Pan-neurotrophin 1: a genetically engineered neurotrophic factor displaying multiple specificities in peripheral neurons in vitro and in vivo

• Pan-neurotrophin 1 (PNT-1) is a synthetic trophic factor engineered by combining active domains of the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT-3) into an NT-3 backbone. This molecule was produced in transiently transfected COS cells or in baculovirus-infected insect cells transfected COS cells or in baculovirus-infected insect cells and subsequently purified to homogeneity. Saturation binding in embryonic spinal sensory neurons demonstrated a greater number of high-affinity binding sites for PNT-1 than for its parental molecule NT-3. PNT-1 was shown to efficiently block the chemical crosslinking of NGF, BDNF, and NT-3 to their cognate Trk receptors and to the low-affintiy NGF receptor expressed on neuronal and nonneuronal cells. PNT-1 stimulated survival and proliferation of MG87 fibroblasts expressing either TrkA, TrkB, or TrkC. PNT-1 also promoted survival of a greater number of embryonic dorsal root ganglion neurons than any of the other neurotrophins alone, and its effects were equivalent to a combination of NGF, BDNF, and NT-3. Analysis of receptor-specific neurotrophic activities demonstrated that PNT-1 efficiently rescued TrkA mRNA-containing sympathetic neurons and TrkB and TrkC mRNA-containing sensory neurons from the dorsal root and nodose ganglia. Finally, PNT-1 showed robust retrograde transport to DRG neurons in vivo after injection into the sciatic nerve. Radiolabeled PNT-1 accumulated in small-, medium-, and large-sized neurons. Coinjection with different unlabeled neurotrophins inhibited PNT-1 transport in distinct subpopulations of neurons of different sizes, suggesting that this molecule affects sensory neurons of different modalities. These results indicate that PNT-1 is a potent and multispecific neurotrophic factor that may be useful in the treatment of peripheral neurophathies and nerve damage.

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