**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Luis O. Cabrera Hernandez, Center for Alzheimer’s and Neurodegenerative Diseases, Peter O’Donnell Jr. Brain Institute, University of Texas Southwestern Medical Center, Dallas, TX

**Main Body of the Abstract**
ATTR amyloidosis results from the deposition of the protein transthyretin (TTR) in various tissues, leading to organ failure and death. Despite growing awareness, diagnosing ATTR amyloidosis occurs at late stages when treatments are less beneficial. Previously, we found that preformed ATTR fibrils, or seeds, can template polymerization of soluble transthyretin, a process known as amyloid seeding (Saelices et al., 2018, PNAS). Our data suggest this process is a potential driver of disease at late stages. We hypothesize that understanding the molecular mechanisms behind ATTR aggregation in the absence or presence of preformed fibrils will enable the development of early diagnostics and additional strategies for treating late-stage ATTR amyloidosis. Here we aim to reproduce pathological amyloid seeding in vitro and determine the molecular structures of seeded fibrils using cryo-electron microscopy, as we previously performed (Nguyen, Singh, Afrin, et al., Nat Comm). We extracted ATTR fibrils from patients and used them to seed the formation of new fibrils from recombinant full-length TTR at different oligomeric states; these are monomeric TTR and tetrameric TTR-V30M and TTR-I84S. We confirmed amyloid fibril extraction using transmission electron microscopy. We monitored amyloid seeding using thioflavin T fluorescence and transmission electron microscopy. We screened and collected cryo-electron microscopy images of seeded fibrils and obtained their density maps. Our results show that full-length transthyretin can form fibrils with patient-derived seeds under physiological pH and denaturing conditions. This methodology shows potential in enabling studies on TTR aggregation and provides a new platform to develop clinical tools for ATTR amyloidosis.



**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Luis O. Cabrera Hernandez, Center for Alzheimer’s and Neurodegenerative Diseases, Peter O’Donnell Jr. Brain Institute, University of Texas Southwestern Medical Center, Dallas, TX

**Main Body of the Abstract**
ATTR amyloidosis results from the deposition of the protein transthyretin (TTR) in various tissues, leading to organ failure and death. Despite growing awareness, diagnosing ATTR amyloidosis occurs at late stages when treatments are less beneficial. Previously, we found that preformed ATTR fibrils, or _seeds_, can template polymerization of soluble transthyretin, a process known as _amyloid seeding_ (Saelices et al., 2018, PNAS). Our data suggest this process is a potential driver of disease at late stages. We hypothesize that understanding the molecular mechanisms behind ATTR aggregation in the absence or presence of preformed fibrils will enable the development of early diagnostics and additional strategies for treating late-stage ATTR amyloidosis. Here we aim to reproduce pathological amyloid seeding _in vitro_ and determine the molecular structures of seeded fibrils using cryo-electron microscopy, as we previously performed (Nguyen, Singh, Afrin, et al., Nat Comm). We extracted ATTR fibrils from patients and used them to seed the formation of new fibrils from recombinant full-length TTR at different oligomeric states; these are monomeric TTR and tetrameric TTR-V30M and TTR-I84S. We confirmed amyloid fibril extraction using transmission electron microscopy. We monitored amyloid seeding using thioflavin T fluorescence and transmission electron microscopy. We screened and collected cryo-electron microscopy images of seeded fibrils and obtained their density maps. Our results show that full-length transthyretin can form fibrils with patient-derived seeds under physiological pH and denaturing conditions. This methodology shows potential in enabling studies on TTR aggregation and provides a new platform to develop clinical tools for ATTR amyloidosis.



In vitro formation of amyloid fibrils from full-length transthyretin templated by ATTRv seeds PB14 (#370)

We invite you to attend the XIX International Symposium on Amyloidosis to be held in Rochester, MN.

This symposium is organized as a hybrid meeting (with the focus on in-person) held from Sunday, May 26 through Thursday, May 30, 2024.

Together with the ISA Board and members of Mayo Clinic, a very attractive scientific hybrid program is being planned. The program will cover a variety of types of systemic amyloidosis: ATTR (hereditary and wild-type), AL (light-chain), AA and less frequent forms. There will be key lectures, specific symposia including those company sponsored, oral presentations and poster sessions of accepted abstracts.

COURSE DESCRIPTION
This program will provide a comprehensive review of state-of-the-art education in systemic amyloidosis: basic science, pathophysiology, diagnosis, current and emerging treatments. Scientific presentations will include competitive oral and poster abstracts. The rapid evolution of scientific discovery and expanding treatment options has created tremendous interest in the field and this meeting will fill and important gap in educating scientists and clinicians.