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Small-molecule flunarizine increases SMN protein in nuclear Cajal bodies and motor function in a mouse model of spinal muscular atrophy

Abstract : The hereditary neurodegenerative disorder spinal muscular atrophy (SMA) is characterized by the loss of spinal cord motor neurons and skeletal muscle atrophy. SMA is caused by mutations of the survival motor neuron (SMN) gene leading to a decrease in SMN protein levels. The SMN deficiency alters nuclear body formation and whether it can contribute to the disease remains unclear. Here we screen a series of small-molecules on SMA patient fibroblasts and identify flunarizine that accumulates SMN into Cajal bodies, the nuclear bodies important for the spliceosomal small nuclear RNA (snRNA)-ribonucleoprotein biogenesis. Using histochemistry, real-time RT-PCR and behavioural analyses in a mouse model of SMA, we show that along with the accumulation of SMN into Cajal bodies of spinal cord motor neurons, flunarizine treatment modulates the relative abundance of specific spliceosomal snRNAs in a tissue-dependent manner and can improve the synaptic connections and survival of spinal cord motor neurons. The treatment also protects skeletal muscles from cell death and atrophy, raises the neuromuscular junction maturation and prolongs life span by as much as 40 percent (p < 0.001). Our findings provide a functional link between flunarizine and SMA pathology, highlighting the potential benefits of flunarizine in a novel therapeutic perspective against neurodegenerative diseases. Protein localization is critical for cellular functions and tissues homeostasis. Survival motor neuron (SMN) protein has a specific localization in the nucleus of eukaryotic cells 1-5. It is found concentrated into the nuclear bodies Cajal bodies (CBs), which are hubs of small non-coding RNAs including the splicing small nuclear (sn) RNAs 6. However, the role of SMN in CBs rem ains elusive. Altered CB localization of SMN protein is a hallmark of childhood spinal muscular atrophy (SMA) disease 2 , and of some other adult motor neuron disorders 7-9. SMA is a hereditary neurodegenerative disease characterized by the death of spinal cord motor neurons and skeletal muscle atrophy. Mutations of SMN1 gene and the presence of SMN2 gene copies account for the deficiency in SMN protein responsible for SMA 10,11 , a leading cau se of infantile mortality. This deficiency occurs due to a specific alternative splicing of SMN2 gene 12-14. Although the genetic basis of SMA is determined 10 , its neuromuscular manifestation and the mechanism underlying the disease severity are not fully understood.
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Delphine Sapaly, Matthieu Dos Santos, Perrine Delers, Olivier Biondi, Gwendoline Quérol, et al.. Small-molecule flunarizine increases SMN protein in nuclear Cajal bodies and motor function in a mouse model of spinal muscular atrophy. Scientific Reports, Nature Publishing Group, 2018, 8 (1), pp.2075. ⟨10.1038/s41598-018-20219-1⟩. ⟨pasteur-02090360⟩



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