Mineralocorticoid Receptor Deficiency in Macrophages Inhibits Atherosclerosis by Affecting Foam Cell Formation and Efferocytosis.

Mineralocorticoid receptor (MR) has been considered as a potential target for treating atherosclerosis. However, the cellular and molecular mechanisms are not completely understood. We aim to explore the functions and mechanisms of macrophage MR in atherosclerosis. Atherosclerosis-susceptible LDLRKO chimeric mice with bone marrow cells from floxed control mice or from myeloid MR knock-out (MRKO) mice were generated and fed with high cholesterol diet. Oil red O staining showed that MRKO decreased atherosclerotic lesion area in LDLRKO mice. In another mouse model of atherosclerosis, MRKO/APOEKO mice and floxed control/APOEKO mice were generated and treated with angiotensin II. Similarly, MRKO inhibited the atherosclerotic lesion area in APOEKO mice. Histological analysis showed that MRKO increased collagen coverage and decreased necrosis and macrophage accumulation in the lesions. In vitro results demonstrated that MRKO suppressed macrophage foam cell formation and up-regulated the expression of genes involved in cholesterol efflux. Furthermore, MRKO decreased accumulation of apoptotic cells and increased effective efferocytosis in atherosclerotic lesions. In vitro study further revealed that MRKO increased the phagocytic index of macrophages without affecting their apoptosis. In conclusion, MRKO reduces high cholesterol- or angiotensin II-induced atherosclerosis and favorably changes plaque composition, likely improving plaque stability. Mechanistically, MR deficiency suppresses macrophage foam cell formation and up-regulates expression of genes related to cholesterol efflux, as well as increases effective efferocytosis and phagocytic capacity of macrophages.

mTOR regulates TLR-induced c-fos and Th1 responses to HBV and HCV vaccines.

Although IL-12 plays a critical role in priming Th1 and cytotoxic T lymphocyte (CTL) responses, Toll-like receptor (TLR) signaling only induces low amounts of IL-12 in dendritic cells and macrophages, implying the existence of stringent regulatory mechanisms. In this study, we sought to uncover the mechanisms underlying TLR-induced IL-12 expression and the Th1 response. By systemic screening, we identified a number of protein kinases involved in the regulation of TLRinduced IL-12 expression. In particular, PI3K, ERK, and mTOR play critical roles in the TLR-induced Th1 response by regulating IL-12 and IL-10 production in innate immune cells. Moreover, we identified c-fos as a key molecule that mediates mTOR-regulated IL-12 and IL-10 expression in TLR signaling. Mechanistically, mTOR plays a crucial role in c-fos expression, thereby modulating NFκB binding to promoters of IL-12 and IL-10. By controlling the expression of a special innate gene program, mTOR can specifically regulate the TLR-induced T cell response in vivo. Furthermore, blockade of mTOR by rapamycin efficiently boosted TLR-induced antigen-specific T and B cell responses to HBV and HCV vaccines. Taken together, these results reveal a novel mechanism through which mTOR regulates TLR-induced IL-12 and IL-10 production, contributing new insights for strategies to improve vaccine efficacy.

Tyrosine phosphatase SHP-2 mediates C-type lectin receptor-induced activation of the kinase Syk and anti-fungal TH17 responses.

Fungal infection stimulates the canonical C-type lectin receptor (CLR) signaling pathway via activation of the tyrosine kinase Syk. Here we identify a crucial role for the tyrosine phosphatase SHP-2 in mediating CLR-induced activation of Syk. Ablation of the gene encoding SHP-2 (Ptpn11; called 'Shp-2' here) in dendritic cells (DCs) and macrophages impaired Syk-mediated signaling and abrogated the expression of genes encoding pro-inflammatory molecules following fungal stimulation. Mechanistically, SHP-2 operated as a scaffold, facilitating the recruitment of Syk to the CLR dectin-1 or the adaptor FcRγ, through its N-SH2 domain and a previously unrecognized carboxy-terminal immunoreceptor tyrosine-based activation motif (ITAM). We found that DC-derived SHP-2 was crucial for the induction of interleukin 1ß (IL-1ß), IL-6 and IL-23 and anti-fungal responses of the TH17 subset of helper T cells in controlling infection with Candida albicans. Together our data reveal a mechanism by which SHP-2 mediates the activation of Syk in response to fungal infection.

Conversion of trichosanthin-induced CD95 (Fas) type I into type II apoptotic signaling during Herpes simplex virus infection.

Trichosanthin (TCS) is a type I ribosome-inactivating protein with wide spectrum of pharmacological activities. It inhibits human immunodeficiency virus type 1 (HIV-1) and Herpes simplex virus type 1 (HSV-1) replication but the mechanism is not clear. From a previous study, TCS was found to be more cytotoxic to HIV-1 infected cells than uninfected cells. Similar finding was confirmed with HSV-1 in the present study. TCS induced cell death in HEp-2 cells and the EC(50) was 24.64µg/mL. When the same experiment was performed in HSV-1 infected HEp-2 cells, the EC(50) decreased to 3.01µg/mL. TCS appeared to cause more death and apoptosis in viral infected cells. This study explored plausible mechanism with respect to the apoptosis signal pathways. In uninfected cells, TCS induced CD95 (Fas)-mediated and caspase-8-dependent type I apoptosis. When cells were infected with HSV-1, apoptosis induced by TCS clearly switched to a more potent type II pathway. This involved mitochondrial depolarization and caspase-9 activation. The major evidences arose from studying the individual signals of the two apoptosis pathways in infected and uninfected cells. In addition, over expression of Bcl-2, which mainly affected the type II pathway reduced TCS induced apoptosis mostly in infected cells. This further demonstrated that the type II pathway was operating in infected cells. The reason for the switching is not entirely clear but it is well known that viral infection affects signal pathways especially those related to apoptosis. In conclusion, TCS selectively induces more apoptosis in HSV-1 infected cells than uninfected cells. The consequence of infection switches the TCS-induced apoptosis pathway from a CD95 (Fas) dependent type I to a more potent type II pathway mediated by mitochondrial depolarization and caspase-9 activation.

Construction of soluble Mamu-b*1703, a class I major histocompatibility complex of Chinese rhesus macaques, monomer and tetramer loaded with a simian immunodeficiency virus peptide.

Chinese-descent rhesus macaques have become more prevalent for HIV infection and vaccine investigation than Indian-origin macaques. Most of the currently available data and reagents such as major histocompatibility complex (MHC) class I tetramers, however, were derived from Indian-origin macaques due to the dominant use of these animals in history. Although there are significant differences in the immunogenetic background between the two macaque populations, they share a few of common MHC class I alleles. We reported in this study the procedure for preparation of a soluble Mamu-B*1703 (a MHC class I molecule of Chinese macaques) monomer and tetramer loaded with a dominant simian immunodeficiency virus (SIV) epitope IW9 (IRYPKTFGW) that was identified to be Mamu-B*1701-restricted in Indian macaques. The DNA fragment encoding the Mamu-B*1703 extracellular domain fused with a BirA substrate peptide (BSP) was amplified from a previously cloned cDNA and inserted into a prokaratic expression vector. In the presence of the antigenic peptide IW9 and light chain beta2-microglobulin, the expressed heavy chain was refolded into a soluble monomer. After biotinylation, four monomers were polymerized as a tetramer by phycoerythrin-conjugated streptavidin. The tetramer, having been confirmed to have the right conformation, was a potential tool for investigation of antigen-specific CD8(+) T-lymphocytes in SIV vaccine models of Chinese macaques. And our results also suggested that some antigenic peptides reported in Indian-origin macaques could be directly recruited as ligands for construction of Chinese macaque MHC tetramers.

The immunosuppressive effect of gossypol in mice is mediated by inhibition of lymphocyte proliferation and by induction of cell apoptosis.

AIM: To investigate the immunosuppressive effect of gossypol in mice both in vitro and in vivo. METHODS: The in vitro effect of gossypol on the proliferation of lymphocytes isolated from lymph nodes of BALB/c mice was determined by CFSE staining and by an MTS assay. Lymphocyte activation and lymphoblastic transformation were evaluated with immunostaining. Cell apoptosis was detected by Annexin-V and Hoechst 33342 staining. The in vivo immunosuppressive effect of gossypol on the DTH reaction was evaluated using a mouse DTH model induced by 2,4-dinitro-1-fluorobenzene (DNFB). The thickness of the ears was measured, and the histological changes of the mouse auricles were observed after hematoxylin-eosin staining. The proliferation capacity of lymphocytes from DTH mice was also assayed. RESULTS: In vitro, gossypol could significantly inhibit the proliferation of mouse lymphocytes stimulated with phorbol ester plus ionomycin in a dose-dependent manner. Although the expression of the early activation antigen CD69 was not affected, the lymphoblastic transformation of both T and B lymphocyte subsets was significantly suppressed by gossypol. Moreover, gossypol could induce apoptosis of lymphocytes, and the effect was time- and dose-dependent. In vivo, the DTH reaction in mice was markedly alleviated by gossypol injected intraperitoneally. Lymphocytes from drug-treated DTH mice had a reduced proliferation capacity as compared with lymphocytes from untreated DTH mice. Gossypol treatment also markedly reduced the number of infiltrated lymphocytes in the auricles of DTH mice. CONCLUSION: Gossypol exhibited immunosuppressive effects in mice, probably by inhibition of lymphocyte proliferation and by induction of cell apoptosis.

Identification of major histocompatibility complex class I alleles in Chinese rhesus macaques.

Major histocompatibility complex (MHC) class I information is vital for understanding variance of immune responses in HIV vaccination and biomedical models. In this study, 9 Mamu-A and 13 Mamu-B alleles were identified from the cDNA products of 10 Chinese-origin rhesus macaques. Except for two alleles that had been reported by others, eight were novel and twelve extended the partial sequences that are available in GenBank. The additional information of MHC class I antigens might be beneficial to the availability of Chinese macaques in human disease studies. Furthermore, the polymorphism of leading peptides and the natural killer receptor recognition motifs in alpha1 domain both implies that Mamu-A and Mamu-B molecules might play key roles in innate immune responses of natural killer cells.