Effect of Intramyocardial Administration of Baculovirus Encoding the Transcription Factor Tbx20 in Sheep With Experimental Acute Myocardial Infarction.

BACKGROUND: Gene therapy has been proposed as a strategy to induce cardiac regeneration following acute myocardial infarction (AMI). Given that Tbx20, a transcription factor of the T-box subfamily, stimulates cell proliferation and angiogenesis, we designed a baculovirus overexpressing Tbx20 (Bv-Tbx20) and evaluated its effects in cultured cardiomyocytes and in an ovine model of AMI. METHODS AND RESULTS: Cell proliferation and angiogenesis were measured in cardiomyocytes transduced with Bv-Tbx20 or Bv-Null (control). Subsequently, in sheep with AMI, Bv-Tbx20 or Bv-Null was injected in the infarct border. Cardiomyocyte cell cycle activity, angioarteriogenesis, left ventricular function, and infarct size were assessed. Cardiomyocytes transduced with BvTbx20 increased cell proliferation, cell cycle regulatory and angiogenic gene expression, and tubulogenesis. At 7 days posttreatment, sheep treated with Bv-Tbx20 showed increased Tbx20, promitotic and angiogenic gene expression, decreased levels of P21, increased Ki67- (17.09±5.73 versus 7.77±7.24 cardiomyocytes/mm2, P<0.05) and PHH3 (phospho-histone H3)-labeled cardiomyocytes (10.10±3.51 versus 5.23±2.87 cardiomyocytes/mm2, P<0.05), and increased capillary (2302.68±353.58 versus 1694.52±211.36 capillaries/mm2, P<0.001) and arteriolar (146.95±53.14 versus 84.06±16.84 arterioles/mm2, P<0.05) densities. At 30 days, Bv-Tbx20 decreased infarct size (9.89±1.92% versus 12.62±1.33%, P<0.05) and slightly improved left ventricular function. Baculoviral gene transfer-mediated Tbx20 overexpression exerted angiogenic and cardiomyogenic effects in vitro. CONCLUSIONS: In sheep with AMI, Bv-Tbx20 induced angioarteriogenesis, cardiomyocyte cell cycle activity, infarct size limitation, and a slight recovery of left ventricular function, suggesting that Bv-Tbx20 gene therapy may contribute to cardiac regeneration following AMI.

Effect of Embryo Aggregation on In Vitro Development of Adipose-Derived Mesenchymal Stem Cell-Derived Bovine Clones.

Somatic cell nuclear transfer (SCNT) is a method with unique ability to reprogram the epigenome of a fully differentiated cell. However, its efficiency remains extremely low. In this work, we assessed and combined two simple strategies to improve the SCNT efficiency in the bovine. These are the use of less-differentiated donor cells to facilitate nuclear reprogramming and the embryo aggregation (EA) strategy that is thought to compensate for aberrant epigenome reprogramming. We carefully assessed the optimal time of EA by using in vitro-fertilized (IVF) embryos and evaluated whether the use of adipose-derived mesenchymal stem cells (ASCs) as donor for SCNT together with EA improves the blastocyst rates and quality. Based on our results, we determined that the EA improves the preimplantation embryo development per well of IVF and SCNT embryos. We also demonstrated that day 0 (D0) is the optimal aggregation time that leads to a single blastocyst with uniform distribution of the original blastomeres. This was confirmed in bovine IVF embryos and then, the optimal condition was translated to SCNT embryos. Notably, the relative expression of the trophectoderm (TE) marker KRT18 was significantly different between aggregated and nonaggregated ASC-derived embryos. In the bovine, no effect of the donor cell is observed on the developmental rate, or the embryo quality. Therefore, no synergistic effect of the use of both strategies is observed. Our results suggest that EA at D0 is a simple and accessible strategy that improves the blastocyst rate per well in bovine SCNT and IVF embryos and influence the expression of a TE-related marker. The aggregation of two ASC-derived embryos seems to positively affect the embryo quality, which may improve the postimplantation development.

Gene Therapy: Targeting Cardiomyocyte Proliferation to Repopulate the Ischemic Heart.

ABSTRACT: Adult mammalian cardiomyocytes show scarce division ability, which makes the heart ineffective in replacing lost contractile cells after ischemic cardiomyopathy. In the past decades, there have been increasing efforts in the search for novel strategies to regenerate the injured myocardium. Among them, gene therapy is one of the most promising ones, based on recent and emerging studies that support the fact that functional cardiomyocyte regeneration can be accomplished by the stimulation and enhancement of the endogenous ability of these cells to achieve cell division. This capacity can be targeted by stimulating several molecules, such as cell cycle regulators, noncoding RNAs, transcription, and metabolic factors. Therefore, the proposed target, together with the selection of the vector used, administration route, and the experimental animal model used in the development of the therapy would determine the success in the clinical field.

High-dose intramyocardial HMGB1 induces long-term cardioprotection in sheep with myocardial infarction.

In rodents with acute myocardial infarction (AMI), high mobility group box 1 (HMGB1) injection has produced controversial results. Given the lack of data in large mammals, we searched the dose that would promote angiogenesis and expression of specific regenerative genes in sheep with AMI (protocol 1) and, subsequently, use this dose to study long-term effects on infarct size and left ventricular (LV) function (protocol 2). Protocol 1: Sheep with AMI received 250 µg (high-dose, n = 7), 25 µg (low-dose, n = 7) HMGB1, or PBS (placebo, n = 7) in 10 intramyocardial injections (0.2 ml each) in the peri-infarct area. Seven days later, only the high-HMGB1-dose group exhibited higher microvascular densities, Ki67-positive cardiomyocytes, and overexpression of VEGF, Ckit, Tbx20, Nkx2.5, and Gata4. Protocol 2: Sheep with AMI received HMGB1 250 µg (n = 6) or PBS (n = 6). At 60 days, HMGB1-treated sheep showed smaller infarcts (8.5 ± 2.11 vs. 12.2 ± 1.97% LV area, P < 0.05, ANOVA-Bonferroni) and higher microvascular density (capillaries, 1798 ± 252 vs. 1266 ± 250/mm2; arterioles, 18.3 ± 3.9 vs. 11.7 ± 2.2/mm2; both P < 0.01). Echocardiographic LV ejection fraction, circumferential shortening, and wall thickening increased from day 3 to 60 with HMGB1 (all P < 0.05). Conclusion: in ovine AMI, high-dose HMGB1 induces angio-arteriogenesis, reduces infarct size, and improves LV function at 2 months post-treatment.

Effect of poly (l-lactic acid) scaffolds seeded with aligned diaphragmatic myoblasts overexpressing connexin-43 on infarct size and ventricular function in sheep with acute coronary occlusion.

Diaphragmatic myoblasts (DM) are stem cells of the diaphragm, a muscle displaying high resistance to stress and exhaustion. We hypothesized that DM modified to overexpress connexin-43 (cx43), seeded on aligned poly (l-lactic acid) (PLLA) sheets would decrease infarct size and improve ventricular function in sheep with acute myocardial infarction (AMI). Sheep with AMI received PLLA sheets without DM (PLLA group), sheets with DM (PLLA-DM group), sheets with DM overexpressing cx43 (PLLA-DMcx43) or no treatment (control group, n = 6 per group). Infarct size (cardiac magnetic resonance) decreased ∼25% in PLLA-DMcx43 [from 8.2 ± 0.6 ml (day 2) to 6.5 ± 0.7 ml (day 45), p < .01, ANOVA-Bonferroni] but not in the other groups. Ejection fraction (EF%) (echocardiography) at 3 days post-AMI fell significantly in all groups. At 45 days, PLLA-DM y PLLA-DMcx43 recovered their EF% to pre-AMI values (PLLA-DM: 61.1 ± 0.5% vs. 58.9 ± 3.3%, p = NS; PLLA-DMcx43: 64.6 ± 2.9% vs. 56.9 ± 2.4%, p = NS), but not in control (56.8 ± 2.0% vs. 43.8 ± 1.1%, p < .01) and PLLA (65.7 ± 2.1% vs. 56.6 ± 4.8%, p < .01). Capillary density was higher (p < .05) in PLLA-DMcx43 group than in the remaining groups. In conclusion, PLLA-DMcx43 reduces infarct size in sheep with AMI. PLLA-DMcx43 and PLLA-DM improve ventricular function similarly. Given its safety and feasibility, this novel approach may prove beneficial in the clinic.

Aligned ovine diaphragmatic myoblasts overexpressing human connexin-43 seeded on poly (L-lactic acid) scaffolds for potential use in cardiac regeneration.

Diaphragmatic myoblasts (DMs) are precursors of type-1 muscle cells displaying high exhaustion threshold on account that they contract and relax 20 times/min over a lifespan, making them potentially useful in cardiac regeneration strategies. Besides, it has been shown that biomaterials for stem cell delivery improve cell retention and viability in the target organ. In the present study, we aimed at developing a novel approach based on the use of poly (L-lactic acid) (PLLA) scaffolds seeded with DMs overexpressing connexin-43 (cx43), a gap junction protein that promotes inter-cell connectivity. DMs isolated from ovine diaphragm biopsies were characterized by immunohistochemistry and ability to differentiate into myotubes (MTs) and transduced with a lentiviral vector encoding cx43. After confirming cx43 expression (RT-qPCR and Western blot) and its effect on inter-cell connectivity (fluorescence recovery after photobleaching), DMs were grown on fiber-aligned or random PLLA scaffolds. DMs were successfully isolated and characterized. Cx43 mRNA and protein were overexpressed and favored inter-cell connectivity. Alignment of the scaffold fibers not only aligned but also elongated the cells, increasing the contact surface between them. This novel approach is feasible and combines the advantages of bioresorbable scaffolds as delivery method and a cell type that on account of its features may be suitable for cardiac regeneration. Future studies on animal models of myocardial infarction are needed to establish its usefulness on scar reduction and cardiac function.

Vascular endothelial growth factor overexpression does not enhance adipose stromal cell-induced protection on muscle damage in critical limb ischemia.

OBJECTIVES: Critical limb ischemia complicates peripheral artery disease leading to tissue damage and amputation. We hypothesized that modifying adipose stromal cells (ASCs) to overexpress human vascular endothelial growth factor 165 (VEGF) would limit ischemic muscle damage to a larger extent than nonmodified ASCs. APPROACH AND RESULTS: Rabbits with critical hindlimb ischemia were injected with allogeneic abdominal fat-derived ASCs transfected with plasmid-VEGF165 (ASCs-VEGF; n=10). Additional rabbits received nontransfected ASCs (ASCs; n=10) or vehicle (placebo; n=10). One month later, ASCs-VEGF rabbits exhibited significantly higher density of angiographically visible collaterals and capillaries versus placebo (both P<0.05) but not versus ASCs (both P=NS). Arteriolar density, however, was increased in both ASCs and ASCs-VEGF groups (both P<0.05 versus placebo). ASCs-VEGF and ASCs showed comparable post-treatment improvements in Doppler-assessed peak systolic velocity, blood pressure ratio, and resistance index. Ischemic lesions were found in 40% of the muscle samples in the placebo group, 19% in the ASCs-VEGF group, and 17% in the ASCs groups (both P<0.05 versus placebo, Fisher test). CONCLUSIONS: In a rabbit model of critical limb ischemia, intramuscular injection of ASCs genetically modified to overexpress VEGF increase angiographically visible collaterals and capillary density. However, both modified and nonmodified ASCs increase arteriolar density to a similar extent and afford equal protection against ischemia-induced muscle lesions. These results indicate that modifying ASCs to overexpress VEGF does not enhance the protective effect of ASCs, and that arteriolar proliferation plays a pivotal role in limiting the irreversible tissue damage of critical limb ischemia.

Efficient plasmid-mediated gene transfection of ovine bone marrow mesenchymal stromal cells.

BACKGROUND AIMS: Given the close similarity between ovine and human cardiomyocytes, sheep models of myocardial infarction and heart failure are increasingly used in studies of stem cell-mediated heart regeneration. In these studies, mesenchymal stromal cells (MSCs) are frequently employed. To enhance the paracrine effects of these MSCs, ex vivo transfection with genes encoding growth factors has been proposed. Although viral vectors exhibit higher transfection efficiency than plasmids, they entail the risks of uncontrolled transgene expression and immune reactions that preclude repeated administration. Our aim was to optimize the efficiency of plasmid-mediated transfection of ovine MSCs, while preserving cell viability. METHODS: Varying amounts of diverse cationic lipids were used to obtain the reagent-to-DNA mass ratio showing highest luciferase activity. Transfection efficiency (flow cytometry) was tested on plasmid-green fluorescent protein-transfected MSCs at increasing DNA mass. RESULTS: Lipofectamine LTX 5 µL and Plus reagent 4 µL with 2 µg of DNA yielded 42.3 ± 4.7% transfection efficiency, while preserving cell viability. Using these transfection conditions, we transfected MSCs with a plasmid encoding human vascular endothelial growth factor (VEGF) and found high VEGF protein concentrations in the culture supernatant from day 2 (1968 ± 324 pg/mL per µg DNA) through at least day 12 (888 ± 386 pg/mL per µg DNA) after transfection. CONCLUSIONS: Plasmid-mediated transfection of ovine MSCs to over-express paracrine heart-regenerative growth factors is feasible and efficient and overcomes the risks and limitations associated with the use of viral vectors.