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The role of liver X receptors (LXR) in rheumatoid arthritis (RA) remains controversial. We studied the effect of LXR agonists on fibroblast‐like synoviocytes (FLS) from RA patients and the K/BxN arthritis model in LXRα and β double‐deficient (Nr1h2/3−/−) mice. Two synthetic LXR agonists, GW3965 and T0901317, were used to activate LXRs and investigate their effects on cell growth, proliferation and matrix metalloproteinases, and chemokine production in cultured FLS from RA patients. The murine model K/BxN serum transfer of inflammatory arthritis in Nr1h2/3−/− animals was used to investigate the role of LXRs on joint inflammation in vivo. LXR agonists inhibited the FLS proliferative capacity in response to TNF, the chemokine‐induced migration, the collagenase activity in FLS supernatant and FLS CXCL12 production. In the K/BxN mouse model, Nr1h2/3−/− animals showed aggravated arthritis, histological inflammation, and joint destruction, as well as an increase in synovial metalloproteases and expression of proinflammatory mediators such as IL‐1β and CCL2 in joints compared with wild type animals. Taken together, these data underscore the importance of LXRs in modulating the joint inflammatory response and highlight them as potential therapeutic targets in RA. [ABSTRACT FROM AUTHOR]

Adrenal chromaffin cells release epinephrine (EPI) and norepinephrine (NE) into the bloodstream as part of the homeostatic response to situations like stress. Here we utilized EPI‐deficient mice generated by knocking out (KO) the phenylethanolamine N‐methyltransferase (Pnmt) gene. These Pnmt‐KO mice were bred to homozygosis but displayed no major phenotype. The lack of EPI was partially compensated by an increase in NE, suggesting that EPI storage was optimized in adrenergic cells. Electron microscopy showed that despite the lack of EPI, chromaffin granules retain their shape and general appearance. This indicate that granules from adrenergic or noradrenergic cells preserve their characteristics even though they contain only NE. Acute insulin injection largely reduced the EPI content in wild‐type animals, with a minimal reduction in NE, whereas there was only a partial reduction in NE content in Pnmt‐KO mice. The analysis of exocytosis by amperometry revealed a reduction in the quantum size (−30%) and Imax (−21%) of granules in KO cells relative to the wild‐type granules, indicating a lower affinity of NE for the granule matrix of adrenergic cells. As amperometry cannot distinguish between adrenergic or noradrenergic cells, it would suggest even a larger reduction in the affinity for the matrix. Therefore, our results demonstrate that adrenergic cells retain their structural characteristics despite the almost complete absence of EPI. Furthermore, the chromaffin granule matrix from adrenergic cells is optimized to accumulate EPI, with NE being a poor substitute. Open Science: This manuscript was awarded with the Open Materials Badge For more information see: https://cos.io/our-services/open-science-badges/ [ABSTRACT FROM AUTHOR]

Single-cell amperometry is a powerful technique that permits the detection of electrochemically active transmitters, such as catecholamines, histamine, or serotonin, released by exocytosis from secretory cells.Amperometry has two main characteristics that make it ideal for the study of exocytosis at the single-cell level with single-vesicle resolution quantal release. (i) It is noninvasive. The carbon fiber microelectrode can be carefully positioned on plasma membrane of a single cell, allowing the detection of the oxidation current of the secreted molecules. (ii) High temporal resolution and sensitivity. Exocytosis can be monitored with a real-time resolution that allows the determination of the kinetics release with an attomol detection sensitivity, which ensures an accurate calculation of the amount of transmitter released.Here, we compile some recommendations and advices to perform amperometry quantal analysis., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)