Person:

Folco, Eduardo

Background Previous reports have suggested that advanced glycation end products (AGE) participate in the pathogenesis of diabetic macroangiopathy. However, current understanding of the mechanisms by which AGE may accelerate atherogenesis remains incomplete. Methods and results Microarray and reverse transcription real-time PCR analyses revealed that exposure to AGE-BSA (BSA, bovine serum albumin) reduced mRNA levels (60%) in the ATP-binding cassette transporter G1 (ABCG1) but not ABCA1 in human macrophages. AGE-BSA also reduced ABCG1 protein levels. These effects occurred mainly through the receptor for AGE (RAGE), as an anti-RAGE antibody significantly limited ABCG1 mRNA reduction. Functional studies demonstrated that exposure to AGE-BSA decreased cholesterol efflux to high-density lipoprotein (HDL) (P < 0.05) but not to apolipoprotein AI, compared to BSA treatment. Although liver X receptors (LXR) augment ABCG1 expression, macrophages treated with AGE-BSA showed no reduction in LXR mRNA levels or in the binding of nuclear proteins to the LXR response element, compared with BSA. Conclusions Our data show that AGE-BSA can decrease cholesterol efflux from macrophages to HDL via an LXR-independent pathway. This novel mechanism may contribute to accelerated foam cell production and atherogenesis in diabetic patients.

Background

Previous reports have suggested that levels of advanced glycation end product-modified LDL (AGE-LDL) increase in patients with diabetes due to elevated plasma glucose. However, understanding of the mechanisms by which AGE-LDL may accelerate atherogenesis remains incomplete. Methods and results

Microarray and reverse transcription real-time PCR (RT-PCR) analyses revealed that AGE-LDL significantly increased levels of CC chemokine receptor 2 (CCR2) mRNA in human macrophages compared with LDL, an effect accompanied by increased levels of CCR2 protein. Flow cytometry also showed that AGE-LDL increases CCR2 expression on the cell surface following stimulation (48 h) (P < 0.05). This effect appeared to depend on the receptor for AGE (RAGE), since an anti-RAGE antibody significantly blocked increased CCR2 mRNA. Functional studies demonstrated that exposure of THP-1 monocytoid cells to AGE-LDL increases chemotaxis mediated by monocyte chemoattractant protein-1 (MCP-1) up to 3-fold compared to LDL treatment (P < 0.05). Conclusions

These data show that AGE-LDL can increase CCR2 expression in macrophages and stimulate the chemotactic response elicited by MCP-1. This novel mechanism may contribute to accelerated atherogenesis in diabetic patients.

Aims Mice deficient in IL-1 receptor 1 (hence unresponsive to both IL-1 isoforms α and β) have impaired expansive arterial remodeling due to diminished expression of matrix-degrading enzymes, especially MMP-3. Emergence of IL-1 as a target in cardiovascular disease prompted the investigation of the redundancy of IL-1α and IL-1β in the induction of MMP-3 and other matrix-remodeling enzymes in human cells. Methods and Results: Human primary vascular smooth muscle cells (VSMCs) and carotid endarterectomy specimens were stimulated with equimolar concentrations of IL-1α or IL-1β and analyzed protease expression by immunoblot and ELISA. Either IL-1α or IL-1β increased the expression of pro-MMP-3 in VSMCs, facilitated VSMC migration through Matrigel, and induced MMP-3 production in specimens from atheromatous plaques. VSMCs also secreted MMP-1 and Cathepsin S (CatS) upon stimulation with IL-1α or IL-1β. IL-1 isoforms similarly increased MMP-1 and MMP-9 expression in carotid endarterectomy specimens. We examined the expression of MMP-3 and IL-1 isoforms by immunostaining of carotid atheromata, calculated the % positive areas, and tested associations by linear regression. MMP-3 colocalized with IL-1 isoforms in atheromata. MMP-3+ area in plaques positively associated with IL-1α+ (R2 = 0.61, P<0.001) and with IL-1β + areas (R2 = 0.68, P<0.001). MMP-3+ area within atheroma also associated with CD68+ area, but not with α-smooth muscle actin area. Conclusions: Either IL-1α or IL-1β can induce the expression of enzymes implicated in remodeling of the arterial extracellular matrix, and facilitate human VSMC migration in vitro. Human atheromata contain both IL-1 isoforms in association with immunoreactive MMP-3. This redundancy of IL-1 isoforms suggests that selective blocking of one IL-1 isoform should not impair expansive arterial remodeling, a finding with important clinical implications for therapeutic targeting of IL-1 in atherosclerosis.