Granulocyte chemotaxis and disease expression are differentially regulated by GRK subtype in an acute inflammatory arthritis model (K/BxN).

OBJECTIVE: Chemokine receptors are G-protein coupled receptors (GPCRs) phosphorylated by G-protein receptor kinases (GRKs) after ligand-mediated activation. We hypothesized that GRK subtypes differentially regulate granulocyte chemotaxis and clinical disease expression in the K/BxN model. METHODS: Clinical, histologic, and cytokine responses in GRK6-/-, GRK5-/-, GRK2+/-, and wildtype mice were evaluated using K/BxN serum transfer. Granulocyte chemotaxis was analyzed by transendothelial migration assays. RESULTS: Both GRK6-/- and GRK2+/- mice had increased arthritis disease severity (p<0.001); whereas GRK5-/- was not different from controls. Acute weight loss was enhanced in GRK6-/- and GRK2+/- mice (p<0.001, days 3-10). However, GRK6-/- mice uniquely had more weight loss (>10%), elevated serum IL-6, and enhanced migration toward LTB4 and C5a in vitro. CONCLUSIONS: GRK6 and -2, but not GRK5, are involved in the pathogenesis of acute arthritis in the K/BxN model. In particular, GRK6 may dampen inflammatory responses by regulating granulocyte trafficking toward chemoattractants.