Beta2‐Adrenergic Receptor Regulates Inflammation in Autoimmune Arthritis: Inhibit or Promote? – Depends on Timing, Immune Organ and Posttranslational Receptor Modifications
Authors: Lorton Dianne , Lubahn Cheri L. , Molinaro Christine , Bellinger Denise L. 
Published: November 2023

Adjuvant‐induced arthritis (AA) differentially affects norepinephrine concentrations in lymph nodes draining affected limbs (DLNs) and spleen, two organs where arthritogenic Th cells develop. Treatment with a β‐adrenergic receptor (β‐AR) agonist also uniquely regulates ex vivo cytokine profiles in these immune organs and has opposing effects if administered before or after onset of AA. Understanding the role of β2‐ARs signaling in AA that underlie these disparate findings is a necessary step to understand molecular mechanisms by which β2‐ARs inhibit or promote inflammation in autoimmunity. We hypothesized that time‐dependent, β2‐AR agonist‐mediated pro‐ or anti‐inflammatory effects in AA depend on the differential phosphorylation of β2‐ARs by protein kinase A (PKA) or G‐protein receptor kinases (GRKs).

To begin to test this hypothesis, rats were immunized with complete Freund's adjuvant (CFA) to induce AA or components of CFA or saline. Using western blots, we examined total, and PKA‐or GRK‐phosphorylation of β2‐ARs in DLN cells and splenocytes on day (D) 7, 14, 21, or 28 post‐challenge (times before, at onset, acute or severe disease, respectively). Ex vivo IL‐2 and IFN‐gamma production in DLN and spleen cells with or without a β2‐AR agonist were assessed with enzyme‐linked immunoassays, since IL‐2 and IFN‐gamma are critical for differentiation and expansion of arthritis‐inducing Th1 cells.

Splenocyte β2‐AR phosphorylation (p β2‐AR) by PKA (p β2‐ARPKA) and GRK (p β2‐ARGRK) increased on D7. By D14, p β2‐ARPKA was reduced, but p β2‐ARGRK remained elevated. During severe disease (D28), p β2‐ARPKA declined, but p β2‐ARGRK increased. Strikingly different patterns of p β2‐AR were found in DLN cells. In contrast to splenocytes, p β2‐ARPKA and p β2‐ARGRK in DLN cells were low on D7. On D14, p β2‐ARPKA and p β2‐ARGRK in DLN cells from CFA‐immunized rats did not differ from rats receiving saline or either component of adjuvant. During severe disease, p β2‐ARPKA in DLN cells rose, but fell during chronic disease, and p β2‐ARGRK increased during both disease stages. Differential changes in p β2‐ARs in mineral oil or mycobacterial‐immunized rats compared with CFA challenge support that the interactions between adjuvant components drive differential p β2‐ARs altering β2‐AR functions. They also implicate pattern recognition (i.e., toll‐like receptors) and aryl hydrocarbon receptors in altering p β2‐AR patterns and function in immune cells from AA rats. Differential p β2‐AR patterns in immune organs across disease stages and immunization groups were consistent with established enzyme‐mediated β2‐AR regulation of IL‐2 and IFN‐gamma production. Collectively, our findings indicate that time‐dependent p β2‐AR expression mediates disease outcomes in AA. Our findings also support sympathetic dysregulation in disease‐driving cytokine production that is immune organ‐specific in AA, with translational implications for rheumatoid arthritis.

Support or Funding Information

NIH Grant R29 MH49050