Author response:
The following is the authors’ response to the original reviews.
Public Reviews:
Reviewer #1 (Public review):
Summary:
The manuscript by Lu and colleagues demonstrates convincingly that PRRT2 interacts with brain voltage-gated sodium channels to enhance slow inactivation in vitro and in vivo. The work is interesting and rigorously conducted. The relevance to normal physiology and disease pathophysiology (e.g., PRRT2-related genetic neurodevelopmental disorders) seems high. Some simple additional experiments could elevate the impact and make the study more complete.
Strengths:
Experiments are conducted rigorously, including experimenter blinding and appropriate controls. Data presentation is excellent and logical. The paper is well written for a general scientific audience.
We thank the reviewer for these positive comments and for the thoughtful evaluation of our work.
Weaknesses:
There are a few missing experiments and one place where data are over-interpreted.
(1) An in vitro study of Nav1.6 is conspicuously absent. In addition to being a major brain Na channel, Nav1.6 is predominant in cerebellar Purkinje neurons, which the authors note lack PRRT2 expression. They speculate that the absence of PRRT2 in these neurons facilitates the high firing rate. This hypothesis would be strengthened if PRRT2 also enhanced slow inactivation of Nav1.6. If a stable Nav1.6 cell were not available, then simple transient co-transfection experiments would suffice.
We thank the reviewer for raising this point. In our previous work, PRRT2 produced broadly similar effects on Nav1.2 and Nav1.6. Therefore, in the initial version of this study, we focused primarily on Nav1.2 as a representative neuronal Nav channel isoform and placed greater emphasis on testing whether PRRT2-dependent regulation of slow inactivation extends across additional Nav isoforms.
We have now performed new heterologous expression experiments to test whether PRRT2 modulates Nav1.6 slow inactivation. Consistent with our findings for other Nav isoforms, PRRT2 significantly enhances the slow inactivation of Nav1.6. We have incorporated these data into the revised Results and Figures, please refer to Page 8, Lines 211-215; Figures 4E and J.
(2) To further demonstrate the physiological impact of enhanced slow inactivation, the authors should consider a simple experiment in the stable cell line experiments (Figure 1) to test pulse frequency dependence of peak Na current. One would predict that PRRT2 expression will potentiate 'run down' of the channels, and this finding would be complementary to the biophysical data.
We thank the reviewer for this helpful suggestion. In the revised manuscript, we performed a pulse-train protocol in the stable Nav1.2 cell line and quantified the use-dependent attenuation (“run-down”) of peak sodium current across successive depolarizations (Figure 1-figure supplement 1C). Compared with control cells, PRRT2-expressing cells exhibited a larger decline in peak current during trains, indicating greater reduction in channel availability during repetitive depolarizations (Figure 1-figure supplement 1C). This pattern is consistent with our observations above showing that PRRT2 enhances Nav channel slow inactivation. These new data have been incorporated into the revised manuscript. Please refer to Page 5, Lines 133-140; Figure 1-figure supplement 1C.
(3) The study of one K channel is limited, and the conclusion from these experiments represents an over-interpretation. I suggest removing these data unless many more K channels (ideally with measurable proxies for slow inactivation) were tested. These data do not contribute much to the story.
We agree with the reviewer’s assessment. To avoid over-interpretation and to maintain focus on PRRT2-dependent regulation of Nav channel slow inactivation, we have removed the potassium channel dataset and the associated conclusions from the revised manuscript.
(4) In Figure 2, the authors should confirm that protein is indeed expressed in cells expressing each truncated PRRT2 construct. Absent expression should be ruled out as an explanation for the enhancement of slow inactivation.
We thank the reviewer’s concern regarding expression of the truncated PRRT2 constructs in the Nav1.2 stable cell line, particularly PRRT2(1-266), which shows little effect on slow inactivation of Nav1.2 channels. In the revised manuscript, we conducted western blot to verify expression of the PRRT2(1-266)-HA construct in the Nav1.2 stable cell line. We have added these results to the revised manuscript, please refer to Page 6, Lines 171-173; Figure 2-figure supplement 1A and B.
Reviewer #2 (Public review):
Summary:
As a member of DspB subfamily, PRRT2 is primarily expressed in the nervous system and has been associated with various paroxysmal neurological disorders. Previous studies have shown that PRRT2 directly interacts with Nav1.2 and Nav1.6, modulating channel properties and neuronal excitability.
In this study, Lu et al. reported that PRRT2 is a physiological regulator of Nav channel slow inactivation, promoting the development of Nav slow inactivation and impeding the recovery from slow inactivation. This effect can be replicated by the C-terminal region (256-346) of PRRT2, and is highly conserved across species from zebrafish, mouse, to human PRRT2. TRARG1 and TMEM233, the other two DspB family members, showed similar effects on Nav1.2 slow inactivation. Co-IP data confirms the interaction between Nav channels and PRRT2. Prrt2-mutant mice, which lack PRRT2 expression, require lower stimulation thresholds for evoking after-discharges when compared to WT mice.
Strengths:
(1) This study is well designed, and data support the conclusion that PRRT2 is a potent regulator of slow inactivation of Nav channels.
(2) This study reveals similar effects on Nav1.2 slow inactivation by PRRT2, TMEM233, and TRARG1, indicating a common regulation of Nav channels by DspB family members (Supplemental Figure 2). A recent study has shown that TMEM233 is essential for ExTxA (a plant toxin)-mediated inhibition on fast inactivation of Nav channels; and PRRT2 and TRARG1 could replicate this effect (Jami S, et al. Nat Commun 2023). It is possible that all three DspB members regulate Nav channel properties through the same mechanism, and exploring molecules that target PRRT2/TRARG1/TMEM233 might be a novel strategy for developing new treatments of DspB-related neurological diseases.
We thank the reviewer for careful evaluation and insightful suggestions.
Weaknesses:
(1) Previously, the authors have reported that PRRT2 reduces Nav1.2 current density and alters biophysical properties of both Nav1.2 and Nav1.6 channels, including enhanced steady-state inactivation, slower recovery, and stronger use-dependent inhibition (Lu B, et al. Cell Rep 2021, Fig 3 & S5). All those changes are expected to alter neuronal excitability and should be discussed.
We thank the reviewer for this suggestion. Although the present study focuses on PRRT2-dependent regulation of slow inactivation, we agree that PRRT2 may influence excitability through additional Nav-dependent mechanisms, including reduced current density and shifts in the voltage dependence of channel inactivation (Fruscione et al., 2018; Lu et al., 2021; Valente et al., 2023). Notably, because PRRT2 facilitates entry of Nav channels into slow-inactivated states both from closed states and from open states during prolonged depolarization, some of these previously reported effects may partly reflect enhanced slow inactivation and the resulting reduction in Nav channel availability. We have expanded the Discussion to integrate these prior findings and to clarify that these additional PRRT2-dependent effects may converge to shape neuronal excitability. Please refer to Page 16, Lines 445-452.
(2) In this study, the fast inactivation kinetics was examined by a single stimulus at 0 mV, which may not be sufficient for the conclusion. Inactivation kinetics at more voltage potentials should be added.
We thank the reviewer for this helpful suggestion. In the revised manuscript, we expanded our analysis of Nav1.2 fast-inactivation kinetics to include a range of test potentials (-20, -10, 0, +10, +20 and +30 mV) in the presence and absence of PRRT2. These experiments showed that PRRT2 expression did not significantly affect Nav1.2 fast-inactivation kinetics under these conditions. We have incorporated these new results into the revised manuscript. Please refer to Page 4, Lines 100-103; Figure 1C.
(3) It is a little surprising that there is no difference in Nav1.2 current density in axon-blebs between WT and Prrt2-mutant mice (Figure 7B). PRRT2 significantly shifts steady-state slow inactivation curve to hyperpolarizing direction, at -70 mV, nearly 70% of Nav1.2 channels are inactivated by slow inactivation in cells expressing PRRT2 when compared to less than 10% in cells expressing GFP (Figure supplement 1B); with a holding potential of -70 mV, I would expect that most of Nav channels are inactivated in axon-blebs from WT mice but not in axon-blebs from Prrt2-mutant mice, and therefore sodium current density should be different in Figure 7B, which was not. Any explanation?
We thank the reviewer for raising this point. In our axonal bleb recordings, although the holding potential was -70 mV, sodium current density was measured after a hyperpolarizing pre-pulse to -110 mV, which was applied before the test depolarization to relieve inactivation as much as possible (as described in the Methods). Therefore, the current density measurement in Figure 7B reflects the available current after this recovery step, rather than the steady-state availability at -70 mV. The lack of a difference in Figure 7B does not contradict the PRRT2-dependent shift in steady-state slow inactivation. In the revised manuscript, we have clarified this point explicitly in the Results and figure legend to avoid confusion. Please refer to Page 10, Lines 294-295.
(4) Besides Nav channels, PRRT2 has been shown to act on Cav2.1 channels as well as molecules involved in neurotransmitter release, which may also contribute to abnormal neuronal activity in Prrt2-mutant mice. These should be mentioned when discussing PRRT2's role in neuronal resilience.
We thank the reviewer for this suggestion. In addition to the Nav-dependent mechanisms, previous studies have shown that PRRT2 also regulates synaptic vesicle cycling (Valente et al., 2016; Coleman et al., 2018; Tan et al., 2018) and presynaptic surface expression of Cav2.1 channels (Ferrante et al., 2021). These effects are also expected to influence neurotransmitter release and, consequently, neuronal and network excitability. In the revised manuscript, we have expanded the Discussion to acknowledge that these additional PRRT2-dependent mechanisms may also contribute to cortical resilience. Please refer to Page 16, Lines 452-457.
Reviewer #3 (Public review):
This paper reveals that the neuronal protein PRRT2, previously known for its association with paroxysmal dyskinesia and infantile seizures, modulates the slow inactivation of voltage-gated sodium ion (Nav) channels, a gating process that limits excitability during prolonged activity. Using electrophysiology, molecular biology, and mouse models, the authors show that PRRT2 accelerates entry of Nav channels into the slow-inactivated state and slows their recovery, effectively dampening excessive excitability. The effect seems evolutionarily conserved, requires the C-terminal region of PRRT2, and is recapitulated in cortical neurons, where PRRT2 deficiency leads to hyper-responsiveness and reduced cortical resilience in vivo. These findings extend the functional repertoire of PRRT2, identifying it as a physiological brake on neuronal excitability. The work provides a mechanistic link between PRRT2 mutations and episodic neurological phenotypes.
We thank the reviewer for this positive evaluation of our work and for the constructive comments.
Comments:
(1) The precise structural interface and the molecular basis of gating modulation remain inferred rather than demonstrated.
We thank the reviewer for this comment. To avoid over-interpretation, we have removed the AlphaFold-based interaction prediction from the revised manuscript. We have also expanded the Limitations section to emphasize that direct structural and biochemical mapping of the PRRT2-Nav channel interface—through approaches such as targeted mutagenesis, crosslinking, and structural determination—will be required to define the binding interface and establish the molecular basis of gating modulation. Please refer to Page 16, Lines 465-468.
(2) The in vivo phenotype reflects a complex circuit outcome and does not isolate slow-inactivation defects per se.
We agree with the reviewer. Impaired slow inactivation in Prrt2-mutant mice is one plausible contributor to reduced cortical resilience. PRRT2 has also been reported to regulate surface exposure of Nav and Cav2.1 channels (Ferrante et al., 2021), as well as neuronal synaptic vesicle cycling (Valente et al., 2016; Coleman et al., 2018; Tan et al., 2018). Each of these PRRT2-associated processes could influence cortical excitability in vivo. We have therefore expanded the Discussion to clarify that the cortical phenotype likely reflects the combined contribution of multiple PRRT2-dependent mechanisms, rather than an isolated defect in slow inactivation alone. Please refer to Page 16, Lines 446-458.
(3) Expression of PRRT2 in muscle or heart is low, so the cross-isoform claims are likely of limited physiological significance.
We thank the review for this comment regarding physiological relevance. In the revised manuscript, we clarify that the cross-isoform analysis was intended to assess mechanistic generality at the channel level, rather than to imply equivalent physiological relevance across tissues. The functional consequence of PRRT2 depend on the Nav isoform composition and cellular context of each tissue. We also note that the broad isoform activity of the PRRT2 should be considered in any future attempt to manipulate PRRT2 function therapeutically. Please refer to Page 14 and 15, Lines 414-416; Lines 429-430.
(4) The mechanistic separation between the trafficking effect of PRRT2 and its gating effects is not clearly resolved.
We thank the reviewer’s concern regarding the possible contribution of trafficking effects to PRRT2-dependent regulation of Nav channel slow inactivation. Previous studies in heterologous overexpression systems have shown that PRRT2 can influence Nav channel trafficking and surface expression, raising the possibility that the observed effects on slow inactivation regulation might be secondary to altered channel abundance or localization. However, slow inactivation develops on a timescale of tens of milliseconds to seconds, whereas detectable changes in Nav channel trafficking and surface abundance generally occur over much longer intervals (minutes to hours) (Freal et al., 2023; Higerd-Rusli et al., 2023). These distinct temporal profiles argue against trafficking as the primary basis for the effects of PRRT2 on Nav channel slow inactivation described here, although direct quantification of dynamic changes in Nav channel surface expression will be required to fully exclude such a contribution (Liu et al., 2022; Tyagi et al., 2025). We have incorporated this point into the Discussion section. Please refer to Pages 13, Lines 378-388.
(5) Additional studies with Nav1.6 should be carried out.
We thank the reviewer for this suggestion. We have performed experiments to directly examine the effects of PRRT2 on Nav1.6 slow inactivation and incorporated these new data into the revised Results and figures, please refer to Page 8, Lines 211-215; Figures 4E and J.
Recommendations for the authors:
Reviewer #1 (Recommendations for the authors):
Suggestions for future experiments (not for this paper)
(1) Exploit the lower protein expression in V5-PRRT2 mice to examine the effects of a hypomorphic allele.
We thank the reviewer for this insightful suggestion. We note that the V5 epitope knock-in reduced PRRT2 protein expression, which may functionally resemble a hypomorphic allele. Accordingly, in addition to its utility for biochemical experiments (e.g., co-immunoprecipitation), this line could serve as a genetic tool to interrogate PRRT2 dose-dependent effects in vivo. We have added this point to the revised manuscript, please refer to Page 9, Lines 265-267.
(2) Examine disease-causing PRRT2 mutations.
We thank the reviewer for this constructive suggestion. Testing disease-associated PRRT2 variants for their ability to regulate Nav channel slow inactivation would be an important next step to strengthen the disease relevance of the mechanism proposed here. Moreover, identifying missense variants that selectively disrupt slow-inactivation regulation could help pinpoint residues that are critical for PRRT2-Nav functional coupling and thereby inform future structure-function studies. We plan to pursue this direction in follow-up work.
(3) Investigate spreading depolarization in PRRT2-deficient mice.
We thank the reviewer for this suggestion. Although we have shown that PRRT2 deficiency facilitates spreading depolarization in the cerebellum, whether PRRT2 exerts similar control over spreading depolarization susceptibility in the cerebral cortex remains to be determined. We plan to address this in an independent study and to test how cortical spreading depolarization relates to other PRRT2-associated neurological disorders.
Reviewer #2 (Recommendations for the authors):
This study is, in general, well executed, and the manuscript is well written. However, I do have some questions.
(1) The authors' previous works have shown that PRRT2 regulates both Nav1.2 and Nav1.6, considering the wide expression Nav1.6 in CNS and its role in neuronal activity, what makes the authors not include Nav1.6 in this study?
We thank the reviewer for raising this question. In our previous work, PRRT2 produced broadly similar effects on Nav1.2 and Nav1.6. Therefore, in the initial version of this study, we focused primarily on Nav1.2 as a representative neuronal Nav channel isoform and placed greater emphasis on testing whether PRRT2-dependent regulation of slow inactivation extends across additional Nav isoforms. In response to reviewers’ concern, we have now performed new experiments to directly examine the effect of PRRT2 on Nav1.6 slow inactivation. These results have been incorporated into the revised manuscript. Please refer to Page 8, Lines 211-215; Figures 4E and J.
(2) Please explain why you chose 0 mV rather than -70 mV (closer to membrane potential) in the slow inactivation protocol.
We thank the reviewer for raising this question. Nav channels can enter into slow inactivation from both resting/closed states and activated/open states. In our steady-state slow-inactivation assays, we found that PRRT2 enhances Nav1.2 slow inactivation under both conditions (Figure 1-figure supplement 1A and B). In whole-cell recordings, Nav1.2 channels typically begin to activate at command voltages more depolarized than approximately -60 mV. Accordingly, a conditioning voltage of -70 mV predominantly probes entry into slow inactivation from closed states, whereas 0 mV drives channel activation and more effectively induces slow inactivation. We therefore chose 0 mV as the primary conditioning potential because it is widely used in conventional slow inactivation protocols and induces slow inactivation more robustly than conditioning voltages at -70 mV. We have added this explanation in Methods section of revised manuscript, please refer to Page 20, Lines 569-571.
(3) The authors mentioned that the insertion of V5 markedly reduced the PRRT2 protein level; thus, Prrt2-V5 knock-in mice could be considered as PRRT2 knock-down mice. Is there any noticeable difference in phenotype between Prrt2-V5 knock-in mouse and Prrt2-mutant mouse? In other words, is PRRT2 knockdown sufficient to affect neuronal excitability, or is a complete PRRT2 ablation required?
We thank the reviewer for raising this concern regarding the functional consequences of reduced PRRT2 expression in the Prrt2-V5 knock-in mice. Given that PRRT2 protein levels are markedly reduced in this line, and that cerebellar stimulation-induced dystonia is a characteristic phenotype of PRRT2 deficiency, we tested whether Prrt2-V5 knock-in mice also exhibit this phenotype. We found that electrical stimulation of the cerebellar cortex induced dystonia-like attacks in a subset of Prrt2-V5 knock-in mice. These dystonic behaviors resembled those previously observed in Prrt2-mutant mice, whereas no such behaviors were induced in wild-type mice (Figure 6-figure supplement 1). These findings indicate that a substantial reduction of PRRT2 expression (approximately 80%) is sufficient to impair neuronal function and elicit a disease-relevant phenotype in a subset of animals, supporting the interpretation that the V5 knock-in allele is hypomorphic. We have incorporated these results into the revised manuscript, please refer to Page 9, Lines 265-267; Figure 6-figure supplement 1.
(4) In Discussion (Page 13, lines 358-361), the authors mentioned a putative interaction between PRRT2 and the Nav channel by modeling, while there is no related data. Please either add modeling data or remove those sentences.
We thank the reviewer for this suggestion. To avoid over-interpretation, we have removed the statements regarding the AlphaFold-based interaction model from the revised manuscript. We agree that the interaction interface remains to be demonstrated experimentally, and we now discuss this point in the Limitations section. Please refer to Page 16, Lines 465-468.
(5) Typo: Page 14, line 399, "TMEM232" should be "TMEM233".
We thank the reviewer for pointing out this typo. We have corrected it in the revised manuscript.
Reviewer #3 (Recommendations for the authors):
(1) Mechanistic depth: While the functional data show altered slow-inactivation kinetics, the mechanistic explanation remains superficial. The AlphaFold-based prediction of PRRT2 interaction with DIV-S3 is speculative. The authors should clarify their illustrative rather than evidential intent and avoid over-interpretation.
We thank the reviewer for this comment. To avoid over-interpretation, we have removed the AlphaFold-based interaction prediction from the revised manuscript. We have also expanded the Limitations section to emphasize that direct structural and biochemical mapping of the PRRT2-Nav interface, including targeted mutagenesis, crosslinking, and structural determination, will be necessary to elucidate the molecular basis of this interaction and its effect on channel gating. Please refer to Page 16, Lines 465-468.
(2) Separation of trafficking vs. gating effects: Previous studies showed PRRT2 influences Nav trafficking and surface expression. Here, surface expression changes are not systematically quantified. Such an analysis would strengthen the argument that gating effects are not secondary to altered channel abundance or localization.
We thank the reviewer’s concern regarding the possible contribution of trafficking effects to PRRT2-dependent regulation of Nav channel slow inactivation. We agree that direct analysis of Nav channel surface localization during prolonged depolarization and hyperpolarization would provide stronger evidence to distinguish gating effects from trafficking-dependent mechanisms. However, such experiments are technically challenging in this context: conventional surface biotinylation assays do not provide the temporal resolution required for these rapid protocols, and live-cell imaging approaches to monitor dynamic changes in Nav channel surface expression during slow-inactivation paradigms have not yet been established in our laboratory.
Although PRRT2 has been reported to regulate Nav channel surface expression in heterologous systems, we consider it unlikely that trafficking is the major determinant of the slow-inactivation effects described here. Slow-inactivation develops on a timescale ranging from tens of milliseconds to seconds, whereas detectable changes in Nav channel trafficking and surface abundance generally occur over much longer timescales (minutes to hours) (Freal et al., 2023; Higerd-Rusli et al., 2023). We have expanded the Discussion in a revised manuscript. Please refer to Pages 13, Lines 378-388.
(3) Isoform generalization: Data on other Nav channel subtypes are presented as evidence of a conserved mechanism. However, given tissue-specific expression of PRRT2, these findings may be of limited in vivo relevance. At the very least, additional studies with Nav1.6 should be carried out.
We thank the review for this suggestion. In response, we conducted new experiments to examine the effect of PRRT2 on Nav1.6 slow inactivation. These results show that PRRT2 promotes entry of Nav1.6 channels into slow-inactivated states and delays their recovery, consistent with its effects on the other Nav isoforms examined in this study. We have incorporated these new data into the revised manuscript. Please refer to Page 8, Lines 211-215; Figures 4E and J.
Furthermore, we clarify that the cross-isoform analysis was intended to assess mechanistic generality at the channel level, rather than to imply equivalent physiological relevance across tissues. The functional consequence of PRRT2 depend on the Nav isoform composition and cellular context of each tissue. We also note that the broad isoform activity of the PRRT2 should be considered in any future attempt to manipulate PRRT2 function therapeutically. Pages 14 and 15, Lines 414-416 and 429-430.
(4) In vivo functional link: The EEG after-discharge threshold assay suggests decreased cortical resilience, but causality between slow-inactivation impairment and hyperexcitability remains indirect. Complementary in vivo recordings would strengthen the physiological link.
We thank the reviewer for this helpful suggestion. To further link impaired slow-inactivation to the hyperexcitability, we applied a repetitive stimulation protocol in corpus callosum slices, a white-matter region of brain enriched in both PRRT2 and Nav channels. During high-frequency stimulation (e.g., 20 Hz), the amplitude of the compound action potential progressively decreased over the course of the stimulus train. This phenomenon, often referred to as adaptation, reflects activity-dependent reduction in Nav channel availability (Fleidervish et al., 1996; Mickus et al., 1999; Kim et al., 2012). Compared with wild-type mice, Prrt2-mutant mice exhibited less adaptation during high-frequency stimulation, consistent with impaired slow inactivation during repetitive activity, which may contribute to hyperexcitability (Figure 7-figure supplement 2). We have added these results to the revised manuscript. Please refer to Pages 11, Lines 311-322; Figure 7-figure supplement 2.
(5) Structural interaction: It remains unclear whether PRRT2 binds the α-subunit directly or through accessory proteins. Crosslinking or detergent-solubilization controls of different stringencies could clarify this.
We thank the reviewer for raising this important issue. We agree that our co-immunoprecipitation data do not distinguish whether PRRT2 associates with the Nav channel α-subunit directly or through other components of the protein complex. To avoid over-interpretation, we have revised the relevant text in the manuscript to remove any implication of direct binding and now describe the result as an association between PRRT2 and Nav channels.
We have also expanded the Limitations section to note that additional experiments, such as crosslinking and structural studies, will be required to define the interaction interface between PRRT2 and Nav channels. Please refer to Page 16, Lines 465-468.
(6) Comparisons to other regulators: The paper positions PRRT2 as distinct from FHFs and β-subunits. The data support this, but the discussion could more critically assess whether PRRT2 acts by stabilizing a pore-based inactivated conformation, as suggested for other slow-inactivation modulators.
We thank the reviewer for this insightful suggestion. At present, relatively few modulators have been characterized in detail with respect to their effects on Nav channel slow-inactivation kinetics. Moreover, even for compounds such as lacosamide, which has been proposed to act as a slow-inactivation modulator, the underlying mechanism remains under debate (Errington et al., 2008; Jo and Bean, 2017). Therefore, in the revised manuscript, we discussed the possible mechanism of PRRT2 in the context of current models of Nav channel slow inactivation.
Previous studies suggest that entry into the slow-inactivated state involves at least two coupled processes: conformational changes in the voltage-sensing domains and structural rearrangements in the pore region, including the selectivity filter and intracellular activation gate (Catterall et al., 2024; Silva, 2014). During prolonged depolarization, voltage sensors become stabilized in the up-state, while the pore undergoes progressive rearrangements associated with slow inactivation (Balser et al., 1996; Vilin et al., 1999). Thus, mechanisms that further stabilize voltage sensors in the up-state and/or facilitate pore-based inactivated conformations could enhance slow inactivation.
Within this framework, PRRT2 may enhance slow inactivation by facilitating one or both of these processes, although direct evidence is still lacking. We have incorporated this discussion in relative section of revised manuscript. Please refer to Page 14, Lines 389-404.
Response references:
Jo S, Bean BP. Lacosamide Inhibition of Nav1.7 Voltage-Gated Sodium Channels: Slow Binding to Fast-Inactivated States. Mol Pharmacol. 2017 Apr;91(4):277-286.
Errington AC, Stöhr T, Heers C, Lees G. The investigational anticonvulsant lacosamide selectively enhances slow inactivation of voltage-gated sodium channels. Mol Pharmacol. 2008 Jan;73(1):157-69.
(7) Behavioral/clinical link: Given the strong human genetics background of PRRT2 disorders, a brief analysis or reference to electrophysiological phenotypes in patient neurons would contextualize the cortical findings.
We thank the reviewer for this suggestion. Previous studies showed that iPSC-derived excitatory neurons from a patient carrying a homozygous PRRT2 mutation exhibited increased sodium currents and neuronal hyperexcitability (Fruscione et al., 2018). Given that slow inactivation regulates Nav channel availability and thereby influences neuronal excitability, these electrophysiological abnormalities in patient-derived neurons may, at least in part, reflect impaired PRRT2-dependent regulation of Nav channel slow inactivation. We have added this point to the relative section of the revised manuscript. Please refer to Pages 15, Lines 432-437.
Minor comments
(1) Figures should include statistical sample sizes (n) and ideally overlay data points rather than only means {plus minus} SEM.
We thank the reviewer for this suggestion. In the revised manuscript, we present both individual data points and mean ± SEM in the column graphs. For the line graphs, individual data points were not overlaid because of space and readability constraints, and these panels therefore display mean ± SEM only. Sample sizes for each group are provided in the corresponding figure legends.
(2) The AlphaFold model should be provided as a supplementary figure with confidence scores indicated.
We thank the reviewer for this suggestion. However, because the predicted Nav1.2-PRRT2 interaction interface has not yet been experimentally validated in our study, we chose to remove the AlphaFold-based model from the revised manuscript to avoid over-interpretation.
(3) Clarify whether TTX sensitivity was verified in the axonal bleb preparation.
We thank the reviewer for raising this point. We verified the identity of the sodium currents in the axonal bleb preparation by their sensitivity to TTX, and this information has now been added to Figure 7A in the revised manuscript. Please refer to Page 10, Line 290; Figure 7A.