Alterations of Arterial Physiology in Osteopontin-Null Mice

Abstract

Objective-In this study, we characterized the effects of an osteopontin (OPN)-null mutation in normal arterial function and remodeling in a murine model. Methods and Results-OPN-null mutant mice were compared with wild-type mice before and after carotid artery ligation.Before ligation, OPN-null mice had increased heart rate, lower blood pressure, and increased circulating lymphocytes compared with wild-type mice. OPN-null vessels also demonstrated greater compliance accompanied by a loosely organized collagen network. After carotid artery ligation, significant differences were also found in the remodeling response of OPN-null animals. 16,17 and shear stress. 9,18,19 We previously found that inhibiting osteopontin (OPN) function after endothelial denudation led to a significant decrease in the extent of neointimal formation in rats. 20 In this study, the arterial effects resulting from the removal of OPN (product of the spp1 gene) were examined.OPN is a secreted integrin-binding protein that is present in small amounts in uninjured arteries 21 but is abundantly expressed by smooth muscle cells, endothelial cells, 21,22 and activated inflammatory cells [23][24][25] in injured arteries. Abundant OPN expression has also been observed in human atherosclerotic lesions 26 and thoracic aneurysms. 27 The functional significance of this increased vascular expression was suggested by work demonstrating OPN activity as a chemoattractant/adhesive substrate for endothelial cells 28 and vascular smooth muscle cells, 29 an inhibitor of vascular smooth muscle calcification, 30,31 and a chemoattractant/activator of inflammatory cells. 32,33 In vivo studies confirmed these important functions of OPN during tissue remodeling and repair. Chiba et al 34 observed that hematopoietic cell overexpression of OPN resulted in increased atherosclerotic lesion formation. In OPN-null mice, recent data have indicated that the nonredundant functions of OPN in vivo involve widespread participation in tissue remodeling, inflammation, 24,32 tumor progression, 35 and angiogenesis. 36 Defective tissue remodeling on an OPN-null background has been observed in tissues including the myocardium, 37 bone, 36,38 -40 skin, 41 kidney, 42-44 lymph nodes, 45 joints, 46 and malignant tissues. 35 Two phenotypes that characterize many of these studies are a change in the immune response and altered matrix remodeling. Therefore, the widespread participation of OPN in tissue remodeling is likely due to its unique functions in basic repair processes. In addition, the role of OPN as a physiological inhibitor of vascular calcification was demonstrated in studies showing that spontaneous vascular calcification in the matrix of Gla protein-null mice was significantly increased on an OPN-null background. 47 Recently, constitutive overexpression of OPN in mice was observed to result in increased neointima formation after cuffing of the femoral artery. 48 Interestingly, this overexpression of OPN in uninjured mice did not result in accumulation of leukocytes in the vessel...

Improved Analysis of the Vascular Response to Arterial Ligation Using a Multivariate Approach

“…We applied regression analysis to a data set in which we have previously used traditional methods to show OPN affects both neointima formation and constrictive remodeling. 15 As was detected previously using Student's t-test, the regression method identified OPN as significantly affecting the lumen area and total area before ligation (the variable OPN is a significant predictor of lumen and total area), and intimal area and total area following ligation (the variable OPN*Ligation is a significant predictor of lumen and total area). However, due to the ability of regression to assign portions of total variance to each variable, regression analysis was more sensitive than Student's t-test as evidenced by increased statistical sig- nificance.…”

“…The data used in this study were taken from the previously published study, 15 and the experimental methods are presented briefly here for clarity. All protocols were approved by the Institutional Animal Care and Use Committee.…”

“…To test the hypothesis that distance from the ligature significantly modifies the remodeling response, we re-analyzed the data from our previously published study, 15 using the alternate method of analysis described below. Interpretation of the data were initiated with scatter plots of the different vessel areas versus distance for each mouse, and mean values for each distance were calculated.…”

“…The practical utility of the method is then demonstrated by application to a data set testing the effects of osteopontin (OPN) on the response to carotid artery ligation. 15 In addition to providing increased significance, regression analysis revealed significant regional differences due to OPN that cannot be appreciated by conventional analysis methods. As regression analysis is a commonly used statistical method, actual calculations are not presented, and the reader is referred to SAS regression procedures 16 for description of the actual calculations performed.…”

Osteopontin is a novel marker of pancreatic ductal tissues and of undifferentiated pancreatic precursors in mice

“…Mice deficient in Opn develop normally, are fertile, and reach adulthood, although there is some evidence of alterations in vascular function, wound healing, and bone resorption in such mice due to the lack of Opn function (Liaw et al, 1998;Yoshitake et al, 1999;Myers et al, 2003). However, to our knowledge, no defects have been reported in the development or the physiology of Opn-deficient pancreatic tissues.…”