Background Hemodynamic load regulates myocardial function and gene expression. We tested the hypothesis that afterload and preload despite similar average load result in different phenotypes. Methods and Results Afterload and preload were compared in mice with transversal aortic constriction (TAC) and aorto-caval shunt (Shunt). When compared to sham mice, six hours after surgery, systolic wall stress (afterload) was increased in TAC (+40%, P<0.05), diastolic wall stress (preload) was increased in Shunt (+277%, P<0.05) and TAC (+74%, P<0.05) and mean total wall stress was similarly increased in TAC (69%) and Shunt (67%) (TAC vs. Shunt: not significant (n.s.), each P<0.05 vs. Sham). At 1 week, left ventricular weight/tibia length was significantly increased by 22% in TAC and 29% in Shunt (n.s. TAC vs. Shunt). After 24 hours and 1 week, calcium/calmodulin dependent protein kinase II (CaMKII) signaling was increased in TAC. This resulted in altered calcium cycling, including increased L-type calcium current, calcium transients, fractional SR release and calcium spark frequency. In Shunt, Akt phosphorylation was increased. TAC was associated with inflammation, fibrosis and cardiomyocyte apoptosis. The latter was significantly reduced in CaMKIIδ-KO TAC mice. 157 mRNAs and 13 microRNAs were differentially regulated in TAC vs. Shunt. After 8 weeks, fractional shortening was lower and mortality higher in TAC Conclusions Afterload results in maladaptive fibrotic hypertrophy with CaMKII-dependent altered calcium cycling and apoptosis. Preload is associated with Akt activation without fibrosis, little apoptosis, better function and lower mortality. This indicates that different loads result in distinct phenotype differences which may require specific pharmacological interventions.

The development of quantitative techniques in mass spectrometry has generated the ability to systematically monitor protein expression. Isobaric tags for relative and absolute quantification (iTRAQ) have become a widely used tool for the quantification of proteins. However, application of iTRAQ methodology using ion traps and hybrid mass spectrometers containing an ion trap such as the LTQOrbitrap was not possible until the development of pulsed Q dissociation (PQD) and higher energy C-trap dissociation (HCD). Both methods allow iTRAQ-based quantification on an LTQ-Orbitrap but are less suited for protein identification at a proteomic scale than the commonly used collisional induced dissociation (CID) fragmentation. We developed an analytical strategy combining the advantages of CID and HCD, allowing sensitive and accurate protein identification and quantitation at the same time. In a direct comparison, the novel method outperformed PQD and HCD regarding its limit of detection, the number of identified peptides and the analytical precision of quantitation. The new method was applied to study changes in protein expression in mouse hearts upon transverse aortic constriction, a model for cardiac stress.

Rationale Telethonin (also known as titin-cap or t-cap) is a 19 kDa Z-disk protein with a unique β-sheet structure, hypothesized to assemble in a palindromic way with the N-terminal portion of titin and to constitute a signalosome participating in the process of cardio-mechanosensing. In addition, a variety of telethonin mutations are associated with the development of several different diseases; however, little is known about the underlying molecular mechanisms and telethonin’s in vivo function. Objective Here we aim to investigate the role of telethonin in vivo and to identify molecular mechanisms underlying disease as a result of its mutation. Methods and Results By using a variety of different genetically altered animal models and biophysical experiments we show that, contrary to previous views, telethonin is not an indispensable component of the titin-anchoring system, nor is deletion of the gene or cardiac specific overexpression associated with a spontaneous cardiac phenotype. Rather, additional titin-anchorage sites, such as actin-titin crosslinks via α-actinin, are sufficient to maintain Z-disk stability despite the loss of telethonin. We demonstrate that a main novel function of telethonin is to modulate the turnover of the pro-apoptotic tumor suppressor p53 after biomechanical stress in the nuclear compartment, thus linking telethonin, a protein well known to be present at the Z-disk, directly to apoptosis (“mechanoptosis”). In addition, loss of telethonin mRNA and nuclear accumulation of this protein is associated with human heart failure, an effect which may contribute to enhanced rates of apoptosis found in these hearts. Conclusions Telethonin knockout mice do not reveal defective heart development or heart function under basal conditions, but develop heart failure following biomechanical stress, owing at least in part to apoptosis of cardiomyocytes, an effect which may also play a role in human heart failure.