J Korean Med Sci.  2013 Mar;28(3):402-408. 10.3346/jkms.2013.28.3.402.

Time-Dependent Expression Patterns of Cardiac Aquaporins Following Myocardial Infarction

• Zhang HZ
• Kim MH
• Lim JH
• Bae HR

• KMID: 1786938
• DOI: http://doi.org/10.3346/jkms.2013.28.3.402

Abstract

Aquaporins (AQPs) are expressed in myocardium and the implication of AQPs in myocardial water balance has been suggested. We investigated the expression patterns of AQP subtypes in normal myocardium and their changes in the process of edema formation and cardiac dysfunction following myocardial infarction (MI). Immunostaining demonstrated abundant expression of AQP1, AQP4, and AQP6 in normal mouse heart; AQP1 in blood vessels and cardiac myocytes, AQP4 exclusively on the intercalated discs between cardiac myocytes and AQP6 inside the myocytes. However, neither AQP7 nor AQP9 proteins were expressed in CD1 mouse myocardium. Echocardiography revealed that cardiac function was reduced at 1 week and recovered at 4 weeks after MI, whereas myocardial water content determined by wet-to-dry weight ratio increased at 1 week and rather reduced below the normal at 4 weeks. The expression of cardiac AQPs was up-regulated in MI-induced groups compared with sham-operated control group, but their time-dependent patterns were different. The time course of AQP4 expression coincided with that of myocardial edema and cardiac dysfunction following MI. However, expression of both AQP1 and AQP6 increased persistently up to 4 weeks. Our findings suggest a different role for cardiac AQPs in the formation and reabsorption of myocardial edema after MI.

Keyword

Myocardial Infarction; Myocytes, Cardiac; Aquaporins; AQP1; AQP4; AQP6

MeSH Terms

Animals
Aquaporin 1/metabolism
Aquaporin 4/metabolism
Aquaporin 6/metabolism
Aquaporins/*metabolism
Edema/pathology
Immunohistochemistry
Mice
Muscle Cells/metabolism
Myocardial Infarction/*metabolism/pathology/ultrasonography
Myocardium/metabolism/pathology
Time Factors
Aquaporin 4
Aquaporin 6
Aquaporins
Aquaporin 1

Figure

• 

  Fig. 1 Immunohistochemical analysis of aquaporins (AQPs) in normal mouse heart. Paraffin-embedded heart sections from normal mice were stained with antibodies against AQPs. AQP1 labels blood vessels and cytoplasm of cardiac myocytes (the arrow in A). AQP4 labeling is restricted to the intercalated discs (the arrow in B) and that of AQP6 distributes in striated pattern within the cardiac myocytes (the arrow in C). Neither AQP7 nor AQP9 are detected in the mouse heart (D and E).

• 

  Fig. 2 Immunofluorescence analysis of aquaporins (AQPs) in normal mouse heart. Frozen heart sections from normal mice were stained with antibodies against AQPs. AQP1 labels blood vessels and cytoplasm of cardiac myocytes (the arrow in A). AQP4 labeling is restricted to the intercalated discs (the arrow in B) and that of AQP6 distributes in striated pattern within the cardiac myocytes (the arrow in C). Neither AQP7 nor AQP9 are detected in the mouse heart (D and E).

• 

  Fig. 3 Histopathological and functional changes following myocardial infarction (MI). (A) Hematoxylin-eosin stains of the heart sections from mice either sham-operated (control) or at 1 week (MI-1W) or 4 weeks (MI-4W) after MI induction. The area of acute infarction containing necrotic myocytes (the filled arrow) and neutrophil infiltrate at 1 week is replaced with proliferating myofibroblasts (the empty arrow) and fibrous tissue at 4 weeks. (B) Echocardiographic analysis of cardiac function. Both left ventricle end-systolic diameter (LVESD) and left ventricle end-diastolic diameter (LVEDD) increase steadily after MI, but left ventricular ejection fraction (LVEF) is maximally reduced at 1 week, then recovered after 4 weeks. Data represent mean ± SD from 6 mice per group. *P < 0.05, †P < 0.01, compared with the corresponding value for control. (C) Myocardial water content (MWC) measured by wet-to-dry ratios. Data represent mean ± SD from 3 mice per group. *P < 0.05, compared with the corresponding value for control.

• 

  Fig. 4 Changes in AQP expression after myocardial infarction (MI). Immunohistochemical staining of AQP1, AQP4 and AQP6 on paraffin-embedded heart sections from mice either sham-operated (control, A, D, and G) or at 1 week (MI-1W, B, E, and H) or 4 weeks (MI-4W, C, F, and I) after MI induction. Labeling intensity of AQP1 in blood vessels and cardiac myocytes (arrows in B and C) increases with progression of MI. AQP4 labeling at intercalated discs is dispersed and undulated at 1 week (the arrows in E), but becomes more organized at 4 weeks (the arrow in F). AQP6 intensity in cardiac myocytes increases with the progression of MI, making the sarcomeric striations clearly discernible (arrows in H and I).

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  Fig. 5 Immunoblot analysis of AQP expression after myocardial infarction (MI). Immunoblotting of crude microsomal extract from myocardium of mice either sham-operated (control) or at 1 week (MI-1W) or 4 weeks (MI-4W) after MI induction. Expression levels of AQP1 and AQP6 increase steadily up to 4 weeks, but that of AQP4 peaks at 1 week then declines.

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