PhD Scientific Days 2022

Molecular Sciences II.

The Symptomes of Autoimmune Arthritis are Mitigated in the Absence of ARHGAP25

Text of the abstract

Introduction:
ARHGAP25 is a GTP-ase activating protein expressed highly in leukocytes. Through the inhibition of Rac activity it has a central role in regulating different neutrophilic functions including phagocytosis, superoxide production and migration.
Aims:
In this study, we investigated functional changes as well as the possible reasons which may lead to reduced arthritic symptoms in ARHGAP25 knockout mice.
Methods:
Wild type (WT) and ARHGAP25 knockout (KO) mice were treated with either arthritic (K/BxN) or control (BxN) serum and clinical score and ankle thickness were followed for 8 days. Articular function was investigated with horizontal grid test and mechanoreceptive threshold was determined with dynamic planar aesthesiomerty (DPA). Hystological sections of ankles were prepared and stained with Hematoxylin Eosin or Safranin o. We measured synovial neutrophil and macrophage counts using flow cytometry and synovial cytokine amounts with ELISA method.
Results:
After arthritic serum treatment, ARHGAP25 KO mice showed decreased signs of arthritis (ankle thickness, clinical score, hyperalgesia and function of the limbs) compared to WT. Hyperalgesia and joint destruction of KO mice was significantly mitigated. Synovial neutrophil and macrophage counts were also decreased in KO animals as well as the amount of two important inflammatory cytokines five days after arthritis induction. In KO bone marrow chimeras arthritic score and ankle thickness were reduced, however the difference was not as pronounced as in the case of full KO animals.
Conclusion:
Our results suggest that ARHGAP25 deletion significantly mitigates the symptoms of autoimmune arthritis in the K/BxN mouse model. Reduced synovial leukocyte infiltration and/or cytokine amounts in ARHGAP25 deficient animals are possibly behind the observed changes, however the exact molecular mechanisms are not understood yet. In preliminary experiments we found that both haemapoietic and non haemapoietic cells are likely to be responsible for the effect of ARHGAP25 on autoimmune arthritis. We also have data about signaling pathways that are possibly important in this regard.
Funding:
EFOP-3.6.3-VEKOP-16-2017-00009, János Bolyai Research Scholarship of the Hungarian Academy of Sciences, ÚNKP-20-5-SE-2, NKFIH FK_18/128376