Aberrant developmental titin splicing and dysregulated sarcomere length in Thymosin ß4 knockout mice.

Sarcomere assembly is a highly orchestrated and dynamic process which adapts, during perinatal development, to accommodate growth of the heart. Sarcomeric components, including titin, undergo an isoform transition to adjust ventricular filling. Many sarcomeric genes have been implicated in congenital cardiomyopathies, such that understanding developmental sarcomere transitions will inform the aetiology and treatment. We sought to determine whether Thymosin ß4 (Tß4), a peptide that regulates the availability of actin monomers for polymerization in non-muscle cells, plays a role in sarcomere assembly during cardiac morphogenesis and influences adult cardiac function. In Tß4 null mice, immunofluorescence-based sarcomere analyses revealed shortened thin filament, sarcomere and titin spring length in cardiomyocytes, associated with precocious up-regulation of the short titin isoforms during the postnatal splicing transition. By magnetic resonance imaging, this manifested as diminished stroke volume and limited contractile reserve in adult mice. Extrapolating to an in vitro cardiomyocyte model, the altered postnatal splicing was corrected with addition of synthetic Tß4, whereby normal sarcomere length was restored. Our data suggest that Tß4 is required for setting correct sarcomere length and for appropriate splicing of titin, not only in the heart but also in skeletal muscle. Distinguishing between thin filament extension and titin splicing as the primary defect is challenging, as these events are intimately linked. The regulation of titin splicing is a previously unrecognised role of Tß4 and gives preliminary insight into a mechanism by which titin isoforms may be manipulated to correct cardiac dysfunction.

Minimal effect of lipid charge on membrane miscibility phase behavior in three ternary systems.

Giant unilamellar vesicles composed of a ternary mixture of phospholipids and cholesterol exhibit coexisting liquid phases over a range of temperatures and compositions. A significant fraction of lipids in biological membranes are charged. Here, we present phase diagrams of vesicles composed of phosphatidylcholine (PC) lipids, which are zwitterionic; phosphatidylglycerol (PG) lipids, which are anionic; and cholesterol (Chol). Specifically, we use DiPhyPG-DPPC-Chol and DiPhyPC-DPPG-Chol. We show that miscibility in membranes containing charged PG lipids occurs over similarly high temperatures and broad lipid compositions as in corresponding membranes containing only uncharged lipids, and that the presence of salt has a minimal effect. We verified our results in two ways. First, we used mass spectrometry to ensure that charged PC/PG/Chol vesicles formed by gentle hydration have the same composition as the lipid stocks from which they are made. Second, we repeated the experiments by substituting phosphatidylserine for PG as the charged lipid and observed similar phenomena. Our results consistently support the view that monovalent charged lipids have only a minimal effect on lipid miscibility phase behavior in our system.

Transthyretin Stabilization by AG10 in Symptomatic Transthyretin Amyloid Cardiomyopathy.

BACKGROUND: Transthyretin (TTR) amyloidosis is an underdiagnosed disease caused by destabilization of TTR due to pathogenic mutations or aging. Both pathogenic and protective mutations illuminate mechanisms of disease and potential interventions. AG10 is a selective, oral TTR stabilizer under development for transthyretin amyloidosis cardiomyopathy (ATTR-CM) that mimics a protective TTR mutation. OBJECTIVES: This randomized, double-blind, placebo-controlled study evaluated safety, tolerability, pharmacokinetics, and pharmacodynamics of AG10 in ATTR-CM patients with symptomatic, chronic heart failure. METHODS: ATTR-CM, New York Heart Association functional class II to III subjects (n = 49, mutant or wild-type) were randomized 1:1:1 to AG10 400 mg, AG10 800 mg, or placebo twice daily for 28 days. Safety and tolerability were assessed by clinical and laboratory criteria. AG10 plasma levels were measured. TTR stability was assessed by changes in serum TTR, and 2 established ex vivo assays (fluorescent probe exclusion and Western blot). RESULTS: AG10 treatment was well-tolerated, achieved target plasma concentrations and demonstrated near-complete stabilization of TTR. TTR stabilization was more complete and less variable at the higher dose with stabilization by fluorescent probe exclusion of 92 ± 10% (mean ± SD) at trough and 96 ± 9% at peak (both p < 10-12 vs. placebo). Average serum TTR increased by 36 ± 21% and 51 ± 38% at 400 and 800 mg, respectively (both p < 0.0001 vs. placebo). Baseline serum TTR in treated subjects was below normal in 80% of mutant and 33% of wild-type subjects. AG10 treatment restored serum TTR to the normal range in all subjects. CONCLUSIONS: AG10 has the potential to be a safe and effective treatment for patients with ATTR-CM. A phase 3 trial is ongoing. (Study of AG10 in Amyloid Cardiomyopathy; NCT03458130).

Non-invasive phenotyping and drug testing in single cardiomyocytes or beta-cells by calcium imaging and optogenetics.

Identification of drug induced electrical instability of the heart curtails development, and introduction, of potentially proarrhythmic drugs. This problem usually requires complimentary contact based approaches such as patch-clamp electrophysiology combined with field stimulation electrodes to observe and control the cell. This produces data with high signal to noise but requires direct physical contact generally preventing high-throughput, or prolonged, phenotyping of single cells or tissues. Combining genetically encoded optogenetic control and spectrally compatible calcium indicator tools into a single adenoviral vector allows the analogous capability for cell control with simultaneous cellular phenotyping without the need for contact. This combination can be applied to single rodent primary adult cardiomyocytes, and human stem cell derived cardiomyocytes, enabling contactless small molecule evaluation for inhibitors of sodium, potassium and calcium channels suggesting it may be useful for early toxicity work. In pancreatic beta-cells it reveals the effects of glucose and the KATP inhibitor gliclazide.