Development and activation of human dendritic cells in vivo in a xenograft model of human hematopoiesis.

Dendritic cells (DCs) are derived from CD34+ progenitors and play a central role in the development of immune responses and in tolerance. Their therapeutic potential underscores the need for in vivo models that accurately recapitulate human DC development and function to provide a better understanding of DC biology in health and disease. Using nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice transplanted with human CD34+ cells as a model of human hematopoiesis, we examined DC ontogeny. Progenitors of both myeloid (m) and plasmacytoid (p) DCs were identified in the bone marrow of mice up to 24 weeks after transplant, indicating ongoing and sustained production of DCs after initial engraftment. To determine whether human DCs derived from transplanted stem cells were functional, their response to acute inflammation using lipopolysaccharide (LPS) was examined. Eighteen hours after LPS administration, a dramatic increase in the plasma levels of the human inflammatory cytokines interleukin (IL)-8, IL-10, tumor necrosis factor-alpha, and IL-12p70 was observed. Only mDCs and not pDCs responded in vivo to LPS by upregulating CD86 and CD83. In vivo activation of human mDCs resulted in a substantial increase in the ability of mDCs to induce the proliferation of naive human T cells. Taken together, these data indicate that human CD34+ cells seem to have differentiated appropriately within the NOD/SCID microenvironment into DCs that are developmentally, phenotypically, and functionally similar to the DC subsets found in humans.

GM1-ganglioside-mediated activation of the unfolded protein response causes neuronal death in a neurodegenerative gangliosidosis.

GM1-ganglioside (GM1) is a major sialoglycolipid of neuronal membranes that, among other functions, modulates calcium homeostasis. Excessive accumulation of GM1 due to deficiency of lysosomal beta-galactosidase (beta-gal) characterizes the neurodegenerative disease GM1-gangliosidosis, but whether the accumulation of GM1 is directly responsible for CNS pathogenesis was unknown. Here we demonstrate that activation of an unfolded protein response (UPR) associated with the upregulation of BiP and CHOP and the activation of JNK2 and caspase-12 leads to neuronal apoptosis in the mouse model of GM1-gangliosidosis. GM1 loading of wild-type neurospheres recapitulated the phenotype of beta-gal-/- cells and activated this pathway by depleting ER calcium stores, which ultimately culminated in apoptosis. Activation of UPR pathways did not occur in mice double deficient for beta-gal and ganglioside synthase, beta-gal-/-/GalNAcT-/-, which do not accumulate GM1. These findings suggest that the UPR can be induced by accumulation of the sialoglycolipid GM1 and this causes a novel mechanism of neuronal apoptosis.