miR6891-5p-regulated X skewing in Sjögren's Disease: molecular mechanism, reversal strategies, and clinical significance

ABSTRACT As the most female-predominant autoimmune disease with a female-to-male ratio of 14:1, primary Sjögren's Disease (SjD) provides a unique opportunity to address the knowledge gap in the molecular basis of sexual dimorphism in autoimmunity. Emerging findings support the role of the X chromosome in impacting the female bias in SjD. However, the exact molecular underpinnings of X-chromosomal dysregulation in SjD remains elusive. Using minor salivary gland-derived mesenchymal stromal cells (MSCs), we discovered striking, global skewing of X-linked genes in SjD, but not control, subjects. Mechanistically, we identified miR6891-5p, a HLA- encoded noncoding RNA, as a critical gatekeeper of X chromosomal allelic balance in MSCs. In pilot studies, we demonstrated that SjD MSCs exhibited reduction in miR6891-5p expression, that inhibition of miR6891-5p in control MSCs led to skewing, and that restoration of miR6891-5p expression in SjD MSCs reversed skewing of X-linked genes. On the chromatin level, miR6891-5p expression restricted CTCF activity in its restoration of allelic balance. Focusing on the phenomenon of X skewing, in this project we propose to address three broad questions, namely 1) the molecular mechanism of miR6891-5p-CTCF-mediated regulation of allelic balance, 2) targeted strategies to reverse skewing in SjD, and 3) the clinical significance of X skewing in SjD patients. Collectively, we will test the hypothesis that miR6891-5p loss leads to X skewing in SjD and targeting of the miR6891-5p pathway has the potential to restore X-chromosomal allelic balance by the following aims: Aim 1. Establish the molecular mechanism of miR6891-5p-regulated X skewing and identify molecular targets to correct skewing Aim 2. Determine the potential of reprogramming as a strategy to globally restore allelic balance in SjD Aim 3. Establish the relationship between miR6891-5p-regulated X skewing and SjD pathogenesis With successful completion of the work proposed, we will have gained insights into the molecular basis underlying sexual dimorphism in SjD. By establishing the miR6891-5p-regulated pathway as a central regulator of X chromosomal allelic balance, we will identify molecular and cellular targets for the reversal of X skewing and personalized management of SjD.