Living myocardial slices for the study of nucleic acid-based therapies

Gene therapy based on viral vectors offers great potential for the study and the treatment of cardiac diseases. Here we explore the use of Living Myocardial Slices (LMS) as a platform for nucleic acid-based therapies. Rat LMS and Adeno-Associated viruses (AAV) were used to optimise and analyse gene transfer efficiency, viability, tissue functionality, and cell tropism in cardiac tissue. Human cardiac tissue from failing (dilated cardiomyopathy) hearts was also used to validate the model in a more translational setting. LMS were cultured at physiological sarcomere length for 72-h under electrical stimulation. Two recombinant AAV serotypes (AAV6 and AAV9) at different multiplicity of infection (MOI) expressing enhanced green fluorescent protein (eGFP) were added to the surface of rat LMS. AAV6 at 20,000 MOI proved to be the most suitable serotype without affecting LMS contractility or kinetics and showing high transduction and penetrability efficiency in rat LMS. This serotype exhibited 40% of transduction efficiency in cardiomyocytes and stromal cells while 20% of the endothelial cells were transduced. With great translational relevance, this protocol introduces the use of LMS as a model for nucleic acid-based therapies, allowing the acceleration of preclinical studies for cardiac diseases.

Nucleic acid-based therapies using living myocardial slices

Background

Gene therapy based on viral vectors is a promising new approach and offers great potential for the study and the treatment of cardiac diseases. Nucleic acid-based transfection of human heart tissue could be considered a valid and translational alternative to the use of transgenic animal models in cardiovascular research.

Purpose

Here we explore the use of Living Myocardial Slices (LMS) as a platform for nucleic acid-based therapies. Rat LMS and Adeno-Associated viruses (AAV) were used to optimise and analyse gene transfer efficiency, viability, tissue functionality, and cell tropism in cardiac tissue. Human cardiac samples from failing (dilated cardiomyopathy) hearts were also used to validate the human model. In addition, we transfected and tested for the first time the regenerative effect of AAV-miR-199a in both healthy and pathologically overloaded LMS.

Methods

LMS (300 μm thick) were prepared and glued to PTFE-coated holders, mounted on custom stretchers, and cultured at physiological sarcomere length for 72-hours under electrical stimulation. Two recombinant AAV serotypes (AAV-6 and AAV-9) at different multiplicity of infection (MOI) expressing green fluorescent protein (GFP) or the miR-199 transgene were added to the surface of the LMS.

Results

AAV6 proved to be the most suitable serotype and 20,000 MOI the most efficient dose, as these conditions were proven not to affect LMS contractility and to have the highest transduction and penetrability efficiency. This serotype exhibited preferential cell tropism to cardiomyocytes and stromal cells (40% of transduction in both) in rat LMS, with lower efficiency in endothelial cells, (20% of transduction). In contrast, AAV6 in human failing LMS showed higher transduction efficiency in endothelial cells and myofibroblasts. Treatment with miR-199a significantly increased the active force of pathologically overstretched LMS, downregulated the expression of its target genes, and affected the proliferative capacity of LMS.

Conclusion

LMS can be used as a model for nucleic acid-based therapies and their transfection protocol can be adapted to samples obtained from failing human hearts. With great translational relevance, this model would accelerate preclinical studies of novel nucleic acid-based therapies for heart failure.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): British Heart Foundation

Extracellular vesicles derived from physiologically loaded living myocardial slices improve the contractility of healthy living myocardial slices

Introduction

Mechanical load is a determinant of the healthy-to-failing myocardium transition. Extracellular vesicles (EVs) found in the range of 30–200 nm contain bioactive cargoes such as DNA, miRNA and proteins, and thus are considered important mediators of the paracrine crosstalk between cells in health and disease. Living myocardial slices (LMS) are 300μm layers of myocardial tissue that allow modelling of the intercellular communication in the heart.

Purpose

To assess whether secretion of EVs derived from physiological or pathological mechanically-loaded LMS regulate changes in myocardial contractility.

Methods

LMS were prepared from adult male Sprague-Dawley rats' left ventricle using a vibratome. LMS were stretched uniaxially using customised stretchers at a sarcomere length of 2.2μm and 2.4μm to recapitulate a physiological (P) and an overload (O) condition, respectively. LMS were cultured for 48-hours under electromechanical stimulation in M-199 media with Earls' salts, catecholamines, dexamethasone and triiodothyronine. After culture, media was harvested and processed for exosomes isolation by size exclusion chromatography. Particle size and concentration was assessed by nanoparticle tracking analysis. To validate the different phenotypes in LMS, force-stretch relationship was assessed after 48-hours culture. EVs isolated from P and O LMS were then used to treat physiologically loaded LMS (1x107 particles/LMS) and the force-stretch relationship was assessed after 48-hours culture.

Results

No significant difference in contractility was found between P and O LMS at any stretch increment (5.99±1.10 vs 2.82±0.92 mN/mm2 max force), whilst a significant increase in the passive tension of myocardial tissue was observed at 25% (15.90±2.77 vs 4.67±0.37 mN/mm2; p<0.05,) and 30% stretch (21.92±3.60 vs 5.73±0.6 mN/mm2; p<0.001) in the P LMS compared to O LMS (n=11 P, n=4 O). EVs quantification showed no significant difference between P and O conditions (1.16329E+11±4587386608 vs 1.08915E+11±7641744894 particles/ml); (n=7 P; n=3 O). However, P EVs-treated LMS showed a significant increase in contractility after 48-hours, compared to PBS-treated LMS at 25% (8.49±0.62 vs 5.34±0.9 mN/mm2) and 30% stretch (9.55±0.42 vs 5.99±1.10 mN/mm2; p<0.05); (n=11 PBS, n=4 P EVs,) and O EVs-treated LMS from 15–30% stretch (9.55±0.42 vs 3.23±0.55 mN/mm2 max force; p<0.0001); (n=4 P EVs, n=5 O EVs). Conversely, no significant differences in contractility were found between PBS-treated LMS and O EVs-treated LMS (5.99±1.10 vs 3.23±0.55 mN/mm2 maximum force); (n=5 O EVs, n=11 PBS).

Conclusions

EVs derived from physiologically loaded LMS improve the contractility of healthy LMS after 48-hours culture compared to PBS-treated LMS. Understanding how mechanical load correlates with specific loading of cargoes in EVs may reveal interesting therapeutic targets for the treatment of heart failure.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): British Heart Foundation Physiological and overloaded phenotypesContractility of EVs treated LMS

Mechanical load modulates the cargo of secreted extracellular vesicles (EVs) from living myocardial slices

Introduction

Mechanical overload plays an important role in the progression of chronic heart failure (CHF). Beside the numerous neurohormonal and chemical stimuli that contribute to structural and functional changes in the myocardium, intercellular communication mediated by extracellular vesicles (EVs), also plays a pivotal role in disease progression. Exosomes are a subset of EVs ranging between 30–150 nm; these mediators carry molecular cargoes such as miRNAs, mRNAs, DNA and several proteins. However, it is still unclear how specific pathological stimuli may induce a change in their release from tissues or a difference in their cargo content.

Living myocardial slices (LMS) are ultra-thin sections of heart tissue, ranging from 100–400 μm in thickness. They retain the multicellularity, electromechanical physiology, biochemistry and extracellular matrix of the adult heart.

Purpose

To investigate whether mechanical load influences both the released amount and content of LMS-derived exosomes after 24 hours culture.

Methods and results

LMS were prepared from the left ventricle of male Sprague Dawley rats using a high precision vibratome. LMS were stretched in the direction of the muscle fibers at a sarcomere length (SL) of 2.2 μm to recapitulate physiological preload, and at 2.4 μm SL to recapitulate a condition of volume overload. LMS were cultured for 24 hours under electromechanical stimulation. Media containing LMS-derived exosomes was harvested after culture and processed for exosome isolation by size exclusion chromatography columns. Particle size and concentration were assessed by nanoparticle tracking analysis and protein quantity by microBCA assay. There was no significant difference in the size of exosomes between overload and physiological conditions, with an average mean size of 113.475±8.35 nm for the physiological and 129.3±16.35 nm for the overload condition (p=0.61; n=4 physiological; n=3 overload). Although there was not significant difference in exosome amount between physiological and overload condition, (7.00E+10±2.53E+09 vs 1.04E+11±5.77E+09 particles/ml) (p=0.57; n=4 physiological; n=3 overload), exosomes released from overloaded LMS showed a significant increase in protein content compared to physiologically loaded LMS (150.57±25.682 vs 66.045±9.855 μg/ml) (p=0.04; n=3 overload; n=2 physiological).

Conclusions

Mechanical load influences the cargo content of EVs secreted from LMS after 24 hours culture under electromechanical stimulation. Understanding how mechanical load correlates with specific cargoes in EVs will reveal novel therapeutic targets for the treatment of CHF.

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): British Heart Foundation (BHF)

An optical supernova associated with the X-ray flash XRF 060218

Long-duration gamma-ray bursts (GRBs) are associated with type Ic supernovae that are more luminous than average and that eject material at very high velocities. Less-luminous supernovae were not hitherto known to be associated with GRBs, and therefore GRB-supernovae were thought to be rare events. Whether X-ray flashes--analogues of GRBs, but with lower luminosities and fewer gamma-rays--can also be associated with supernovae, and whether they are intrinsically 'weak' events or typical GRBs viewed off the axis of the burst, is unclear. Here we report the optical discovery and follow-up observations of the type Ic supernova SN 2006aj associated with X-ray flash XRF 060218. Supernova 2006aj is intrinsically less luminous than the GRB-supernovae, but more luminous than many supernovae not accompanied by a GRB. The ejecta velocities derived from our spectra are intermediate between these two groups, which is consistent with the weakness of both the GRB output and the supernova radio flux. Our data, combined with radio and X-ray observations, suggest that XRF 060218 is an intrinsically weak and soft event, rather than a classical GRB observed off-axis. This extends the GRB-supernova connection to X-ray flashes and fainter supernovae, implying a common origin. Events such as XRF 060218 are probably more numerous than GRB-supernovae.

Discovery of a transient absorption edge in the X-ray spectrum of GRB 990705

We report the discovery of a transient equivalent hydrogen column density with an absorption edge at approximately 3.8 kiloelectron volts in the spectrum of the prompt x-ray emission of gamma-ray burst (GRB) 990705. This feature can be satisfactorily modeled with a photoelectric absorption by a medium located at a redshift of approximately 0.86 and with an iron abundance of approximately 75 times the solar one. The transient behavior is attributed to the strong ionization produced in the circumburst medium by the GRB photons. The high iron abundance points to the existence of a burst environment enriched by a supernova along the line of sight. The supernova explosion is estimated to have occurred about 10 years before the burst. Our results agree with models in which GRBs originate from the collapse of very massive stars and are preceded by a supernova event.

Detection of 33.8 Millisecond X-Ray Pulsations in SAX J0635+0533

We revisited the BeppoSAX observation of SAX J0635+0533, which was suggested as a possible counterpart to the gamma-ray source 2EG J0635+0521. We have discovered a 33.8 ms pulsation from the source and derived an improved position, consistent with the location of the Be star proposed as a binary companion. We interpret the periodicity as the spin period of a neutron star in a binary system with a Be companion.

Lack of association between body weight, bone mineral density and vitamin D receptor gene polymorphism in normal and osteoporotic women

In an ethnically homogeneous population of women living in Tuscany, Italy, the relationships between age, body weight, bone mineral density and the vitamin D receptor (VDR) gene polymorphism were studied, with the objective of recognizing patients at risk for osteoporosis. In 275 women bone mineral density was measured by Dual Energy X-rays Absorptiometry (DEXA). In 50 of them the individual genetic pattern for VDR was evaluated by DNA extraction followed by PCR amplification of the VDR gene, and digestion with the restriction enzyme BsmI. Age and bone mineral density were inversely related (R2 = 0.298). Body weight was associated with bone mineral density (R2 = 0.059), but not with age. In osteoporotic women, mean (+/- SD) body weight was 59.9 +/- 6.5 Kg, lower than that recorded in non osteoporotic women (64.2 +/- 9.4 Kg), even though not significantly different (p = 0.18). No association was found between VDR gene polymorphism, bone density or body weight. The performance of anthropometric and genetic components appear to be poor, and, at least for the time being, bone mineral density measurement by means of MOC-DEXA represents the optimal method to detect women at risk for postmenopausal osteoporosis.

Photometry and spectroscopy of the GRB 970508 optical counterpart

An optical transient within the error box of the gamma ray burst GRB 970508 was imaged 4 hours after the event. It displayed a strong ultraviolet excess, and reached maximum brightness 2 days later. The optical spectra did not show any emission lines, and no variations on time scales of minutes were observed for 1 hour during the decline phase. According to the fireball and afterglow models, the intensity should rise monotonically before the observed optical maximum, but the data indicate that another physical mechanism may be responsible for the constant phase seen during the first hours after the burst.

[The determination of BB genotype of vitamin D receptors identifies patients at risk for osteoporosis]

The gene responsible for peak bone mass has been recently identified as the gene coding for the Vitamin D Receptor (VDR); there exist two alleles, termed "B" and "b", determining a typical allelic polymorphism. We determined the VDR genotype of 50 young post-menopausal women (mean age: 56 years), and measured bone density by Dual Energy X ray Absorptiometry (DEXA) twice: at the beginning of the study and after one year. VDR genotype was determined using the DNA extracted from hair cells, thus avoiding the use of blood samples. The frequency of VDR genotypes (BB or bb homozygous; Bb heterozygous) was approximately the same in the two groups of subjects (i.e., normal controls and osteoporotic women). The bone density of normal subjects (36) was measured for the second time one year after the first measurement. All BB homozygous subjects showed significantly decreased bone density values; 50% of them showed values below 0.750 g/cm2 at the second measurement, thus being classified as osteoporotic. However, neither bb homozygous nor Bb heterozygous subjects showed any significant decrease in bone density values (about 4% of the initial value). Therefore, determining the VDR genotype was critical for identifying the subjects who were normal at the first measurement, but had markedly decreased bone density values later, thus being at risk of developing osteoporosis.