Background/Purpose: MicroRNAs (miRNAs) are small, non-coding RNAs that suppress gene expression at post-transcriptional level. MiRNAs can regulate innate and adaptive immunity. Moreover, they have been found deregulated in various autoimmune diseases emerging as biomarkers and novel therapeutic targets. Giant cell arteritis (GCA) is an autoimmune inflammatory vasculitis affecting large and medium-sized arteries. Temporal artery biopsy (TAB) showing resident immune cells is the gold standard for the diagnosis of GCA. Nevertheless, a negative TAB does not rule out GCA and some patients receive a diagnosis of TAB-negative GCA according to clinical and laboratory parameters. The present study aimed to identify miRNAs deregulated in GCA and to determine if miRNA levels might allow to discriminate between patients with GCA and those without.
Methods: 48 patients undergoing TAB for suspected GCA were included in the study and divided into 3 groups: GCA with positive TABs (n=23), GCA with negative TABs (n=7) and non-GCA with negative TABs receiving a different diagnosis (n=18). 1990 ACR classification criteria for GCA were satisfied in all GCA patients with positive TABs, in 6 of the 7 GCA patients with negative TABs and in none of the non-GCA patients. To identify candidate miRNAs deregulated in GCA, expression of 1209 miRNAs was profiled with a miRNA array (Ocean Ridge Biosciences, Palm Beach Gardens, FL ) in inflamed TABs from 7 GCA patients versus normal TABs from 8 non-GCA patients. MiRNAs showing a >2 fold, statistically significant differential expression with a false discovery rate <10%, were selected for further analyses. Their expression was validated by real-time PCR (QIAGEN, Milan, Italy) in different TAB samples as well as PBMCs and PMN cells isolated from GCA and non-GCA patients. To identify which cell type expressed miR-21 in TABs, in situ hybridization (Exiqon, Vedbaek, Denmark) was performed on FFPE tissue sections.
Results: 10 miRNAs emerged deregulated in inflamed TABs from GCA patients by a high throughput miRNA profiling assay. Subsequent real-time PCRs confirmed that miR-146b-5p, -146a, -155, -150 and -21 were significantly more expressed in TABs from GCA patients positive for a transmural inflammatory infiltrate. Negative TABs from GCA patients had a miRNA profile similar to negative TABs from non-GCA patients suggesting that miRNAs might be downstream inflammation. Expression of miR-146b-5p was particularly promising in a diagnostic perspective because it was possible to set a threshold level which correctly classified TABs as inflamed or normal. Within inflamed TABs, miRNA expression levels did not positively correlate with the load of infiltrating immune cells suggesting that miRNAs might be expressed by tissue cells. Indeed, in inflamed TABs, miR-21 was mainly expressed by spindle shaped cells of the media layer and stellate fibroblast-like cells of the intima layer. Moreover, miRNAs were expressed at comparable levels by circulating PBMCs and PMN cells from GCA and non-GCA patients.
Conclusion: miR-146a, -21, -150 and -155 and above all miR-146b-5p emerged as markers of inflammation in TABs from GCA patients, might be involved in GCA pathogenesis thus further investigated as therapeutics targets.
Disclosure:
S. Croci,
None;
A. Zerbini,
None;
L. Boiardi,
None;
F. Muratore,
None;
A. Bisagni,
None;
G. Pazzola,
None;
L. Cimino,
None;
A. Moramarco,
None;
D. Nicoli,
None;
E. Farnetti,
None;
B. Casali,
None;
A. Cavazza,
None;
M. Parmeggiani,
None;
C. Salvarani,
Novartis Pharma AG,
2.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-signature-of-micrornas-overexpressed-in-inflamed-temporal-arteries-of-patients-with-giant-cell-arteritis/