Neuronal activity regulates DROSHA via autophagy in spinal muscular atrophy

Abstract

Dysregulated miRNA expression and mutation of genes involved in miRNA biogenesis have been reported in motor neuron diseases including spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS). Therefore, identifying molecular mechanisms governing miRNA expression is important to understand these diseases. Here, we report that expression of DROSHA, which is a critical enzyme in the microprocessor complex and essential for miRNA biogenesis, is reduced in motor neurons from an SMA mouse model. We show that DROSHA is degraded by neuronal activity induced autophagy machinery, which is also dysregulated in SMA. Blocking neuronal activity or the autophagy-lysosome pathway restores DROSHA levels in SMA motor neurons. Moreover, reducing DROSHA levels enhances axonal growth. As impaired axonal growth is a well described phenotype of SMA motor neurons, these data suggest that DROSHA reduction by autophagy may mitigate the phenotype of SMA. In summary, these findings suggest that autophagy regulates RNA metabolism and neuronal growth via the DROSHA/miRNA pathway and this pathway is dysregulated in SMA.

Synergistic interactions between Cajal bodies and the miRNA processing machinery

“…In regard to the contribution of CBs to miRNA biogenesis, recent work has implicated miRNA dysregulation as a contributor to spinal muscular atrophy (SMA), the leading genetic cause of infant mortality ( Goncalves et al , 2018 ). Most cases of SMA are caused by insufficient levels of SMN, the survival of motor neuron protein ( Lefebvre et al , 1995 ), and reduced amounts of Drosha are observed in SMA ( Goncalves et al , 2018 ). The involvement of CBs in the formation of miRNAs encoded in gene clusters more clearly links SMN with the miRNA processing machinery.…”

Stasimon Contributes to the Loss of Sensory Synapses and Motor Neuron Death in a Mouse Model of Spinal Muscular Atrophy

“…Recent studies have shown that Stasimon is an ER-resident, six-transmembrane-pass protein that is essential for mouse embryonic development (Van Alstyne et al, 2018b) and functions in autophagy (Moretti et al, 2018;Morita et al, 2018;Shoemaker et al, 2019). There have also been reports of autophagy dysregulation in SMA, but there is disagreement about whether this pathway is inhibited (Custer and Androphy, 2014;Periyakaruppiah et al, 2016;Rodriguez-Muela et al, 2018) or stimulated (Gonç alves et al, 2018;Piras et al, 2017) by SMN deficiency. Therefore, although autophagy inhibition has been shown to ameliorate the phenotype of SMA mice by blocking p62-mediated SMN degradation (Rodriguez-Muela et al, 2018), it remains to be established whether autophagy defects directly contribute to SMA pathology.…”

“…Stasimon Deficiency Is Sufficient to Induce p53 S18 Phosphorylation Recent studies have shown that Stasimon is required for autophagy in cultured mammalian cells (Moretti et al, 2018;Morita et al, 2018;Shoemaker et al, 2019). There have also been reports of autophagy dysregulation in SMA (Custer and Androphy, 2014;Gonç alves et al, 2018;Periyakaruppiah et al, 2016;Piras et al, 2017;Rodriguez-Muela et al, 2018). Therefore, we sought to investigate the possible involvement of Stasimon-dependent autophagy defects in SMA pathogenesis.…”

Mitochondrial Defects in the Respiratory Complex I Contribute to Impaired Translational Initiation via ROS and Energy Homeostasis in SMA Motor Neurons

“…SMN is an RNA binding protein that performs multiple essential cellular functions including biogenesis of small nuclear ribonucleoproteins (snRNPs) [8] and tra cking of mRNAs to axon terminals [9][10][11]. Furthermore, SMA cells show dysregulated splicing and miRNA processing [12,13], hyperexcitability and impaired Ca 2+ homeostasis [14][15][16], reduced protein synthesis e ciency [10,17,18] and impaired axon growth [11].…”

“…Cells were incubated with MitoTracker® Red CMXRos (Thermo Fisher Scienti c) at a nal concentration of 100 nM for 15 min and xed with paraformaldehyde (PFA) [13]. The information about antibodies can be found in Supplementary Table 3.…”