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Spinal muscular atrophy patient-derived motor neurons exhibit hyperexcitability.

Liu H, Lu J, Chen H, Du Z, Li XJ, Zhang SC - Sci Rep (2015)

Bottom Line: Using SMA induced pluripotent stem cells (iPSCs), we found that SMA MNs displayed hyperexcitability with increased membrane input resistance, hyperpolarized threshold, and larger action potential amplitude, which was mimicked by knocking down full length survival motor neuron (SMN) in non-SMA MNs.We further discovered that SMA MNs exhibit enhanced sodium channel activities with increased current amplitude and facilitated recovery, which was corrected by restoration of SMN1 in SMA MNs.Together we propose that SMN reduction results in MN hyperexcitability and impaired neurotransmission, the latter of which exacerbate each other via a feedback loop, thus contributing to severe symptoms at an early stage of SMA.

View Article: PubMed Central - PubMed

Affiliation: Waisman center, University of Wisconsin, Madison, WI, 53705, USA.

ABSTRACT
Spinal muscular atrophy (SMA) presents severe muscle weakness with limited motor neuron (MN) loss at an early stage, suggesting potential functional alterations in MNs that contribute to SMA symptom presentation. Using SMA induced pluripotent stem cells (iPSCs), we found that SMA MNs displayed hyperexcitability with increased membrane input resistance, hyperpolarized threshold, and larger action potential amplitude, which was mimicked by knocking down full length survival motor neuron (SMN) in non-SMA MNs. We further discovered that SMA MNs exhibit enhanced sodium channel activities with increased current amplitude and facilitated recovery, which was corrected by restoration of SMN1 in SMA MNs. Together we propose that SMN reduction results in MN hyperexcitability and impaired neurotransmission, the latter of which exacerbate each other via a feedback loop, thus contributing to severe symptoms at an early stage of SMA.

No MeSH data available.


Related in: MedlinePlus

Na+ currents in SMA MNs following SMN expression.(a) Typical Na+ current traces from SMA-1 iPSC-derived MNs expressing Flag-GFP (SMA-1+GFP) or Flag-SMN1 (SMA-1+SMN1) upon sequential depolarization with a series of inter-pulse intervals. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (b) Quantification of the amplitude of the 1st INa elicited at −15 mV depolarization. (c) Time course of the recovery of Na+ currents for each group. Data were collected and analyzed as described in Fig. 6e. (d) Summary of recovery time constant for each group (e) Model for hyperexcitability in SMA MNs. As compared to control MNs where there are normal AP activities and neurotransmission, the loss of SMN-FL in SMA MNs results into hyperexcitability due to increased Na+ channel activities and reduced neurotransmission, which perpetuate each other to maximize transmitter release upon stimulation. Such a “vicious” feedback results in failed neuromuscular transmission, contributing to severe symptoms at an early stage. All data shown represent mean ± SEM. **p < 0.01, ***p < 0.001; unpaired Student’s t-test. N = 18 neurons for each group from 2 independent experiments.
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f7: Na+ currents in SMA MNs following SMN expression.(a) Typical Na+ current traces from SMA-1 iPSC-derived MNs expressing Flag-GFP (SMA-1+GFP) or Flag-SMN1 (SMA-1+SMN1) upon sequential depolarization with a series of inter-pulse intervals. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (b) Quantification of the amplitude of the 1st INa elicited at −15 mV depolarization. (c) Time course of the recovery of Na+ currents for each group. Data were collected and analyzed as described in Fig. 6e. (d) Summary of recovery time constant for each group (e) Model for hyperexcitability in SMA MNs. As compared to control MNs where there are normal AP activities and neurotransmission, the loss of SMN-FL in SMA MNs results into hyperexcitability due to increased Na+ channel activities and reduced neurotransmission, which perpetuate each other to maximize transmitter release upon stimulation. Such a “vicious” feedback results in failed neuromuscular transmission, contributing to severe symptoms at an early stage. All data shown represent mean ± SEM. **p < 0.01, ***p < 0.001; unpaired Student’s t-test. N = 18 neurons for each group from 2 independent experiments.

Mentions: Since SMN reduction is responsible for hyperexcitability (Figs 3 and 4) and altered Na+-channel activities underlie the abnormal AP pattern, we hypothesize that restoration of SMN-FL corrects hyperexcitability by restoring Na+-current activities. Indeed, expression of SMN1 in SMA MNs (Fig. 4) decreased the peak amplitude of Na+-current (Fig. 7a,b). Similarly, the recovery of Na+-current in SMN1-expressing SMA MNs was significantly delayed as compared to the GFP group (Fig. 7c,d), close to the level seen in control MNs (Fig. 6f).


Spinal muscular atrophy patient-derived motor neurons exhibit hyperexcitability.

Liu H, Lu J, Chen H, Du Z, Li XJ, Zhang SC - Sci Rep (2015)

Na+ currents in SMA MNs following SMN expression.(a) Typical Na+ current traces from SMA-1 iPSC-derived MNs expressing Flag-GFP (SMA-1+GFP) or Flag-SMN1 (SMA-1+SMN1) upon sequential depolarization with a series of inter-pulse intervals. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (b) Quantification of the amplitude of the 1st INa elicited at −15 mV depolarization. (c) Time course of the recovery of Na+ currents for each group. Data were collected and analyzed as described in Fig. 6e. (d) Summary of recovery time constant for each group (e) Model for hyperexcitability in SMA MNs. As compared to control MNs where there are normal AP activities and neurotransmission, the loss of SMN-FL in SMA MNs results into hyperexcitability due to increased Na+ channel activities and reduced neurotransmission, which perpetuate each other to maximize transmitter release upon stimulation. Such a “vicious” feedback results in failed neuromuscular transmission, contributing to severe symptoms at an early stage. All data shown represent mean ± SEM. **p < 0.01, ***p < 0.001; unpaired Student’s t-test. N = 18 neurons for each group from 2 independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507262&req=5

f7: Na+ currents in SMA MNs following SMN expression.(a) Typical Na+ current traces from SMA-1 iPSC-derived MNs expressing Flag-GFP (SMA-1+GFP) or Flag-SMN1 (SMA-1+SMN1) upon sequential depolarization with a series of inter-pulse intervals. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (b) Quantification of the amplitude of the 1st INa elicited at −15 mV depolarization. (c) Time course of the recovery of Na+ currents for each group. Data were collected and analyzed as described in Fig. 6e. (d) Summary of recovery time constant for each group (e) Model for hyperexcitability in SMA MNs. As compared to control MNs where there are normal AP activities and neurotransmission, the loss of SMN-FL in SMA MNs results into hyperexcitability due to increased Na+ channel activities and reduced neurotransmission, which perpetuate each other to maximize transmitter release upon stimulation. Such a “vicious” feedback results in failed neuromuscular transmission, contributing to severe symptoms at an early stage. All data shown represent mean ± SEM. **p < 0.01, ***p < 0.001; unpaired Student’s t-test. N = 18 neurons for each group from 2 independent experiments.
Mentions: Since SMN reduction is responsible for hyperexcitability (Figs 3 and 4) and altered Na+-channel activities underlie the abnormal AP pattern, we hypothesize that restoration of SMN-FL corrects hyperexcitability by restoring Na+-current activities. Indeed, expression of SMN1 in SMA MNs (Fig. 4) decreased the peak amplitude of Na+-current (Fig. 7a,b). Similarly, the recovery of Na+-current in SMN1-expressing SMA MNs was significantly delayed as compared to the GFP group (Fig. 7c,d), close to the level seen in control MNs (Fig. 6f).

Bottom Line: Using SMA induced pluripotent stem cells (iPSCs), we found that SMA MNs displayed hyperexcitability with increased membrane input resistance, hyperpolarized threshold, and larger action potential amplitude, which was mimicked by knocking down full length survival motor neuron (SMN) in non-SMA MNs.We further discovered that SMA MNs exhibit enhanced sodium channel activities with increased current amplitude and facilitated recovery, which was corrected by restoration of SMN1 in SMA MNs.Together we propose that SMN reduction results in MN hyperexcitability and impaired neurotransmission, the latter of which exacerbate each other via a feedback loop, thus contributing to severe symptoms at an early stage of SMA.

View Article: PubMed Central - PubMed

Affiliation: Waisman center, University of Wisconsin, Madison, WI, 53705, USA.

ABSTRACT
Spinal muscular atrophy (SMA) presents severe muscle weakness with limited motor neuron (MN) loss at an early stage, suggesting potential functional alterations in MNs that contribute to SMA symptom presentation. Using SMA induced pluripotent stem cells (iPSCs), we found that SMA MNs displayed hyperexcitability with increased membrane input resistance, hyperpolarized threshold, and larger action potential amplitude, which was mimicked by knocking down full length survival motor neuron (SMN) in non-SMA MNs. We further discovered that SMA MNs exhibit enhanced sodium channel activities with increased current amplitude and facilitated recovery, which was corrected by restoration of SMN1 in SMA MNs. Together we propose that SMN reduction results in MN hyperexcitability and impaired neurotransmission, the latter of which exacerbate each other via a feedback loop, thus contributing to severe symptoms at an early stage of SMA.

No MeSH data available.


Related in: MedlinePlus