Neutrophil Elastase Induces Chondrocyte Apoptosis and Facilitates the Occurrence of Osteoarthritis via Caspase Signaling Pathway.

Osteoarthritis (OA) is the most common and prevalent chronic joint disorders in the elderly population across the globe, resulting in severe disability and impairment of quality of life. Existing treatment can only alleviate the symptoms and delay the progression of OA. Therefore, novel and effective therapeutics strategies for OA need to be developed. Our present study first found that neutrophil elastase (NE) was significantly increased in OA patients' synovial fluid. Next, we examined the effect of neutrophil elastase (NE) on chondrocytes in vitro and in vivo. The results showed that NE suppressed cell proliferation, induced apoptosis and prevented cell migration in chondrocytes in vitro, accompanied by the elevation of intracellular ROS and calcium level. Moreover, NE enhanced the cleaved caspase-3 levels and disrupted the mitochondrial transmembrane potential balance. Meanwhile, chondrocytes apoptosis induced by NE can be alleviated by caspase inhibitor, zVAD-FMK and antioxidants, GSH. Besides, treatment of sivelestat, the inhibitor of NE, significantly reduced the pathological processes in OA model rats in vivo. The results of our study suggested that NE is an important factor in OA, which induces chondrocyte apoptosis and facilitates the occurrence of OA via caspase signaling pathway, and targeting the crucial signal centering around NE may be the potential therapies for OA.

Krill Oil Perturbs Proliferation and Migration of Mouse Colon Cancer Cells in vitro by Impeding Extracellular Signal-Regulated Protein Kinase Signaling Pathway.

The prevalence of colorectal cancer (CRC) continues to increase. Treatment of CRC remains a significant clinical challenge, and effective therapies for advanced CRC are desperately needed. Increasing attention and ongoing research efforts have focused on krill oil that may provide health benefits to the human body. Here we report that krill oil exerts in vitro anticancer activity through a direct inhibition on proliferation, colony formation, migration, and invasion of mouse colon cancer cells. Krill oil inhibited the proliferation and colony formation of CT-26 colon cancer cells by causing G0/G1 cell cycle arrest and apoptosis. Cell cycle arrest was attributable to reduction of cyclin D1 levels in krill oil-treated cells. Further studies revealed that krill oil induced mitochondrial-dependent apoptosis of CT-26 cells, including loss of mitochondrial membrane potential, increased cytosolic calcium levels, activation of caspase-3, and downregulation of anti-apoptotic proteins MCL-1 and BCL-XL. Krill oil suppressed migration of CT-26 cells by disrupting the microfilaments and microtubules. Extracellular signal-regulated protein kinase (ERK) plays crucial roles in regulating proliferation and migration of cancer cells. We found that krill oil attenuated the activation of ERK signaling pathway to exert the effects on cell cycle, apoptosis, and migration of colon cancer cells. We speculate that polyunsaturated fatty acids of krill oil may dampen ERK activation by decreasing the phospholipid saturation of cell membrane. Although findings from in vitro studies may not necessarily translate in vivo, our study provides insights into the possibility that krill oil or its components could have therapeutic potential in colon cancer.

G-CSF shifts erythropoiesis from bone marrow into spleen in the setting of systemic inflammation.

The anemia of inflammation is related in part to abnormal erythropoiesis in bone marrow. G-CSF regulates granulopoiesis and is increased during systemic inflammation. Here, we have showed that high levels of G-CSF are associated with repression of bone marrow erythropoiesis and expansion of splenic erythropoiesis in Escherichia coli-infected mice and lipopolysaccharide-treated mice. Under lipopolysaccharide-induced systemic inflammatory conditions in mice, G-CSF neutralization with antibody alleviated the blockage of bone marrow erythropoiesis, prevented the enhancement of splenic erythropoiesis, ameliorated splenomegaly, and reduced the brittleness of spleen. We further demonstrated that after lipopolysaccharide treatment, TLR4-knockout mice display low levels of G-CSF, healthy bone marrow erythropoiesis, almost no stress erythropoiesis in the spleen, and normal size and toughness of spleen. In addition, we found HIF-mediated erythropoietin production is essential for splenic erythropoiesis in the setting of G-CSF-induced suppression of bone marrow erythropoiesis. Our findings identify G-CSF as a critical mediator of inflammation-associated erythropoiesis dysfunction in bone marrow and offer insight into the mechanism of G-CSF-induced splenic erythropoiesis. We provide experimentally significant dimension to the biology of G-CSF.

Arginine methyltransferase PRMT5 negatively regulates cGAS-mediated antiviral immune response.

Cyclic GMP-AMP synthase (cGAS) functions as an essential DNA sensor, which senses the cytoplasmic double-stranded DNA and activates the antiviral response. However, the posttranslational modification of cGAS remains to be fully understood and whether it has arginine methylation modification remains unknown. Here, we identified protein arginine methyltransferase 5 (PRMT5) as a direct binding partner of cGAS, and it catalyzed the arginine symmetrical dimethylation of cGAS at the Arg124 residue. Further investigation demonstrated that methylation of cGAS by PRMT5 attenuated cGAS-mediated antiviral immune response by blocking the DNA binding ability of cGAS. Oral administration of PRMT5 inhibitors significantly protected mice from HSV-1 infection and prolonged the survival time of these infected mice. Therefore, our findings revealed an essential regulatory effect of PRMT5 on cGAS-mediated antiviral immune response and provided a promising potential antiviral strategy by modulating PRMT5.

Breast cancer cells promote CD169+ macrophage-associated immunosuppression through JAK2-mediated PD-L1 upregulation on macrophages.

Macrophages are recognized as one of the major cell types in tumor microenvironment, and macrophage infiltration has been predominantly associated with poor prognosis among patients with breast cancer. Using the murine models of triple-negative breast cancer in CD169-DTR mice, we found that CD169+ macrophages support tumor growth and metastasis. CD169+ macrophage depletion resulted in increased accumulation of CD8+ T cells within tumor, and produced significant expansion of CD8+ T cells in circulation and spleen. In addition, we observed that CD169+ macrophage depletion alleviated tumor-induced splenomegaly in mice, but had no improvement in bone loss and repression of bone marrow erythropoiesis in tumor-bearing mice. Cancer cells and tumor associated macrophages exploit the upregulation of the immunosuppressive protein PD-L1 to subvert T cell-mediated immune surveillance. Within the tumor microenvironment, our understanding of the regulation of PD-L1 protein expression is limited. We showed that there was a 5-fold higher relative expression of PD-L1 on macrophages as compared with 4T1 tumor cells; coculture of macrophages with 4T1 cells augmented PD-L1 levels on macrophages, but did not upregulate the expression of PD-L1 on 4T1 cells. JAK2/STAT3 signaling pathway was activated in macrophages after coculture, and we further identified the JAK2 as a critical regulator of PD-L1 expression in macrophages during coculture with 4T1 cells. Collectively, our data reveal that breast cancer cells and CD169+ macrophages exhibit bidirectional interactions that play a critical role in tumor progression, and inhibition of JAK2 signaling pathway in CD169+ macrophages may be potential strategy to block tumor microenvironment-derived immune escape.