Blood-derived inflammatory dendritic cells in lymph nodes stimulate acute T helper type 1 immune responses.

T helper type 1 (T(H)1)-polarized immune responses, which confer protection against intracellular pathogens, are thought to be initiated by dendritic cells (DCs) that enter lymph nodes from peripheral tissues. Here we found after viral infection or immunization, inflammatory monocytes were recruited into lymph nodes directly from the blood to become CD11c(+)CD11b(hi)Gr-1(+) inflammatory DCs, which produced abundant interleukin 12p70 and potently stimulated T(H)1 responses. This monocyte extravasation required the chemokine receptor CCR2 but not the chemokine CCL2 or receptor CCR7. Thus, the accumulation of inflammatory DCs and T(H)1 responses were much lower in Ccr2(-/-) mice, were preserved in Ccl2(-/-) mice and were relatively higher in CCL19-CCL21-Ser-deficient plt mutant mice, in which all other lymph node DC types were fewer in number. We conclude that blood-derived inflammatory DCs are important in the development of T(H)1 immune responses.

Central and peripheral interactions between the agouti-related protein and leptin.

The agouti-related protein (AgRP) is a powerful appetite modulator expressed in the hypothalamus and the adrenal gland and regulated by leptin. Here we report the robust expression of AgRP in epididymal fat and its upregulation in this tissue by feeding rather than by fasting. This was observed in both the obesity-susceptible C57BL/6J and the obesity-resistant CAST/Ei mouse strains. Surprisingly, AgRP expression was higher in the hypothalamus and the adrenal gland in the leaner and obesity-resistant CAST/Ei strain. In vitro leptin treatment upregulated endogenous AgRP in mouse hypothalamus and adrenal cells, after an acute 6-h exposure, but it downregulated AgRP after a long-term 60-h exposure. AgRP, on the other hand, upregulated its own endogenous expression in the hypothalamus and the adrenal cells and also upregulated endogenous leptin in the adrenal cells. These results reveal a novel feedback loop and reciprocal transcriptional regulation between AgRP and leptin centrally and peripherally.

Regulation of the Fanconi anemia group C protein through proteolytic modification.

The function of the Fanconi anemia group C protein (FANCC) is still unknown, though many studies point to a role in damage response signaling. Unlike other known FA proteins, FANCC is mainly localized to the cytoplasm and is thought to act as a messenger of cellular damage rather than an effector of repair. FANCC has been shown to interact with several cytoplasmic and nuclear proteins and to delay the onset of apoptosis through redox regulation of GSTP1. We investigated the fate and function of FANCC during apoptosis. Here we show that FANCC undergoes proteolytic modification by a caspase into a predominant 47-kDa ubiquitinated protein fragment. Lack of proteolytic modification at the putative cleavage site delays apoptosis but does not affect MMC complementation. These results suggest that FANCC function is regulated through proteolytic processing.

A promoter genotype and oxidative stress potentially link resistin to human insulin resistance.

Insulin resistance is a component of type 2 diabetes and often precedes pancreatic beta-cell failure. Contributing factors include obesity and a central pattern of fat accumulation with a strong genetic component. The adipocyte secreted hormone resistin has been proposed as a link between the adipocyte and insulin resistance by inhibition of insulin-stimulated glucose uptake and/or blocking adipocyte differentiation. Here we report that the G/G genotype of a single nucleotide polymorphism (SNP) in the promoter of the human resistin gene, -180C>G, had significantly increased basal promoter activity in adipocytes. These data were recapitulated in vivo, where G/G homozygotes had significantly higher resistin mRNA levels in human abdominal subcutaneous fat. A significant interaction was also found between the -180C>G SNP, a marker of oxidative stress (NAD[P]H quinone oxidoreductase mRNA) and homeostasis model assessment of insulin resistance. In addition, resistin mRNA was positively and independently correlated with insulin resistance and hepatic fat as measured by liver X-ray attenuation. These data implicate resistin in the pathophysiology of the human insulin resistance syndrome, an effect mediated by the -180C>G promoter SNP and potentially cellular oxidative stress.

Hematopoietic stem cells from fancc(-/-) mice have lower growth and differentiation potential in response to growth factors.

Fanconi anemia (FA) is a complex recessive genetic disease characterized by progressive bone marrow (BM) failure. We have previously shown that stem cells from the FA group C mouse model have lower long-term primary and secondary reconstitution ability, and that bone marrow of Fancc(-/-) mice contained fewer lineage-negative (Lin(-))Thy1.2(low)Sca-1(+)c-kit(+) CD34(+) cells but normal levels of Lin(-)Thy1.2(low)Sca-1(+)c-kit(+)CD34(-) primitive cells. These data suggest that CD34(+) primitive cells have either a lower growth or differentiation potential, or that these cells have greater apoptosis levels. To investigate the role Fancc might have on the growth and differentiation potentials of primitive hematopoietic stem cells, we used a single-cell culture system and monitored cell viability, doubling potential, and apoptosis levels of Fancc(-/-) primitive Lin(-)Thy1.2(-)Sca-1(+) (LTS)-CD34(+) and LTS-CD34(-) stem cells. Results showed that Fancc(-/-) LTS-CD34(-) and LTS-CD34(+) cells had altered growth and apoptosis responses to combinations of stimulatory cytokines, most dramatically in response to a combination of factors that included interleukin-3 (IL-3) and IL-6. In addition, Fancc(-/-) LTS-CD34(-) and LTS-CD34(+) cells showed a lower differentiation potential than Fancc(+/+) cells. These results support a role for Fancc in the growth and differentiation of primitive hematopoietic cells and suggest that an altered response to stimulatory cytokines may contribute to BM aplasia in FA patients.