Abstract-Apoptosis of cardiomyocytes is increased in heart failure and has been implicated in disease progression. The activation of "proapoptotic" caspases represents a key step in cardiomyocyte apoptosis. In contrast, the role of "proinflammatory" caspases (caspases 1, 4, 5, 11, 12) is unclear. Here, we study the cardiac function of caspase-1. Gene array analysis in a murine heart failure model showed upregulation of myocardial caspase-1. In addition, we found increased expression of caspase-1 protein in murine and human heart failure. Mice with cardiomyocyte-specific overexpression of caspase-1 developed heart failure in the absence of detectable formation of interleukin (IL)-1␤ or IL-18 and inflammation. Transgenic caspase-1 induced primary cardiomyocyte apoptosis before structural and molecular signs of myocardial remodeling occurred. In contrast, deletion of endogenous caspase-1 was beneficial in the setting of myocardial infarction-induced heart failure. Furthermore, caspase-1-deficient mice were protected from ischemia/reperfusion-induced cardiomyocyte apoptosis. Studies in primary rat cardiomyocytes indicated that caspase-1 induces cardiomyocyte apoptosis primarily through activation of caspases-3 and -9. In contrast to previous findings, which imply a proinflammatory role of caspase-1, these data suggest a primary proapoptotic role for caspase-1 in cardiomyocytes. Our findings support a functional role for caspase-1-mediated myocardial apoptosis contributing to the progression of heart failure. (Circ Res. 2007;100:645-653.)

Hypertrophy represents the major physiological response of the heart to adapt to chronically enhanced workload, but is also crucial in the development of heart failure. Although we know of numerous inducers of cardiac hypertrophy, little is known about mechanisms that limit cardiac hypertrophy. Here, we describe the transcriptional repressor NAB1 as an endogenous regulator of cardiac growth. We identified NAB1 as being upregulated in both mouse and human heart failure. Nab1 is highly expressed in mammalian cardiac myocytes and it inhibited cardiomyocyte hypertrophy through repression of its targets, transcription factor Egr. Transgenic mice with cardiac-specific overexpression of Nab1 showed that Nab1 is a potent inhibitor of cardiac growth in response to pathological stimuli in vivo. Nab1 overexpression suppressed adrenergically induced and pressure overload-induced hypertrophy, whereas physiological growth during development and in response to exercise was not affected. These findings implicate the Nab1-Egr1 axis as a crucial regulator of pathological cardiac growth.

Efficacy of anticancer monoclonal antibodies (mAb) is limited by the exhaustion of effector mechanisms. IgG mAbs mediate cellular effector functions through FcgRs expressed on effector cells. IgA mAbs can also induce efficient tumor killing both in vitro and in vivo. IgA mAbs recruit FcaRI-expressing effector cells and therefore initiate different effector mechanisms in vivo compared with IgG. Here, we studied killing of tumor cells coexpressing EGFR and HER2 by the IgG mAbs cetuximab and trastuzumab and their IgA variants. In the presence of a heterogeneous population of effector cells (leukocytes), the combination of IgG and IgA mAbs to two different tumor targets (EGFR and HER2) led to enhanced cytotoxicity compared with each isotype alone. Combination of two IgGs or two IgAs or IgG and IgA against the same target did not enhance cytotoxicity. Increased cytotoxicity relied on the presence of both the peripheral blood mononuclear cell and the polymorphonuclear (PMN) fraction. Purified natural killer cells were only cytotoxic with IgG, whereas cytotoxicity induced by PMNs was strong with IgA and poor with IgG. Monocytes, which coexpress FcgRs and FcaRI, also displayed increased cytotoxicity by the combination of IgG and IgA in an overnight killing assay. Coinjection of cetuximab and IgA2-HER2 resulted in increased antitumor effects compared with either mAb alone in a xenograft model with A431-luc2-HER2 cells. Thus, the combination of IgG and IgA isotypes optimally mobilizes cellular effectors for cytotoxicity, representing a promising novel strategy to improve mAb therapy.

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