Kupffer cells prevent pancreatic ductal adenocarcinoma metastasis to the liver in mice

Adaptor protein 3BP2 regulates gene expression in addition to the ubiquitination and proteolytic activity of MALT1 in dectin-1-stimulated cells

Dectin-1, a C-type lectin, plays important roles in the induction of antifungal immunity. Caspase recruitment domain-containing protein 9 (CARD9) is essential for the dectin-1-induced production of cytokines through the activation of NF-κB. However, the molecular mechanisms underlying the dectin-1-mediated activation of CARD9 have not been fully elucidated. Recently, we reported that the adaptor protein SH3 domain-binding protein 2 (3BP2) is required for the dectin-1-induced production of cytokines and activation of NF-κB, although the relationship between 3BP2 and CARD9 in dectin-1-mediated signaling remains unclear. Here, we report that 3BP2 is required for dectin-1-induced expression of several genes that may contribute to antifungal immunity in bone marrow-derived dendritic cells (BMDCs). The results of reporter assays using HEK-293T cells indicate that 3BP2 induces CARD9-mediated activation of NF-κB through B-cell leukemia/lymphoma 10, mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1), and TNF receptor-associated factor 6-dependent mechanisms. In addition, we show that 3BP2 induces CARD9-mediated ubiquitination of cellular proteins and that MALT1 cleaves 3BP2 in a CARD9-dependent manner. Furthermore, we show that 3BP2 is required for the ubiquitination, in addition to the activation, of MALT1, which leads to MALT1-depenedent cleavage of 3BP2 in dectin-1-stimulated BMDCs. Finally, we identified hematopoietic cell-specific Lyn substrate 1 as a target of 3BP2, which is essential for dectin-1-induced expression of interleukin 10 in BMDCs. These results indicate that 3BP2 regulates gene expression and functions of MALT1 in dectin-1-stimulated cells and that 3BP2 plays an important role in the dectin-1-mediated antifungal immunity.

Alternations in inflammatory macrophage niche drive phenotypic and functional plasticity of Kupffer cells

Inflammatory signals lead to recruitment of circulating monocytes and induce their differentiation into pro-inflammatory macrophages. Therefore, whether blocking inflammatory monocytes can mitigate disease progression is being actively evaluated. Here, we employ multiple lineage-tracing models and show that monocyte-derived macrophages (mo-mac) are the major population of immunosuppressive, liver metastasis-associated macrophages (LMAM), while the proportion of Kupffer cells (KC) as liver-resident macrophages is diminished in metastatic nodules. Paradoxically, genetic ablation of mo-macs results in only a marginal decrease in LMAMs. Using a proliferation-recording system and a KC-tracing model in a monocyte-deficient background, we find that LMAMs can be replenished either via increased local macrophage proliferation or by promoting KC infiltration. In the latter regard, KCs undergo transient proliferation and exhibit substantial phenotypic and functional alterations through epigenetic reprogramming following the vacating of macrophage niches by monocyte depletion. Our data thus suggest that a simultaneous blockade of monocyte recruitment and macrophage proliferation may effectively target immunosuppressive myelopoiesis and reprogram the microenvironment towards an immunostimulatory state.

Establishment of a Transplantation Model of PDAC-Derived Liver Metastases

BACKGROUND

The highly metastatic nature of pancreatic ductal adenocarcinoma (PDAC) and the difficulty to achieve favorable patient outcomes emphasize the need for novel therapeutic solutions. For preclinical evaluations, genetically engineered mouse models are often used to mimic human PDAC but frequently fail to replicate synchronous development and metastatic spread. This study aimed to develop a transplantation model to achieve synchronous and homogenous PDAC growth with controlled metastatic patterns in the liver.

METHODS

To generate an orthotopic PDAC model, the DT6606 cell line was injected into the pancreas head of C57BL/6 mice, and their survival was monitored over time. To generate a heterotopic transplantation model, growing doses of three PDAC cell lines (DT6606, DT6606lm, and K8484) were injected into the portal vein of mice. Magnetic resonance imaging (MRI) was used to monitor metastatic progression, and histologic analysis was performed.

RESULTS

Orthotopically injected mice succumbed to the tumor within an 11-week period (average survival time, 78.2 ± 4.45 days). Post-mortem examinations failed to identify liver metastasis. In the intraportal model, 2 × 105 DT6606 cells resulted in an absence of liver metastases by day 21, whereas 5 × 104 DT6606lm cells and 7 × 104 K8484 cells resulted in steady metastatic growth. Higher doses caused significant metastatic liver involvement. The use of K8484 cells ensured the growth of tumors closely resembling the histopathologic characteristics of human PDAC.

CONCLUSIONS

This report details the authors' efforts to establish an "optimal" murine model for inducing metastatic PDAC, which is critical for advancing our understanding of the disease and developing more effective treatments.

The Role of Human and Animal Monocytes and Macrophages in Homeostasis and Disease

Monocytes and macrophages are the innate immune cells that are the first-line responders to invading pathogens or foreign objects[...].