Copyright © 2005, European Society of Cardiology
Direct effects of leptin on size and extracellular matrix components of human pediatric ventricular myocytes
aDepartment of Biology, York University, Toronto, Canada M3J 1P3
bToronto General Research Institute, Toronto General Hospital, Canada
* Corresponding author. Tel.: +1 416 736 2100x66635; fax: +1 416 736 5698. Email address: gsweeney{at}yorku.ca
Objective: There is a well-documented association between obesity and heart failure although the mechanistic basis for this correlation is unclear. Both extracellular matrix remodeling and left ventricular hypertrophy are well-defined components of remodeling in heart failure, and here we further investigate the role of leptin, the obese gene product, on these parameters.
Methods: We used primary human pediatric ventricular cardiomyocytes combined with gelatin zymography, quantitative PCR analysis, proline and leucine incorporation assays, and investigation of kinase activation by Western blotting.
Results: We show using gelatin zymography that leptin dose-dependently (0–60 nM) increased proteolytic activity at ~72 kDa. Accordingly, upon quantitative PCR analysis we found that leptin increased expression of matrix metalloproteinase-2 (MMP-2). Leptin also caused an increase in collagen type III and IV mRNA expression and a decrease in collagen type I mRNA expression. This was reflected in no significant change in total collagen synthesis, measured by [3H]proline incorporation, in response to leptin. A statistically significant increase in cell size, [3H]leucine incorporation, and expression of well-characterized markers of cardiac hypertrophy, namely cardiac 
-actin and myosin light chain, were observed in response to leptin. We demonstrate activation of Janus-activated kinase and mitogen-activated protein kinase pathways by leptin, and using pharmacological inhibitors we show that these signaling pathways play a role in mediating the effects of leptin.
Conclusions: Our findings show that leptin regulates cell size, stimulates MMP-2 expression, and alters the profile, but not the total content, of collagen in human cardiomyocytes. This indicates the potential for altered leptin sensitivity to directly regulate cardiac remodeling in obesity.
KEYWORDS Leptin; obesity; heart failure; extracellular matrix; hypertrophy
Time for primary review 19 days
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