Serum progranulin level is a novel tool for monitoring disease activity of dermatomyositis with antimelanoma differentiation‐associated protein 5 antibodies

Dermatomyositis (DM) is an autoimmune disease that presents with a wide variety of clinical manifestations. Patients with DM or clinically amyopathic dermatomyositis (CADM) with antimelanoma differentiation‐associated protein 5 (anti‐MDA5) antibodies are frequently associated with interstitial pneumonia, especially rapidly progressive interstitial lung disease. Progranulin (PGRN) is an autocrine growth factor involved in inflammation. Elevated serum PGRN levels have been reported in the patients with systemic lupus erythematosus and rheumatoid arthritis. However, they have not been precisely studied in DM/CADM. We assessed PGRN levels as a potential biomarker for DM/CADM with anti‐MDA5 antibodies.


Dermatomyositis (DM) is a systemic autoimmune and inflammatory
disease that involves not only the muscle and skin, but also several other organs, such as the lungs and joints. Clinically amyopathic DM (CADM) is a distinct subtype of DM that causes the same cutaneous symptoms as classic DM, but with little or no evidence of muscular manifestations. 1,2 Disease-specific autoantibodies, known as myositis-specific autoantibodies, are strongly associated with distinct clinical phenotypes and are used to classify patients into groups with more homogenous clinical features. These include antibodies against melanoma differentiation-associated protein 5 (MDA5; anti-CADM 140 antibody), 2-5 aminoacyl-tRNA synthetases, 6,7 Mi-2 protein, 8 transcriptional intermediary factor-1 (TIF1; anti-155/140 antibody), 9,10 and NXP-2. 11 Patients with anti-MDA5 antibodies have a high rate of concomitant interstitial lung disease (ILD), especially at risk for rapidly progressive interstitial lung disease (RP-ILD), [3][4][5][12][13][14] and usually do not show muscular symptoms. In DM or CADM (DM/CADM) with anti-MDA5 antibodies, three different phenotypes have recently been reported: RP-ILD group with a very high mortality rate, pure dermato-rheumatologic symptom (such as arthralgia) group with a good prognosis, and severe skin vasculopathy group with frequent signs of myositis associated with an intermediate prognosis. 15 Several biomarkers of disease activity have been reported, such as serum ferritin, 13,16 interferonα, 17 19,20 PGRN has been shown to directly bind to TNF receptors and block TNFα signaling, thereby reducing the development of arthritis in mice. 19 Elevated serum PGRN levels are associated with systemic lupus erythematosus (SLE) 21 and rheumatoid arthritis. 22 However, PGRN levels have not been studied precisely in DM/CADM. 23 In this study, we assessed the PGRN levels as a potential biomarker in DM/CADM patients with anti-MDA5 antibodies.

| Patients
We examined adult Japanese patients with DM/CADM who visited

| Clinical characteristics, treatments, and clinical courses
We compared the skin lesions (Gottron's papules/sign, heliotrope rash, mechanics' hands, palmar papules/erythema, ulcer, calcinosis, periungual hemorrhage, and Raynaud's phenomenon; Figure 1) and general symptoms (fever, muscular symptoms, ILD, and arthropathy) between the anti-MDA5 antibody-positive and antibody-negative groups and followed at least 6 months after the start of treatment. Treatment outcomes and death rates within 6 months were compared.

| Laboratory data
We measured the levels of KL-6, C-reactive protein (CRP), erythrocyte sedimentation rate at 1 h (ESR), ferritin, and lactate dehydrogenase (LD) before and after the start of treatment, at approximately 1-month interval. The sera and ELISA Kits were stored at −80°C before use. The PGRN levels were measured before and after the start of the treatment at approximately 1-month interval.

| Statistical analyses
Data analysis was performed using Excel Statistics, 2012 (Social Survey Information). Statistically significant differences between groups were calculated using the chi-square test for categorical variables and the Mann-Whitney U-test for nonparametric, continuous variables. Pearson's correlation was used to examine the correlation between two continuous variables. p < 0.05 was considered statistically significant.

| Clinical findings and clinical course
Patients with anti-MDA5 antibodies had ILD more frequently, and fever and muscular symptoms less frequently. With regard to cutaneous manifestations, palmar papules/erythema ( Figure 1) was observed more often, but heliotrope rash less in these patients.
Of the 24 patients with anti-MDA5 antibody-positive DM/ CADM, there were four patients in the RP-ILD group, 15 of in the pure dermato-rheumatologic symptom group, and five in the severe skin vasculopathy group with myositis. 15 Steroid pulse therapy was administered more often in patients with anti-MDA5 antibodies (Table 1). Of the 24 DM/CADM patients with anti-MDA5 antibodies, three died in the following 6 months.
Four patients experienced recurrence with re-elevation of PGRN levels associated with increased antibody titers, while re-elevation of KL-6 and ferritin levels was seen, in three patients and in one patient, respectively.

| Serum PGRN levels in MDA5 antibodypositive vs MDA5 antibody-negative DM/ CADM patients
Among the DM/CADM patients, serum PGRN levels were compared between anti-MDA5 antibody-positive and anti-MDA5 antibodynegative patients. Serum PGRN levels were significantly higher in the former group, both before and after the start of treatment (p < 0.01), and were also found to have reduced after the start of treatment in both patient groups (Figure 3).

| Clinical course and serum PRGN levels
Serum PGRN levels gradually decreased with treatment in eight DM/CADM patients with anti-MDA5 antibodies ( Figure 4A), who were followed-up periodically for at least 6 months.
The mean PGRN levels decreased after treatment initiation ( Figure 4B).

| Correlation between laboratory data and serum PRGN levels
Serum PGRN levels were positively correlated with anti-MDA-5 antibody titers, and ferritin and KL-6 levels. However, CRP, ESR, and LD levels did not correlate with PGRN levels ( Figure 5). The accumulation of ferritin-producing macrophages has been shown in a CADM-related acute interstitial pneumonia autopsy case. 29 Since macrophage activation is also considered to underlie the pathogenesis of DM/CADM, serum IL-6 30   Our study showed that PGRN could be a useful biomarker for disease activity in DM patients with ILD. These findings will provide new insights into the pathogenesis and treatment of DM. Further studies are required to reveal the mechanisms of PGRN in human autoimmune diseases more precisely.

ACK N OWLED G M ENTS
The authors would like to thank Mrs Kayoko Tanaka, Mrs Naoko Abe, and Mrs Miho Mabuchi for assisting with data collection.

CO N FLI C T O F I NTE R E S T
The authors declares no conflict of interest.

AUTH O R CO NTR I B UTI O N S
AF had full access to all of the data in the study and takes respon-