Quantification of GADD34 Expression in RA
Condition: Rheumatoid Arthritis
MeSH terms: Arthritis; Arthritis, Rheumatoid
Study type: Interventional

Summary: 
      GADD34 is an inducible cofactor of protein phosphatase 1, which has an important role in the
      Unfolded Protein Response (UPR). UPR is a cellular response to ER stress which is implicated
      in several autoimmune diseases. GADD34 has been shown to be necessary for proinflammatory
      cytokine production in response to viral infection in murine models. Nevertheless, the role
      of GADD34 in cytokine production in humans remains to be elucidated. Here, we investigate the
      interest of GADD34 in rheumatoid arthritis (RA), in which proinflammatory cytokines have an
      important pathogenic role.

      A case-control study on GADD34 gene expression in PBMC of patients (n=75) with RA and age-
      and sex-matched healthy controls (n=25). GADD34 gene expression levels in PBMC were measured
      by quantitative PCR.
    

Detailed description: 
      The endoplasmic reticulum (ER) is the subcellular compartment where transmembrane and
      secreted proteins are produced. In normal conditions biosynthesis rate, folding and
      trafficking of the proteins are tightly regulated through an efficient 'quality control'
      system. The ER responds to the accumulation of misfolded proteins in its lumen through
      different signaling pathways known as the unfolded protein response (UPR) [1]. Upon
      activation, the ER transmembrane protein PERK phosphorylates the alpha subunit of the
      eukaryotic initiation factor eIF2 [2]. Under these conditions, the transcription factor ATF4
      directs the expression of genes involved in resistance to oxidative stress, in amino acid
      metabolism, as well as the expression of GADD34 (Growth arrest and DNA damage-inducible gene
      34) [3]. GADD34 is a regulatory subunit of PP1 phosphatase which dephosphorylates eIF2alpha
      [4], representing a negative feedback loop of UPR, essential for protein synthesis recovery
      and cell survival [5].

      The UPR is more than just an adaptive response to unfolded protein accumulation in the ER,
      and UPR signaling pathways intersect with immune responses at many levels [6]. In B
      lymphocytes activation of UPR is part of the normal program of cell differentiation, playing
      an important role in immunoglobulin synthesis [7]. ER stress has also been implicated in the
      pathogenesis of many human diseases, including metabolic, neurodegenerative diseases, and
      cancer [8]. A direct link between UPR and inflammation has been demonstrated for the
      development of autoimmune diseases such as inflammatory bowel disease [9].

      Rheumatoid arthritis is a chronic multifactorial inflammatory disease. Proinflammatory
      cytokines, such as TNF-alpha and IL-6, secreted by macrophages and monocytes have an
      important pathogenic role in the phases of inflammation, synovial proliferation and cartilage
      damage [10]. Rheumatoid factor (RF) has been the most widely used antibody to diagnose RA
      [11]; anti-citrullinated protein antibodies (ACPA) have also been included in the diagnostic
      criteria of ACR/EULAR in 2010 [12] and they are highly associated with the development of
      erosive RA [13].

      GADD34 has recently been shown to be necessary for the production of proinflammatory
      cytokines by dendritic cells and fibroblasts exposed to double-strand RNA in a murine model
      [14]. In fibroblasts, GADD34 expression is dependent on PKR (Protein Kinase RNA-activated)
      activation, showing a direct link between pathogen detection and the eIF2alphaP/ATF4 pathway
      of UPR. The importance of this link for anti-viral immunity has been demonstrated by the
      mortality of GADD34-deficient neonate mice infected by Chikungunya virus, due to a
      significant reduction of IFN-beta production [15]. It has been proposed that GADD34 could
      have a qualitative role on the selection of mRNAs being translated in particular conditions,
      such as viral infections [16]. These results suggest that GADD34 might be a key molecule of
      inflammatory processes in human pathologies as well; however, the role of GADD34 in cytokine
      production in humans remains to be elucidated. The aim of our study was to investigate GADD34
      expression in RA patients.

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        2. Harding, H.P., et al., Perk is essential for translational regulation and cell survival
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        3. Harding, H.P., et al., An integrated stress response regulates amino acid metabolism and
           resistance to oxidative stress. Mol Cell, 2003. 11 (3): p. 619-33.

        4. Novoa, I., et al., Feedback inhibition of the unfolded protein response by
           GADD34-mediated dephosphorylation of eIF2alpha. J Cell Biol, 2001. 153 (5): p. 1011-22.

        5. Novoa, I., et al., Stress-induced gene expression requires programmed recovery from
           translational repression. Embo J, 2003. 22 (5): p. 1180-7.

        6. Janssens, S., B. Pulendran, and B.N. Lambrecht, Emerging functions of the unfolded
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        7. Iwakoshi, N.N., et al., Plasma cell differentiation and the unfolded protein response
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        9. Kaser, A., et al., XBP1 links ER stress to intestinal inflammation and confers genetic
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       10. McInnes, I.B. and G. Schett, The pathogenesis of rheumatoid arthritis. N Engl J Med. 365
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       11. Ingegnoli, F., R. Castelli, and R. Gualtierotti, Rheumatoid factors: clinical
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       12. Aletaha, D., et al., 2010 Rheumatoid arthritis classification criteria: an American
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       13. Majka, D.S., et al., Duration of preclinical rheumatoid arthritis-related autoantibody
           positivity increases in subjects with older age at time of disease diagnosis. Ann Rheum
           Dis, 2008. 67 (6): p. 801-7.

       14. Clavarino, G., et al., Protein phosphatase 1 subunit Ppp1r15a/GADD34 regulates cytokine
           production in polyinosinic:polycytidylic acid-stimulated dendritic cells. Proc Natl Acad
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       15. Clavarino, G., et al., Induction of GADD34 is necessary for dsRNA-dependent
           interferon-beta production and participates in the control of Chikungunya virus
           infection. PLoS Pathog. 8 (5): p. e1002708.

       16. Claudio, N., et al., Mapping the crossroads of immune activation and cellular stress
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Intervention name(s): Blood test
Intervention type(s): Other
Intervention description(s): blood test
Intervention model: Single Group Assignment
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: GADD34; Unfolded Protein Response; Anti-citrullinated protein antibodies