Lauren Jacobson - US grants

AIDS is a multifaceted disease characterized by severe immunodeficiency and body wasting (cachexia). Anorexia, comprising either absolute decreases in food intake or inadequate intake relative to energy expenditure, is widely recognized to be a major risk factor in AIDS wasting. We will test the hypothesis that corticotropin-releasing hormone (CRH), a potent inhibitor of feeding, is a significant mediator of the anorexia and hormonal changes contributing to wasting syndromes. CRH could be elevated by several different mechanisms in AIDS, including elevated cytokine expression stimulated by HIV or secondary infection, and loss of glucocorticoid inhibition due to primary adrenal insufficiency. We postulate that protein malnutrition can also result in CRH dysregulation. Elevated plasma cortisol, documented in some AIDS patients, is also suggestive of increased CRH drive and may itself contribute to wasting. We will control adrenal hormone levels in rodent models of wasting (nutrient deprivation or intracerebroventricular IL- 1beta infusion) to evaluate the potential role of malnutrition- or cytokine-induced CRH production in AIDS-related cachexia. We will test the possibility that nutritional supplementation or appetite stimulants ameliorate cachexia at least in part via changes in CRH. We will further assess the CRH dependence of these effects by comparing hypothalamic- pituitary-adrenal (HPA) and feeding activity in normal and CRH-deficient (-/-, knock-out) mice during nutrient restriction or icv IL-1 infusion. This work will elucidate endocrine signals potentially involved in wasting in AIDS and the conditions under which alimentation may be successful in attenuating cachexia.

Aging is often associated with an imbalance between food intake and metabolism, reflected in increased body weight and fat at middle age and reduced food intake at old age. Weight gain, particularly as abdominal fat, is a major risk factor for type II diabetes, heart disease, and stroke, which can significantly reduce lifespan and quality of life. Inadequate food intake late in life can also impair maintenance of lean body mass and immunity. Disruption of hypothalamic melanocortin pathways has been implicated in appetite dysregulation, as well as hyperinsulinemia, leptin resistance, and weight gain, all of which have been reported in aging. Hypothalamic pro-opiomelanocortin (POMC), a major source of melanocortin receptor ligands proposed to inhibit appetite, has been shown to decrease during aging in experimental animals. Glucocorticoids have been found to increase with aging, and to promote food intake, insulin resistance and fat deposition in a leptin-independent manner. We hypothesize that decreased hypothalamic POMC expression and increased glucocorticoid production contribute to leptin resistance, representing reduced sensitivity to signals of nutritional repletion. This leptin resistance results in weight gain at middle age, while age-related loss of brain corticosteroid receptors and compensation for inadequate POMC expression may account for anorexia in old age. To test this hypothesis, we will compare leptin and corticosteroid regulation of food intake, body composition, plasma hormones, and gene expression of corticosteroid receptors, POMC and related melanocortin ligands and receptors, in young and aging mice. These studies will identify neuropharmacological mechanisms for regulating food intake and metabolism that will aid in optimizing appetite and body weight control for healthy aging.

[unreadable] DESCRIPTION (provided by applicant): Hypoglycemia unawareness and counterregulatory failure are dangerous complications of intensive insulin therapy in type I diabetes. Hypoglycemia-induced glucocorticoid secretion has been implicated in promoting loss of autonomic responses to hypoglycemia. However, glucocorticoids are both counterregulatory hormones themselves and essential for maintaining secretion of epinephrine, one of the most rapid and effective counterregulatory responses. The relative influence of these opposing glucocorticoid actions on defenses against recurrent hypoglycemia are unknown. In addition, glucocorticoids and their primary neural regulator, corticotropin-releasing hormone (CRH), not only influence one another reciprocally but may also have opposing effects on sympathetic tone. Elucidating the mechanisms and impact of glucocorticoid effects on autonomic activity will aid in preventing hypoglycemia unawareness in diabetic patients. To address these issues, this R21 application proposes to (Aim 1) refine a mouse model of hypoglycemia-induced counterregulatory failure, working closely with investigators at the Mouse Metabolic Physiology Core of Vanderbilt University to use hypoglycemic clamp techniques in protocols for recurrent hypoglycemia in mice. Focusing on adrenomedullary epinephrine secretion as a key, glucocorticoid-dependent aspect of counterregulation, we will (Aim 2) use physiological glucocorticoid replacement in CRH knockout mice (CRH KO) to define the relative influence of glucocorticoids vs. CRH on counterregulatory hormone secretion and adrenomedullary activation induced by acute hypoglycemia. We will then (Aim 3) combine the recurrent hypoglycemia procedures defined in Aim 1 with the glucocorticoid manipulations of Aim 2 to test the hypothesis that glucocorticoids inhibit sympathoadrenal responses to recurrent hypoglycemia independently of CRH. Lastly, to identify potential neural mechanisms for the opposing effects of glucocorticoids on epinephrine secretion, we will (Aim 4) map glucocorticoid-dependent changes in expression of marker genes for neuronal activity (c-fos) and specific neurotransmitters in brains of acutely and recurrently hypoglycemic WT and CRH KU mice from Aim 3. These experiments will establish a mouse model for hypoglycemia unawareness, resolve the conflicting effects of glucocorticoids on sympathoadrenal activity, and reveal potential mechanisms for hypoglycemia-induced counterregulatory failure.

DESCRIPTION (provided by applicant): Hypoglycemia unawareness and counterregulatory failure are serious and life-threatening drawbacks to the use of intensive insulin therapy to control type 1 diabetes. Adrenomedullary epinephrine secretion is one of the most rapidly effective and readily preserved defenses against hypoglycemia. Elucidating neural pathways underlying the regulation of counterregulatory responses, and of epinephrine in particular, will aid in designing therapies to combat hypoglycemia unawareness. We have recently found that reduced brain histaminergic activity correlates with impaired counterregulation, and that inhibiting histamine synthesis decreases epinephrine responses to hypoglycemia. As part of an overall goal to identify neural mechanisms for hypoglycemia unawareness, we hypothesize that brain histamine neurons are involved in hypoglycemia-induced secretion of epinephrine, and possibly other counterregulatory hormones. We further hypothesize that manipulation of central histamine levels will aid in identifying additional neural pathways controlling these responses. To address our hypotheses, we will: (1) use specific histamine antagonists and measure counterregulatory hormones to test if hypoglycemia-induced epinephrine secretion will be selectively (a) inhibited by brain-penetrant histamine H1- or H2- receptor antagonists, (b) unaffected by nonpenetrant antagonists, and (c) enhanced by increasing central histamine with the H3 autoreceptor antagonist, thioperamide. We will also (2) integrate hypoglycemic clamp techniques in unrestrained, chronically cannulated mice to test (a) the impact of streptozotocin (STZ)-diabetes on the progression of counterregulatory failure and (b) the hypothesis that thioperamide-evoked increases in central histamine will reverse counterregulatory deficits induced by recurrent hypoglycemia in STZ mice. Finally (3), using brains of mice from Aims 1 and 2, we will combine in situ hybridization analysis of neuronal c-fos gene expression with histochemical analysis (histidine decarboxylase mRNA) or histamine antagonist administration, to test the hypotheses that (a) defined neural pathways, including hypothalamic histamine neurons, exhibit altered activity after recurrent hypoglycemia, and (b) experimental alterations in central histaminergic tone will reveal additional neuron populations relevant to counterregulation. These studies will provide novel information on the neuropharmacology of glucose control that may reveal therapeutic strategies to prevent hypoglycemia unawareness.

DESCRIPTION (provided by applicant): Hypoglycemia unawareness and counterregulatory failure are serious and life-threatening drawbacks to the use of intensive insulin therapy to control type 1 diabetes. Adrenomedullary epinephrine secretion is one of the most rapidly effective and readily preserved defenses against hypoglycemia. Elucidating neural pathways underlying the regulation of counterregulatory responses, and of epinephrine in particular, will aid in designing therapies to combat hypoglycemia unawareness. We have recently found that reduced brain histaminergic activity correlates with impaired counterregulation, and that inhibiting histamine synthesis decreases epinephrine responses to hypoglycemia. As part of an overall goal to identify neural mechanisms for hypoglycemia unawareness, we hypothesize that brain histamine neurons are involved in hypoglycemia-induced secretion of epinephrine, and possibly other counterregulatory hormones. We further hypothesize that manipulation of central histamine levels will aid in identifying additional neural pathways controlling these responses. To address our hypotheses, we will: (1) use specific histamine antagonists and measure counterregulatory hormones to test if hypoglycemia-induced epinephrine secretion will be selectively (a) inhibited by brain-penetrant histamine H1- or H2- receptor antagonists, (b) unaffected by nonpenetrant antagonists, and (c) enhanced by increasing central histamine with the H3 autoreceptor antagonist, thioperamide. We will also (2) integrate hypoglycemic clamp techniques in unrestrained, chronically cannulated mice to test (a) the impact of streptozotocin (STZ)-diabetes on the progression of counterregulatory failure and (b) the hypothesis that thioperamide-evoked increases in central histamine will reverse counterregulatory deficits induced by recurrent hypoglycemia in STZ mice. Finally (3), using brains of mice from Aims 1 and 2, we will combine in situ hybridization analysis of neuronal c-fos gene expression with histochemical analysis (histidine decarboxylase mRNA) or histamine antagonist administration, to test the hypotheses that (a) defined neural pathways, including hypothalamic histamine neurons, exhibit altered activity after recurrent hypoglycemia, and (b) experimental alterations in central histaminergic tone will reveal additional neuron populations relevant to counterregulation. These studies will provide novel information on the neuropharmacology of glucose control that may reveal therapeutic strategies to prevent hypoglycemia unawareness.

DESCRIPTION (provided by applicant): The use of elevated HPA activity as a biomarker for depression is limited by uncertainty as to the relationship between HPA activity, mood, and antidepressant (AD) effects. Increased HPA activity in depression has been attributed to impaired glucocorticoid feedback inhibition that can be corrected by antidepressant-induced increases in brain glucocorticoid (GR) and mineralocorticoid (MR) receptors. However, benefits to some depressed patients from antiglucocorticoid therapies suggest that increasing GR or MR may not be required or appropriate for antidepressant action, and further suggest that by increasing glucocorticoids, elevated HPA activity might be a cause, as well as a marker, of depression. To discriminate the role of decreased GR from that of increased glucocorticoid levels in HPA-related depression pathology, this proposal uses forebrain GR knockout (FBGRKO) mice, a model of HPA-hyperactive depression, to test the hypothesis that that basal and antidepressant-induced changes in depression behaviors depend on changes in glucocorticoid secretion. Aim I will define the relationship of basal and stress-induced HPA activity to acute and chronic antidepressant actions to identify conditions for testing glucocorticoid and antidepressant effects. Aim II will determine glucocorticoid effects on basal behavior by testing if adrenalectomy and fixed glucocorticoid replacement normalizes depression-like behavior in FBGRKO mice. Aim III will determine the role of glucocorticoids in antidepressant action by using adrenalectomized FBGRKO and floxed GR controls with and without fixed glucocorticoid replacement to test if chronic antidepressant treatment normalizes behavior and hypothalamic- pituitary activity independently of changes in glucocorticoids. These studies address long-standing theories and contradictions of the roles of corticosteroid receptors and glucocorticoids in depression. Forebrain GR- and glucocorticoid-independent effects identified by this work could explain how antidepressants normalize elevated HPA activity in depression without facilitating adverse glucocorticoid effects on mood. This information could be used to predict and monitor antidepressant response more accurately in HPA-hyperactive depression. PUBLIC HEALTH RELEVANCE This project will determine if adrenal glucocorticoid hormones, which often increase in depression, might contribute to depression symptoms and influence antidepressant effects. This information could help to identify more effective antidepressants for depressed patients with abnormal glucocorticoid levels and to design hormone tests that detect antidepressant response more accurately. Since depression recovery depends on early effective treatment, results from this work could ultimately reduce the public health costs of depression by maximizing initial treatment success.