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Biology subjects

Leonardi, C.

Publications and source records attributed to Leonardi, C..

4 recordsLinked to original sources

Multi-scale modeling of human tissues from spatial transcriptomics with TERRA

Spatial transcriptomics maps gene expression at cellular resolution, revealing how cells organize into multicellular niches. Yet computational analyses remain dataset-specific, without a transferable representation of tissue organization that generalizes across datasets, tasks and tissues or predicts how tissues behave under perturbation. We present TERRA, a foundation model pretrained on 112 million human cells profiled by spatial transcriptomics. From a single pretrained backbone, TERRA yields embeddings at the scale of cells, the genes they express and the neighborhoods in which they reside, and supports spatial in silico perturbation, all applied zero-shot to unseen tissues. At the cell level, in newly generated spatial data for developing pancreas, TERRA identified an islet-associated capillary state which we posit represents a developmental precursor of the mature islet microvasculature. At the gene level, in untreated kidney sections, in silico knockout of immune-checkpoint targets predicted a gene program of immune-checkpoint-blockade-associated nephrotoxicity, which we validated in treatment-exposed tissue and recovered in blood. At the neighborhood level, TERRA mapped macrophages across tissues to identify recurring cross-organ niches, which we term archetypes, including a tumor-boundary niche associated with poor prognosis in kidney cancer. Together, TERRA captures the spatial and multicellular logic of human tissue and predicts, in silico, its response to perturbation, providing a multi-scale framework for tissue biology, therapeutic development and clinical application.

genomics↗

Self-supervised learning for a gene program-centric view of cell states

Single-cell omics has extended the biological interrogation of cell state from examining the expression of individual genes to unbiased profiling of tens of thousands of genes at once. However, extracting biological insights from such high-dimensional data remains challenging. To enable downstream analyses, many computational approaches compress cell state into a single latent representation. This can obscure the structure of underlying gene programs (GP), defined as coordinated sets of biologically related genes, such as signalling pathway response modules or transcription factor targets. Here, we present Tripso, a self-supervised transformer deep learning model which learns multiple GP-specific embeddings from predefined GPs, while also enabling the discovery of novel, data-driven GPs. Tripso facilitates principled comparisons across development, disease, and experimental systems. Firstly, in a dataset of human hematopoietic cells spanning prenatal development through adulthood and aging and including newly generated data, Tripso resolved age-specific GP patterns, including elevated JAK-STAT activity in pediatric hematopoietic cells and postnatal shifts in IKZF1 GP activity during B cell differentiation. Secondly, leveraging Tripso GP embeddings and comparing in vivo to in vitro data, we hypothesized and experimentally validated that inhibition of the SEC61 translocon improved maintenance of hematopoietic stem cells in culture. Finally, Tripsos capacity for data-driven GP discovery revealed a previously uncharacterized tissue-resident memory T cell GP with increased activity in atopic dermatitis. Its spatial co-localization with sebaceous gland-associated immune niches was demonstrated in spatial transcriptomic and proteomic data. Thus, by moving beyond single embeddings of cellular states, Tripso enables interpretable and actionable discoveries, demonstrating how GP-centric modelling can generate hypotheses with substantial biomedical relevance. By anchoring cellular representations in meaningful GPs, Tripso establishes a principled and biologically grounded framework towards the development of interpretable virtual cell models.

bioinformatics↗

Tau catalyzes amyloid-β aggregation in a fold-dependent manner

Interactions between amyloidogenic proteins are emerging as critical drivers of neurodegenerative diseases, yet the molecular mechanisms remain poorly understood. In Alzheimers disease (AD) and chronic traumatic encephalopathy (CTE), co-deposition of tau and amyloid-{beta} (A{beta}) leads to accelerated disease progression. Here, we investigated the direct interaction between A{beta} and tau, combining in vitro reconstruction, computational modeling, and in vivo models. We show that tau aggregates with AD paired helical filament (PHF) and CTE folds catalyze the primary nucleation of A{beta}42 in a fold-specific manner, through an enzyme-like kinetic with recognition mechanisms. CTE fibrils exhibit the highest catalytic activity, also constraining A{beta}42 polymorphism. PHF and CTE tau fibrils increase A{beta}42 toxicity in SH-SY5Y neuroblastoma cells and transgenic Caenorhabditis elegans. Catalytic heterotypic interactions between amyloidogenic proteins offer new insights into the pathological mechanisms of multiple proteinopathies. The mechanisms described here may guide the structure-based design of new therapeutic agents targeting specific amyloidogenic interactions.

biochemistry↗

Elucidating the mechanism of cyclodextrins in the treatment of Niemann-Pick Disease Type C using crosslinked 2-hydroxypropyl-β-cyclodextrin

Niemann-Pick Disease Type C (NPC) is a severe neurovisceral disorder that is pathophysiologically characterized by intracellular transport abnormalities leading to cytoplasmic accumulation of lipids such as cholesterol and multiple sphingolipids, including sphingosine. The compound 2-hydroxypropyl-{beta}-cyclodextrin (HP{beta}CD) is a compound with high cholesterol complexation capacity and is currently under clinical investigation for the treatment of NPC. However, due to its short blood half-life, high doses are required to produce a therapeutic effect. It has been reported in mice that HP{beta}CDs circulation time and efficacy can be improved by increasing its size via polymerization, but the biodegradable nature of these systems did not allow the contribution of the macromolecule to the activity to be determined. In this work, stable forms of polymerized HP{beta}CD were generated (via epichlorohydrin crosslinking) to investigate their in vitro mechanisms of action and in vivo effects. Crosslinked CDs (8-312 kDa) displayed a 10-fold greater complexation capacity towards cholesterol than monomeric HP{beta}CD but were taken up by cells to a lower extent (in a size-dependent fashion), resulting in an overall comparable in vitro effect on intracellular cholesterol accumulation that was dependent on cholesterol complexation. When tested in vivo, the crosslinked 19.3 kDa HP{beta}CD exhibited a longer terminal half-life than the monomeric HP{beta}CD. However, it did not increase the life span of Npc1 mice, possibly due to reduced organ penetration and brain diffusion consequence of its large molecular weight. This could be circumvented by the application of magnetic resonance imaging-guided low intensity-pulsed focused ultrasound (MRIg-FUS), which increased the brain penetration of the CD. In conclusion, stable forms of polymerized HP{beta}CD constitute valuable tools to elucidate CDs mechanism of action. Moreover, the use of MRIg-FUS to maximize CDs tissue penetration warrants further investigation, as it may be key to harnessing CDs full therapeutic potential in the treatment of NPC. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=107 SRC="FIGDIR/small/230136v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@3dbaf1org.highwire.dtl.DTLVardef@bc255dorg.highwire.dtl.DTLVardef@390e7borg.highwire.dtl.DTLVardef@1e5e5c5_HPS_FORMAT_FIGEXP M_FIG C_FIG The 2-hydroxypropyl-{beta}-cyclodextrin (HP{beta}CD) is a well-established pharmaceutical excipient that can complex cholesterol and is currently under clinical investigation to treat Niemann-Pick Disease Type C (NPC). However, high doses of the drug are needed to achieve a therapeutic effect. Using stable and long circulating crosslinked HP{beta}CDs, this study attempts to further understand the mechanisms behind CDs activity.

pharmacology and toxicology↗