Local atrial natriuretic peptide signaling prevents hypertensive cardiac hypertrophy in endothelial nitric-oxide synthase-deficient mice

The crucial functions of atrial natriuretic peptide (ANP) and endothelial nitric oxide/NO in the regulation of arterial blood pressure have been emphasized by the hypertensive phenotype of mice with systemic inactivation of either the guanylyl cyclase-A receptor for ANP (GC-A-/-) or endothelial nitric-oxide synthase (eNOS-/-). Intriguingly, similar levels of arterial hypertension are accompanied by marked cardiac hypertrophy in GC-A-/-, but not in eNOS-/-, mice, suggesting that changes in local pathways regulating cardiac growth accelerate cardiac hypertrophy in the former and protect the heart of the latter. Our recent observations in mice with conditional, cardiomyocyte-restricted GC-A deletion demonstrated that ANP locally inhibits cardiomyocyte growth. Abolition of these local, protective effects may enhance the cardiac hypertrophic response of GC-A-/- mice to persistent increases in hemodynamic load. Notably, eNOS-/- mice exhibit markedly increased cardiac ANP levels, suggesting that increased activation of cardiac GC-A can prevent hypertensive heart disease. To test this hypothesis, we generated mice with systemic inactivation of eNOS and cardiomyocyte-restricted deletion of GC-A by crossing eNOS-/- and cardiomyocyte-restricted GC-A-deficient mice. Cardiac deletion of GC-A did not affect arterial hypertension but significantly exacerbated cardiac hypertrophy and fibrosis in eNOS-/- mice. This was accompanied by marked cardiac activation of both the mitogen-activated protein kinase (MAPK) ERK 1/2 and the phosphatase calcineurin. Our observations suggest that local ANP/GC-A/cyclic GMP signaling counter-regulates MAPK/ERK- and calcineurin/nuclear factor of activated T cells-dependent pathways of cardiac myocyte growth in hypertensive eNOS-/- mice.     

Slowly reversible de-epoxidation of lutein-epoxide in deep shade leaves of a tropical tree legume may 'lock-in' lutein-based photoprotection during acclimation to strong light

The kinetics of response to strong light have been examined in deeply shaded leaves of the tropical tree legume (Inga sp.) which have extraordinarily high levels of the alpha-xanthophyll lutein-epoxide that are co-located in pigment-protein complexes of the photosynthetic apparatus with the beta-xanthophyll violaxanthin. As in other species, rapidly reversible photoprotection (measured as non-photochemical chlorophyll fluorescence quenching) is initiated within the time frame of sun-flecks (minutes), before detectable conversion of violaxanthin to antheraxanthin or zeaxanthin. Photoprotection is stabilized within hours of exposure to strong light by simultaneously engaging the reversible violaxanthin cycle and a slowly reversible conversion of lutein-epoxide to lutein. It is proposed that this lutein 'locks in' a primary mechanism of photoprotection during photoacclimation in this species, converting efficient light-harvesting antennae of the shade plant into potential excitation dissipating centres. It is hypothesized that lutein occupies sites L2 and V1 in light-harvesting chlorophyll protein complexes of photosystem II, facilitating enhanced photoprotection through the superior singlet and/or triplet chlorophyll quenching capacity of lutein.     

Imaging of colorectal adenocarcinoma using FT-IR microspectroscopy and cluster analysis

In this paper, three different clustering algorithms were applied to assemble infrared (IR) spectral maps from IR microspectra of tissues. Using spectra from a colorectal adenocarcinoma section, we show how IR images can be assembled by agglomerative hierarchical (AH) clustering (Ward's technique), fuzzy C-means (FCM) clustering, and k-means (KM) clustering. We discuss practical problems of IR imaging on tissues such as the influence of spectral quality and data pretreatment on image quality. Furthermore, the applicability of cluster algorithms to the spatially resolved microspectroscopic data and the degree of correlation between distinct cluster images and histopathology are compared. The use of any of the clustering algorithms dramatically increased the information content of the IR images, as compared to univariate methods of IR imaging (functional group mapping). Among the cluster imaging methods, AH clustering (Ward's algorithm) proved to be the best method in terms of tissue structure differentiation.     

One Enzyme,Two Functions: PON2 PREVENTS MITOCHONDRIAL SUPEROXIDE FORMATION AND APOPTOSIS INDEPENDENT FROM ITS LACTONASE ACTIVITY*

The human enzyme paraoxonase-2 (PON2) has two functions, an enzymatic lactonase activity and the reduction of intracellular oxidative stress. As a lactonase, it dominantly hydrolyzes bacterial signaling molecule 3OC12 and may contribute to the defense against pathogenic Pseudomonas aeruginosa. By its anti-oxidative effect, PON2 reduces cellular oxidative damage and influences redox signaling, which promotes cell survival. This may be appreciated but also deleterious given that high PON2 levels reduce atherosclerosis but may stabilize tumor cells. Here we addressed the unknown mechanisms and linkage of PON2 enzymatic and anti-oxidative function. We demonstrate that PON2 indirectly but specifically reduced superoxide release from the inner mitochondrial membrane, irrespective whether resulting from complex I or complex III of the electron transport chain. PON2 left O₂^˙̄ dismutase activities and cytochrome c expression unaltered, and it did not oxidize O₂^˙̄ but rather prevented its formation, which implies that PON2 acts by modulating quinones. To analyze linkage to hydrolytic activity, we introduced several point mutations and show that residues His¹¹⁴ and His¹³³ are essential for PON2 activity. Further, we mapped its glycosylation sites and provide evidence that glycosylation, but not a native polymorphism Ser/Cys³¹¹, was critical to its activity. Importantly, none of these mutations altered the anti-oxidative/anti-apoptotic function of PON2, demonstrating unrelated activities of the same protein. Collectively, our study provides detailed mechanistic insight into the functions of PON2, which is important for its role in innate immunity, atherosclerosis, and cancer.     

BCL-xL: time-dependent dissociation between modulation of apoptosis and invasiveness in human malignant glioma cells

Conditionally BCL-xL-overexpressing LNT-229 Tet-On glioma cell clones were generated to investigate whether the 'antiapoptosis phenotype' and the 'motility phenotype' mediated by BCL-2 family proteins in glioma cells could be separated. BCL-xL induction led to an immediate and concentration-dependent protection of LNT-229 cells from apoptosis. BCL-xL induction for up to 3 days did not result in altered invasiveness. In contrast, long-term BCL-xL induction for 21 days resulted in increased transforming growth factor-beta2 expression, and in metalloproteinase-2 and -14 dependent, but integrin independent, increased invasiveness. Withdrawal of doxycycline (Dox) abolished the protection from apoptosis whereas the 'invasion phenotype' remained stable. Dox stimulation of BCL-xL-inducible LNT-229 cells conferred infiltrative growth to BCL-xL-positive glioma cells in vivo and reduced the survival of tumor-bearing mice. These data allow to dissect a direct antiapoptotic action of BCL-xL from an indirect effect, presumably mediated by altered gene expression, which modifies tumor cell invasiveness in vitro and in vivo.