Pharmacological Properties of Chromobacterium violaceum Violacein at the Human Serotonin 2C Receptor.

The monoamine neurotransmitter serotonin (5-HT) plays a role in many physiological responses by interacting with various receptor subtypes. The 5-HT2C receptor subtype is a 7-transmembrane, G protein-coupled receptor (GPCR) that is involved in neuronal excitability, spatial learning, mood, and appetite. The microorganism Chromobacterium violaceum produces a purple pigment, violacein, which can be extracted and purified. Violacein has antibiotic, antileishmanial, antifungal and antitumoral properties in various cancer cell lines. Violacein is derived from the amino acid tryptophan as is 5-HT and therefore, the two have similar chemical structures. However, no one has reported the activity of violacein at 5-HT receptors. Therefore the Fentress lab decided to investigate whether or not violacein had an effect on 5-HT2C receptor trafficking. Human Embryonic Kidney (HEK) 293 cells expressing fluorescently-tagged 5-HT2C receptor were treated with 5-HT, violacein, water or vehicle and then cells were fixed and visualized with fluorescent microscopy. Violacein treatment did not cause receptor internalization. Recent studies suggest that the 5-HT2C receptor can activate the JAK/STAT pathway. To see if violacein can modulate this pathway, HEK 293 cells expressing 5-HT2C receptor were treated with either 5-HT, violacein, or pretreated with violacein followed by incubation with 5-HT. Phosphorylation states of JAK2 and STAT3 were examined by immunoblotting. Results determined that 5-HT2C receptor activation had no effect on JAK2 phosphorylation and that violacein blocked STAT3 phosphorylation. Primary radioligand binding determined that violacein has a low affinity for 5-HT2C receptor but has a higher affinity for adrenergic receptors. Future studies will examine G protein-coupling by measuring phosphoinositide hydrolysis and cAMP assay to investigate adrenergic pathways.

Molecular Mechanisms of Obesity-Induced Osteoporosis and Muscle Atrophy.

Obesity and osteoporosis are two alarming health disorders prominent among middle and old age populations, and the numbers of those affected by these two disorders are increasing. It is estimated that more than 600 million adults are obese and over 200 million people have osteoporosis worldwide. Interestingly, both of these abnormalities share some common features including a genetic predisposition, and a common origin: bone marrow mesenchymal stromal cells. Obesity is characterized by the expression of leptin, adiponectin, interleukin 6 (IL-6), interleukin 10 (IL-10), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), macrophage colony stimulating factor (M-CSF), growth hormone (GH), parathyroid hormone (PTH), angiotensin II (Ang II), 5-hydroxy-tryptamine (5-HT), Advance glycation end products (AGE), and myostatin, which exert their effects by modulating the signaling pathways within bone and muscle. Chemical messengers (e.g., TNF-α, IL-6, AGE, leptins) that are upregulated or downregulated as a result of obesity have been shown to act as negative regulators of osteoblasts, osteocytes and muscles, as well as positive regulators of osteoclasts. These additive effects of obesity ultimately increase the risk for osteoporosis and muscle atrophy. The aim of this review is to identify the potential cellular mechanisms through which obesity may facilitate osteoporosis, muscle atrophy and bone fractures.

The effects of chronic AMPK activation on hepatic triglyceride accumulation and glycerol 3-phosphate acyltransferase activity with high fat feeding.

BACKGROUND: High fat feeding increases hepatic fat accumulation and is associated with hepatic insulin resistance. AMP Activated Protein Kinase (AMPK) is thought to inhibit lipid synthesis by the acute inhibition of glycerol-3-phosphate acyltransferase (GPAT) activity and transcriptional regulation via sterol regulatory element binding protein-1c (SREBP-1c). METHODS: The purpose of this study was to determine if chronic activation of AMPK prevented an increase in GPAT1 activity in rats fed a high fat diet. Rats were fed a control (C), or a high fat (HF) diet (60% fat) for 6 weeks and injected with saline or a daily aminoimidazole carboxamide ribnucleotide (AICAR) dose of 0.5 mg/g body weight. RESULTS: Chronic AMPK activation by AICAR injections resulted in a significant reduction in hepatic triglyceride accumulation in both the C and HF fed animals (C, 5.5±0.7; C+AICAR, 2.7 ±0.3; HF, 21.8±3.3; and HF+AICAR, 8.0±1.8 mg/g liver). HF feeding caused an increase in total GPAT and GPAT1 activity, which was not affected by chronic AMPK activation (GPAT1 activity vs. C, C+AICAR, 92±19%; HF, 186±43%; HF+AICAR, 234±62%). Markers of oxidative capacity, including citrate synthase activity and cytochrome c abundance, were not affected by chronic AICAR treatment. Interestingly, HF feeding caused a significant increase in long chain acyl-CoA dehydrogenase or LCAD (up 66% from C), a marker of fatty acid oxidation capacity. CONCLUSIONS: These results suggest that chronic AMPK activation limits hepatic triglyceride accumulation independent of a reduction in total GPAT1 activity.