Biology subjects

Sharda, A.

Publications and source records attributed to Sharda, A..

3 recordsLinked to original sources

bioRxiv2025

Differentiation stage-specific use of cap-independent and cap-dependent translation initiation in hematopoiesis

Cell stress can increase the use of m7G-cap-independent, IRES-mediated translation initiation relative to cap-dependent translation (IRES/Cap). Reporters that quantify IRES/Cap have demonstrated differential activity across cultured cell types and stress conditions. By generating an IRES/Cap reporter mouse, we were able to systematically evaluate IRES/Cap across distinct tissues and cell types during physiological stresses and lineage commitment. Caloric stress invoked the expected boost in IRES/Cap translation regardless of differentiation state, but unexpectedly IRES/Cap progressively increased during hematopoietic and epithelial (hair follicle) differentiation under normal, homeostatic conditions. This was independent of total protein output or cell cycle. Even within cells of a given differentiation state, cells with lower relative-IRES utilization had markedly higher multipotent capability in vivo. The RNA processing protein PTBP1 is a mediator of this translation initiation preference. Therefore, low IRES/Cap is a signature of high stemness and suggests modulation of translation initiation participates in cell differentiation state.

developmental biology↗

bioRxiv2025

Human progenitor T-cell differentiation regulated by the mechanical resistance of thymus-mimetic extracellular matrices

Therapeutic T-cell engineering ex vivo from human hematopoietic stem cells (HSCs) focuses on recapitulating notch1-signaling and 4{beta}1-integrin-mediated adhesion within the thymic niche with supportive stromal cell feeder-layers or surface-immobilized recombinant protein-based engineered thymic niches (ETNs). The relevant Notch1-DLL-4 and 4{beta}1-integrin-VCAM-1 interactions are known to respond to mechanical forces that regulate their bond dissociation behaviors and downstream signal transduction, yet manipulating the mechanosensitive features of these key receptor-ligand interactions in thymopoiesis has been largely ignored in current ETN designs. Here, we demonstrate that human T-cell development from cord blood-derived CD34+ HSCs is regulated via molecular cooperativity in notch1 and integrin-mediated mechanotransduction. Mechanically confining interpenetrating network (IPN) hydrogel-based 3D cell culture comprised of collagen type I and alginate polysaccharides functionalized with DLL-4 and VCAM-1 is used as a model viscoelastic 3D ETN to manipulate human progenitor (pro)T-cell differentiation. This ETN enables orthogonal control of the mechanical and biomolecular features of the thymic niche, including thymopoietic ligand density, modulus, and viscoelastic properties (e.g., stress relaxation kinetics). We identify that soft, viscous matrices that enhance activation of the notch1-pathway, and subsequently notch1 intracellular domain (NICD) nuclear import sustain the T-cell development gene regulatory network during proT-cell differentiation. Conversely, stiff, elastic matrices inhibit HSC commitment to the T-lineage, and rather promotes Myeloid-cell differentiation. Our observations indicate mechanical reciprocity in signaling pathways indispensable to thymopoiesis, and highlights extracellular matrix mechanics as a variable in controlling hematopoietic stem cell fate decisions.

bioengineering↗

bioRxiv2024

Congenital T cell activation impairs transitional to follicular B cell maturation in humans

CTLA4-deficient patients exhibit profound humoral immune dysfunction, yet the basis for the B cell defect is not known. We observed a marked reduction in transitional to follicular B cell development in CTLA4-deficient patients, correlating with decreased CTLA4 function in regulatory T cells and increased mTORC1 signaling in transitional B cells. Treatment of transitional B cells with CD40L was sufficient to induce mTORC1 signaling and inhibit follicular B cell maturation in vitro. Frequent cell-cell contacts between CD40L+ T cells and naive IgD+CD27- B cells were observed in patient lymph nodes. Follicular B cell maturation in CTLA-deficient patients was partially rescued following CTLA4 replacement therapy in vivo. We conclude that functional regulatory T cells and the containment of excessive T cell activation are required for follicular B cells to mature and attain metabolic quiescence and thus acquire a state of immunological self-tolerance. One Sentence SummaryCongenital T cell activation in CTLA4-deficient patients impairs transitional to follicular B cell maturation and can be rescued by CTLA4 replacement therapy in vivo.

immunology↗