Tumor necrosis factor-alpha stimulates HIV-1 production in primary culture of human adipocytes.

Adipose tissue of HIV-1-infected patients shows severe abnormalities such as profound changes in adipose tissue morphology and metabolism. Does HIV-1 infect the adipose cell remains an unsolved question since previous attempts showed that HIV-1 poorly infects human adipocytes in vitro. In the present study, preadipose cells from human subcutaneous fat pads were differentiated in vitro, checked for HIV receptor expression, then infected with R5 and X4 HIV1 strains. Using a sensitive RT-PCR assay, we showed that HIV-1 tat and rev early viral transcripts were expressed in infected adipocytes giving a clear evidence of HIV-1 transcriptional activity in these cells. However, at the same time, no sign of productive infection was demonstrated since infected adipocytes did not efficiently produce Gag p24 antigen. We hypothesized that such a limitation could result from the lack of activation of adipocyte-signaling pathways able to stimulate HIV-1 gene expression in quiescent adipocytes. Indeed, a significant increase in Gag p24 production was observed after stimulation of infected adipocytes with pro-inflammatory cytokines, such as tumor necrosis factor alpha or interleukin-1-beta. Taken together, these results demonstrate that HIV-1 does infect human adipose cells in vitro and suggest that the initial limited infection can be overcome upon pro-inflammatory cytokine treatment.

Human adipose cells as candidates in defense and tissue remodeling phenomena.

Macrophages are part of the immunity defense mechanism via oxidative burst and phagocytosis. They are also involved in tissue remodeling via cytokine secretion and apoptotic body clearance. Previously, we demonstrated that adipose cells and macrophages share some of their features and functions. Our aim was to further test this hypothesis in humans. We first demonstrated that human preadipocytes exhibit phagocytosis of yeast, this effect being specific compared to another fibroblastic cell type, the skin fibroblast. Furthermore, as in rodents, human preadipocytes exhibit anti-microbial activity. Finally, for the first time, it was shown that these cells were able to phagocyte apoptotic lymphocytes. Altogether, these data suggest an active involvement of fat cells in host defense and tissue remodeling, which might play an important role at the level of the whole organism due to the large amount of adipose tissue. This gives support for some observations linking obesity or cachexia to immunological disorders.

Evidence for a functional role of the cholecystokinin-B/gastrin receptor in the human fetal and adult pancreas.

Gastrin (G) and cholecystokinin (CCK) are gastrointestinal neuropeptides that are released into circulation during a meal. G is also transiently expressed during embryogenic and early ontogenic development of the pancreas and is believed to act on islet-cell development. Both peptides act on pancreatic endocrine function; however, the effects are dependent on the species and on cellular and molecular underlying mechanisms that remain poorly characterized. Since CCK-B/G subtype receptor is predominant over the CCK-A subtype in the human pancreas, we hypothesized that it could be expressed by islet cells. Here we present reverse transcription-polymerase chain reaction and immunohistochemistry data demonstrating that the CCK-B/G receptor is expressed in islet cells and that islet glucagon-producing cells are the major site of CCK-B/G receptor expression in adult and fetal pancreas. Moreover, G immunoreactivity was detected in the fetal human pancreas at embryogenic week 22. G- and CCK-stimulated glucagon are released from purified human islets. Concentration of CCK and G eliciting a half-maximal level of glucagon secretion were 13 +/- 6 and 8 +/- 5 pmol/l, respectively. Maximal glucagon secretion was achieved in the presence of 30 pmol/l peptides and was similar to that obtained in the presence of 10 mmol/l L-arginine (1.6 pmol x ml(-1) x 90 min(-1)). The nonpeptide antagonist of the CCK-B/G receptor, RPR-101048, fully inhibited CCK- and G-stimulated glucagon secretion at 100 nmol/l concentration. These data are consistent with the view that the CCK-B/G receptor is involved in glucose homeostasis in adult humans and mediates the autocrine effects of G on islet differentiation and growth in the fetal pancreas.

Transgenic CCK-B/gastrin receptor mediates murine exocrine pancreatic secretion.

BACKGROUND & AIMS: The presence of cholecystokinin (CCK)-B/gastrin receptors in the pancreas of higher mammals including humans has been shown, but their physiological function in the normal pancreas is unknown. The aim of this study was to investigate whether they couple to the secretory machinery of normal acinar cells. METHODS: A transgenic mouse strain expressing the human CCK-B/gastrin receptor in the exocrine pancreas was created. The transgenic construction used the promoter region of the elastase I gene and the human CCK-B/gastrin receptor gene. Analysis of ElasCCKB mice included polymerase chain reaction and receptor autoradiography. Molecular and binding features of the CCK-B/gastrin receptor were determined by Western blot and radioligand binding studies. Amylase secretion and inositol phosphate production assays were used in functional characterization. RESULTS: The CCK-B/gastrin receptor was expressed in the exocrine pancreas and had typical molecular and binding features. CCK and sulfated gastrin stimulated enzyme secretion with identical potencies and efficacies. They activated phospholipase C, but CCK was 60-fold less potent than sulfated gastrin. CONCLUSIONS: The data show that the CCK-B/gastrin receptor mediates exocytosis in acinar cells and can differentially couple to phospholipase C depending on the agonist. The ElasCCKB mice provide a useful model to study phospholipase C-dependent and -independent intracellular transduction pathways leading to pancreatic exocrine secretion.