Sphingolipid signaling and treatment during remodeling of the uninfarcted ventricular wall after myocardial infarction

Abstract

The sphingosine kinase (SphK)/sphingosine 1-phosphate (S1P) pathway, known to determine the fate and growth of various cell types, can enhance cardiac myocyte survival in vitro and provide cardioprotection in acute ex vivo heart preparations. However, the relevance of these findings to chronic cardiac pathology has never been demonstrated. We hypothesized that S1P signaling is impaired during chronic remodeling of the uninfarcted ventricle during the evolution of post-myocardial infarction (MI) cardiomyopathy and that a therapeutic enhancement of S1P signaling would ameliorate ventricular dysfunction. SphK expression and activity were measured in the remote, uninfarcted myocardium (RM) of C57Bl/6 mice subjected to coronary artery ligation. The mRNA expression of S1P receptor isoforms was also measured, as was the activation of the downstream S1P receptor mediators. A cardioprotective role for S1P(1) receptor agonism was tested via the administration of the S1P(1)-selective agonist SEW2871 during and after MI. As a result, the expression data suggested that a dramatic reduction in SphK activity in the RM early after MI may reflect a combination of posttranscriptional and posttranslational modulation. SphK activity continued to decline gradually during chronic post-MI remodeling, when S1P(1) receptor mRNA also fell below baseline. The S1P(1)-specific agonism with oral SEW2871 during the first 2-wk after MI reduced apoptosis in the RM and resulted in improved myocardial function, as reflected in the echocardiographic measurement of fractional shortening. In conclusion, these results provide the first documentation of alterations in S1P-mediated signaling during the in situ development of cardiomyopathy and suggest a possible therapeutic role for the pharmacological S1P receptor agonism in the post-MI heart.

Fig. 1.

Relative abundance of mRNA for sphingosine kinases (SphK; A) and sphingosine 1-phosphate (S1P) receptors (B) in normal mouse (m) heart (n = 4 animals).

Fig. 2.

A: Gomori trichrome stain of infracted mouse myocardium at 1 and 12 wk (W) post-myocardial infarction (MI). B and C: changes in myocardial apoptosis (B) and total SphK activity (C) in the remote myocardium during the evolution of post-MI remodeling in mice. *P < 0.05; n = 10–14 animals for A and n = 4–6 animals for B and C.

Fig. 3.

A: mRNA expression of SphK1 and SphK2 in the remote, uninfarcted myocardium (RM) after MI in mouse hearts over time (*P < 0.05, ‡P = 0.08, n = 4–6 animals). B: Western blot of SphK1 and Sphk2 in lysates from the RM, early and late after MI, compared with sham-operated controls. C: SphK1 and -2 protein expression in lysate from the RM, early and late after MI, compared with sham-operated controls.

Fig. 4.

mRNA expression of S1P₁, S1P₂, and S1P₃ receptors in the RM of post-MI mouse hearts over time. *P < 0.05 and †P < 0.01; n = 4–6 animals.

Fig. 5.

A: Akt, p70S6 kinase, and ERK1/2 phosphorylation at 2 wk after MI in the RM of mouse hearts treated either with SEW2871 (SEW) or vehicle (Veh) (*P < 0.05 and †P < 0.01; n = 5 animals). B: apoptosis in SEW2871- and vehicle-treated mice at 2 wk after MI compared with uninfarcted control (†P < 0.01). C: fibrosis scores from Gomori trichrome-stained sections of remote myocardium (*P = 0.03). D: wall thickness of the remote myocardium in SEW2871- and vehicle-treated mice at 2 wk after MI (P = 0.08). E: myocyte cross-sectional surface area in the remote myocardium in Veh- and SEW-treated hearts, 1 and 2 wk after MI. N, normal; LV, left ventricular.