HDAC6 modulates myofibril stiffness and diastolic function of the heart

Passive stiffness of the heart is determined largely by extracellular matrix and titin, which functions as a molecular spring within sarcomeres. Titin stiffening is associated with the development of diastolic dysfunction (DD), while augmented titin compliance appears to impair systolic performance in dilated cardiomyopathy. We found that myofibril stiffness was elevated in mice lacking histone deacetylase 6 (HDAC6). Cultured adult murine ventricular myocytes treated with a selective HDAC6 inhibitor also exhibited increased myofibril stiffness. Conversely, HDAC6 overexpression in cardiomyocytes led to decreased myofibril stiffness, as did ex vivo treatment of mouse, rat, and human myofibrils with recombinant HDAC6. Modulation of myofibril stiffness by HDAC6 was dependent on 282 amino acids encompassing a portion of the PEVK element of titin. HDAC6 colocalized with Z-disks, and proteomics analysis suggested that HDAC6 functions as a sarcomeric protein deacetylase. Finally, increased myofibril stiffness in HDAC6-deficient mice was associated with exacerbated DD in response to hypertension or aging. These findings define a role for a deacetylase in the control of myofibril function and myocardial passive stiffness, suggest that reversible acetylation alters titin compliance, and reveal the potential of targeting HDAC6 to manipulate the elastic properties of the heart to treat cardiac diseases.

Method for selective ablation of undifferentiated human pluripotent stem cell populations for cell-based therapies

Human pluripotent stem cells (PSCs), which are composed of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), provide an opportunity to advance cardiac cell therapy-based clinical trials. However, an important hurdle that must be overcome is the risk of teratoma formation after cell transplantation due to the proliferative capacity of residual undifferentiated PSCs in differentiation batches. To tackle this problem, we propose the use of a minimal noncardiotoxic doxorubicin dose as a purifying agent to selectively target rapidly proliferating stem cells for cell death, which will provide a purer population of terminally differentiated cardiomyocytes before cell transplantation. In this study, we determined an appropriate in vitro doxorubicin dose that (a) eliminates residual undifferentiated stem cells before cell injection to prevent teratoma formation after cell transplantation and (b) does not cause cardiotoxicity in ESC-derived cardiomyocytes (CMs) as demonstrated through contractility analysis, electrophysiology, topoisomerase activity assay, and quantification of reactive oxygen species generation. This study establishes a potentially novel method for tumorigenic-free cell therapy studies aimed at clinical applications of cardiac cell transplantation.

Spatial and temporal dynamics of the cardiac mitochondrial proteome

Mitochondrial proteins alter in their composition and quantity drastically through time and space in correspondence to changing energy demands and cellular signaling events. The integrity and permutations of this dynamism are increasingly recognized to impact the functions of the cardiac proteome in health and disease. This article provides an overview on recent advances in defining the spatial and temporal dynamics of mitochondrial proteins in the heart. Proteomics techniques to characterize dynamics on a proteome scale are reviewed and the physiological consequences of altered mitochondrial protein dynamics are discussed. Lastly, we offer our perspectives on the unmet challenges in translating mitochondrial dynamics markers into the clinic.

Antibiotic lock solutions for the prevention of catheter-related bacteraemia in haemodialysis patients

OBJECTIVE

To investigate the effect of antibiotic lock solutions for preventing catheter-related bacteraemia in patients receiving haemodialysis.

DESIGN

Retrospective study.

SETTING

University teaching hospital, Hong Kong.

PATIENTS

Consecutive patients from March 2006 to April 2007 who had central venous catheter insertion for haemodialysis in our centre were included in this historically controlled study. In all, 75 patients had catheters with heparin solution alone and 74 had catheters with a gentamicin antibiotic lock. The majority of catheters were non-tunnelled (95%). Cumulative catheter survival free of catheter-related bacteraemia in the two groups was compared.

RESULTS

Baseline characteristics in the two groups were similar apart from a slightly lower serum albumin level in those with gentamicin locks. There were 18 and five catheter-related bacteraemia episodes before and after recourse to gentamicin antibiotic locks, respectively. Staphylococcus aureus contributed to over half (65%) of the total bacteraemia episodes. Use of gentamicin antibiotic locks significantly reduced catheter-related bacteraemia episodes per 1000 catheter days from 4.6 to 1.5 (P=0.002). Kaplan-Meier survival analysis using the log rank test showed significantly better bloodstream infection-free survival associated with using gentamicin antibiotic locks (P=0.032). A similar survival advantage was associated with gentamicin antibiotic locks when the analysis was restricted to non-tunnelled catheters. There was no significant association of catheter-related bacteraemia with patient age, obesity, gender, baseline serum albumin level, or diabetes mellitus. No serious adverse events were attributable to the use of gentamicin antibiotic locks.

CONCLUSION

Use of gentamicin lock solutions effectively reduced catheter-related bacteraemia in haemodialysis patients, including those with non-tunnelled catheters.