Aplicación móvil para monitoreo del arrecife mesoamericano

ITESO, A.C

Akt regulates L-type Ca2+ channel activity by modulating Cavα1 protein stability

The insulin IGF-1–PI3K–Akt signaling pathway has been suggested to improve cardiac inotropism and increase Ca2+ handling through the effects of the protein kinase Akt. However, the underlying molecular mechanisms remain largely unknown. In this study, we provide evidence for an unanticipated regulatory function of Akt controlling L-type Ca2+ channel (LTCC) protein density. The pore-forming channel subunit Cavα1 contains highly conserved PEST sequences (signals for rapid protein degradation), and in-frame deletion of these PEST sequences results in increased Cavα1 protein levels. Our findings show that Akt-dependent phosphorylation of Cavβ2, the LTCC chaperone for Cavα1, antagonizes Cavα1 protein degradation by preventing Cavα1 PEST sequence recognition, leading to increased LTCC density and the consequent modulation of Ca2+ channel function. This novel mechanism by which Akt modulates LTCC stability could profoundly influence cardiac myocyte Ca2+ entry, Ca2+ handling, and contractility

Ischemia/Reperfusion Injury Protection by Mesenchymal Stem Cell Derived Antioxidant Capacity

Mesenchymal stem cell (MSC) transplantation after ischemia/reperfusion (I/R) injury reduces infarct size and improves cardiac function. We used mouse ventricular myocytes (VMs) in an in vitro model of I/R to determine the mechanism by which MSCs prevent reperfusion injury by paracrine signaling. Exposure of mouse VMs to an ischemic challenge depolarized their mitochondrial membrane potential (Ψ(mito)), increased their diastolic Ca(2+), and significantly attenuated cell shortening. Reperfusion of VMs with Ctrl tyrode or MSC-conditioned tyrode (ConT) resulted in a transient increase of the Ca(2+) transient amplitudes in all cells. ConT-reperfused cells exhibited a decreased number early after depolarization (EADs) (ConT: 6.3% vs. Ctrl: 28.4%) and prolonged survival (ConT: 58% vs. Ctrl: 33%). Ψ(mito) rapidly recovered in Ctrl as well as ConT-treated VMs on reperfusion; however, in Ctrl solution, an exaggerated hyperpolarization of Ψ(mito) was determined that preceded the collapse of Ψ(mito). The ability of ConT to attenuate the hyperpolarization of Ψ(mito) was suppressed on inhibition of the PI3K/Akt signaling pathway or I(K,ATP). However, protection of Ψ(mito) was best mimicked by the reactive oxygen species (ROS) scavenger mitoTEMPO. Analysis of ConT revealed a significant antioxidant capacity that was linked to the presence of extracellular superoxide dismutase (SOD3) in ConT. In conclusion, MSC ConT protects VMs from simulated I/R injury by its SOD3-mediated antioxidant capacity and by delaying the recovery of Ψ(mito) through Akt-mediated opening of I(K,ATP). These changes attenuate reperfusion-induced ROS production and prevent the opening of the permeability transition pore and arrhythmic Ca(2+) release

The Loss of p21-Activated Kinase (Pak1) Promotes Atrial Arrhythmic Activity

Background: Atrial fibrillation (AF) is initiated through arrhythmic atrial excitation from outside the sinus node or remodeling of atrial tissue that allows reentry of excitation. Angiotensin II (AngII) has been implicated in initiation and maintenance of AF through changes in Ca2+ handling and production of reactive oxygen species (ROS). Objective: We aimed to determine the role of Pak1, a downstream target in the AngII signaling cascade, in atrial electrophysiology and arrhythmia. Method: WT and Pak1-/- mice were used to determine atrial function in vivo, on the organ and cellular level based on the quantification of electrophysiological and Ca2+-handling properties. Results: We demonstrate that reduced Pak1 activity increases the inducibility of atrial arrhythmia in vivo and in vitro. On the cellular level, Pak1-/- AMs exhibit increased basal and AngII (1 µM)-induced ROS production, sensitive to the NOX inhibitor apocynin (1 µM), and enhanced membrane translocation of Rac1 that is part of the multi-molecular NOX2 complex. Upon stimulation with AngII, Pak1-/- AMs exhibit an exaggerated increase in [Ca2+]i, and arrhythmic events that were sensitive to the NCX inhibitor KB-R7943 (1 µM) and suppressed in AMs from NOX2 deficient (gp91phox-/- ) mice. Pak1 stimulation (FTY720: 200 nM) in WT AMs and AMs from a canine model of ventricular tachypacing-induced AF prevented AngII-induced arrhythmic Ca2+ overload, by attenuating NCX activity in a NOX2 dependent manner. Conclusion: Overall the experiments support that during AF Pak1 stimulation can attenuate NCX dependent Ca2+ overload and trigger activity by suppressing NOX2 dependent ROS production

The C-terminus of the long AKAP13 isoform (AKAP-Lbc) is critical for development of compensatory cardiac hypertrophy

The objective of this study was to determine the role of A-Kinase Anchoring Protein (AKAP)-Lbc in the development of heart failure, by investigating AKAP-Lbc-protein kinase D1 (PKD1) signaling in vivo in cardiac hypertrophy. Using a gene-trap mouse expressing a truncated version of AKAP-Lbc (due to disruption of the endogenous AKAP-Lbc gene), that abolishes PKD1 interaction with AKAP-Lbc (AKAP-Lbc-ΔPKD), we studied two mouse models of pathological hypertrophy: i) angiotensin (AT-II) and phenylephrine (PE) infusion and ii) transverse aortic constriction (TAC)-induced pressure overload. Our results indicate that AKAP-Lbc-ΔPKD mice exhibit an accelerated progression to cardiac dysfunction in response to AT-II/PE treatment and TAC. AKAP-Lbc-ΔPKD mice display attenuated compensatory cardiac hypertrophy, increased collagen deposition and apoptosis, compared to wild-type (WT) control littermates. Mechanistically, reduced levels of PKD1 activation are observed in AKAP-Lbc-ΔPKD mice compared to WT mice, resulting in diminished phosphorylation of histone deacetylase 5 (HDAC5) and decreased hypertrophic gene expression. This is consistent with a reduced compensatory hypertrophy phenotype leading to progression of heart failure in AKAP-Lbc-ΔPKD mice. Overall, our data demonstrates a critical in vivo role for AKAP-Lbc-PKD1 signaling in the development of compensatory hypertrophy to enhance cardiac performance in response to TAC-induced pressure overload and neurohumoral stimulation by AT-II/PE treatment