gp130 Plays a Critical Role in Pressure Overload-induced Cardiac Hypertrophy
2001; Elsevier BV; Volume: 276; Issue: 25 Linguagem: Inglês
10.1074/jbc.m100814200
ISSN1083-351X
AutoresHiroki Uozumi, Yukio Hiroi, Yunzeng Zou, Eiki Takimoto, Haruhiro Toko, Pei Niu, Masaki Shimoyama, Yoshio Yazaki, Ryozo Nagai, Issei Komuro,
Tópico(s)Viral Infections and Immunology Research
Resumogp130, a common receptor for the interleukin 6 family, plays pivotal roles in growth and survival of cardiac myocytes. In the present study, we examined the role of gp130 in pressure overload-induced cardiac hypertrophy using transgenic (TG) mice, which express a dominant negative mutant of gp130 in the heart under the control of α myosin heavy chain promoter. TG mice were apparently healthy and fertile. There were no differences in body weight and heart weight between TG mice and littermate wild type (WT) mice. Pressure overload-induced increases in the heart weight/body weight ratio, ventricular wall thickness, and cross-sectional areas of cardiac myocytes were significantly smaller in TG mice than in WT mice. Northern blot analysis revealed that pressure overload-induced up-regulation of brain natriuretic factor gene and down-regulation of sarcoplasmic reticulum Ca2+ ATPase 2 gene were attenuated in TG mice. Pressure overload activated ERKs and STAT3 in the heart of WT mice, whereas pressure overload-induced activation of STAT3, but not of ERKs, was suppressed in TG mice. These results suggest that gp130 plays a critical role in pressure overload-induced cardiac hypertrophy possibly through the STAT3 pathway. gp130, a common receptor for the interleukin 6 family, plays pivotal roles in growth and survival of cardiac myocytes. In the present study, we examined the role of gp130 in pressure overload-induced cardiac hypertrophy using transgenic (TG) mice, which express a dominant negative mutant of gp130 in the heart under the control of α myosin heavy chain promoter. TG mice were apparently healthy and fertile. There were no differences in body weight and heart weight between TG mice and littermate wild type (WT) mice. Pressure overload-induced increases in the heart weight/body weight ratio, ventricular wall thickness, and cross-sectional areas of cardiac myocytes were significantly smaller in TG mice than in WT mice. Northern blot analysis revealed that pressure overload-induced up-regulation of brain natriuretic factor gene and down-regulation of sarcoplasmic reticulum Ca2+ ATPase 2 gene were attenuated in TG mice. Pressure overload activated ERKs and STAT3 in the heart of WT mice, whereas pressure overload-induced activation of STAT3, but not of ERKs, was suppressed in TG mice. These results suggest that gp130 plays a critical role in pressure overload-induced cardiac hypertrophy possibly through the STAT3 pathway. interleukin transgenic dominant negative myosin heavy chain wild type left ventricular end-diastolic internal diameter left ventricular end-systolic internal diameter brain natriuretic factor sarcoplasmic reticulum Ca2+ ATPase signal transducers and activators of transcription extracellular signal-regulated kinase(s) terminal deoxynucleotidyl transferase assay Because recent clinical studies have suggested that cardiac hypertrophy is an independent risk factor of cardiac morbidity and mortality (1Levy D. Garrison R.J. Savage D.D. Kannel W.B. Castelli W.P. N. Engl. J. Med. 1990; 322: 1561-1566Crossref PubMed Scopus (4910) Google Scholar), it has become even more important to clarify the mechanism of how cardiac hypertrophy is developed. Cardiomyocyte hypertrophy can be induced by a variety of factors such as mechanical stress (2Komuro I. Katoh Y. Kaida T. Shibazaki Y. Kurabayashi M. Takaku F. Yazaki Y. J. Biol. Chem. 1991; 266: 1265-1268Abstract Full Text PDF PubMed Google Scholar), cathecholamines (3Simpson P. Circ. Res. 1985; 56: 884-894Crossref PubMed Scopus (409) Google Scholar), angiotensin II (4Baker K.M. Aceto J.F. Am. J. Physiol. 1990; 259: H610-H618PubMed Google Scholar), endothelin-1 (5Shubeita H.E. McDonough P.M. Harris A.N. Knowlton K.U. Glembotski C.C. Brown J.H. Chien K.R. J. Biol. Chem. 1990; 265: 20555-20562Abstract Full Text PDF PubMed Google Scholar), and cytokines (6Yamamori T. Fukada K. Aebersold R. Korsching S. Fann M.J. Patterson P.H. Science. 1989; 246: 1412-1416Crossref PubMed Scopus (503) Google Scholar). Among them, hemodynamic overload, namely mechanical stress, is clinically most important. We and others (7Yamazaki T. Komuro I. Kudoh S. Zou Y. Shiojima I. Hiroi Y. Mizuno T. Maemura K. Kurihara H. Aikawa R. Takano H. Yazaki Y. J. Biol. Chem. 1996; 271: 3221-3228Abstract Full Text Full Text PDF PubMed Scopus (344) Google Scholar, 8Yamazaki T. Komuro I. Kudoh S. Zou Y. Shiojima I. Mizuno T. Takano H. Hiroi Y. Ueki K. Tobe K. Circ. Res. 1995; 77: 258-265Crossref PubMed Scopus (266) Google Scholar, 9Sadoshima J. Xu Y. Slayter H.S. Izumo S. Cell. 1993; 75: 977-984Abstract Full Text PDF PubMed Scopus (1171) Google Scholar) have reported that mechanical stress induces cardiomyocyte hypertrophy through vasoactive peptides such as angiotensin II and endothelin-1. Cardiotrophin-1, a member of the interleukin 6 (IL-6)1 family, was isolated and found to have a potent hypertrophic effect on cultured cardiomyocytes (10Pennica D. King K.L. Shaw K.J. Luis E. Rullamas J. Luoh S.M. Darbonne W.C. Knutzon D.S. Yen R. Chien K.R. Baker J.B. Wood W.I. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 1142-1146Crossref PubMed Scopus (504) Google Scholar). The IL-6 family of cytokines promotes cell type-specific pleiotropic effects by engaging multimeric receptor complexes that share the common affinity converter/signal-transducing subunit gp130 (11Hilton D.J. Trends Biochem. Sci. 1992; 17: 72-76Abstract Full Text PDF PubMed Scopus (214) Google Scholar, 12Taga T. Kishimoto T. Annu. Rev. Immunol. 1997; 15: 797-819Crossref PubMed Scopus (1310) Google Scholar, 13Hirano T. Int. Rev. Immunol. 1998; 16: 249-284Crossref PubMed Scopus (681) Google Scholar). Cardiotrophin-1 has been reported to induce hypertrophy of cardiac myocytes in vitro (14Wollert K.C. Taga T. Saito M. Narazaki M. Kishimoto T. Glembotski C.C. Vernallis A.B. Heath J.K. Pennica D. Wood W.I. Chien K.R. J. Biol. Chem. 1996; 271: 9535-9545Abstract Full Text Full Text PDF PubMed Scopus (337) Google Scholar). It has been reported that transgenic mice expressing both IL-6 and soluble IL-6 receptor, in which the gp130 is continuously activated, showed marked hypertrophy of the ventricular myocardium (15Hirota H. Yoshida K. Kishimoto T. Taga T. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 4862-4866Crossref PubMed Scopus (454) Google Scholar) and that targeted disruption of gp130 leads to severe anemia and a hypoplastic ventricular myocardium in the embryo (16Yoshida K. Taga T. Saito M. Suematsu S. Kumanogoh A. Tanaka T. Fujiwara H. Hirata M. Yamagami T. Nakahata T. Hirabayashi T. Yoneda Y. Tanaka K. Wang W.Z. Mori C. Shiota K. Yoshida N. Kishimoto T. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 407-411Crossref PubMed Scopus (575) Google Scholar). These results suggest that activation of gp130 induces cardiac hypertrophy, and it is still unknown whether gp130 mediates load-induced cardiac hypertrophy. Cardiotrophin-1 has been reported to promote survival of cardiac myocytes (17Sheng Z. Knowlton K. Chen J. Hoshijima M. Brown J.H. Chien K.R. J. Biol. Chem. 1997; 272: 5783-5791Abstract Full Text Full Text PDF PubMed Scopus (352) Google Scholar). Ventricular-restricted gp130 knockout mice showed marked ventricular wall dilatation with marked cardiomyocyte apoptosis and died in a week by pressure overload (18Hirota H. Chen J. Betz U.A. Rajewsky K. Gu Y. Ross J.J. Muller W. Chien K.R. Cell. 1999; 97: 189-198Abstract Full Text Full Text PDF PubMed Scopus (592) Google Scholar). These results suggest that gp130 signalings prevent cardiomyocytes from apoptotic cell death during the pressure overload. In the present study, to determine the physiological significance of gp130 in load-induced cardiac hypertrophy, we generated transgenic (TG) mice, which express a dominant negative form of gp130 specifically in the heart and examined hypertrophic responses by pressure overload produced by constriction of the abdominal aorta. A dominant negative mutant of gp130 (D.N.gp130) was constructed by converting cysteine at 702 to a stop codon as described previously (19Kumanogoh A. Marukawa S. Kumanogoh T. Hirota H. Yoshida K. Lee I.S. Yasui T. Yoshida K. Taga T. Kishimoto T. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 2478-2482Crossref PubMed Scopus (29) Google Scholar). D.N.gp130 cDNA was inserted into the unique KpnI site of pαMHCSA, which carries the mouse α myosin heavy chain (αMHC) promoter (20Ng W.A. Grupp I.L. Subramaniam A. Robbins J. Circ. Res. 1991; 68: 1742-1750Crossref PubMed Scopus (186) Google Scholar). αMHC promoter-D.N.gp130-poly(A) DNA was excised by XhoI and NotI and microinjected into the pronuclei of fertilized BDF1 mouse eggs. Offsprings from eggs microinjected with the DNA were selected by Southern blot analysis and polymerase chain reaction. Male TG and littermate wild type (WT) mice of 20 weeks old were used in the present study. Mice were housed under climate-controlled conditions with a 12-h light/dark cycle and were provided with standard food and water ad libitum. All protocols were approved by local institutional guidelines. Pressure overload was produced by constriction of the abdominal aorta as described previously in our laboratory (21Komuro I. Kurabayashi M. Takaku F. Yazaki Y. Circ. Res. 1988; 62: 1075-1079Crossref PubMed Scopus (199) Google Scholar, 22Harada K. Komuro I. Shiojima I. Hayashi D. Kudoh S. Mizuno T. Kijima K. Matsubara H. Sugaya T. Murakami K. Yazaki Y. Circulation. 1998; 97: 1952-1959Crossref PubMed Scopus (233) Google Scholar). Briefly, mice were anesthetized by intraperitoneal injection of sodium pentobarbital (30 mg/kg). The abdominal aorta was constricted at the suprarenal level with 7–0 nylon strings by ligation of the aorta with a blunted 27-gauge needle, which was pulled out thereafter. Transthoracic echocardiography was performed with HP Sonos 100 (Hewlett-Packard Co.) with a 10-MHz imaging transducer as described previously (22Harada K. Komuro I. Shiojima I. Hayashi D. Kudoh S. Mizuno T. Kijima K. Matsubara H. Sugaya T. Murakami K. Yazaki Y. Circulation. 1998; 97: 1952-1959Crossref PubMed Scopus (233) Google Scholar, 23Kojima M. Shiojima I. Yamazaki T. Komuro I. Zou Z. Wang Y. Mizuno T. Ueki K. Tobe K. Kadowaki T. Circulation. 1994; 89: 2204-2211Crossref PubMed Scopus (225) Google Scholar). Mice were anesthetized with ketamine (10 mg/kg intraperitoneal) and xylazine (15 mg/kg intraperitoneal). After a good quality two-dimensional image was obtained, M-mode images of the left ventricle were recorded. Left ventricular end-diastolic internal diameter (LVEDD), left ventricular end-systolic internal diameter (LVESD), intraventricular septum thickness, and left ventricular posterior wall thickness were measured. All measurements were performed by use of the leading edge-to-leading edge convention adopted by the American Society of Echocardiography (24Sahn D.J. DeMaria A. Kisslo J. Weyman A. Circulation. 1978; 58: 1072-1083Crossref PubMed Scopus (7228) Google Scholar). Fractional shortening was calculated as fractional shortening = ((LVEDD − LVESD)/LVEDD) × 100. Ejection fraction was calculated by the cubed method as follows: ejection fraction = ((LVEDD)3 − (LVESD)3)/LVEDD3. For histological analysis, hearts were fixed with 10% formalin by perfusion fixation. Fixed hearts embedded in paraffin were sectioned at 4-μm thickness and stained with hematoxylin-eosin. Cross-sectional areas of cardiac myocytes were measured from 10 sections. Suitable cross-sections were defined as having nearly circular capillary profiles and nuclei. The left ventricle was excised, and total RNA (10 μg) was prepared using ZolB (Biotecx Laboratories, Inc.), fractionated in 1% formaldehyde agarose gel, and transferred to nylon membrane. The blots were hybridized with the cDNA fragments of gp130, brain natriuretic factor (BNP), and sarcoplasmic reticulum Ca2+ ATPase 2 (SERCA2) genes. Polyclonal antibody to STAT3 (C-20) was purchased from Santa Cruz Biotechnology, Inc. The left ventricle was excised and lysed in lysis buffer (25 mm Tris-HCl, 25 mm NaCl, 1 mm sodium orthovanadate, 10 mm NaF, 10 mm sodium pyrophosphate, 10 nm okadaic acid, 0.5 mm EGTA, and 1 mm phenylmethylsulfonyl fluoride), and equal amounts (100 μg) of protein were incubated with 1 μg of anti-STAT3 for 1 h at 4 °C. The immune complexes were precipitated with protein A-Sepharose, and the immuneprecipitates were separated by SDS polyacrylamide gel electrophoresis and transferred to nitrocellulose membrane. The membranes were then blocked and incubated with anti-phosphotyrosine antibody (4G10), and the phosphotyrosine was detected by ECL (Amersham Pharmacia Biotech). The activities of ERKs were measured using myelin basic protein-containing gel (25Yamazaki T. Tobe K. Hoh E. Maemura K. Kaida T. Komuro I. Tamemoto H. Kadowaki T. Nagai R. Yazaki Y. J. Biol. Chem. 1993; 268: 12069-12076Abstract Full Text PDF PubMed Google Scholar). In brief, lysates of the left ventricles were subjected to electrophoresis on an SDS polyacrylamide gel containing 0.5 mg/ml myelin basic protein. ERKs in the gel were denatured in guanidine HCl and renatured in Tris-HCl (pH 8.0) containing 0.04% Triton X-100 and 2-mercaptoethanol (5 mm). Phosphorylation activities of ERKs were assayed by incubating the gel with [γ-32P]ATP. The 4-μm thickness paraffin sections were deparaffinized by immersing in xylene, rehydrated, and incubated with proteinase K (20 μg/ml). Next, the sections were incubated in methanol with 3% H2O2 to inactivate endogenous peroxidases, washed in phosphate-buffered saline, and incubated with terminal deoxynucleotidyl transferase and fluorescein isothiocyanate-dUTP for 90 min and horseradish peroxidase-conjugated anti-fluorescein isothiocyanate for 30 min at 37 °C using an apoptosis detection kit (Takara Biochemicals). The sections were stained with diaminobenzine and hematoxylin and mounted for light microscopic observations. Differences within groups were compared by the one-way analysis of variance (ANOVA) and Dunnett's t test. The accepted level of significance was p < 0.05. The carboxyl-terminal region of gp130 containing box3 is considered to play a critical role in gp130-mediated biological responses (26Ernst M. Novak U. Nicholson S.E. Layton J.E. Dunn A.R. J. Biol. Chem. 1999; 274: 9729-9737Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). D.N.gp130 TG mice were generated by overexpression of a box3-deleted form of gp130 under the control of αMHC promoter (Fig. 1). Six founders containing the transgene were identified, and three transgenic lines, in particular number 3, were used in this study. TG mice were apparently healthy and fertile, and there was no difference in the heart weight to body weight ratio between TG mice and WT mice, at baseline (Fig. 2).Figure 2Heart weight/body weight ratio. Pressure overload was produced by constriction of the abdominal aorta for 4 weeks. Mean ± S.E. of the heart weight/body weight ratio was shown (n = 3 in sham-operated mice, n = 4 in constricted mice). *p < 0.05; N.S., not significant.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Constriction of the abdominal aorta is an established method to produce pressure overload-induced cardiac hypertrophy (21Komuro I. Kurabayashi M. Takaku F. Yazaki Y. Circ. Res. 1988; 62: 1075-1079Crossref PubMed Scopus (199) Google Scholar, 22Harada K. Komuro I. Shiojima I. Hayashi D. Kudoh S. Mizuno T. Kijima K. Matsubara H. Sugaya T. Murakami K. Yazaki Y. Circulation. 1998; 97: 1952-1959Crossref PubMed Scopus (233) Google Scholar). 4 weeks after the operation, all mice were healthy, and the blood pressure monitored at right carotid artery was elevated as reported before in our laboratory (22Harada K. Komuro I. Shiojima I. Hayashi D. Kudoh S. Mizuno T. Kijima K. Matsubara H. Sugaya T. Murakami K. Yazaki Y. Circulation. 1998; 97: 1952-1959Crossref PubMed Scopus (233) Google Scholar) without any differences between TG mice and WT mice (data not shown). Echocardiography at 4 weeks after the operation revealed that left ventricular wall thickness was markedly increased (intraventricular septum thickness, sham 0.50 ± 0.03versus constriction 0.81 ± 0.03; left ventricular posterior wall thickness, sham 0.54 ± 0.04 versusconstriction 0.83 ± 0.08) in WT mice; however, TG mice showed less increase in left ventricular wall thickness (intraventricular septum thickness, sham 0.48 ± 0.03 versus constriction 0.59 ± 0.00; left ventricular posterior wall thickness, sham 0.52 ± 0.00 versus constriction 0.64 ± 0.04) (Table I). Furthermore, constriction of the abdominal aorta for 4 weeks increased the heart weight/body weight ratio by 40 ± 4% in WT mice and 15 ± 3% in TG mice (Fig. 2). The left ventricle of WT mice showed more marked hypertrophy than that of TG mice (Fig.3 A). Microscopic analysis showed that cross-sectional areas of cardiac myocytes of WT mice were more enlarged by pressure overload than those of TG mice (Fig.3 B). These results suggest that cardiac hypertrophy induced by pressure overload was attenuated in D.N.gp130 TG mice.Table IAnalysis of cardiac size and functionWT MiceTG MiceSham (n = 3)Constriction (n = 4)Sham (n = 3)Constriction (n = 4)LVEDD (mm)2.87±0.043.06±0.202.93±0.012.97±0.04LVESD (mm)1.56±0.051.53±0.081.53±0.081.42±0.03IVST (mm)0.50±0.030.81±0.031-aP < 0.05versus WT mice without constriction.0.48±0.030.59±0.001-bP < 0.05 TG mice after constriction versus WT mice after constriction.LVPWT (mm)0.54±0.040.83±0.081-aP < 0.05versus WT mice without constriction.0.52±0.000.64±0.041-bP < 0.05 TG mice after constriction versus WT mice after constriction.FS(%)46±350±348±452 ± 1EF0.84±0.030.87±0.030.86±0.030.89±0.01LVESD, left ventricular end-systolic internal diameter; IVST, intraventricular septum thickness; LVPWT, left ventricular posterior wall thickness; FS, fractional shortening; EF, ejection fraction.1-a P < 0.05versus WT mice without constriction.1-b P < 0.05 TG mice after constriction versus WT mice after constriction. Open table in a new tab LVESD, left ventricular end-systolic internal diameter; IVST, intraventricular septum thickness; LVPWT, left ventricular posterior wall thickness; FS, fractional shortening; EF, ejection fraction. Pressure overload by the constriction of the abdominal aorta up-regulates fetal-type cardiac genes and down-regulates SERCA2 gene (27Komuro I. Yazaki Y. Annu. Rev. Physiol. 1993; 55: 55-75Crossref PubMed Scopus (301) Google Scholar). We therefore examined the expression of BNP and SERCA2 in the hearts of WT and TG mice at the early and late phase after constriction of the abdominal aorta. BNP gene was slightly up-regulated at 2 days after pressure overload and markedly at 28 days in WT mice (Fig. 4). In TG mice, although BNP gene was also up-regulated by pressure overload, the expression levels were quite low compared with those of WT mice. In WT mice, SERCA2 gene was down-regulated from 2 days by pressure overload (Fig. 4). The down-regulation of SERCA2 gene by pressure overload was also attenuated in TG mice. Activation of gp130 evokes two distinct pathways, Janus kinase-STAT pathway and Ras-ERKs pathway (28Ernst M. Oates A. Dunn A.R. J. Biol. Chem. 1996; 271: 30136-30143Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar). We examined which pathway is important in the pressure overload-induced cardiac hypertrophy (Fig.5). Pressure overload activated both STAT3 and ERKs in the heart of WT mice. However, in TG mice, activation of STAT3 was barely detectable. In contrast, there was no difference in activation of ERKs between TG and WT mice. These results collectively suggest that pressure overload-induced activation of STAT3, but not of ERKs, is dependent on gp130 and that STAT3 may play a critical role in pressure overload-induced cardiac hypertrophy. It has been reported that activation of gp130 promotes survival of cardiac myocytes (17Sheng Z. Knowlton K. Chen J. Hoshijima M. Brown J.H. Chien K.R. J. Biol. Chem. 1997; 272: 5783-5791Abstract Full Text Full Text PDF PubMed Scopus (352) Google Scholar) and that ventricular-restricted gp130 knockout mice showed marked cardiomyocyte apoptosis and marked ventricular wall dilatation by pressure overload (18Hirota H. Chen J. Betz U.A. Rajewsky K. Gu Y. Ross J.J. Muller W. Chien K.R. Cell. 1999; 97: 189-198Abstract Full Text Full Text PDF PubMed Scopus (592) Google Scholar). We therefore examined whether TG mice showed cardiomyocyte apoptosis during pressure overload. As shown in Fig. 6, there was no increase in the number of TUNEL-positive cardiomyocytes in the heart of TG mice at the basal and by pressure overload compared with those of WT mice. It has been reported that gp130 is implicated in regulating cell growth, differentiation, and cell death in response to external stimuli in various tissues. In the present study, the TG mice were apparently healthy with no cardiac abnormalities at basal condition, suggesting that gp130 is not necessary for the development and the physiological function of the heart after birth. In contrast, gp130 plays a critical role in pressure overload-induced cardiac hypertrophy. By constriction of the abdominal aorta, TG mice showed less increase in the heart weight/body weight ratio and less changes in expression of BNP and SERCA2 genes compared with WT mice. We used number 3 line of transgenic mice, which expressed D.N.gp130 most abundantly. Mice of number 1 and number 2 lines also showed similar results with mild degree (data not shown). These results suggest that D.N.gp130 dose-dependently suppresses cardiac hypertrophy. The intracellular signaling pathways evoked by gp130 activation include the Janus kinase-induced STAT pathway and the Ras-ERKs pathway (28Ernst M. Oates A. Dunn A.R. J. Biol. Chem. 1996; 271: 30136-30143Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar). Activated STAT3 has been reported to form a homodimer that subsequently forms cis-inducing factor complexes and induces hypertrophy of cardiac myocytes (29Kodama H. Fukuda K. Pan J. Makino S. Baba A. Hori S. Ogawa S. Circ. Res. 1997; 81: 656-663Crossref PubMed Scopus (138) Google Scholar). It has been reported that STAT3 plays a critical role in generating the hypertrophic signal (30Kunisada K. Tone E. Fujio Y. Matsui H. Yamauchi T.K. Kishimoto T. Circulation. 1998; 98: 346-352Crossref PubMed Scopus (205) Google Scholar) and that mice overexpressing STAT3 showed marked cardiac hypertrophy (31Kunisada K. Negoro S. Tone E. Funamoto M. Osugi T. Yamada S. Okabe M. Kishimoto T. Yamauchi T.K. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 315-319Crossref PubMed Scopus (230) Google Scholar). In the present study, pressure overload activated ERKs and STAT3 in the heart of WT mice, whereas pressure overload-induced activation of STAT3, but not of ERKs, was suppressed in TG mice. These results suggest that pressure overload-induced activation of STAT3, but not of ERKs, is dependent on gp130 and that STAT3 may play a critical role in pressure overload-induced cardiac hypertrophy. Hirota et al. (18Hirota H. Chen J. Betz U.A. Rajewsky K. Gu Y. Ross J.J. Muller W. Chien K.R. Cell. 1999; 97: 189-198Abstract Full Text Full Text PDF PubMed Scopus (592) Google Scholar) have reported that ventricular-restricted knockout mice of gp130 showed dilatation of left ventricular wall and died within a week by constriction of transverse aorta without progression of adaptive hypertrophy of left ventricle (18Hirota H. Chen J. Betz U.A. Rajewsky K. Gu Y. Ross J.J. Muller W. Chien K.R. Cell. 1999; 97: 189-198Abstract Full Text Full Text PDF PubMed Scopus (592) Google Scholar). Although cardiac hypertrophy was attenuated, there was no sign of heart failure such as dilatation of left ventricular wall and reduced cardiac function nor death by constriction of the abdominal aorta in the D.N.gp130 TG mice. There are several possibilities for this discrepancy. First, the methods applied to produce the pressure overload were different. Transverse aortic constriction, applied in their experiment, induces stronger pressure overload than constriction of the abdominal aorta. It is possible that if the pressure overload is too strong, heart failure, but not adaptive cardiac hypertrophy, would be induced. To determine the role of gp130 in pressure overload-induced cardiac hypertrophy, we used a mild pressure overload model of abdominal aortic constriction. Second, they used gp130 null mice, whereas we used D.N.gp130-overexpressing mice. Because pressure overload-induced activation of STAT3 was abolished in the heart of D.N.gp130 TG mice, endogenous gp130 activity is thought to be strongly suppressed by overexpression of D.N.gp130. However, there is a possibility that the two mice have different gp130 activity. The transgene lacks box3 but has box1 and box2 regions of the cytoplasmic domain of gp130. Although box3 is indispensable for the Janus kinase-induced activation of STAT3 (26Ernst M. Novak U. Nicholson S.E. Layton J.E. Dunn A.R. J. Biol. Chem. 1999; 274: 9729-9737Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar), there is a possibility that box1 and box2 have some biological functions. There is a possibility that the two mice have different ERK activities, which they did not examine (18Hirota H. Chen J. Betz U.A. Rajewsky K. Gu Y. Ross J.J. Muller W. Chien K.R. Cell. 1999; 97: 189-198Abstract Full Text Full Text PDF PubMed Scopus (592) Google Scholar). It has been reported that the ERK signaling pathway is important for the gp130-dependent cell survival of cardiac myocytes (17Sheng Z. Knowlton K. Chen J. Hoshijima M. Brown J.H. Chien K.R. J. Biol. Chem. 1997; 272: 5783-5791Abstract Full Text Full Text PDF PubMed Scopus (352) Google Scholar) and that the tyrosine-containing motif, Tyr116-Xaa-Xaa-Val, of the cytoplasmic domain of gp130 is indispensable for the activation of SHP-2, a key molecule for the gp130-mediated signaling pathway leading to ERKs (26Ernst M. Novak U. Nicholson S.E. Layton J.E. Dunn A.R. J. Biol. Chem. 1999; 274: 9729-9737Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar, 32Takahashi T.M. Yoshida Y. Fukada T. Ohtani T. Yamanaka Y. Nishida K. Nakajima K. Hibi M. Hirano T. Mol. Cell. Biol. 1998; 18: 4109-4117Crossref PubMed Scopus (252) Google Scholar). Although the transgene lacks this motif, pressure overload induced activation of ERKs also in TG mice. These results suggest that some other factors such as angiotensin II and endothelin-1, which exert their effects through G protein-coupled receptors, play a predominant role in the activation of ERKs and cardiomyocyte survival in the TG mice. Although it remains to be determined how pressure overload induces production of the IL-6 family of cytokines in the heart, the present study suggests that gp130 plays a critical role in pressure overload-induced cardiac hypertrophy possibly through the STAT3 pathway. D.N.gp130 cDNA was generously provided by Tetsuya Taga (Kumamoto University, Japan).
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