Adenylyl cyclase isoform 1 contributes to sinoatrial node automaticity via functional microdomains.

Sinoatrial node (SAN) cells are the heart's primary pacemaker. Their activity is tightly regulated by ß-adrenergic receptor (ß-AR) signaling. Adenylyl cyclase (AC) is a key enzyme in the ß-AR pathway that catalyzes the production of cAMP. There are current gaps in our knowledge regarding the dominant AC isoforms and the specific roles of Ca2+-activated ACs in the SAN. The current study tests the hypothesis that distinct AC isoforms are preferentially expressed in the SAN and compartmentalize within microdomains to orchestrate heart rate regulation during ß-AR signaling. In contrast to atrial and ventricular myocytes, SAN cells express a diverse repertoire of ACs, with ACI as the predominant Ca2+-activated isoform. Although ACI-KO (ACI-/-) mice exhibit normal cardiac systolic or diastolic function, they experience SAN dysfunction. Similarly, SAN-specific CRISPR/Cas9-mediated gene silencing of ACI results in sinus node dysfunction. Mechanistically, hyperpolarization-activated cyclic nucleotide-gated 4 (HCN4) channels form functional microdomains almost exclusively with ACI, while ryanodine receptor and L-type Ca2+ channels likely compartmentalize with ACI and other AC isoforms. In contrast, there were no significant differences in T-type Ca2+ and Na+ currents at baseline or after ß-AR stimulation between WT and ACI-/- SAN cells. Due to its central characteristic feature as a Ca2+-activated isoform, ACI plays a unique role in sustaining the rise of local cAMP and heart rates during ß-AR stimulation. The findings provide insights into the critical roles of the Ca2+-activated isoform of AC in sustaining SAN automaticity that is distinct from contractile cardiomyocytes.

Noncoding RNAs in Cardiac Hypertrophy and Heart Failure.

Heart failure is a major global health concern. Noncoding RNAs (ncRNAs) are involved in physiological processes and in the pathogenesis of various diseases, including heart failure. ncRNAs have emerged as critical components of transcriptional regulatory pathways that govern cardiac development, stress response, signaling, and remodeling in cardiac pathology. Recently, studies of ncRNAs in cardiovascular disease have achieved significant development. Here, we discuss the roles of ncRNAs, including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs) that modulate the cardiac hypertrophy and heart failure.

The THO Complex Coordinates Transcripts for Synapse Development and Dopamine Neuron Survival.

Synaptic vesicle and active zone proteins are required for synaptogenesis. The molecular mechanisms for coordinated synthesis of these proteins are not understood. Using forward genetic screens, we identified the conserved THO nuclear export complex (THOC) as an important regulator of presynapse development in C. elegans dopaminergic neurons. In THOC mutants, synaptic messenger RNAs are retained in the nucleus, resulting in dramatic decrease of synaptic protein expression, near complete loss of synapses, and compromised dopamine function. CRE binding protein (CREB) interacts with THOC to mark synaptic transcripts for efficient nuclear export. Deletion of Thoc5, a THOC subunit, in mouse dopaminergic neurons causes severe defects in synapse maintenance and subsequent neuronal death in the substantia nigra compacta. These cellular defects lead to abrogated dopamine release, ataxia, and animal death. Together, our results argue that nuclear export mechanisms can select specific mRNAs and be a rate-limiting step for neuronal differentiation and survival.

Phosphodiesterase-5 inhibition preserves renal hemodynamics and function in mice with diabetic kidney disease by modulating miR-22 and BMP7.

Diabetic Nephropathy (DN) is the leading cause of end-stage renal disease. Preclinical and experimental studies show that PDE5 inhibitors (PDE5is) exert protective effects in DN improving perivascular inflammation. Using a mouse model of diabetic kidney injury we investigated the protective proprieties of PDE5is on renal hemodynamics and the molecular mechanisms involved. PDE5i treatment prevented the development of DN-related hypertension (P < 0.001), the increase of urine albumin creatinine ratio (P < 0.01), the fall in glomerular filtration rate (P < 0.001), and improved renal resistive index (P < 0.001) and kidney microcirculation. Moreover PDE5i attenuated the rise of nephropathy biomarkers, soluble urokinase-type plasminogen activator receptor, suPAR and neutrophil gelatinase-associated lipocalin, NGAL. In treated animals, blood vessel perfusion was improved and vascular leakage reduced, suggesting preserved renal endothelium integrity, as confirmed by higher capillary density, number of CD31+ cells and pericyte coverage. Analysis of the mechanisms involved revealed the induction of bone morphogenetic protein-7 (BMP7) expression, a critical regulator of angiogenesis and kidney homeostasis, through a PDE5i-dependent downregulation of miR-22. In conclusion PDE5i slows the progression of DN in mice, improving hemodynamic parameters and vessel integrity. Regulation of miR-22/BMP7, an unknown mechanism of PDE5is in nephrovascular protection, might represent a novel therapeutic option for treatment of diabetic complications.

Characterization of the interaction between the dopamine D4 receptor, KLHL12 and ß-arrestins.

Dopamine receptors are G protein-coupled receptors involved in regulation of cognition, learning, movement and endocrine signaling. The action of G protein-coupled receptors is highly regulated by multifunctional proteins, such as ß-arrestins which can control receptor desensitization, ubiquitination and signaling. Previously, we have reported that ß-arrestin 2 interacts with KLHL12, a BTB-Kelch protein which functions as an adaptor in a Cullin3-based E3 ligase complex and promotes ubiquitination of the dopamine D4 receptor. Here, we have investigated the molecular basis of the interaction between KLHL12 and ß-arrestins and questioned its functional relevance. Our data demonstrate that ß-arrestin 1 and ß-arrestin 2 bind constitutively to the most common dopamine D4 receptor polymorphic variants and to KLHL12 and that all three proteins can interact within a single macromolecular complex. Surprisingly, stimulation of the receptor has no influence on the association between these proteins or their cellular distribution. We found that Cullin3 also interacts with both ß-arrestins but has no influence on their ubiquitination. Knockout of one of the two ß-arrestins hampers neither interaction between the dopamine D4 receptor and KLHL12, nor ubiquitination of the receptor. Finally, our results indicate that p44/42 MAPK phosphorylation, the signaling pathway which is often regulated by ß-arrestins is not influenced by KLHL12, but seems to be exclusively mediated by Gαi protein upon dopamine D4 receptor stimulation.

Gadd45ß is transcriptionally activated by p53 via p38α-mediated phosphorylation during myocardial ischemic injury.

UNLABELLED: Growth arrest and DNA damage-inducible 45ß (Gadd45ß) have been shown to play a role in inducing cardiomyocyte apoptosis under ischemia/anoxia. The well-known transcription factor p53 is known to cause apoptosis in cardiomyocytes under ischemia. Based on the common role of Gadd45ß and p53 in ischemia-induced apoptosis, we investigated whether p53 is involved in the mechanisms responsible for Gadd45ß expression in both in vitro and in vivo models of ischemic heart injury. A chromatin immunoprecipitation assay revealed direct binding of p53 to the Gadd45ß promoter region during anoxia, and this binding was confirmed by surface plasmon resonance imaging. In rat heart-derived H9c2 cells, silencing of p53 abrogated the increase of Gadd45ß promoter-luciferase reporter (Gadd45ß-Luc) activity and the expression of Gadd45ß under anoxia and overexpression of p53 enhanced Gadd45ß-Luc activity and Gadd45ß expression. Gadd45ß mRNA and protein expression were significantly inhibited by p53 siRNA in a rat ischemic heart model. In addition, p38α-mediated phophorylation of p53 at both Ser15 and Ser20 was shown to be essential for the expression of Gadd45ß mRNA and protein during anoxia. These results reveal the p38α-p53-Gadd45ß axis as a novel signaling module in the anoxia-induced apoptotic death pathway. In conclusion, this study provides molecular evidence that Gadd45ß is a novel downstream target gene of p53 under ischemia/anoxia and suggests the therapeutic potential of targeting Gadd45ß as a treatment of ischemic heart injury. KEY MESSAGE: Gadd45ß is transcriptionally induced by p53 via direct binding under ischemia/anoxia. The induction of Gadd45ß expression requires the p53 phosphorylation at Ser15/Ser20. p38α mediates the p53 phosphorylation at Ser15/Ser20 and the Gadd45ß expression. Ischemia/anoxia-p38α-p53-Gadd45ß axis serves as a novel apoptotic signaling module.