Involvement of oxidation in LDL-induced collagen gene regulation in mesangial cells

Abstract

Oxidized low-density lipoprotein (Ox-LDL) is present in the lesions of focal segmental glomerulosclerosis (FSGS), but the role of Ox-LDL in the disease process is not clear. Recent studies have shown that LDL stimulates the type IV collagen mRNA expression in cultured mesangial cells. Thus, we examined whether oxidative stress is responsible for the stimulation of LDL-induced collagen gene expression in cultured human mesangial cells (HMCs). When quiescent HMCs were exposed to serum-free media containing LDL for 48 hours, peroxidation of LDL was induced as shown by the increased production of thiobarbituric acid-reactive substances (TBARS). LDL stimulated the alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA expression in a dose-dependent manner. At a concentration of 200 micrograms/ml, LDL enhanced the levels of alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA by 3.7-, 3.8- and 3.2-fold, respectively, over the levels in the control cells. These transcripts were further increased 5.4-, 6.7-, and 5.9-fold, respectively, by the addition of 500 micrograms/ml of LDL. Cu(2+)-catalyzed Ox-LDL at a concentration of 200 micrograms/ml also stimulated the alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA expression 4.4-, 5.9-, and 2.8-fold, respectively, compared with the control cells. The addition of monoclonal antibody (mAb) OL-10, which recognizes the malondialdehyde (MDA)-modified peptide epitope, or vitamin E (50 microM) to cultured HMC exposed to LDL markedly inhibited the stimulation of collagen gene expression. When HMCs were incubated with MDA (200 microM), alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA levels increased by two- to threefold compared to control cells. Immunohistochemical staining utilizing mAb OL-10 demonstrated the presence of MDA-modified proteins in the cytoplasm of HMC exposed to either LDL or MDA. These results suggest that peroxidative products of LDL stimulate collagen gene expression possibly via modification of proteins, which are responsible for the expression of collagen genes in cultured HMCs. Given that, lipid peroxidation of LDL may be implicated in the development of glomerulosclerosis by facilitating excessive mesangial matrix generation.

Determining the Relationship Between Homocysteinemia and Biomarkers of Inflammation, Oxidative Stress and Functional Kidney Status in Patients with Diabetic Nephropathy

“…Ujihara et al (52) reported significantly higher serum oxLDL levels only in diabetics with macroalbuminuria, compared to normoalbuminuric and microalbuminuric patients and healthy controls (16.8±7.5 vs. 13.7±3.9 vs. 12.8±3.9 vs. 12.5±4.2 U/mL, respectively). These findings may suggest an association between oxLDL and progression of renal dysfunction in diabetic patients, which may also be corroborated by the fact that oxLDL stimulates collagen IV production in mesangial cells (53).…”

Role of Sterol Regulatory Element-binding Protein 1 in Regulation of Renal Lipid Metabolism and Glomerulosclerosis in Diabetes Mellitus

“…Previous studies in renal mesangial and tubular cells grown in culture have shown that incubation of these cells with low density lipoprotein or very low density lipoprotein causes upregulation of growth factors, including TGF-␤ and plateletderived growth factor (36), plasminogen activator inhibitor 1 (37,38), extracellular matrix proteins (36,39), pro-inflammatory cytokines including interleukins and tumor necrosis factor ␣ (36), adhesion molecules including monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) (40,41), and lipid peroxidation and glycoxidation (42). Our studies in vivo indicate that accumulation of renal triglycerides in streptozotocin-treated diabetic rats and SREBP-1a transgenic mice causes increased expression of TGF-␤ and VEGF as well as collagen and fibronectin, resulting in glomerulosclerosis and proteinuria.…”

Oxidized low-density lipoproteins bind to the scavenger receptor, CD36, of hepatic stellate cells and stimulate extracellular matrix synthesis

“…10,13 Through this, 3 important consequences arise: 1) antigen formation 13,14 ; 2) loss of affinity to the normal LDL receptor (Apo B/E receptor) 14 ; and 3) cellular uptake of ox-LDL by scavenger receptors, resulting in foam cell formation. 12,14,15 Except for its role in foam cell formation, growing interest has developed in oxLDL effects on cell viability, regulation of gene expression, monocyte and lymphocyte recruitment, and macrophage propagation. 16 Recent evidence suggests that oxLDL might exert a direct stimulatory effect on the synthesis of DNA and connective tissue components in vascular smooth muscle cells and mesangial cells.…”

“…8 Lipid-peroxidative modification of LDL to oxidized lowdensity lipoproteins (oxLDL) is known to be the crucial event in atherosclerosis 3,9,10 and certain forms of glomerulosclerosis. 11,12 Malondialdehyde (MDA) and 4-hydroxynonenal, which represent the most common aldehydes produced during lipid peroxidation, form adducts with the apoprotein moiety of LDL. 10,13 Through this, 3 important consequences arise: 1) antigen formation 13,14 ; 2) loss of affinity to the normal LDL receptor (Apo B/E receptor) 14 ; and 3) cellular uptake of ox-LDL by scavenger receptors, resulting in foam cell formation.…”

“…16 Recent evidence suggests that oxLDL might exert a direct stimulatory effect on the synthesis of DNA and connective tissue components in vascular smooth muscle cells and mesangial cells. 11,12,[17][18][19] The human CD36 antigen is a class B scavenger receptor and cell adhesion molecule expressed by platelets, monocytes, and microvascular endothelial cells, among other cell types. 15 CD36 has been implicated in hemostasis, thrombosis, malaria, inflammation, lipid metabolism, and atherogenesis.…”