Interleukin 26 Induces Macrophage IL-9 Expression in Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is an autoimmune disease with chronic inflammation, bone erosion, and joint deformation. Synovial tissue in RA patients is full of proinflammatory cytokines and infiltrated immune cells, such as T help (Th) 9, Th17, macrophages, and osteoclasts. Recent reports emphasized a new member of the interleukin (IL)-10 family, IL-26, an inducer of IL-17A that is overexpressed in RA patients. Our previous works found that IL-26 inhibits osteoclastogenesis and conducts monocyte differentiation toward M1 macrophages. In this study, we aimed to clarify the effect of IL-26 on macrophages linking to Th9 and Th17 in IL-9 and IL-17 expression and downstream signal transduction. Murine and human macrophage cell lines and primary culture cells were used and stimulated by IL26. Cytokines expressions were evaluated by flow cytometry. Signal transduction and transcription factors expression were detected by Western blot and real time-PCR. Our results show that IL-26 and IL-9 colocalized in macrophage in RA synovium. IL-26 directly induces macrophage inflammatory cytokines IL-9 and IL-17A expression. IL-26 increases the IL-9 and IL-17A upstream mechanisms IRF4 and RelB expression. Moreover, the AKT-FoxO1 pathway is also activated by IL-26 in IL-9 and IL-17A expressing macrophage. Blockage of AKT phosphorylation enhances IL-26 stimulating IL-9-producing macrophage cells. In conclusion, our results support that IL-26 promotes IL-9- and IL-17-expressing macrophage and might initiate IL-9- and IL-17-related adaptive immunity in rheumatoid arthritis. Targeting IL-26 may a potential therapeutic strategy for rheumatoid arthritis or other IL-9 plus IL-17 dominant diseases.

Golgin Imh1 and GARP complex cooperate to restore the impaired SNARE recycling transport induced by ER stress.

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces the unfolded protein response (UPR), which acts through various mechanisms to reduce ER stress. While the UPR has been well studied for its effects on the ER, its impact on the Golgi is less understood. The Golgi complex receives transport vesicles from the endosome through two types of tethering factors: long coiled-coil golgin and the multisubunit Golgi-associated retrograde protein (GARP) complex. Here, we report that ER stress increases the phosphorylation of golgin Imh1 to maintain the GARP-mediated recycling of the SNAREs Snc1 and Tlg1. We also identify a specific function of the Golgi affected by ER stress and elucidate a homeostatic response to restore this function, which involves both an Ire1-dependent and a MAP kinase Slt2/ERK2-dependent mechanism. Furthermore, our findings advance a general understanding of how two different types of tethers act cooperatively to mediate a transport pathway.

Interleukin 26 Skews Macrophage Polarization Towards M1 Phenotype by Activating cJUN and the NF-κB Pathway.

Interleukin 26 (IL-26) is a new member of the IL-10 family that is highly expressed in rheumatoid arthritis (RA). However, the functions of IL-26 produced by macrophages in RA have not been elucidated. In the present work, we evaluated the effects and the mechanisms of IL-26 on M1 and M2 macrophage differentiation. Human or mouse macrophage cells were treated with lipopolysaccharides (LPS), interferon gamma (IFNγ), or IL-4 alone or concurrently treated with IL-26 to monitor M1 or M2 macrophage subtypes. The expression level of M1 or M2 macrophage genes was evaluated by reverse transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). The molecular mechanisms of downstream signaling activation during differentiation were investigated by immunoblotting assay. Our results found that IL-26 promoted macrophage cells from CD80+ M1 macrophage differentiation, not from the CD206+ M2 phenotype. The messenger RNA of M1-type macrophage markers tumor necrosis factor alpha (TNFα) and inducible nitric oxide synthase (iNOS) was up-regulated in the IL-26-treated group. Also, the M1-related proinflammatory cytokines TNFα and IL-6 were induced after IL-26 stimulation. Interestingly, IL-10, a cytokine marker of M2 macrophage, was also elevated after IL-26 stimulation. Moreover, the M1-like macrophage stimulated by IL-26 underwent cJUN, nuclear factor kappa B (NF-κB), and signal transducer and activator of transcription 1 (STAT1) activation. Our findings suggested the role of IL-26 in synovial macrophages of active rheumatoid arthritis and provided a new insight into IL-26 as a candidate therapeutic target in rheumatoid arthritis.

Action of Arl1 GTPase and golgin Imh1 in Ypt6-independent retrograde transport from endosomes to the trans-Golgi network.

The Arf and Rab/Ypt GTPases coordinately regulate membrane traffic and organelle structure by regulating vesicle formation and fusion. Ample evidence has indicated that proteins in these two families may function in parallel or complementarily; however, the manner in which Arf and Rab/Ypt proteins perform interchangeable functions remains unclear. In this study, we report that a Golgi-localized Arf, Arl1, could suppress Ypt6 dysfunction via its effector golgin, Imh1, but not via the lipid flippase Drs2. Ypt6 is critical for the retrograde transport of vesicles from endosomes to the trans-Golgi network (TGN), and its mutation leads to severe protein mislocalization and growth defects. We first overexpress the components of the Arl3-Syt1-Arl1-Imh1 cascade and show that only Arl1 and Imh1 can restore endosome-to-TGN trafficking in ypt6-deleted cells. Interestingly, increased abundance of Arl1 or Imh1 restores localization of the tethering factor Golgi associated retrograde-protein (GARP) complex to the TGN in the absence of Ypt6. We further show that the N-terminal domain of Imh1 is critical for restoring GARP localization and endosome-to-TGN transport in ypt6-deleted cells. Together, our results reveal the mechanism by which Arl1-Imh1 facilitates the recruitment of GARP to the TGN and compensates for the endosome-to-TGN trafficking defects in dysfunctional Ypt6 conditions.