Apelin-13 infusion salvages the peri-infarct region to preserve cardiac function after severe myocardial injury.

BACKGROUND: Apelin-13 (A13) regulates cardiac homeostasis. However, the effects and mechanism of A13 infusion after an acute myocardial injury (AMI) have not been elucidated. This study assesses the restorative effects and mechanism of A13 on the peri-infarct region in murine AMI model. METHODS: 51 FVB/N mice (12weeks, 30g) underwent AMI. A week following injury, continuous micro-pump infusion of A13 (0.5µg/g/day) and saline was initiated for 4-week duration. Dual contrast MRI was conducted on weeks 1, 2, 3, and 5, consisting of delayed-enhanced and manganese-enhanced MRI. Four mice in each group were followed for an extended period of 4weeks without further infusion and underwent MRI scans on weeks 7 and 9. RESULTS: A13 infusion demonstrated preserved LVEF compared to saline from weeks 1 to 4 (21.9±3.2% to 23.1±1.7%* vs. 23.5±1.7% to 16.9±2.8%, *p=0.02), which persisted up to 9weeks post-MI (+1.4%* vs. -9.4%, *p=0.03). Mechanistically, dual contrast MRI demonstrated significant decrease in the peri-infarct and scar % volume in A13 group from weeks 1 to 4 (15.1 to 7.4% and 34.3 to 25.1%, p=0.02, respectively). This was corroborated by significant increase in 5-ethynyl-2'-deoxyuridine (EdU(+)) cells by A13 vs. saline groups in the peri-infarct region (16.5±3.1% vs. 8.1±1.6%; p=0.04), suggesting active cell mitosis. Finally, significantly enhanced mobilization of CD34(+) cells in the peripheral blood and up-regulation of APJ, fibrotic, and apoptotic genes in the peri-infarct region were found. CONCLUSIONS: A13 preserves cardiac performance by salvaging the peri-infarct region and may contribute to permanent restoration of the severely injured myocardium.

Calcineurin mediates homeostatic synaptic plasticity by regulating retinoic acid synthesis.

Homeostatic synaptic plasticity is a form of non-Hebbian plasticity that maintains stability of the network and fidelity for information processing in response to prolonged perturbation of network and synaptic activity. Prolonged blockade of synaptic activity decreases resting Ca(2+) levels in neurons, thereby inducing retinoic acid (RA) synthesis and RA-dependent homeostatic synaptic plasticity; however, the signal transduction pathway that links reduced Ca(2+)-levels to RA synthesis remains unknown. Here we identify the Ca(2+)-dependent protein phosphatase calcineurin (CaN) as a key regulator for RA synthesis and homeostatic synaptic plasticity. Prolonged inhibition of CaN activity promotes RA synthesis in neurons, and leads to increased excitatory and decreased inhibitory synaptic transmission. These effects of CaN inhibitors on synaptic transmission are blocked by pharmacological inhibitors of RA synthesis or acute genetic deletion of the RA receptor RARα. Thus, CaN, acting upstream of RA, plays a critical role in gating RA signaling pathway in response to synaptic activity. Moreover, activity blockade-induced homeostatic synaptic plasticity is absent in CaN knockout neurons, demonstrating the essential role of CaN in RA-dependent homeostatic synaptic plasticity. Interestingly, in GluA1 S831A and S845A knockin mice, CaN inhibitor- and RA-induced regulation of synaptic transmission is intact, suggesting that phosphorylation of GluA1 C-terminal serine residues S831 and S845 is not required for CaN inhibitor- or RA-induced homeostatic synaptic plasticity. Thus, our study uncovers an unforeseen role of CaN in postsynaptic signaling, and defines CaN as the Ca(2+)-sensing signaling molecule that mediates RA-dependent homeostatic synaptic plasticity.

Calcineurin signaling regulates neural induction through antagonizing the BMP pathway.

Development of the nervous system begins with neural induction, which is controlled by complex signaling networks functioning in concert with one another. Fine-tuning of the bone morphogenetic protein (BMP) pathway is essential for neural induction in the developing embryo. However, the molecular mechanisms by which cells integrate the signaling pathways that contribute to neural induction have remained unclear. We find that neural induction is dependent on the Ca(2+)-activated phosphatase calcineurin (CaN). Fibroblast growth factor (FGF)-regulated Ca(2+) entry activates CaN, which directly and specifically dephosphorylates BMP-regulated Smad1/5 proteins. Genetic and biochemical analyses revealed that CaN adjusts the strength and transcriptional output of BMP signaling and that a reduction of CaN activity leads to an increase of Smad1/5-regulated transcription. As a result, FGF-activated CaN signaling opposes BMP signaling during gastrulation, thereby promoting neural induction and the development of anterior structures.

Potent kinetic stabilizers that prevent transthyretin-mediated cardiomyocyte proteotoxicity.

A valine-to-isoleucine mutation at position 122 of the serum protein transthyretin (TTR), found in 3 to 4% of African Americans, alters its stability, leading to amyloidogenesis and cardiomyopathy. In addition, 10 to 15% of individuals older than 65 years develop senile systemic amyloidosis and cardiac TTR deposits because of wild-type TTR amyloidogenesis. Although several drugs are in development, no approved therapies for TTR amyloid cardiomyopathy are yet available, so the identification of additional compounds that prevent amyloid-mediated cardiotoxicity is needed. To this aim, we developed a fluorescence polarization-based high-throughput screen and used it to identify several new chemical scaffolds that target TTR. These compounds were potent kinetic stabilizers of TTR and prevented TTR tetramer dissociation, partial unfolding, and aggregation of both wild type and the most common cardiomyopathy-associated TTR mutant, V122I-TTR. High-resolution co-crystal structures and characterization of the binding energetics revealed how these diverse structures bound to tetrameric TTR. These compounds effectively inhibited the proteotoxicity of V122I-TTR toward human cardiomyocytes. Several of these ligands stabilized TTR in human serum more effectively than diflunisal, which is a well-studied inhibitor of TTR aggregation, and may be promising leads for the treatment or prevention of TTR-mediated cardiomyopathy.

FKBP8 cell-autonomously controls neural tube patterning through a Gli2- and Kif3a-dependent mechanism.

Signaling by Sonic hedgehog (Shh) represents an important process by which many types of neural progenitor cells become properly organized along the dorsal-ventral axis of the vertebrate neural tube in a concentration-dependent manner. However, the mechanism by which Shh signals are transduced with high fidelity and the relationship between the Shh signaling pathway and other patterning systems remain unclear. Here we focus on the role of FK506-binding protein 8 (FKBP8) in controlling neural cell identity through its antagonism of the Shh pathway. Our data indicate that disruption of FKBP8 function activates the Shh signaling pathway cell-autonomously at a step that is independent of the transmembrane protein Smoothened but dependent on the Gli2 transcription factor. This activation is also dependent on the kinesin-2 subunit Kif3a, a component of the intraflagellar transport (IFT) machinery used to generate cilia. Our data also indicate that non-cell-autonomous effects of the Fkbp8 mutation further contribute to the neural patterning phenotype and suggest that FKBP8 plays an indirect role in promoting Bone morphogenetic protein (BMP) signaling through antagonism of the Shh pathway.