Analysis of affected cellular targets causing cell-autonomous and non-cell-autonomous disease mechanisms in a mouse model for spinal muscular atrophy with respiratory distress type 1 (SMARD1).

• Applicant: Privatdozentin Dr. Sibylle Jablonka
• Subject Area: Experimental Models for the Understanding of Nervous System Diseases
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 467428013

Muscle atrophy, and diaphragmatic palsy are the clinical characteristics of spinal muscular atrophy with respiratory distress type 1 (SMARD1), well represented in the neuromuscular degeneration (Nmd2J) mouse. Both in humans and mice mutations in the IGHMBP2 gene lead to motoneuron degeneration. IGHMBP2 is a ribosome-associated ATPase/helicase supposed to be involved in ribosomal and translational events/processes. However, disease mechanisms on cellular level leading to SMARD1 are still far from being understood.An analysis of primary Ighmbp2-deficient motoneurons from Nmd2J mouse embryos exhibit only minor morphological changes such as a slight increase of axonal branches. RNA sequencing of Ighmbp2-deficient motoneurons revealed only a few transcriptome alterations (e. g. Sparcl1 down-regulation and FGFR1 upregulation). Likewise, we did not detect any global changes in protein synthesis. However, we observed reduced β-actin protein levels at the growth cone of Ighmbp2-deficient motoneurons. This is accompanied by reduced levels of IMP1/ZBP1 in soma and growth cone, corresponding to a decrease of total IMP1 but consistent IMP1 mRNA amount. Based on these data, our project will focus on the following objectives:(1) Does IMP1 overexpression compensates for functional alterations in Ighmbp-2deficient motoneurons? (2) To what extend non-cell-autonomous disease mechanisms contribute to motoneuron degeneration in SMARD1?In order to discover, to what extend IMP1 contributes to cellular dysfunctions in Nmd2J motoneurons and in neuronal precursor cells (NPCs) from SMARD1 patients, IMP1 will be overexpressed by lentiviral gene transfer. Morphological and functional analyses will reveal whether IMP1 overexpression rescues affected axonal branching, β-actin deficit in the distal axon and re-balances mRNA profiles. The contribution of IMP1 to the functional dysregulations in Ighmbp2-deficient motoneurons will be investigated by IMP1 overexpression and knockdown approaches including high resolution microscopy, mass spectrometry analysis, and with the aid of RiboTag/ChAT-Cre mouse experiments. In addition, we will extend our studies on a newly identified interaction partner of IMP1, the FGFR1 mRNA. In vitro/vivo studies on how dysregulation of FGFR1 signaling influences motoneuron survival under Ighmbp2 defciency will give us first insights into non-cell-autonomous disease mechanisms in Nmd2J mice. Objective (2) will focus exclusively on non-cell autonomous disease mechanisms in the SMARD1 mouse model primarily based on astrocyte/motoneuron co-cultures. Results from the co-cultures, the transcriptome data, the analysis of the spinal "tripartite" synapse and the synaptic input will increase our knowledge about disease mechanisms and progression in SMARD1.

• DFG Programme: Research Grants