Role of α-Synuclein in the Prefrontal Cortex: From Physiological Synaptic Modulation to Synaptic Failure in Parkinson’s Disease

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Argibay et al provide a review on role of alpha-synuclein in the prefrontal cortex. The pathogenesis of neurodegenerative diseases is insufficiently recognized, certain points require adressing issues:

1. While the topic of the reviews highlights the significance of alpha-synuclein, the context of multiple system atrophy is not emphasized
2. Authors should consider implementing a wider view on factors impacting the pathogenesis of Parkinson's disease and other synucleinopathies acknowledging multiple concepts - neuroinflammation, metabolic abnormalities, oxidative factors, environmental factors among others - Ref. McGeer PL, McGeer EG. Inflammation and neurodegeneration in Parkinson's disease. Parkinsonism Relat Disord. 2004;10 Suppl 1:S3-S7. doi:10.1016/j.parkreldis.2004.01.005 / Importance of hypoglycemia episodes and glycemic variability in parkinsonian syndromes. Neurol Neurochir Pol. 2025;59(6):501-503. doi:10.5603/pjnns.109238
3. The heterogenerous alpha-synuclein expression patterns should be discussed in the context of their significance in the evolution of PD to different subtypes 
4. The discussed in the manuscript pathological role of Α-Syn in Pfc Glutamatergic and Gabaergic Synapses should be additionally assessed in terms of. its impact depending on the presence in various clinical entities, moreover authors should consider analyzing the possibility of co-pathologies
5. PDD should be analyzed a distinct entity in the evaluation of the role of alpha-synuclein
6. The study limitations could be separately evaluated in a critical manner. Additionally the literature search should be examined in terms of the strengths and weaknesses of the studies, authos could separately elaborate on the clinical and mice-experimental models.
7. The language of the manuscript could be improved.

Comments on the Quality of English Language

Could be improved by a Native-speaker.

Author Response

1. While the topic of the reviews highlights the significance of alpha-synuclein, the context of multiple system atrophy is not emphasized.

We thank the Reviewer for highlighting this point. We agree that providing a broader context of α-synucleinopathies, including multiple system atrophy (MSA), is important for a comprehensive overview. We have now expanded the introduction to explicitly mention MSA, incidental Lewy body disease (iLBD), and mixed proteinopathies (such as Alzheimer's disease with Lewy bodies). However, we have also clarified that because the primary scope of our review is to deeply analyze the physiological and pathological effects of α-Syn in the prefrontal cortex, the main text naturally focuses more heavily on conditions like Parkinson's disease (PD), PD dementia (PDD), and dementia with Lewy bodies (DLB), which predominantly affect these cortical networks.  Page 1, Lines 56-67

 

2. Authors should consider implementing a wider view on factors impacting the pathogenesis of Parkinson's disease and other synucleinopathies acknowledging multiple concepts - neuroinflammation, metabolic abnormalities, oxidative factors, environmental factors among others - Ref. McGeer PL, McGeer EG. Inflammation and neurodegeneration in Parkinson's disease. Parkinsonism Relat Disord. 2004;10 Suppl 1:S3-S7. doi:10.1016/j.parkreldis.2004.01.005 / Importance of hypoglycemia episodes and glycemic variability in parkinsonian syndromes. Neurol Neurochir Pol. 2025;59(6):501-503. doi:10.5603/pjnns.109238

We sincerely thank the Reviewer for this insightful comment. We fully agree that the pathogenesis of PD and other synucleinopathies is a highly complex, multi-scale process driven by diverse mechanisms. As the Reviewer rightly points out, neuronal αSyn aggregation in Lewy body diseases is closely linked with neuroinflammation. Furthermore, at the subcellular level, pathological αSyn conformers disrupt a wide range of organelles and regulatory compartments, profoundly affecting mitochondrial dynamics, ER–Golgi trafficking, and endolysosomal degradation.

However, the central and specific aim of our review is to analyze the dual and localized role of α-Syn within the prefrontal cortex circuitry, specifically the transition from its physiological modulation of synaptic vesicle dynamics to its role in triggering synaptic failure and E/I imbalance –an aspect that has been less explored in the pathology of PD–. To preserve the depth and coherence of this focused neurophysiological narrative, we have chosen to maintain our detailed scope on synaptic processes rather than broadening it to a comprehensive review of the overall pathogenesis of the disease.

Nevertheless, we fully recognize the importance of contextualizing the synaptic focus within the broader pathophysiological landscape. Consequently, we have amended point 3. Pathological Role of α-Syn in PFC Glutamatergic and GABAergic Synapses, to include a brief overview of these key mechanisms, specifically acknowledging neuroinflammation, oxidative stress, metabolic abnormalities, among others. Pages 8, Lines 236-249.

3. The heterogenerous alpha-synuclein expression patterns should be discussed in the context of their significance in the evolution of PD to different subtypes 

We thank the reviewer for this insightful comment. We fully agree that linking the heterogeneous physiological expression of α-Syn to the selective vulnerability and evolution of specific PD subtypes significantly strengthens the manuscript. We have now expanded the discussion in the revised text to explicitly connect the region- and cell-specific expression patterns of endogenous α-Syn (e.g., its high abundance in monoaminergic cells, VGLUT1-positive cortical neurons, etc.) with the α-Syn origin site and connectome (SOC) model. The revised text clarifies how these baseline expression differences provide abundant substrates for template-directed seeding, thereby driving the specific pathological propagation pathways seen in "brain-first" versus "body-first" PD subtypes. Page 9, Lines 256-266.

4. The discussed in the manuscript pathological role of Α-Syn in Pfc Glutamatergic and Gabaergic Synapses should be additionally assessed in terms of. its impact depending on the presence in various clinical entities, moreover authors should consider analyzing the possibility of co-pathologies.

We sincerely thank the reviewer for highlighting this critical aspect. We fully agree that the synaptic impact of α-Syn in the prefrontal cortex (PFC) is not uniform and depends heavily on the specific clinical entity, such as the early cortical involvement seen in DLB compared to the later progression typical of PDD. Furthermore, we acknowledge that studying pure α-synucleinopathies often does not reflect clinical reality, as co-pathologies (e.g., Amyloid-β and Tau) are highly prevalent and synergistically exacerbate synaptic failure.

However, it is important to note that there is currently a significant scarcity of studies both in rodent models and in postmortem human samples across different α-synucleinopathy phenotypes, that specifically investigate the functional and structural alterations of glutamatergic and GABAergic synapses within the PFC. Historically, the vast majority of research in the field has focused predominantly on the hippocampus and basal ganglia.

 

5. PDD should be analyzed a distinct entity in the evaluation of the role of alpha-synuclein

We sincerely thank the reviewer for this precise and important observation. We completely agree that Parkinson’s disease dementia (PDD) must be analyzed as a distinct entity. While PDD and dementia with Lewy bodies (DLB) share a common molecular hallmark and eventual neocortical synaptic failure, their temporal and spatial pathological trajectories are fundamentally different. In PDD, the prefrontal cortex and other neocortical areas are typically overwhelmed by α-Syn pathology at a much later stage, following years of subcortical, motor-predominant disease and prolonged periods of synaptic compensation.

To properly reflect this distinction in the revised manuscript, we have expanded our introduction to explicitly describe the distinct clinical phenotypes of α-synucleinopathies, including PD, PDD, and DLB (please refer to Page 1, Lines 56-67). Furthermore, in Section 4, we systematically review the literature regarding synaptopathy assessed via the 11C-UCB-J radioligand, taking care to clearly differentiate the specific synaptic alterations occurring across PD, PDD, and DLB. 

 

6. The study limitations could be separately evaluated in a critical manner. Additionally the literature search should be examined in terms of the strengths and weaknesses of the studies, authos could separately elaborate on the clinical and mice-experimental models.

We sincerely thank the reviewer for this excellent suggestion. We completely agree that a critical evaluation of the current literature’s strengths and limitations provides essential context for our conclusions and highlights critical gaps for future research.

To address this, we have added a completely new section titled "Limitations and Critical Evaluation of Current Literature" just before the Conclusions. In this new section, we systematically dissect the methodological strengths and weaknesses of the reviewed studies. As requested, we have separated this critical appraisal into two distinct subsections: one evaluating preclinical mice-experimental models (addressing physiological α-Syn expression, brain spreading, and neuroanatomical homology) and another evaluating clinical/neuroimaging studies (addressing neuroimaging resolution limits, metabolic biomarker overlap, and post-mortem co-pathologies). We believe this addition significantly enhances the rigor and depth of the manuscript. Pages 18 and 19, Lines 583-626.

7. The language of the manuscript could be improved.

We appreciate the reviewer’s feedback. The manuscript has undergone a comprehensive language revision by a professional editing service to ensure improved clarity, grammar, and flow. All language-related changes are tracked and highlighted in red throughout the revised manuscript.

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript entitled “Role of α-Synuclein in the Prefrontal Cortex: From Physiological Synaptic Modulation to Synaptic Failure in Parkinson’s Disease” by  Argibay et al., presents a timely and comprehensive overview of the physiological and pathological roles of α-synuclein (α-Syn) within prefrontal cortical circuits. The authors successfully integrate molecular, synaptic, neuroimaging, and behavioral evidence to support the concept that prefrontal synaptopathy contributes substantially to the cognitive and neuropsychiatric manifestations of Parkinson’s disease (PD), Parkinson’s disease dementia (PDD), and dementia with Lewy bodies (DLB). The manuscript is well organized, clearly written, and addresses an area that has received considerably less attention than the classical nigrostriatal pathology of PD. The discussion of synaptic vesicle dynamics, glutamatergic and GABAergic neurotransmission, dendritic spine pathology, SV2A imaging, and emerging neuroplasticity-based therapeutic approaches provides an informative and valuable synthesis of the current literature.

Major Comments:

Despite these strengths, several aspects of the review would benefit from further development before publication.

1. One notable limitation is the relatively limited discussion of concomitant proteinopathies, particularly β-amyloid (Aβ) and tau. Although the review appropriately focuses on α-synuclein-mediated synaptic dysfunction, increasing evidence indicates that cortical proteinopathies rarely occur in isolation, especially in patients with PDD and DLB. Numerous neuropathological studies have demonstrated that cortical Aβ deposition and tau accumulation are common in Lewy body disorders and are associated with accelerated cognitive decline, increased dementia risk, and more severe executive dysfunction. Importantly, recent experimental findings suggest that Aβ pathology may not merely coexist with α-synucleinopathy but may actively promote α-synuclein aggregation and propagation. For example, Bassil et al. (2020) demonstrated that Aβ plaques facilitate the seeding and spreading of α-synuclein pathology in vivo, whereas Vadukul et al. (2023) showed that soluble Aβ-containing oligomers can directly trigger α-synuclein aggregation through heterogeneous primary nucleation mechanisms. These observations raise the possibility that early cortical Aβ accumulation may act as a catalyst for subsequent α-synuclein misfolding and synaptic dysfunction. Given the manuscript’s emphasis on early synaptic pathology as a driver of cognitive decline, the incorporation of a brief discussion addressing Aβ–α-synuclein cross-seeding and tau interactions would substantially strengthen the pathogenic framework presented by the authors.
2. The manuscript would also benefit from a more extensive discussion of neuroinflammatory mechanisms. Synaptic loss is presented as a central pathological event throughout the review, yet the cellular processes responsible for synapse elimination receive comparatively limited attention. Recent evidence indicates that microglial activation, complement-mediated synaptic pruning, astrocytic dysfunction, and chronic inflammatory signaling play important roles in α-synuclein-mediated synaptopathy. Moreover, α-synuclein aggregates can directly activate innate immune pathways, leading to sustained neuroinflammation and subsequent synaptic remodeling. Because synapse elimination is increasingly recognized as an active biological process rather than a passive consequence of degeneration, greater integration of neuroimmune mechanisms would provide a more complete picture of cortical vulnerability in PD and DLB.
3. Another issue concerns the interpretation of GABAergic alterations. The review appropriately highlights emerging evidence for subtype-specific interneuron vulnerability and compensatory remodeling of inhibitory circuits. However, the current literature remains relatively limited and occasionally conflicting. Several conclusions regarding alterations in gephyrin expression, SST interneurons, and inhibitory synaptic organization appear stronger than the available evidence presently supports. A more cautious interpretation, acknowledging the scarcity of human data and the considerable regional heterogeneity observed across cortical areas, would improve the balance of the discussion.
4. The section devoted to ketamine and psilocybin is interesting and highlights an emerging area of therapeutic investigation. Nevertheless, this portion of the review occasionally adopts an optimism that exceeds the currently available evidence. While both compounds demonstrate robust neuroplastic effects in experimental systems and have shown promise in early clinical studies, definitive evidence for disease modification in α-synucleinopathies remains lacking. Many of the proposed mechanisms remain hypothetical, and the available clinical studies are generally small pilot investigations focused primarily on psychiatric symptoms. The authors may therefore wish to distinguish more clearly between established findings, mechanistic hypotheses, and future therapeutic possibilities. A more cautious tone would improve the scientific balance of this section.
5. The review repeatedly emphasizes the concept that PD, PDD, and DLB represent a spectrum of related synucleinopathies. While this viewpoint is increasingly supported by clinical and neuropathological observations, important biological differences remain between these disorders, particularly regarding the extent of cortical involvement and the burden of concomitant Aβ and tau pathology. A concise summary discussing similarities and differences among PD, PDD, and DLB would help readers better appreciate the broader clinical context.

 

Minor comments:

1. Several minor points should also be considered. The section describing the physiological role of α-synuclein provides a thorough overview of protein structure, membrane interactions, and SNARE-complex regulation; however, some sections could be condensed to maintain a stronger focus on prefrontal cortical circuitry. In addition, the discussion of postsynaptic glutamate receptors correctly identifies a significant knowledge gap regarding alterations in NMDA and AMPA receptor function in the prefrontal cortex. However, many mechanistic conclusions are extrapolated from striatal or hippocampal studies and should be explicitly presented as indirect evidence rather than as established cortical mechanisms.
2. Finally, Figure 1 effectively summarizes the major concepts of the review and represents a valuable visual overview. Nevertheless, the figure could be strengthened by incorporating neuroinflammatory pathways and illustrating potential interactions between α-synuclein, Aβ, and tau pathology. Such additions would provide a more comprehensive representation of the multifactorial mechanisms contributing to cortical synaptic dysfunction and cognitive decline.

 

In summary, this is a well-written, informative, and timely review that addresses an important and emerging area of Parkinson’s disease research. The manuscript provides an excellent synthesis of evidence supporting the role of prefrontal cortical synaptopathy in cognitive dysfunction. Incorporating additional discussion of Aβ and tau co-pathology, α-synuclein cross-seeding mechanisms, neuroinflammatory pathways, and the current limitations of neuroplasticity-based therapeutic approaches would further strengthen the review and broaden its relevance to the field. Subject to revision, I believe the manuscript would make a valuable contribution to the literature.

Suggested references to support the Aβ → α-synuclein interaction:

Bassil F, Brown HJ, Pattabhiraman S, et al. Amyloid-Beta (Aβ) Plaques Promote Seeding and Spreading of Alpha-Synuclein and Tau in a Mouse Model of Lewy Body Disorders. Neuron. 2020;105(2):260-275.e6., doi:10.1016/j.neuron.2019.10.010

Vadukul DM, Vrancx C, Steyaert J, et al.  Amyloid β-Containing Oligomers Promote α-Synuclein Aggregation by Heterogeneous Primary Nucleation. Journal of the American Chemical Society. 2023;145:14761–14772. doi:10.1021/jacs.3c02817

Twohig D, Nielsen HM. Alpha-synuclein in the pathophysiology of Alzheimer's disease. Molecular Neurodegeneration. 2019;14:23. doi:10.1186/s13024-019-0320-x

Recent evidence suggests that Aβ pathology may actively promote α-synuclein misfolding, aggregation, and propagation through cross-seeding mechanisms, raising the possibility that early cortical Aβ accumulation in PD and DLB contributes directly to the development of synaptic dysfunction and cognitive decline in PDD and DLB.

 

Author Response

Comments and Suggestions for Authors

The manuscript entitled “Role of α-Synuclein in the Prefrontal Cortex: From Physiological Synaptic Modulation to Synaptic Failure in Parkinson’s Disease” by Argibay et al., presents a timely and comprehensive overview of the physiological and pathological roles of α-synuclein (α-Syn) within prefrontal cortical circuits. The authors successfully integrate molecular, synaptic, neuroimaging, and behavioral evidence to support the concept that prefrontal synaptopathy contributes substantially to the cognitive and neuropsychiatric manifestations of Parkinson’s disease (PD), Parkinson’s disease dementia (PDD), and dementia with Lewy bodies (DLB). The manuscript is well organized, clearly written, and addresses an area that has received considerably less attention than the classical nigrostriatal pathology of PD. The discussion of synaptic vesicle dynamics, glutamatergic and GABAergic neurotransmission, dendritic spine pathology, SV2A imaging, and emerging neuroplasticity-based therapeutic approaches provides an informative and valuable synthesis of the current literature.

We sincerely thank the Reviewer for the time and effort dedicated to reading our manuscript and for their highly positive and encouraging assessment.

1. One notable limitation is the relatively limited discussion of concomitant proteinopathies, particularly β-amyloid (Aβ) and tau. Although the review appropriately focuses on α-synuclein-mediated synaptic dysfunction, increasing evidence indicates that cortical proteinopathies rarely occur in isolation, especially in patients with PDD and DLB. Numerous neuropathological studies have demonstrated that cortical Aβ deposition and tau accumulation are common in Lewy body disorders and are associated with accelerated cognitive decline, increased dementia risk, and more severe executive dysfunction. Importantly, recent experimental findings suggest that Aβ pathology may not merely coexist with α-synucleinopathy but may actively promote α-synuclein aggregation and propagation. For example, Bassil et al. (2020) demonstrated that Aβ plaques facilitate the seeding and spreading of α-synuclein pathology in vivo, whereas Vadukul et al. (2023) showed that soluble Aβ-containing oligomers can directly trigger α-synuclein aggregation through heterogeneous primary nucleation mechanisms. These observations raise the possibility that early cortical Aβ accumulation may act as a catalyst for subsequent α-synuclein misfolding and synaptic dysfunction. Given the manuscript’s emphasis on early synaptic pathology as a driver of cognitive decline, the incorporation of a brief discussion addressing Aβ–α-synuclein cross-seeding and tau interactions would substantially strengthen the pathogenic framework presented by the authors.

We would like to express our sincere thanks to Reviewer 2 for this insightful and constructive comment. We fully agree that the interaction between α-Syn and associated proteinopathies, specifically Aβ and tau protein, is a critical factor in the pathogenesis of PDD and DLB.

As the reviewer rightly points out, although our manuscript focuses largely on early synaptic pathology driven by α-Syn in PD, PDD, and DLB, we recognize that explicitly addressing the mechanical interaction and cross-propagation between these proteins provides a much more robust and realistic pathogenic framework. Therefore, in our revised manuscript, we briefly highlight the different pathological entities in which a complex mixed proteinopathy involving Aβ, tau, α-Syn and TDP-43 exists (see the response to comment 1 from Reviewer 1). We also have incorporated a new paragraph in the section titled ‘Pathological role of α-Syn in glutamatergic and GABAergic synapses in PFC’. This addition explicitly addresses the mechanisms of Aβ-α-Syn cross-propagation and interactions with tau, appropriately citing the seminal studies by Bassil et al. (2020) and Vadukul et al. (2023) that Reviewer 2 kindly suggested. Page 12, lines 371–381.

 

2. The manuscript would also benefit from a more extensive discussion of neuroinflammatory mechanisms. Synaptic loss is presented as a central pathological event throughout the review, yet the cellular processes responsible for synapse elimination receive comparatively limited attention. Recent evidence indicates that microglial activation, complement-mediated synaptic pruning, astrocytic dysfunction, and chronic inflammatory signaling play important roles in α-synuclein-mediated synaptopathy. Moreover, α-synuclein aggregates can directly activate innate immune pathways, leading to sustained neuroinflammation and subsequent synaptic remodeling. Because synapse elimination is increasingly recognized as an active biological process rather than a passive consequence of degeneration, greater integration of neuroimmune mechanisms would provide a more complete picture of cortical vulnerability in PD and DLB.

We sincerely thank the Reviewer for highlighting the critical role of neuroinflammatory mechanisms and active synaptic pruning in the context of α-synuclein-mediated synaptopathy. We fully agree that synaptic pruning is an active biological process and that neuroimmunological pathways are key factors in disease progression. Whilst we fully recognize the importance of this topic, we respectfully note that providing an in-depth and comprehensive analysis of the specific cellular and immunological mechanisms responsible for α-Syn aggregation and subsequent synaptic pruning falls slightly outside the main scope of this review. Almost all of the studies reported on these mechanisms involve the nigrostriatal pathway, but not the PFC. Our manuscript focuses primarily on the functional consequences of α-Syn pathology on the excitatory/inhibitory (E/I) balance, synaptic vesicle dynamics, and large-scale prefrontal connectivity. 

Nevertheless, we agree that the manuscript should acknowledge these pathways. Consequently, we have ensured that the key processes leading to aggregation and active synaptic clearance are listed in our pathogenic framework. Specifically, throughout the manuscript we have highlighted that preclinical studies suggest that the spread of α-Syn oligomers causes synaptic abnormalities in the prefrontal cortex (PFC) by promoting microglia-mediated synaptic phagocytosis.  Furthermore, the pathogenesis is driven and exacerbated by systemic factors, including neuroinflammation and immune system dysfunction, as well as metabolic and bioenergetic abnormalities, and environmental and lifestyle factors. For quick review, all changes in the revised version are highlighted in red.

 

3. Another issue concerns the interpretation of GABAergic alterations. The review appropriately highlights emerging evidence for subtype-specific interneuron vulnerability and compensatory remodeling of inhibitory circuits. However, the current literature remains relatively limited and occasionally conflicting. Several conclusions regarding alterations in gephyrin expression, SST interneurons, and inhibitory synaptic organization appear stronger than the available evidence presently supports. A more cautious interpretation, acknowledging the scarcity of human data and the considerable regional heterogeneity observed across cortical areas, would improve the balance of the discussion.

We thank the reviewer for this insightful and constructive comment. We fully agree that the current literature on cortical GABAergic alterations in α-synucleinopathies remains very limited. Following the reviewer’s recommendation, we have thoroughly revised this section to present a much more cautious interpretation. We now explicitly acknowledge the scarcity of translational data in humans, highlight the contradictory nature of some preliminary findings, and emphasize the considerable regional heterogeneity of inhibitory synaptic reorganization across different cortical areas. Page 10, lines 316-321.

 

4. The section devoted to ketamine and psilocybin is interesting and highlights an emerging area of therapeutic investigation. Nevertheless, this portion of the review occasionally adopts an optimism that exceeds the currently available evidence. While both compounds demonstrate robust neuroplastic effects in experimental systems and have shown promise in early clinical studies, definitive evidence for disease modification in α-synucleinopathies remains lacking. Many of the proposed mechanisms remain hypothetical, and the available clinical studies are generally small pilot investigations focused primarily on psychiatric symptoms. The authors may therefore wish to distinguish more clearly between established findings, mechanistic hypotheses, and future therapeutic possibilities. A more cautious tone would improve the scientific balance of this section.

We would like to express our sincere thanks to the Reviewer for this critical and highly relevant comment. We agree that our previous wording conveyed an overly optimistic view of the disease-modifying potential of ketamine and psilocybin in clinical populations, based on current clinical trials. In line with this reviewer’s suggestion, we have thoroughly revised the section ‘Advances in cortical neuroprotection α-synucleinopathies to provide a more balanced scientific perspective. Specifically, we have toned down the language to clearly distinguish between established preclinical findings (e.g., structural plasticity in rodent models) and mechanistic hypotheses regarding human pathology. We have explicitly clarified that current clinical evidence on ketamine and psilocybin derives primarily from clinical trials focused on alleviating psychiatric comorbidities (such as depression and anxiety), as well as on changes in synaptic density and the functional reorganization of neural networks and the underlying pathways of neuroplasticity and inflammation; rather than halting neurodegeneration. We have reframed the proposed neuroprotective mechanisms as future therapeutic possibilities. The revised text can be found on Pages 17 and 18; Lines 555-580 of the updated manuscript.

 

5. The review repeatedly emphasizes the concept that PD, PDD, and DLB represent a spectrum of related synucleinopathies. While this viewpoint is increasingly supported by clinical and neuropathological observations, important biological differences remain between these disorders, particularly regarding the extent of cortical involvement and the burden of concomitant Aβ and tau pathology. A concise summary discussing similarities and differences among PD, PDD, and DLB would help readers better appreciate the broader clinical context.

We thank the Reviewer for this appropriate observation. We fully agree that it is crucial to clearly delineate the biological and neuropathological differences between these entities. Specifically, highlighting the spatiotemporal progression of cortical involvement and the variable burden of mixed proteinopathies adds essential clinical context to the manuscript. To address this, we have incorporated a new concise summary in the section "A Comprehensive Analysis of SV2A Synaptic Loss, Prefrontal Connectivity Dysfunction, and Altered Excitatory/Inhibitory Balance in PD and DLB." This new paragraph contrasts the progressive cortical spread in PDD with the early cortical vulnerability and higher concomitant burden of β-amyloid and tau observed in DLB. The revised text can be found on Page 13, Lines 392-404 of the updated manuscript.

 

Minor comments:

1. Several minor points should also be considered. The section describing the physiological role of α-synuclein provides a thorough overview of protein structure, membrane interactions, and SNARE-complex regulation; however, some sections could be condensed to maintain a stronger focus on prefrontal cortical circuitry. In addition, the discussion of postsynaptic glutamate receptors correctly identifies a significant knowledge gap regarding alterations in NMDA and AMPA receptor function in the prefrontal cortex. However, many mechanistic conclusions are extrapolated from striatal or hippocampal studies and should be explicitly presented as indirect evidence rather than as established cortical mechanisms.

We thank the Reviewer for pointing out these important nuances. We completely agree that simplifying the details of structural biology allows for a clearer focus on the prefrontal cortical circuit. To address these points, we have made the following changes to the manuscript:

• We have condensed the paragraphs detailing the molecular structure of α-Syn, its specific domains, and the extensive lists of its interactome. This keeps the focus firmly on its role in synaptic vesicle recycling and makes a direct transition to its function in the PFC. Page 5, Lines 144-145; Page 6, Lines 165-169.
• In the section on postsynaptic glutamate receptors, we have revised the text to explicitly state which current data are derived from striatal and hippocampal models, and which come from studies in cortical circuits. Page 11, Lines 354-358; Page 12, Lines 371-381.

 

 

2. Finally, Figure 1 effectively summarizes the major concepts of the review and represents a valuable visual overview. Nevertheless, the figure could be strengthened by incorporating neuroinflammatory pathways and illustrating potential interactions between α-synuclein, Aβ, and tau pathology. Such additions would provide a more comprehensive representation of the multifactorial mechanisms contributing to cortical synaptic dysfunction and cognitive decline.

We thank the Reviewer for this constructive suggestion. We fully agree that acknowledging the multifactorial nature of cortical synaptic failure, including neuroinflammatory pathways, immunomodulation, and endolysosomal degradation, etc., that have been recognized throughout the manuscript provides a more accurate and comprehensive picture of α-synucleinopathies. However, to preserve the visual clarity of this schematic, we purposely maintained its strict focus on the specific alterations in cortical synaptic plasticity. To ensure your valuable point is properly addressed, we have instead expanded the legend to thoroughly detail the diverse factors converging in the transition from physiological to pathological α-Syn.

In summary, this is a well-written, informative, and timely review that addresses an important and emerging area of Parkinson’s disease research. The manuscript provides an excellent synthesis of evidence supporting the role of prefrontal cortical synaptopathy in cognitive dysfunction. Incorporating additional discussion of Aβ and tau co-pathology, α-synuclein cross-seeding mechanisms, neuroinflammatory pathways, and the current limitations of neuroplasticity-based therapeutic approaches would further strengthen the review and broaden its relevance to the field. Subject to revision, I believe the manuscript would make a valuable contribution to the literature.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have satisfactorily addressed the major concerns raised during review. The revised manuscript now provides a more balanced discussion of co-pathologies, neuroinflammatory mechanisms, limitations of current evidence, and the clinical heterogeneity among PD, PDD, and DLB. The revisions strengthen the manuscript and improve its translational relevance.