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Inhibition of lysosomal degradation increases expression of mutant ADA2 in DADA2 monocytes
Lisa Ehlers1, Marjon Wouters2, Bethany Pillay2
1Department of Microbiology, Immunology and Transplantation, Laboratory for Inborn Errors of Immunity, KU Leuven, Leuven, Belgium; Department of Pediatric Respiratory Medicine, Immunology and Critical Care Medicine, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany; Berlin Institute of Health at Charité - Universitätsmedizin Berlin, Berlin, Germany; German Center for Child and Adolescent Health, partner site Berlin, Berlin, Germany; Deutsches Rheuma-Forschungszentrum, an Institute of the Leibniz Association, Berlin, Germany.
Background:
Deficiency of adenosine deaminase 2 (DADA2) is an inborn error of immunity causing vasculitis and bone marrow failure. Bone marrow failure is mostly unresponsive to TNF-α inhibitors. The limited understanding of the pathomechanisms driving the disease impedes the development of new treatment options. Unlike cellular model systems expressing pathogenic ADA2 variants, primary monocytes from patients with DADA2 lack ADA2 protein expression.
Objectives:
This study aimed to analyze the role of protein degradation in the pathogenesis of DADA2 and the therapeutic potential of the lysosomotropic drug hydroxychloroquine in the treatment of patients with DADA2.
Methods:
ADA2 protein expression in CD14+ monocytes from healthy controls (n = 8) and patients with DADA2 (n = 11) was determined by Western blot after inhibition of lysosomal and proteasomal degradation, as well as after hydroxychloroquine treatment in vivo in 1 patient with DADA2. Lipidation of microtubule associated protein 1 light chain 3 beta (LC3B) was analyzed as a measure of autophagic activity. Clinical and laboratory data were recorded in cytopenic patients with DADA2 treated with hydroxychloroquine, 200 mg per day.
Results:
We demonstrated that inhibition of lysosomal degradation restores ADA2 protein expression in DADA2 monocytes in vitro. DADA2 monocytes exhibited increased autophagic activity. We observed clinical improvement in 2 cytopenic patients with DADA2 who were treated with hydroxychloroquine, and we showed a concomitant increase in ADA2 protein levels in monocytes from one of these patients in vivo.
Conclusion:
We identified lysosomal protein degradation of ADA2 as a pathomechanism of DADA2 and introduced hydroxychloroquine as a potential treatment option in patients with DADA2 with refractory cytopenia.
Insights
Lysosomal degradation of adenosine deaminase 2 (ADA2) protein contributes to Deficiency of ADA2 (DADA2), a rare immune disorder. Hydroxychloroquine treatment improved symptoms and restored ADA2 levels in patients with DADA2.
Area of Science:
- Immunology
- Genetics
- Pharmacology
Background:
- Deficiency of adenosine deaminase 2 (DADA2) is an inherited immune disorder characterized by vasculitis and bone marrow failure.
- Current understanding of DADA2 pathogenesis is limited, hindering effective treatment development, especially for bone marrow failure unresponsive to TNF-α inhibitors.
- Primary monocytes from DADA2 patients lack ADA2 protein, unlike in vitro models expressing pathogenic ADA2 variants.
Purpose of the Study:
- To investigate the role of protein degradation in DADA2 pathogenesis.
- To evaluate hydroxychloroquine, a lysosomotropic drug, as a potential therapeutic agent for DADA2.
Main Methods:
- Assessed ADA2 protein expression in monocytes from healthy controls and DADA2 patients using Western blot.
- Examined autophagic activity via LC3B lipidation.
- Analyzed clinical and laboratory data of DADA2 patients treated with hydroxychloroquine.
Main Results:
- Inhibition of lysosomal degradation restored ADA2 protein expression in DADA2 monocytes in vitro.
- DADA2 monocytes displayed heightened autophagic activity.
- Two cytopenic DADA2 patients showed clinical improvement with hydroxychloroquine, with one exhibiting increased monocyte ADA2 levels in vivo.
Conclusions:
- Lysosomal protein degradation of ADA2 is a key pathomechanism in DADA2.
- Hydroxychloroquine shows promise as a treatment for DADA2 patients with refractory cytopenia.
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