2007 Abstracts: Syndecan-1 Is Expressed During the Course of Atherosclerosis and May Serve As A Biomarker of Peripheral Arterial Disease Activity

Background: Syndecan-1 is a member of a family of cell surface heparan sulfate proteoglycans that modulate inflammatory and growth-stimulating responses relevant to acute tissue repair and chronic injury responses. Syndecan-1 expression during the course of atherosclerotic lesion formation has not been previously investigated nor has its potential utility as a biomarker of peripheral arterial disease (PAD) been examined.
Methods: ApoE-deficient mice were maintained on an atherogenic diet for 8 weeks with concurrent infusion of angiotensin II (0.75 mg/kg/day SQ). The expression of syndecan-1, -2, and -4 in the aortic wall was characterized by immunohistochemical staining and co-localization determined by double fluorescent immunostaining. Quantitative real-time PCR (QRT-PCR), FACS, and slot blot analyses were used to define the role of angiotensin II and responsible signaling pathways involved in regulation of syndecan-1 expression in RAW264.7 macrophages. Syndecan-1 levels were measured by ELISA in serum samples collected from 20 male patients with severe PAD (mean age +/- SE: 65.4 +/- 1.9 yrs; mean ABI +/- SE: 0.63 +/- 0.05; mean C-reactive protein +/- SE: 5.5 +/- 1.7 mg/mL)
Results: Syndecan-4 was localized to smooth muscle cells of the native aortic wall of normotensive mice maintained on a chow diet. Neither syndecan-1 nor syndecan-2 could be detected in the aortic wall. After initiating a high fat diet and infusion of angiotensin II, syndecan-1 was abundantly expressed in infiltrating macrophages found in early atherosclerotic lesions, as well as advanced complex lipid cores. As the lesion matured, syndecan-4 was expressed within alpha-actin positive cells of the fibrous cap.
Angiotensin II regulates the expression of syndecan-1 mRNA in macrophages in a time- and dose-dependent manner (Fig. 1). QRT-PCR demonstrated that maximum syndecan-1 mRNA upregulation occurred at 6 h after 500 nM angiotensin II stimulation (n = 3). Both constitutive and angiotensin II induced syndecan-1 mRNA expression were regulated by ERK/MAPK, as well as by the PI3K and JNK pathways. In contrast, blockade of the p38 or the PKC pathways did not affect syndecan-1 mRNA expression (Fig. 2). FACS analysis confirmed that 6 hours of angiotensin II stimulation resulted in an increase in cell surface syndecan-1 protein expression (MFI 147 +/- 10 vs 175 +/- 8; p < 0.05; n = 3). Serum syndecan-1 levels measured in patients with PAD were 317.3 +/- 31.3 U/mL, three-fold higher than reported in healthy adults.
Conclusions: The expression of syndecan-1 is significantly increased in the vascular wall of hypertensive, hyperlipidemic mice and is present in patients with severe PAD. Given the role of syndecan-1 as a regulator of inflammatory and growth-stimulating events, the presence of elevated serum levels of syndecan-1 may be indicative of an active inflammatory state in the vascular wall.