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Fluid shear stress modulates vascular production of endothelial superoxide anion ([[O.sub.2].sup.-]) and nitric oxide (NO). Whether the characteristics of shear stress influence the spatial variations in mitochondrial manganese superoxide dismutase (Mn-SOD) expression in vasculatures is not well defined. We constructed a three-dimensional computational fluid dynamics model simulating spatial variations in shear stress at the arterial bifurcation. In parallel, explants of arterial bifurcations were sectioned from the human left main coronary bifurcation and right coronary arteries for immunohistolocalization of Mn-SOD expression. We demonstrated that Mn-SOD staining was prominent in the pulsatile shear stress (PSS)-exposed and atheroprotective regions, but it was nearly absent in the oscillatory shear stress (OSS)-exposed regions and lateral wall of arterial bifurcation. In cultured bovine aortic endothelial cells, PSS at mean shear stress ([[tau].sub.ave]) of 23 dyn/[cm.sup.2] upregulated Mn-SOD mRNA expression at a higher level than did OSS at [[tau].sub.ave] = 0.02 dyn/[cm.sup.2] [+ or -] 3.0 dyn x [cm.sup.-2] x [s.sup.-1] and at 1 Hz (PSS by 11.3 [+ or -] 0.4-fold vs. OSS by 5.0 [+ or -] 0.5-fold vs. static condition; P < 0.05, n = 4). By liquid chromatography and tandem mass spectrometry, it was found that PSS decreased the extent of low-density lipoprotein (LDL) nitration, whereas OSS increased nitration (P < 0.05, n = 4). In the presence of LDL, treatment with Mn-SOD small interfering RNA increased intracellular nitrotyrosine level (P < 0.5, n = 4), a fingerprint for nitrotyrosine formation. Our findings indicate that shear stress in the atheroprone versus atheroprotective regions regulates spatial variations in mitochondrial Mn-SOD expression with an implication for modulating LDL nitration. superoxide dismutase; superoxide anion; nitric oxide; nitrotyrosine; low-density lipoprotein

Exposure to atmospheric fine particulate matter (PM(2.5)) is a modifiable risk factor of cardiovascular disease. Ultrafine particles (UFP, diameter <0.1 μm), a subfraction of PM(2.5), promote vascular oxidative stress and inflammatory responses. Epidemiologic studies suggest that PM exposure promotes vascular calcification. Here, we assessed whether UFP exposure promotes vascular calcification via NF-κB signaling. UFP exposure at 50 μg/ml increased alkaline phosphatase (ALP) activity by 4.4 ± 0.2-fold on day 3 (n = 3, P < 0.001) and matrix calcification by 3.5 ± 1.7-fold on day 10 (n = 4, P < 0.05) in calcifying vascular cells (CVC), a subpopulation of vascular smooth muscle cells with osteoblastic potential. Treatment of CVC with conditioned media derived from UFP-treated macrophages (UFP-CM) also led to an increase in ALP activities and matrix calcification. Furthermore, both UFP and UFP-CM significantly increased NF-κB activity, and cotreatment with an NF-κB inhibitor, JSH23, attenuated both UFP- and UFP-CM-induced ALP activity and calcification. When low-density lipoprotein receptor-null mice were exposed to UFP at 359.5 μg/m(3) for 10 wk, NF-κB activation and vascular calcification were detected in the regions of aortic roots compared with control filtered air-exposed mice. These findings suggest that UFP promotes vascular calcification via activating NF-κB signaling.

Vulnerable plaque remains clinically undetectable, and there is no accepted in vitro model. We characterize the calcific nodules produced by calcifying vascular cells (CVC) in ApoE-null mice, demonstrating increased destabilization of cultured nodules in the presence of oxidized low-density lipoprotein (oxLDL) and monocytes under pulsatile shear stress. CVC implanted in the subcutaneous space of hyperlipidemic mice produced nodules revealing features of calcific atherosclerotic plaque including a fibrous cap, cholesterol clefts, thin shoulder, lipids, and calcium mineral deposits. CVC nodules seeded in the pulsatile flow channel (τ(avg) = 23 dyn/cm(2), ∂τ/∂t = 71 dyn·cm(-2)·s(-1)) underwent deformation and destabilization. Computational fluid dynamics revealed distinct shear force profiles on the nodules. Presence of oxLDL or monocytic THP-1 cells significantly increased the numbers of nodules destabilized from the substrate. Both oxLDL and THP-1 increased matrix metalloproteinase (MMP) activity in CVC. The MMP inhibitor GM6001 significantly reversed oxLDL- and THP-1-induced nodule destabilization, whereas overexpression of MMP-9 increased destabilization. These findings demonstrate that CVC-derived nodules resembled calcific atherosclerotic plaque and were destabilized in the presence of active lipids and monocytes via induction of MMPs.