Myeloperoxidase Modulates Inflammation in Generalized Pustular Psoriasis and Additional Rare Pustular Skin Diseases

Abstract

Generalized pustular psoriasis (GPP) is a severe multi-systemic inflammatory disease characterized by neutrophilic pustulosis and triggered by pro-inflammatory IL-36 cytokines in skin. While 19%–41% of affected individuals harbor bi-allelic mutations in IL36RN , the genetic cause is not known in most cases. To identify and characterize new pathways involved in the pathogenesis of GPP, we performed whole-exome sequencing in 31 individuals with GPP and demonstrated effects of mutations in MPO encoding the neutrophilic enzyme myeloperoxidase (MPO). We discovered eight MPO mutations resulting in MPO -deficiency in neutrophils and monocytes. MPO mutations, primarily those resulting in complete MPO deficiency, cumulatively associated with GPP (p = 1.85E−08; OR = 6.47). The number of mutant MPO alleles significantly differed between 82 affected individuals and >4,900 control subjects (p = 1.04E−09); this effect was stronger when including IL36RN mutations (1.48E−13) and correlated with a younger age of onset (p = 0.0018). The activity of four proteases, previously implicated as activating enzymes of IL-36 precursors, correlated with MPO deficiency. Phorbol-myristate-acetate-induced formation of neutrophil extracellular traps (NETs) was reduced in affected cells (p = 0.015), and phagocytosis assays in MPO-deficient mice and human cells revealed altered neutrophil function and impaired clearance of neutrophils by monocytes (efferocytosis) allowing prolonged neutrophil persistence in inflammatory skin. MPO mutations contribute significantly to GPP’s pathogenesis. We implicate MPO as an inflammatory modulator in humans that regulates protease activity and NET formation and modifies efferocytosis. Our findings indicate possible implications for the application of MPO inhibitors in cardiovascular diseases. MPO and affected pathways represent attractive targets for inducing resolution of inflammation in neutrophil-mediated skin diseases.

Genetic Analysis of MPO Variants in Four Psoriasis Subtypes in Patients from Germany

“…Recently, we and others identified MPO (myeloperoxidase) as an additional major susceptibility gene in GPP (Haskamp et al, 2020, Vergnano et al, 2020. Deficiency of neutrophilic enzyme MPO impairs phagocytosis of dying neutrophils and increases J o u r n a l P r e -p r o o f the activity of IL-36 activating proteases, thereby driving inflammation in pustules (Haskamp et al, 2020). Additionally, GPP patients with MPO variants are more likely to have PPP, tongue manifestations and a positive family history of psoriasis compared to patients without (Haskamp et al, 2020).…”

“…Deficiency of neutrophilic enzyme MPO impairs phagocytosis of dying neutrophils and increases J o u r n a l P r e -p r o o f the activity of IL-36 activating proteases, thereby driving inflammation in pustules (Haskamp et al, 2020). Additionally, GPP patients with MPO variants are more likely to have PPP, tongue manifestations and a positive family history of psoriasis compared to patients without (Haskamp et al, 2020). And an increased serum amount of MPO has been detected in PsV and PsA patients, suggesting a potentially protective role of MPO variants in common psoriatic manifestations (Cretu et al, 2018).…”

“…We genotyped 3,663 individuals (1,105 PsV, 1,313 PsA, 271 PPP, 52 SAPHO syndrome and 922 control individuals) for seven of the most common functionally relevant MPO variants ( Supplementary Table 1) (Haskamp et al, 2020) using GSA microarrays and single SNP genotyping assays (Supplements). We extensively validated genotyping quality with several approaches including repeated genotyping with different assays and Sanger sequencing in individuals with MPO variants and randomly selected genotypes (Supplements).…”

“…We extensively validated genotyping quality with several approaches including repeated genotyping with different assays and Sanger sequencing in individuals with MPO variants and randomly selected genotypes (Supplements). We determined the cumulative frequency of all variants in psoriatic subtypes and in control individuals as described before (Haskamp et al, 2020) (Table 1) At genotype level when considering combination of two MPO variants, we observed mainly combinations resulting in partial MPO-deficiency and estimated loss in enzyme activity of 65-90% in patients (Supplementary Table 2) (Haskamp et al, 2020, Marchetti et al, 2004, Nauseef et al, 1994. Although the percentage of psoriasis patients with two variants was increased 1.5-fold compared to control individuals due to higher percentages in PsV and PPP (0.54%/ 0.74% vs. 0.27%), we did not observe a significant difference in overall numbers of MPO variants (Supplementary MPO variants with age of onset ( Supplementary Figure 1), severity of disease (Supplementary Table 5) and positive family history ( Supplementary Table 6), we obtained negative findings, with a tendency to a negative correlation regarding severity of disease (p=0.09).…”

“…Supplementary Table 1 The degree of MPO-deficiency was estimated based on functional studies of the missense variants described previously (Haskamp et al, 2020, Marchetti et al, 2004, Nauseef et al, 1994, Romano et al, 1997…”