The Mechanism of Hematological Abnormalities in Systemic Autoimmunity

ABSTRACT Systemic autoimmune diseases such as systemic lupus erythematosus (SLE) are mediated by autoantibodies against key tissue constituents, accompanied by the activation of innate immune system. In addition, systemic autoimmunity is frequently associated with hematological complications such as lymphopenia, anemia and/or thrombocytopenia, which can be debilitating and even life-threatening. These abnormalities are typically considered as isolated symptoms caused by autoantibodies against the respective blood cell types, and are treated by immunosuppressive therapies. On the other hand, it is possible that frequent hematopoietic abnormalities in SLE may reflect a defect in the source of hematopoiesis, i.e. hematopoietic stem cells (HSC) and/or progenitors. This model has important implications for the pathogenesis and treatment of SLE; however, it remains to be supported by genetic and mechanistic evidence. Our preliminary studies suggest that the bone marrow from mice with SLE-like disease showed impaired ability to reconstitute irradiated recipients. Moreover, HSCs in moribund mice showed increased proliferation and upregulation of transcripts associated with stem cell exhaustion. We therefore hypothesize that clinical SLE-like disease impairs the activity of HSC, which may further exacerbate hematological abnormalities and inflammation. This hypothesis will be tested using two Specific Aims. In Aim 1, we will characterize HSC impairment in a mouse model of SLE-like disease, including its cell-extrinsic nature and relevance to endogenous hematopoiesis. In Aim 2, we will characterize the epigenome of disease-affected HSC, as well as molecular pathways that cause HSC impairment in this model. Collectively, these studies may support the paradigm of impaired HSC activity as a source of hematopoietic abnormalities and "trained autoimmunity" in SLE. As such, they may pave the way for future studies of stem/progenitor function in human SLE and of its potential therapeutic modulation.