Parabiosis experiments indicate that impaired regeneration in aged mice is reversible by exposure to a young circulation, suggesting that young blood contains humoral “rejuvenating” factors that can restore regenerative function. Here, we demonstrate that the circulating protein Growth Differentiation Factor 11 (GDF11) is a rejuvenating factor for skeletal muscle. Supplementation of systemic GDF11 levels, which normally decline with age, by heterochronic parabiosis or systemic delivery of recombinant protein, reversed functional impairments and restored genomic integrity in aged muscle stem cells (satellite cells). Increased GDF11 levels in aged mice also improved muscle structural and functional features and increased strength and endurance exercise capacity. These data indicate that GDF11 systemically regulates muscle aging and may be therapeutically useful for reversing age-related skeletal muscle and stem cell dysfunction.

BACKGROUND & AIMS Hepatocyte transplantation is a potential therapeutic approach for liver disease. However, most patients with chronic hepatic damage have cirrhosis and fibrosis, which limit the potential for cell-based therapy of the liver. The development of an ectopic liver as an additional site of hepatic function represents a new approach for patients with an end-stage liver disease. We investigated the development and function of liver tissue in lymph nodes in mice with liver failure. METHODS Hepatocytes were isolated from 8 to 12-week-old mice and transplanted by intraperitoneal injection into 8- to 12-week-old Fah-/- mice, a model of the human liver disease tyrosinemia type I. Survival was monitored and the locations and functions of the engrafted liver cells were determined. RESULTS Lymph nodes of Fah-/- mice were colonized by transplanted hepatocytes; Fah+ hepatocytes were detected adjacent to the CD45+ lymphoid cells of the lymphatic system. Ten weeks after transplantation, these mice had substantial improvements in serum levels of transaminases, bilirubin, and amino acids. Homeostatic expansion of donor hepatocytes in lymph nodes rescued the mice from lethal hepatic failure. CONCLUSIONS Functional ectopic liver tissue in lymph nodes rescues mice from lethal hepatic disease; lymph nodes might therefore be used as sites for hepatocyte transplantation.

The identification of resident stem cells in the mouse gallbladder is to date, unexplored. In addition, the relationship between adult gallbladder stem cells and intrahepatic bile duct (IHBD) cells is not well understood. The goal of this study was to isolate stem cells from an adult mouse gallbladder and determine if they were unique compared to IHBD cells. By limiting dilution analyses and index sorts, we found that an EpCAM+CD49fhi sub-population from primary gallbladder is enriched in colony forming cells compared to EpCAM+CD49flo cells. EpCAM+CD49fhi cells expressed CD29, CD133 and Sca1 but were negative for lineage markers CD31, CD45 and F4/80. Using a novel feeder cell culture system, we observed long-term (>passage 20) and clonal expansion of the EpCAM+CD49fhi cells in vitro. In a matrigel differentiation assay, EpCAM+CD49f+ cells expanding in vitro underwent organotypic morphogenesis forming ductular structures and cysts. These structures are similar to, and recapitulate a transport function of primary gallbladder. EpCAM+CD49f+ cells also engraft into the subcutaneous space of recipient mice. We compared primary gallbladder and IHBD cells by flow cytometry and found phenotypic differences in expression of CD49f, CD49e, CD81, CD26, CD54 and CD166. In addition, oligonucleotide microarrays showed that the expanded EpCAM+CD49f+ gallbladder cells and IHBD cells exhibit differences related to lipid and drug metabolism. Notable genes that were different are cytochrome P450, glutathione-S-transferase, Indian hedgehog and solute carrier family genes. Conclusion we have isolated an epithelial cell population from primary mouse gallbladder with stem cell characteristics and found it to be unique compared to IHBD cells.

There are currently no reports of the identification of stem cells in the human gallbladder. The differences between human gallbladder and intrahepatic bile duct (IHBD) cells have also not been explored. The goals of this study were to evaluate if human fetal gallbladder contains a candidate stem cell population and if fetal gallbladder cells are distinct from fetal IHBD cells. We found that EpCAM+CD44+CD13+ cells represent the cell population most enriched for clonal self-renewal from primary gallbladder. Primary EpCAM+CD44+CD13+ cells gave rise to EpCAM+CD44+CD13+ and EpCAM+CD44+CD13− cells in vitro, and gallbladder cells expanded in vitro exhibited short-term engraftment in vivo. Last, we found that CD13, CD227, CD66, CD26 and CD49b were differentially expressed between gallbladder and IHBD cells cultured in vitro indicating clear phenotypic differences between the two cell populations. Microarray analyses of expanded cultures confirmed that both cell types have unique transcriptional profiles with predicted functional differences in lipid, carbohydrate, nucleic acid and drug metabolism. In conclusion, we have isolated a distinct clonogenic population of epithelial cells from primary human fetal gallbladder with stem cell characteristics and found it to be unique compared to IHBD cells.

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BackgroundThe identification and characterization of stem cells within the biliary system has great importance for basic biology and potential cell‐based therapy. Currently, there is a paucity of data regarding stem cells in the gallbladder. Recent data have shown that the intra‐hepatic and extra‐hepatic biliary systems develop from separate progenitors. Therefore, in the adult hepatobiliary system extra‐hepatic stem cells would be unique compared to intra‐hepatic bile duct stem cells.AimTo isolate and characterize stem cells from the adult mouse gallbladder and determine their uniqueness relative to intra‐hepatic bile duct (IHBD) cells.MethodsGallbladder cells were expanded in vitro on feeders. Limiting Dilution Analyses and Index sorts were performed to evaluate candidate stem cells markers. A matrigel‐based assay was used to examine lineage commitment of the gallbladder cells.ConclusionsWe identify CD49f as a gallbladder stem cell marker. Gallbladder stem cells exhibit clonogenic self‐renewal and morphogenesis in vitro, expand and form structures in vivo short term. Primary gallbladder and IHBD cells exhibit different phenotypic profiles by flow cytometry. Microarray analyses on gallbladder stem cells and IHBD cells in vitro indicate different genomic expression patterns. These data underscore the uniqueness of gallbladder stem cells.This work was in part supported by the Commonwealth of Pennsylvania and by the NIH grant R01 DK085711.

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