Production and analysis of transgenic mice exhibiting concentric hypertrophy in a heart using Cre-loxP system

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Interleukin-1 (IL-1) is a physiologically active factor produced and secreted by a variety of cells including those responsible for controlling immunity, and it plays an important role in immunity reactions. IL-1 is known to inhibit contractility in isolated heart and myocytes, and also cause hypertrophy in cultured myocytes. All these findings came from the in vitro events, and therefore in vivo experiments using transgenic (Tg) mice are required In the past few years, we generated two lines overexpressing human IL-1α (hIL-1α) under control of CMV enhancer/chicken β-actin promoter (CAG) system, and found that of two lines one exhibited concentric hypertrophy with cardiomyocyte hypertrophy and died before sexual maturation (Isoda et al., J. Cardiac Failure 7, 355-364, 2001). Several analyses of this line revealed that the heart was composed by cells like proliferative fetal myocytes. This finding suggests that constitutively elevated levels of IL-1α in a heart may keep myocytes in a ju … More venile state even after birth. For further study, it was required for maintaining Tg mice expressing hIL-1α as those capable of producing offspring. For this purpose, we employed Cre-loxP system. We produced Tg mice carrying a CELIZ transgene comprising CAG promoter, loxP-floxed EGFP/CAT, hIL-1α cDNA, IRES and lacZ gene. We obtained two lines all of which appeared to express EGFP relatively strongly, as evaluated for the strength of EGFP fluorescence under UV illumination. When these Tg mice were mated to MNCE Tg mice (Sato et al., Mol Reprod Dev 60, 446-456, 2001) which expressed Cre gene ubiquitously, the resulting double Tg mice (aged 8-10 weeks) exhibited expression of hIL-1α and lacZ gene in various tissues including heart, but did not concentric hypertrophy in their hearts. This is probably due to extremely low level of hIL-1α produced in these double Tg mice, since Northern blot analysis failed to detect distinct band for hIL-1α mRNA. Further attempt to increase the level of hIL-1α is strictly required for manifestation of concentric hypertrophy in murine heart. Less