OP0334 GGTASE DEFICIENT MACROPHAGES ALTER INTEGRIN EXPRESSION ON LYMPHOCYTES AND FACILITATE DEVELOPMENT OF ARTHRITIS
Authors: K. M. Andersson, E. Malmhäll-Bah, M. C. Erlandsson, M. Brisslert, M. Akula, O. Khan, I. M. Jonsson, M. Bergö, M. I. Bokarewa
Journal: Annals of the Rheumatic Diseases (2020)

Background: Geranylgeranyltransferase type I (GGTaseI) is the enzyme responsible for the prenylation/ lipidation of the RhoA family proteins, which keeps them attached to the cell membrane. We reported that GGTaseI-deficient (GLC) mice develop a spontaneous and age-dependent arthritis, reproducing the pathology of RA 1 . Targeting GGTaseI activates RhoA proteins. Objectives: To study which of the activated Rho proteins is responsible for development of arthritis, we deleted individual RhoA, Rac1 or Cdc42 genes in GLC mice. We study consequences of GGTaseI deficiency for lymphocyte function. Methods: Double deficient mice that lack Rac1 (GLC Rac1fl/fl), RhoA (GLC RhoAfl/fl) and Cdc42 (GLC Cdc42fl/fl) were developed by Cre-technology using the LysM-promotor, and were on a mixed genetic background (129Ola/Hsd-C57BL/6) 2 . Joints of the hind paws were assessed for signs of arthritis histologically and by micro CT at age of 16 weeks. Phenotype of spleen CD4 and CD8 T cells was analysis by flow cytometry. Proliferation and cytokine production was assessed in spleen cultures by ELISA. Gene expression profile was analyzed by RT-PCR. Results: Deletion of Rho proteins had divergent effect on development of arthritis in GLC mice. We observed a reduction of the arthritis index in GLC Rac1fl/fl (n=19, p=0.027) and GLC RhoAfl/fl (n=4, p=0.007) mice compared to GLC (n=16), while GLC Cdc42fl/fl (n=4) had no change in arthritis development. GLC RhoAfl/fl mice increased the bone mass compared to GLC (p=0.029). Flow cytometry analysis showed that RA-prone GLC and GLC Cdc42fl/fl mice had lower number of CD4 cells in spleen. CD4 cells of RA-prone GLC and GLC Cdc42 mice had significantly higher subsets of the regulatory FoxP3+ and FOXp3+CD25+ cells (p=0.016-0.029 and p=0.016-0.029 respectively) compared to control and GLC RhoAfl/fl mice. Additionally, RA-prone mice had higher expression of receptors to extracellular matrix proteins collagen (α2β2) and fibronectin (α5β1) compared to control mice (p=0.016 and p=0.011 resp) and to RA-protected mice (GLC Rac1fl/fl and GLC RhoAfl/fl, p=0.0004 and p=0.011, resp). In total, both the number of FoxP3+ CD4 cells and the expression of α5β1 receptors on CD4 cells correlated strongly with the synovitis score (r=0.72, p=0.0017 and r=0.59, p=0.012, respectively). GGTaseI gene lays under the control of HOX proteins essential for cell homing. Importantly, HOX regulate the expression of integrins. Studying the expression of HoxA genes in spleen, we found that RA prone GLC and GLC Cdc42 mice tended to have lower expression of HoxA2 and higher expression of HoxA9 compared to RA-protected GLC Rac1 and GLC RhoA and to control mice. The Hoxa9/Hoxa2 ratio was significantly higher in RA prone mice compared to RA-protected mice (p=0.0085) and control mice (p=0.019). This ratio correlated with α5β1 receptors (r=0.55, p=0.0084), FOXP3+ CD4 cells (r=0.50, p=0.017), and the arthritis index (r=0.50, p=0.033). Conclusion: Taken together this study shows that Rho proteins play divergent role in development of arthritis. Activation of Rac1 and RhoA by GGTaseI deletion changes the pattern of HOXA proteins and increases expression of integrin receptors, which facilitates leukocyte influx in the paw joints. Deletion of Rac1 and RhoA has RA-protective effect in GLC mice. References: [1]Khan, O.M. , et al . J Clin Invest 121 , 628 (2011). [2]Akula, M.K. , et al . Nat Commun 10 , 3975 (2019). Disclosure of Interests: None declared