Biology subjects

Girard, T.

Publications and source records attributed to Girard, T..

5 recordsLinked to original sources

bioRxiv2026

TNFα drives platelet hyperreactivity and thromboinflammation through regulation of hematopoietic stem and progenitor cells.

TNF is the primary age-related cytokine responsible for hyperreactive platelet formation. In mouse models, increased TNF induced abnormal megakaryocyte development and platelet activity. Here, we extend these findings to demonstrate that TNF drives this thrombotic phenotype through expansion of the hematopoietic stem and progenitor cell (HSPCs) compartment. Using HSPC-specific TNF receptor labeling and single cell RNA sequencing, we found that TNF receptors are absent from megakaryocytes and their progenitors (MkPs) indicating that TNF does not directly act on these cells. Chronic TNF exposure expanded HSPCs in the bone marrow and extramedullary tissues - and these expanded HSPCs retained functional repopulation capacity. Using species-specificity TNF receptor activation, we further demonstrate that TNFR1 signaling is sufficient to induce platelet hyperreactivity independent of HSPC expansion. Unlike emergency hematopoiesis, chronic TNF promoted megakaryopoiesis through the canonical hematopoietic hierarchy as demonstrated by lineage-tracing studies. Mechanistically, chronic TNF induced a distinct transcriptional program in single cell RNA sequencing of HSPCs and megakaryocytes. Together, these findings establish that chronic TNF promotes hyperreactive platelet formation not through direct effects on megakaryocytes or MkPs but by expanding and transcriptionally reprogramming HSPCs, thereby imprinting a TNF dependent program that persists through megakaryopoiesis and ultimately produces hyperreactive platelets.

cell biology↗

bioRxiv2024

Advancing Liver Gene Therapy: Enhanced Transduction with GalNAc-Bioconjugated rAAV Capsids

This study investigates novel approaches to improve targeted gene delivery to the liver, a crucial organ for metabolic processes that faces vulnerabilities from various pathologies. Adeno-associated virus (AAV)-based gene therapy has emerged as a promising approach for liver targeting, with numerous investigational avenues. However, administration of high doses of AAV vectors present safety concerns, often requiring the use of corticosteroids and immunosuppression to mitigate immune adverse events. To address this, substantial efforts are underway to engineer optimized capsids to enhance the efficiency and specificity of recombinant AAV (rAAV) targeting hepatocytes, aiming to reduce required dosages. In this study, we employed bioconjugation chemistry to target the Asialoglycoprotein receptor (ASGPR), a C-type lectin abundantly expressed at the surface of hepatocyte membranes. We demonstrated that covalently attaching carbohydrates derived from GalNAc (a known ASGPR ligand) to lysine amino-acids on the rAAV2 capsid significantly enhanced in vivo liver transduction efficiency in mice. These optimized vectors present a promising avenue for the treatment of a spectrum of liver diseases, providing an alternative solution within the framework of liver gene therapy.

bioengineering↗

bioRxiv2022

Updated Variant Curation Expert Panel Criteria and Pathogenicity Classifications for 251 Variants for RYR1-related Malignant Hyperthermia Susceptibility

The ClinGen malignant hyperthermia susceptibility (MHS) variant curation expert panel specified the ACMG/AMP criteria for RYR1-related MHS and a pilot analysis of 84 variants was published. We have now classified an additional 251 variants for RYR1-related MHS according to current ClinGen standards and updated the criteria where necessary. Criterion PS4 was modified such that individuals with multiple RYR1 variants classified as pathogenic (P), likely pathogenic (LP) or variant of uncertain significance (VUS) were not considered as providing evidence for pathogenicity. Critera PS1 and PM5 were revised to consider LP variants at the same amino acid residue as providing evidence for pathogenicity at reduced strength. Finally, PM1 was revised such that if PS1 or PM5 are used PM1, if applicable, should be downgraded to supporting. Of the 251 RYR1 variants, 42 were classified as P/LP, 16 as B/LB, and 193 as VUS. The primary driver of 176 VUS classifications was insufficient evidence supporting pathogenicity, rather than evidence against pathogenicity. Functional data supporting PS3/BS3 was identified for only 13 variants. Based on the posterior probabilities of pathogenicity and variant frequencies in gnomAD, we estimated the prevalence of individuals with RYR1-related MHS pathogenic variants to be between 1/300 and 1/1,075, considerably higher than current estimates. We have updated ACMG/AMP criteria for RYR1-related MHS and classified 251 variants. We suggest that prioritization of functional studies is needed to resolve the large number of VUS classifications and allow for appropriate risk assessment. RYR1-related MHS pathogenic variants are likely to be more common than currently appreciated.

genetics↗

bioRxiv2022

Aquatic long-term persistence of Francisella tularensis ssp. holarctica is driven by water temperature and transition to a viable but non-culturable state

Francisella tularensis is a highly virulent bacterium causing tularemia zoonosis. An increasing proportion of infections occur through contaminated hydro-telluric sources, especially for the subspecies holarctica (Fth). Although this bacterium has been detected in several aquatic environments, the mechanisms of its long-term persistence in water are not yet elucidated. We evaluated the culturability and the viability of a virulent Fth strain in independent microcosms filled with nutrient-poor water. At 37{degrees}C, the bacteria remained culturable for only one week, while culturability was extended to 6 weeks at 18{degrees}C and up to 11 weeks at 4{degrees}C. However, while the viability of the bacteria declined similarly to culturability at 37{degrees}C, the viability of the bacteria remained stable overtime at 18{degrees}C and 4{degrees}C for more than 24 months, long after loss of culturability. We identified water temperature as one of the major factors driving the aquatic survival of Fth through a transition of the whole Fth population in a viable but non-culturable (VBNC) state. Low temperature of water ([≤]18{degrees}C) favors the persistence of the bacteria in a VBNC state, while a temperature above 30{degrees}C kills culturable and VBNC Fth bacteria. These findings provide new insights into the environmental cycle of Francisella tularensis that suggest that the yet unidentified primary reservoir of the subspecies holarctica may be the aquatic environment itself in which the bacteria could persist for months or years without the need for a host.

microbiology↗

bioRxiv2020

Variant Curation Expert Panel Recommendations for RYR1 Pathogenicity Assertions in Malignant Hyperthermia Susceptibility

PurposePrevention of malignant hyperthermia (MH) requires an understanding of RYR1 variant pathogenicity to assess the risk of exposure to triggering agents. Personalized medicine, especially secondary findings and eventually genomic screening, will contribute toward this goal. MethodsWe specified ACMG/AMP criteria for variant interpretation for RYR1 and MH. Proposed rules were piloted on 84 variants. We applied quantitative evidence calibration for several criteria using likelihood ratios based on the Bayesian framework. ResultsSeven ACMG/AMP criteria were adopted without changes, ten were adopted with RYR1-specific modifications, and nine were dropped. The in silico (PP3 and BP4) and hot spot criteria (PM1) were evaluated quantitatively. REVEL gave an OR of 23:1 for PP3 and 16:1 for BP4 using trichotomized cut-offs of >0.85 (pathogenic) and <0.5 (benign). The PM1 hotspot criterion had an OR of 24:1. PP3 and PM1 were implemented at moderate strength. Applying the revised ACMG criteria to 44 recognized MH variants, 30 were assessed as pathogenic, 12 as likely pathogenic, and two as VUS. ConclusionCuration of these variants will facilitate interpretation of RYR1/MH genomic testing results, which is especially important for secondary findings analyses. Our approach to quantitatively calibrating criteria are generalizable to other variant curation expert panels.

genetics↗