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M P Stenzel-Poore

Publications and source records attributed to M P Stenzel-Poore.

At least 19 recordsLinked to original sources
PubMed2002

Mice overexpressing CRH show reduced responsiveness in plasma corticosterone after a5-HT1A receptor challenge.

Corticotropin-releasing hormone (CRH) overproduction and serotonergic dysfunction have both been implicated in a range of psychiatric disorders, such as anxiety and depression, and several studies have shown interactions between these two neurotransmitter systems. In this study, we investigated the effects of CRH challenge on hypothalamo-pituitary-adrenal (HPA) axis activity in female transgenic mice overproducing CRH. Furthermore, the effects of mild stress on HPA axis activity and body temperature were investigated in these mice. Pre- and post-synaptic 5-HT1A receptor function were studied by monitoring body temperature and plasma corticosterone levels after challenge with the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propyl-amino)-tetralin (8-OH-DPAT). Hypothermia in response to 8-OH-DPAT treatment did not differ between transgenic and wild type mice, indicating unaltered somatodendritic 5-HT1A autoreceptor function in mice overproducing CRH. In wild type mice 8-OH-DPAT increased plasma corticosterone levels, but not in transgenic animals. CRH injection, however, increased corticosterone levels in both groups. These data suggest desensitization of post-synaptic, but not pre-synaptic, 5-HT1A receptors in mice overproducing CRH. These findings resemble those seen in depressed patients following 5-HT1A challenge, which is in accord with the hypothesized role of CRH in the pathogenesis of depression.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2001

A genetic model of stress displays decreased lymphocytes and impaired antibody responses without altered susceptibility to Streptococcus pneumoniae.

Stress pathways affect immune function, the most notable of these pathways being activation of the hypothalamic-pituitary-adrenal (HPA) axis. Although HPA activation has generally been relegated to an immunosuppressive role, recent evidence suggests that stress and HPA activation can be immunoenhancing in certain situations. To investigate specific effects of stress on immune function, we used a genetic model of chronic stress wherein transgenic mice overexpress corticotropin-releasing hormone (CRH), a primary mediator of the stress response. In these mice, CRH is overproduced in the brain, leading to chronic activation of the HPA axis. We found that CRH-transgenic mice have decreased leukocyte numbers in lymphoid compartments, with preferential loss of B lymphocytes. They also exhibit decreased Ab production and impaired isotype switching in response to immunization with a thymus-dependent Ag, phosphocholine-keyhole limpet hemocyanin. Despite these deficits, immunization protected CRH-transgenic and wild-type mice equally well against lethal challenge with Streptococcus pneumoniae, an encapsulated Gram-positive bacterium known to require Ab-mediated opsonization for clearance. While IgG responses are severely depressed in these mice, IgM titers are only modestly decreased. This fairly robust IgM response may be sufficient to protect against S. pneumoniae. Additionally, while total leukocyte numbers are decreased in these mice, neutrophil numbers are increased. This increase in number of neutrophils may compensate for the depressed IgG response, allowing adequate host defense during chronic stress.

Animals↗
PubMed2001

Animal models of CRH excess and CRH receptor deficiency display altered adaptations to stress.

This review highlights new information gained from studies using recently developed animal models that harbor specific alterations in corticotropin-releasing hormone (CRH) pathways. We discuss features of a transgenic mouse model of chronic CRH overexpression and two mouse models that lack either CRH receptor type 1 (CRH-R1) or type 2 (CRH-R2). Together these models provide new insights into the role of CRH pathways in promoting stability through adaptive changes, a process known as allostasis.

Animals↗
PubMed2001

IL-1alpha and TNFalpha down-regulate CRH receptor-2 mRNA expression in the mouse heart.

Two receptors (CRH receptor type 1 and CRH receptor type 2) have been identified for the stress-induced neuropeptide, CRH and related peptides, urocortin, and urocortin II. We previously found marked down-regulation of cardiac CRH receptor type 2 expression following administration of bacterial endotoxin, lipopolysaccharide, a model of systemic immune activation, and inflammation. We postulated that inflammatory cytokines may regulate CRH receptor type 2. We show that systemic IL-1alpha administration significantly down-regulates CRH receptor type 2 mRNA in mouse heart. In addition, TNFalpha treatment also reduces CRH receptor type 2 mRNA expression, although the effect was not as marked as with IL-1alpha. However, CRH receptor type 2 mRNA expression is not altered in adult mouse ventricular cardiomyocytes stimulated in vitro with TNFalpha or IL-1alpha. Thus, cytokine regulation may be indirect. Exogenous administration of corticosterone in vivo or acute restraint stress also reduces cardiac CRH receptor type 2 mRNA expression, but like cytokines, in vitro corticosterone treatment does not modulate expression in cardiomyocytes. Interestingly, treatment with urocortin significantly decreases CRH receptor type 2 mRNA in cultured cardiomyocytes. We speculate that in vivo, inflammatory mediators such as lipopolysaccharide and/or cytokines may increase urocortin, which in turn down-regulates CRH receptor type 2 expression in the heart. Because CRH and urocortin increase cardiac contractility and coronary blood flow, impaired CRH receptor type 2 function during systemic inflammation may ultimately diminish the adaptive cardiac response to adverse conditions.

Animals↗
PubMed2000

Abnormal adaptations to stress and impaired cardiovascular function in mice lacking corticotropin-releasing hormone receptor-2.

The actions of corticotropin-releasing hormone (Crh), a mediator of endocrine and behavioural responses to stress, and the related hormone urocortin (Ucn) are coordinated by two receptors, Crhr1 (encoded by Crhr) and Crhr2. These receptors may exhibit distinct functions due to unique tissue distribution and pharmacology. Crhr-null mice have defined central functions for Crhr1 in anxiety and neuroendocrine stress responses. Here we generate Crhr2-/- mice and show that Crhr2 supplies regulatory features to the hypothalamic-pituitary-adrenal axis (HPA) stress response. Although initiation of the stress response appears to be normal, Crhr2-/- mice show early termination of adrenocorticotropic hormone (Acth) release, suggesting that Crhr2 is involved in maintaining HPA drive. Crhr2 also appears to modify the recovery phase of the HPA response, as corticosterone levels remain elevated 90 minutes after stress in Crhr2-/- mice. In addition, stress-coping behaviours associated with dearousal are reduced in Crhr2-/- mice. We also demonstrate that Crhr2 is essential for sustained feeding suppression (hypophagia) induced by Ucn. Feeding is initially suppressed in Crhr2-/- mice following Ucn, but Crhr2-/- mice recover more rapidly and completely than do wild-type mice. In addition to central nervous system effects, we found that, in contrast to wild-type mice, Crhr2-/- mice fail to show the enhanced cardiac performance or reduced blood pressure associated with systemic Ucn, suggesting that Crhr2 mediates these peripheral haemodynamic effects. Moreover, Crhr2-/- mice have elevated basal blood pressure, demonstrating that Crhr2 participates in cardiovascular homeostasis. Our results identify specific responses in the brain and periphery that involve Crhr2.

Adaptation, Physiological↗
PubMed1999

Temporal modulation of cytokine expression following focal cerebral ischemia in mice.

There is increasing evidence that the inflammatory response plays an important role in CNS ischemia. The murine model of focal ischemia, however, remains incompletely characterized. In this study we examined expression of several cytokines and the vascular adhesion molecule E-selectin, in order to characterize the molecular events following stroke in the C57BL/6J mouse. Using a multi-probe RNAse protection assay (RPA), mRNA for 19 cytokines was analyzed following permanent and transient occlusion of the middle cerebral artery in mice. In addition, samples from the same mice were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) to evaluate E-selectin mRNA expression levels. Several cytokine mRNAs showed a similar expression pattern in both permanent and transient CNS ischemia while others showed a temporal expression pattern that was dependent on the type of stroke. For both models, mRNA levels of TNFalpha rose early (4 h) followed by IL-6 (10-18 h) and a comparatively late increase (96 h) in TGFbeta1. IL-1alpha, IL-1beta and IL-1ra levels showed a model dependent shift in temporal expression. Reperfusion appeared to delay the induction of these cytokines. Temporal changes in cytokine mRNA expression in the mouse CNS occur following ischemic damage. Our findings demonstrate the utility and power of multi-probe RPA for evaluation of changes in cytokine mRNA levels. Moreover, this study is, to our knowledge the first to show temporal changes in cytokine mRNA in mouse cerebral ischemia, forming a basis for further exploration of the roles of these cytokines in modulating ischemic neuronal damage in this model.

Animals↗
PubMed1999

Replacements in the exposed loop of the T15 antibody VH CDR2 affect carrier recognition of PC-containing pathogens.

A panel of mutant antibodies of the phosphocholine (PC)-binding antibody, T15, was tested for binding to PC-protein, Streptococcus pneumoniae, Trichinella spiralis and Ascaris suum. Relative to wildtype T15, all the mutant antibodies showed differential recognition of the panel of PC-associated antigens. These mutant antibodies contain amino acid replacements in the CDR2 region of the heavy chain variable region, indicating the importance of CDR2 in recognition of carrier determinants. A model of T15 is shown that illustrates the strategic placement of mutations that could allow interaction with determinants associated with PC. A direct implication of this finding is that the T15 antibody combining site accommodates structures larger than phosphocholine and that recognition of associated carrier determinants could be a significant force in shaping the immune response to PC-containing pathogens.

Amino Acid Sequence↗
PubMed1998

Harmful somatic mutations: lessons from the dark side.

The ability of somatic mutation to modify the course of an immune response is well documented. However, emphasis has been placed almost exclusively on the ability of somatic mutation to improve the functional characteristics of representative antibodies. The harmful effects of somatic mutation, its dark side, have been far less well characterized. Yet evidence suggests that the number of B cells directed to wastage pathways as a result of harmful somatic mutation probably far exceeds the number of cells whose antibodies have been improved. Here we review our recent findings in understanding the structural and functional consequences of V-region mutation.

Animals↗
PubMed1997

Endotoxin regulates corticotropin-releasing hormone receptor 2 in heart and skeletal muscle.

We tested the effect of endotoxin on the peripheral corticotropin-releasing hormone receptor (CRH-R2), which is highly expressed in the heart. Systemic injection of LPS markedly downregulated CRH-R2 mRNA levels in the heart in a dose and time dependent manner. In contrast, CRH-R2 levels in skeletal muscle increased following exposure to endotoxin. These results suggest that CRH-R2 may be differentially regulated in cardiac tissue and skeletal muscle. Finding that CRH-R2 expression in the heart is modulated by endotoxin, a potent inducer of cardiovascular dysregulation, suggests a possible link between CRH and the cardiovascular response to stress.

Animals↗
PubMed1997

Somatic mutation in VH complementarity-determining region 2 and framework region 2: differential effects on antigen binding and Ig secretion.

The extent to which somatic mutation impairs the Ig complementarity-determining region (CDR) and framework region (FRW) structure/function is not clear. Previously, we found that the VH CDR2 of the murine T15 Ab is highly sensitive to mutation; 56% (26 of 46) of Abs mutated in vitro had reduced or no Ag binding capability, and 9% were secretion impaired. Here we test whether the T15 VH CDR2 structure is unique by mutating the VH CDR2 of the anti-PC-protein murine Ab, PCG1-1. PCG1-1 VH is encoded by the M141 gene and is unrelated in sequence or structure to that of T15 VH1. The majority (54%, 20 of 37) of PCG1-1 mutants carrying one to five mutations in VH CDR2 had reduced or abolished Ag binding, while 10% were secretion impaired. Taken together, mutational analysis of the VH1 and VH M141 genes demonstrates that impaired binding and secretion may be common outcomes of CDR2 somatic mutation. We also tested the tolerance of the VH FRW2 of T15 to mutation, expecting this sequence-conserved region to be highly sensitive to alterations. However, FRW2 accommodated many nonconservative changes, and only 12% (3 of 25) of secreted mutants had impaired Ag binding. Moreover, mutations in FRW2 caused secretion defects in 24% (8 of 33), a frequency twice that of VH CDR2 mutants. A total of 16 unique secretion mutants have now been identified. These findings suggest that B cell losses from somatic mutation may be extensive and due to varied causes not all related to Ag binding.

Animals↗
PubMed1996

Deletion in HCDR3 rescues T15 antibody mutants from a secretion defect caused by mutations in HCDR2.

We recently described mutants of the murine anti-phosphocholine Ab T15, with changes in heavy chain complementarity determining region 2 (HCDR2) that caused loss of secretion. Surprisingly, the T15 HCDR2 mutations did not alter secretion when placed into the related anti-phosphocholine Ab D16, which differs from T15 only in HCDR3 and light (L) chain. Here, we exploit the differences between these two Abs to assess the basis of the secretion defect. The T15 L chain is not secreted in the absence of heavy (H) chain. In contrast, D16 L chain is secreted in the absence of H chain, as are most L chains. We co-expressed the T15 wild-type (wt) and mutant H chains with the D16 L chain, as well as with another secreted L chain, J558L. The mutant H chains were not secreted when expressed with either heterologous L chain. These results establish that the T15 L chain is not uniquely associated with the defect. The T15 and D16 Abs also differ in HCDR3 length in that D16 lacks four amino acid residues (Ser99, Ser100, Tyr100a, Trp100b) present in T15. We deleted these four residues from T15 wt and mutant H chains. Secretion of T15 wt was unaffected by the deletion, but shortening HCDR3 restored secretion in the HCDR2 mutants regardless of L chain association. Together these data demonstrate that both the HCDR2 and HCDR3 domains contain structural information that may affect the secretion competence of Abs.

Amino Acid Sequence↗
PubMed1996

Learning impairment in transgenic mice with central overexpression of corticotropin-releasing factor.

The present studies were designed to test the learning and memory capacities of transgenic mice with central overexpression of corticotropin-releasing factor in a forced alternation water T-maze task and in the Morris water maze. In T-maze testing, littermate control mice reached a criterion of 70% correct responses after five days of trials, while the performance of transgenic subjects was still random after the same training. In Morris maze testing, control subjects reached the submerged platform significantly faster (F(1.48) = 4.51, P < 0.05) after three days of trials, while the performance of transgenic mice was unimproved over the same period. The deficit in Morris maze performance in transgenic mice was reversed when the platform was visible above the surface of the water. Pre-test administration of the benzodiazepine anxiolytic, chlordiazepoxide (10 mg/kg), before acquisition training also produced a significant (F(4.40) = 16.61, P < 0.001) and persistent improvement in Morris maze performance in transgenic mice when compared to vehicle-treated transgenic litter mates. Finally, there was no evidence of hippocampal cell loss in transgenic brains. The results suggest that corticotropin-releasing factor-overexpressing mice exhibit a profound learning deficit without sensory or motor-related impairments, and that memory plasticity can be restored by anxiolytic pre-treatment. Thus, constitutive overabundance of brain corticotropin-releasing factor may produce hyperemotionality that interferes with learned behaviors. Stress-related disorders characterized by co-morbid deficits in learning/memory may benefit from pharmacological normalization of brain corticotropin-releasing factor systems.

Animals↗
PubMed1996

Corticotropin-releasing hormone receptor expression and functional coupling in neonatal cardiac myocytes and AT-1 cells.

CRH is the principal mediator of the stress response in mammals. In addition to pituitary and central nervous system effects, peripheral effects of CRH have been observed involving the immune and cardiovascular systems. Two CRH receptor subtypes, CRH-R1 and CRH-R2, have been cloned and show significant amino acid homology (69%), but differ in their tissue distribution. CRH-R1 is expressed predominantly in the brain and pituitary, whereas the CRH-R2 subtype is highly expressed in heart and skeletal muscle. To investigate the role of CRH in cardiac signaling, we analyzed the effect of CRH on freshly isolated neonatal rat cardiomyocytes and murine atrial cardiomyocyte tumor cells, AT-1, which express CRH-R2 messenger RNA. We show that stimulation of these cells with CRH and the CRH-related peptides, sauvagine from frog and urotensin I from fish, elicits large increases in the intracellular level of cAMP. This stimulation is transient, reaching a maximum in 5-15 min in neonatal cardiomyocytes and in 2-4 min in AT-1 cells, followed by a rapid decline. We show that stimulation of AT-1 cells by these peptides is specific for CRH receptors, as the CRH antagonist, alpha-helical CRH-(9-41) inhibits cAMP increases. Furthermore, we show that CRH, sauvagine, and urotensin I stimulations are dose dependent in both neonatal cardiomyocytes and AT-1 cells. Sauvagine and urotensin I are more potent than CRH at stimulating an increase in intracellular cAMP in neonatal cardiomyocytes (EC50 = 1.74, 2.61, 6.42 nM, respectively) and AT-1 cells (EC50 = 16.2, 15.8, and 149 nM, respectively). This rank order is consistent with that previously demonstrated in CRH-R2-transfected HEK293 cells and parallels the in vivo vasodilatory activity of these peptides. In summary, this is the first evidence that CRH, sauvagine, and urotensin I act directly on cardiac myocytes to stimulate increases in intracellular cAMP, presumably through CRH-R2. In addition, these results indicate that cardiac myocytes may be an informative in vitro model to investigate the effects of CRH and its role in the cardiovascular response to stress.

Amphibian Proteins↗
PubMed1995

Enhancement and destruction of antibody function by somatic mutation: unequal occurrence is controlled by V gene combinatorial associations.

We examined the positive and negative effects of somatic mutation on antibody function using saturation mutagenesis in vitro to mimic the potential of the in vivo process to diversify antibodies. Identical mutations were introduced into the second complementarity determining region of two anti-phosphocholine antibodies, T15 and D16, which share the same germline VH gene sequence. T15 predominates in primary responses and does not undergo affinity maturation. D16 is representative of antibodies that co-dominate in memory responses and do undergo affinity maturation. We previously reported that > 50% of T15 mutants had decreased antigen binding capacity. To test if this high frequency of binding loss was unique to T15 or a consequence of random point mutations applicable to other combining sites, we analyzed the same mutations in D16. We show that D16 suffers a similar loss of function, indicating an equally high potential for B-cell wastage. However, only D16 displayed the capacity for somatic mutation to improve antigen binding, which should enhance its persistence in memory responses. Mutation of residues contacting the haptenic group, as determined by molecular modeling, did not improve binding. Instead, productive mutations occurred in residues that either contacted carrier protein or were distant from the antigen binding site, possibly increasing binding site flexibility through long-range effects. Targeting such residues for mutation should aid in the rational design of improved antibodies.

Amino Acid Sequence↗
PubMed1995

Identification of a novel murine receptor for corticotropin-releasing hormone expressed in the heart.

Corticotropin-releasing hormone (CRH) is the principal regulator of the stress response. CRH stimulates production of ACTH via specific CRH receptors located on pituitary corticotropes. In addition to pituitary and central nervous system effects, peripheral effects of CRH have been observed involving the immune and cardiovascular systems. Specific CRH binding studies in several peripheral organs, as well as functional studies, have implied the existence of peripheral CRH receptors. Although a pituitary/brain CRH receptor has recently been identified, it is expressed at very low levels in peripheral sites where CRH effects have been observed. We report here the identification of a novel murine CRH receptor that is highly expressed in the heart. The newly cloned CRH receptor cDNA (CRH-R2) was isolated from a mouse heart cDNA library and encodes a 430-amino acid protein containing seven putative transmembrane domains characteristic of G protein-coupled receptors. CRH-R2 is 69% identical with the previously identified murine pituitary CRH receptor and is encoded by a distinct gene. In addition to a high level of expression in the heart, weak expression was also observed in the brain and lungs. Functional studies using CRH-R2-transfected cells indicate that CRH and the CRH-related amphibian peptide, sauvagine, bind with high affinity to CRH-R2 and stimulate intracellular accumulation of cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

Overproduction of corticotropin-releasing factor in transgenic mice: a genetic model of anxiogenic behavior.

Corticotropin-releasing factor (CRF) is released in response to various stressors and regulates adrenocorticotropin secretion and glucocorticoid production. In addition to its endocrine functions, CRF acts as a neuromodulator in extra-hypothalamic systems and has been shown to play a role in behavioral responses to stress. CRF overproduction has been implicated in affective disorders such as depression and anorexia nervosa. A transgenic mouse model of CRF overproduction has been developed in order to examine the endocrine and behavioral effects of chronic CRF excess. CRF transgenic animals exhibit endocrine abnormalities involving the hypothalamic-pituitary-adrenal axis such as elevated plasma levels of ACTH and glucocorticoids. The present series of experiments tested the hypothesis that chronic overproduction of CRF throughout the life-span of these animals may lead to an anxiogenic behavioral state. CRF transgenic mice and normal littermate controls were tested by measuring locomotor activity in a novel environment and through the use of an elevated plus-maze as indices of anxiety. CRF transgenic animals exhibited an increase in anxiogenic behavior, an effect known to occur following central administration of CRF in mice and rats. Injection of the CRF antagonist alpha-helical CRF 9-41 into the lateral cerebral ventricles reversed the anxiogenic state observed in the CRF transgenics. This finding supports the possibility that central CRF overproduction may mediate the anxiogenic behavior exhibited in this animal model. Thus, CRF transgenic mice represent a genetic model of CRF overproduction that provides a valuable tool for investigating the long-term effects of CRF excess and dysregulation in the CNS.

Adrenocorticotropic Hormone↗
PubMed1992

Development of Cushing's syndrome in corticotropin-releasing factor transgenic mice.

CRF is released in response to various stressors and regulates ACTH secretion and glucocorticoid production. CRF overproduction has been implicated in affective disorders, such as depression and anorexia nervosa, and may lead to Cushing's syndrome. To test whether CRF overproduction leads to Cushing's syndrome and to develop an animal model of chronic pituitary-adrenal activation, the CRF gene was expressed under control of the metallothionein promoter in transgenic mice. CRF transgenic animals exhibit endocrine abnormalities involving the hypothalamic-pituitary-adrenal axis, such as elevated plasma levels of ACTH and glucocorticoids. These animals display physical changes similar to those of patients with Cushing's syndrome, such as excess fat accumulation, muscle atrophy, thin skin, and alopecia. These findings indicate that chronic production of excess CRF results in sustained stimulation of pituitary corticotrope cells, resulting in elevated ACTH and consequent glucocorticoid overproduction, a condition that leads to the development of Cushing's syndrome. Analysis of CRF mRNA distribution revealed that transgene expression is primarily restricted to cells that express the endogenous CRF gene and does not follow the pattern predicted of a metallothionein-regulated gene. These results suggest that DNA elements located outside of the CRF promoter but present within the CRF intron, coding, or 3'-flanking regions may contribute to the cell type specificity of CRF gene expression.

Animals↗