Regulation of Tie2 Expression by Angiopoietin—Potential Feedback System

To study a potential feedback system in the angiopoietin (Ang)-Tie2 system, the authors examined effects of Ang1 and Ang2 on Tie2 expression on human umbilical vein endothelial cells (HUVECs) with or without stimulation by a potent inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha). Ang1, but not Ang2, down-regulated Tie2 expression on HUVECs without TNF-alpha stimulation. Both Ang1 and Ang2 attenuated TNF-alpha-induced Tie2 up-regulation. Regulation of Tie2 expression by Ang1 or Ang2 was not dependent on phosphatidylinositol 3-kinase. The Ang-Tie2 system appears to have an autoregulatory feedback system that may be regulating the overall activity of the Tie2 system in both physiological and pathological conditions.

Muscle spindle feedback differs between the soleus and gastrocnemius in humans

The Hoffmann (H) reflex and motor (M) response were studied in soleus and gastrocnemius during voluntary contraction in eight male volunteers.

AIMS

To determine if the strength of spindle input to the muscles is the same. To assess if the M response size changes during contraction.

RESULTS

The size of the maximum M response (M max) changed during contraction in each subject. Hence, all H reflex measurements were normalized to the M max at each level of contraction for each subject. The largest H/M max was bigger in soleus than gastrocnemius at every contraction level. The overall largest H/M max for soleus (97%) and gastrocnemius (55%) were achieved at 40 and 100% maximum voluntary contraction (MVC), respectively.

CONCLUSION

Soleus receives greater spindle feedback than the gastrocnemius both at rest and during voluntary contraction.

Lipid and insulin infusion-induced skeletal muscle insulin resistance is likely due to metabolic feedback and not changes in IRS-1, Akt, or AS160 phosphorylation

Type 2 diabetes is characterized by hyperlipidemia, hyperinsulinemia, and insulin resistance. The aim of this study was to investigate whether acute hyperlipidemia-induced insulin resistance in the presence of hyperinsulinemia was due to defective insulin signaling. Hyperinsulinemia (approximately 300 mU/l) with hyperlipidemia or glycerol (control) was produced in cannulated male Wistar rats for 0.5, 1 h, 3 h, or 5 h. The glucose infusion rate required to maintain euglycemia was significantly reduced by 3 h with lipid infusion and was further reduced after 5 h of infusion, with no difference in plasma insulin levels, indicating development of insulin resistance. Consistent with this finding, in vivo skeletal muscle glucose uptake (31%, P < 0.05) and glycogen synthesis rate (38%, P < 0.02) were significantly reduced after 5 h compared with 3 h of lipid infusion. Despite the development of insulin resistance, there was no difference in the phosphorylation state of multiple insulin-signaling intermediates or muscle diacylglyceride and ceramide content over the same time course. However, there was an increase in cumulative exposure to long-chain acyl-CoA (70%) with lipid infusion. Interestingly, although muscle pyruvate dehydrogenase kinase 4 protein content was decreased in hyperinsulinemic glycerol-infused rats, this decrease was blunted in muscle from hyperinsulinemic lipid-infused rats. Decreased pyruvate dehydrogenase complex activity was also observed in lipid- and insulin-infused animals (43%). Overall, these results suggest that acute reductions in muscle glucose metabolism in rats with hyperlipidemia and hyperinsulinemia are more likely a result of substrate competition than a significant early defect in insulin action or signaling.

Targeted therapy for malignant glioma patients: lessons learned and the road ahead

Molecularly targeted therapies are transforming the care of patients with malignant gliomas, including glioblastoma, the most common malignant primary brain tumor of adults. With an arsenal of small molecule inhibitors and antibodies that target key components of the signal transduction machinery that are commonly activated in gliomas, neuro-oncologists and neurosurgeons are poised to transform the care of these patients. Nonetheless, successful application of targeted therapies remains a challenge. Strategies are lacking for directing kinase inhibitor or other pathway-specific therapies to individual patients most likely to benefit. In addition, response to targeted agents is determined not only by the presence of the key mutant kinases, but also by other critical changes in the molecular circuitry of cancer cells, such as loss of key tumor suppressor proteins, the selection for kinase-resistant mutants, and the deregulation of feedback loops. Understanding these signaling networks, and studying them in patients, will be critical for developing rational combination therapies to suppress resistance for malignant glioma patients. Here we review the current status of molecular targeted therapies for malignant gliomas. We focus initially on identifying some of the insights gained to date from targeting the EGFR/PI3K/Akt/mTOR signaling pathway in patients and on how this has led toward a reconceptualization of some of the challenges and directions for targeted treatment. We describe how advances from the world of genomics have the potential to transform our approaches toward targeted therapy, and describe how a deeper understanding of the complex nature of cancer, and its adeptness at rewiring molecular circuitry to evade targeted agents, has raised new challenges and identified new leads.

NTPDases in the neuroendocrine hypothalamus: possible energy regulators of the positive gonadotrophin feedback

BACKGROUND

Brain-derived ectonucleoside triphosphate diphosphohydrolases (NTPDases) have been known as plasma membrane-incorporated enzymes with their ATP-hydrolyzing domain outside of the cell. As such, these enzymes are thought to regulate purinergic intercellular signaling by hydrolyzing ATP to ADP-AMP, thus regulating the availability of specific ligands for various P2X and P2Y purinergic receptors. The role of NTPDases in the central nervous system is little understood. The two major reasons are the insufficient knowledge of the precise localization of these enzymes in neural structures, and the lack of specific inhibitors for the various NTPDases. To fill these gaps, we recently studied the presence of neuron-specific NTPDase3 in the mitochondria of hypothalamic excitatory neurons by morphological and functional methods. Results from those studies suggested that intramitochondrial regulation of ATP levels may play a permissive role in the neural regulation of physiological functions by tuning the level of ATP-carried energy that is needed for neuronal functions, such as neurotransmission and/or intracellular signaling.

PRESENTATION OF THE HYPOTHESIS

In the lack of highly specific inhibitors, the determination of the precise function and role of NTPDases is hardly feasable. Yet, here we attempt to find an approach to investigate a possible role for hypothalamic NTPDase3 in the initiation of the midcycle luteinizing hormone (LH) surge, as such a biological role was implied by our recent findings. Here we hypothesize that NTPDase-activity in neurons of the AN may play a permissive role in the regulation of the estrogen-induced pituitary LH-surge.

TESTING THE HYPOTHESIS

We propose to test our hypothesis on ovariectomized rats, by stereotaxically injecting 17beta-estradiol and/or an NTPDase-inhibitor into the arcuate nucleus and determine the consequential levels of blood LH, mitochondrial respiration rates from arcuate nucleus synaptosomal preparations, NTPDase3-expression from arcuate nucleus tissue samples, all compared to sham and intact controls.

IMPLICATIONS OF THE HYPOTHESIS

Results from these studies may lead to the conclusion that estrogen may modulate the activity of mitochondrial, synapse-linked NTPDase3, and may show a correlation between mitochondrial NTPDase3-activity and the regulation of LH-release by estrogen.

Computing paths and cycles in biological interaction graphs

BACKGROUND

Interaction graphs (signed directed graphs) provide an important qualitative modeling approach for Systems Biology. They enable the analysis of causal relationships in cellular networks and can even be useful for predicting qualitative aspects of systems dynamics. Fundamental issues in the analysis of interaction graphs are the enumeration of paths and cycles (feedback loops) and the calculation of shortest positive/negative paths. These computational problems have been discussed only to a minor extent in the context of Systems Biology and in particular the shortest signed paths problem requires algorithmic developments.

RESULTS

We first review algorithms for the enumeration of paths and cycles and show that these algorithms are superior to a recently proposed enumeration approach based on elementary-modes computation. The main part of this work deals with the computation of shortest positive/negative paths, an NP-complete problem for which only very few algorithms are described in the literature. We propose extensions and several new algorithm variants for computing either exact results or approximations. Benchmarks with various concrete biological networks show that exact results can sometimes be obtained in networks with several hundred nodes. A class of even larger graphs can still be treated exactly by a new algorithm combining exhaustive and simple search strategies. For graphs, where the computation of exact solutions becomes time-consuming or infeasible, we devised an approximative algorithm with polynomial complexity. Strikingly, in realistic networks (where a comparison with exact results was possible) this algorithm delivered results that are very close or equal to the exact values. This phenomenon can probably be attributed to the particular topology of cellular signaling and regulatory networks which contain a relatively low number of negative feedback loops.

CONCLUSION

The calculation of shortest positive/negative paths and cycles in interaction graphs is an important method for network analysis in Systems Biology. This contribution draws the attention of the community to this important computational problem and provides a number of new algorithms, partially specifically tailored for biological interaction graphs. All algorithms have been implemented in the CellNetAnalyzer framework which can be downloaded for academic use at http://www.mpi-magdeburg.mpg.de/projects/cna/cna.html.

Postnatal glucocorticoid excess due to pituitary glucocorticoid receptor deficiency: differential short- and long-term consequences

A tight regulation of hypothalamic-pituitary-adrenal (HPA) axis activity is essential for successful adaptation to stressful stimuli. Disruption of normal HPA axis development is a main risk factor for diseases such as posttraumatic stress disorder or depression, but the molecular mechanisms that lead to these long-term consequences are poorly understood. Here, we test the hypothesis that the pituitary glucocorticoid receptor (GR) is involved in regulating HPA axis function in neonatal and adult animals. Furthermore, we investigate whether postnatal hypercortisolism induced by pituitary GR deficiency is a main factor contributing to the persistent effects of early-life stress. Conditional knockout mice with a deletion of the GR at the pituitary (GR(POMCCre)) show excessive basal corticosterone levels during postnatal development, but not in adulthood. The hypercortisolemic state of neonatal GR(POMCCre) mice is accompanied by central gene expression changes of CRH and vasopressin in the paraventricular nucleus, but these alterations normalize at later ages. In adult mice, pituitary GR deficiency results in impaired glucocorticoid negative feedback. Furthermore, adult GR(POMCCre) mice display a more active coping strategy in the forced swim test, with no alterations in anxiety like behavior or cognitive functions. Postnatal GR antagonist treatment is able to prevent the long-term behavioral effects in GR(POMCCre) mice. In conclusion, we show that pituitary GRs are centrally involved in regulating HPA axis activity in neonates and mediate negative feedback regulation in adult animals. Postnatal glucocorticoid excess results in an altered stress-coping behavior in adult animals, with no effects on anxiety like behavior or cognition.

Free fatty acids inhibit growth hormone/signal transducer and activator of transcription-5 signaling in human muscle: a potential feedback mechanism

CONTEXT

Stimulation of lipolysis, leading to increased blood concentrations of free fatty acids (FFAs), is a primary effect of GH and phosphorylation of intracellular signal transducer and activator of transcription (STAT)-5 is a primary mediator of the effects of GH.

OBJECTIVE

Based on preliminary results, we intended to test whether FFAs exert a negative feedback inhibition of STAT5 phosphorylation in skeletal muscle.

DESIGN AND PARTICIPANTS

Eight healthy young men were investigated for 8 h on four occasions at four different FFA levels in a single blind, randomized manner. Acipimox was used to suppress FFA levels and Intralipid was infused to obtain appropriate FFA concentrations. Somatostatin was infused to control GH levels and GH, insulin, and glucagon were replaced. Muscle biopsies were taken after 8 h and compared with a fifth biopsy taken under normal basal conditions.

SETTING

The study was conducted at a university clinical research unit.

RESULTS

GH concentrations remained steady and comparable in all studies and FFA concentrations varied between 0.01 and 1.71 mmol/liter on the four occasions (P < 0.05). We observed a dose-dependent 40% decrease of STAT5 phosphorylation in skeletal muscle with increasing concentrations of FFAs.

CONCLUSIONS

Our results strongly suggest the existence of a negative feedback loop, whereby effects of GH may be dampened by FFA inhibition of GH-dependent STAT5 phosphorylation. The mechanisms behind and biological consequences of this finding awaits additional studies.

A computational analysis of localized Ca2+-dynamics generated by heterogeneous release sites

We investigate the role of heterogeneous expression of IP3R and RyR in generating diverse elementary Ca2+ signals. It has been shown empirically (Wojcikiewicz and Luo in Mol. Pharmacol. 53(4):656-662, 1998; Newton et al. in J. Biol. Chem. 269(46):28613-28619, 1994; Smedt et al. in Biochem. J. 322(Pt. 2):575-583, 1997) that tissues express various proportions of IP3 and RyR isoforms and this expression is dynamically regulated (Parrington et al. in Dev. Biol. 203(2):451-461, 1998; Fissore et al. in Biol. Reprod. 60(1):49-57, 1999; Tovey et al. in J. Cell Sci. 114(Pt. 22):3979-3989, 2001). Although many previous theoretical studies have investigated the dynamics of localized calcium release sites (Swillens et al. in Proc. Natl. Acad. Sci. U.S.A. 96(24):13750-13755, 1999; Shuai and Jung in Proc. Natl. Acad. Sci. U.S.A. 100(2):506-510, 2003a; Shuai and Jung in Phys. Rev. E, Stat. Nonlinear Soft Matter Phys. 67(3 Pt. 1):031905, 2003b; Thul and Falcke in Biophys. J. 86(5):2660-2673, 2004; DeRemigio and Smith in Cell Calcium 38(2):73-86, 2005; Nguyen et al. in Bull. Math. Biol. 67(3):393-432, 2005), so far all such studies focused on release sites consisting of identical channel types. We have extended an existing mathematical model (Nguyen et al. in Bull. Math. Biol. 67(3):393-432, 2005) to release sites with two (or more) receptor types, each with its distinct channel kinetics. Mathematically, the release site is represented by a transition probability matrix for a collection of nonidentical stochastically gating channels coupled through a shared Ca2+ domain. We demonstrate that under certain conditions a previously defined mean-field approximation of the coupling strength does not accurately reproduce the release site dynamics. We develop a novel approximation and establish that its performance in these instances is superior. We use this mathematical framework to study the effect of heterogeneity in the Ca2+-regulation of two colocalized channel types on the release site dynamics. We consider release sites consisting of channels with both Ca2+-activation and inactivation ("four-state channels") and channels with Ca2+-activation only ("two-state channels") and show that for the appropriate parameter values, synchronous channel openings within a release site with any proportion of two-state to four-state channels are possible, however, the larger the proportion of two-state channels, the more sensitive the dynamics are to the exact spatial positioning of the channels and the distance between channels. Specifically, the clustering of even a small number of two-state channels interferes with puff/spark termination and increases puff durations or leads to a tonic response.

Boolean network-based analysis of the apoptosis network: irreversible apoptosis and stable surviving

To understand the design principles of the molecular interaction network associated with the irreversibility of cell apoptosis and the stability of cell surviving, we constructed a Boolean network integrating both the intrinsic and extrinsic pro-apoptotic pathways with pro-survival signal transduction pathways. We performed statistical analyses of the dependences of cell fate on initial states and on input signals. The analyses reproduced the well-known pro- and anti-apoptotic effects of key external signals and network components. We found that the external GF signal by itself did not change the apoptotic ratio from randomly chosen initial states when there is no external TNF signal, but can significantly offset apoptosis induced by the TNF signal. While a complete model produces the expected irreversibility of the apoptosis process, alternative models missing one or more of four selected inter-component connections indicate that the feedback loops directly involving the caspase 3 are essential for maintaining irreversibility of apoptosis. The feedback loops involving P53 showed compensating effects when those involving caspase 3 have been removed. The GF signal significantly increases the stability of the surviving states of the network. The apoptosis network seems to use different modules by design to control the irreversibility of the apoptosis process and the stability of the surviving states. Such a design may accommodate the needed plasticity for the network to adapt to different cellular environments: depending on the strength of external pro-surviving signals, apoptosis can be induced either easily or difficultly by pro-apoptotic signal of varying strengths, but proceed with invariable irreversibility.

Cortisol disrupts the ability of estradiol-17beta to induce the LH surge in ovariectomized ewes

Stress disrupts the preovulatory luteinizing hormone (LH) surge in females, but the mechanisms are unknown. We tested the hypothesis that cortisol compromises the ability of estrogen to induce a preovulatory-like LH surge in ovariectomized ewes in both the breeding and nonbreeding season. Luteinizing hormone surges were induced in ovariectomized ewes by treatment with progesterone followed by a surge-inducing estradiol-17beta (E2) stimulus using a crossover design. The experiment was replicated in the breeding and nonbreeding seasons. Cortisol reduced the incidence of LH surges irrespective of season. Cortisol increased the latency from E2 stimulus to the onset of the surge in the breeding season only and suppressed the LH surge amplitude during both seasons (P<0.01). We conclude that cortisol can interfere with the LH surge in several ways: delay, blunt, and in extreme cases prevent the E2-induced LH surge. Furthermore, the effect of cortisol to delay the E2-induced LH surge is more pronounced in the breeding season. These results show that cortisol disrupts the positive feedback effect of E2 to trigger an LH surge and suggest the involvement of multiple mechanisms.

Organizational actions of postnatal estradiol in female sheep treated prenatally with testosterone: programming of prepubertal neuroendocrine function and the onset of puberty

Prenatal testosterone (T) exposure defeminizes reproductive neuroendocrine function in female sheep, although the LH surge dysfunctions are initially less severe in gonadally intact females than in females subject to neonatal ovariectomy and estradiol (E) replacement. Because prepubertal ovarian production of E differs quantitatively and qualitatively from chronic E replacement, we tested the hypothesis that postnatal E exacerbates the consequences of prenatal T on the positive, but not the negative, steroid feedback controls of GnRH secretion. Our approach was to characterize prepubertal sensitivity to E negative feedback, the onset and maintenance of progestagenic cycles, and the LH surge response in ovary intact, prenatally untreated (control), and T-treated (T) sheep that were exposed postnatally to only endogenous E, or exposed to excess E by s.c. implant. Sensitivity to E negative feedback was reduced in T females, but excess postnatal E did not further increase LH pulse frequency. Excess E prevented ovarian cycles in several control females, and increased cycle irregularity in T females. However, the LH surge mechanism was functional in all control females (regardless of postnatal E exposure) and in some T females without excess E, but nonfunctional in T females with excess E. These findings suggest that postnatal E does not program increased resistance to E negative feedback, but excess postnatal E does disrupt other mechanisms required for ovarian cyclicity. We conclude that in this precocial species, prenatal steroids are sufficient to program controls of tonic LH secretion, but the LH surge mechanism is susceptible to further programming by postnatal E.

Does walking change the Romberg sign?

The Romberg sign helps demonstrate loss of postural control as a result of severely compromised proprioception. There is still no standard approach to applying the Romberg test in clinical neurology and the criteria for and interpretation of an abnormal result continue to be debated. The value of this sign and its adaptation when walking was evaluated. Detailed clinical examination of 50 consecutive patients of cervical myelopathy was performed prospectively. For the walking Romberg sign, patients were asked to walk 5 m with their eyes open. This was repeated with their eyes closed. Swaying, feeling of instability or inability to complete the walk with eyes closed was interpreted as a positive walking Romberg sign. This test was compared to common clinical signs to evaluate its relevance. Whilst the Hoffman's reflex (79%) was the most prevalent sign seen, the walking Romberg sign was actually present in 74.5% of the cases. The traditional Romberg test was positive in 17 cases and 16 of these had the walking Romberg positive as well. Another 21 patients had a positive walking Romberg test. Though not statistically significant, the mean 30 m walking times were slower in patients with traditional Romberg test than in those with positive walking Romberg test and fastest in those with neither of these tests positive. The combination of either Hoffman's reflex and/or walking Romberg was positive in 96% of patients. The walking Romberg sign is more useful than the traditional Romberg test as it shows evidence of a proprioceptive gait deficit in significantly more patients with cervical myelopathy than is found on conventional neurological examination. The combination of Hoffman's reflex and walking Romberg sign has a potential as useful screening tests to detect clinically significant cervical myelopathy.

TGF-mediated dynamics in a system of many coupled nephrons

This paper presents a mathematical model of a system of many coupled nephrons branching from a common cortical radial artery, and accompanying analysis of that system. This modeling effort is a first step in understanding how coupling magnifies the tendency of nephrons to oscillate owing to tubuloglomerular feedback. Central to the present work is the single nephron integral model (as in Pitman et al., The IMA Volumes in Mathematics and Its Applications, vol. 129, pp. 345-364, 2002 and in Zaritski, Ph.D. Dissertation, 1999) which is a simplification of the single nephron PDE model of Layton et al. (Am. J. Physiol. 261, F904-F919, 1991). A second principal idea used in the present model is a coupling of model nephrons, generalizing the work of Pitman et al. (Bull. Math. Biol. 66, 1463-1492, 2004) who proposed a model of two coupled nephrons. In this study, we couple nephrons through a nearest neighbor interaction.Speaking generally, our results suggest that a series of similar nephrons coupled to their nearest neighbors are more prone to be found in an oscillatory mode, relative to a single nephron with the same properties. More specifically, we show analytically that, for N coupled identical nephrons, the region supporting oscillatory solutions in the time delay-gain parameter plane increases with N. Numerical simulations suggest that, if N nephrons have gains and time delays that do not differ by much, the system is, again, more prone to oscillate, relative to a single nephron, and the oscillations tend to be approximately synchronous and in-phase. We examine the effect of parameters on bifurcation. We also examine alternative models of coupling; this analysis allows us to conclude that the increased propensity of coupled nephrons to oscillate is a robust finding, true for several models of nephron interaction.

Oestrogen, kisspeptin, GPR54 and the pre-ovulatory luteinising hormone surge

Ovulation is central to mammalian fertility, yet the precise mechanism through which oestrogen triggers the gonadotrophin-releasing hormone (GnRH) surge that generates the pre-ovulatory luteinising hormone (LH) surge has remained elusive. The recent discovery that kisspeptin-GPR54 signalling is an essential regulator of the neuroendocrine axis at puberty has led investigators to evaluate the role of kisspeptin in the pre-ovulatory GnRH surge mechanism. Kisspeptin neurones are known to express oestrogen and progesterone receptors and have their cell bodies located in brain regions implicated in the positive-feedback mechanism in several mammalian species. In rodents, kisspeptin neurones located in the rostral periventricular area of the third ventricle (RP3V) are positively regulated by oestrogen and most likely are activated by oestrogen at the time of positive feedback. A similar scenario appears to exist for a sub-population of kisspeptin neurones located in the mediobasal hypothalamus of sheep and primates. The majority of GnRH neurones express GPR54, and kisspeptin causes an intense electrical activation of these cells. In concordance with this, kisspeptin administration in vivo results in an abrupt and prolonged release of LH in all mammalian species examined to date. Functional evidence from immunoneutralisation and knockout studies suggests that RP3V kisspeptin neurones projecting to GnRH neurones are an essential component of the surge mechanism in rodents. Taken together, the studies undertaken to date provide substantial evidence in support of a key role of kisspeptin-GPR54 signalling in the generation of the oestrogen-induced pre-ovulatory surge mechanism in mammals.

Minireview: Thyrotropin-releasing hormone and the thyroid hormone feedback mechanism

Thyroid hormone (TH) plays a critical role in development, growth, and cellular metabolism. TH production is controlled by a complex mechanism of positive and negative regulation. Hypothalamic TSH-releasing hormone (TRH) stimulates TSH secretion from the anterior pituitary. TSH then initiates TH synthesis and release from the thyroid gland. The synthesis of TRH and TSH subunit genes is inhibited at the transcriptional level by TH, which also inhibits posttranslational modification and release of TSH. Although opposing TRH and TH inputs regulate the hypothalamic-pituitary-thyroid axis, TH negative feedback at the pituitary was thought to be the primary regulator of serum TSH levels. However, study of transgenic animals showed an unexpected, dominant role for TRH in regulating the hypothalamic-pituitary-thyroid axis and an unanticipated involvement of the thyroid hormone receptor ligand-dependent activation function (AF-2) domain in TH negative regulation. These results are summarized in the review.

Neurobiological mechanisms underlying oestradiol negative and positive feedback regulation of gonadotrophin-releasing hormone neurones

The feedback actions of ovarian oestradiol during the female reproductive cycle are among the most unique in physiology. During most of the cycle, oestradiol exerts homeostatic, negative feedback upon the release of gonadotrophin-releasing hormone (GnRH). Upon exposure to sustained elevated oestradiol levels, however, there is a switch in the feedback effects of this hormone to positive, resulting in induction of a surge in the release of GnRH that serves as a neuroendocrine signal to initiate the ovulatory cascade. We review recent developments stemming from studies in an animal model exhibiting daily switches between positive and negative feedback that have probed the neurobiological mechanisms, including changes in neural networks and intrinsic properties of GnRH neurones, underlying this switch in oestradiol action.

A HIF-1alpha-dependent autocrine feedback loop promotes survival of serum-deprived prostate cancer cells

BACKGROUND

We previously reported that normoxic, serum-deprived prostate cancer (PCa) cells upregulate hypoxia-inducible factor-1alpha (HIF-1alpha) protein, which promotes survival during serum deprivation via insulin-like growth factor-2 (IGF-2) upregulation. This study investigated the molecular mechanism of autocrine regulation of HIF-1alpha, IGF-2 and cell survival in serum-deprived PC-3 and LNCaP PCa cells.

METHODS

Cell viability was assessed by trypan blue assay. PI3K activity was inhibited with LY294002, and PTEN overexpression. mRNA was assessed by RT-PCR, and IGF-2 protein by ELISA. Activated insulin-like growth factor-I receptor (IGF-IR) was detected by probing immunoprecipitated IGF-IR for phospho-tyrosine. IGF-IR activity was inhibited with IGF-2 neutralizing antibody and IGF-IR-specific siRNA. HIF-1alpha, phospho-Akt, total-Akt and IGF-IR protein was assessed by immunoblots. HIF-1alpha was suppressed with siRNA.

RESULTS

We detected a time-dependent increase in Akt activation during serum deprivation, and inhibition of Akt activation attenuated the serum deprivation-mediated increase in HIF-1alpha and cell survival. Importantly, IGF-2 secretion significantly increased during serum deprivation, and was accompanied by increased activation of its receptor, IGF-IR. Additionally, inhibition of IGF-2 activity markedly attenuated the serum deprivation-mediated increase in IGF-IR and Akt activation, HIF-1alpha expression, and also its own transcription, suggesting autocrine regulation of HIF-1alpha expression via IGF-2. Cross-talk between IGF-2/ IGF-IR system and PI3K-Akt pathway was further demonstrated by findings wherein IGF-IR suppression inhibited Akt activation, and IGF-IR activation was inhibited following PI3K inhibition. Furthermore, HIF-1alpha suppression attenuated the serum deprivation-mediated increase in Akt and IGF-IR activation.

CONCLUSION

Collectively, our study demonstrates existence of a pro-survival HIF-1alpha-dependent autocrine feedback loop in normoxic, serum-deprived PCa cells.

Isoforms and functions of NAD(P)H oxidase at the macula densa

Macula densa cells produce superoxide (O2-) during tubuloglomerular feedback primarily via NAD(P)H oxidase (NOX). The purpose of the present study was to determine NOXs expressed by the macula densa and the role of each one in NaCl-induced O2- production. To identify which isoforms are expressed, we applied single-cell RT-PCR to macula densa cells isolated by laser capture microdissection and to MMDD1 cells (a macula densa-like cell line). The captured cells expressed neuronal NOS (marker of macula densa), NOX2, and NOX4 but not NOX1. Expression of the NOXs and neuronal NOS was essentially identical in the MMDD1 cells. Thus, we used MMDD1 cells to investigate which isoform is responsible for NaCl-induced O2- production. We used small-interfering RNA to knock down NOX2 or NOX4 in MMDD1 cells and measured O2- exposed to low-salt solution (LS; 70 mmol/L of NaCl) or high-salt solution (HS; 140 mmol/L of NaCl). Exposing control cells (scrambled small-interfering RNA) to HS increased O2- concentrations from 0.75+/-0.28 to 1.48+/-0.46 U/min per 10(5) cells in LS and HS, respectively (P<0.001). Inhibiting NOX2 blocked the HS-induced increase in O2- (0.62+/-0.39 versus 0.76+/-0.31 U/min per 10(5) cells in LS and HS groups, respectively). Blocking NOX4 did not affect HS-induced O2- levels. O2- levels in the control cells during LS and HS were 0.80+/-0.30 and 1.56+/-0.49 U/min per 10(5) cells, respectively (P<0.001); whereas O2- levels in NOX4-small-interfering RNA-treated cells during LS and HS were 0.40+/-0.25 and 1.26+/-0.51 U/min per 10(5) cells, respectively (P<0.001). We conclude that, whereas macula densa cells express the NOX2 and NOX4 isoforms, NOX2 is primarily responsible for NaCl-induced O2- generation.

The aging male hypothalamic-pituitary-gonadal axis: pulsatility and feedback

Aging results in insidious decremental changes in hypothalamic, pituitary and gonadal function. The foregoing three main anatomic loci of control are regulated by intermittent time-delayed signal exchange, principally via gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and testosterone/estradiol (Te/E(2)). A mathematical framework is required to embody these dynamics. The present review highlights integrative adaptations in the aging male hypothalamic-pituitary-gonadal axis, as assessed by recent objective ensemble models of the axis as a whole.

Modeling cerebral blood flow and regulation

Cerebral autoregulation is a homeostatic mechanism which maintains blood flow despite changes in blood pressure in order to meet local metabolic demands. Several mechanisms play a role in cerebral autoregulation in order to adjust vascular tone and caliber of the cerebral vessels, but the exact etiology of the dynamics of these mechanism is not well understood. In this study, we discuss two patient specific models predicting cerebral blood flow velocity during postural change from sitting to standing. One model characterises cerebral autoregulation, the other describes the beat-to-beat distribution of blood flow to the major regions of the brain. Both models have been validated against experimental data from a healthy young subject.

Signal-response modeling of partial hormone feedback networks

BACKGROUND

Endocrine feedback control networks are typically complex and contain multiple hormones, pools, and compartments. The hormones themselves commonly interact via multiple pathways and targets within the networks, and a complete description of such relationships may involve hundreds of parameters. In addition, it is often difficult, if not impossible, to collect experimental data pertaining to every component within the network. Therefore, the complete simultaneous analysis of such networks is challenging. Nevertheless, an understanding of these networks is critical for furthering our knowledge of hormonal regulation in both physiologic and pathophysiologic conditions.

METHODS

We propose a novel approach for the analysis of dose-response relationships of subsets of hormonal feedback networks. The algorithm and signal-response quantification (SRQuant) software is based on convolution integrals, and tests whether several discretely measured input signals can be individually delayed, spread in time, transformed, combined, and discretely convolved with an elimination function to predict the time course of the concentration of an output hormone. Signal-response quantification is applied to examples from the endocrine literature to demonstrate its applicability to the analysis of the different endocrine networks.

RESULTS

In one example, SRQuant determines the dose-response relationship by which one hormone regulates another, highlighting its advantages over other traditional methods. In a second example, for the first time (to the best of our knowledge), we show that the secretion of glucagon may be jointly controlled by the β and the δ cells.

CONCLUSION

We have developed a novel convolution integral-based approach, algorithm, and software (SRQuant) for the analysis of dose-response relationships within subsets of complex endocrine feedback control networks.

Real-time implementation of biofidelic SA1 model for tactile feedback

In order for the functionality of an upper-limb prosthesis to approach that of a real limb it must be able to, accurately and intuitively, convey sensory feedback to the limb user. This paper presents results of the real-time implementation of a 'biofidelic' model that describes mechanotransduction in Slowly Adapting Type 1 (SA1) afferent fibers. The model accurately predicts the timing of action potentials for arbitrary force or displacement stimuli and its output can be used as stimulation times for peripheral nerve stimulation by a neuroprosthetic device. The model performance was verified by comparing the predicted action potential (or spike) outputs against measured spike outputs for different vibratory stimuli. Furthermore experiments were conducted to show that, like real SA1 fibers, the model's spike rate varies according to input pressure and that a periodic 'tapping' stimulus evokes periodic spike outputs.

[Using of adaptive biocontrolling feedbak in the treatment of irritable bowel syndrome]

In original research are compared results of treatment of irritable bowel syndrome (IBS) by standard technique and treatment with to additional application of the control of a biofeedback. The analysis was carried out on dynamics of clinical symptoms in 1 and 6 months after course of treatment. Research showed improvement of results of treatment IBS in the group with additional treatment of a biofeedback.