Aims: Cellular senescence and its secretory phenotype (senescence-associated secretory phenotype [SASP]) develop after long-term expansion of mesenchymal stromal cells (MSCs). Further investigation of this phenotype is required to improve the therapeutic efficacy of MSC-based cell therapies. In this study, we show that positive feedback between SASP and inherent senescence processes plays a crucial role in the senescence of umbilical cord blood-derived MSCs (UCB-MSCs). Results: We found that monocyte chemoattractant protein-1 (MCP-1) was secreted as a dominant component of the SASP during expansion of UCB-MSCs and reinforced senescence via its cognate receptor chemokine (c-c motif) receptor 2 (CCR2) by activating the ROS-p38-MAPK-p53/p21 signaling cascade in both an autocrine and paracrine manner. The activated p53 in turn increased MCP-1 secretion, completing a feed-forward loop that triggered the senescence program in UCBMSCs. Accordingly, knockdown of CCR2 in UCB-MSCs significantly improved their therapeutic ability to alleviate airway inflammation in an experimental allergic asthma model. Moreover, BMI1, a polycomb protein, repressed the expression of MCP-1 by binding to its regulatory elements. The reduction in BMI1 levels during UCB-MSC senescence altered the epigenetic status of MCP-1, including the loss of H2AK119Ub, and resulted in derepression of MCP-1. Innovation: Our results provide the first evidence supporting the existence of the SASP as a causative contributor to UCB-MSC senescence and reveal a so far unappreciated link between epigenetic regulation and SASP for maintaining a stable senescent phenotype. Conclusion: Senescence of UCB-MSCs is orchestrated by MCP-1, which is secreted as a major component of the SASP and is epigenetically regulated by BMI1. Antioxid. Redox Signal. 24, 471-485.

Asthma is a chronic airway inflammatory disease typically associated with T helper cell type 2 (Th2) cytokines. IL-32, first reported as an inducer of tumor necrosis factor (TNF)-α, is an inflammatory cytokine involved in various autoinflammatory diseases, viral infection, and cancer-related inflammation. However, the role of IL-32γ in asthma has not been clearly elucidated. In this study, the levels of IL-32γ in sputum from patients with asthma were measured by ELISA, and IL-32γ function was investigated in murine models of asthma with human IL-32γ-overexpressed transgenic (IL-32γ TG) mice. The therapeutic effect of recombinant IL-32γ (rIL-32γ) on allergic inflammation was also evaluated through bronchoalveolar lavage fluid analysis and histopathologic examinations. Sputum IL-32γ levels from patients with asthma were lower than those from healthy control subjects. In an acute mouse model of asthma, IL-32γ TG mice exhibited significantly reduced airway inflammation compared with that in wild-type mice. The production of Th1 cytokines, such as TNF-α and IFN-γ, and Th2 cytokines, such as IL-4, IL-5, and IL-13, was decreased in the lungs of IL-32γTG mice. On the contrary, the expression of IL-10 and IL-10-producing CD11b(+) monocytic cells was significantly increased in the lungs of ovalbumin-sensitized IL-32γ TG mice. In addition, rIL-32γ treatment revealed a suppressive effect on the airway inflammation in a chronic mouse model of asthma. The results of this study suggest that IL-32γ may have a preventive role in the development of allergic airway inflammation and could be a potential novel therapeutic target for bronchial asthma.

Recruitment and activation of dendritic cells (DCs) in the lungs are critical for Th2 responses in asthma, and CCL20 secreted from bronchial epithelial cells (BECs) is known to influence the recruitment of DCs. Because asthma is a disease that is closely associated with oxidative stress, we hypothesized that clusterin, an oxidative stress regulatory molecule, may have a role in the development of allergic airway inflammation. The aim of this study was to examine whether clusterin regulates CCL20 production from the BECs and the subsequent DC recruitment in the lungs. To verify the idea, clusterin knockout (Clu−/−), clusterin heterogeneous (Clu+/−), and wild-type mice were exposed intranasally to house dust mite (HDM) extract to induce allergic airway inflammation. We found that the total number of immune cells in bronchoalveolar lavage fluid and the lung was increased in Clu−/− and Clu+/− mice. Of these immune cells, inflammatory DCs (CD11b+CD11c+) and Ly6Chigh monocyte populations in the lung were significantly increased, which was accompanied by increased levels of various chemokines, including CCL20 in bronchoalveolar lavage fluid, and increased oxidative stress markers in the lung. Moreover, HDM-stimulated human BECs with either up- or downregulated clusterin expression showed that CCL20 secretion was negatively associated with clusterin expression. Interestingly, clusterin also reduced the level of intracellular reactive oxygen species, which is related to induction of CCL20 expression after HDM stimulation. Thus, the antioxidant property of clusterin is suggested to regulate the expression of CCL20 in BECs and the subsequent recruitment of inflammatory DCs in the airway.

Although chronic eosinophilic inflammation is a common feature in patients with asthma, some patients have neutrophil-dominant inflammation, which is known to be associated with severe asthma.Human mesenchymal stem cells (hMSCs) have shown promise in treating various refractory immunological diseases. Thus, hMSCs may represent an alternative therapeutic option for asthma patients with neutrophil-dominant inflammation, in whom current treatments are ineffective. BALB/c mice exposed to ovalbumin and polyinosinic:polycytidylic acid (Poly I:C) to induce neutrophilic airway inflammation were systemically treated with hMSCs to examine whether the hMSCs can modulate neutrophilic airway inflammation. In addition, cytokine production was evaluated in co-cultures of hMSCs with either anti-CD3/CD28-stimulated peripheral blood mononuclear cells (PBMCs) obtained from asthmatic patients or cells of the human bronchial epithelial cell line BEAS-2B to assess the response to hMSC treatment. The total number of immune cells in bronchoalveolar lavage fluid (BALF) showed a dramatic decrease in hMSC-treated asthmatic mice, and, in particular, neutrophilic infiltration was significantly attenuated. This phenomenon was accompanied by reduced CXCL15 production in the BALF. BEAS-2B cells co-cultured with hMSCs showed reduced secretion of IL-8. Moreover, decreased secretion of IL-4, IL-13 and IFN-γ was observed when human PBMCs were cultured with hMSCs, whereas IL-10 production was greatly enhanced. Our data imply that hMSCs may have a role in reducing neutrophilic airway inflammation by downregulating neutrophil chemokine production and modulating T-cell responses.