RETROGRADE GENE TRANSFER OF HUMAN HEPATOCYTE GROWTH FACTOR INTO RAT NERVOUS SYSTEM USING NONVIRAL HVJ-LIPOSOME METHOD: NOVEL THERAPEUTIC STRATEGY FOR CRUSHED NERVE

Abstract

Crush injury is one of the categories of nerve injury, which is often encountered in the clinical field. There is no doubt that crushed nerves, which have anatomical continuity, regenerate spontaneously and somehow reinnervate their target tissues, such as muscle and skin. However, the longer it takes to reinnervate the target tissues, the more profoundly the atrophy of these target tissues progresses, resulting in a poor outcome. Clinically, it is therefore crucial to accelerate nerve regeneration if excellent results are to be achieved. Hepatocyte growth factor (HGF) is well known to be involved in many biological functions, such as organ regeneration and angiogenesis, and to exert neurotrophic effects on motor, sensory, and parasympathetic neurons. This raised hopes that HGF protein might be useful for the clinical treatment of nervous system disorders. However, administration of HGF as a recombinant protein is still beset by a number of problems, such as a short serum half-life and poor access to the central nervous system by the systemic route because of the presence of the blood-brain barrier. These problems can be major obstacles to the therapeutic use of such factors, and this has highlighted the need to develop innovative therapeutic strategies for more efficient delivery into the nervous system. Gene transfer into the nervous system has enormous therapeutic potential for a wide variety of disorders. It appears to have advantages over the administration of single or multiple bolus doses of a recombinant protein because gene transfer can achieve an optimally high, local concentration within the nervous system. Recently, two different strategies have been reported. Firstly gene transfer by local intraneural injection and secondly gene transfer via retrograde axonal transport. In crush injury, it is well known that some axons in the crushed nerve can remain intact. It is from this evidence that the idea of performing gene transfer via retrograde axonal transport arose. In this study, we gave repeated intramuscular injections of the human HGF gene, using nonviral HVJ (Hemagglutinating Virus of Japan) liposome method, to examine whether transfection of the rat nervous system with this gene is able to exert neurotrophic effects facilitating recovery of a crushed nerve. The expression of HGF protein and HGF mRNA indicated that gene transfer into the nervous system did occur via retrograde axonal transport. At 4 weeks after crush, electrophysiological examination of the crushed nerve showed a significantly shorter mean latency and a significantly greater mean maximum M-wave amplitude with repeated injections of HGF gene. Furthermore, histological findings showed that the mean diameter of the axons, the axon number and the axon population were significantly larger in the group with repeated injections of HGF gene. The above results show that repeated human HGF gene transfer into the rat nervous system is able to promote crushed-nerve recovery, both electrophysiologically and histologically, and suggest that HGF gene transfer has potential for the treatment of crushed nerve.