Tissue macrophages arise during embryogenesis from yolk-sac (YS) progenitors that give rise to primitive YS macrophages. Until recently, it has been impossible to isolate or derive sufficient numbers of YS-derived macrophages for further study, but data now suggest that induced pluripotent stem cells (iPSCs) can be driven to undergo a process reminiscent of YS-hematopoiesis in vitro. We asked whether iPSC-derived primitive macrophages (iMacs) can terminally differentiate into specialized macrophages with the help of growth factors and organ-specific cues. Co-culturing human or murine iMacs with iPSC-derived neurons promoted differentiation into microglia-like cells in vitro. Furthermore, murine iMacs differentiated in vivo into microglia after injection into the brain and into functional alveolar macrophages after engraftment in the lung. Finally, iPSCs from a patient with familial Mediterranean fever differentiated into iMacs with pro-inflammatory characteristics, mimicking the disease phenotype. Altogether, iMacs constitute a source of tissue-resident macrophage precursors that can be used for biological, pathophysiological, and therapeutic studies.

BackgroundAlthough fibroblast growth factor 19 (FGF19) can promote liver carcinogenesis in mice, its involvement in human hepatocellular carcinoma (HCC) has not been well investigated. FGF19, a member of the FGF family, has unique specificity for its receptor FGFR4. This study aimed to clarify the involvement of FGF19 in the development of HCC.MethodsWe investigated human FGF19 and FGFR4 expression in 40 hepatocellular carcinoma specimens using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) analysis and immunohistochemistry. Moreover, we examined the expression and the distribution of FGF19 and FGFR4 in 5 hepatocellular carcinoma cell lines (HepG2, HuH7, HLE, HLF, and JHH7) using RT-PCR and immunohistochemistry. To test the role of the FGF19/FGFR4 system in tumor progression, we used recombinant FGF19 protein and small interfering RNA (siRNA) of FGF19 and FGFR4 to regulate their concentrations.ResultsWe found that FGF19 was significantly overexpressed in HCCs as compared with corresponding noncancerous liver tissue (P < 0.05). Univariate and multivariate analyses revealed that the tumor FGF19 mRNA expression was an independent prognostic factor for overall and disease-free survival. Moreover, we found that the FGF19 recombinant protein could increase the proliferation (P < 0.01, n = 12) and invasion (P < 0.01, n = 6) capabilities of human hepatocellular carcinoma cell lines and inhibited their apoptosis (P < 0.01, n = 12). Inversely, decreasing FGF19 and FGFR4 expression by siRNA significantly inhibited proliferation and increased apoptosis in JHH7 cells (P < 0.01, n = 12). The postoperative serum FGF19 levels in HCC patients was significantly lower than the preoperative levels (P < 0.01, n = 29).ConclusionsFGF19 is critically involved in the development of HCCs. Targeting FGF19 inhibition is an attractive potential therapeutic strategy for HCC.

Tumor lymphangiogenesis is now known to play a causal role in lymph node metastasis, and thus its inhibition would have great significance for the prevention of lymph node metastasis in cancer therapy. VEGF-C has recently been identified as a key molecule that involved in tumor lymphangiogenesis and lymphatic metastasis. However, the expressional regulation of VEGF-C is not fully understood. We investigated the role of mTOR, which is a downstream kinase of the phosphatidylinositol 3-kinase/Akt pathway, and the MAPK family (MEK1/2, p38, and JNK) in the regulation of VEGF-C and VEGF-A expression in B13LM cells, a lymphatic metastasis-prone pancreatic tumor cell line. We also investigated the antilymphangiogenic effect of rapamycin, a specific inhibitor of mTOR in vivo using male BALB/c nu/nu mice. VEGF-C expression was inhibited by the inhibitors for mTOR, p38, and JNK, but not by the inhibitor for MEK1/2, whereas VEGF-A expression was inhibited by all four of these inhibitors. The serum starvationinduced expression of VEGF-C was inhibited by rapamycin, whereas that of VEGF-A was incompletely inhibited. The metastatic experiment in vivo demonstrated that the number and the area of lymphatic vessels in the primary tumors were significantly decreased by rapamycin. Finally, the lymph node metastasis was significantly suppressed in rapamycin-treated mice. Our results suggest that mTOR, p38, and JNK play important roles in VEGF-C expression, and that rapamycin has an antilymphangiogentic effect and exerts the expected inhibition of lymphatic metastasis.

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