PP2A dysfunction mediated by PPP2R1A deficiency drives cGAS-STING-dependent hyperinflammation in SLE CD14+ monocytes

Objective: This study aims to investigate the role of protein Phosphatase 2A (PP2A) dysfunction in the hyperinflammatory response observed in systemic lupus erythematosus (SLE) monocytes. The focus is on elucidating the functional connection between dysregulation of PP2A subunits, loss of enzymatic activity, and aberrant innate immune activation through the Cyclic GMP-AMP Synthase (cGAS)-stimulator of interferon response cGAMP interactor 1 (STING) pathway in monocytes.

Methods: CD14⁺ monocytes were isolated from 88 SLE patients and 40 healthy controls (HCs). PP2A subunits (PPP2R1A, PPP2CA, PPP2CB) mRNA expression was analyzed and correlated with autoantibody profiles. PP2A Phosphatase activity and inhibitory phosphorylation (PP2Ac-Y307) were assessed. Functional effects of PP2A modulation were evaluated by pharmacologically inhibiting PP2A (LB-100) in HCs monocytes or activating it (FTY720) in SLE monocytes, followed by cGAS-STING stimulation with cGAMP. Inflammatory parameters, including interferon-stimulated gene (ISG15, ISG20, IFIT3) expression and cytokine (IL-6, IL-1β, IFN-α) secretion, were measured.

Results: Monocytes derived from patients with SLE demonstrated a selective downregulation of the PP2A structural subunit, PPP2R1A, which led to a reduction in PP2A Phosphatase activity and an increase in phosphorylation at PP2Ac-Y307. Functionally, the pharmacological inhibition of PP2A in monocytes from HCs resulted in an amplification of cGAS-STING-dependent expression of ISGs and hypersecretion of cytokines, thereby mimicking the hyperinflammatory phenotype observed in SLE. In contrast, activation of PP2A through FTY720 in SLE monocytes significantly curtailed this exaggerated immune response.

Conclusion: These findings position PP2A hypofunction as a critical pathogenic driver in SLE and highlight the therapeutic potential of targeting this Phosphatase. The restoration of PP2A activity mitigates dysregulated innate immune responses, presenting a promising strategy for immunomodulation in SLE. Key Points • The downregulation of PPP2R1A expression and the concomitant reduction in PP2A Phosphatase activity constitute a pathological mechanism in SLE monocytes. • PP2A agonist FTY720 reverses cGAS-STING pathway activation in SLE monocytes.

Cyclic GMP-AMP synthase; Innate immunity; Protein phosphatase 2A; Stimulator of interferon response cGAMP interactor 1; Systemic lupus erythematosus.