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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

Inactivation and recovery of Na+ current in SMA MNs.(a) Representative current response evoked by step depolarization to 10 mV, applied every 3 s, from different condition potentials (from −80 mV to 0 mV for 40 ms in 10 mV increment) for each group. Upper panel illustrates the stimulation protocol. (b) The peak amplitude of INa were normalized to the peak of the first INa from condition potential of −80 mV (INa(−80 mV)) and plotted vs condition voltage to construct the inactivation of sodium channels. Data were fitted using equation 1 (lines) to calculate potential for half-inactivation (V1/2, c) of sodium channels. (c) Quantification of V1/2 of inactivation for each group. (d) Representative INa traces upon to sequential depolarization with a series of inter-pulse interval (Δt) from different groups. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (e) Normalizing the peak amplitude of 2nd Na+ current (INa2) to 1st Na+ current (INa1), and then plotting the normalization vs Δt to reveal the time course of the recovery of Na+ currents. Data were fitted using equation 2 (lines) to calculate recovery time constant (f). (f) Summary of recovery time constant for each group. All data shown represent mean ± SEM. ***p < 0.001; one-way ANOVA with post hoc test. N = 18 ~ 20 neurons for each group.
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f6: Inactivation and recovery of Na+ current in SMA MNs.(a) Representative current response evoked by step depolarization to 10 mV, applied every 3 s, from different condition potentials (from −80 mV to 0 mV for 40 ms in 10 mV increment) for each group. Upper panel illustrates the stimulation protocol. (b) The peak amplitude of INa were normalized to the peak of the first INa from condition potential of −80 mV (INa(−80 mV)) and plotted vs condition voltage to construct the inactivation of sodium channels. Data were fitted using equation 1 (lines) to calculate potential for half-inactivation (V1/2, c) of sodium channels. (c) Quantification of V1/2 of inactivation for each group. (d) Representative INa traces upon to sequential depolarization with a series of inter-pulse interval (Δt) from different groups. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (e) Normalizing the peak amplitude of 2nd Na+ current (INa2) to 1st Na+ current (INa1), and then plotting the normalization vs Δt to reveal the time course of the recovery of Na+ currents. Data were fitted using equation 2 (lines) to calculate recovery time constant (f). (f) Summary of recovery time constant for each group. All data shown represent mean ± SEM. ***p < 0.001; one-way ANOVA with post hoc test. N = 18 ~ 20 neurons for each group.

Mentions: Hyperexcitability may also be attributed to voltage dependent inactivation and recovery of Na+ channels. To investigate voltage dep-endent inactivation of Na+ channels, we recorded INa upon a voltage jump to +10 mV from a series of condition potentials (from −80 to 0 mV in 10 mV increment) (Fig. 6a). The amplitude of INa was normalized to the first response (at −80 mV) and plotted as a function of the condition potential (Fig. 6b). Similarly, when a Boltzmann function was used to reveal the voltages of the half-inactivation (V1/2), no difference was observed between SMA and non-SMA MNs (Fig. 6c), indicating that the voltage dependent inactivation of Na+ channel was not altered in SMA MNs.


Spinal muscular atrophy patient-derived motor neurons exhibit hyperexcitability.

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

Inactivation and recovery of Na+ current in SMA MNs.(a) Representative current response evoked by step depolarization to 10 mV, applied every 3 s, from different condition potentials (from −80 mV to 0 mV for 40 ms in 10 mV increment) for each group. Upper panel illustrates the stimulation protocol. (b) The peak amplitude of INa were normalized to the peak of the first INa from condition potential of −80 mV (INa(−80 mV)) and plotted vs condition voltage to construct the inactivation of sodium channels. Data were fitted using equation 1 (lines) to calculate potential for half-inactivation (V1/2, c) of sodium channels. (c) Quantification of V1/2 of inactivation for each group. (d) Representative INa traces upon to sequential depolarization with a series of inter-pulse interval (Δt) from different groups. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (e) Normalizing the peak amplitude of 2nd Na+ current (INa2) to 1st Na+ current (INa1), and then plotting the normalization vs Δt to reveal the time course of the recovery of Na+ currents. Data were fitted using equation 2 (lines) to calculate recovery time constant (f). (f) Summary of recovery time constant for each group. All data shown represent mean ± SEM. ***p < 0.001; one-way ANOVA with post hoc test. N = 18 ~ 20 neurons for each group.
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Related In: Results  -  Collection

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f6: Inactivation and recovery of Na+ current in SMA MNs.(a) Representative current response evoked by step depolarization to 10 mV, applied every 3 s, from different condition potentials (from −80 mV to 0 mV for 40 ms in 10 mV increment) for each group. Upper panel illustrates the stimulation protocol. (b) The peak amplitude of INa were normalized to the peak of the first INa from condition potential of −80 mV (INa(−80 mV)) and plotted vs condition voltage to construct the inactivation of sodium channels. Data were fitted using equation 1 (lines) to calculate potential for half-inactivation (V1/2, c) of sodium channels. (c) Quantification of V1/2 of inactivation for each group. (d) Representative INa traces upon to sequential depolarization with a series of inter-pulse interval (Δt) from different groups. Upper panel illustrates the stimulation protocol (Δt is from 1 ms to 25 ms in 1 ms increment) (e) Normalizing the peak amplitude of 2nd Na+ current (INa2) to 1st Na+ current (INa1), and then plotting the normalization vs Δt to reveal the time course of the recovery of Na+ currents. Data were fitted using equation 2 (lines) to calculate recovery time constant (f). (f) Summary of recovery time constant for each group. All data shown represent mean ± SEM. ***p < 0.001; one-way ANOVA with post hoc test. N = 18 ~ 20 neurons for each group.
Mentions: Hyperexcitability may also be attributed to voltage dependent inactivation and recovery of Na+ channels. To investigate voltage dep-endent inactivation of Na+ channels, we recorded INa upon a voltage jump to +10 mV from a series of condition potentials (from −80 to 0 mV in 10 mV increment) (Fig. 6a). The amplitude of INa was normalized to the first response (at −80 mV) and plotted as a function of the condition potential (Fig. 6b). Similarly, when a Boltzmann function was used to reveal the voltages of the half-inactivation (V1/2), no difference was observed between SMA and non-SMA MNs (Fig. 6c), indicating that the voltage dependent inactivation of Na+ channel was not altered in SMA MNs.

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