Abstract-Osteopontin (OPN), an extracellular matrix protein, is expressed in the myocardium with hypertrophy and failure. We tested the hypothesis that OPN plays a role in left ventricular (LV) remodeling after myocardial infarction (MI). Accordingly, OPN expression and LV structural and functional remodeling were determined in wild-type (WT) and OPN knockout (KO) mice 4 weeks after MI. Northern analysis showed increased OPN expression in the infarcted region, peaking 3 days after MI and gradually decreasing over the next 28 days. In the remote LV, OPN expression was biphasic, with peaks at 3 and 28 days. In situ hybridization and immunohistochemical analyses showed increased OPN mRNA and protein primarily in the interstitium. Infarct size, heart weight, and survival were similar in KO and WT mice after MI (PϭNS), whereas the lung wet weight/dry weight ratio was increased in the KO mice (PϽ0.005 versus sham-operated mice). Peak LV developed pressure was reduced to a similar degree after MI in the KO and WT mice. Key Words: extracellular matrix proteins Ⅲ osteopontin Ⅲ collagen Ⅲ myocyte slippage Ⅲ myocyte elongation T he dynamic synthesis and breakdown of extracellular matrix (ECM) proteins may play an important role in myocardial remodeling. 1,2 Recently, using spontaneously hypertensive and aortic-banded rats, we showed increased expression of osteopontin (OPN), an ECM protein, coincident with the development of heart failure. 3 Although first isolated from mineralized bone matrix, OPN has since been shown to be synthesized by several cell types, including cardiac myocytes, microvascular endothelial cells, and fibroblasts. 4 -6 OPN, an adhesive glycophosphoprotein with an arginineglycine-aspartic acid (RGD) sequence, has been shown to interact with integrins (␣ V ␤ 3 , ␣ V ␤ 1 , and ␣ V ␤ 5 ) and the CD44 receptor in an RGD-dependent manner. 4,7 OPN appears capable of mediating diverse biological functions, including cell adhesion, chemotaxis, and signaling. 4,8 OPN has also been shown to interact with fibronectin and collagen, suggesting its possible role in matrix organization and/or stability. 9 -11 Recently, using a mammary cell line, we observed that suppression of OPN synthesis leads to increased activity of matrix metalloproteinase (MMP)-2. 12 In fact, there is increased expression of OPN in several tissues in response to injury, suggesting a role in wound healing. Using a skin incision model, Liaw et al 13 observed disorganization of the matrix and alteration of collagen fibrillogenesis, leading to collagen fibrils with smaller diameters in OPN knockout (KO) mice. Similarly, OPN has been shown to play a critical role in the generation of interstitial fibrosis in the kidney after obstructive nephropathy. 14 Remodeling after myocardial infarction (MI) is associated with left ventricular (LV) dilation, decreased cardiac function, and increased mortality. 15 Early dilation of the LV is likely due to scar expansion in the infarcted region, 16 -18 followed later by progressive remodeling 19 in the noninf...

Rationale High-sensitivity in vivo phenotyping of cardiac function is essential for evaluating genes of interest and novel therapies in small animal models of cardiovascular disease. Transthoracic echocardiography is the principal method currently used for assessing cardiac structure and function; however, standard echocardiographic techniques are relatively insensitive to early or subtle changes in cardiac performance, particularly in mice. Objective To develop and validate an echocardiographic strain imaging methodology for sensitive and rapid cardiac phenotyping in small animal models. Methods and Results Herein, we describe a modified echocardiographic technique that utilizes speckle-tracking based strain analysis for the non-invasive evaluation of cardiac performance in adult mice. This method is found to be rapid, reproducible, and highly sensitive in assessing both regional and global left ventricular (LV) function. Compared to conventional echocardiographic measures of LV structure and function, peak longitudinal strain and strain rate were able to detect changes in adult mouse hearts at an earlier time point following myocardial infarction (post-MI) and predicted the later development of adverse LV remodeling. Moreover, speckle-tracking based strain analysis was able to clearly identify subtle improvement in LV function that occurred early in response to standard post-MI cardiac therapy. Conclusions Our results highlight the utility of speckle-tracking based strain imaging for detecting discrete functional alterations in mouse models of cardiovascular disease in an efficient and comprehensive manner. Echocardiography speckle-tracking based strain analysis represents a method for relatively high-throughput and sensitive cardiac phenotyping, particularly in evaluating emerging cardiac agents and therapies in mice.

Background-Increased rates of glucose uptake and glycolysis have been repeatedly observed in cardiac hypertrophy and failure. Although these changes have been considered part of the fetal gene reactivation program, the functional significance of increased glucose utilization in hypertrophied and failing myocardium is poorly understood. Methods and Results-We generated transgenic (TG) mice with cardiac-specific overexpression of insulin-independent glucose transporter GLUT1 to recapitulate the increases in basal glucose uptake rate observed in hypertrophied hearts. Isolated perfused TG hearts showed a greater rate of basal glucose uptake and glycolysis than hearts isolated from wild-type littermates, which persisted after pressure overload by ascending aortic constriction (AAC). The in vivo cardiac function in TG mice, assessed by echocardiography, was unaltered. When subjected to AAC, wild-type mice exhibited a progressive decline in left ventricular (LV) fractional shortening accompanied by ventricular dilation and decreased phosphocreatine to ATP ratio and reached a mortality rate of 40% at 8 weeks. In contrast, TG-AAC mice maintained LV function and phosphocreatine to ATP ratio and had Ͻ10% mortality. Conclusions-We found that increasing insulin-independent glucose uptake and glycolysis in adult hearts does not compromise cardiac function. Furthermore, we demonstrate that increasing glucose utilization in hypertrophied hearts protects against contractile dysfunction and LV dilation after chronic pressure overload.