Tendon healing in vitro: genetic modification of tenocytes with exogenous PDGF gene and promotion of collagen gene expression

Expression of PSACH-associated mutant COMP in tendon fibroblasts leads to increased apoptotic cell death irrespective of the secretory characteristics of mutant COMP

OBJECTIVE

Pseudoachondroplasia (PSACH) is a dominantly inherited chondrodysplasia associated with mutations of cartilage oligomeric matrix protein (COMP), characterized clinically by disproportionate dwarfism and laxity of joints and ligaments. Studies in chondrocytes and cartilage biopsies suggest that the cartilage disease is caused by retention of mutant COMP in the endoplasmic reticulum of chondrocytes and by disruption of the collagen network of the extracellular matrix. The pathogenesis of the tendon disease remains unclear in the absence of a cell culture model, with available tendon biopsies leading to conflicting results with respect to the intracellular retention of mutant COMP.

METHODS

We established a cell culture model using adenoviral gene transfer in tendon fibroblast cultures. We compared the effect of expression of three PSACH-associated COMP mutants and the wildtype protein on COMP secretion, matrix composition and cellular viability.

RESULTS

Our results show that mutants D475N and D469Delta are retained within the endoplasmic reticulum of tendon cells similar to what is known from chondrocytes, whereas mutant H587R is secreted like wildtype COMP. In spite of this difference, the collagen I matrix formed in culture appears disturbed for all three mutants. All COMP-mutants induce apoptotic cell death irrespective of their differing secretion patterns.

CONCLUSION

Pathogenic pathways leading to tendon disease in humans appear to be heterogeneous between different COMP mutants.

Tendon Healing In Vitro: Adeno-Associated Virus-2 Effectively Transduces Intrasynovial Tenocytes with Persistent Expression of the Transgene, but Other Serotypes Do Not

BACKGROUND

Transfer of exogenous growth factor genes to injured tendons offers a promising method for strengthening tendon repairs. Adeno-associated virus vectors have advantages of being both nonpathogenic and nontoxic. The authors explored the efficiency of transduction of intrasynovial tenocytes with different serotypes of adeno-associated virus (AAV) and the persistency of its expression of a growth factor transgene.

METHODS

Tenocytes were obtained from cultures of rat intrasynovial tendons and distributed to 82 wells in eight culture plates and to 30 culture dishes. The tenocytes in the wells were treated with AAV1, AAV2, AAV3, AAV4, AAV5, AAV7, and AAV8 vectors containing the lacZ gene, and plasmid vectors (pCMVbeta-lacZ). The tenocytes were stained with in situ beta-galactosidase 5 days later. The basic fibroblast growth factor (bFGF) gene was cloned to the AAV2 vector to construct the AAV2-bFGF vector, which transduced tenocytes in culture dishes. Expression of the transgene was measured over 3 weeks and analyzed statistically.

RESULTS

AAV2 effectively delivered exogenous genes to proliferating intrasynovial tenocytes. In contrast, other tested adeno-associated viruses transduced tenocytes minimally or not at all. The efficiency of gene transfer by AAV2, indicated by the percentage of cells with positive beta-galactosidase staining, was significantly greater than that by a plasmid vector (p = 0.001). Expression of the bFGF gene in tenocytes transduced with the AAV2-bFGF was significantly higher than that in the control over the 3-week period (p < 0.01).

CONCLUSIONS

Gene transfer to tenocytes by AAV2 is more efficient than that by a plasmid vector. However, other adeno-associated virus serotypes cannot effectively transduce tenocytes. The bFGF gene can be delivered to intrasynovial tenocytes by the AAV2 vector effectively, and the gene transfer significantly increases expression of bFGF gene over 3 weeks.

Tissue reactions of adenoviral, adeno-associated viral, and liposome-plasmid vectors in tendons and comparison with early-stage healing responses of injured flexor tendons

PURPOSE

Delivery of growth factor genes that may substantially increase the healing rate of injured digital flexor tendons is a new application of gene therapy. Adenoviral, adeno-associated viral (AAV), and liposome-plasmid vectors have been used to deliver genes to tendons, but the tendon reactions to these vectors--particularly in contrast to the healing responses in the injured tendons--were unknown. This study was designed to compare the tissue reactions of the earlier-mentioned vectors in tendons with the healing responses of injured flexor tendons.

METHODS

Forty-two flexor digitorum profundus tendons of 6 New Zealand white rabbits were used. Eighteen tendons were divided into 3 groups of 6 each and injected with different vectors: adenoviral vector, AAV2-luciferase vector, or pCMV-beta vector with liposome. Another 12 tendons were cut and repaired. At 3, 7, and 14 days, the tendons were harvested and stained with hematoxylin and eosin. Normal flexor tendons were harvested as controls.

RESULTS

The tissue reactions of the liposome-plasmid vector in tendons were the most prominent among the 3 vectors tested. The adenoviral vector elicited a moderate degree of tissue reaction. The AAV2 vector caused remarkable reactions in epitenon but almost no reactions in endotenon. Early-stage tissue reactions were more robust in the injured tendons. Compared with early-stage inflammatory and healing responses, the reactions elicited by these vectors were less severe.

CONCLUSIONS

The 3 gene delivery systems tested elicit less severe tissue reactions in flexor tendons compared with early-stage inflammatory changes in injured tendons. Adenoviral and AAV vectors elicit less severe tissue reactions than liposome-plasmid vectors. The AAV2 vector appears to cause almost no reaction in endotenon. In terms of tissue reactions, the adenoviral and AAV2 vectors, in particular AAV2, are suitable gene delivery systems for future gene transfer to the tendon in vivo.

Tendon injuries across the world: treatment

This article outlines current status of primary and secondary surgical treatment of flexor and extensor tendon injuries in the hand and rehabilitation regimens worldwide. Unsolved problems associated with tendon repairs in the hand are tendon adhesions, rupture of the repairs, finger stiffness, power of hand motion, and surgical skills. Future development may include improvement of tendon healing through biological approaches, repair techniques, and, in particular, establishment of adequate rehabilitation systems and training of surgeons in some regions of the world.

[Role of gene therapy in trauma and orthopedic surgery]

Mit Hilfe molekularbiologischer und gentechnologischer Methoden kann durch den Transfer von spezifischen Genen das Erbgut einer Zelle verändert werden. Hierdurch werden die Zellfunktionen so moduliert, dass die Zelle, die durch das implantierte Gen verschlüsselte Funktionen erhält, Proteine synthetisiert, die sie normalerweise nicht oder nur in geringen Mengen produziert.

Wie erste tierexperimentelle Studien zeigen, kann die Gentherapie die Heilungs- und Regenerationsfähigkeit der Haut, von Sehnen, Knorpel und Knochen unterstützen und beschleunigen. In jüngster Zeit werden in Tierversuchen neue Vektoren mit einer geringeren Immunogenität und verbesserten Steuerbarkeit sowie einer erhöhten Transfersicherheit getestet. Es ist zu erwarten, dass die Gentherapie in den nächsten Jahrzehnten bei der Frakturheilung, der Sanierung von Knorpelschäden und für die Behandlung von Infektionen einen bedeutenden Stellenwert einnehmen wird.

Patterns of mRNA expression for matrix molecules and growth factors in flexor tendon injury: differences in the regulation between tendon and tendon sheath

PURPOSE

Injuries to tendons, particularly flexor tendons, can lead to loss of function after healing due to adhesion formation and other complications. The aim of this study was to increase our understanding of the healing process in tendons and tendon sheaths to develop methods to affect the healing process and improve the outcome of tendon repair in the future.

METHODS

In a rabbit model of flexor tendon injury, tissues were harvested 3, 6, 12, and 24 days after surgery (n = 6 for each group). After RNA extraction, messenger RNA (mRNA) levels for relevant genes in tendon and tendon sheaths were measured using the reverse transcription polymerase chain reaction. Messenger RNA levels for a subset of relevant molecules at different time points after injury were compared with those of uninjured controls for tendons and tendon sheaths.

RESULTS

Initially after injury, there was a shift in collagen expression with a marked increase in type III mRNA levels in both the tendon and tendon sheath, whereas those for collagen I increased only in the sheath at later time points. Aggrecan and versican mRNA levels were increased in both tissues, but temporal aspects of the changes were different. The mRNA levels for biglycan and lumican were all upregulated throughout the healing interval examined, whereas those for decorin were significantly decreased throughout in the tendon more so than the sheath. The mRNA levels for basic fibroblastic growth factor and transforming growth factor beta were elevated after injury in the tendon but not in the sheath. In contrast, mRNA levels for connective tissue growth factor were unaltered or decreased in both tissues throughout the interval assessed.

CONCLUSIONS

Healing after injury to the rabbit flexor tendon and tendon sheath follow a reproducible pattern of gene expression; however, the pattern in the tendon is very different from that in the sheath. These findings indicate that interventions developed to improve healing of these tissues will have to address these differences, because they will likely affect the outcomes.

Tendon tissue engineering and gene transfer: the future of surgical treatment

Technologic improvements in the field of tissue engineering are leading to new potential developments in the currently used approaches to treat tendon injuries including difficult clinical scenarios such as zone II flexor tendon injuries of the hand and the mutilated hand with extensive tendon defects. A combination of mesenchymal (adult stem) cells, growth factors, and bioresorbable polymers can provide a solution for the treatment of difficult tendon injuries. Extensive research is needed to show that the extracellular matrix produced in response to the cell/growth factor/polymer composites in vivo is effective and functional as a regenerate tissue. Further exciting advances are foreseen in cell-based genetic engineering with the transfer of DNA to the site of tendon lacerations. These treatment modalities require improved safety precautions to reduce the risks and enhance the benefits of gene therapy.

Tendon healing in vitro: bFGF gene transfer to tenocytes by adeno-associated viral vectors promotes expression of collagen genes

PURPOSE

Adeno-associated virus-mediated gene transfer is promising in the delivery of genes to tendons because this vector stimulates few adverse tissue reactions. Basic fibroblast growth factor (bFGF) promotes collagen production in healing tendons. We transferred the exogenous bFGF gene to proliferating tenocytes by adeno-associated viral (AAV) vectors and investigated its effects on the expression of the collagen genes in an in vitro tenocyte model.

METHODS

AAV2 vectors harboring the rat bFGF gene were constructed. Tenocytes were obtained from explant cultures of rat intrasynovial tendons and were distributed into 21 culture dishes and 8 wells. Tenocytes in 7 dishes were treated with AAV2 bFGF for 3 hours and then were cultured for 10 days. Tenocytes in 14 dishes (sham vector and nontreatment controls) did not receive the transgene. Efficiency of the gene transfer was evaluated by in situ beta-galactosidase staining in 8 wells after treatment with AAV2 lacZ. Expression of the target genes was assessed by reverse-transcription polymerase chain reactions with primers specifically amplifying the target genes. Expression of bFGF and type I and III collagen genes was determined by quantitative analysis of the polymerase chain reaction products.

RESULTS

Positive beta-galactosidase staining confirmed the effectiveness of AAV2-mediated gene delivery to tenocytes. The level of expression of the bFGF gene was increased significantly after gene transfer. Levels of expression of type I and III collagen genes after transfer of the exogenous bFGF gene were increased significantly compared with those in the cells treated with sham vectors or in nontreatment controls.

CONCLUSIONS

Delivery of exogenous bFGF gene to tenocytes can increase significantly the levels of expression of the bFGF and type I and III collagen genes. AAV2 vectors provide a novel method for delivering growth factor genes to tenocytes. These findings warrant future in vivo study of the delivery of genes pertinent to tendon healing through AAV2-based gene therapy to enhance repairs of injured flexor tendons.

Efficacy of Combination Gene Therapy with Multiple Growth Factor cDNAs to Enhance Skin Flap Survival in a Rat Model

The objective of this study was to investigate the efficacy of combination gene therapy with multiple angiogenic growth factor cDNAs to enhance survival of ischemic skin flaps in a rat model. Sixty Sprague-Dawley rats were divided into six groups. Varying combinations of VEGF165, PDGF-B, and bFGF-plasmids were injected to prefabricate the flaps. Random skin flaps were raised on the dorsal aspect of rats following prefabrication with growth factor cDNAs. Flap viability was determined by measurement of percentage area of survival. The efficacy of gene therapy was evaluated by flap survival and neovascularization of representative histologic sections stained immunohistologically. The VEGF165 plus bFGF cDNAs enhanced the viability of the flap and neovascularization most effectively; the flap survival area was 64.3 +/- 8.7% after transfer of these two growth factor genes. Addition of PDGF-B cDNA is deleterious to the effects of combined VEGF165 and bFGF, leading to a significant decrease in flap viability (44.9 +/- 2.7%). Viability of the flaps with combined VEGF165 and bFGF cDNA transfer was significantly greater than that of the flaps with VEGF165 transfer alone (57.6 +/- 5.2%) or sham plasmid control (52.3 +/- 5.0%). Combined transfer of VEGF165 and bFGF cDNA is the most effective combination of multiple growth factor genes to improve flap viability in this model. Simultaneous transfer of three growth factor genes (VEGF165, PDGF-B, and bFGF) is deleterious to flap survival, at least for the ratio of lipofectin:transgene employed.

Clinical outcomes associated with flexor tendon repair

Review of the outcomes of clinical flexor tendon repairs reported over the past 15 years showed advances in the outcomes with excellent or good functional return in more than three fourths of primary tendon repairs following a variety of postoperative passive/active mobilization treatments. Strickland and Glogovac criteria are the most commonly adopted methods to assess function. Repair ruptures (4%-10% for zone II finger flexors and 3%-17% for the FPL tendon), adhesion formations, and stiffness of finger joints remain frustrating problems in flexor tendon repairs and rehabilitation. Four approaches are suggested to improve outcomes of the repairs and to solve these difficult problems,which include stronger surgical repairs, appropriate pulleys or sheath management, optimization of rehabilitation regimens, and modern biologic approaches.

Tendon healing in vitro: modification of tenocytes with exogenous vascular endothelial growth factor gene increases expression of transforming growth factor beta but minimally affects expression of collagen genes

PURPOSE

It is not clear how the transfer of exogenous growth factor genes to tenocytes affects collagen production. An increase in collagen production enhances the repair but an increase in growth factors that stimulate tissue fibrosis may cause adhesion. Gene therapy is a new way to regulate tendon healing but it has been explored rarely. We genetically modified tenocytes with the vascular endothelial growth factor (VEGF) gene and investigated the expression of the genes for collagen production in an in vitro model of the proliferating tenocytes.

METHODS

Tenocytes were obtained from cultures of rat intrasynovial tendons and distributed randomly to 25 dishes. The tenocytes in the experimental dishes (n = 9) were treated for 12 hours with plasmid containing the VEGF complementary deoxyribonucleic acid and then were cultured for 5 days; the tenocytes in the control dishes (n = 8) did not receive the exogenous gene. Tenocytes in the other dishes received exogenous platelet-derived growth factor (PDGF) gene for comparison of the effects of VEGF gene therapy. Efficiency of the gene transfer was evaluated by presence of the transgene in the tenocytes which was detected by reverse transcription polymerase chain reactions. Levels of expression of types I and III collagen and transforming growth factor (TGF)-beta genes were determined by quantitative analysis of the products of reverse transcription polymerase chain reactions.

RESULTS

Expression of the TGF-beta gene increased significantly in the cells treated with exogenous VEGF cDNA. Expression of type I and III collagen genes by tenocytes was affected minimally by transfer of the VEGF gene to the tenocytes and was significantly weaker than that stimulated by PDGF gene therapy. Efficient gene transfer was confirmed by the presence of the VEGF complementary deoxyribonucleic acid in the tenocytes receiving the transferred gene.

CONCLUSIONS

Transfer of exogenous VEGF gene has very limited effects on the promotion of collagen production in the proliferating tenocytes. This study suggests that VEGF gene therapy is not as beneficial as PDGF gene therapy to tendon healing and may increase the activities of TGF-beta that are associated with adhesion formations.