Intrinsic B cell epigenetic mediators as therapeutic targets in lupus

Our hypothesis is that the enzyme Tet2 stimulates B cells to make harmful antibodies, while the enzyme Sirt1 reduces their production.  To test our hypothesis, we will find out whether the levels of these enzymes are abnormal in B cells from mice and patients with lupus. We will also give lupus-prone mice chemicals that increase levels of Sirt1 or reduce levels of Tet2 and test whether the animals produce less of the destructive antibodies. Our project will also search for other molecules that inhibit Tet2 or stimulate Sirt1 that could be developed into lupus treatments.

What this study means for people with lupus

“In lupus, immune cells known as B cells release destructive proteins called antibodies that target patients’ own tissues. We will test whether two enzymes increase or reduce the amount of antibodies that B cells produce. We will also identify molecules that switch these enzymes on or off and that could be turned into lupus therapies.”

B cell epigenetic factors, processes and marks interact with genetic programs to modulate immunoglobulin somatic hypermutation (SHM) and class switch DNA recombination (CSR) through regulation of AID (gene: Aicda) and plasma cell generation/maintenance through regulation of Blimp-1 (gene: Prdm1), thereby instructing the antibody response. In lupus B cells, epigenetic dysregulation compounds genetic susceptibility to dysregulate SHM/CSR and plasma cell differentiation, thereby giving rise to pathogenic autoantibodies. Among epigenetic mediators, Sirt1 is the most abundant NAD+-dependent histone deacetylase in inactivated B cells, and regulates gene expression through histone deacetylation. Methylcytosine dioxygenases function as active DNA demethylator by converting 5’methylcytosine to 5’-hydroxyl-methylcytosine. Here, we hypothesize that Sirt1-mediated histone deacetylation and methylcytosine dioxygenase-mediated active DNA demethylation play a major role in the regulation of expression of AID and Blimp-1, respectively, thereby controlling the lupus autoantibody response. The rationale stems from our compelling findings that: (i) Sirt1 expression was downregulated in B cells upon application of SHM/CSR-inducing stimuli, while methylcytosine dioxygenase expression was upregulated in B cells induced to differentiate into plasma cells; (ii) in lupus B cells, Sirt1 was downregulated and methylcytosine dioxygenases were upregulated; (iii) Sirt1 inhibited AID, thereby dampening SHM/CSR and the antibody response. methylcytosine dioxygenase promoted Blimp-1 expression and, therefore, plasma cell differentiation and the antibody response; (iv) Sirt1 and methylcytosine dioxygenase exert their functions in a B cell-intrinsic fashion; (v) boosting Sirt1 activity by using small molecule SRT1720 downregulated AID, while inhibiting active DNA methylation downregulated Blimp-1; and, finally, (vi) treatment of lupus-prone mice with SRT1720 or active DNA methylation inhibitor dramatically dampened the autoantibody response and immunopathology. To test our hypothesis, we will analyze expression of Sirt1 and active DNA demethylator in human and mouse B cells induced to undergo SHM/CSR and plasma cell differentiation, as well as their dysregulation in B cells and plasma cells from SLE patients and lupus-prone mice (Aim 1.1). We will also analyze genome-wide as well as Aicda- and Prdm1-specific dysregulation by Sirt1-mediated histone deacetylation and methylcytosine dioxygenase-mediated active DNA demethylation in mouse lupus B cells (Aim 1.2). We will define the B cell-intrinsic roles of Sirt1 and methylcytosine dioxygenase in lupus autoantibody responses by overexpressing Sirt1 (Aim 2.1) or knockout methylcytosine dioxygenase in B cells (Aim 2.2). Finally, we will address the impact of nutritional/metabolic elements that modulate Sirt1 or methylcytosine dioxygenase activities on the lupus autoantibody response (Aim 3.1) and identify small molecule Sirt1 activators and methylcytosine dioxygenase inhibitors that blunt the autoantibody response (Aim 3.2). By unveiling B cell-intrinsic epigenetic mechanisms underlying the lupus autoantibody response, these experiments would identify modulators of such mechanisms as new lupus therapeutics.