Krueppel-like factor 15 regulates Wnt/beta-catenin transcription and controls cardiac progenitor cell fate in the postnatal heart

Wnt/beta-catenin signalling controls adult heart remodelling in part via regulation of cardiac progenitor cell (CPC) differentiation. An enhanced understanding of mechanisms controlling CPC biology might facilitate the development of new therapeutic strategies in heart failure. We identified and characterized a novel cardiac interaction between Krueppel-like factor 15 and components of the Wnt/beta-catenin pathway leading to inhibition of transcription. In vitro mutation, reporter assays and co-localization analyses revealed that KLF15 requires both the C-terminus, necessary for nuclear localization, and a minimal N-terminal regulatory region to inhibit transcription. In line with this, functional Klf15 knock-out mice exhibited cardiac beta-catenin transcriptional activation along with functional cardiac deterioration in normal homeostasis and upon hypertrophy. We further provide in vivo and in vitro evidences for preferential endothelial lineage differentiation of CPCs upon KLF15 deletion. Via inhibition of beta-catenin transcription, KLF15 controls CPC homeostasis in the adult heart similar to embryonic cardiogenesis. This knowledge may provide a tool for reactivation of this apparently dormant CPC population in the adult heart and thus be an attractive approach to enhance endogenous cardiac repair

Biological role of hepoxilins: Upregulation of phospholipid hydroperoxide glutathione peroxidase as a cellular response to oxidative stress?

The 12S-lipoxygenase (12S-LOX) pathway of arachidonic acid (AA) metabolism is bifurcated at 12(S)-hydroperoxy-5Z,8Z,10E (12S-HpETE) in the reduction route to form 12S-hydroxy-eicosatetraenoic acid (12S-HETE) and in 8(S/R)-hydroxy-11(S),12S-trans-epoxyeicosa-5Z,9E,14Z-trienoic acid (HXA3) synthase pathway, previously known as isomerization route, to form hepoxilins. Earlier we showed that the HXA3 formation is restricted to cellular systems devoid of hydroperoxide reducing enzymes, e.g. GPxs, thus causing a persistent oxidative stress situation. Here, we show that HXA3 at as low as 100 nM concentration upregulates phospholipid hydroperoxide glutathione peroxidase (PHGPx) mRNA and protein expressions, whereas other metabolites of AA metabolism 12S-HpETE and 12S-HETE failed to stimulate the PHGPx. Moreover, the decrease in 12S-HpETE below a threshold value of the hydroperoxide tone causes both suppression of the overall 12S-LOX activity and a shift from HXA3 formation towards 12S-HETE formation. We therefore propose that under persistent oxidative stress the formation of HXA3 and the HXA3-induced upregulation of PHGPx constitute a compensatory defense response to protect the vitality and functionality of the cell. © 2007 Elsevier Ltd. All rights reserved

Hepoxilin A(3) protects beta-cells from apoptosis in contrast to its precursor, 12-hydroperoxyeicosatetraenoic acid

Pancreatic beta-cells have a deficit of scavenging enzymes such as catalase (Cat) and glutathione peroxidase (GPx) and therefore are susceptible to oxidative stress and apoptosis. Our previous work showed that, in the absence of cytosolic GPx in insulinoma RINm5F cells, an intrinsic activity of 12 lipoxygenase (12(S)-LOX) converts 12S-hydroperoxyeicosatetraenoic acid (12(S)-HpETE) to the bioactive epoxide hepoxilin A(3) (HXA(3)). The aim of the present study was to investigate the effect of HXA(3) on apoptosis as compared to its precursor 12(S)-HpETE and shed light upon the underlying pathways. In contrast to 12(S)-HpETE, which induced apoptosis via the extrinsic pathway, we found HXA(3) not only to prevent it but also to promote cell proliferation. In particular, HXA(3) suppressed the pro-apoptotic BAX and upregulated the anti-apoptotic Bcl-2. Moreover, HXA(3) induced the anti-apoptotic 12(S)-LOX by recruiting heat shock protein 90 (HSP90), another anti-apoptotic protein. Finally, a co-chaperone protein of HSP90, protein phosphatase 5 (PP5), was upregulated by HXA(3), which counteracted oxidative stress-induced apoptosis by dephosphorylating and thus inactivating apoptosis signal-regulating kinase 1 (ASK1). Taken together, these findings suggest that HXA(3) protects insulinoma cells from oxidative stress and, via multiple signaling pathways, prevents them from undergoing apoptosis

NF-κB activation is required for adaptive cardiac hypertrophy

AIMS: We have previously shown that cardiac-specific inhibition of NF-{kappa}B attenuates Angiotensin II (AngII) induced left ventricular (LV) hypertrophy in vivo. We now tested whether NF-{kappa}B inhibition is able to block LV-remodeling upon chronic pressure overload and chronic AngII-stimulation. METHODS: Cardiac-restricted NF-{kappa}B inhibition was achieved by expression of a stabilized I{kappa}B{alpha} mutant (I{kappa}B{alpha}DeltaN) in cells with an active {alpha}MHC promoter employing the Cre/lox technique. Upon low gradient trans -aortic constriction (TAC, gradient 21+/-3 mmHg), hypertrophy was induced in both male and female control mice after 4 weeks. RESULTS: At this time, LV-hypertrophy was blocked in transgenic male but not female mice with NF-{kappa}B inhibition. Amelioration of LV-hypertrophy was associated with activation of NF-{kappa}B by dihydrotestosterone in isolated neonatal cardiomyocytes. LV remodeling was not attenuated by NF-{kappa}B inhibition after 8 weeks TAC, demonstrated by decreased fractional shortening (FS) in both control and TG mice irrespective of gender. Similar results were obtained, when TAC was performed with higher gradients (48+/-4mmHG): In TG mice FS dropped to similar low levels over the same time course (FS sham: 29+/-1% (mean+/-SEM), FS control+14days TAC: 13+/-3%, FS TG+14days TAC: 9+/-5%). Similarly, LV remodeling was accelerated by NF-{kappa}B inhibition in an AngII-dependent genetic heart failure model (AT1-R({alpha}MHC)) associated with significantly increased cardiac fibrosis in double AT1-R({alpha}MHC)/TG mice. CONCLUSIONS: NF-{kappa}B inhibition attenuates cardiac hypertrophy in a gender specific manner but does not alter the course of stress-induced LV remodeling indicating NF-{kappa}B to be required for adaptive cardiac hypertrophy