Virender Singh

In the paper by Nguyen et al, published in Nature Communications in 2024 ¹ , we describe structural polymorphism in fibrils extracted from patients with ATTR amyloidosis. ATTR amyloidosis is characterized by deposition of transthyretin amyloid fibrils across multiple organs, resulting in marked phenotypic variability. Previous studies on ATTR suggest its phenotypic variability may be linked to differences in fibril structure, as demonstrated in amyloid diseases such as AA amyloidosis, tauopathies, or synucleinopathies ^2–4 . Thus far, most ATTR fibrils adopt a strikingly similar fold across patients and affected organs ^5–8 . The most notable exception is described in the study by Nguyen et al., where we report the identification of two co-existing polymorphs in cardiac fibrils from three patients with the ATTRv-I84S variant. These cardiac polymorphs differ in conformation of the segment Gly57 to Gly67, termed the gate , which regulates access to a central polar channel within the fibril core. In one polymorph, the gate adopts an open conformation, exposing the channel, whereas in the other it is closed, shielding it ¹ . Whether these polymorphs extend beyond cardiac tissue remains unknown. Here, we address this question by extending our analysis to additional organs from a fourth patient with ATTRv-I84S amyloidosis.

The immune system is a dynamic, energy-dependent network regulated by temporal biology. Advances in circadian biology have revealed that the molecular transcription–translation feedback loop coordinates approximately 15% of the human transcriptome, synchronizing metabolism, immune surveillance, tissue repair, and adaptation to environmental cycles. Here, we propose a metabolomic, endocrine, neurological chromodynamic model of immune health, based on time of day rhythms. Immune resilience is defined by synchronization among four “wheels”: i) the central circadian clocks, ii) food-entrainable metabolic oscillators, iii) peripheral cellular clocks, and iv) neuroimmune regulatory pathways. The model provides a framework to optimize these interconnected systems to maintain metabolic efficiency, minimize unnecessary inflammation, and enable precise immune responses through temporal gating. External factors of modern lifestyle disruptions, including irregular feeding patterns, sleep deprivation, and chronic stress, induce internal circadian desynchrony, contributing to persistent low-grade inflammation, metabolic dysfunction, immune aging, and chronic non-communicable diseases. We propose that immune health is characterized not merely by the absence of disease, but by stable circadian phase coherence, low inflammatory noise, and adaptive immune flexibility. A propose a panel of chrono-biomarkers of metabolomic and endocrine parameters, that may provide a functional assessment of immune resilience, defined by inflammatory tone, immune adaptability, metabolic integrity, and repair capacity. This framework integrates chronobiology, endocrine and immunometabolism to shift medicine from reactive disease management toward proactive assessment and restoration of biological resilience.

Hereditary apolipoprotein A-I (AApoA‑I) amyloidosis is a rare systemic disease caused by the deposition of amyloid fibrils formed by apolipoprotein A‑I in multiple organs, leading to severe clinical outcomes. With no available therapies or diagnostic tools, defining the structure of AApoA‑I fibrils is crucial to understanding disease mechanisms and guiding intervention. Here we use cryo-electron microscopy to analyze AApoA‑I fibrils from the heart, kidney, liver, and spleen of patients carrying G26R, L90P, and R173P mutations. G26R fibrils, regardless of organ, exhibits untwisted morphologies and cannot be resolved structurally. Conversely, L90P and R173P fibrils display a compact diabolo-shaped conformation in all organs analyzed. Their high-resolution maps enable visualization of cis -Proline 66, which may represent a potential conformational switch during fibril formation. Our findings suggest that mutation-driven polymorphism may influence organ tropism and clinical presentation. This work advances our understanding of AApoA‑I fibril assembly and provides insights toward developing targeted clinical tools.

ALECT2 amyloidosis is a rare systemic disease characterized by the pathological deposition of leukocyte cell-derived chemotaxin-2 (LECT2) as amyloid fibrils, primarily affecting the kidneys and liver. The molecular mechanisms underlying LECT2 aggregation remain poorly defined, hindering diagnostic and therapeutic development. Here, we present cryo-electron microscopy structures of ex-vivo ALECT2 fibrils extracted from a patient’s kidney. We identified three fibril polymorphs: a predominant single-protofilament morphology and two minor double-protofilament morphologies. The dominant single-protofilament morphology comprises the full-length 133-residue LECT2 protein and retains all three native disulfide bonds. Low-resolution reconstructions of double-protofilament morphologies suggest they adopt a similar fold to the single protofilament morphology, but form paired assemblies with different inter-filament interfaces. Mass spectrometry also reveals acetylation within the fibrils. These findings offer critical insights into the structural basis of ALECT2 amyloid formation and identify molecular features that could inform future diagnostic and therapeutic approaches.

ATTR amyloidosis is a phenotypically heterogeneous disease characterized by the pathological deposition of transthyretin in the form of amyloid fibrils into various organs. ATTR amyloidosis may result from mutations in variant (ATTRv) amyloidosis, or aging in wild-type (ATTRwt) amyloidosis. ATTRwt generally manifests as cardiomyopathy, whereas ATTRv may present as polyneuropathy, cardiomyopathy, or mixed, in combination with many other symptoms deriving from multisystem organ involvement. Over 220 different mutational variants of transthyretin have been identified, many of them being linked to specific disease symptoms. Yet, the role of these mutations in explaining differential disease manifestations remains unclear. Using cryo-electron microscopy, here we structurally characterized fibrils from the heart and the liver of an ATTRv patient carrying the V122∆ mutation, which is predominantly associated with polyneuropathy. Our results show that these fibrils are polymorphic, presenting as both single and double filaments. Our study alludes to a structural connection contributing to phenotypic variation in ATTR amyloidosis, as polymorphism in ATTR fibrils may manifest in patients with predominantly polyneuropathic phenotypes.

Summary: ATTR amyloidosis results from the systemic accumulation of wild-type (ATTRwt) or mutant (ATTRv) transthyretin amyloids, leading to multi-organ dysfunction and death. The disease exhibits variable pathology and penetrance, and its relationship with the amyloid structure remains unclear. Patients carrying the neuropathy-associated variants ATTRvI84S and ATTRv-V122Δ present polymorphic ATTR fibrils, in contrast to the consistent morphology reported for most ATTR fibrils to date. Here, we aim to elucidate a potential link between neuropathic symptomatology, distinct mutations, and amyloid structural diversity, using cryo-EM. We determined the ex-vivo fibril structures from the variants ATTRv-P24S, ATTRv-A25S, and ATTRv-D38A, whose patients presented variable clinical manifestations, including neuropathy. Our findings revealed that, despite differences in mutations and diverse clinical phenotypes, these variants share a common amyloid core previously identified in ATTRwt and several other cardiac ATTRv. This structural consistency is significant for the development of structure-guided diagnostic tools capable of addressing the diverse spectrum of ATTR amyloidosis. Highlights: Determines transthyretin amyloid structures of three human ATTRv by cryo-EM Determines the structure of three ex-vivo ATTRv fibrils linked to polyneuropathy. Reveals structural similarities of ATTRv amyloid cores. Reveals a common fold despite the different mutations and symptomatology. Contributes to the understanding of transthyretin aggregation in patients with diverse phenotypes

Immunoglobulin light chain (AL) amyloidosis is a systemic disorder caused by the misfolding and aggregation of free immunoglobulin light chains (LCs) secreted by abnormal plasma cells. The resulting amyloid fibrils deposit in multiple organs, leading to progressive dysfunction and increased morbidity and mortality. Despite recent advances, the molecular determinants of LC aggregation and phenotypic variability remain poorly understood. Structural characterization of ex-vivo fibrils provides key insights into these pathogenic processes. Here, we report cryo-electron microscopy structures of cardiac AL amyloid fibrils derived from an IGLV6 light chain. The fibrils display two distinct morphologies composed of single and double protofilaments, each adopting a previously unobserved fold. Comparison with previously reported AL fibril structures reveals that while individual mutations can alter the local conformation, IGLV6-derived fibrils share conserved structural motifs that may underlie common aggregation pathways. These findings expand the disease structural landscape and highlight sequence-dependent yet structurally constrained mechanisms of LC fibril formation.

ATTR amyloidosis results from the conversion of transthyretin into amyloid fibrils that deposit in tissues causing organ failure and death. This conversion is facilitated by mutations in ATTRv amyloidosis, or aging in ATTRwt amyloidosis. ATTRv amyloidosis exhibits extreme phenotypic variability, whereas ATTRwt amyloidosis presentation is consistent and predictable. Previously, we found unique structural variabilities in cardiac amyloid fibrils from polyneuropathic ATTRv-I84S patients. In contrast, cardiac fibrils from five genotypically different patients with cardiomyopathy or mixed phenotypes are structurally homogeneous. To understand fibril structure’s impact on phenotype, it is necessary to study the fibrils from multiple patients sharing genotype and phenotype. Here we show the cryo-electron microscopy structures of fibrils extracted from four cardiomyopathic ATTRwt amyloidosis patients. Our study confirms that they share identical conformations with minimal structural variability, consistent with their homogenous clinical presentation. Our study contributes to the understanding of ATTR amyloidosis biopathology and calls for further studies.

ATTR amyloidosis is a degenerative disorder characterized by the systemic deposition of the protein transthyretin. These amyloid aggregates of transthyretin (ATTR) can deposit in different parts of the body causing diverse clinical manifestations. Our laboratory aims to investigate a potential relationship between the different genotypes, organ of deposition, clinical phenotypes, and the structure of ATTR fibrils. Using cryo-electron microscopy, we have recently described how the neuropathic related mutations ATTRv-I84S and ATTRv-V122Δ can drive structural polymorphism in ex vivo fibrils. Here we question whether the mutation ATTRv-T60A, that commonly triggers cardiac and neuropathic symptoms, has a similar effect. To address this question, we extracted and determined the structure of ATTR-T60A fibrils from multiple organs (heart, thyroid, kidney, and liver) from the same patient and from the heart of two additional patients. We have found a consistent conformation among all the fibril structures, acquiring the “closed-gate morphology” previously found in ATTRwt and others ATTRv related to cardiac or mixed manifestations. The closed-gate morphology is composed by two segments of the protein that interact together forming a polar channel, where the residues glycine 57 to isoleucine 68 act as a gate of the polar cavity. Our study indicates that ATTR-T60A fibrils present in peripheral organs adopt the same structural conformation in all patients, regardless of the organ of deposition.