Retroviral gene transfer of tissue-type plasminogen activator targets thrombolysis in vitro and in vivo

Role of Purine-Rich Regions in Mason-Pfizer Monkey Virus (MPMV) Genomic RNA Packaging and Propagation

A distinguishing feature of the Mason-Pfizer monkey virus (MPMV) packaging signal RNA secondary structure is a single-stranded purine-rich sequence (ssPurines) in close vicinity to a palindromic stem loop (Pal SL) that functions as MPMV dimerization initiation site (DIS). However, unlike other retroviruses, MPMV contains a partially base-paired repeat sequence of ssPurines (bpPurines) in the adjacent region. Both purine-rich sequences have earlier been proposed to act as potentially redundant Gag binding sites to initiate the process of MPMV genomic RNA (gRNA) packaging. The objective of this study was to investigate the biological significance of ssPurines and bpPurines in MPMV gRNA packaging by systematic mutational and biochemical probing analyses. Deletion of either ssPurines or bpPurines individually had no significant effect on MPMV gRNA packaging, but it was severely compromised when both sequences were deleted simultaneously. Selective 2′ hydroxyl acylation analyzed by primer extension (SHAPE) analysis of the mutant RNAs revealed only mild effects on structure by deletion of either ssPurines or bpPurines, while the structure was dramatically affected by the two simultaneous deletions. This suggests that ssPurines and bpPurines play a redundant role in MPMV gRNA packaging, probably as Gag binding sites to facilitate gRNA capture and encapsidation. Interestingly, the deletion of bpPurines revealed an additional severe defect on RNA propagation that was independent of the presence or absence of ssPurines or the gRNA structure of the region. These findings further suggest that the bpPurines play an additional role in the early steps of MPMV replication cycle that is yet to be identified.

Retrovirus-Mediated Transfection of the Tissue-type Plasminogen Activator Gene Results in Increased Thrombolysis of Blood Clots

Tissue-type plasminogen activator (tPA) is involved in the lysis of blood clots. In this study, we attempted to target thrombolysis and enhance blood clot lysis by generating a construct (pLEGFP-N1-tPA) to integrate tPA gene into the genome of different cell lines. pLEGFP-N1-tPA construct was generated and used to target the tPA gene in different cell lines. The thrombolytic effects mediated by the supernatant from transfected HeLa cells and Linx cells were assessed using plasma thrombus plates. Furthermore, enhanced green fluorescent protein (EGFP), which was fused to the tPA gene in the pLEGFP-N1-tPA construct, was analyzed under the fluorescent microscope to assess tPA localization. We also monitored tPA activity and expression in the transfected cell lines. As part of the study, we successfully generated the pLEGFP-N1-tPA construct. The sequence of this construct was verified and the construct was subsequently used to generate the PT67/pLEGFP-N1-tPA cell line. The pLEGFP-N1-tPA construct was also used to transfect HeLa cells and Linx cells. We observed that supernatants from transfected cells were capable of lysing thrombi. In addition, tPA activity and tPA concentration were elevated in the latter supernatants and tPA was rapidly and stably expressed in the transfected cell lines. These results reveal a potentially important thrombolytic role for tPA-targeted gene therapy following cardiac valve replacement.

Tissue-type plasminogen activator gene targets thrombolysis in atriums

Our previous investigations showed that retroviral gene transfer of tissue-type plasminogen activator (tPA) effectively targeted thrombolysis in vitro and in the model of inferior caval veins of rabbits. This study is to identify the target thrombolysis of retroviral vector recombinant pLEGFP-N1-tPA transferred into the tissue around the Dacron patch (the same materials making of the ring of mechanical valve) in left atriums of rabbits. 70 Dacron patches were transplanted into the left atriums of 70 New Zealand white rabbits. The rabbits were randomly divided into three groups according to the different handling methods, including local pLEGFP-N1-tPA transferred group (gene therapy group, 30 animals), pLEGFP-N1 transferred group (control group, 20 animals), medium DMEM + 10% neonate calf serum (NCS) injected group (blank control group, 20 animals). Samples of blood, Dacron pieces and left atriums (auricles) wall from half of above in each group were harvested on second day and another half were harvested on 75th day after surgery. The EGFP expression of harvested left atriums (auricles) wall were observed under the confocal. The thrombi on the surface of Dacron patches were detected by stereoscope and electron microscope. The tPA expression in left atriums (auricles) wall and in blood from left atriums were detected by Western blot and their thrombolysis and activities were observed and calculated in plasma plates. ELISA were used to identify the contents of tPA. No thrombus was seen on the surface of Dacron patches that were transplanted in left atriums by tPA locally transferring around them. Activity and content of tPA were high in local tissue of left atrium and in blood of left atrium. It demonstrated effectively thrombolysis by tPA rapidly, efficiently and long expressing. This puts the foundation of mechanical valve replacement model for tPA gene valve, next.

Study on construction of nano tPA plasmid to prevent thrombosis after mechanical valve replacement in dogs

BACKGROUND

Mechanical valve is inclined to induce thrombosis. We intend to elucidate the transfection of nano tissue-type plasminogen activator (tPA) gene plasmid to prevent thrombosis after tricuspid mechanical valve replacement in dogs.

METHODS

A dog model of mechanical tricuspid valve replacement was constructed. A constructed chitosan nano tPA gene plasmid was used to transfect the dog cardiocytes at the same time of tricuspid valve replacement. The effect of this gene on the survival of dogs, anticoagulation (prothrombin time, INR and D-dimer contents, thrombosis in heart), and the expressions of tPA were observed.

RESULTS

Nano tPA gene plasmid was successfully constructed and transfected into cardiocytes. The gene could significantly increase the survival of animals and the contents of D-dimer (P < 0.01), and could prevent thrombus formation on mechanical valves, but there was no significant difference of prothrombin time and INR between two groups (P > 0.05).

CONCLUSION

The constructed nano tPA gene plasmid could prevent thrombus formation after mechanical valve replacement, which provides a clue for clinical use.

Efficient inhibition of hepatitis B virus replication by hepatitis delta virus ribozymes delivered by targeting retrovirus

Background

Hepatitis delta virus (HDV) ribozyme is an attractive molecular tool that can specifically recognize and catalyze the self-cleavage of the viral RNA phosphodiester backbone. However, a major obstacle in the medical application of the HDV ribozyme is the lack of specificity in the delivery of the ribozyme to defined target cells.

Results

The objective of this study was to determine whether retroviral vectors can deliver the HDV ribozyme into the target cells and to elucidate whether HDV ribozyme plays a role in hepatitis B virus (HBV) replication. In our study, the transduction of helper-free pseudotyped retrovirus, which showed a broad host range, in human hepatoma cells was performed under 2 conditions, that is, in the presence of polymerized human serum albumin (pHSA) and in the absence of pHSA. The transduction ability in the presence of pHSA was higher than in the absence of pHSA. Moreover, HBsAg and HBeAg levels after transductions with pHSA were significantly lower than those in the absence of pHSA, thus indicating that the recombinant retrovirus had HBV-specific cleavage activity and targeted HepG2215 cells.

Conclusions

These data suggest that this system provides a new approach for targeting hepatocytes and has a great potential in gene therapy for HBV infection.