (KO) mice at all time points. Data, shown as mean ± s.d., are based on measurements in 8–10 animals in each group. *P < 0.05 vs. corresponding sham ischemia group; ^‡P < 0.05 vs. WT group; n = 6.

Figure 3. Kidney weight and inflammation following left coronary artery (LCA) ligation

(a) Representative pictures of kidneys from the wild-type (WT) and lipoprotein receptor-1 (LOX-1) knockout (KO) groups. The lower panel shows summary data, shown as mean ± s.d., on kidney weight per body weight (mg/g, n = 6). *P < 0.05 compared to corresponding sham ischemia; ^‡P < 0.05 compared to WT groups subjected to total LCA ligation. (b) Renal histology shows polymorphonuclear leukocytes (PMNLs) in the peritubular regions (original magnification × 600). In contrast to WT mice, the number of PMNLs was much less in the LOX-1 KO mice. (c) Representative protein expression of interleukin-1β (IL-1β), vascular cell adhesion molecule-1 (VCAM-1), and tumor growth factor-β1 (TGF-β1) in the mice kidneys. (d) Quantification of accumulation of PMNLs. H.p.f.: high power field. At least 100 glomeruli and tubules were examined in each slice, and at least four slices were examined in each kidney and the data averaged. *P < 0.05 compared to corresponding sham ischemia; ^‡P < 0.05 compared to WT groups subjected to total LCA ligation.

Figure 4. Accelerated fibrosis in the kidney after prolonged myocardial ischemia

(a) Representative sections of kidney stained with Masson’s trichrome (original magnification × 200) after left coronary artery (LCA) ligation. (b) Kidney section using Masson’s trichrome staining (original magnification × 600) revealed less tubulointerstitial fibrosis and glomerulosclerosis in the lipoprotein receptor-1 (LOX-1) knockout (KO) mice at Day 3 after LCA occlusion. (c) Summary data, shown as mean ± s.d., on the area of collagen deposition in the kidneys of WT and LOX-1 KO mice. At least four slices were examined in each kidney and summary data were obtained from six mice in each group. *P < 0.05 compared to corresponding sham ischemia group; ^‡P < 0.05 compared to WT chronic ischemia. (d) Representative western blots of fibrosis-related proteins (collagen IV-α2 and procollagen-1) and β-actin expression.

Figure 5. Serum concentration of pro-inflammatory cytokines during the first 3 days after left coronary artery (LCA) ligation

Summary data, shown as mean ± s.d., from six mice in each group. ^‡P < 0.05 vs. WT group. GM-CSF, granulocyte–macrophage colony-stimulating factor; IFN, interferon; IL, interleukin; KO, knockout; TNF, tumor necrosis factor; WT, wild type.

Figure 6. Oxidative stress and activation of lipoprotein receptor-1 (LOX-1) and nuclear factor-κB (NF-κB) pathway in the kidney

(a) Serum malondialdehyde (MDA) levels (n = 12–15 mice in each group). (b) Levels of thiobarbituric acid-reactive substances (TBARS, n = 6) in the kidney. (c) Representative western blots of LOX-1, IκBα, and its phosphorylation. (d) Quantification of western blot data (n = 4). A.u. indicates arbitrary units. Data are shown as mean ± s.d. *P < 0.05 compared to corresponding sham ischemia; ^‡P < 0.05 compared to WT chronic ischemia. KO, knockout; WT, wild-type.