Intrinsic-mediated caspase activation is essential for cardiomyocyte hypertrophy.

Cardiomyocyte hypertrophy is the cellular response that mediates pathologic enlargement of the heart. This maladaptation is also characterized by cell behaviors that are typically associated with apoptosis, including cytoskeletal reorganization and disassembly, altered nuclear morphology, and enhanced protein synthesis/translation. Here, we investigated the requirement of apoptotic caspase pathways in mediating cardiomyocyte hypertrophy. Cardiomyocytes treated with hypertrophy agonists displayed rapid and transient activation of the intrinsic-mediated cell death pathway, characterized by elevated levels of caspase 9, followed by caspase 3 protease activity. Disruption of the intrinsic cell death pathway at multiple junctures led to a significant inhibition of cardiomyocyte hypertrophy during agonist stimulation, with a corresponding reduction in the expression of known hypertrophic markers (atrial natriuretic peptide) and transcription factor activity [myocyte enhancer factor-2, nuclear factor kappa B (NF-κB)]. Similarly, in vivo attenuation of caspase activity via adenoviral expression of the biologic effector caspase inhibitor p35 blunted cardiomyocyte hypertrophy in response to agonist stimulation. Treatment of cardiomyocytes with procaspase 3 activating compound 1, a small-molecule activator of caspase 3, resulted in a robust induction of the hypertrophy response in the absence of any agonist stimulation. These results suggest that caspase-dependent signaling is necessary and sufficient to promote cardiomyocyte hypertrophy. These results also confirm that cell death signal pathways behave as active remodeling agents in cardiomyocytes, independent of inducing an apoptosis response.

Wnt11 promotes cardiomyocyte development by caspase-mediated suppression of canonical Wnt signals.

Specification and early patterning of the vertebrate heart are dependent on both canonical and noncanonical wingless (Wnt) signal pathways. However, the impact of each Wnt pathway on the later stages of myocardial development and differentiation remains controversial. Here, we report that the components of each Wnt signal conduit are expressed in the developing and postnatal heart, yet canonical/ß-catenin activity is restricted to nonmyocardial regions. Subsequently, we observed that noncanonical Wnt (Wnt11) enhanced myocyte differentiation while preventing stabilization of the ß-catenin protein, suggesting active repression of canonical Wnt signals. Wnt11 stimulation was synonymous with activation of a caspase 3 signal cascade, while inhibition of caspase activity led to accumulation of ß-catenin and a dramatic reduction in myocyte differentiation. Taken together, these results suggest that noncanonical Wnt signals promote myocyte maturation through caspase-mediated inhibition of ß-catenin activity.

Anion-induced adsorption of ferrocenated nanoparticles.

Au nanoparticles fully coated with omega-ferrocenyl hexanethiolate ligands, with average composition Au225(omega-ferrocenyl hexanethiolate)43, exhibit a unique combination of adsorption properties on Pt electrodes. The adsorbed layer is so robust that electrodes bearing submonolayer, monolayer, and multilayer quantities of these nanoparticles can be transferred to fresh electrolyte solutions and there exhibit stable ferrocene voltammetry over long periods of time. The kinetics of forming the robustly adsorbed layer are slow; monolayer and submonolayer deposition can be described by a rate law that is first order in nanoparticle concentration and in available electrode surface. The adsorption mechanism is proposed to involve entropically enhanced (multiple) ion-pair bridges between oxidized (ferrocenium) sites and certain specifically adsorbed electrolyte anions on the electrode. Adsorption is promoted by scanning to positive potentials (through the ferrocene wave) and by high concentrations of Bu4N+ X- electrolyte (X- = ClO4(-), PF6(-)) in the CH2Cl2 solvent; there is no adsorption if X- = p-toluenesulfonate or if the electrode is coated with an alkanethiolate monolayer. The electrode double layer capacity is not appreciably diminished by the adsorbed ferrocenated nanoparticles, which are gradually desorbed by scanning to potentials more negative than the electrode's potential of zero charge. At very slow scan rates, voltammetric current peaks are symmetrical and nearly reversible, but exhibit E(fwhm) considerably narrower (typically 35 mV) than ideally expected (90.6 mV, at 298 K) for a one-electron transfer or for reactions of multiple, independent redox centers with identical formal potentials. The peak narrowing is qualitatively explicable by a surface-activity effect invoking large, attractive lateral interactions between nanoparticles and, or alternatively, by a model in which ferrocene sites react serially at formal potentials that become successively altered as ion-pair bridges are formed. At faster scan rates, both deltaE(peak) and E(fwhm) increase in a manner consistent with a combination of uncompensated ohmic resistance of the electrolyte solution and of the adsorbed film, as distinct from behavior produced by slow electron transfer.

Size limitations for the formation of ordered striped nanoparticles.

A combination of immiscible molecules in the ligand shell of a gold nanoparticle (NP) has been shown to phase separate into a rippled structure; this phase separation can be used to direct the assembly of the NPs into chains. Here we demonstrate that only NPs within a certain size range can form chains, and we conclude that the rippled morphology of the ligand shell also exists only within that given size range. We corroborate this result with simulations of the ligand arrangement on NPs of various sizes.