Usp22 is an intracellular regulator of systemic emergency hematopoiesis

Emergency hematopoiesis is a concerted response geared towards enhanced protection from infection, involving multiple cell types and developmental stages across the immune system. Despite its importance, the underlying molecular regulation remains poorly understood. The deubiquitinase USP22 regulates the levels of monoubiquitinated histone H2B (H2Bub1), which is involved in intracellular interferon responses. Here we show that, in the absence of infection or inflammation, mice lacking Usp22 in blood and immune cells display profound systemic emergency hematopoiesis, evident by increased hematopoietic stem cell proliferation, myeloid bias, and extramedullary hematopoiesis. Functionally, loss of Usp22 results in elevated phagocytosis by neutrophilic granulocytes, and enhanced innate protection against Listeria monocytogenes infection. At the molecular level, we find this state of emergency hematopoiesis associated with transcriptional signatures of myeloid priming, enhanced mitochondrial respiration, as well as innate and adaptive immunity and inflammation. Augmented inflammatory gene expression was linked to elevated locus-specific H2Bub1 levels. Collectively, a tunable epigenetic state promotes systemic emergency hematopoiesis in a cell-autonomous manner and enhances innate protection, paving potential ways towards immune enhancement. To uncover potential cell-intrinsic and systemic functions of Usp22 in hematopoiesis and immunity in vivo, we analyzed conditional Usp22 KO mice, with multiple omics approaches, including bulk and single-cell transcriptomics analysis, and epigenome profiling using ATAC and ChIP sequencing.