Systemic delivery of human growth hormone by injection of genetically engineered myoblasts

Potentialities of Gene Therapy in Pediatric Endocrinology

Gene therapy has become an appealing therapeutic option in many pediatric fields, including endocrinology. Unlike traditional drugs based on molecules that require repeated and frequent burdensome administrations, a single genetic therapeutic intervention may allow durable and curative clinical benefits. Although this highly innovative technology holds a great promise for the treatment of monogenic diseases, its clinical applications in the field of endocrinology have been so far challenging. In this review, we will discuss various ex vivo and in vivo approaches and potential applications of gene addition and gene editing approaches for treating hyperfunctional and hypofunctional endocrine diseases due to intrinsic defects or autoimmune origin. We will focus on the recent advances in gene therapy approaches aimed at treating type 1 diabetes and monogenic forms of endocrinopathies such as growth hormone deficiency, congenital adrenal hyperplasia, diabetes insipidus, IPEX, as well as their trends and future directions.

Underactive bladder: A review of the current treatment concepts

According to the International Continence Society standardization reports, underactive bladder (UAB) is a decrease in detrusor contraction and/or shortening of the contraction time, resulting in an incomplete and/or prolongation of the bladder emptying within the normal time frame. It has been indicated that idiopathic, neurogenic, myogenic, and iatrogenic factors play a role in the etiology. To make a diagnosis, it is absolutely necessary to perform a pressure-flow study. Treatment alternatives are generally based on the evacuation of the lower urinary tract, independent of the etiology. UAB treatments are listed under the headings of conservative methods and clean intermittent catheterization, pharmacotherapy (alpha-blockers, cholinesterase inhibitors, muscarinic agonists, prostaglandin E2, and acotiamide), surgical treatments (sacral nerve stimulation-electrical stimulation, injections into the external sphincter, surgeries to be performed for bladder outlet obstruction, reduction cystoplasty, and latissimus dorsi detrusor myoplasty), and stem cell and gene therapies. It is still controversial whether satisfactory success is achieved in the treatment of patients with UAB. Owing to the better understanding of the pathophysiology, future developments in the pharmaceutical industry, gene therapy, and biomedical applications are expected to close the gap in the treatment.

Spin infection enables efficient gene delivery to muscle stem cells

Viral vector-mediated foreign gene expression in cultured cells has been extensively used in stem cell studies to explore gene function. However, it is difficult to obtain high-quality stem cells and primary cells after viral vector infection. Here, we describe a new protocol for high-efficiency retroviral infection of primary muscle stem cell (satellite cell) cultures. We compared multiple commercially available transfection reagents to determine which was optimal for retroviral infections of primary myoblasts. Centrifugation force was also tested, and a spin infection protocol with centrifugation at 2800 × g for 90 min had the highest infection efficiency for primary myoblasts. We confirmed that infected muscle stem cells maintain cell proliferation and the capacity for in vitro and in vivo myogenic differentiation. Our new, efficient retroviral infection protocol for muscle stem cells can be applied to molecular biology experiments as well as translational studies.

Use of Repeating Dispensers to Increase the Efficiency of the Intramuscular Myogenic Cell Injection Procedure

Intramuscular myoblast transplantation in humans and nonhuman primates requires precise repetitive cell injections very close to each other. Performed with syringes operated manually throughout large regions, this procedure takes a lot of time, becoming tiring and thus imprecise. We tested two repetitive dispensers with Hamilton syringes as cell injection devices to facilitate this procedure. Monkeys received intramuscular allotransplantations of β-galactosidase-labeled myoblasts, using either a monosyringe or a multisyringe repeating dispenser. The monosyringe repeating dispenser allowed performing cell injections faster and easier than with a manually operated syringe. The multisyringe dispenser accelerated the procedure still more, but it was not ergonomic. Biopsies of the myoblast-injected sites 1 month later showed abundant β-galactosidase-positive myofibers, with the same density and morphological pattern observed following myoblast transplantation with a syringe operated manually. We recommend the monosyringe repeating dispenser for myoblast transplantation in skeletal muscles and maybe in the heart.

Arterial Delivery of Genetically Labelled Skeletal Myoblasts to the Murine Heart: Long-Term Survival and Phenotypic Modification of Implanted Myoblasts

The ability to replace damaged myocardial tissue with new striated muscle would constitute a major advance in the treatment of diseases that irreversibly injure cardiac muscle cells. The creation of focal grafts of skeletal muscle has been reported following the intramural injection of skeletal myoblasts into both normal and injured myocardium. The goals of this study were to determine whether skeletal myoblast-derived cells can be engrafted into the murine heart following arterial delivery. The murine heart was seeded with genetically labeled C2C12 myoblasts introduced into the arterial circulation of the heart via a transventricular injection. A transventricular injection provided access to the coronary and systemic circulations. Implanted cells were characterized using histochemical staining for β-galactosidase, immunofluorescent staining for muscle-specific antigens, and electron microscopy. Initially the injected cells were observed entrapped in myocardial capillaries. One week after injection myoblasts were present in the myocardial interstitium and were largely absent from the myocardial capillary bed. Implanted cells underwent myogenic development, characterized by the expression of a fast-twitch skeletal muscle sarco-endoplasmic reticulum calcium ATPase (SERCA1) and formation of myofilaments. Four months following injection myoblast-derived cells began to express a slow-twitch/cardiac protein, phospholamban, that is normally not expressed by C2C12 cells in vitro. Most surprisingly, regions of close apposition between LacZ labeled cells and native cardiomyocytes contained structures that resembled desmosomes, fascia adherens junctions, and gap junctions. The cardiac gap junction protein, connexin43, was localized to some of the interfaces between implanted cells and cardiomyocytes. Collectively, these findings suggest that arterially delivered myoblasts can be engrafted into the heart, and that prolonged residence in the myocardium may alter the phenotype of these skeletal muscle-derived cells. Further studies are necessary to determine whether arterial delivery of skeletal myoblasts can be developed as treatment for myocardial dysfunction.

Electroporation as a method to induce myofiber regeneration and increase the engraftment of myogenic cells in skeletal muscles of primates

Engraftment of intramuscularly transplanted myogenic cells in mice can be optimized after induction of massive myofiber damage that triggers myofiber regeneration and recruitment of grafted cells; this generally involves either myotoxin injection or cryodamage. There are no effective methods to produce a similar process in the muscles of large mammals such as primates. In this study, we tested the use of intramuscular electroporation for this purpose in 11 macaques. The test sites were 1 cm of skeletal muscle. Each site was treated with 3 penetrations of a 2-needle electrode with 1 cm spacing, applying 3 pulses of 400 V/cm, for a duration of 5 milliseconds and a delay of 200 milliseconds during each penetration. Transplantation of β-galactosidase-labeled myoblasts was done in electroporated and nonelectroporated sites. Electroporation induced massive myofiber necrosis that was followed by efficient muscle regeneration. Myoblast engraftment was substantially increased in electroporated compared with nonelectroporated sites. This suggests that electroporation may be a useful tool to study muscle regeneration in primates and other large mammals and as a method for increasing the engraftment of myoblasts and other myogenic cells in intramuscular transplantation.

Pleiotrophin gene therapy for peripheral ischemia: evaluation of full-length and truncated gene variants

Pleiotrophin (PTN) is a growth factor with both pro-angiogenic and limited pro-tumorigenic activity. We evaluated the potential for PTN to be used for safe angiogenic gene therapy using the full length gene and a truncated gene variant lacking the domain implicated in tumorigenesis. Mouse myoblasts were transduced to express full length or truncated PTN (PTN or T-PTN), along with a LacZ reporter gene, and injected into mouse limb muscle and myocardium. In cultured myoblasts, PTN was expressed and secreted via the Golgi apparatus, but T-PTN was not properly secreted. Nonetheless, no evidence of uncontrolled growth was observed in cells expressing either form of PTN. PTN gene delivery to myocardium, and non-ischemic skeletal muscle, did not result in a detectable change in vascularity or function. In ischemic hindlimb at 14 days post-implantation, intramuscular injection with PTN-expressing myoblasts led to a significant increase in skin perfusion and muscle arteriole density. We conclude that (1) delivery of the full length PTN gene to muscle can be accomplished without tumorigenesis, (2) the truncated PTN gene may be difficult to use in a gene therapy context due to inefficient secretion, (3) PTN gene delivery leads to functional benefit in the mouse acute ischemic hindlimb model.

Prevascularization of porous biodegradable polymers

Highly porous biocompatible and biodegradable polymers in the form of cylindrical disks of 13.5 mm diameter were implanted in the mesentery of male syngeneic Fischer rats for a period of 35 days to study the dynamics of tissue ingrowth and the extent of tissue vascularity, and to explore their potential use as substrates for cell transplantation. The advancing fibrovascular tissue was characterized from histological sections of harvested devices by image analysis techniques. The rate of tissue ingrowth increased as the porosity and/or the pore size of the implanted devices increased. The time required for the tissue to fill the device depended on the polymer crystallinity and was smaller for amorphous polymers. The vascularity of the advancing tissue was consistent with time and independent of the biomaterial composition and morphology. Poly(L-lactic acid) (PLLA) devices of 5 mm thickness, 24.5% crystallinity, 83% porosity, and 166 mum median pore diameter were filled by tissue after 25 days. However, the void volume of prevascularized devices (4%) was minimal and not practical for cell transplantation. In contrast, for amporphous PLLA devices of the same dimensions, and the similar porosity of 87% and median pore diameter of 179 mum, the tissue did not fill completely prevascularized devices, and an appreciable percentage (21%) of device volume was still available for cell engraftment after 25 days of implantation. These studies demonstrate the feasibility of creating vascularized templates of amorphous biodegradable polymers for the transplantation of isolated or encapsulated cell populations to regenerate metabolic organs and tissues.

A First Semimanual Device for Clinical Intramuscular Repetitive Cell Injections

Intramuscular cell transplantation in humans requires so far meticulous repetitive cell injections. Performed percutaneously with syringes operated manually, the procedure is very time consuming and requires a lot of concentration to deliver the cells exactly in the required region. This becomes impractical and inaccurate for large volumes of muscle. In order to accelerate this task, to render it more precise, and to perform injections more reproducible in large volumes of muscle, we developed a specific semimanual device for intramuscular repetitive cell injections. Our prototype delivers very small quantities of cell suspension, homogeneously throughout several needles, from a container in the device. It was designed in order to deliver the cells as best as possible only in a given subcutaneous region (in our case, skeletal muscles accessible from the surface), avoiding wasting in skin and hypodermis. The device was tested in monkeys by performing intramuscular allotransplantations of β-galactosidase-labeled myoblasts. During transplantations, it was more ergonomic and considerably faster than manually operated syringes, facilitating the cell graft in whole limb muscles. Biopsies of the myoblast-injected muscles 1 month later showed abundant β-galactosidase-positive myofibers with homogeneous distribution through the biopsy sections. This is the first device specifically designed for the needs of intramuscular cell transplantation in a clinical context.

Sustained baculovirus-mediated expression in myogenic cells

BACKGROUND

Baculovirus has emerged as a promising gene delivery vector due to its low cytotoxicity and nonreplication nature in mammalian cells. However, baculovirus-mediated expression is transient and generally lasts less than 14 days, which could restrict its application in the treatment of diseases requiring stable transgene expression.

METHODS

We transduced myoblast cell lines C2C12, Sol 8 and primary myoblasts with a baculovirus expressing the enhanced green fluorescent protein (EGFP) under the control of cytomegalovirus immediate-early promoter and measured the transduction efficiency by flow cytometry. Myogenic differentiation was induced after transduction and the longevity of EGFP expression was monitored by fluorescence microscopy. The myogenic differentiation was confirmed by reverse transcription-polymerase chain reaction (RT-PCR). The persistence of the egfp DNA and transcripts was monitored by real-time PCR and quantitative real-time RT-PCR.

RESULTS

Baculovirus efficiently transduced C2C12, Sol 8 and the primary myoblasts. The transgene expression persisted for a prolonged period of time (at least 63 days) in the cells differentiating into myotubes, but was transient in HeLa cells (<7 days). The sustained expression paralleled the myogenic differentiation and stemmed from the intracellular persistence of egfp DNA and mRNA.

CONCLUSIONS

The transgene delivered by baculovirus persists in the myotubes and endows sustained expression, which is distinct from its rapid degradation and transient expression in other cell types. These findings justify the future use of baculovirus for muscle-based gene therapy.

Cloning and expression of canine clotting factor IX cDNAin vitro mediated by retroviral vector

Oligonucleotide of cFIX cDNA (canine FIX, cFIX) was used to transcript mRNA of dog liver cell to cDNA by RT-PCR, and further construct it on the plasmid vector pGEM-T. The correct sequence of cFIX cDNA was obtained which covered the entire cFIX coding region. Furthermore, G1NaCcIX (driven by hCMV promoter) and G1NaMBcIX (driven by MCK enhancer and beta-actin promoter) were constructed using the retroviral vector backbone of G1Na. Canine skin fibroblast (CSF) was used as target cell, transduced with the above constructors respectively. The results showed that these modified CSF cells could express cFIX and that the expression levels were 173 ng/10(6) cell/24 h (G1NaCcIX) and 211 ng/10(6) cell/V24 h (G1NaMBcIX) respectively. Those data offered a promising result for further animal study.

Change of p16(INK4a) and PCNA protein expression in myocardium after injection of hIGF-1 gene modified skeletal myoblasts into post-infarction rats

This study examined the change of p16(INK4a) and PCNA protein expression in myocardium after injection of hIGF-1 gene modified skeletal myoblasts into post-infarction rats. HIGF-1 gene modified skeletal myoblasts (hIGF-1-myoblasts) were injected into hind limb muscles of 18 post-infraction rats (experimental group). Primary-myoblasts were injected into 18 post-infraction rats (control group) and 12 non-infarction rats (sham group). Expression of p16(INK4a) and PCNA protein in myocardiums were separately detected immunocytochemically 1, 2 and 4 weeks after the injection. The level of hIGF-1 and rIGF-1 protein in serum and myocardium were detected by enzyme-linked immunosorbent assay (ELISA). Compared with the sham group, the percentage of p16(INK4a) and PCNA positive cells reached a peak after 1 week in the control group and the experimental group (P<0.01). Moreover, the percentage of p16(INK4a)-positive cells in the experimental group was lower than in control group whereas the percentage of PCNA-positive cells was lower in the control group than in the experimental group (P<0.01). The percentage of p16(INK4a)-positive cells in the experimental group and the percentage of PCNA-positive cells in the control group were close to that in the sham group from the 2nd week (P>0.05). ELISA analysis disclosed that the myocardium level of rIGF-1 protein increased gradually in the controls and especially in the experimental group (P<0.01). The serum level of rIGF-1 decreased significantly in post-infraction rats, but these conditions were improved in the experimental group (P<0.01). The hIGF-1 protein in serum and myocardium were detected from the 1st week to the 4th week in the experimental group. Statistical analysis revealed significant associations of myocardium level of hIGF-1 protein with expression of p16(INK4a) and PCNA protein (r=-0.323, P<0.05; r=0.647, P<0.01). It is concluded that genetically hIGF-1-myoblast provides a means for constant synthesis and release of hIGF-1. It could not only improve the expression of rIGF-1 and PCNA protein in myocardium, but also suppress the expression of p16(INK4a) protein for 30 days in post-infraction rats. Myoblasts-mediated IGF-1 gene therapy may provide a new alternative for the clinical treatment of heart failure.

Moloney murine leukemia virus decay mediated by retroviral reverse transcriptase degradation of genomic RNA

Retroviral vectors are powerful tools for the introduction of transgenes into mammalian cells and for long-term gene expression. However, their application is often limited by a rapid loss of bioactivity: retroviruses spontaneously loose activity at 37 degrees C, with a half-life of 4 to 9 h depending on the retrovirus type. We sought to determine which components of the retrovirus are responsible for this loss in bioactivity and to obtain a quantitative characterization of their stability. To this end, we focused on RNA and viral proteins, two major components that we hypothesized may undergo degradation and negatively influence viral infectivity. Reverse transcription PCR (RT-PCR) targeting RNA encoding portions of the viral genome clearly demonstrated time-dependent degradation of RNA which correlated with the loss in viral bioactivity. Circular dichroism spectroscopy, SDS-PAGE and two-dimensional SDS-PAGE analyses of viral proteins did not show any change in secondary structure or evidence of proteolysis. The mechanism underlying the degradation of viral RNA was investigated by site-directed mutagenesis of proteins encoded by the viral genome. Reverse transcriptase and protease mutants exhibited enhanced RNA stability in comparison to wild type recombinant virus, suggesting that the degradation of RNA, and the corresponding virus loss of activity, is mediated by the reverse transcriptase enzyme.

Preclinical assessment of wt GNE gene plasmid for management of hereditary inclusion body myopathy 2 (HIBM2)

Hereditary Inclusion Body Myopathy (HIBM2) is a chronic progressive skeletal muscle wasting disorder which generally leads to complete disability before the age of 50 years. There is currently no effective therapeutic treatment for HIBM2. Development of this disease is related to expression in family members of an autosomal recessive mutation of the GNE gene, which encodes the bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE/MNK). This is the rate limiting bifunctional enzyme that catalyzes the first 2 steps of sialic acid biosynthesis. Decreased sialic acid production, consequently leads to decreased sialyation of a variety of glycoproteins including the critical muscle protein alpha-dystroglycan (alpha-DG). This in turn severely cripples muscle function and leads to the onset of the syndrome. We hypothesize that replacing the mutated GNE gene with the wildtype gene may restore functional capacity of GNE/MNK and therefore production of sialic acid, allowing for improvement in muscle function and/or delay in rate of muscle deterioration. We have constructed three GNE gene/CMV promoter plasmids (encoding the wildtype, HIBM2, and Sialuria forms of GNE) and demonstrated enhanced GNE gene activity following delivery to GNE-deficient CHO-Lec3 cells. GNE/MNK enzyme function was significantly increased and subsequent induction of sialic acid production was demonstrated after transfection into Lec3 cells with the wild type or R266Q mutant GNE vector. These data form the foundation for future preclinical and clinical studies for GNE gene transfer to treat HIBM2 patients.

Gene delivery to muscle

The delivery of genes to skeletal muscle by myoblast implantation, DNA injection, or viral transduction has therapeutic applications for human neuromuscular and systemic disorders, many of which are now represented by transgenic or "knockout" mouse models. This unit describes the isolation and retroviral transduction of mouse myoblasts, the injection of myoblasts and plasmid DNA into mouse muscle, and histological methods for analyzing the recipient muscle. A procedure describing the injection of plasmid DNA into muscle with or without electric charge is also included.

Angiogenesis Enhances Factor IX Delivery and Persistence from Retrievable Human Bioengineered Muscle Implants

Human muscle progenitor cells transduced with lentiviral vectors secreted high levels of blood clotting factor IX (FIX). When bioengineered into postmitotic myofibers as human bioartificial muscles (HBAMs) and subcutaneously implanted into immunodeficient mice, they secreted FIX into the circulation for >3 months. The HBAM-derived FIX was biologically active, consistent with the cells' ability to conduct the necessary posttranslational modifications. These bioengineered muscle implants are retrievable, an inherent safety feature that distinguishes this "reversible" gene therapy approach from most other gene therapy strategies. When myofibers were bioengineered from human myoblasts expressing FIX and vascular endothelial growth factor, circulating FIX levels were increased and maintained long term within the therapeutic range, consistent with the generation of a vascular network around the HBAM. The present study implicates an important role for angiogenesis in the efficient delivery of therapeutic proteins using tissue engineered stem cell-based gene therapies.

IGF-I increases bone marrow contribution to adult skeletal muscle and enhances the fusion of myelomonocytic precursors

Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

The mitotic clock in skeletal muscle regeneration, disease and cell mediated gene therapy

The regenerative capacity of skeletal muscle will depend on the number of available satellite cells and their proliferative capacity. We have measured both parameters in ageing, and have shown that although the proliferative capacity of satellite cells is decreasing during muscle growth, it then stabilizes in the adult, whereas the number of satellite cells decreases during ageing. We have also developed a model to evaluate the regenerative capacity of human satellite cells by implantation into regenerating muscles of immunodeficient mice. Using telomere measurements, we have shown that the proliferative capacity of satellite cells is dramatically decreased in muscle dystrophies, thus hampering the possibilities of autologous cell therapy. Immortalization by telomerase was unsuccessful, and we currently investigate the factors involved in cell cycle exits in human myoblasts. We have also observed that insulin-like growth factor-1 (IGF-1), a factor known to provoke hypertrophy, does not increase the proliferative potential of satellite cells, which suggests that hypertrophy is provoked by increasing the number of satellite cells engaged in differentiation, thus possibly decreasing the compartment of reserve cells. We conclude that autologous cell therapy can be applied to specific targets when there is a source of satellite cells which is not yet exhausted. This is the case of Oculo-Pharyngeal Muscular Dystrophy (OPMD), a late onset muscular dystrophy, and we participate to a clinical trial using autologous satellite cells isolated from muscles spared by the disease.

Enhanced fusion of myoblasts with myofibers for efficient gene delivery induced by a partially purified protein fraction from rat muscle extract

The biggest challenge to gene therapy is how to efficiently deliver the desired therapeutic gene into a sufficient number of recipient cells to achieve significant clinical efficacy. Here, we identified a partially purified extract from rat muscle probably containing myoblast specific fusion factor(s) (MSF), which significantly enhanced fusion of donor myoblast with host muscle fibers. Once incorporated, the introduced genetic construct could instruct the machinery of the hybrid cells to express the desired protein(s). Rat satellite cells containing a plasmid carrying a marker bone morphogenetic protein-4 (BMP-4) coding sequence were used as foreign gene delivery vehicle. BrdU labeling of the MSF-pretreated satellite cells allowed tracing the fate of the genetically modified satellite cells in the host muscles. Immunohistochemistry using anti-BMP-4 antibody demonstrated the translation of the introduced gene construct. It was demonstrated that in the presence of MSF, numerous BrdU positive nuclei and the expression of BMP-4 polypeptides could be observed in host hybrid fibers, while in the control group using rat serum to replace MSF containing fraction, only a few BrdU positive signals were detected. The expression of osteocalcin and the elevated alkaline phosphatase activity detected in the hybrid fibers indicated the proper folding, secretion and, post-translational modification of the expressed foreign protein. This strategy of enhanced myoblast-mediated gene transfer would break the major barrier in current practice of normal or engineered myoblast transplantation in the management of genetic muscle diseases or systemic genetic disorders.

Sca-1 negatively regulates proliferation and differentiation of muscle cells

Satellite cells are tissue-specific stem cells critical for skeletal muscle growth and regeneration. Upon exposure to appropriate stimuli, satellite cells produce progeny myoblasts. Heterogeneity within a population of myoblasts ensures that a subset of myoblasts readily differentiate to form myotubes, whereas other myoblasts remain undifferentiated and thus available for future muscle growth. The mechanisms that contribute to this heterogeneity in myoblasts are largely unknown. We show that satellite cells are Sca-1(neg) but give rise to myoblasts that are heterogeneous for sca-1 expression. The majority of myoblasts are sca-1(neg), rapidly divide, and are capable of undergoing myogenic differentiation to form myotubes. In contrast, a minority population is sca-1(pos), divides slower, and does not readily form myotubes. Sca-1 expression is not static but rather dynamically modulated by the microenvironment. Gain-of-function and loss-of-function experiments demonstrate that sca-1 has a functional role in regulating proliferation and differentiation of myoblasts. Myofiber size of sca-1 null muscles is altered in an age-dependent manner, with increased size observed in younger mice and decreased size in older mice. These studies reveal a novel system that reversibly modulates the myogenic behavior of myoblasts. These studies provide evidence that, rather than being a fixed property, myoblast heterogeneity can be modulated by the microenvironment.

A new potent hFIX plasmid for hemophilia B gene therapy

PURPOSE

The purpose of this work was to construct and characterize a new potent hFIX plasmid, p2SV-hFIX, which has two hFIX expression units containing the SV40 promoter/enhancer for hemophilia B gene therapy.

METHODS

p1SV-hFIX was constructed by insertion of amplified hFIX cDNA at the ECORI and Xbal sites of pSI expression vector containing simian virus 40 (SV40) promoter/enhancer. To construct p2SV-hFIX, the hFIX expression cassette was isolated from p1SV-hFIX by digestion with restriction enzymes, and the purified expression cassette was inserted at the BglII site of another plSV-hFIX. The gene expression of p1SV-hFIX, p2SV-hFIX, and a plasmid containing a liver-specific apoE enhancer and alpha antitrypsin promoter, pAAV-hAAT-hFIX. were evaluated in various cell lines using polyethylenimine (PEI) as a gene carrier in vitro.

RESULTS

The construction of p1SV-hFIX and p2SV-hFIX were confirmed by restriction enzyme studies. The transfection efficiency of p2SV-hFIX was 3.83-fold and 7.16-fold higher than that of pAAV-hAAT-hFIX in C2C12 and NIH3T3 cells, respectively. p2SV-hFIX also showed higher transfection efficiency than p1SV-hFIX in both cells.

CONCLUSIONS

In accordance with these results, p2SV-hFIX is a new potent hFIX plasmid that can be transfected in various cells. Systemic delivery of p2SV-hFIX via intravenous or intramuscular injection is feasible for treatment of hemophilia B.

A comparative study of three different biomaterials in the engineering of skeletal muscle using a rat animal model

Defects caused by traumatic or postsurgical loss of muscle mass may result in severe impairments of the functionality of skeletal muscle. Tissue engineering represents a possible approach to replace the lost or defective muscle. The aim of this study was to compare the suitability of three different biomaterials as scaffolds for rat myoblasts, using a new animal model. PKH26-fluorescent-stained cultured rat myoblasts were either seeded onto polyglycolic acid meshes or, alternatively, suspended in alginate or in hyaluronic acid-hydrogels. In each of the eight Fisher CDF-344 rats, four capsule pouches were induced by subcutaneous implantation of four silicone sheets. After two weeks the silicone sheets were removed and myoblast-biomaterial-constructs were implanted in the preformed capsules. Specimens were harvested after four weeks and examined histologically by H&E-staining and fluorescence microscopy. All capsules were well-vascularized. Implanted myoblasts fused by forming multinucleated myotubes. This study demonstrates that myoblasts seeded onto different biomaterials can be successfully transplanted into preformed highly vascularized capsule pouches. Our animal model has paved the way for studies of myoblast-biomaterial transplantations into an ectopic non-muscular environment.

Electroporation for gene transfer to skeletal muscles: current status

Naked plasmid DNA can be used to introduce genetic material into a variety of cell types in vivo. However, such gene transfer and expression is generally very low compared with that achieved with viral vectors and so is unsuitable for clinical therapeutic application in most cases. This difference in efficiency has been substantially reduced by the introduction of in vivo electroporation to enhance plasmid delivery to a wide range of tissues including muscle, skin, liver, lung, artery, kidney, retina, cornea, spinal cord, brain, synovium, and tumors. The precise mechanism of in vivo electroporation is uncertain, but appears to involve both electropore formation and an electrophoretic movement of the plasmid DNA. Skeletal muscle is a favored target tissue for three reasons: there is a pressing need to develop effective therapies for muscular dystrophies; skeletal muscle can act as an effective platform for the long-term secretion of therapeutic proteins for systemic distribution; and introduction of DNA vaccines into skeletal muscle promotes strong humoral and cellular immune responses. All of these applications are significantly improved by the application of in vivo electroporation. Importantly, the increased efficiency of plasmid delivery following electroporation is seen in larger species as well as rodents, in contrast to the decreasing efficiencies with increasing body size for simple intramuscular injection of naked plasmid DNA. As this electroporation-enhanced non-viral gene delivery system works well in larger species and avoids the vector-specific immune responses associated with recombinant viruses, the prospects for clinical application are promising.

Dynamics of the early immune cellular reactions after myogenic cell transplantation

The role of immune cells in the early donor cell death/survival following myoblast transplantation is confusing, one of the reasons being the lack of data about the immune reactions following cell transplantation. We used outbred mice as hosts for transplantation of primary cultured muscle cells and T-antigen-immortalized myoblasts. The host muscles were analyzed 1 h to 7 days after cell injection. No net loss of the donor primary cultured cell population was observed in this period. The immune cellular reaction in this case was: 1) a brief (<48 h) neutrophil invasion; 2) macrophage infiltration from days 1 to 7; 3) a specific response involving CTL and few NK cells (days 6 and 7), preceded by a low CD4+ cell infiltration starting at day 3. In contrast, donor-immortalized myoblasts completely disappeared during the 7-day follow-up. In this case, an intense infiltration of CTL and macrophages, with moderate CD4+ infiltration and lower amounts of NK cells, was observed starting at day 2. The nonspecific immune response at days 0 and 1 was similar for both types of donor cells. The present observations set a basis to interpret the role of immune cells on the early death/survival of donor cells following myoblast transplantation.

Glucose-regulated glucose uptake by transplanted muscle cells expressing glucokinase counteracts diabetic hyperglycemia

Type 1 diabetic patients depend on insulin replacement therapy. However, chronic hyperglycemia due to failure to maintain proper glycemic control leads to microvascular, macrovascular, and neurological complications. Increased glucose disposal by tissues engineered to overexpress key regulatory genes in glucose transport or phosphorylation can reduce diabetic hyperglycemia. Here we report that differentiated myoblast cells expressing the glucose-phosphorylating enzyme glucokinase (GK) showed a glucose-dependent increase in glucose uptake and utilization in vitro. Transplantation of GK-expressing myotubes into healthy mice did not alter blood glucose levels and recipient mice maintained normoglycemia. After streptozotocin treatment, mice transplanted with GK-expressing myotubes counteracted hyperglycemia, polydipsia, and polyphagia, whereas mice transplanted with control myotubes developed diabetes. Similarly, diabetic mice transplanted with control myotubes remained hyperglycemic. In contrast, transplantation of GK-expressing myotubes into diabetic mice lowered hyperglycemia. These results suggest that the use of genetically engineered muscle cells to express glucokinase may provide a glucose-regulated approach to reduce diabetic hyperglycemia.

Transient production of alpha-smooth muscle actin by skeletal myoblasts during differentiation in culture and following intramuscular implantation

alpha-smooth muscle actin (SMA) is typically not present in post-embryonic skeletal muscle myoblasts or skeletal muscle fibers. However, both primary myoblasts isolated from neonatal mouse muscle tissue, and C2C12, an established myoblast cell line, produced SMA in culture within hours of exposure to differentiation medium. The SMA appeared during the cells' initial elongation, persisted through differentiation and fusion into myotubes, remained abundant in early myotubes, and was occasionally observed in a striated pattern. SMA continued to be present during the initial appearance of sarcomeric actin, but disappeared shortly thereafter leaving only sarcomeric actin in contractile myotubes derived from primary myoblasts. Within one day after implantation of primary myoblasts into mouse skeletal muscle, SMA was observed in the myoblasts; but by 9 days post-implantation, no SMA was detectable in myoblasts or muscle fibers. Thus, both neonatal primary myoblasts and an established myoblast cell line appear to similarly reprise an embryonic developmental program during differentiation in culture as well as differentiation within adult mouse muscles.

Formation of the biopulsatile vascular pump by cardiomyocyte transplants circumvallating the abdominal aorta

In spite of the fact that patients with heart diseases requiring heart transplantation are increasing in the world, there are a lack of donors, which makes it hard to offer them these life-saving transplants. As a way to overcome this dilemma, we have researched the addition of the new biopump, which consists of the cultured embryonic cardiomyocytes grafted around the abdominal aorta and contracts spontaneously, which subsequently supports the function of the host heart. Ventricular tissues from ICR 14-day-old embryos were cultured and were injected to BALB/c nude mice (male, 8-week-old) subperitoneally around the abdominal aorta. At 3 and 7 days after implantation, action potential of the grafts was measured. Grafts were prepared for histological study. The grafts survived, showed vigorous angiogenesis, and contracted spontaneously. The cardiomyocytes in the grafts showed irregular arrangement, containing myofibrils with sarcomeres and intercalated disks. It was confirmed by immunohistochemistry that the cardiomyocytes in the grafts matured in accordance with normal development. The grafts were very quickly invaded by small vessels from the surrounding tissues showing the formation of new circulation. Embryonic cardiomyocytes have the ability to remodel the abdominal aorta into a spontaneous pulsating apparatus and to function as a vascular pump.

Enhanced animal growth via ligand-regulated GHRH myogenic-injectable vectors

Regulated animal growth occurred following a single electroporated injection of a mixture of two plasmids (10 microg of DNA), one expressing the GeneSwitch regulator protein, the other an inducible growth hormone releasing hormone (GHRH) gene, into the tibialis anterior muscles of adult SCID mice. Administration of the ligand mifepristone (MFP) up-regulated GHRH expression, as shown by elevations of IGF-I levels, and when MFP dosing was withdrawn, IGF-I returned to baseline levels. Five cycles of IGF-I induction were observed during a five-month period. Chronic MFP dosing for 25 days increased lean body mass, weight gain, and bone mineral density significantly compared with non-MFP treated controls. In summary, long-term drug-regulated GHRH expression was achieved following plasmid-based gene therapy, and chronic induction of GHRH expression in adult animals led to improvements in weight gain and body composition.

Plasmid gene delivery to human keratinocytes through a fibrin-mediated transfection system

We have developed a matrix-mediated transfection system to deliver plasmids to human keratinocytes. The matrix is a soluble, self-hardening fibrin matrix (Tissucol), Baxter) that has been used clinically. Recently it has been shown that full thickness burn wounds can be successfully treated with a keratinocyte fibrin glue suspension. Further, it has been demonstrated that hEGF transfected cells accelerate wound healing. In this study, we inoculated the matrix with the hEGF expression plasmid and resuspended the matrix with either cultured or noncultured human keratinocytes. We obtained successful transfection rates of these cells (up to a 100-fold increase compared to controls containing no EGF expression plasmid) in vitro. After transplantation to full thickness wounds on athymic mice we were able to show a 180-fold increase in EGF concentration compared to controls, which persisted over the entire 7-day monitored period, decreasing from 180 to 20 pg/mL at day seven. This unique approach indicates the possible utility to combine a matrix for cell transplantation with a transfection system to release therapeutic proteins in vitro and in vivo.

Noninvasive optical imaging of firefly luciferase reporter gene expression in skeletal muscles of living mice

The ability to monitor reporter gene expression noninvasively offers significant advantages over current techniques such as postmortem tissue staining or enzyme activity assays. Here we demonstrate a novel method of repetitively tracking in vivo gene expression of firefly luciferase (FL) in skeletal muscles of mice using a cooled charged coupled device (CCD) camera. We first show that the cooled CCD camera provides consistent and reproducible results within +/-8% standard deviation from mean values, and a detection sensitivity (range tested: 1 x 10(4) - 1 x 10(9) plaque form-ing units (pfu)) of 1 x 10(6) pfu of E1-deleted adenovirus expressing FL driven by a cytomegalovirus promoter (Ad-CMV-FL). The duration and magnitude of adenoviral mediated (1 x 10(9) pfu) FL gene expression were then followed over time. FL gene expression in immunocompetent Swiss Webster mice peaks within the first 48 hours, falls by 98% after 20 days, and persists for >150 days. In contrast, FL activity in nude mice remains elevated for >110 days. Finally, transduced Swiss Webster and nude mice were sacrificed to show that the in vivo CCD signals correlate well with in vitro luciferase enzyme assays (r(2)=0.91 and 0.96, respectively). Our findings demonstrate the ability of the cooled CCD camera to sensitively and noninvasively track the location, magnitude, and persistence of FL gene expression. Monitoring of gene therapy studies in small animals may be aided considerably with further extensions of this technique.

Co-transplantation of plasmid-transfected myoblasts and myotubes into rat brains enables high levels of gene expression long-term

We have previously proposed the use of primary muscle cells as a "platform," or "vehicle" for intracerebral transgene expression. Brain grafts of minced muscle, or cultured muscle cells persisted in rat brains for at least 6 mo without any decrease in graft size, or tumor formation. Stable, but moderate levels of intracerebral transgene expression were obtained by transplanting plasmid-transfected myotubes in culture. In the present study, high and stable levels of intracerebral transgene expression were achieved by the co-transplantation of plasmid-transfected myoblasts and myotubes in culture. Approximately 5 X 10(5) myoblasts and myotubes were transfected with 10 micrograms pRSVL plasmid DNA, and 30 micrograms Lipofectin (BRL), respectively. They were mixed together (total cell number was 1 million), and stereotactically injected into the caudate nucleus of an adult rat brain. The activity of luciferase, the product of transgene expression, was stable for at least 4 mo, and much higher than the levels in myotube grafts, or co-grafts of myoblasts and minced muscle. Presumably, the myotubes served as a framework on which the myoblasts can form myotubes. The sections of brains transplanted with co-graft of myoblasts, and myotubes transfected with pRSVLac-Z were stained immunofluorescently for beta-galactosidase activity. The muscle grafts contained beta-galactosidase positive myofibers 4 mo after transplantation. Such high and stable levels of in vivo expression after postnatal gene transfer have rarely been achieved. Primary muscle cells are useful vehicle for transgene expression in brains, and potentially valuable for gene therapy of degenerative neurological disorders.

Autologous primary muscle-derived cells transfer into the lower urinary tract

The goal of these experiments was to establish the basic methodology for future clinical applications of muscle-derived cells (MDC) tissue engineering and gene transfer for the treatment of urological dysfunction. Primary MDC isolated via preplating techniques from adult female SD rats were transduced with retrovirus encoding the expression of beta-galactosidase reporter gene. The MDC were injected into the right and left lateral walls of the bladder and proximal urethra of the autologous animals (n = 6) with a 10 microl Hamilton micro syringe. The amount of injected MDC ranged from 1 to 2 x 10(6) cells. The injected tissue was harvested after 7, 14, and 28 days, sectioned and examined histologically for beta-galactosidase and immunohistochemically for fast myosin heavy chain specific to skeletal muscle. The tissues were also stained for anti-CD4 and anti-CD8 antibodies to assess for cellular immune reaction. We have detected a large number of autologous MDC expressing beta-galactosidase and positively stained for fast myosin heavy chain in the bladder and urethral wall. Many injected myoblasts and myotubes were also seen in the bladder and urethral wall at each time point. Staining of lymphocytes with anti-CD4 and anti-CD8 antibodies was negative after MDC injection at each time point. We have demonstrated the long-term survival of autologous MDC and MDC mediated gene transfer into the bladder and urethral wall. Autologous MDC and MDC mediated gene transfer may be a promising treatment to augment bladder and urethral sphincter function.

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.

Gene therapy strategies for urological dysfunction

Novel molecular techniques such as conventional and ex vivo gene therapy, and tissue engineering have only recently been introduced to the field of urology. The lower urinary tract is ideally suited for minimally invasive therapy, and also ex vivo approaches would limit the risk of systemic side effects. Muscle-derived stem cells have been used successfully to treat stress incontinence, and rats with diabetic bladder dysfunction benefited from nerve growth factor (NGF)-based gene therapy. Nitric oxide synthase and capase-7 might provide suitable gene therapy targets for erectile dysfunction and benign prostatic hyperplasia, respectively.

Muscle-based gene therapy and tissue engineering for the musculoskeletal system

The recent expansion of molecular biology techniques has opened the gates for a rapid advancement in our knowledge of disease mechanisms. These techniques, in addition to advances in cell biology and polymer chemistry, are resulting in novel approaches to treating musculoskeletal disorders. Surgeons, who have traditionally used the tools of excision and reconstruction to treat patients, might now serve as surgical 'gardeners', who create microenvironments that are conducive for tissue regeneration. This review will update readers on the principles and current advances in muscle-based gene therapy and tissue engineering for the musculoskeletal system.

Purification of mouse primary myoblasts based on alpha 7 integrin expression

Fundamental insights have come from the study of myogenesis. Primary myoblasts isolated directly from muscle tissue more closely approximate myogenesis than established cell lines. However, contamination of primary muscle cultures with nonmyogenic cells can complicate the results. To overcome this problem, we previously described a method for myoblast purification based on novel culture conditions (T. A. Rando and H. M. Blau, 1994, J. Cell Biol. 125, 1275--1287). Here we report a refinement of this method that leads directly to an enriched population of mouse primary myoblasts, within significantly fewer population doublings. The method described here avoids using adhesion as a criterion for selection. This advance capitalizes on the ability of the antibody CA5.5 to recognize alpha 7 integrin, a muscle-specific cell surface antigen. Enrichment of myoblasts to greater than 95% of the cell population can be achieved by a single round of flow cytometry or magnetic bead separation. This is the first description of a mouse myoblast purification method based on a cell-type-specific antigen. The ease of this procedure for isolating primary myoblasts should expand the opportunities for (1) using these cells in cell transplantation studies in animal models of human disease, (2) isolating and characterizing mutant myoblasts from transgenic animals, and (3) allowing in vitro studies of molecules that regulate muscle cell growth, differentiation, and neoplasia.

The effect of bone morphogenetic protein-2 expression on the early fate of skeletal muscle-derived cells

The identification of bone morphogenetic proteins (BMPs) has stimulated intense interest in BMP delivery approaches. Ex vivo BMP-2 gene delivery has recently been described using skeletal muscle-derived cells. Skeletal muscle-derived cells, because of proven efficient transgene delivery and osteocompetence, represent an attractive cell population on which to base ex vivo BMP-2 gene delivery. However, the early in vivo fate of BMP-2-expressing muscle-derived cells is unknown. This study investigates the in vivo effects of BMP-2 secretion on skeletal muscle-derived cells in terms of cell survival and cell differentiation. The first experiment compared survival of BMP-2-expressing cells with control cells during the first 48 h after in vivo implantation. The results demonstrate that BMP-2 secretion did not adversely affect cell survival 8, 24, or 48 h after intramuscular implantation. The second experiment histologically compared the fate of BMP-2-expressing muscle-derived cells to the same cells not expressing BMP-2. The results show that BMP-2 expression prevented in vivo myogenic differentiation and promoted osteogenic differentiation of the transduced cells. This study further supports the existence of osteoprogenitor cells residing within skeletal muscle. Moreover, it is demonstrated that BMP-2 secretion does not adversely affect early cell survival of muscle-derived cells. These data are important for future investigations into BMP-2 gene delivery approaches to the musculoskeletal system.

Flow cytometric characterization of myogenic cell populations obtained via the preplate technique: potential for rapid isolation of muscle-derived stem cells

Myoblast transplantation has been investigated as a therapy for muscle-related diseases and as a gene delivery vehicle for therapeutic recombinant proteins. Clinical successes involving muscle cell transplantation have been limited, in part because of poor donor cell survival, and the heterogeneous nature of myogenic donor cells has largely been ignored. We have previously reported an isolation technique, preplating, that results in purified myogenic cells that are capable of significantly higher rates of donor cell survival leading to enhanced gene transfer to skeletal muscle. Characterization of these purified cells revealed that they display markers common to stem cells and are capable of multilineage differentiation. This study was performed to phenotypically characterize, by flow cytometry, muscle-derived cell populations obtained by the preplate technique for the purpose of eventually developing a method to quickly identify and isolate viable muscle cells best suited for transplantation. Muscle cell cultures were analyzed for expression of the surface proteins Sca-1, c-Kit, and CD34. We found that the preplate technique purifies distinct myogenic cell subpopulations expressing CD34 alone (Sca-1 negative) and Sca-1 alone (CD34 negative), but that this expression is subject to change with time in culture. Isolation and transplantation of phenotypically pure Sca-1-positive myogenic cells, obtained by magnetic cell sorting, demonstrates the ability to quickly select viable myogenic cells capable of regenerating skeletal muscle and restoring dystrophin expression within dystrophic host skeletal muscle. Flow cytometric described phenotypes will aid in the rapid isolation of specific donor cell populations for muscle cell transplants and muscle cell-mediated gene therapies, thereby enhancing their future success.

Delivery of FGF-2 but not VEGF by encapsulated genetically engineered myoblasts improves survival and vascularization in a model of acute skin flap ischemia

Stimulating angiogenesis by gene transfer approaches offers the hope of treating tissue ischemia which is untreatable by currently practiced techniques of vessel grafting and bypass surgery. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2) are potent angiogenic molecules, making them ideal candidates for novel gene transfer protocols designed to promote new blood vessel growth. In this study, an ex vivo gene therapy approach utilizing cell encapsulation was employed to deliver VEGF and FGF-2 in a continuous and localized manner. C(2)C(12) myoblasts were genetically engineered to secrete VEGF(121), VEGF(165) and FGF-2. These cell lines were encapsulated in hollow microporous polymer membranes for transplantation in vivo. Therapeutic efficacy was evaluated in a model of acute skin flap ischemia. Capsules were positioned under the distal, ischemic region of the flap. Control flaps showed 50% necrosis at 1 week. Capsules releasing either form of VEGF had no effect on flap survival, but induced a modest increase in distal vascular supply. Delivery of FGF-2 significantly improved flap survival, reducing necrosis to 34.2% (P < 0.001). Flap vascularization was significantly increased by FGF-2 (P < 0.01), with numerous vessels, many of which had a large lumen diameter, growing in the proximity of the implanted capsules. These results demonstrate that FGF-2, delivered from encapsulated cells, is more efficacious than either VEGF(121) or VEGF(165) in treating acute skin ischemia and improving skin flap survival. Furthermore, these data attest to the applicability of cell encapsulation for the delivery of angiogenic factors for the treatment and prevention of tissue ischemia.

Muscle-derived cell transplantation and differentiation into lower urinary tract smooth muscle

OBJECTIVES

To explore the feasibility of primary skeletal muscle-derived cell (MDC)-based tissue engineering and gene transfer into the lower urinary tract and to explore whether the injected primary skeletal MDCs can persist and differentiate into myotubes and myofibers in the bladder wall.

METHODS

Primary MDCs isolated from normal mice were first transduced with adenovirus encoding the expression of the beta-galactosidase reporter gene. Adult severe combined immunodeficiency mice (n = 12) were used in this study. The MDCs were injected into the right and left lateral bladder walls with a 10-microL Hamilton microsyringe. The amount of injected MDCs ranged from 1 to 1.5 x 10(6) cells. The tissue was harvested after 5, 35, and 70 days, sectioned, stained for fast myosin heavy chain, and assayed for beta-galactosidase expression.

RESULTS

We observed a large number of cells expressing beta-galactosidase in the bladder wall at each time point. Many myotubes and myofibers expressing beta-galactosidase and positively stained for fast myosin heavy chain were also seen in the bladder wall at 35 and 70 days after injection. Additionally, the size of the injected MDCs significantly increased during the course of the study (P <0.05).

CONCLUSIONS

We have demonstrated the long-term survival and beta-galactosidase expression of MDCs injected into the bladder wall. Moreover, our results suggest that some injected MDCs can differentiate into myofibers. These results suggest that MDCs can be a desirable substance for tissue engineering and an ex vivo method for gene transfer into the lower urinary tract.

Posttranslational modifications of recombinant myotube-synthesized human factor IX

Recent data demonstrate that the introduction into skeletal muscle of an adeno-associated viral (AAV) vector expressing blood coagulation factor IX (F.IX) can result in long-term expression of the transgene product and amelioration of the bleeding diathesis in animals with hemophilia B. These data suggest that biologically active F.IX can be synthesized in skeletal muscle. Factor IX undergoes extensive posttranslational modifications in the liver, the normal site of synthesis. In addition to affecting specific activity, these posttranslational modifications can also affect recovery, half-life in the circulation, and the immunogenicity of the protein. Before initiating a human trial of an AAV-mediated, muscle-directed approach for treating hemophilia B, a detailed biochemical analysis of F.IX synthesized in skeletal muscle was carried out. As a model system, human myotubes transduced with an AAV vector expressing F.IX was used. F.IX was purified from conditioned medium using a novel strategy designed to purify material representative of all species of rF.IX in the medium. Purified F.IX was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), N-terminal sequence analysis, chemical gamma-carboxyglutamyl analysis, carbohydrate analysis, assays for tyrosine sulfation, and serine phosphorylation, and for specific activity. Results show that myotube-synthesized F.IX has specific activity similar to that of liver-synthesized F.IX. Posttranslational modifications critical for specific activity, including removal of the signal sequence and propeptide, and gamma-carboxylation of the N-terminal glutamic acid residues, are also similar, but carbohydrate analysis and assessment of tyrosine sulfation and serine phosphorylation disclose differences. In vivo experiments in mice showed that these differences affect recovery but not half-life of muscle-synthesized F.IX.

Persistence and survival of autologous muscle derived cells versus bovine collagen as potential treatment of stress urinary incontinence

PURPOSE

We explored the use of autologous muscle derived cells as a method of treating stress urinary incontinence. We determined whether urethral muscle derived cell injection is feasible and compared it with bovine collagen injection.

MATERIALS AND METHODS

Muscle derived cells isolated from female Sprague-Dawley rats were first transduced with retrovirus carrying the transgene for beta-galactosidase. We injected approximately 1 to 1.5 x 106 cells into the bladder wall and proximal urethra of 6 autologous animals. Tissue was harvested after 3 and 30 days, sectioned, stained for fast myosin heavy chain and assayed for beta-galactosidase. To compare muscle derived cell and bovine collagen injections 100 microl. of commercially available bovine collagen were also injected in Sprague-Dawley female rats. Tissue was harvested in 3 animals each after 3 and 30 days, sectioned and stained for trichrome. Subsequently, 3 adult SCID mice were used to compare the level of transgene expression at each time point after injecting 1.5 x 106 cells per injection, which were transduced with adenovirus carrying the transgene for beta-galactosidase.

RESULTS

A large number of cells expressing beta-galactosidase were observed in the bladder and urethral wall 3 and 30 days after autologous cell injection in Sprague-Dawley rats. The persistence of primary muscle derived cells at 3 days was similar to that of collagen. However, at 30 days there was significant cell persistence while only a minimal amount of injected bovine collagen was detectable. Approximately 88% of the beta-galactosidase expression at day 3 remained at day 30 in SCID mice.

CONCLUSIONS

We present 2 new findings important for the emerging field of urological tissue engineering, including the feasibility of injecting autologous skeletal muscle derived cells into the lower urinary tract and the greater persistence of such injected cells versus injected bovine collagen. Therefore, autologous muscle derived cell injection may be an attractive alternative treatment option for stress urinary incontinence.

Treatment of severe hypercholesterolemia in apolipoprotein E-deficient mice by intramuscular injection of plasmid DNA

We report on systemic delivery and long-term biological effects of apolipoprotein E (apoE) obtained by intramuscular (i.m.) plasmid DNA injection. ApoE plays an important role in lipoprotein catabolism and apoE knock-out mice develop severe hypercholesterolemia and diffuse atherosclerosis. We have injected apoE-deficient mice with 80 microg of a plasmid vector (pCMV-E3) encoding the human apoE3 cDNA under the control of the CMV promoter-enhancer in both posterior legs. Local expression of the transgene was demonstrated throughout 16 weeks. Human apoE3 recombinant protein reached 0.6 ng/ml serum level. After i.m. injection of pCMV-E3 expression vector the mean serum cholesterol concentrations decreased from 439 +/- 57 mg/dl to 253 +/- 99 mg/dl (P < 0.05) 2 weeks after injection and persisted at a significantly reduced level throughout the 16 weeks observation period (P < 0.005). Serum cholesterol was unaffected and reached an absolute level of 636 +/- 67 mg/dl in control groups. Finally, injection of pCMV-E3 into apoE-deficient mice resulted in a redistribution of cholesterol content between lipoprotein fractions, with a marked decrease in VLDL, IDL and LDL cholesterol content and an increase in HDL cholesterol. These results demonstrate that severe hypercholesterolemia in apoE-deficient mice can be effectively reversed by i.m. DNA injection, and indicate that this approach could represent a useful tool to correct several hyperlipidemic conditions resulting in atherosclerosis.

Pluripotential mesenchymal cells repopulate bone marrow and retain osteogenic properties

Precursor cells, isolated from bone marrow, can develop into various cell types and may contribute to skeletal growth, remodeling, and repair. The D1 cell line was cloned from a multipotent mouse bone marrow stromal precursor and has osteogenic, chondrogenic, and adipogenic properties. The osteogenic phenotype of these precursor cells is relevant to the process of fracture healing and osteointegration of prosthetic implants. The D1 cells were labeled genetically using a replication incompetent retroviral vector encoding beta-galactosidase, an enzyme which is used as a marker. Labeled cells are readily identifiable by staining with 5-bromo-4-chloro-3-indoyl-beta-D-galactoside and by flow cytometry, and retain the desired osteogenic characteristics in vivo as shown by von Kossa staining, alkaline phosphatase assay, an increase in cyclic adenosine monophosphate in response to parathyroid hormone, osteocalcin messenger ribonucleic acid production, and bone formation in diffusion chambers. In addition, the cells cloned from marrow stroma repopulate the marrow of host mice, persist for several weeks, and retain their osteogenic potential ex vivo. The data suggest that such cells may be used to replenish the number of osteoprogenitors in marrow, which appear to decrease with age, thereby leading to recovery from bone loss and improved bone growth and repair. Labeling these cells creates a model in which to study the potential of such cells to participate in fracture repair, ingrowth around prosthetic implants, treatment of osteoporosis, and to explore the possibility of gene delivery to correct mutations or defects in metabolism that are responsible for certain skeletal abnormalities.