End-organ resistance to growth hormone and IGF-I in epiphyseal chondrocytes of rats with chronic renal failure

End-organ resistance to growth hormone and IGF-I in epiphyseal chondrocytes of rats with chronic renal failure. We tested the hypothesis that there is direct end-organ resistance to growth hormone (GH) and IGF-I in chronic renal failure (CRF) independent of circulating inhibitors. Male Sprague-Dawley rats underwent 5/6 nephrectomy and were pair-fed with weight matched (100 g) sham operated controls for two weeks. Rats with CRF had significantly higher serum creatinine and blood urea nitrogen (P < 0.01 in both cases) and gained significantly less weight and length (P < 0.01 in both cases) compared with controls. Epiphyseal chondrocytes were grown in 10% fetal calf serum (FCS). Both CRF cells and control cells maintained chondrogenic phenotypes, and showed immunohistochemical staining with antibodies to collagen II and proteoglycan (aggrecan). Distribution of the cell subpopulations according to cell size (by flow cytometry) and alkaline phosphatase activity of CRF and control chondrocyte cultures were not different. Growth responses of CRF chondrocytes were reduced (P < 0.01) compared with control chondrocytes when grown in 10% FCS and 10% normal rat serum. Under serum free conditions, growth responses of CRF chondrocytes were reduced to GH and IGF-I at concentrations of 10, 30 and 100 ng/ml, and to insulin at 100, 300 and 1,000 ng/ml compared with controls cells (P < 0.01). To show that this resistance is specific for the GH/IGF system, growth responses to fibroblast growth factor and transforming growth factor β1 were studied and showed no difference between CRF and control cells. Thus, the present study provides direct evidence of specific end-organ resistance to GH, IGF-I in CRF chondrocytes in the absence of circulating factors

Chronic Exposure to the Herbicide, Atrazine, Causes Mitochondrial Dysfunction and Insulin Resistance

There is an apparent overlap between areas in the USA where the herbicide, atrazine (ATZ), is heavily used and obesity-prevalence maps of people with a BMI over 30. Given that herbicides act on photosystem II of the thylakoid membrane of chloroplasts, which have a functional structure similar to mitochondria, we investigated whether chronic exposure to low concentrations of ATZ might cause obesity or insulin resistance by damaging mitochondrial function. Sprague-Dawley rats (n = 48) were treated for 5 months with low concentrations (30 or 300 µg kg−1 day−1) of ATZ provided in drinking water. One group of animals was fed a regular diet for the entire period, and another group of animals was fed a high-fat diet (40% fat) for 2 months after 3 months of regular diet. Various parameters of insulin resistance were measured. Morphology and functional activities of mitochondria were evaluated in tissues of ATZ-exposed animals and in isolated mitochondria. Chronic administration of ATZ decreased basal metabolic rate, and increased body weight, intra-abdominal fat and insulin resistance without changing food intake or physical activity level. A high-fat diet further exacerbated insulin resistance and obesity. Mitochondria in skeletal muscle and liver of ATZ-treated rats were swollen with disrupted cristae. ATZ blocked the activities of oxidative phosphorylation complexes I and III, resulting in decreased oxygen consumption. It also suppressed the insulin-mediated phosphorylation of Akt. These results suggest that long-term exposure to the herbicide ATZ might contribute to the development of insulin resistance and obesity, particularly where a high-fat diet is prevalent

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Roles of ERK and p38 mitogen-activated protein kinases in phorbol ester-induced NF-κB activation and COX-2 expression in human breast epithelial cells

Inappropriate up-regulation of cyclooxygenase-2 (COX-2) has been implicated in pathogenesis of various types of human cancer. Thus, COX-2 has been recognized as an important target for the chemoprevention of several human malignancies including breast cancer. COX-2 expression is known to be regulated by the eukaryotic transcription factor NF-kappa B. In an attempt to link the NF-kappa B activation and COX-2 induction during mammary carcinogenesis, we have examined the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA), a prototype tumor promoter and a mitogen, on NF-kappa B activation and COX-2 expression in the immortalized human breast epithelial cell line (MCF10A). Treatment of MCF10A cells with TPA resulted in transient induction of NF-kappa B DNA binding with maximal activation observed at 30 min. Increased DNA binding of NF-kappa B was accompanied by enhancement of its transcriptional activity as determined by the luciferase reporter gene assay. Under the same experimental conditions, expression of COX-2 mRNA and its protein product peaked at 2 h and 4 h, respectively. TPA treatment caused an increase in the production of prostaglandin E-2. Treatment of cells with the NF-kappa B inhibitor pyrrolidine dithiocarbamate resulted in significant suppression of TPA-induced COX-2 expression. TPA induced activation of ERK1/2 and p38 mitogen-activated protein kinases (MAPK) via phosphorylation. PD98059 (ERK inhibitor) and SB203580 (p38 MAPK inhibitor) down-regulated the COX-2 expression induced by TPA. Furthermore, TPA-induced COX-2 induction as well as NF-kappa B activation was blocked in MCF10A cells transfected with dominant negative mutant ERK1/2 or p38 MAPK. These results suggest that both p38 and ERK MAPKs activates NF-kappa B signaling, which in turn induces COX-2 expression in TPA-stimulated human mammary epithelial cells. (c) 2007 Elsevier Ireland Ltd. All rights reserved

Role of hypothalamic Foxo1 in the regulation of food intake and energy homeostasis

Insulin signaling in the hypothalamus plays a role in maintaining body weight. Studies suggest that the forkhead transcription factor Foxo1 is an important mediator of insulin signaling in peripheral tissues. Here we demonstrate that in normal mice, hypothalamic Foxo1 expression is reduced by the anorexigenic hormones insulin and leptin. These hormones' effects on feeding are inhibited when hypothalamic Foxo1 is activated, establishing a new signaling pathway through which insulin and leptin regulate food intake in hypothalamic neurons. Moreover, activation of Foxo1 in the hypothalamus increases food intake and body weight, whereas inhibition of Foxo1 decreases both. Foxo1 stimulates the transcription of the orexigenic neuropeptide Y and Agouti-related protein through the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway, but suppresses the transcription of anorexigenic proopiomelanocortin by antagonizing the activity of signal transducer-activated transcript-3 (STAT3). Our data suggest that hypothalamic Foxo1 is an important regulator of food intake and energy balance