Serum Response Factor (SRF) regulates motoneuron vulnerability and activity- dependent neuroprotection in Amyotrophic Lateral Sclerosis.

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Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative condition affecting primarily motoneurons (MN), in particular lower motoneurons in the spinal cord. Recently, neuronal activity and firing patterns were shown to have a strong impact on disease progression in murine ALS models such as the SOD1(G93A) ALS mouse model. Here, chemogenetically elevated firing in MNs slowed down the disease burden whereas interference with neuronal activity accelerated accumulation of disease markers (e.g. autophagy induction). In this study we want to analyze the role of SRF (serum response factor), a prototypical neuronal activity-induced transcription factor (TF). SRF mediates neuronal-activity induced gene transcription of immediate early genes (IEGs) such as c-Fos, Egr1 and Npas4 upon physiological and pathological (e.g. epilepsy, acute stress) induction of neuronal activity in neurons. Thus, we hypothesize that the beneficial impact of neuronal activity on delaying ALS disease progression works through activation of SRF-mediated gene transcription in MNs. To test this hypothesis we already established a conditional Srf mutant mouse line and documented exclusive SRF depletion in motoneurons (ChAT-Cre+/-; Srf fl/fl). We further bred this mouse line to the established mouse ALS model SOD1(G93A) to obtain ChAT-Cre+/-;Srf fl/fl;SOD1(G93A) mice. In first previous work we observed additional weight loss and grip strength reduction in Srf mutant/SOD1 mice compared to the SOD1 mice alone.With these mice at hand we follow two objectives: i) Does MN-restricted SRF depletion worsen disease progression in the SOD1 ALS model? For this, we analyze several behavioral parameters (grip strength, ladder walk, clinical score, inverted grid, open field) and perform a detailed histological inspection including markers for autophagy, MN numbers, inflammation and synapse formation. Finally, we perform a laser-capture mediated isolation of MNs to identify the ALS- and SRF-dependent transcriptome in these mice by RNA-SEQ.ii) Is SRF a downstream target in mediating chemogenetically-induced, activity-dependent neuroprotection in MNs? Here we use chemogenetics to virally overexpress activating or inhibitory channels (cation-permeable actPSAM or anion-permeable inhPSAM) in the spinal cord that alleviate or worsen disease progression in the SOD1 ALS mouse model, respectively. These experiments will be performed in the Srf mutant/SOD1 mice in comparison to SOD1 mice only. Based on our hypothesis attributing SRF a pivotal role in mediating neuronal activity in neurons we expect that chemogenetically-driven neuronal activation fails to protect from ALS inflicted neurodegeneration upon SRF depletion.In summary, this project analyzes whether neuronal activity and specifically neuronal-activity mediated gene transcription mediated by SRF is a novel factor in ALS progression that may also serve as a future potential drug target to alleviate the impact of ALS in patients.