Synergism between psychosocial and metabolic stressors: impact on reproductive function in cynomolgus monkeys

The role of energy imbalance versus psychosocial stress in the pathogenesis of female reproductive dysfunction characterized by anovulation and amenorrhea remains controversial. In women, functional hypothalamic amenorrhea can develop in the absence of significant weight loss, excessive exercise, or profound psychosocial disruption. We posited, therefore, that commonplace, seemingly minor stressors that alone would have minimal impact upon reproductive function might interact synergistically such that combinations of stressors would cause a greater impairment of the reproductive axis than any single stressor alone. We then developed a monkey model to test this hypothesis. Adult female cynomolgus monkeys with normal menstrual cycles were randomized into three experimental groups and studied over four menstrual cycles. The groups were: low-level psychosocial stress (i.e., moving to a new housing environment; Move, n = 8), moderate energy imbalance (Exercise + Diet, n = 9); and all stressors in combination (Move + Exercise + Diet, n = 10). Food intake, body weight, menstrual cyclicity, and reproductive hormones were assessed for two control menstrual cycles followed by two experimental cycles during which the monkeys experienced the stressors. Abnormal cycles were considered to be abnormally long or anovulatory cycles. Few abnormal cycles occurred in the Move group (1 of 8 monkeys) and in the Exercise + Diet group (1 of 9 monkeys). In contrast, 7 of 10 monkeys in the Move + Exercise + Diet group displayed at least one abnormal cycle (chi(2) = 9.61, P = 0.008). These findings suggest that infertility due to hypothalamic hypogonadism can result from the combination of commonplace, seemingly minor stressors that often escape clinical attention.     

Exercise training enhances flow-induced vasodilation in skeletal muscle resistance arteries of aged rats: role of PGI2 and nitric oxide

Flow-induced vasodilation is attenuated with old age in rat skeletal muscle arterioles. The purpose of this study was to determine whether diminished cyclooxygenase (COX) signaling contributes to the age-induced attenuation of flow-induced vasodilation in gastrocnemius muscle arterioles and to determine whether, and through which mechanism(s), exercise training restores this deficit in old rats. Fischer 344 rats (3 and 22 mo old) were assigned to a sedentary or exercise-trained group. First-order arterioles were isolated from the gastrocnemius muscles, cannulated, and pressurized to 70 cm H(2)O. Diameter changes were determined in response to graded increases in intraluminal flow in the presence and absence of nitric oxide synthase (NOS) inhibition [10(-5) M N(G)-nitro-L-arginine methyl ester (L-NAME)], COX inhibition (10(-5) M indomethacin), or combination NOS (10(-5) M L-NAME) plus COX (10(-5) M indomethacin) inhibition. Aging reduced flow-induced vasodilation in gastrocnemius muscle arterioles. Exercise training restored responsiveness to flow in arterioles of aged rats and enhanced flow-induced vasodilation in arterioles from young rats. L-NAME inhibition of flow-induced vasodilation was greater in arterioles from old rats compared with those from young rats and was increased after exercise training in arterioles from both young and old rats. Although the indomethacin-sensitive portion of flow-induced dilation was not altered by age or training, both COX-1 mRNA expression and PGI(2) production increased with training in arterioles from old rats. These data demonstrate that exercise training restores flow-induced vasodilation in gastrocnemius muscle arterioles from old rats and enhances flow-induced vasodilation in gastrocnemius muscle arterioles from young rats. In arterioles from both old and young rats, the exercise training-induced enhancement of flow-induced dilation occurs primarily through a NOS mechanism.     

NADPH oxidase modulates myocardial Akt, ERK1/2 activation, and angiogenesis after hypoxia-reoxygenation

Recent studies have demonstrated that reactive oxygen species (ROS) mediate myocardial ischemia-reperfusion (I/R) and angiogenesis via the mitogen-activated protein kinases and the serine-threonine kinase Akt/protein kinase B pathways. NADPH oxidases are major sources of ROS in endothelial cells and cardiomyocytes. In the present study, we investigated the role of NADPH oxidase-derived ROS in hypoxia-reoxygenation (H/R)-induced Akt and ERK1/2 activation and angiogenesis using porcine coronary artery endothelial cells (PCAECs) and a mouse myocardial I/R model. Our data demonstrate that exposure of PCAECs to hypoxia for 2 h followed by 1 h of reoxygenation significantly increased ROS formation. Pretreatment with the NADPH oxidase inhibitors, diphenyleneiodonium (DPI, 10 microM) and apocynin (Apo, 200 and 600 microM), significantly attenuated H/R-induced ROS formation. Furthermore, exposure of PCAECs to H/R caused a significant increase in Akt and ERK1/2 activation. Exposure of PCAEC spheroids and mouse aortic rings to H/R significantly increased endothelial spheroid sprouting and vessel outgrowth, whereas pharmacological inhibition of NADPH oxidase or genetic deletion of the NADPH oxidase subunit, p47(phox) (p47(phox-/-)), significantly suppressed these changes. With the use of a mouse I/R model, our data further show that the increases in myocardial Akt and ERK1/2 activation and vascular endothelial growth factor (VEGF) expression were markedly blunted in the p47(phox-/-) mouse subjected to myocardial I/R compared with the wild-type mouse. Our findings underscore the important role of NADPH oxidase and its subunit p47(phox) in modulating Akt and ERK1/2 activation, angiogenic growth factor expression, and angiogenesis in myocardium undergoing I/R.     

Effects of increased suspended sediment on growth rate and gill condition of two southern Appalachian minnows

Despite the recognition that increased suspended sediment concentration (SSC) is a correlate of imperilment for native riverine fishes, research is limited on the effects of SSC on small non-game species. This study quantifies the impact of suspended sediment on fish growth and gill condition of two stream-dwelling minnows. Specific growth rate (i.e., percent change in mass per day) and gill condition (i.e., lamellar thickness and interlamellar area) were measured in young-of-year whitetail shiners, Cyprinella galactura, and federally threatened spotfin chubs, Erimonax monachus, exposed for 21 days to increased SSC (0, 25, 50, 100, and 500 mg L⁻¹). Exposure to elevated SSC caused a significant decrease in specific growth rate in both species and at all life stages tested. The effect of increased SSC was greatest in spotfin chubs, which exhibited a 15-fold decrease in specific growth rate at the highest treatment (500 mg L⁻¹). Effects of increased SSC were least for 8–9-month-old whitetail shiners, which had growth rates similar to controls for 25, 50, and 100 mg L⁻¹ treatments. These minnows exhibited a greater response to increasing SSC than salmonids at low to moderate SSC, and a lesser response at higher sediment levels. Gill damage was minimal at the three lowest treatment levels, moderate at 100 mg L⁻¹ and severe at 500 mg L⁻¹, indicating that respiratory surfaces of upland minnows may be much more sensitive than other species. Specific growth rate decreased significantly with increasing gill lamellar thickness, suggesting that respiratory impairment is one mechanism responsible for negative impacts of excessive sediment on small riverine fishes.     

An RNA-binding Protein,Lin28, Recognizes and Remodels G-quartets in the MicroRNAs (miRNAs) and mRNAs It Regulates

Lin28 is an evolutionarily conserved RNA-binding protein that inhibits processing of pre-let-7 microRNAs (miRNAs) and regulates translation of mRNAs that control developmental timing, pluripotency, metabolism, and tumorigenesis. The RNA features that mediate Lin28 binding to the terminal loops of let-7 pre-miRNAs and to Lin28-responsive elements (LREs) in mRNAs are not well defined. Here we show that Lin28 target datasets are enriched for RNA sequences predicted to contain stable planar structures of 4 guanines known as G-quartets (G4s). The imino NMR spectra of pre-let-7 loops and LREs contain resonances characteristic of G4 hydrogen bonds. These sequences bind to a G4-binding fluorescent dye, N-methyl-mesoporphyrin IX (NMM). Mutations and truncations in the RNA sequence that prevent G4 formation also prevent Lin28 binding. The addition of Lin28 to a pre-let-7 loop or an LRE reduces G4 resonance intensity and NMM binding, suggesting that Lin28 may function to remodel G4s. Further, we show that NMM inhibits Lin28 binding. Incubation of a human embryonal carcinoma cell line with NMM reduces its stem cell traits. In particular it increases mature let-7 levels, decreases OCT4, HMGA1, CCNB1, CDK4, and Lin28A protein, decreases sphere formation, and inhibits colony formation. Our results suggest a previously unknown structural feature of Lin28 targets and a new strategy for manipulating Lin28 function.     

Protocol for rat single muscle fiber isolation and culture

To attain a superior in vitro model of mature muscle fibers, we modified the established protocol for isolating single muscle fibers from rat skeletal muscle. Muscle fiber cultures with high viability were obtained using flexor digitorum brevis muscle and lasted for at least 7 days. We compared the expression levels of adult myosin heavy chain (MyHC) isoforms in these single muscle fibers with myotubes formed from myoblasts; isolated fibers contained markedly more abundant adult MyHC isoforms than myotubes. This muscle fiber model, therefore, will be useful for studying the various functions and cellular processes of mature muscles in vitro.