Neural precursor/stem cell-based therapy for Rett syndrome

MECP2 mutations cause Rett syndrome (RTT), the first cause of severe intellectual disability in girls. No cure is available and the identification of therapies is hampered by the need of maintaining physiological protein levels in the brain and the limited comprehension of RTT pathophysiology. Several studies proved that reduced levels of neurotrophic factors play a major role in RTT and their augmentation represents a valid therapeutic approach. Indeed, manipulation of their levels or activation of the downstream pathways represents one of the most promising therapeutic strategy that, however, is limited by the low blood brain barrier permeability. Neural Precursor/Stem Cell (NPC) transplantation was proved safe and efficacious in many neurological disorders, including autism. Willing to respond to the unmet need of a cure for RTT, we are investigating the therapeutic potential of adult NPCs in Mecp2 null mice, modelling RTT. Although the long-thought prime mechanism of NPC action is the replacement of damaged cells, it is now clear that transplanted cells often exert their benefits through a “bystander” mechanism. Indeed, by sensing the pathological environment, they promote immunomodulation, neuroprotection and brain plasticity through the secretion of a plethora of molecules, including neurotrophic factors and immunomodulatory substances. Therefore, transplanted NPCs adapt their fate and functions to the specific pathological context and can engage in a rich talk with resident cells, thus forming a close network that can persist after administration. Our data demonstrate that NPC transplantation can significantly prolong the lifespan of Mecp2 null mice, restoring memory and motor functions. By immunofluorescence, we report that transplanted NPC localize along the meninges in the caudal zone of the brain by maintaining an immature phenotype, strongly suggesting the involvement of a paracrine effect. Therefore, using an in vitro transwell-based co-culture system, we confirmed the paracrine action of NPCs to promote morphological and synaptic rescues in Mecp2 null neurons. In addition, by exploring the beneficial effects of their secreted factors, we prove the NPC ability to adapt their phenotype depending on the pathological context, since their exposure on Mecp2 null neurons promotes the release of protective molecules. In order to identify the molecular mechanisms behind NPC efficacy, we started performing an RNA-seq study on transplanted brains and, supported by bioinformatics analysis, we prioritized one molecular pathway, the validation of which is currently under investigation by in vivo and in vitro experiments. In particular, the selected recombinant molecule is effective in reverting the motor impairments in Mecp2 null animals and in improving the synaptic alterations of null neurons. Together, our data provide the "proof of concept" of a NPC-based therapeutic strategy for RTT and suggest the involvement of a putative molecule, which might be proposed as a novel therapeutic strategy.