Attenuation of cardiac remodeling after myocardial infarction by muscle LIM protein-calcineurin signaling at the sarcomeric Z-disc

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National Academy of Sciences

RESUMO

Adverse left ventricular (LV) remodeling after myocardial infarction (MI) is a major cause for heart failure. Molecular modifiers of the remodeling process remain poorly defined. Patients with heart failure after MI have reduced LV expression levels of muscle LIM protein (MLP), a component of the sarcomeric Z-disk that is involved in the integration of stress signals in cardiomyocytes. By using heterozygous MLP mutant (MLP+/—) mice, we explored the role of MLP in post-MI remodeling. LV dimensions and function were similar in sham-operated WT and MLP+/— mice. After MI, however, MLP+/— mice displayed more pronounced LV dilatation and systolic dysfunction and decreased survival compared with WT mice, indicating that reduced MLP levels predispose to adverse LV remodeling. LV dilatation in MLP+/— mice was associated with reduced thickening but enhanced elongation of cardiomyocytes. Activation of the stress-responsive, prohypertrophic calcineurin–nuclear factor of activated T-cells (NFAT) signaling pathway was reduced in MLP+/— mice after MI, as shown by a blunted transcriptional activation of NFAT in cardiomyocytes isolated from MLP+/—/NFAT-luciferase reporter gene transgenic mice. Calcineurin was colocalized with MLP at the Z-disk in WT mice but was displaced from the Z-disk in MLP+/— mice, indicating that MLP is essential for calcineurin anchorage to the Z-disk. In vitro assays in cardiomyocytes with down-regulated MLP confirmed that MLP is required for stress-induced calcineurin–NFAT activation. Our study reveals a link between the stress sensor MLP and the calcineurin–NFAT pathway at the sarcomeric Z-disk in cardiomyocytes and indicates that reduced MLP–calcineurin signaling predisposes to adverse remodeling after MI.

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