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The role of progenitor cells in liver repair and fibrosis has been extensively described, but their purification remains a challenge, hampering their characterization and use in regenerative medicine. To address this issue, we developed an easy and reproducible liver progenitor cell (LPC) isolation strategy based on aldehyde dehydrogenase (ALDH) activity, a common feature shared by many progenitor cells. We demonstrate that a subset of nonparenchymal mouse liver cells displays high levels of ALDH activity, allowing the isolation of these cells by fluorescence‐activated cell sorting. Immunocytochemistry and qPCR analyses on freshly isolated ALDH+ cells reveal an enrichment in cells expressing liver stem cell markers such as EpCAM, CK19, CD133, and Sox9. In culture, the ALDH+ population can give rise to functional hepatocyte‐like cells as illustrated by albumin and urea secretion and cytochrome P450 activity. ALDH1A1 expression can be detected in canals of Hering and bile duct epithelial cells and is increased on liver injury. Finally, we showed that the isolation and differentiation toward hepatocyte‐like cells of LPCs with high ALDH activity is also successfully applicable to human liver samples. Conclusion: High ALDH activity is a feature of LPCs that can be taken advantage of to isolate these cells from untreated mouse as well as human liver tissues. This novel protocol is practically relevant, because it provides an easy and nontoxic method to isolate liver stem cells from normal tissue for potential therapeutic purposes. (HEPATOLOGY 2012)

Accumulation of fat in the liver increases the risk to develop fibrosis and cirrhosis and is associated with development of the metabolic syndrome. Here, to identify genes or gene pathways that may underlie the genetic susceptibility to fat accumulation in liver, we studied A/J and C57Bl/6 mice that are resistant and sensitive to diet-induced hepatosteatosis and obesity, respectively. We performed comparative transcriptomic and lipidomic analysis of the livers of both strains of mice fed a high fat diet for 2, 10, and 30 days. We found that resistance to steatosis in A/J mice was associated with the following: (i) a coordinated up-regulation of 10 genes controlling peroxisome biogenesis and ␤-oxidation; (ii) an increased expression of the elongase Elovl5 and desaturases Fads1 and Fads2. In agreement with these observations, peroxisomal ␤-oxidation was increased in livers of A/J mice, and lipidomic analysis showed increased concentrations of long chain fatty acid-containing triglycerides, arachidonic acid-containing lysophosphatidylcholine, and 2-arachidonylglycerol, a cannabinoid receptor agonist. We found that the anti-inflammatory CB2 receptor was the main hepatic cannabinoid receptor, which was highly expressed in Kupffer cells. We further found that A/J mice had a lower proinflammatory state as determined by lower plasma levels and IL-1␤ and granulocyte-CSF and reduced hepatic expression of their mRNAs, which were found only in Kupffer cells. This suggests that increased 2-arachidonylglycerol production may limit Kupffer cell activity. Collectively, our data suggest that genetic variations in the expression of peroxisomal ␤-oxidation genes and of genes controlling the production of an anti-inflammatory lipid may underlie the differential susceptibility to diet-induced hepatic steatosis and pro-inflammatory state.The current view of obesity-associated metabolic deregulations proposes that excessive accumulation of fat in adipose tissue initiates an inflammatory reaction characterized by cytokine production by adipocytes and infiltrating leukocytes (1, 2). This leads to the development of insulin resistance in adipocytes and increased release of free fatty acids. Secreted cytokines and free fatty acids then induce insulin resistance in muscle and liver, through activation of serine/threonine kinases that phosphorylate essential signaling proteins such as the insulin receptor or its main substrates IRS1 and IRS2 (3). In the liver, insulin resistance leads to unrestrained glucose production causing hyperglycemia. However, insulin still normally activates the lipogenic transcription factor SREBP-1c leading to hepatosteatosis, increased secretion of VLDL, and elevated plasma triglycerides (4). Therefore, there is a correlation between the degree of inflammation in the adipose tissue and liver fat content and insulin resistance (5), and studies in human have demonstrated a correlation between the level of fat accumulation in the liver and various parameters of the metabolic syndrome (6, 7).Changes in liver metaboli...

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One of the consequences of HIV infection is a progressive loss of T cell functions, resulting in decreased cytokine secretion and proliferation and an increased sensitivity to apoptosis. Therefore, successful therapeutic vaccination approaches should aim at restoring the functionality of existing HIV-specific T cells, as well as to efficiently induce potent, HIV-specific T cells from naïve T cells. In this study, we wanted to determine the stimulatory capacity of DCs coelectroporated with mRNA encoding for different costimulatory molecules of the TNFSF, together with HIV antigen-encoding mRNA. We show that DCs electroporated with 4-1BBL can enhance the proliferation, functionality, cytokine production, and survival of HIV-specific CD8(+) T cells. Furthermore, we are the first to show that a combination of 4-1BBL and CD40L overexpression on DCs dramatically enhances CD4(+) and CD8(+) T cell responses. Finally, we demonstrate that signaling through 4-1BB, but not through CD40, can alleviate the suppressive effect of Tregs on CD8(+) T cell proliferation. Thus, the combination of 4-1BBL and CD40L enhances HIV-specific CD8(+) T cell responses in a synergistic way, resulting in enhanced proliferation of CD4(+) and CD8(+) T cell subsets, an increased cytokine secretion, and a reduced sensitivity to Treg-mediated immune suppression.