Neutrophil-Driven M2-Like Macrophages Are Critical for Skin Fibrosis in a Systemic Sclerosis Model.

Systemic sclerosis (SSc) is a challenging autoimmune disease characterized by progressive fibrosis affecting the skin and internal organs. Despite the known infiltration of macrophages and neutrophils, their precise contributions to SSc pathogenesis remain elusive. In this study, we elucidated that CD206hiMHCIIlo M2-like macrophages constitute the predominant pathogenic immune cell population in the fibrotic skin of a bleomycin-induced SSc mouse model. These cells emerged as pivotal contributors to the profibrotic response by orchestrating the production of TGF-ß1 through a MerTK signaling-dependent manner. Notably, we observed that neutrophil infiltration was a prerequisite for accumulation of M2-like macrophages. Strategies such as neutrophil depletion or inhibition of CXCR1/2 were proven effective in reducing M2-like macrophages, subsequently mitigating SSc progression. Detailed investigations revealed that in fibrotic skin, neutrophil-released neutrophil extracellular traps were responsible for the differentiation of M2-like macrophages. Our findings illuminate the significant involvement of the neutrophil-macrophage-fibrosis axis in SSc pathogenesis, offering critical information for the development of potential therapeutic strategies.

Glucocorticoid activates STAT3 and NF-κB synergistically with inflammatory cytokines to enhance the anti-inflammatory factor TSG6 expression in mesenchymal stem/stromal cells.

Glucocorticoid (GC) is essential for maintaining immune homeostasis. While GC is known to regulate the expression of genes related to inflammation in immune cells, the effects of GC, especially in the presence of inflammation, on non-immune cells remain largely unexplored. In particular, the impact of GC on inflammatory cytokine-induced immune modulatory responses of tissue stromal cells is unknown, though it has been widely used to modulate tissue injuries. Here we found that GC could enhance the expression of TSG6, a vital tissue repair effector molecule, in IFNγ and TNFα treated human umbilical cord (UC)-MSCs. NF-κB activation was found to be required for GC-augmented TSG6 upregulation. STAT3, but not STAT1, was also found to be required for the TSG6 upregulation in MSCs exposed to IFNγ, TNFα and GC. Moreover, the phosphorylation (activation) of STAT3 was attenuated when NF-κB was knocked down. Importantly, human UC-MSCs pretreated with a cocktail containing GC, IFNγ, and TNFα could significantly enhance the therapeutic effect of human UC-MSCs in an acute lung injury mouse model, as reflected by reduced infiltration of immune cells and down-regulation of iNOS in macrophages in the lung. Together, the findings reveal a novel link between GR, NF-κB and STAT3 in regulating the immunomodulatory and regenerative properties of MSCs, providing novel information for the understanding and treatment of inflammatory conditions.

PML-mediated nuclear loosening permits immunomodulation of mesenchymal stem/stromal cells under inflammatory conditions.

Nuclear configuration plays a critical role in the compartmentalization of euchromatin and heterochromatin and the epigenetic regulation of gene expression. Under stimulation by inflammatory cytokines IFN-γ and TNF-α, human mesenchymal stromal cells (hMSCs) acquire a potent immunomodulatory function enabled by drastic induction of various effector genes, with some upregulated several magnitudes. However, whether the transcriptional upregulation of the immunomodulatory genes in hMSCs exposed to inflammatory cytokines is associated with genome-wide nuclear reconfiguration has not been explored. Here, we demonstrate that hMSCs undergo remarkable nuclear reconfiguration characterized by an enlargement of the nucleus, downregulation of LMNB1 and LMNA/C, decondensation of heterochromatin, and derepression of repetitive DNA. Interestingly, promyelocytic leukaemia-nuclear bodies (PML-NBs) were found to mediate the nuclear reconfiguration of hMSCs triggered by the inflammatory cytokines. Significantly, when PML was depleted, the immunomodulatory function of hMSCs conferred by cytokines was compromised, as reflected by the attenuated expression of effector molecules in hMSCs and their failure to block infiltration of immune cells to lipopolysaccharide (LPS)-induced acute lung injury. Our results indicate that the immunomodulatory function of hMSCs conferred by inflammatory cytokines requires PML-mediated chromatin loosening.

Nitric oxide-dependent immunosuppressive function of thymus-derived mesenchymal stromal/stem cells.

BACKGROUND: The thymus is required for T cell development and the formation of the adaptive immunity. Stromal cells, which include thymic epithelial cells (TECs) and mesenchymal stromal cells (MSCs), are essential for thymic function. However, the immunomodulatory function of thymus-derived MSCs (T-MSCs) has not been fully explored. METHODS: MSCs were isolated from mouse thymus and their general characteristics including surface markers and multi-differentiation potential were characterized. The immunomodulatory function of T-MSCs stimulated by IFN-γ and TNF-α was evaluated in vitro and in vivo. Furthermore, the spatial distribution of MSCs in the thymus was interrogated by using tdTomato-flox mice corssed to various MSC lineage Cre recombinase lines. RESULTS: A subset of T-MSCs express Nestin, and are mainly distributed in the thymic medulla region and cortical-medulla junction, but not in the capsule. The Nestin-positive T-MSCs exhibit typical immunophenotypic characteristics and differentiation potential. Additionally, when stimulated with IFN-γ and TNF-α, they can inhibit activated T lymphocytes as efficiently as BM-MSCs, and this function is dependent on the production of nitric oxide (NO). Additionally, the T-MSCs exhibit a remarkable therapeutic efficacy in acute liver injury and inflammatory bowel disease (IBD). CONCLUSIONS: Nestin-positive MSCs are mainly distributed in medulla and cortical-medulla junction in thymus and possess immunosuppressive ability upon stimulation by inflammatory cytokines. The findings have implications in understanding the physiological function of MSCs in thymus.

Mesenchymal stem cells alleviate systemic sclerosis by inhibiting the recruitment of pathogenic macrophages.

Systemic sclerosis (SSc) is a recalcitrant autoimmune disease for which there is no cure. Mesenchymal stem cell (MSC)-based treatment has emerged as a promising therapeutic option for several autoimmune diseases. Previously, we found that the immunoregulatory potential of MSCs can be greatly enhanced by IFN-γ and TNF-α. Here, we found that IFN-γ- and TNF-α-pretreated MSCs significantly alleviated skin fibrosis in a bleomycin (BLM)-induced SSc model. Macrophages were found to be the predominant profibrotic immune cell population in the pathogenesis of SSc. The accumulation of macrophages was significantly decreased by MSC treatment. Importantly, MSCs primarily reduced the population of maturing macrophages with high CCR2 expression by inhibiting the generation of CCL2 from fibroblasts and macrophages. This finding may help to improve MSC-based clinical treatments for SSc patients.

Mesenchymal stem/stromal cells primed by inflammatory cytokines alleviate psoriasis-like inflammation via the TSG-6-neutrophil axis.

Psoriasis is currently an incurable skin disorder mainly driven by a chronic inflammatory response. We found that subcutaneous application of umbilical cord- derived mesenchymal stem/stromal cells (MSCs) primed by IFN-γ and TNF-α, referred to as MSCs-IT, exhibited remarkable therapeutic efficacy on imiquimod (IMQ)-induced psoriasis-like inflammation in mice. Neutrophil infiltration, a hallmark of psoriasis, was significantly reduced after treatment with MSCs-IT. We further demonstrated that the effects of MSCs-IT were mediated by tumor necrosis factor (TNF) stimulating gene-6 (TSG-6), which was greatly upregulated in MSCs upon IFN-γ and TNF-α stimulation. MSCs transduced with TSG-6 siRNA lost their therapeutic efficacy while recombinant TSG-6 applied alone could also reduce neutrophil infiltration and alleviate the psoriatic lesions. Furthermore, we demonstrated that TSG-6 could inhibit neutrophil recruitment by decreasing the expression of CXCL1, which may be related to the reduced level of STAT1 phosphorylation in the keratinocytes. Thus, blocking neutrophil recruitment by MSCs-IT or TSG-6 has potential for therapeutic application in human psoriasis.

Functional network analysis reveals biological roles of lncRNAs and mRNAs in MOG35-55 specific CD4+T helper cells.

Long non-coding RNAs have the potential to regulate immune responses. Their impact on multiple sclerosis has remained elusive. For illustrating their roles in experimental autoimmune encephalomyelitis (EAE) pathogenesis, we investigated the differential expression of lncRNAs and mRNAs in CD4+Th cells obtained from myelin oligodendrocytic glycoprotein35-55(MOG35-55)-induced EAE and complete Freund's adjuvant (CFA) controls. We observed differential expression of 1112 lncRNAs and 519 mRNAs in CD4+Th cells. The functional network showed lncRNAs had the capacity to modulate EAE pathogenesis via regulating many known EAE regulators such as Ptpn6. Predicting the function of lncRNAs demonstrated that dysregulated lncRNAs were closely associated with the development of EAE. These dysregulated lncRNAs may have function in EAE and they could be novel biomarkers and therapeutic targets of EAE. However, the precise mechanisms and biological functions of these specific lncRNAs in EAE pathogenesis require further study.