The role of endothelin-1 in myocarditis and inflammatory cardiomyopathy: old lessons and new insights.

Endothelin-1 has emerged as an important participant in the pathophysiology of a variety of cardiovascular diseases, where it may act on endocrine, paracrine and autocrine bases. Here we review its regulated biosynthesis, receptor-mediated signaling, and functional consequences in the heart, with particular emphasis on cardiac development and disease. Exploring published data employing molecular genetic mouse models of endothelin dysregulation, we highlight its heretofore underappreciated role as a pro-inflammatory cytokine. We also present novel micro-array data from one such mouse model, which implicate the specific downstream pathways that may mediate endothelin-1's effects.

Conditional cardiac overexpression of endothelin-1 induces inflammation and dilated cardiomyopathy in mice.

BACKGROUND: Myocardial expression of endothelin-1 (ET-1) and its receptors ET(A) and ET(B) is increased in heart failure. However, the role of ET-1 and its signaling pathways in the pathogenesis of myocardial diseases is unclear. METHODS AND RESULTS: Human ET-1 cDNA was placed downstream of a promoter responsive to a doxycycline (DOX)-regulated transcriptional activator (tTA). This line (ET+) was bred with one harboring cardiac myocyte-restricted expression of tTA (alphaMHC-tTA). Myocardial ET-1 peptide levels were significantly increased in binary transgenic (BT, ET+/tTA+) compared with nonbinary transgenic (NBT, ET+/tTA-; ET-/tTA+; ET-/tTA-) or DOX-treated BT littermates (40.1+/-4.7 versus 2.6+/-1.2 fmol/mL, P<0.003). BT mice demonstrated progressive mortality between 5 and 11 weeks after DOX withdrawal, associated with left ventricular dilatation and contractile dysfunction (peak +dP/dT, 4673+/-468 versus 5585+/-658 mm Hg/s, P<0.05). An interstitial inflammatory infiltrate, including macrophages and T lymphocytes, was evident in the myocardium of BT mice, associated with sequential increases in nuclear factor-kappaB translocation and expression of tumor necrosis factor-alpha, interferon-gamma, interleukin-1 and interleukin-6. Significant prolongation of survival was observed with the combined ET(A)/ET(B) antagonist LU420627 (n=8, P<0.05) in BT mice but not the ET(A)-selective antagonist LU135252 (n=5, P=0.9), consistent with an important role for ET(B) in this model. CONCLUSIONS: These are the first data to demonstrate that cardiac overexpression of ET-1 is sufficient to cause increased expression of inflammatory cytokines and an inflammatory cardiomyopathy leading to heart failure and death.

Calcineurin-independent regulation of plasma membrane Ca2+ ATPase-4 in the vascular smooth muscle cell cycle.

Calcineurin mediates repression of plasma membrane Ca2+-ATPase-4 (PMCA4) expression in neurons, whereas c-Myb is known to repress PMCA1 expression in vascular smooth muscle cells (VSMC). Here, we describe a novel mouse VSMC line (MOVAS) in which 45Ca efflux rates decreased 50%, fura 2-AM-based intracellular Ca2+ concentrations ([Ca2+]i) increased twofold, and real-time RT-PCR and Western blot revealed a approximately 40% decrease in PMCA4 expression levels from G0 to G1/S in the cell cycle, where PMCA4 constituted approximately 20% of total PMCA protein. Although calcineurin activity increased fivefold as MOVAS progressed from G0 to G1/S, inhibition of this increase with either BAPTA or retroviral transduction with peptide inhibitors of calcineurin (CAIN), or its downstream target nuclear factor of activated T cells (NFAT) (VIVIT), had no effect on the repression of PMCA4 mRNA expression at G1/S. By contrast, Ca2+-independent activity of the calmodulin-dependent protein kinase-II (CaMK-II) increased eightfold as MOVAS progressed from G0 to G1/S, and treatment with an inhibitor of CaMK-II (KN-93) or transduction of a c-Myb-neutralizing antibody significantly alleviated the G1/S-associated repression of PMCA4. These data show that G1/S-specific PMCA4 repression in proliferating VSMC is brought about by c-Myb and CaMK-II and that calcineurin may regulate cell cycle-associated [Ca2+]i through alternate targets.