Abstract 431: Nlrp3 Inflammasome Inhibits Cholesterol Efflux in Macrophages by Downregulating Gpr109a Expression. A Novel Proatherogenic Mechanism

Recent studies suggest that Nlrp3 inflammasome activation plays a critical role in the development of atherosclerosis and Chlamydia pneumoniae (Cpn ) infection has been shown to accelerate atherogenesis. Herein, we asked whether Cpn infection induced acceleration is via Nlrp3 inflammasome activation in hypercholestrolemia mouse model. Nlrp3 -/- Ldlr -/- , Casp1 -/- Ldlr -/- and Ldlr -/- mice were infected intranasally with Cpn followed by western diet (WD) for 16 weeks. Ldlr -/- mice infected with Cpn infection had markedly increased lesion size in the aortic sinus and aorta en face compared to WD only group. Casp1 activation in lesion macrophages in Ldlr -/- mice was also increased in Cpn group vs controls. Nlrp3 -/- Ldlr -/- or Casp1 -/- Ldlr -/- mice with and without Cpn resulted in significantly smaller of plaques in aortic root and aorta compare to Ldlr -/- mice. However, no difference was observed between Cpn infected and uninfected groups in the double knockout animals. Furthermore, foam cell formation of Nlrp3 -/- , and Casp1 -/- peritoneal macrophages after treatment with OxLDL and Cpn was significantly reduced when compared with WT cells. Interestingly, expression levels of the cholesterol efflux transporter, ATP-binding cassette A1 (ABCA1), was increased by RT PCR and western analysis in the KO macrophages. Further investigations found that the niacin receptor Gpr109a, a known positive regulator of ABCA1, was upregulated in Nlrp3 KO macrophages during foam cell formation. Hydroxy-butyrate, an activating ligand of GPR109, was produced by macrophages after Cpn infection indicating a feedback loop. Intact IL-1 signaling suppressed Gpr109a expression suggesting a pathway by which the inflammasome and IL-1β could enhance foam cell formation. In aortic root lesions, macrophage expression of Gpr109a was increased in Nlrp3 -/- Ldlr - - mice compare with Ldlr -/- mice on WD and infected with Cpn . In conclusion, the activation of the NLRP3 inflammasome negatively regulate Gpr109a receptor and its downstream cholesterol efflux transporter ABCA1, which leads to more foam cell formation and acceleration of atherosclerosis in Ldlr -/- mice.

This work was supported by the National Institutes of Health grant HL111483 (to S. Chen)

Abstract 1459: Revealing the underlying causes of the gender disparity in melanoma: Role of testosterone

Introduction: At advanced age, men have increasingly higher incidence of melanoma compared with women, as well as continuously decreasing levels of testosterone. With the low rate of survival for distant metastatic patients with melanoma, especially in men, studies aimed at elucidating the immunological and hormonal mechanisms underlying the gender disparity are warranted.

Procedures: To investigate the gender disparity observed between men and women affected by melanoma, we used an experimental murine model where B16 melanoma cells were injected i.v. into C57BL/6 mice and lung colonization was assessed at day 14. The roles of neutrophils and NK cells were then investigated by specific cell depletion using anti-Ly6G(1A8) and anti-NK1.1 monoclonal antibodies, respectively. Depleting antibodies or control IgG were injected every 3 days, starting one day before melanoma cell injection. To elucidate the role of hormones, ovariectomy or castration surgeries were performed 4 weeks before B16 injection and 60 day slow release pellets were inserted at the time of surgery. Findings were reproduced with a second murine melanoma cell line (YUMM1.7) derived from a genetically engineered mouse harboring human mutations in BrafV600, as well as loss of Cdkn2a and PTEN.

Data: Compared with males, naïve female mice injected with melanoma (B16 or YUMM1.7) cells have higher lung tumor burden, reduced neutrophil infiltration, and decreased NK cell activation. Ovariectomy of female mice did not affect lung tumor burden, indicating that estrogen and progesterone are not protective. Interestingly, castrated males revealed increased lung metastasis and worse survival rates compared with sham male mice, suggesting a protective role for testosterone. Further, testosterone replacement in castrated mice significantly reduced the elevated lung tumor burden to equal levels observed in sham males. Depletion of NK cells greatly increased tumor burden in both male and female mice in a gender independent manner. In contrast, neutrophil depletion increased lung tumor burden only in male mice and had no significant affect in female mice, indicating a potential gender difference in neutrophils. Moreover, neutrophil depletion in male mice also reduced NK activation and IFN-γ production, suggesting a stimulatory relationship between neutrophils and NK cells.

Conclusion: Our data indicates that both neutrophils and NK cells are important for the initial response against melanoma colonization of the lung. Neutrophil depletion, as well as our castration data, indicate that there is a gender specific differential response, which may contribute to the gender disparity seen in human melanoma incidence and survival. Further, testosterone replacement at physiological levels may benefit a subset of melanoma patients.

Citation Format: Janet Markman, Daiko Wakita, Timothy Crother, Moshe Arditi. Revealing the underlying causes of the gender disparity in melanoma: Role of testosterone. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1459.

Proteome Analysis of Lipid Rafts in Jurkat Cells Characterizes a Raft Subset That Is Involved in NF-κB Activation

Lipid rafts are detergent-insoluble membrane domains that play a key role in signal transduction by the T-cell antigen receptor. Proteome analysis revealed the presence of amidosulfobetaine-soluble signal transducing, integral membrane, cytoskeletal, heat shock, and GTP-binding proteins in rafts prepared from Jurkat cells. Several of these proteins were recruited to rafts by CD3/CD28 costimulation. Of particular interest is the inducible association of activated IkappaB kinase complexes with raft vesicles that could be captured with anti-flotillin-1 antibodies. Following amidosulfobetaine solubilization, flotillin-beta and IKKbeta underwent reciprocal co-immunoprecipitation. Treatment of Jurkat cells with methyl-beta-cyclodextrin disrupted the assembly and activation of this raft complex and also interfered in CD3/ CD28-induced activation of a NF-kappaB response element in the IL-2 promoter.