宮脇 昭光

Acute myocarditis is a self-limiting disease. Most patients with myocarditis recover without cardiac dysfunction in spite of limited capacity of myocardial regeneration. Therefore, to address intrinsic reparative machinery of inflamed hearts, we investigated the cellular dynamics of cardiomyocytes in response to inflammation using experimental autoimmune myocarditis (EAM) model. EAM was induced by immunization of BALB/c mice with alpha-myosin heavy chain peptides twice. The inflammatory reaction was evoked with myocardial damage with the peak at 3 wk after the first immunization (EAM3w). Morphological and functional restoration started from EAM3w, when active protrusion formation, a critical process of myocardial healing, was observed in cardiomyocytes. Shotgun proteomics revealed that cytoskeletal proteins were preferentially increased in cardiomyocytes at EAM3w, compared with preimmunized (EAM0w) hearts, and that moesin was the most remarkably upregulated among them. Immunoblot analyses demonstrated that the expression of both total and phosphorylated moesin was upregulated in isolated cardiomyocytes from EAM3w hearts. Immunofluorescence staining showed that moesin was localized at cardiomyocyte protrusions at EAM3w. Adenoviral vectors expressing wild-type, constitutively active and inactive form of moesin (wtMoesin, caMoesin, and iaMoesin, respectively) were transfected in neonatal rat cardiomyocytes. The overexpression of wtMoesin and caMoesin resulted in protrusion formation, while not iaMoesin. Finally, we found that cardiomyocyte protrusions were accompanied by cell-cell contact formation. The expression of moesin was upregulated in cardiomyocytes under inflammation, inducing protrusion formation in a phosphorylation-dependent fashion. Moesin signal could be a novel therapeutic target that stimulates myocardial repair by promoting contact formation of cardiomyocytes.

STAT3 is a cardioprotective molecule against acute myocardial injury; however, recent studies have suggested that chronic STAT3 activation in genetically modified mice was detrimental after myocardial infarction (MI). In the present study, we assessed the biological significance of STAT3 activity in subacute MI using tamoxifen (TM)inducible cardiac-specific STAT3 knockout (STAT3 iCKO) mice. After coronary ligation, STAT3 was rapidly activated in hearts, and its activation was sustained to the subacute phase. To make clear the pathophysiological roles of STAT3 activation specifically in subacute MI, MI was generated in STAT3 iCKO mice followed by TM treatment for 14 consecutive days beginning from day 11 after MI, which ablated the STAT3 gene in the subacute phase. Intriguingly, mortality was increased by TM treatment in STAT3 iCKO mice, accompanied by an increased heart weight-to-body weight ratio. Masson's trichrome staining demonstrated that cardiac fibrosis was dramatically exacerbated in STAT3 iCKO mice 24 days after MI (fibrotic circumference: 58.3 +/- 6.7% in iCKO mice and 40.8 +/- 9.3% in control mice), concomitant with increased expressions of fibrosis-related gene transcripts, including matrix metalloproteinase 9, procollagen 1, and procollagen 3. Echocardiography clarified that cardiac function was deteriorated in STAT3 iCKO mice (fractional shortening: 20.6 +/- 4.1% in iCKO mice and 29.1 +/- 6.0% in control mice). Dihydroethidium fluorescence analysis revealed that superoxide production was increased in STAT3 iCKO mice. Moreover, immunohistochemical analyses revealed that capillary density was decreased in STAT3 iCKO mice. Finally, STAT3 deletion in subacute MI evoked severe cardiac hypertrophy in the border zone. In conclusion, the intrinsic activity of STAT3 in the myocardium confers the resistance to cardiac remodeling in subacute MI.

Obana M, Miyamoto K, Murasawa S, Iwakura T, Hayama A, Yamashita T, Shiragaki M, Kumagai S, Miyawaki A, Takewaki K, Matsumiya G, Maeda M, Yoshiyama M, Nakayama H, Fujio Y. Therapeutic administration of IL-11 exhibits the postconditioning effects against ischemia-reperfusion injury via STAT3 in the heart. Am J Physiol Heart Circ Physiol 303: H569-H577, 2012. First published June 15, 2012; doi:10.1152/ajpheart.00060.2012.-Activation of cardiac STAT3 by IL-6 cytokine family contributes to cardioprotection. Previously, we demonstrated that IL-11, an IL-6 cytokine family, has the therapeutic potential to prevent adverse cardiac remodeling after myocardial infarction; however, it remains to be elucidated whether IL-11 exhibits postconditioning effects. To address the possibility that IL-11 treatment improves clinical outcome of recanalization therapy against acute myocardial infarction, we examined its postconditioning effects on ischemia/reperfusion (I/R) injury. C57BL/6 mice were exposed to ischemia (30 min) and reperfusion (24 h), and IL-11 was intravenously administered at the start of reperfusion. I/R injury mediated the activation of STAT3, which was enhanced by IL-11 administration. IL-11 treatment reduced I/R injury, analyzed by triphenyl tetrazolium chloride staining [PBS, 46.7 +/- 14.4%; IL-11 (20 mu g/kg), 28.6 +/- 7.5% in the ratio of infarct to risk area]. Moreover, echocardiographic and hemodynamic analyses clarified that IL-11 treatment preserved cardiac function after I/R. Terminal deoxynucleotide transferase-mediated dUTP nick-end labeling staining revealed that IL-11 reduced the frequency of apoptotic cardiomyocytes after I/R. Interestingly, IL-11 reduced superoxide production assessed by in situ dihydroethidium fluorescence analysis, accompanied by the increased expression of metallothionein 1 and 2, reactive oxygen species (ROS) scavengers. Importantly, with the use of cardiac-specific STAT3 conditional knockout (STAT3 CKO) mice, it was revealed that cardiac-specific ablation of STAT3 abrogated IL-11-mediated attenuation of I/R injury. Finally, IL-11 failed to suppress the ROS production after I/R in STAT3 CKO mice. IL-11 administration exhibits the postconditioning effects through cardiac STAT3 activation, suggesting that IL-11 has the clinical therapeutic potential to prevent I/R injury in heart.