SRF deletion results in earlier disease onset in a mouse model of amyotrophic lateral sclerosis
Jialei Song, Natalie Dikwella, Daniela Sinske, Francesco Roselli, Bernd Knöll
Jialei Song, Natalie Dikwella, Daniela Sinske, Francesco Roselli, Bernd Knöll
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Research Article Neuroscience

SRF deletion results in earlier disease onset in a mouse model of amyotrophic lateral sclerosis

Abstract

Changes in neuronal activity modulate the vulnerability of motoneurons (MNs) in neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). So far, the molecular basis of neuronal activity’s impact in ALS is poorly understood. Herein, we investigated the impact of deleting the neuronal activity–stimulated transcription factor (TF) serum response factor (SRF) in MNs of SOD1G93A mice. SRF was present in vulnerable MMP9+ MNs. Ablation of SRF in MNs induced an earlier disease onset starting around 7–8 weeks after birth, as revealed by enhanced weight loss and decreased motor ability. This earlier disease onset in SRF-depleted MNs was accompanied by a mild elevation of neuroinflammation and neuromuscular synapse degeneration, whereas overall MN numbers and mortality were unaffected. In SRF-deficient mice, MNs showed impaired induction of autophagy-encoding genes, suggesting a potentially new SRF function in transcriptional regulation of autophagy. Complementary, constitutively active SRF-VP16 enhanced autophagy-encoding gene transcription and autophagy progression in cells. Furthermore, SRF-VP16 decreased ALS-associated aggregate induction. Chemogenetic modulation of neuronal activity uncovered SRF as having important TF-mediating activity–dependent effects, which might be beneficial to reduce ALS disease burden. Thus, our data identify SRF as a gene regulator connecting neuronal activity with the cellular autophagy program initiated in degenerating MNs.

Authors

Jialei Song, Natalie Dikwella, Daniela Sinske, Francesco Roselli, Bernd Knöll

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Figure 8

SRF-VP16 enhances autophagy Poly-GA aggregate clearance.

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SRF-VP16 enhances autophagy Poly-GA aggregate clearance. (A–D) HEK293 ce...
(A–D) HEK293 cells transfected with a p62-GFP-mCherry construct coexpressed either SRF-VP16ΔMADS (A and B) or SRF-VP16 (C and D). Cells were imaged over 90 minutes, and pictures show the starting time point (0 minutes; A and C) or 60 minutes (B and D). Enhanced autophagy is indicated by a color change from yellow to red. SRF-VP16 enhanced autophagy propagation as indicated by yellow vesicles at t = 0 (C) turning at t = 60 minutes into red (D). In SRF-VP16ΔMADS–expressing cells, the ratio between GFP/mCherry remained constant (A and B). (E–H) HEK293 cells expressing Poly-GA aggregates (green) were stained with lysotracker (red). SRF-VP16 (G and H), but not as much SRF-VP16ΔMADS (E and F), reduced aggregate size and enhanced colocalization of aggregates with lysosomes (yellow in G and H). (I) The GFP/mCherry ratio was decreased in SRF-VP16 compared with SRF-VP16ΔMADS–expressing cells, indicating enhanced autophagic flux by SRF-VP16 (n = 20 cells each; 3 technical replicates). Data show mean ± SEM. (J) The area of Poly-GA aggregates was lower in SRF-VP16 compared with SRF-VP16ΔMADS–expressing cells (n = 40 cells each). Data show mean ± SD. (K) In SRF-VP16–expressing cells, the Poly-GA/lysosome ratio was higher, suggesting more colocalization of aggregates in lysosomes compared with SRF-VP16ΔMADS (n = 40 cells each; 4 technical replicates). Data show mean ± SEM. Statistical testing was performed by 1-tailed t tests. Scale bar: 10 μm.