Resumen de Gene therapy targeting neuregulins for the treatment of amyotrophic lateral sclerosis
Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder with no effective treatment currently available. The molecular mechanisms that are involved in the motoneuron (MN) death are complex and include several MN dysfunctions, and contribution of surrounding cells such as microglia and astrocytes. Neuregulin 1 (NRG1) is a neurotrophic factor highly expressed in MNs and neuromuscular junctions that supports axonal and neuromuscular development and maintenance. Recent studies have suggested a crucial role for NRG1 and their ErbB receptors in ALS, particularly for isoform I (NRG1-I) in the collateral reinnervation process, and isoform III (NRG1-III) in the preservation of the MNs, opening a new window for developing novel ALS therapies. However, further studies are needed to clarify the role of the NRG1-ErbB pathway on MN survival and to provide the proof of concept of its therapeutical efficacy.
In the present thesis we have evaluated the therapeutic effect of NRG1 overexpression in the central and the peripheral nervous system. For this purpose, we first characterized the role of exogenous NRG1 using an in vitro model of spinal cord organotypic cultures (SCOC) subject to chronic excitotoxicity caused by DL-threo-β-hydroxyaspartic acid. Our results revealed that addition of recombinant human NRG1 (rhNRG1) to the medium significantly increased MN survival through the activation of ErbB receptors, which was blocked by addition of lapatinib, an ErbB inhibitor, and reduced microglial reactivity overcoming the excitotoxicity effects. rhNRG1 activated the pro-survival PI3K/AKT pathway and restored the autophagic flux in the spinal cord culture. Furthermore, addition of rhNRG1 to the medium promoted motor and sensory neurite outgrowth.
We have then directed gene therapies based on adeno-associated viruses to overexpress NRG1-I in the skeletal muscles, and NRG1-III in the spinal cord to preserve the MNs in the in vivo model of ALS, the SOD1G93A mice. Our results indicate that both gene therapies were able to preserve the neuromuscular function of the hindlimb muscles, improve the locomotor performance, increase the number of surviving MNs and reduce the astrocyte and microglial reactivity in the treated female SOD1G93A mice at the end-stage of the disease. Furthermore, in the spinal cord the NRG1-III/ErbB4 axis regulates MN excitability through the KCC2 transporter and reduces the expression of the MN vulnerability marker MMP-9. NRG1-I expressed in the skeletal muscle signals with ErbB2 and 3 receptors present in terminal Schwann cells to promote axonal reinnervation. However, when we aimed to combine both viral-mediated therapies we did not find a synergic effect. Altogether, our results indicate that NRG1 isoforms play an important role on MN survival and that a viral-mediated overexpression may be considered as a potential novel therapy to treat ALS.
