Role of the Cell Death Machinery in a Somatic Autoinflammatory Syndrome

PROJECT SUMMARY The autoinflammatory syndromes are a group of genetic diseases often caused by defects in innate immune genes. In December 2020, a novel somatically acquired autoinflammatory syndrome termed VEXAS (vacuoles, E1-ubiquitin-activating enzyme, X-linked, autoinflammatory, somatic) was reported. VEXAS is caused by somatic mutations in the ubiquitin-activating enzyme UBA1, most of which occur at an internal translation start site (Met41). As UBA1 is X-linked, VEXAS primarily affects males who mosaically harbor UBA1 mutations in hematopoietic stem and progenitor cells and their myeloid, but not lymphoid, progeny. These patients develop a constellation of clinical sequelae, including hematologic abnormalities, recurrent fevers, arthritis, and skin and lung inflammation. As a result, patients may require allogeneic bone marrow transplantation and suffer significant morbidity and mortality. Currently, our molecular and cellular understanding of VEXAS pathogenesis is limited by a lack of experimental model systems. To address this, we deploy an adenine base-editing system to recreate one of the most common VEXAS mutations in mouse or human macrophages and hematopoietic stem/progenitor cells (HSPCs). Using this system, we have found that mouse and human macrophages with a VEXAS-associated UBA 1 mutation undergo aberrant cell death during responses to tumor necrosis factor (TNF) or lipopolysaccharide (LPS, a toll-like receptor (TLR)4 ligand), and that VEXAS HSPCs spontaneously differentiate into myeloid cells. These cellular phenotypes correlate with key aspects of VEXAS pathogenesis in humans (i.e. autoinflammation and myeloid expansion) and thereby offer a platform for deciphering disease- driving mechanisms. In Aim 1, we will use this newly developed cell system to determine the mechanisms of TNF- and TLR4-driven cell death in macrophages carrying a VEXAS-associated UBA1 mutation. In Aim 2, we will investigate the role of ubiquitin-dependent signaling in this cell death phenotype. In Aim 3, we will elucidate mechanisms underlying the spontaneous myeloid differentiation of HSPCs with a VEXAS-associated UBA1 mutation. If successful, our proposal promises to yield fundamental insights into a devastating autoinflammatory disease with potential implications for understanding the interrelationships between clonal hematopoiesis and inflammation.