Triglycerides Promote Lipid Homeostasis during Hypoxic Stress by Balancing Fatty Acid Saturation.

Lipid droplets, which store triglycerides and cholesterol esters, are a prominent feature of clear cell renal cell carcinoma (ccRCC). Although their presence in ccRCC is critical for sustained tumorigenesis, their contribution to lipid homeostasis and tumor cell viability is incompletely understood. Here we show that disrupting triglyceride synthesis compromises the growth of both ccRCC tumors and ccRCC cells exposed to tumor-like conditions. Functionally, hypoxia leads to increased fatty acid saturation through inhibition of the oxygen-dependent stearoyl-CoA desaturase (SCD) enzyme. Triglycerides counter a toxic buildup of saturated lipids, primarily by releasing the unsaturated fatty acid oleate (the principal product of SCD activity) from lipid droplets into phospholipid pools. Disrupting this process derails lipid homeostasis, causing overproduction of toxic saturated ceramides and acyl-carnitines as well as activation of the NF-κB transcription factor. Our work demonstrates that triglycerides promote homeostasis by "buffering" specific fatty acids.

Hif1α Deletion Limits Tissue Regeneration via Aberrant B Cell Accumulation in Experimental Pancreatitis.

Pancreatitis is an inflammatory disease of the exocrine pancreas and ranks among the most common gastrointestinal disorders. Inflamed tissues frequently experience conditions of insufficient oxygen availability, or hypoxia. Here, we demonstrate that hypoxia and consequent stabilization of the hypoxia-inducible factor 1α (HIF1α) transcription factor occur in murine and human pancreatitis. Mice lacking pancreas-specific HIF1α expression display markedly impaired pancreatic regeneration following cerulein-induced pancreatitis, which is associated with excessive intrapancreatic B cell accumulation. Notably, B cell depletion in mice with established pancreatitis significantly enhances tissue regeneration. Our study reveals a crosstalk between pancreatic HIF1α expression and B cell trafficking that regulates tissue regeneration, and identifies plausible molecular targets for treating pancreatitis patients.

Hif1a Deletion Reveals Pro-Neoplastic Function of B Cells in Pancreatic Neoplasia.

UNLABELLED: Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer-related deaths worldwide, with an exceedingly low 5-year survival rate. PDAC tumors are characterized by an extensive desmoplastic stromal response and hypovascularity, suggesting that tumor hypoxia could regulate PDAC initiation and/or progression. Using a well-defined, autochthonous Kras(G12D)-driven murine model, as well as human tumors, we demonstrate that hypoxia and stabilization of hypoxia-inducible factor 1α (HIF1α), a principal mediator of hypoxic adaptation, emerge early during preinvasive stages of PDAC. Surprisingly, pancreas-specific Hif1a deletion drastically accelerated Kras(G12D)-driven pancreatic neoplasia and was accompanied by significant increases in intrapancreatic B lymphocytes, featuring prominent influx of a rare "B1b" B-cell subtype. Finally, treatment of HIF1α-deficient mice with B cell-depleting αCD20 monoclonal antibodies inhibited progression of pancreatic intraepithelial neoplasia (PanIN). Our data reveal a previously unrecognized role for B cells in promoting pancreatic tumorigenesis and implicate HIF1α as a critical regulator of PDAC development. SIGNIFICANCE: We show here that pancreas-specific Hif1a deletion promotes PDAC initiation, coincident with increased intrapancreatic accumulation of B cells, and that B-cell depletion suppresses pancreatic tumorigenesis. We therefore demonstrate a protective role for HIF1α in pancreatic cancer initiation and uncover a previously unrecognized function of B cells.

CD133 expression correlates with membrane beta-catenin and E-cadherin loss from human hair follicle placodes during morphogenesis.

Genetic studies suggest that the major events of human hair follicle development are similar to those in mice, but detailed analyses of this process are lacking. In mice, hair follicle placode "budding" is initiated by invagination of Wnt-induced epithelium into the underlying mesenchyme. Modification of adherens junctions (AJs) is clearly required for budding. Snail-mediated downregulation of AJ component E-cadherin is important for placode budding in mice. Beta-catenin, another AJ component, has been more difficult to study owing to its essential functions in Wnt signaling, a prerequisite for hair follicle placode induction. Here, we show that a subset of human invaginating hair placode cells expresses the stem cell marker CD133 during early morphogenesis. CD133 associates with membrane beta-catenin in early placodes, and its continued expression correlates with loss of beta-catenin and E-cadherin from the cell membrane at a time when E-cadherin transcriptional repressors Snail and Slug are not implicated. Stabilization of CD133 via anti-CD133 antibody treatment of human fetal scalp explants depresses beta-catenin and E-cadherin membrane localization. We discuss this unique correlation and suggest a hypothetical model whereby CD133 promotes morphogenesis in early hair follicle placodes through the localized removal of membrane beta-catenin proteins and subsequent AJ dissolution.

Fgf9 from dermal γδ T cells induces hair follicle neogenesis after wounding.

Understanding molecular mechanisms for regeneration of hair follicles provides new opportunities for developing treatments for hair loss and other skin disorders. Here we show that fibroblast growth factor 9 (Fgf9), initially secreted by γδ T cells, modulates hair follicle regeneration after wounding the skin of adult mice. Reducing Fgf9 expression decreases this wound-induced hair neogenesis (WIHN). Conversely, overexpression of Fgf9 results in a two- to threefold increase in the number of neogenic hair follicles. We found that Fgf9 from γδ T cells triggers Wnt expression and subsequent Wnt activation in wound fibroblasts. Through a unique feedback mechanism, activated fibroblasts then express Fgf9, thus amplifying Wnt activity throughout the wound dermis during a crucial phase of skin regeneration. Notably, humans lack a robust population of resident dermal γδ T cells, potentially explaining their inability to regenerate hair after wounding. These findings highlight the essential relationship between the immune system and tissue regeneration. The importance of Fgf9 in hair follicle regeneration suggests that it could be used therapeutically in humans.