Knockdown of lncRNA HAGLR promotes Treg cell differentiation through increasing the RUNX3 level in dermatomyositis

Dermatomyositis (DM) is a systemic autoimmune disease. It's known that the number of regulatory T (Treg) cells was decreased in DM. Besides, Treg cells were increased after treatment in DM patients. Forkhead box P3 (Foxp3) is specifically expressed in Treg cells and Runt-related transcription factor (RUNX3) could regulate Foxp3 transcription. And our previous experiment showed that Homeobox D gene cluster antisense growth-associated long noncoding RNA (HAGLR) was up-regulated in DM patients. Here, we aimed to explore whether HAGLR regulated the differentiation of Treg cells through RUNX3-mediated transcription of Foxp3, thus affecting the progression of DM. The levels of HAGLR, Foxp3, and RUNX3 were examined by quantitative real-time PCR. The protein levels of Foxp3 and RUNX3 were examined by western blot. The proportions of Treg cells in CD4⁺ T cells were detected by flow cytometry. Hematoxylin and eosin staining was conducted to observe the histopathological changes of the muscle. RNA pull-down assay was performed to detect the interaction between HAGLR and RUNX3. A dual-luciferase reporter gene assay was conducted to examine the effect of HAGLR on the transcriptional regulation of Foxp3 by RUNX3. HAGLR was up-regulated and Foxp3 was down-regulated in DM patients. Besides, RUNX3 protein levels were decreased in DM patients, while its mRNA levels did not change significantly. The proportion of Treg cells was down-regulated in DM patients. In addition, interference with HAGLR could increase the levels of Foxp3, RUNX3 protein level, and the proportion of Treg cells. Besides, there was an interaction between HAGLR and RUNX3. We also found that knockdown of HAGLR and RUNX3 restored the increased Treg cells induced by HAGLR knockdown alone. In vivo experiments indicated that injection with adv-HAGLR increased Treg cell proportion and attenuated DM development. Interference with HAGLR could increase the protein levels of RUNX3, high levels of RUNX3 further promoted the expression of the Foxp3, thus restoring the number of Treg cells and easing the development of DM.