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Description
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Spinal Muscular Atrophy (SMA) is one of the most common genetic causes of infant mortality. SMA is characterized by the progressive degeneration of lower motor neurons (MNs) and caused by disruptions of Smn1 gene. Humans have a nearly identical gene called Smn2; however a C-to-T change in Smn2 causes exon 7 skipping, giving rise to a truncated rapidly degraded protein. Since Smn2 is present in different copy numbers in the genome and is able to produce very low levels of functional protein, it acts as a genetic modifier when Smn1 is altered and the levels of Smn2 expression are responsible for the severity of the disease. FDA and EMA have approved three revolutionary SMN-dependent treatments. These therapeutic strategies are focused on increasing the production of the SMN protein through splicing correction of the SMN2 gene by antisense oligonucleotides or by gene therapy approaches with viral transduction of the SMN1 gene. However, these approaches present some limitations. Treated patients might simply present delayed instead of rescued symptoms, if recovery of the neuromuscular system is incomplete. Moreover, the SMN therapies appear inefficient to address the slow neurodegenerative process in less severe SMA types; a large number of older patients living with chronic symptoms might not benefit from SMN-inducing treatments. In fact, all treatments have narrow therapeutic windows, do not grant complete rescue, have sparse efficacy and only target specific tissues. Moreover, they are not accessible to all patients or countries, present high costs and they can induce toxicity, as recently demonstrated by the long-term AAV9-mediated SMN overexpression in mice. Therefore, a comprehensive therapeutic approach that comprises all symptomatic cases and all SMA clinical phenotypes, thus involving SMN-independent strategies, is urgently needed and strongly asked by patients’ families. To develop a complementary approach, we used an invertebrate animal model, Caenorhabditis elegans, that allowed us studying the nervous system in vivo and performing a High Content drug screening. With this approach we identified new FDA-approved drugs that rescued the neurodegeneration. These compounds were also successfully tested in vitro on primary cortical neurons from SMA mice. In this setting the drugs significantly improved all the defective neuronal phenotypes, including the cell body area and the length of both axons and dendrites, acting in a SMN-independent way. We now want to use the results obtained so far to complete the characterization of the leading compounds using three different model systems: C.elegans, primary cell cultures and mice. Taking advantage of the incredible power of these three systems and their perfect complementarity, the project will use genetic manipulations, pharmacological treatments, anatomical morphometry and behavioral tests aimed at: understanding the mechanisms and time of action of the drugs; identifying the tissues in which these drugs are active; testing the drugs on other models of neurodegenerative diseases; expand the number of positive hits and mode of administration; performing extensive tests using in vitro cell cultures; testing the drugs on mice SMA models; testing the drugs on mice SMA models in combination with gene therapy. We expect to deliver major progresses in defining new SMN-independent drugs and targets and therefore to identify new therapeutic strategies for preventing neuronal death caused by SMN1 loss in multiple SMA models, including a well-established mammalian one. This approach represents a powerful and effective strategy for biomedical research. The new drugs identified thanks to our research project can be combined with SMN-dependent treatment in SMA patients to obtain a better tissue targeting and improve efficacy. |
