Mitofusin-2 (Mfn2) suppresses smooth muscle cell proliferation through inhibition of the Ras-
extracellular signal-regulated kinases (ERK1/2) pathway. Since the ERK1/2 pathway is implicated in mediating hypertrophic signaling, we studied the changes in Mfn2 in
cardiac hypertrophy using in vitro and in vivo models.
Phenylephrine was used to induce
hypertrophy in neonatal rat ventricular myocytes (NRVMs). In vivo
hypertrophy models included spontaneously hypertensive rats (SHR), pressure-overload
hypertrophy by transverse aortic constriction (TAC),
hypertrophy of non-infarcted myocardium following
myocardial infarction (MI), and
cardiomyopathy due to cardiac-restricted overexpression of beta(2)-adrenergic receptors (beta(2)-TG). We determined hypertrophic parameters and analysed expression of
atrial natriuretic peptide (
ANP) and Mfn2 by real-time PCR. Phosphorylated-ERK1/2 (phospho-ERK) was measured by Western blot. Mfn2 was downregulated in
phenylephrine treated NRCMs (by approximately 40%), hypertrophied hearts from SHR (by approximately 80%), mice with TAC (at 1 and 3 weeks, by approximately 50%), and beta(2)-TG mice (by approximately 20%). However, Mfn2 was not downregulated in hypertrophied hearts with 15 weeks of TAC, nor in hypertrophied non-infarcted myocardium following MI. phospho-ERK1/2 was increased in hypertrophied myocardium at 1 week post-TAC, but not in non-infarcted myocardium after MI, indicating that downregulated Mfn2 may be accompanied by an increase of phospho-ERK1/2. This study shows, for the first time, downregulated Mfn2 expression in hypertrophied hearts, which depends on the etiology and time course of
hypertrophy. Further study is required to examine the causal relationship between Mfn2 and
cardiac hypertrophy.