Tumor necrosis-like weak inducer of apoptosis as a proinflammatory cytokine in human adipocyte cells: up-regulation in severe obesity is mediated by inflammation but not hypoxia.

CONTEXT Adipose tissue hypoxia and endoplasmic reticulum (ER) stress may link the presence of chronic inflammation and macrophage infiltration in severely obese subjects. We previously reported the up-regulation of TNF-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor-inducible 14 (Fn14) axis in adipose tissue of severely obese type 2 diabetic subjects. OBJECTIVES The objective of the study was to examine TWEAK and Fn14 adipose tissue expression in obesity, severe obesity, and type 2 diabetes in relation to hypoxia and ER stress. DESIGN In the obesity study, 19 lean, 28 overweight, and 15 obese nondiabetic subjects were studied. In the severe obesity study, 23 severely obese and 35 control subjects were studied. In the type 2 diabetes study, 11 type 2 diabetic and 36 control subjects were studied. The expression levels of the following genes were analyzed in paired samples of sc and visceral adipose tissue: Fn14, TWEAK, VISFATIN, HYOU1, FIAF, HIF-1a, VEGF, GLUT-1, GRP78, and XBP-1. The effect of hypoxia, inflammation, and ER stress on the expression of TWEAK and Fn14 was examined in human adipocyte and macrophage cell lines. RESULTS Up-regulation of TWEAK/Fn14 and hypoxia and ER stress surrogate gene expression was observed in sc and visceral adipose tissue only in our severely obese cohort. Hypoxia modulates TWEAK or Fn14 expression in neither adipocytes nor macrophages. On the contrary, inflammation up-regulated TWEAK in macrophages and Fn14 expression in adipocytes. Moreover, TWEAK had a proinflammatory effect in adipocytes mediated by the nuclear factor-kappaB and ERK but not JNK signaling pathways. CONCLUSIONS Our data suggest that TWEAK acts as a pro-inflammatory cytokine in the adipose tissue and that inflammation, but not hypoxia, may be behind its up-regulation in severe obesity.

Localization of peroxisome proliferator-activated receptor alpha (PPARα) and N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD) in cells expressing the Ca(2+)-binding proteins calbindin, calretinin, and parvalbumin in the adult rat hippocampus.

The N-acylethanolamines (NAEs), oleoylethanolamide (OEA) and palmithylethanolamide (PEA) are known to be endogenous ligands of PPARα receptors, and their presence requires the activation of a specific phospholipase D (NAPE-PLD) associated with intracellular Ca(2+) fluxes. Thus, the identification of a specific population of NAPE-PLD/PPARα-containing neurons that express selective Ca(2+)-binding proteins (CaBPs) may provide a neuroanatomical basis to better understand the PPARα system in the brain. For this purpose, we used double-label immunofluorescence and confocal laser scanning microscopy for the characterization of the co-existence of NAPE-PLD/PPARα and the CaBPs calbindin D28k, calretinin and parvalbumin in the rat hippocampus. PPARα expression was specifically localized in the cell nucleus and, occasionally, in the cytoplasm of the principal cells (dentate granular and CA pyramidal cells) and some non-principal cells of the hippocampus. PPARα was expressed in the calbindin-containing cells of the granular cell layer of the dentate gyrus (DG) and the SP of CA1. These principal PPARα(+)/calbindin(+) cells were closely surrounded by NAPE-PLD(+) fiber varicosities. No pyramidal PPARα(+)/calbindin(+) cells were detected in CA3. Most cells containing parvalbumin expressed both NAPE-PLD and PPARα in the principal layers of the DG and CA1/3. A small number of cells containing PPARα and calretinin was found along the hippocampus. Scattered NAPE-PLD(+)/calretinin(+) cells were specifically detected in CA3. NAPE-PLD(+) puncta surrounded the calretinin(+) cells localized in the principal cells of the DG and CA1. The identification of the hippocampal subpopulations of NAPE-PLD/PPARα-containing neurons that express selective CaBPs should be considered when analyzing the role of NAEs/PPARα-signaling system in the regulation of hippocampal functions.

Localization of the cannabinoid CB1 receptor and the 2-AG synthesizing (DAGLα) and degrading (MAGL, FAAH) enzymes in cells expressing the Ca(2+)-binding proteins calbindin, calretinin, and parvalbumin in the adult rat hippocampus.

The retrograde suppression of the synaptic transmission by the endocannabinoid sn-2-arachidonoylglycerol (2-AG) is mediated by the cannabinoid CB1 receptors and requires the elevation of intracellular Ca(2+) and the activation of specific 2-AG synthesizing (i.e., DAGLα) enzymes. However, the anatomical organization of the neuronal substrates that express 2-AG/CB1 signaling system-related molecules associated with selective Ca(2+)-binding proteins (CaBPs) is still unknown. For this purpose, we used double-label immunofluorescence and confocal laser scanning microscopy for the characterization of the expression of the 2-AG/CB1 signaling system (CB1 receptor, DAGLα, MAGL, and FAAH) and the CaBPs calbindin D28k, calretinin, and parvalbumin in the rat hippocampus. CB1, DAGLα, and MAGL labeling was mainly localized in fibers and neuropil, which were differentially organized depending on the hippocampal CaBPs-expressing cells. CB(+) 1 fiber terminals localized in all hippocampal principal cell layers were tightly attached to calbindin(+) cells (granular and pyramidal neurons), and calretinin(+) and parvalbumin(+) interneurons. DAGLα neuropil labeling was selectively found surrounding calbindin(+) principal cells in the dentate gyrus and CA1, and in the calretinin(+) and parvalbumin(+) interneurons in the pyramidal cell layers of the CA1/3 fields. MAGL(+) terminals were only observed around CA1 calbindin(+) pyramidal cells, CA1/3 calretinin(+) interneurons and CA3 parvalbumin(+) interneurons localized in the pyramidal cell layers. Interestingly, calbindin(+) pyramidal cells expressed FAAH specifically in the CA1 field. The identification of anatomically related-neuronal substrates that expressed 2-AG/CB1 signaling system and selective CaBPs should be considered when analyzing the cannabinoid signaling associated with hippocampal functions.