Myocardial hypoxia-inducible HIF-1α, VEGF, and GLUT1 gene expression is associated with microvascular and ICAM-1 heterogeneity during endotoxemia

Abstract

The systemic inflammatory response to infection is the leading cause of mortality in North American intensive-care units. Although much is known about inflammatory mediators, the relationships between microregional inflammation, microvascular heterogeneity, hypoxia, hypoxia-inducible gene expression, and myocardial dysfunction are unknown. Male Sprague-Dawley rats were injected intraperitoneally with LPS to test the hypothesis that sepsis-induced local inflammation and increased microvascular heterogeneity are spatially and temporally associated with hypoxia, hypoxia-inducible gene expression, and decreased left-ventricular contractility. Using a combination of three-dimensional microvascular imaging, tissue Po2, and pressure-volume conductance measurements, we found that 5 h after LPS, minimum oxygen-diffusion distances increased ( P < 0.05), whereas tissue oxygenation and contractility both decreased ( P < 0.05) in the left ventricle. Real-time RT-PCR analysis revealed that the hypoxia-inducible genes hypoxia-inducible factor (HIF)-1α, VEGF, and glucose transporter (GLUT) 1 were all upregulated ( P < 0.05) in the left ventricle. Tissue regions expressing ICAM-1, obtained by using laser-capture microdissection, had increased HIF-1α and GLUT1 ( P < 0.05) gene expression. VEGF gene expression was more diffuse. In LPS rats, GLUT1 gene expression correlated ( P < 0.05) with left-ventricular contractility. In 5-h hypoxic cardiomyocytes, we found strong transient HIF-1α, weak VEGF, and greater prolonged GLUT1 gene expression. By comparison, the HIF-1α-GLUT1 gene-induction pattern was reversed in the left ventricle of LPS rats. Together, these results show that LPS induces hypoxia in the left ventricle associated with increased microvascular heterogeneity and decreased contractility. HIF-1α and GLUT1 gene induction are related to a heterogeneous ICAM-1 expression and may be cardioprotective during the onset of septic injury.