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Tag Archives: Tak Mak

Friday Science Review: February 18, 2011

Mapping the Development of the Pancreatic Lineage

McEwen Centre for Regenerative Medicine ♦ Published in Development, Mar. 2011 (Epub ahead of print)

Human pluripotent stem cells (PSCs) are being investigated as a means to produce insulin-positive cells for the treatment of diabetes. The most efficient mode of producing functional cell types in vitro is to navigate the signaling pathways and temporal cues that lead to their formation during embryonic development. In the case of insulin-producing cells the key is to recreate the pivotal steps in pancreatic development including the induction of definite endoderm, specification of endoderm to the pancreatic fate, and finally the generation of mature endocrine/exocrine cells. Despite the scientific community having a grasp on pancreatic development, current differentiation protocols suffer from low efficiency and an inability to produce homogenous results across a variety of PSC lines using identical treatments. We have yet to identify the optimal signaling pathways that must be leveraged to produce insulin+ cells. Robust differentiation protocols are also hampered by variations in the characteristics of PSC lines which lead to variability in the quality of differentiation cultures. Dr. Gordon Keller and his lab team ambitiously probed this issue by mapping the pancreatic development of several different PSC lines in order to identify the optimal signaling pathways and temporal requirements essential for producing cells of the pancreatic fate.

Keller’s team found that temporally modulating activin/nodal signaling early in the differentiation protocol was crucial for the development of definite endoderm and ultimately for pancreatic differentiation. Wnt signaling and inhibition of BMP signaling at various stages was also prerequisite for the production of insulin+ cells, noting that the degree of BMP inhibition required for efficient differentiation varied extensively amongst PSC lines. By implementing this stage-specific optimization approach for different cell lines, Keller and his colleagues were able to increase insulin expression in cell cultures by a whopping 250 times; some populations contained as much as 25% C-peptide+ cells (prior to C-peptide being cleaved from the pro-insulin molecule, it acts as a linker between the A and B chains of insulin).

This is the second, recent, body of research from Gordon Keller’s lab that emphasizes the importance of identifying the crucial temporal steps that must be satisfied for highly efficient differentiation to terminal cell fates. This paper also reminds us that individual PSC lines will likely require unique treatments in culture to produce maximal results for transplantation therapy.

IL-7 Therapy: A Stimulus Package for the Immune System

Campbell Family Institute for Cancer Research ♦ Published in Cell, Feb. 18, 2011 (Epub ahead of print)

After the immune system succumbs to uncontrollable viral turnover, it eventually fails, leaving the host prone to any number of opportunistic infections. This is the case with HIV infection. One of the primary focuses of HIV research today is the modulation of immune response to encourage the clearance of chronic viral infections. It appears that a certain cytokine, interleukin-7 (IL-7), may be able to prop up the immune system allowing it to move around mechanisms that circumvent immune response during times of chronic infection. In this study led by Dr. Tak Mak, researchers hypothesized that cytokines supporting homeostatic proliferation would be promising candidates for promoting immune response. Indeed, IL-7 did just that.

After administering IL-7 to mice that were chronically infected with lymphocytic chorimeningitis virus (LCMV) variant clone 13, researchers observed an increase in size of the naive T-cell pool, and an enhanced function and cytokine output in LCMV-specific T-cells. IL-7 therapy resulted in clearance of LCMV from chronically infected mice. The cytokine also appears to serve a second function — bolstering levels of the cytoprotective cytokine IL-22. An increase in IL-22 levels has the added benefit of protecting the liver from viral infection, an organ that is particularly prone to damage under the circumstances. Researchers believe IL-7 exerts its effects by downregulating suppressor of cytokine signaling 3 (Socs3) expression in T-cells through the suppression of the FoxO transcription factors.

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