Aldo Keto Reductase 1B7 and Prostaglandin F2α Are Regulators of Adrenal Endocrine Functions

Prostaglandin F2α (PGF2α), represses ovarian steroidogenesis and initiates parturition in mammals but its impact on adrenal gland is unknown. Prostaglandins biosynthesis depends on the sequential action of upstream cyclooxygenases (COX) and terminal synthases but no PGF2α synthases (PGFS) were functionally identified in mammalian cells. In vitro, the most efficient mammalian PGFS belong to aldo-keto reductase 1B (AKR1B) family. The adrenal gland is a major site of AKR1B expression in both human (AKR1B1) and mouse (AKR1B3, AKR1B7). Thus, we examined the PGF2α biosynthetic pathway and its functional impact on both cortical and medullary zones. Both compartments produced PGF2α but expressed different biosynthetic isozymes. In chromaffin cells, PGF2α secretion appeared constitutive and correlated to continuous expression of COX1 and AKR1B3. In steroidogenic cells, PGF2α secretion was stimulated by adrenocorticotropic hormone (ACTH) and correlated to ACTH-responsiveness of both COX2 and AKR1B7/B1. The pivotal role of AKR1B7 in ACTH-induced PGF2α release and functional coupling with COX2 was demonstrated using over- and down-expression in cell lines. PGF2α receptor was only detected in chromaffin cells, making medulla the primary target of PGF2α action. By comparing PGF2α-responsiveness of isolated cells and whole adrenal cultures, we demonstrated that PGF2α repressed glucocorticoid secretion by an indirect mechanism involving a decrease in catecholamine release which in turn decreased adrenal steroidogenesis. PGF2α may be regarded as a negative autocrine/paracrine regulator within a novel intra-adrenal feedback loop. The coordinated cell-specific regulation of COX2 and AKR1B7 ensures the generation of this stress-induced corticostatic signal

Cushing's Syndrome and Fetal Features Resurgence in Adrenal Cortex–Specific Prkar1a Knockout Mice

Carney complex (CNC) is an inherited neoplasia syndrome with endocrine overactivity. Its most frequent endocrine manifestation is primary pigmented nodular adrenocortical disease (PPNAD), a bilateral adrenocortical hyperplasia causing pituitary-independent Cushing's syndrome. Inactivating mutations in PRKAR1A, a gene encoding the type 1 α-regulatory subunit (R1α) of the cAMP–dependent protein kinase (PKA) have been found in 80% of CNC patients with Cushing's syndrome. To demonstrate the implication of R1α loss in the initiation and development of PPNAD, we generated mice lacking Prkar1a specifically in the adrenal cortex (AdKO). AdKO mice develop pituitary-independent Cushing's syndrome with increased PKA activity. This leads to autonomous steroidogenic genes expression and deregulated adreno-cortical cells differentiation, increased proliferation and resistance to apoptosis. Unexpectedly, R1α loss results in improper maintenance and centrifugal expansion of cortisol-producing fetal adrenocortical cells with concomitant regression of adult cortex. Our data provide the first in vivo evidence that loss of R1α is sufficient to induce autonomous adrenal hyper-activity and bilateral hyperplasia, both observed in human PPNAD. Furthermore, this model demonstrates that deregulated PKA activity favors the emergence of a new cell population potentially arising from the fetal adrenal, giving new insight into the mechanisms leading to PPNAD

Identification and origins of neutral fecal sterols in adult Large White sows : occurrence of externally-secreted intestinal cholesterol

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Specific signals involved in the long-term maintenance of radiation-induced fibrogenic differentiation: A role for CCN2 and low concentration of TGF-β1

The fibrogenic differentiation of resident mesenchymal cells is a key parameter in the pathogenesis of radiation fibrosis and is triggered by the profibrotic growth factors transforming growth factor (TGF)-β1 and CCN2. TGF-β1 is considered the primary inducer of fibrogenic differentiation and is thought to control its long-term maintenance, whereas CCN2 is considered secondary effector of TGF-β1. Yet, in long-term established fibrosis like that associated with delayed radiation enteropathy, in situ TGF-β1 deposition is low, whereas CCN2 expression is high. To explore this apparent paradox, cell response to increasing doses of TGF-β1 was investigated in cells modeling initiation and maintenance of fibrosis, i.e., normal and fibrosis-derived smooth muscle cells, respectively. Activation of cell-specific signaling pathways by low TGF-β1 doses was demonstrated with a main activation of the Rho/ROCK pathway in fibrosis-derived cells, whereas the Smad pathway was mainly activated in normal cells. This leads to subsequent and cell-specific regulation of the CCN2 gene. These results suggested a specific profibrotic role of CCN2 in fibrosis-initiated cells. Furthermore, the modulation of CCN2 expression by itself and the combination of TGF-β1 and CCN2 was investigated in fibrosis-derived cells. In fibrosis-initiated cells CCN2 triggered its autoinduction; furthermore, low concentration of TGF-β1-potentiated CCN2 autoinduction. Our findings showed a differential requirement and action of TGF-β1 in the fibrogenic response of normal vs. fibrosis-derived cells. This study defines a novel Rho/ROCK but Smad3-independent mode of TGF-β signaling that may operate during the chronic stages of fibrosis and provides evidence of both specific and combinatorial roles of low TGF-β1 dose and CCN2. Copyright © 2008 the American Physiological Society

PECAM-1 (CD31) is required for interactions of platelets with endothelial cells after irradiation

Sustained adhesion of platelets to endothelial cells (EC) is believed to contribute to thrombosis and vascular occlusions following radiation exposure leading to organ functional impairment and even death. Our objective was to evaluate the role of platelet endothelial cell adhesion molecule (PECAM)-1 in the prothrombotic response of EC after irradiation. Endothelial PECAM-1 expression was determined by cell-enzyme linked immunosorbent assay (ELISA) on human microvascular EC from lung (HMVEC-L) up to 21 days after a 10 Gy irradiation. Platelet- and leukocyte-endothelial cell interactions were assessed using a flow adhesion assay with fluorescently labeled whole blood, and the function of PECAM-1 in these processes was measured by using blocking antibody. PECAM-1 expression was significantly increased on irradiated HMVEC-L and remained elevated at 21 days. Anti-PECAM-1 antibody significantly inhibited adhesion of single platelets and thrombi on irradiated HMVEC-L. This inhibitory effect persisted at day 21. Anti-PECAM-1 also reduced leukocyte adhesion to irradiated HMVEC-L. The up-regulation of endothelial PECAM-1 following radiation exposure is persistent. PECAM-1 plays a key role platelet adhesion/aggregation on irradiated EC. Therefore, strategies targeting this adhesion molecule may prevent the development of radiation pathologies. © 2004 International Society on Thrombosis and Haemostasis

Regional cholesterol synthesis in the intestinal mucosa of the genetically hyper cholesterolaemic RICO rat : kinetic study following whole-body gamma-irradiation

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Involvement of primary afferent nerves after abdominal irradiation: consequences on ileal contractile activity and inflammatory mediator release in the rat.

International audienceIn this study we analyzed the role of substance P (SP) from afferent nerves in ileum contractibility and in the release of inflammatory mediators (neurotensin, Il-1beta, and TNF-alpha) in ileal mucosa and muscularis layers after a 10-Gy gamma-irradiation of the abdomen. Six hours after irradiation, SP concentrations were lower than in control rats, and 3 days after irradiation SP-induced contractile activity was higher. Irradiation significantly increased the levels of neurotensin, Il-1beta, and TNF-alpha in both layers. Pretreatment with capsaicin depleted afferent nerve endings of SP and reduced SP levels by about 50%. Capsaicin treatment reduced SP concentrations further, beyond the levels due to irradiation, thereby suggesting that all sources of SP are affected by irradiation. Capsaicin treatment prevented the irradiation from affecting SP-induced contractile response or increasing neurotensin levels. This finding suggests that SP released by afferent nerve endings controls these functions. Proinflammatory cytokine release was not reduced by capsaicin treatment

Alterations in water and electrolyte absorption in the rat colon following neutron irradiation: Influence of neutron component and irradiation dose

Purpose: To study the absorptive function of rat colon following whole-body exposure to neutron irradiation, either to the same total dose with varying proportion of neutrons or to the same neutron proportion with an increasing irradiation dose. Materials and methods: Different proportions of neutron irradiation were produced from the reactor SILENE using a fissile solution of uranium nitrate (8, 47 and 87% neutron). Water and electrolyte fluxes were measured in the rat in vivo under anaesthesia by insertion into the descending colon of an agarose gel cylinder simulating the faeces. Functional studies were completed by histological analyses. In the first set of experiments, rats received 3.8 Gy with various neutron percentages and were studied from 1 to 14 days after exposure. In the second set of experiments, rats were exposed to increasing doses of irradiation (1-4 Gy) with a high neutron percentage (87%n) and were studied at 4 days after exposure. Results and conclusions: The absorptive capacity of rat colon was diminished by irradiation at 3-5 days, with a nadir at 4 days. The results demonstrate that an increase in the neutron proportion is associated with an amplification of the effects. Furthermore, a delay in the re-establishment of normal absorption was observed with the high neutron proportion (87%n). A dose-dependent reduction of water absorption by rat colon was also observed following neutron irradiation (87%n), with a 50% reduction at 3 Gy. Comparison of this dose-effect curve with the curve obtained following gamma 60Co-irradiation indicates an RBE of 2.2 for absorptive colonic function in rat calculated at 4 days after exposure