Depicting pathogenesis of osteomyelitis by single cell RNA-sequencing and an involvement of Morrbid in the autoinflammatory disease

Autoinflammatory diseases (AIDs) are defined as abnormal activation of the innate immune system leading to spontaneous and uncontrolled inflammation. The AIDs affect bone tissue and lead to chronic recurrent multifocal osteomyelitis (CRMO). However, the etiology and treatment of CRMO remain elusive. A mouse strain, Pstpip2cmo/cmo (cmo: chronic multifocal osteomyelitis), exhibits phenotypic characteristics similar to human CRMO. Morrbid is a long non-coding RNA gene and has been indicated in leukemogenesis in our previous studies. In this study, we demonstrated that Morrbid and Pstpip2 are co-expressed in mature myeloid cells and hypothesized a role of Morrbid in osteomyelitis. The Pstpip2-/- mice have the same phenotype as Pstpip2cmo/cmo, mimicking CRMO, while loss of Morrbid in Pstpip2-/-mice significantly inhibited the initiation and progression of CRMO symptoms, as well as the dysregulated activation of myeloid cells and the excessive release of inflammatory cytokines. Furthermore, single-cell RNA-sequencing (scRNA-seq) analysis from the Pstpip2-/- mice and the compound mutant mice supports that reduction of osteoclasts and inflammatory cells caused by Morrbid loss. The study systematically profiles the etiology of CRMO by scRNA-seq and warrants that inhibiting the lifespan of inflammatory myeloid cells by targeting Morrbid is an effective therapeutic strategy for osteomyelitis. HighlightsO_LIWe generated a frameshift mutant mouse strain Pstpip2-/-, which have a classic CRMO-like phenotype as same as Pstpip2cmo/cmo and could be used for testing various anti-inflammation perturbations. C_LIO_LILoss of Morrbid significantly inhibited the autoinflammatory symptoms in Pstpip2-/- mice, suggesting that Morrbid is a novel target for mitigating CRMO. C_LIO_LIscRNA-seq analysis of the affected bone marrow cells in Pstpip2-/-revealed the abnormalities of osteoclasts (OC), neutrophils (NE) and granulocyte macrophage progenitors (GMP) in both their fractions and inflammatory activities. C_LIO_LIUpon loss of Morrbid, we observed reduced composition and proliferation of OC and decreased activity of Nfkb2 and Rela in the compound mutants. C_LI