Biology subjects

Zec, K.

Publications and source records attributed to Zec, K..

4 recordsLinked to original sources

bioRxiv2025

The synovial lining macrophage layer develops in the first weeks of life in a CSF1- and TGFβ- dependent but monocyte-independent process.

Synovial joints harbor a protective lining layer, consisting of fibroblasts and macrophages, which form an epithelial-like barrier. In inflamed joints, lining macrophages regulate both early inflammatory cell influx and resolution. Despite these critical functions, it is currently unknown at what stage during development the synovial macrophage lining is established, and which signals drive this process. Here, we use a combination of genetic models and in vivo perturbations, single cell transcriptomics and imaging to delineate the process of lining formation in mice. We find that the synovial lining is immature at birth and becomes established within the first 3 weeks of life. In this window, the lining is gradually populated with macrophages that originate from fetal sources, proliferate and acquire the lining-specific transcriptional identity. In contrast, monocytes contribute only minimally to the developing lining, and their input remains limited in healthy adulthood. We identify CSF1 and TGF{beta} as key signals in this process, which also involves mechanosensing through PIEZO1. Our study thus identifies the early postnatal window as a critical period for lining macrophage development, with potential lifelong impact on joint health and disease.

immunology↗

bioRxiv2025

Perivascular RELM-positive synovial macrophages recruit monocytes at the onset of inflammatory arthritis

Macrophages, monocytes and neutrophils are major types of myeloid cells involved in inflammatory diseases, such as rheumatoid arthritis (RA). Recent scRNA-seq studies identified a remarkable diversity of synovial macrophages but, with the exception of lining macrophages, their geographical location and specific roles remain largely unexplored. Here, we localised the RELM-positive macrophages, predicted to produce high levels of monocyte-recruiting chemokines, to the synovial interstitium and more specifically, to the vicinity of interstitial blood vessels. Using complementary reporter mouse models, CCL2mCherry to label CCL2-producing cells, and CCR2CRE/mKate2 marking CCR2 expressing monocytes, we demonstrated that RELM-positive perivascular macrophages secrete CCL2 to recruit monocytes predominantly to the synovial interstitium at the onset of antigen-induced arthritis. The inflamed synovial environment guides the differentiation of the recruited monocytes into tissue-resident macrophages, including but not limited to macrophages expressing VSIG4, a characteristic marker of lining macrophages. Thus, RELM-positive macrophages orchestrate monocyte recruitment to the synovium during articular inflammation, contributing to a local replenishment of synovial lining macrophages.

immunology↗

bioRxiv2024

Autophagy acts as a brake on obesity-related fibrosis by controlling purine nucleoside signalling

A hallmark of obesity is a pathological expansion of white adipose tissue (WAT), accompanied by marked tissue dysfunction and fibrosis. Autophagy promotes adipocyte differentiation and lipid homeostasis, but its role in obese adipocytes and adipose tissue dysfunction remains incompletely understood. Here, we demonstrate that autophagy is a key tissue-specific regulator of WAT remodelling in diet-induced obesity. Importantly, loss of adipocyte autophagy substantially exacerbates pericellular fibrosis in visceral WAT. Change in WAT architecture correlates with increased infiltration of macrophages with tissue-reparative, fibrotic features. We uncover that autophagy regulates purine nucleoside metabolism in obese adipocytes, preventing excessive release of the purine catabolites xanthine and hypoxanthine. Purines signal cell-extrinsically for fibrosis by driving macrophage polarisation towards a tissue reparative phenotype. Our findings reveal a novel role for adipocyte autophagy in regulating tissue purine nucleoside metabolism, thereby limiting obesity-associated fibrosis and maintaining the functional integrity of visceral WAT. Purine signals may serve as a critical balance checkpoint and therapeutic target in fibrotic diseases.

cell biology↗

bioRxiv2022

LAT1 enables T cell activation under inflammatory conditions: a new therapeutic target for rheumatoid arthritis

ObjectiveTo assess the L-type amino acid transporter-1 (LAT1) as a possible therapeutic target for rheumatoid arthritis (RA). MethodsSynovial LAT1 expression was monitored by immunohistochemistry and transcriptomic datasets. The contribution of LAT1 to gene expression and immune synapse formation was assessed by RNA-sequencing and total internal reflection fluorescent (TIRF) microscopy, respectively. Mouse models of RA were used to assess the impact of therapeutic targeting of LAT1. ResultsLAT1 was strongly expressed by CD4+ T cells in the synovial membrane of patients with active RA and the level of expression correlated with levels of ESR and CRP as well as DAS-28 scores. Deletion of LAT1 in murine CD4+ T cells inhibited the development of experimental arthritis and prevented the differentiation of CD4+ T cells expressing IFN-{gamma} and TNF-, without affecting regulatory T cells. LAT1 deficient CD4+ T cells demonstrated reduced transcription of genes associated with TCR/CD28 signalling, including Akt1, Akt2, Nfatc2, Nfkb1 and Nfkb2. Functional studies using TIRF microscopy revealed a significant impairment of immune synapse formation with reduced recruitment of CD3{zeta} and phospho-tyrosine signalling molecules in LAT1 deficient CD4+ T cells from the inflamed joints but not the draining lymph nodes of arthritic mice. Finally, it was shown that a small molecule LAT1 inhibitor, currently undergoing clinical trials in man, was highly effective in treating experimental arthritis in mice. ConclusionsIt was concluded that LAT1 plays a critical role in activation of pathogenic T cell subsets under inflammatory conditions and represents a promising new therapeutic target for RA. Key MessagesO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LILAT1 is an amino acid transporter that has previously been shown to play a role in T cell activation. C_LI What does this study add?O_LILAT1 is expressed by synovial T cells in human rheumatoid arthritis and the level of expression correlates with disease severity. C_LIO_LILAT1 expression by T cells is necessary for development of severe arthritis in animal models. C_LIO_LILAT1 is required for immune synapse formation and activation of pathogenic CD4+ T cell subsets in the inflamed joint, but not the lymph nodes. C_LIO_LIA small molecular weight LAT1 inhibitor, currently in clinical trials for cancer, is highly effective in animal models of rheumatoid arthritis. C_LI How might this impact on clinical practice of future developments?O_LIThe context-specific nature of LAT1 involvement in T cell activation positions it as an ideal therapeutic target to distinguish between pathogenic and protective T cell responses and this study provides the scientific rationale for clinical evaluation of LAT1 inhibitors in the treatment of rheumatoid arthritis. C_LI

immunology↗