Reply to: Recent Advances in the Field of 3D Modelling for Neurodegeneration
We would like to congratulate Drs. Bolognin, Antony, and Schwamborn on their excellent publication regarding a 3D human neural cell culture model of PD. We are very excited to see that the 3D Matrigel-based cell culture system accelerates pathogenic cascades in hiPSC-derived PD neurons as we have shown with AD neurons (Choi et al., 2014). In our previous study, we showed that the 3D Matrigel cell culture system accelerated accumulation/aggregation of pathogenic amyloid beta species and also increased the expression of adult neural markers including adult 4-repeat tau isoform, which is crucial for developing robust tau pathology. It is quite interesting that the 3D Matrigel cell culture system also accelerated mitochondrial deficits and neuronal death in human PD iPSC-derived neurons. It is possible that similar mechanisms may play a role. Although α-synuclein aggregation was not detected in Dr. Bolognin’s 3D PD cellular model, we think it will be intriguing to check whether soluble pathogenic proteins, including extracellular alpha-synuclein, selectively accumulate in 3D Matrigel with PD iPSC-derived neurons.
We also agree with Dr. Bolognin that these new 3D human cellular models provide a new research tool to study the pathogenic mechanism of neurodegeneration in a human brain-like environment. However, many challenges lie ahead for comprehensively recapitulating brain conditions during human neurodegeneration: 1) mimicking aging aspects to 3D neural cell culture models; 2) precisely reconstituting brain structures that are damaged during neurodegeneration, as Dr. Bolognin addressed; 3) generating sporadic disease models; 4) adding neuroinflammatory elements. In an attempt to more precisely mimic the disease conditions, our lab, in collaboration with Dr. Cho’s lab at UNCC, recently developed 3D triculture models that mimic neuroinflammation in AD by adding human microglia cells into our 3D neuron-astrocyte AD models (Park et al., 2018). We think it will be interesting to find whether adding neuroinflammatory elements to 3D PD cellular models can further accelerate pathogenic cascades in PD iPSC-derived neurons.
Finally, we would like to briefly comment on implications of the 3D cell culture models for drug discovery. As pointed by Dr. Bolognin, there are many challenges to adapt self-assembling 3D organoid models into high-throughput drug screening system. However, ours and Dr. Bolognin’s 3D culture models can be easily adapted to large-scale drug testing since they do not need complex self-organization of neural stem cells. Although there are many limitations in current 3D neurodegeneration models, we strongly believe that some of the 3D models are already useful enough for drug screening.
-Doo Yeon Kim, Joseph Park, Mehdi Jorfi, Rudolph E. Tanzi
Choi, S.H., Kim, Y.H., Hebisch, M., Sliwinski, C., Lee, S., D'Avanzo, C., Chen, H., Hooli, B., Asselin, C., Muffat, J., et al. (2014). A three-dimensional human neural cell culture model of Alzheimer’s disease. Nature 515, 274–278.
Park, J., Wetzel, I., Marriott, I., Dréau, D., D'Avanzo, C., Kim, D.Y., Tanzi, R.E., and Cho, H. (2018). A 3D human triculture system modeling neurodegeneration and neuroinflammation in Alzheimer's disease. Nat Neurosci 21, 941–951.
Reply to: Prion Protein and Alzheimer's Disease
Zafar’s comments and the final questions she made regarding the interplay between Αβ and PrP are central in both AD and prion diseases. Recent research demonstrated that amyloid and prion can interact each other: however it is still unclear whether oligomeric Aβ (OAβ) influences PrP activity or, vice versa, PrP modulates Aβ aggregation and toxicity… or both. The concept of Aβ “strains” and their role in AD phenotypes is still undercover, and the PrP role in Aβ “strain” modulation is a relatively new and still unwritten history.
Alzheimer’s, compared to Prion, even considering its intrinsic variability, is a very different disease whose overall picture must necessarily consider some characters that are related to each other: presenilins, apolipoprotein E and AβPP. How PrP can be fitted in this framework is still controversial. It is interesting, from this point of view, the recent report by Pagano K. Et al.,  in which they show that PrP is able to differently interact with the forming Aβ oligomers, even with the highly toxic pyroglutamate-modified N-truncated isoform, driving their internalisation and toxicity. Besides, if OAβ induce neurotoxicity and Tau aggregation, why Aβ-based therapies failed? The elephant in the room in the AD field resides in the unclear pathological relationship between Aβ and Tau: how Aβ influences or induces Tau aggregation? Many hypothesis, but few certainty. There is a PrP effect on this? Is maybe PrP the link between Aβ and Tau? Although it is tempting to run on the easy road considering OAβ the direct target of PrP, it is rather more likely that the involvement of PrP in vesicles recycling and cell-signalling events would represent a more suitable path that group also the above mentioned characters of this abnormally intricate history [3,4].
 Tabaton M, Gambetti P. (2006) Soluble amyloid-beta in the brain: the scarlet pimpernel. J Alzheimers Dis 9(3 Suppl), 127-32
 Pagano K, Galante D, D'Arrigo C, Corsaro A, Nizzari M, Florio T, Molinari H, Tomaselli S, Ragona L. (2018) Effects of Prion protein on Aβ42 and pyroglutamate-modified AβpΕ3-42 oligomerization and toxicity. Mol Neurobiol Jul 6.[Epub ahead of print]
 Zafar S, Shafiq M, Younas N, Schmitz M, Ferrer I, Zerr I (2017) Prion protein interactome: identifying novel targets in slowly and rapidly progressive forms of Alzheimer's disease. J Alzheimers Dis 59, 265-275.
 Uchiyama K, Muramatsu N, Yano M, Usui T, Miyata H, Sakaguchi S. (2013) Prions disturb post-Golgi trafficking of membrane proteins. Nat Commun 4, 1846.
Reply to: Dr. Oskar Fischer’s Mysterious Little Alzheimer’s Germ
A 2018 study by Tricco et al. ranking the safety and effectiveness of the four leading drugs now taken to enhance concentration, memory, alertness and moods in, found that donepezil (Aricept®) was most likely to effectively improve cognition in patients with Alzheimer’s dementia. However, patients who took donepezil were more likely to experience side effects including nausea, vomiting and diarrhea than those who received a placebo, according to the study, published online in the Journal of the American Geriatrics Society . And an earlier study showed that almost 19% of patients in an Aricept 23 mg daily group discontinued treatment due to side effects . The fact is that as for all conventional drugs used in Alzheimer’s treatment –only a small percentage of AD victims are helped by them. Yet, in both the case of FDA approved and alternative treatments presently available, much can be gleaned by scrutinizing which pathogen or pathogens the bulk of their activity is directed towards. It seems that several compounds said to have effects upon the neuronal systems in Alzheimer’s may also exert influence through other mechanisms, such as antimicrobial actions.
Reference: Broxmeyer L. “Alzheimer’s FDA Approved Drugs & Alternatives: What are They Really Treating?” Current Opinions in Neurological Science 3.1 (2018): 613-623. DOI: 10.5281/zenodo.2247890. https://scientiaricerca.com/srcons/pdf/SRCONS-03-00085.pdf https://scientiaricerca.com/srcons/SRCONS-03-00085.php
Reply to: Dr. Oskar Fischer’s Mysterious Little Alzheimer’s Germ
It is always of critical importance to scrutinize biomedical studies for accuracy, especially those even suggesting benefits of novel applications for widely used medications. An example is a 2018 retrospective Taiwanese study in which Tzeng claims that patients with HSV infections ‘may have’ a 2.56-fold increased risk of developing dementia. Furthermore, and more appropriate to the title of his paper (Anti-herpetic Medications and Reduced Risk of Dementia in Patients with Herpes Simplex Virus Infections-a Nationwide, Population-Based Cohort Study in Taiwan), Tzeng claimed that the usage of anti-herpetic medications was associated with a decreased risk of dementia. However imperfections in the study suggest the need for a more controlled study. For example, in the HSV-group merely 13.7% (1147 in 8362) did not receive anti-herpetic medications.
Also, in January of 2006, Catherine Helmer first published a similar study: Herpes simplex virus, anti-herpetic medication, and dementia: Results from the three-city population-based cohort. But Helmer et al. concluded that their results regarding anti-herpetic medications were “not significant” for lessening dementia. Helmer presented this paper once again, this time for Alzheimer’s & Dementia in July, 2015.
Broxmeyer L, Perry G. Alzheimer’s: Do Anti-Herpetics Reduce the Risk of Dementia and if so, Why? Current Opinions in Neurological Science. 2:6 (2018):594-598. http://scientiaricerca.com/srcons/SRCONS-02-00082.php https://scientiaricerca.com/srcons/pdf/SRCONS-02-00082.pdf
Reply to: Chronic Traumatic Encephalopathy
We appreciate the thought-provoking letter by Dr. Jellinger in response to our original article, Chronic Traumatic Encephalopathy and Neurodegeneration in Contact Sports and American Football. It is only through constructive conversation that the study of CTE in sports can progress. Our manuscript focused primarily on American football, and we certainly omitted several key articles regarding CTE in boxers. As Dr. Jellinger states, many of the early studies of CTE, or “dementia pugilistica”, were conducted in boxers. In fact, these early boxing studies were far ahead of their time, as they foreshadow the same controversies with which we struggle a century later.
Perhaps the most scientifically prescient question raised in the autopsy studies of 20th century boxers is the occurrence of concomitant neurodegenerative pathology. Dr. Jellinger astutely states that early-onset Alzheimer pathology, neurofibrillary degeneration, and numerous comorbidities were all seen in postmortem boxing studies. Fast-forward to the 21st century, many notable studies of CTE in athletes report the same concomitant neuropathology [1-4]. Mixed neurodegenerative pathology was seen in 17 of 50 football players in a 2013 convenience sample , 20 of 21 athletes in a study of the Mayo Clinic Jacksonville Brain Bank, and 32 of 111 athletes in a larger convenience sample. The high prevalence of concomitant neuropathology leaves us with many unanswered questions, the answers to which may drastically alter the narrative of CTE in sports:
1) Is the single phosphorylated-tau (p-tau) lesion at the depths of cortical sulci required to diagnose CTE independent of or related to other neurodegenerative disease processes? Similarly, is CTE truly its own disease, or part of a cascade of pathologic changes from other neurodegenerative disorders?
2) Is there truly a clinicopathological correlation between neurobehavioral antemortem clinical presentations and postmortem pathological findings?
3) Which disease comes first, CTE or the concomitant neurodegenerative finding(s)?
4) Is it in fact established by an international neuropathology consensus that the presence of CTE pathology diagnostically supersedes the presence of other neuropathology?
5) Is there international neuropathology consensus that relative amounts of neuropathology are required to arrive at a primary neuropathological diagnosis?
We wholeheartedly agree with Dr. Jellinger’s assertion, that, “…despite extensive research, neither the etiopathogenesis of CTE nor that of AD are fully understood yet.” If the answers to some of these questions are clarified in coming years, the lens with which we view head impacts in sport may be dramatically changed. At the same time, when such crucial information remains to be elucidated, one is left wondering how the public and select research experts can view a hypothesis with so many remaining questions and unclear answers as resolved with complete certainty.
Scott L. Zuckerman, MD, MPH
Benjamin L. Brett, PhD
Aaron Jeckell, MD
Aaron M. Yengo-Kahn, MD
Gary S. Solomon, PhD
 Hazrati LN, Tartaglia MC, Diamandis P, Davis KD, Green RE, Wennberg R, Wong JC, Ezerins L, Tator CH (2013) Absence of chronic traumatic encephalopathy in retired football players with multiple concussions and neurological symptomatology. Front Hum Neurosci 7, 222.
 McKee AC, Stern RA, Nowinski CJ, Stein TD, Alvarez VE, Daneshvar DH, Lee HS, Wojtowicz SM, Hall G, Baugh CM, Riley DO, Kubilus CA, Cormier KA, Jacobs MA, Martin BR, Abraham CR, Ikezu T, Reichard RR, Wolozin BL, Budson AE, Goldstein LE, Kowall NW, Cantu RC (2013) The spectrum of disease in chronic traumatic encephalopathy. Brain 136, 43-64.
 Bieniek KF, Ross OA, Cormier KA, Walton RL, Soto-Ortolaza A, Johnston AE, DeSaro P, Boylan KB, Graff-Radford NR, Wszolek ZK, Rademakers R, Boeve BF, McKee AC, Dickson DW (2015) Chronic traumatic encephalopathy pathology in a neurodegenerative disorders brain bank. Acta Neuropathol 130, 877-889.
 Mez J, Daneshvar DH, Kiernan PT, Abdolmohammadi B, Alvarez VE, Huber BR, Alosco ML, Solomon TM, Nowinski CJ, McHale L, Cormier KA, Kubilus CA, Martin BM, Murphy L, Baugh CM, Montenigro PH, Chaisson CE, Tripodis Y, Kowall NW, Weuve J, McClean MD, Cantu RC, Goldstein LE, Katz DI, Stern RA, Stein TD, McKee AC (2017) Clinicopathological evaluation of chronic traumatic encephalopathy in players of American football. JAMA 318, 360-370.
Reply to: Prion Protein and Alzheimer's Disease
Zafar’s blog discussing the involvement of prion protein in Alzheimer’s disease (AD) is pertinent after pioneering descriptions of PrPC co-localization with β-amyloid in amyloid plaques in AD .
Although those preliminary studies suggested that β-amyloid was likely not bound to PrP, subsequent studies have identified fine interactions of these proteins which have implications in the pathogenesis of the disease. Moreover, interactions of PrPC are not limited to β-amyloid but interactions also implicate other proteins as α-synuclein and tau.
Several membrane receptors can bind to oligomeric β-amyloid (Aβo). Among these receptors, PrPC interacts with Aβo neurotoxic species; the N-terminal residues 23-27 and the CC2 region (amino acids 94-110) of PrPC are relevant for PrPC interactions with Aβo, as the removal of any of these regions results in a reduction of PrPC/Aβo binding. In addition, the C-terminal domain (aa 120-144) of PrPC participates in Aβ fibril formation. In parallel, binding Aβo to PrPC also triggers an increase in tau phosphorylation.
PrPC is also a binding partner of α-synuclein and modulates α-synuclein neuronal spreading: the absence of PrPC decreases α-synuclein spreading in vivo, whereas PrPC over-expression enhances α-synuclein spreading and α-synuclein phosphorylation. Aβo and α-synuclein share the CC2 domain of PrPC as a binding domain .
Strong interplay among α-synuclein, tau and Aβ may synergistically promote shared seeding. The identification of PrPC as a receptor for Aβo and α-synuclein opens new avenues for drug discovery.
 Ferrer I, Blanco R, Carmona M, Puig B, Ribera R, Rey MJ, Ribalta T (2001) Prion protein expression in senile plaques in Alzheimer's disease. Acta Neuropathol 101, 49-56.
 del Río JA, Ferrer I, Gavín R (2018) Role of cellular prion protein in interneuronal amyloid transmission. Progr Neurobiol 165-167, 87-102.