Cardiac-Specific Activation of IKK2 Leads to Defects in Heart Development and Embryonic Lethality.

Bärbel Kraut,Thomas Braun,Sawa Kostin,Harald J Maier,Katja Fiedler,Thomas Boettger,Annett Illing,Enikö Kókai,Thomas Wirth,Paul Walther,Diego Fraidenraich

doi:10.1371/journal.pone.0141591

Abstract

The transcription factor NF-κB has been associated with a range of pathological conditions of the heart, mainly based on its function as a master regulator of inflammation and pro-survival factor. Here, we addressed the question what effects activation of NF-κB can have during murine heart development. We expressed a constitutively active (CA) mutant of IKK2, the kinase activating canonical NF-κB signaling, specifically in cardiomyocytes under the control of the α-myosin heavy chain promoter. Expression of IKK2-CA resulted in embryonic lethality around E13. Embryos showed defects in compact zone formation and the contractile apparatus, and overall were characterized by widespread inflammation with infiltration of myeloid cells. Gene expression analysis suggested an interferon type I signature, with increased expression of interferon regulatory factors. While apoptosis of cardiomyocytes was only increased at later stages, their proliferation was decreased early on, providing an explanation for the disturbed compact zone formation. Mechanistically, this could be explained by activation of the JAK/STAT axis and increased expression of the cell cycle inhibitor p21. A rescue experiment with an IκBα superrepressor demonstrated that the phenotype was dependent on NF-κB. We conclude that activation of NF-κB is detrimental during normal heart development due to excessive activation of pro-inflammatory pathways.

Highlights

NF-κB is a pleiotropic transcription factor that has been associated with diverse biological functions such as cell proliferation, cell survival, immunity, and inflammation
Mice expressing the tetracycline transactivator under the control of the cardiomyocyte-specific α-myosin heavy chain (α-MyHC) promoter [10] were crossed with mice carrying a constitutively active IKK2 transgene (IKK2-CA) and a luciferase reporter gene regulated by a bidirectional, tTA-responsive promoter (Fig 1A) [9]
When mice were bred in the absence of doxycycline, i.e. under conditions that allow the transgene to be expressed, the number of double transgenic animals was strongly reduced in comparison to single transgenic and non-transgenic animals: Only 3.3% of the born animals (4 out of 122) carried both transgenes (Table 1)

Summary

Introduction

NF-κB is a pleiotropic transcription factor that has been associated with diverse biological functions such as cell proliferation, cell survival, immunity, and inflammation. These NF-κB dimers remain inactive and sequestered in the cytoplasm by inhibitory κB (IκB) proteins Different signals, such as engagement of cytokine or Toll-like receptors, trigger a signaling cascade that eventually converges on and activates the IκB kinase complex (IKK). This complex is composed of the catalytic subunits IKK1 ( known as IKKα) and IKK2 (IKKβ), and the regulatory subunit NEMO (IKKγ). IKK in turn can phosphorylate IκB proteins and thereby mark them for ubiquitin-mediated degradation This releases NF-κB dimers, which are free to translocate to the nucleus and activate specific target genes [2]

Methods

Results

Conclusion