Phenotypic change of macrophages in the progression of diabetic nephropathy; sialoadhesin-positive activated macrophages are increased in diabetic kidney.

BACKGROUND: Inflammatory process is involved in pathogenesis of diabetic nephropathy, although the activation and phenotypic change of macrophages in diabetic kidney has remained unclear. Sialoadhesin is a macrophage adhesion molecule containing 17 extracellular immunoglobulin-like domains, and is an I-type lectin which binds to sialic acid ligands expressed on hematopoietic cells. The aim of this study is to clarify the activation and phenotypic change of macrophages in the progression of diabetic nephropathy. METHODS: We examined the expression of surface markers for pan-macrophages, resident macrophages, sialoadhesin, major histocompatibility complex class II and α-smooth muscle actin in the glomeruli of diabetic rats using immunohistochemistry at 0, 1, 4, 12, and 24 weeks after induction of diabetes by streptozotocin. Expression of type IV collagen and the change of mesangial matrix area were also measured. The mechanism for up-regulated expression of sialoadhesin on macrophages was evaluated in vitro. RESULTS: The number of macrophages was increased in diabetic glomeruli at 1 month after induction of diabetes and the increased number was maintained until 6 months. On the other hand, sialoadhesin-positive macrophages were increased during the late stage of diabetes concomitantly with the increase of α-smooth muscle actin-positive mesangial cells, mesangial matrix area and type IV collagen. Gene expression of sialoadhesin was induced by stimulation with interleukin (IL)-1ß and tumor necrosis factor-α but not with IL-4, transforming growth factor-ß and high glucose in cultured human macrophages. CONCLUSION: The present findings suggest that sialoadhesin-positive macrophages may contribute to the progression of diabetic nephropathy.

Intercellular adhesion molecule-1 plays a critical role in glomerulosclerosis after subtotal nephrectomy.

BACKGROUND: Hyperfiltration in the glomeruli have been considered to be an important cause of glomerular injury; however, the role of intercellular adhesion molecule (ICAM)-1 in the pathogenesis of glomerulosclerosis is not known. METHODS: To elucidate the effects of ICAM-1 depletion on hyperfiltration-induced glomerular disorder, we used subtotally nephrectomized ICAM-1(+/+) and ICAM-1(-/-) mice. We evaluated macrophage infiltration, mesangial matrix expansion, transforming growth factor (TGF)-ß and type IV collagen accumulation in glomeruli. RESULTS: Macrophage infiltration into the glomeruli and mesangial matrix expansion coincident with increased expression of both ICAM-1 and TGF-ß, and accumulation of type IV collagen were ameliorated in subtotally nephrectomized ICAM-1(-/-) mice compared to ICAM-1(+/+) mice. ICAM-1 depletion significantly reduced hyperfiltration-induced glomerular injury after renal ablation. CONCLUSIONS: Our present findings suggest that glomerular hyperfiltration is the leading cause of glomerulosclerosis, and it is mediated, at least in part, by ICAM-1 expression and macrophage infiltration.

Macrophage scavenger receptor-a-deficient mice are resistant against diabetic nephropathy through amelioration of microinflammation.

Microinflammation is a common major mechanism in the pathogenesis of diabetic vascular complications, including diabetic nephropathy. Macrophage scavenger receptor-A (SR-A) is a multifunctional receptor expressed on macrophages. This study aimed to determine the role of SR-A in diabetic nephropathy using SR-A-deficient (SR-A(-/-)) mice. Diabetes was induced in SR-A(-/-) and wild-type (SR-A(+/+)) mice by streptozotocin injection. Diabetic SR-A(+/+) mice presented characteristic features of diabetic nephropathy: albuminuria, glomerular hypertrophy, mesangial matrix expansion, and overexpression of transforming growth factor-beta at 6 months after induction of diabetes. These changes were markedly diminished in diabetic SR-A(-/-) mice, without differences in blood glucose and blood pressure levels. Interestingly, macrophage infiltration in the kidneys was dramatically decreased in diabetic SR-A(-/-) mice compared with diabetic SR-A(+/+) mice. DNA microarray revealed that proinflammatory genes were overexpressed in renal cortex of diabetic SR-A(+/+) mice and suppressed in diabetic SR-A(-/-) mice. Moreover, anti-SR-A antibody blocked the attachment of monocytes to type IV collagen substratum but not to endothelial cells. Our results suggest that SR-A promotes macrophage migration into diabetic kidneys by accelerating the attachment to renal extracellular matrices. SR-A may be a key molecule for the inflammatory process in pathogenesis of diabetic nephropathy and a novel therapeutic target for diabetic vascular complications.

Intercellular adhesion molecule-1-deficient mice are resistant against renal injury after induction of diabetes.

Diabetic nephropathy is a leading cause of end-stage renal failure. Several mechanisms, including activation of protein kinase C, advanced glycation end products, and overexpression of transforming growth factor (TGF)-beta, are believed to be involved in the pathogenesis of diabetic nephropathy. However, the significance of inflammatory processes in the pathogenesis of diabetic microvascular complications is poorly understood. Accumulation of macrophages and overexpression of leukocyte adhesion molecules and chemokines are prominent in diabetic human kidney tissues. We previously demonstrated that intercellular adhesion molecule (ICAM)-1 mediates macrophage infiltration into the diabetic kidney. In the present study, to investigate the role of ICAM-1 in diabetic nephropathy, we induced diabetes in ICAM-1-deficient (ICAM-1(-/-)) mice and ICAM-1(+/+) mice with streptozotocin and examined the renal pathology over a period of 6 months. The infiltration of macrophages was markedly suppressed in diabetic ICAM-1(-/-) mice compared with that of ICAM-1(+/+) mice. Urinary albumin excretion, glomerular hypertrophy, and mesangial matrix expansion were significantly lower in diabetic ICAM-1(-/-) mice than in diabetic ICAM-1(+/+) mice. Moreover, expressions of TGF-beta and type IV collagen in glomeruli were also suppressed in diabetic ICAM-1(-/-) mice. These results suggest that ICAM-1 is critically involved in the pathogenesis of diabetic nephropathy.