Calcineurin/NFAT Coupling Participates in Pathological, but not Physiological, Cardiac Hypertrophy

TLDR

Calcineurin is a calcium‑activated phosphatase that activates NFAT transcription factors, yet its precise role in initiating versus maintaining pathological versus physiological cardiac hypertrophy remains controversial. The study aimed to clarify calcineurin‑NFAT signaling in cardiac hypertrophy by creating and characterizing NFAT‑luciferase reporter transgenic mice. NFAT‑luciferase transgenic mice were generated, validated, and subjected to pressure‑overload, myocardial infarction, exercise training, and GH‑IGF‑1 stimulation, with luciferase activity inhibited by cyclosporin A. NFAT activity rose in delayed, sustained fashion during pathological hypertrophy and heart failure but was absent in exercise‑induced or GH‑IGF‑1–mediated physiological hypertrophy, and calcineurin‑Aβ knockout mice still hypertrophied, indicating calcineurin‑NFAT signaling is specific to maladaptive cardiac growth.

Abstract

Calcineurin (PP2B) is a calcium/calmodulin-activated, serine-threonine phosphatase that transmits signals to the nucleus through the dephosphorylation and translocation of nuclear factor of activated T cell (NFAT) transcription factors. Whereas calcineurin-NFAT signaling has been implicated in regulating the hypertrophic growth of the myocardium, considerable controversy persists as to its role in maintaining versus initiating hypertrophy, its role in pathological versus physiological hypertrophy, and its role in heart failure. To address these issues, NFAT-luciferase reporter transgenic mice were generated and characterized. These mice showed robust and calcineurin-specific activation in the heart that was inhibited with cyclosporin A. In the adult heart, NFAT-luciferase activity was upregulated in a delayed, but sustained manner throughout eight weeks of pathological cardiac hypertrophy induced by pressure-overload, or more dramatically following myocardial infarction-induced heart failure. In contrast, physiological hypertrophy as produced in two separate models of exercise training failed to show significant calcineurin-NFAT coupling in the heart at multiple time points, despite measurable increases in heart to body weight ratios. Moreover, stimulation of hypertrophy with growth hormone–insulin-like growth factor-1 (GH-IGF-1) failed to activate calcineurin-NFAT signaling in the heart or in culture, despite hypertrophy, activation of Akt, and activation of p70 S6K. Calcineurin Aβ gene–targeted mice also showed a normal hypertrophic response after GH-IGF-1 infusion. Lastly, exercise- or GH-IGF-1–induced cardiac growth failed to show induction of hypertrophic marker gene expression compared with pressure-overloaded animals. Although a direct cause-and-effect relationship between NFAT-luciferase activity and pathological hypertrophy was not proven here, our results support the hypothesis that separable signaling pathways regulate pathological versus physiological hypertrophic growth of the myocardium, with calcineurin-NFAT potentially serving a regulatory role that is more specialized for maladaptive hypertrophy and heart failure.