Mesenchymal stromal cell-derived extracellular vesicles rescue radiation damage to murine marrow hematopoietic cells

Mesenchymal stromal cells (MSCs) have been shown to reverse radiation damage to marrow stem cells. We have evaluated the capacity of MSC-derived extracellular vesicles (MSC-EVs) to mitigate radiation injury to marrow stem cells at 4 h to 7 days after irradiation. Significant restoration of marrow stem cell engraftment at 4, 24 and 168 h post irradiation by exposure to MSC-EVs was observed at 3 weeks to 9 months after transplant and further confirmed by secondary engraftment. Intravenous injection of MSC-EVs to 500cGy exposed mice led to partial recovery of peripheral blood counts and restoration of the engraftment of marrow. The murine hematopoietic cell line, FDC-P1 exposed to 500cGy, showed reversal of growth inhibition, DNA damage and apoptosis on exposure to murine or human MSC-EVs. Both murine and human MSC-EVs reverse radiation damage to murine marrow cells and stimulate normal murine marrow stem cell/progenitors to proliferate. A preparation with both exosomes and microvesicles was found to be superior to either microvesicles or exosomes alone. Biologic activity was seen in freshly isolated vesicles and in vesicles stored for up to 6 months in 10% dimethyl sulfoxide at -80 °C. These studies indicate that MSC-EVs can reverse radiation damage to bone marrow stem cells.

The murine long-term multi-lineage renewal marrow stem cell is a cycling cell

Prevailing wisdom holds that hematopoietic stem cells (HSCs) are predominantly quiescent. Although HSC cycle status has long been the subject of scrutiny, virtually all marrow stem cell research has been based on studies of highly purified HSCs. Here we explored the cell cycle status of marrow stem cells in un-separated whole bone marrow (WBM). We show that a large number of long-term multi-lineage engraftable stem cells within WBM are in S/G2/M phase. Using bromodeoxyuridine, we show rapid transit through the cell cycle of a previously defined relatively dormant purified stem cell, the long-term HSC (LT-HSC; Lineage(-)/c-kit(+)/Sca-1(+)/Flk-2(-)). Actively cycling marrow stem cells have continually changing phenotype with cell cycle transit, likely rendering them difficult to purify to homogeneity. Indeed, as WBM contains actively cycling stem cells, and highly purified stem cells engraft predominantly while quiescent, it follows that the population of cycling marrow stem cells within WBM are lost during purification. Our studies indicate that both the discarded lineage-positive and lineage-negative marrow cells in a stem cell separation contain cycling stem cells. We propose that future work should encompass this larger population of cycling stem cells that is poorly represented in current studies solely focused on purified stem cell populations.

Microvesicular-mediated gene transfer of prostate tumor markers

e16076

Background: Microvesicles have been a subject of research for many years. Recent work has focused on the potential for cancer vaccines via microvesicles. It has also been demonstrated that various cell-specific phenotypes can be transferred from one cell type to another through microvesicle transfer. Studies in our laboratory have demonstrated that co-culture of murine lung tissue with marrow cells across a cell impermeable membrane can induce elevations in lung-specific mRNA expression in human donor marrow stem cells. Our objective is to determine whether there is transfer of genetic or transcriptional factors via microvesicles from human prostate cancer cells to fresh human marrow cells. Methods: Fresh prostate tissue was harvested from surgical specimens following radical retropubic prostatectomy. Samples were histologically confirmed to contain prostatic adenocarcinoma. Co-cultures were established using a transwell system in which 0.05–0.100 grams of prostate tissue was minced and co-cultured with 1–3 million normal, human donor marrow cells for 2–7 days. Marrow not co-cultured with tumorserved as a control. Target cells were collected and total RNA was analyzed for prostate-specific gene expression byReal Time RT-PCR. Fold differences in expression of the genes were analyzed, using TaqMan®, gene assays (Applied Biosystems) and were expressed in relation to the marrow control. Results: We have observed significant increases in gene expression in marrow cells co-cultured with prostate tumor cells (Gleason grades 6–9). Variable increases in expression were seen in 3 patient samples, as high as 7-fold for ERG, greater than 10-fold for ACPP and greater than 100-fold for STEAP, PART, TMPRSS2, PSCA and ETV1. Conclusions: These studies demonstrate that prostate specific genes are present in fresh human marrow cells after co-culture with tumor tissue. This establishes a base to begin evaluating the significance of microvesicle-mediated genetic transfer, mechanisms of transfer and therapeutic options for blocking or manipulating such transfer to influence the disease process.

No significant financial relationships to disclose.

Marrow cell genetic phenotype change induced by human lung cancer cells

11108

Background: Murine lung-derived microvesicles are capable of inducing lung-specific mRNA in marrow cells, when co-cultured across from these cells, but separated from them by a cell-impermeable (0.4 micron) membrane. These converted murine marrow cells showed mRNA elevations, lung-specific protein production and enhanced capacity to convert to lung epithelial cells after in vivo transplantation into irradiated mice. We examine here whether fresh tissue from lung cancer patients would have the same capacity to genetically alter co-cultured human marrow cells. Methods: Lung cancer samples were collected from 5 patients undergoing surgery. Minced tumor tissue at 50–100 mg was co-cultured in a semi-permeable culture plate insert opposite 3.0 ×106 human marrow cells. The marrow cells were harvested after 2–7 days of co-culture. Marrow cell RNA was analyzed for lung specific mRNA using real time RT-PCR. Relative levels of gene expression was expressed a fold increase compared to level in controls. Results: Lung cancers studied were adenocarcinoma, endobronchial alveolar carcinoma, bronchioloalveolar carcinoma, non-small cell carcinoma and squamous cell carcinoma. mRNAs for aquaporin 1–5, specific for type I pneumocytes and surfactant A-D, specific for type II pneumocytes, were measured. Aquaporin I was elevated in marrow cells from co culture with all lung cancers; elevations ranging from 2.15 to 56.7 fold (mean 23 fold). Similarly surfactant B mRNA was induced in marrow cells by all lung cancers with fold elevations ranging from 7.9 to 2164 (mean fold elevation 668). More variable elevations were also seen with aquaporin 3, 4, and 5, surfactant A, surfactant C, and surfactant D. Ultracentrifugation (28,000 g) of conditioned media from these cancers revealed the presence of microvesicles with diameters of 100–180 nm. Conclusions: These observations indicate that the genetic phenotype of cells in the vicinity of lung cancer cells can be altered and that these alterations might be mediated by microvesicle transfer of genetic information.

No significant financial relationships to disclose.

Therapeutic potential of implanted tissue-engineered bioartificial muscles delivering recombinant proteins to the sheep heart

Tissue-engineered primary adult sheep muscle cells genetically engineered to express either rhVEGF or rhIGF-1 secreted the bioactive proteins locally in the sheep heart for at least 30 days.

Recombinant vascular endothelial growth factor secreted from tissue-engineered bioartificial muscles promotes localized angiogenesis

BACKGROUND

Therapeutic angiogenesis by the administration of recombinant vascular endothelial growth factor (rVEGF) is a novel strategy for the treatment of ischemic disorders. rVEGF has been delivered as a protein, by plasmid DNA, and by genetically engineered cells with different pharmacokinetic and physiological properties. In the present study, we examined a new method for delivery of rVEGF using implantable bioartificial muscle (BAM) tissues made from genetically modified primary skeletal myoblasts. Our goal was to determine whether the rVEGF delivered by this technique promoted controlled angiogenesis in nonischemic and/or ischemic adult mouse tissue.

METHODS AND RESULTS

Primary adult mouse myoblasts were retrovirally transduced to secrete human or mouse rVEGF and tissue-engineered into implantable 1x10 to 15-mm BAMs containing parallel arrays of postmitotic myofibers. In vitro, they secreted 290 to 511 ng of bioactive mouse or human VEGF/BAM per day. rVEGF BAMs implanted subcutaneously into syngeneic mice caused a 30-fold increase in the number of CD31-positive capillary cells within the BAM by 1 week compared with control BAMs. Implantation of rVEGF-secreting BAMs into ischemic hindlimbs resulted in a 2- to 3-fold increase in capillary density of neighboring host muscle by 1 week and out to 4 weeks with no evidence of hemangioma formation.

CONCLUSIONS

Local delivery of rVEGF from BAMs rapidly increases capillary density both within the BAM itself and in adjacent ischemic muscle tissue. Genetically engineered muscle tissue provides a method for therapeutic protein delivery in a dose-regulated fashion.

Space travel directly induces skeletal muscle atrophy

Space travel causes rapid and pronounced skeletal muscle wasting in humans that reduces their long-term flight capabilities. To develop effective countermeasures, the basis of this atrophy needs to be better understood. Space travel may cause muscle atrophy indirectly by altering circulating levels of factors such as growth hormone, glucocorticoids, and anabolic steroids and/or by a direct effect on the muscle fibers themselves. To determine whether skeletal muscle cells are directly affected by space travel, tissue-cultured avian skeletal muscle cells were tissue engineered into bioartificial muscles and flown in perfusion bioreactors for 9 to 10 days aboard the Space Transportation System (STS, i.e., Space Shuttle). Significant muscle fiber atrophy occurred due to a decrease in protein synthesis rates without alterations in protein degradation. Return of the muscle cells to Earth stimulated protein synthesis rates of both muscle-specific and extracellular matrix proteins relative to ground controls. These results show for the first time that skeletal muscle fibers are directly responsive to space travel and should be a target for countermeasure development.

Tissue-engineered human bioartificial muscles expressing a foreign recombinant protein for gene therapy

Murine skeletal muscle cells transduced with foreign genes and tissue engineered in vitro into bioartificial muscles (BAMs) are capable of long-term delivery of soluble growth factors when implanted into syngeneic mice (Vandenburgh et al., 1996b). With the goal of developing a therapeutic cell-based protein delivery system for humans, similar genetic tissue-engineering techniques were designed for human skeletal muscle stem cells. Stem cell myoblasts were isolated, cloned, and expanded in vitro from biopsied healthy adult (mean age, 42 +/- 2 years), and elderly congestive heart failure patient (mean age, 76 +/- 1 years) skeletal muscle. Total cell yield varied widely between biopsies (50 to 672 per 100 mg of tissue, N = 10), but was not significantly different between the two patient groups. Percent myoblasts per biopsy (73 +/- 6%), number of myoblast doublings prior to senescence in vitro (37 +/- 2), and myoblast doubling time (27 +/- 1 hr) were also not significantly different between the two patient groups. Fusion kinetics of the myoblasts were similar for the two groups after 20-22 doublings (74 +/- 2% myoblast fusion) when the biopsy samples had been expanded to 1 to 2 billion muscle cells, a number acceptable for human gene therapy use. The myoblasts from the two groups could be equally transduced ex vivo with replication-deficient retroviral expression vectors to secrete 0.5 to 2 microg of a foreign protein (recombinant human growth hormone, rhGH)/10(6) cells/day, and tissue engineered into human BAMs containing parallel arrays of differentiated, postmitotic myofibers. This work suggests that autologous human skeletal myoblasts from a potential patient population can be isolated, genetically modified to secrete foreign proteins, and tissue engineered into implantable living protein secretory devices for therapeutic use.

Attenuation of skeletal muscle wasting with recombinant human growth hormone secreted from a tissue-engineered bioartificial muscle

Skeletal muscle wasting is a significant problem in elderly and debilitated patients. Growth hormone (GH) is an anabolic growth factor for skeletal muscle but is difficult to deliver in a therapeutic manner by injection owing to its in vivo instability. A novel method is presented for the sustained secretion of recombinant human GH (rhGH) from genetically modified skeletal muscle implants, which reduces host muscle wasting. Proliferating murine C2C12 skeletal myoblasts stably transduced with the rhGH gene were tissue engineered in vitro into bioartificial muscles (C2-BAMs) containing organized postmitotic myofibers secreting 3-5 microg of rhGH/day in vitro. When implanted subcutaneously into syngeneic mice, C2-BAMs delivered a sustained physiologic dose of 2.5 to 11.3 ng of rhGH per milliliter of serum. rhGH synthesized and secreted by the myofibers was in the 22-kDa monomeric form and was biologically active, based on downregulation of a GH-sensitive protein synthesized in the liver. Skeletal muscle disuse atrophy was induced in mice by hindlimb unloading, causing the fast plantaris and slow soleus muscles to atrophy by 21 to 35% ( < 0.02). This atrophy was significantly attenuated 41 to 55% (p < 0.02) in animals that received C2-BAM implants, but not in animals receiving daily injections of purified rhGH (1 mg/kg/day). These data support the concept that delivery of rhGH from BAMs may be efficacious in treating muscle-wasting disorders.

Tissue-engineered skeletal muscle organoids for reversible gene therapy

Genetically modified murine skeletal myoblasts were tissue engineered in vitro into organ-like structures (organoids) containing only postmitotic myofibers secreting pharmacological levels of recombinant human growth hormone (rhGH). Subcutaneous organoid implantation under tension led to the rapid and stable appearance of physiological sera levels of rhGH for up to 12 weeks, whereas surgical removal led to its rapid disappearance. Reversible delivery of bioactive compounds from postmitotic cells in tissue engineered organs has several advantages over other forms of muscle gene therapy.