AB0807 ANALYSIS OF THE PROTEOME IN MINOR SALIVARY GLANDS FROM SJOEGREN’S SYNDROME PATIENTS
Authors: N. Štucin, K. Perdan Pirkmajer, A. Hočevar, B. Maurer, P. Zigon, S. Čučnik, K. Klein
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Sjoegren's syndrome (SjS) is an understudied systemic autoimmune disease with heterogeneous presentation and many unmet clinical needs. The underlying molecular pathomechanisms that drive SjS are not fully elucidated. <h3>Objectives:</h3> Our aim was to assess the proteome profiles of the minor salivary gland (MSG) tissues and to identify different subgroups of patients with SjS. <h3>Methods:</h3> Flash frozen MSG from 18 SjS patients, fulfilling the 2016 ACR/EULAR classification criteria, and 6 sicca controls not fulfilling the classification criteria, were analyzed. Clinical, imaging, functional, laboratory, and histological parameters, including age, gender, salivary gland ultrasound score, Schirmer's test, unstimulated salivary flow (USF) test, presence of autoantibodies, cryoglobulins, levels of complement components, focus score, numbers of germinal centers, and presence of lymphoepithelial lesions, were collected. Proteome analysis of the MSG tissues was performed by tandem mass spectrometry. Proteins were identified and quantified using Spectronaut software. Differentially expressed proteins were identified using Bayes test. Pearson correlation coefficient r was calculated between log2 protein intensities and the clinical features. Unsupervised hierarchical clustering was performed based on the expression of all detected proteins to identify groups of patients with similar protein expression profiles. Mann-Whitney U test was used to statistically analyze the differences in clinical parameters between the identified clusters. <h3>Results:</h3> We identified 5577 proteins, 7 of which were differentially expressed between SjS and sicca controls (log2FC &gt;2; p-adj &lt;0,05). All 7 differentially expressed proteins, namely PTPRCAP, IKZF1, CD3E, HDAC3, PIK3CD, SH2D1A, and DOCK10, were upregulated in SjS patients compared to sicca controls (Table 1). PTPRCAP (r=0.585, p-adj=0.013), CD3E (r=0.616, p-adj=0.009), HDAC3 (r=0.448, p-adj=0.0565), PIK3CD (r=0.413, p-adj=0.075), SH2D1A (r=0.671, p-adj=0.004) and DOCK10 (r=0.540, p-adj=0.024) correlated with the focus score in MSG tissues. SH2D1A additionally correlated with cryoglobulins (r=0.590, p-adj=0.067). Unsupervised hierarchical clustering, based on all detected proteins, identified two separate clusters of patients with SjS. Patients from cluster 1 (n=8) had significantly lower focus score compared to patients from cluster 2 (n=10) (median focus score 1.21 vs, 2.0, p=0.002). Additionally, patients from cluster 1 had higher levels of USF compared to patients from cluster 2 (median 0.13 ml/min vs. 0,02 ml/min, p=0,400). Notably, only 29% of patients in cluster 1 tested positive in the USF test, while 70% of patients in cluster 2 showed pathological results. <h3>Conclusion:</h3> The total number of proteins identified in our analysis exceeds that of previous studies and allows us to provide the first list of differentially expressed proteins in MSG tissues in SjS and controls that correlate with SjS-relevant measures. Our results indicate that MSG tissues from patients with different levels of lymphocyte infiltration and salivary gland dysfunction differ in the protein expression profiles. <h3>REFERENCES:</h3> <b>NIL.</b> <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> Neža Štucin: None declared, Katja Perdan Pirkmajer: None declared, Alojzija Hočevar: None declared, Britta Maurer Boehringer-Ingelheim, GSK, Novartis, Otsuka, MSD, Novartis, Boehringer Ingelheim, Jannsen-Cilag, GSK, Novartis, Polona Zigon: None declared, Saša Čučnik: None declared, Kerstin Klein: None declared.