Mesenchymal Hox6 function is required for mouse pancreatic endocrine cell differentiation.

Despite significant advances in our understanding of pancreatic endocrine cell development, the function of the pancreatic mesodermal niche in this process is poorly understood. Here we report a novel role for mouse Hox6 genes in pancreatic organogenesis. Hox6 genes are expressed exclusively in the mesoderm of the developing pancreas. Genetic loss of all three Hox6 paralogs (Hoxa6, Hoxb6 and Hoxc6) leads to a dramatic loss of endoderm-derived endocrine cells, including insulin-secreting ß-cells, and to mild delays and disruptions in pancreatic branching and exocrine differentiation. Ngn3-expressing pan-endocrine progenitor cells are specified normally in Hox6 mutant pancreata, but fail to mature into hormone-producing cells. Reduced expression of Wnt5a is observed in mutant pancreatic mesenchyme, leading to subsequent loss of expression of the crucial Wnt inhibitors Sfrp3 and Dkk1 in endocrine progenitor cells. These results reveal a key role for Hox6 genes in establishing Wnt mesenchymal-epithelial crosstalk in pancreatic development.

Hox6 genes modulate in vitro differentiation of mESCs to insulin-producing cells.

The differentiation of glucose-responsive, insulin-producing cells from ESCs in vitro is promising as a cellular therapy for the treatment of diabetes, a devastating and common disease. Pancreatic ß-cells are derived from the endoderm in vivo and therefore most current protocols attempt to generate a pure population of first endoderm, then pancreas epithelium, and finally insulin-producing cells. Despite this, differentiation protocols result in mixed populations of cells that are often poorly defined, but also contain mesoderm. Using an in vitro mESC-to-ß cell differentiation protocol, we show that expression of region-specific Hox genes is induced. We also show that the loss of function of the Hox6 paralogous group, genes expressed only in the mesenchyme of the pancreas (not epithelium), affect the differentiation of insulin-producing cells in vitro. This work is consistent with the important role for these mesoderm-specific factors in vivo and highlights contribution of supporting mesenchymal cells in in vitro differentiation.

Small Molecule Inhibitors Limit Endothelial Cell Invasion by Staphylococcus aureus.

Staphylococcus aureus is a leading causative agent in sepsis, endocarditis, and pneumonia. An emerging concept is that prognosis worsens when the infecting S. aureus strain has the capacity to not only colonize tissue as an extracellular pathogen, but to invade host cells and establish intracellular bacterial populations. In previous work, we identified host CDC42 as a central regulator of endothelial cell invasion by S. aureus. In the current work, we report that ML 141, a first-in-class CDC42 inhibitor, decreases invasion and resultant pathogenesis in a dose-dependent and reversible manner. Inhibition was found to be due in part to decreased remodeling of actin that potentially drives endocytic uptake of bacteria/fibronectin/integrin complexes. ML 141 decreased binding to fibronectin at these complexes, thereby limiting a key pathogenic mechanism used by S. aureus to invade. Structural analogs of ML 141 were synthesized (designated as the RSM series) and a subset identified that inhibit invasion through non-cytotoxic and non-bactericidal mechanisms. Our results support the development of adjunctive therapeutics targeting host CDC42 for mitigating invasive infection at the level of the host.