No abstract

In infections, microbial components provide signals that alert the immune system to danger and promote the generation of immunity. In the absence of such signals, there is often no immune response or tolerance may develop. This has led to the concept that the immune system responds only to antigens perceived to be associated with a dangerous situation such as infection. Danger signals are thought to act by stimulating dendritic cells to mature so that they can present foreign antigens and stimulate T lymphocytes. Dying mammalian cells have also been found to release danger signals of unknown identity. Here we show that uric acid is a principal endogenous danger signal released from injured cells. Uric acid stimulates dendritic cell maturation and, when co-injected with antigen in vivo, significantly enhances the generation of responses from CD8+ T cells. Eliminating uric acid in vivo inhibits the immune response to antigens associated with injured cells, but not to antigens presented by activated dendritic cells. Our findings provide a molecular link between cell injury and immunity and have important implications for vaccines, autoimmunity and inflammation.

Somatic cells can be induced into pluripotent stem cells (iPSCs) with a combination of four transcription factors, Oct4/Sox2/Klf4/c-Myc or Oct4/Sox2/Nanog/LIN28. This provides an enabling platform to obtain patient-specific cells for various therapeutic and research applications. However, several problems remain for this approach to be therapeutically relevant due to drawbacks associated with efficiency and viral genome integration. Recently, it was shown that neural progenitor cells (NPCs) transduced with Oct4/Klf4 can be reprogrammed into iPSCs. However, NPCs express Sox2 endogenously, possibly facilitating reprogramming in the absence of exogenous Sox2. In this study, we identified a small-molecule combination, BIX-01294 and BayK8644, that enables reprogramming of Oct4/Klf4-transduced mouse embryonic fibroblasts, which do not endogenously express the factors essential for reprogramming. This study demonstrates that small molecules identified through a phenotypic screen can compensate for viral transduction of critical factors, such as Sox2, and improve reprogramming efficiency.

Human pluripotent stem cells represent a potentially unlimited source of functional pancreatic endocrine lineage cells. Here we report a highly efficient approach to induce human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells to differentiate into mature insulin-producing cells in a chemical-defined culture system. The differentiated human ES cells obtained by this approach comprised nearly 25% insulin-positive cells as assayed by flow cytometry analysis, which released insulin/C-peptide in response to glucose stimuli in a manner comparable to that of adult human islets. Most of these insulin-producing cells co-expressed mature β cell-specific markers such as NKX6-1 and PDX1, indicating a similar gene expression pattern to adult islet β cells in vivo. In this study, we also demonstrated that EGF facilitates the expansion of PDX1-positive pancreatic progenitors. Moreover, our protocol also succeeded in efficiently inducing human iPS cells to differentiate into insulin-producing cells. Therefore, this work not only provides a new model to study the mechanism of human pancreatic specialization and maturation in vitro, but also enhances the possibility of utilizing patient-specific iPS cells for the treatment of diabetes.

Conventional mouse and human embryonic stem cells (ESCs) can be typically derived by in vitro culture of blastocysts (Martin, 1981;Thomson et al., 1998), and induced pluripotent stem cells (iPSCs) can be generated by reprogramming somatic cells using defined genetic transduction methods (Takahashi et al., 2007;Takahashi and Yamanaka, 2006;Yu et al., 2007). In both cases, different signaling pathways appear to regulate pluripotency with different characteristics in the two species. However, while rat ESClike cells have been established based on certain traits (Demers et al., 2007;Ruhnke et al., 2003;Schulze et al., 2006;Ueda et al., 2008), to date, these lines fall short of exhibiting true pluripotency (e.g., fail to form teratoma or no/little contribution to chimerism) and thus cannot be considered authentic rat ESCs. Here, we reveal combined genetic reprogramming and chemical conditions that generate and maintain rat iPSCs (riPSCs) that can give rise to teratomas and contribute extensively to chimeric rats. The same strategy is also sufficient to generate atypical human iPSCs (hiPSCs) that exhibit similar colony morphology and self-renewal requirements/signaling responses as those of mESCs.Pluripotent stem cells have also been derived from the postimplantation egg cylinder stage epiblasts of mouse and rat (Brons et al., 2007;Tesar et al., 2007). These populations have been termed epiblast stem cells (EpiSCs). EpiSCs seem to correspond very closely to conventional hESCs with respect to colony morphology and the culture/ signaling requirements that maintain pluripotency but exhibit a range of significant phenotypic and signaling response differences from conventional mESCs. For