Chronic and intermittent hypoxia differentially regulate left ventricular inflammatory and extracellular matrix responses

Abstract

We evaluated the left ventricle (LV) response to hypoxia by comparing male Sprague Dawley rats exposed for 7 days to normoxia (control; n=18), chronic sustained hypoxia (CSH; n=12) and chronic intermittent hypoxia (CIH; n=12). Out of the 168 inflammatory, extracellular matrix and adhesion molecule genes evaluated, Ltb, Cdh4, Col5a1, Ecm1, MMP-11 and TIMP-2 increased in the LV (range: 87-138%), whereas Tnfrsf1a decreased 27%, indicating an increase in inflammatory status with CSH (all P<0.05). CIH decreased Ltb, Spp1 and Ccl5 levels, indicating reduced inflammatory status. While Laminin β2 gene levels increased 123%, MMP-9 and fibronectin gene levels both decreased 74% in CIH (all P<0.05). Right ventricle/body weight ratios increased in CSH (1.1±0.1 g g(-1)) compared with control (0.7±0.1 g g(-1)) and CIH (0.8±0.1 g g(-1); both P<0.05). Lung to body weight increased in CSH, while LV/body weight ratios were similar among all three groups. With CIH, myocyte cross sectional areas increased 25% and perivascular fibrosis increased 100% (both P<0.05). Gene changes were independent of global changes and were validated by protein levels. MMP-9 protein levels decreased 94% and fibronectin protein levels decreased 42% in CIH (both P<0.05). Consistent with a decreased inflammatory status, HIF-2α and eNOS protein levels were 36% and 44% decreased, respectively, in CIH (both P<0.05). In conclusion, our results indicate that following 7 days of hypoxia, inflammation increases in response to CSH and decreases in response to CIH. This report is the first to demonstrate specific and differential changes seen in the LV during chronic sustained and CIH.

Figure 1.

(a) Myocyte cross sectional area increases in CIH LV as compared with the control LV. (b) Sample images of Picrosirius Red stained LV tissue used to measure perivascular fibrosis that increased in CIH compared with the control and CSH LV (c). Data are mean±s.e.m., with control set to 1.0. *P<0.05 vs. control, †P<0.05 vs. control and CSH.

Figure 2

LV immunoblotting of MMP-9, Laminin β2, Laminin γ1 (C1) and Fibronectin. (a) MMP-9 protein levels showed a significant decrease in the CIH rats compared with the control and CSH rats. (b) Laminin β2 increased in the CSH and CIH rats compared with the control. (c) Laminin γ1 (laminin C1) also increased in CSH compared with the control, but decreased in the CIH LV. (d–f) Fibronectin protein (full length and the 120 and 180 kDa fragments) decreased from control to CSH and CIH, and full length fibronectin was further decreased from CSH to CIH LV. Data are mean±s.e.m. arbitrary densitometry units, which were normalized to total protein densitometry values. Control n=18, CSH n=12 and CIH n=12. *P<0.05 vs. control, †P<0.05 vs. CSH.

Figure 3

LV immunoblotting of eNOS and HIF-2α. (a) eNOS protein levels showed a significant change in all three groups compared to each other, with levels decreasing from control to CSH to CIH. (b) HIF-2α levels decreased in the CIH group compared with the control and CSH. Data are mean±s.e.m. arbitrary densitometry units, which were normalized to total protein densitometry values. Control n=18, CSH n=12 and CIH n=12. *P<0.05 vs. control; †P<0.05 vs. CSH.