Housseau, Franck

Abstract Cellular senescence is a state of permanent growth arrest that plays an important role in wound healing, tissue fibrosis, and tumor suppression. Despite senescent cells’ (SnC) pathological role and therapeutic interest, their phenotype in vivo remains poorly defined. Here, we developed an in vivoderived senescence signature using a foreign body response (FBR) fibrosis model in a SnC reporter mouse. We identified pericytes and “cartilage-like” fibroblasts as senescent and defined cell typespecific senescence associated secretory phenotypes (SASP). Transfer learning and senescence scoring identified these two SnC populations along with endothelial and epithelial SnCs in new and publicly available murine and human data single cell RNAseq (scRNAseq) datasets from diverse pathologies. Signaling analysis uncovered crosstalk between SnCs and myeloid cells via an IL34- CSF1R-TGFßR signaling axis, contributing to tissue balance of vascularization and matrix production. Overall, our study provides a senescence signature and a computational approach that may be broadly applied to identify transcriptional profiles and SASP factors produced by SnCs that regulate tissue structure and pathology.

B7-DC is a recently discovered member of the B7 family that binds to PD-1 and is selectively expressed by dendritic cells (DCs). It has been shown to either costimulate or inhibit T cell responses. To assess the role of B7-DC in DC–T cell interactions, DCs from B7-DC knockout (KO) mice were generated and compared with DCs from wild-type (WT) and B7–1/B7–2 double KO mice. B7–1/B7–2–deficient DCs, while strongly diminished in their ability to stimulate naive CD4+ T cells, nonetheless retain partial activity. DCs from B7-DC KO mice are diminished in their ability to activate CD4+ T cells, demonstrating that DC-expressed B7-DC serves a predominantly stimulatory rather than inhibitory function in the initiation of T cell responses. B7-DC costimulates expression of CD40L with faster kinetics than B7–1 and displays potent synergy with B7–1 and B7–2 for T cell proliferation and cytokine production, indicating that these B7 family members work in concert to stimulate T cells. Finally, costimulation with B7-DC alone or in conjunction with B7–1 is PD-1 independent, indicating that B7-DC costimulates T cells via a second receptor.